Heat shock protein paradigms in cancer progression: future therapeutic perspectives

Abstract

Heat-shock proteins (HSPs), also known as stress proteins, are ubiquitously present in all forms of life. They play pivotal roles in protein folding and unfolding, the formation of multiprotein complexes, the transportation and sorting of proteins into their designated subcellular compartments, the regulation of the cell cycle, and signalling processes. These HSPs encompass HSP27, HSP40, HSP70, HSP60, and HSP90, each contributing to various cellular functions. In the context of cancer, HSPs exert influence by either inhibiting or activating diverse signalling pathways, thereby impacting growth, differentiation, and cell division. This article offers an extensive exploration of the functions of HSPs within the realms of pharmacology and cancer biology. HSPs are believed to play substantial roles in the mechanisms underlying the initiation and progression of cancer. They hold promise as valuable clinical markers for cancer diagnosis, potential targets for therapeutic interventions, and indicators of disease progression. In times of cellular stress, HSPs function as molecular chaperones, safeguarding the structural and functional integrity of proteins and aiding in their proper folding. Moreover, HSPs play a crucial role in cancer growth, by regulating processes such as angiogenesis, cell proliferation, migration, invasion, and metastasis.

Introduction

Despite the advancement of many pharmaceutical medicines and targeted delivery systems, cancer treatment often falls short of completely eradicating most tumours. One of the major reasons for the limited success of cancer therapy is that tumour cells are widely resistant to drug-induced cell death. Tumour stem cells play a pivotal role in regulating this resistance and promoting the recurrence of tumours. When a tumour cell develops resistance to the toxic effects of one or more chemotherapeutic drugs, this phenomenon is referred to as drug resistance (Edwards et al. 1980; Douglas Hanahan and Bergsland 2000). Within this context, a family of proteins known as heat shock proteins (HSPs) plays a crucial role in shielding cells from the detrimental effects of environmental stressors. Multiple studies suggest that there is an interlink between HSPs with drug resistance and cancer cell proliferation (Yun et al. 2020). These HSPs encompass HSP27, HSP40, HSP60, HSP70, and HSP90, each contributing to various cellular functions. In the context of cancer, HSPs either inhibit or activate diverse signalling pathways, thereby impacting growth, differentiation, and cell division. (Fig. 1).

Fig. 1.

HSPs in the Hallmarks of cancer

Overview of types of HSPs

Heat shock proteins (HSPs) constitute a diverse group of proteins that encompass HSP27, HSP40, HSP60, HSP70, and HSP90 with pivotal roles in various aspects of cancer biology.

HSP27 This protein is involved in multiple cancer-promoting processes, including cancer cell proliferation, migration, invasion, and metastasis. In addition, it has an impact on interleukins, while contributing to complex signaling pathways. Studies have revealed its involvement in angiogenesis, making it particularly significant in ovarian cancer. Furthermore, HSP27 regulates key factors like p53, procaspase-9, and apoptotic protease activating factor-1 (APAF-1), ultimately leading to the inhibition of caspase activation (Freshney et al. 1994; Abisambra et al. 2010).

HSP40 Considered homologous to bacterial DNAJ (A heat shock protein with J domain), HSP40 proteins are crucial for regulating essential cellular functions, including protein folding, unfolding, translation, translocation, and degradation. They do so by activating the ATPase activity of HSP70. Notably, HSP40 proteins exhibit a dual role in cancer, with some members, such as Tid1, demonstrating anti-cancer activity. For instance, in lung cancer, HLJ1 (also known as DNAJB4) restricts the ability of lung cancer cells to progress through the cell cycle, while DNAJB6 has shown reduced malignant activity in breast cancer (Hata and Ohtsuka 1998; Mitra et al. 2008; Chen et al. 2009; Sterrenberg et al. 2011).

HSP60 Initially known as chaperonin, HSP60, is a versatile protein present in peripheral blood, on the cell surface, and in the extracellular space. It interacts with HSP10 and HSP70 and participates in immune responses by binding to Toll-like receptors and serving as an antigen for T and B lymphocytes. HSP60 plays a major role in cellular events like angiogenesis, metastasis, and cellular transformation. Inhibition of HSP60 leads to changes in mitochondrial permeability transition, caspase-dependent apoptosis, and tumour development regulation. Additionally, HSP60 plays a role in the regulation of activity like IkB kinase (KK), particularly in human cervical carcinoma cells, and modulates the stability of mitochondrial survivin (SVV) to regulate apoptosis (Wadhwa et al. 2005; Ghosh et al. 2010).

HSP70 HSP70 functions primarily in protein folding and maintaining protein homeostasis. HSP72, a specific member of this family, directly contributes to cancer malignancy. HSP70 has been shown to suppress various oncogene-induced senescence pathways in various cancer types, including breast, colon, lung, ovarian, and pancreatic cancer cells. It exerts its effect through both p53-independent (via Ras/ERK) and p53-dependent (via PI3K) mechanisms. HSP70 also plays a role in inhibiting apoptosis through various intrinsic and extrinsic pathways, which will be discussed in detail later (Gabai et al. 2009; Wang et al. 2014; Khalouei et al. 2014).

HSP90 HSP90 is the most extensively studied protein within this group. It exerts significant control over tumour development, metastasis, angiogenesis, apoptosis, and invasion. Inhibition of HSP90 has been associated with reduced angiogenesis and cell motility. HSP90 inhibition leads to the downregulation of factors like HIF-1/ and NF-kB, preventing colorectal cancer cells from migrating, infiltrating tissues, and becoming invasive (Aoyagi et al. 2005; Nagaraju et al. 2015).

HSPS' role in the onset, progression, and treatment of cancer

HSP27 and cancer

Among the HSP family, HSP 27 is a small member with a molecular weight of 12–43 kDa. In humans, it is controlled by phosphorylation at Ser-15, 78, and 82. The structure of HSP27 is explained in Fig. 2. Their upsurge is seen in response to stress by MAPKAPKs 3 and 2 pathways and parallelly they are activated by phosphorylated p38 MAPK (Mitogen-activated protein kinase) (Moretti-Rojas et al. 1988; Ferns et al. 2006). HSP27 in humans is encompassed with 205 amino acids. They are formed by the gene HSPB (Mammalian small heat shock protein family), which is sited at the 7q11.23 chromosome (Stetler et al. 2009).HSF-1(Heat shock factor protein 1) binds to the HSE (Heat Shock Elements) and induces the production of HSP27 in response to hemin therapy and heat stress; they have a wide range of interactions with various molecules, along with histone and b-catenin(Tokunaga et al. 2022). A wide range of diseases such as atherosclerosis, neurological disorder, ischemia, and cancer include deacetylases-6 (HDAC6) and procaspase-3 STAT-2 (Freshney et al. 1994; Mathias et al. 2015).

Fig. 2.

Human HSP27's structure. The N-terminal domain, the alpha-crystallin domain, and the C-terminal domain make up the fundamental structure of human HSP27. A WDPF motif found in the N-terminal domain is crucial for multimer formation and chaperone action. Ser-15, which is close to the WDPF motif, can be phosphorylated by protein kinases affiliated with the mitogen-activated protein kinase (MAPK) (marked as MK2). A stretch that varies in length depending on the species connects the WDPF motif to the alpha-crystallin domain, which is found at residues Glu87-Pro168. With a length of 18–20 amino acids and an alpha-crystallin motif that is largely conserved across species, the C-terminal domain plays a crucial role in the creation of a flexible structure required for chaperone activities

HSPs show tumorigenic properties by interacting with STAT3/STAT5 transcription pathway and it also regulates the differentiation, activation, and cytokine secretion; this eventually results in immunosuppression and potentially promotes tumour progression (Jego et al. 2020).

Cancer development

The proteins are involved in regulating the apoptosis, metastasis, growth, as well as drug resistance of cancer cells. HSP27 may indicate a poor prognosis for the illness. Suppression of protein-27 will ultimately result in cancer proliferation, migration, and invasion. Also stimulate the matrix metalloproteinase (MMP), and EMT (Epithelial-to-mesenchymal transition) (Cayado-Gutiérrez et al. 2013). The levels of TGF-b increase during prostate cancer, and the elevated levels of TGF-b activate the HSP-27 protein. The activation results in the stimulation of MMP2, which ultimately causes the invasion of cells. HSP27 is also considered the target for the ILK and also aids in cell migration during bladder cancer (Abisambra et al. 2010). From different studies, it is observed that the overexpression of the protein leads to metastasis in epithelial ovarian cancer in the peripheral area, and encourages angiogenesis. An increase in VEGF results in phosphorylation of HSP 27, which later regulates metastasis cell growth and invasion in case of breast cancer (Shibuya 2011).

Additionally, studies have been done on the molecular mechanisms through which HSP27 contributes to the emergence of cancer. p53 signalling is regulated by HSP27; by inhibiting p53 from producing p21 in cancer cells, they stop cellular senescence (O’Callaghan-Sunol et al. 2007). In the case of breast cancer, when HSP 27 is downregulated, the tumour suppressor gene, phosphatase, and PTEN are activated (Cayado-Gutiérrez et al. 2013). The activator protein-1 is reportedly triggered by HSP27, increasing cell proliferation in lung cancer cells (Zhang et al. 2015). It has been shown that HSP27 strongly regulates the activity of two proapoptotic enzymes, procaspase-9 and apoptotic protease activating factor-1 (APAF-1), to prevent caspase activation. Upon binding of the HSP-27 for cytochrome-c will block the interaction with procaspase 1 and 9 to inhibit their activation (Bruey et al. 2000). In Colorectal cancer, HSP27 is constitutively active, and HSP27 is required to prevent caspase-3 and -9 cleavage in CD133 + cells (a type of cancer stem cells). When HSP27 is suppressed, CD133 + cells undergo more apoptosis, which is caused by hypoxia and serum deprivation (Lin et al. 2012). Additionally, by preventing HSP27 activation, inhibitor t-AUCB, the soluble epoxide hydrolase increases caspase-3 activity and encourages cell death in glioblastoma cells (Li et al. 2012).

Biomarker applications and diagnosis

HSP27 is a biomarker that may be used to diagnose and predict certain malignancies since it is overexpressed in almost all tumours. A wide range of cancers, like high-grade astrocytoma, pediatric blood cancer, and oral squamous cell carcinoma, have been associated with the HSP27 gene. However, the immunohistochemical investigation showed that neuroblastoma cells express less HSP27 (Zanini et al. 2008). According to several studies, high expression of HSP27 has been linked to poor prognosis and poor differentiation of cancers, such as colon cancer, anaplastic astrocytoma, and glioblastoma (Li et al. 2012).

Treatment and therapeutics

HSP27 is a possible target for chemotherapy since it also impacts drug resistance. For instance, nasopharyngeal carcinoma cells express the protein HSP27, which is connected to radiation resistance (Gomez-Monterrey et al. 2013). Human pancreatic cancer cells resistant to gemcitabine overexpress HSP27, which suggests that HSP27 is a factor in gemcitabine resistance (Liu et al. 2012b). In a mouse xenograft model, HSP27 suppression improves colon cancer susceptibility to 5-FU (Hayashi et al. 2012). Patients with peritoneal carcinomatosis who had gone through cytoreductive surgery and then hyperthermic intraperitoneal treatment had their levels of HSP27 evaluated by Kepenetkian et al. While HSP27 levels declined following hyperthermic intraperitoneal chemotherapy, they increased following cytoreductive surgery, suggesting that HSP27 inhibition might lessen cancer cell growth to the combination of chemotherapy and surgery (Kepenekian et al. 2013). Patients with low HSP27 and p-HSP27 levels with oesophagal cancer reacted better to oxaliplatin/cisplatin—or 5-FU-based treatment. Patients with elevated levels of GRP 94, 78, HSP70, and 60 did not react well to treatment(Slotta-Huspenina et al. 2013). The apoptosis caused by melatonin in gastric cancer cells is increased by a reduction in heat shock protein-27, which is controlled through the pathway p38/phosphoinositide 3-kinase (PI3K)/AKT (protein kinase B) (Deng et al. 2016). In addition, by downregulating HSP27, human colon cancer cells became more sensitive to doxorubicin and were encouraged to undergo apoptosis (O’Callaghan-Sunol et al. 2007). It has been observed that the tyrosine kinase inhibitor imatinib is more effective in reducing resistance to doxorubicin in breast cancer cells by disrupting pathways like STAT3/HSP27/p38/AKT (Sims et al. 2013). From the above statement, there might be a chance that doxorubicin targets HSP27 to regulate the extent of drug resistance in cancer cells. According to Xu and Bergan, genistein may successfully inhibit MMP2 activation in prostate cancer cells by preventing the instigation of TGF-b (Transforming growth factor-beta)-induced MAPKAPK2 and HSP27. These data suggest that heat shock protein -27 may be the beneficial focus of genistein (Xu and Bergan 2006).

Leukaemia chemotherapy treatments may be more effective if they are directed against HSP27. Increased chemosensitivity of tumour cells and death brought on by doxorubicin and cytosine arabinoside was seen when HSP27 expression was knocked down (Deng et al. 2016). Decreased HSP27 was allied with increased cell death (Apoptosis) and lowered the resistance of cisplatin in oral cancer cells. A general HSP 27 inhibitor, quercetin, also constrains HSP90 and 70. Gemcitabine proved effective against tumour xenografts in vitro and in vivo when combined with KNK437 or IFN-g, benzylidene lactam that may constrain the HSP40 (Kuramitsu 2012; Liu et al. 2012a).

Phase II clinical studies are now taking place for the antisense oligonucleotide OGX-427 (apatorsen), which inhibits HSP27. In phase I clinical trials, patients with metastatic prostate cancer are treated with apatorsen. The treatment showed inhibition in metastasis and a decline in circulating tumour cells (Shiota et al. 2013). Brivudine (RP101), an antiviral medication, binds to HSP27 and prevents it from interacting with its binding partners. Consequently, cell death (Apoptosis) was enhanced in brivudine-treated cancer cells, and caspase-9 activity increased. Additionally, Briviudine increased the effectiveness of chemotherapy in individuals with late-stage pancreatic cancer and successfully extended the life of a rat xenograft sarcoma model (Heinrich et al. 2011). A chemical called 1,3,5-trihydroxy-13,13- dimethyl-2H-pyran (TDP) efficiently inhibits cell proliferation and encourages apoptosis in hepatocellular cancer by suppressing HSP 27( Fu et al. 2012).

HSP40 and cancer

Homologs of the bacterial DnaJ HSPs are the HSP40/DNAJ family of proteins, which can influence protein folding, unfolding, translation, translocation, and degradation by activating the ATPase activity of HSP70 (Hata and Ohtsuka 1998; Qiu et al. 2006; Sterrenberg et al. 2011). Given that most of its members have a "J" domain that enables them to interact with HSP 70, they are also called Hsp70 co-chaperones. The HSP40 family has the most members among the leading human HSP families. Three DNAJ subclasses—DNAJA, B, and C—are used to group proteins from the HSP40 family, and the structure is represented in Fig. 3 (Kampinga et al. 2009).

Fig. 3.

Classification of the Functional Domains of HSP40/DNAJ

(A) Based on the presence or absence of three domains, the HSP40 family is divided into three subclasses (DNAJA, DNAJB, and DNAJC): I the J domain; (ii)glycine/phenylalanine-rich region (G/F) and the cysteine-repeat motif; and (iii) the C-terminal domain, which has been thoroughly defined. DNAJA subclass polypeptides have domain structures that are exactly like Escherichia coli DnaJ. These domain structures include an N-terminal J domain, a glycine/phenylalanine-rich domain (G/F), and a C-terminal domain with conserved CXXCXGXG residues (X represents any amino acids) for zinc ion binding to the zinc finger motif. The cysteine-repeat motif and the C-terminal domain are absent from the DNAJB subclass, which has the N-terminal J and G/F domains. A J domain that may be found anywhere in the protein is present in DNAJC subclass polypeptides, which also have specific polypeptide-binding domains that can identify their substrates.

Cancer development

It has been discovered that several members of the HSP40 family of proteins play a significant role in the development of cancer. The proteins of the HSP40 family serve a dual role in pro- and anti-cancer activities. A crucial regulator of cell death in the body has been found as Tid1 (also known as DNAJA3)(Asgharzadeh et al. 2022). HSP70 proteins, which are involved in cell and stem cell death, interact with Tid1 in several ways. Additionally, it works directly with p53. As a result, intrinsic apoptosis is induced in breast cancer MCF-7 cells, and the complex is translocated to the mitochondria. Overexpression of Tid1 decreases migration, cell growth, invasion, & tumour growth in vitro as well as tumour development and reappearance in vivo in the neck and head squamous cell carcinoma. Tid1 serves as a tumour suppressor (Chen et al. 2009; Trinh et al. 2010).

Tumour invasion negatively correlates with HLJ1 (also called DNAJB4), a tumour suppressor (Wang et al. 2005). In human hepatocarcinoma cells, a transcription factor Yin Yang 1 (YY1) and activator protein-1 combine to activate HLJ1 (Zhang et al. 2011). Lung cancer cells' motility, invasion, and growth, are inhibited by HLJ1. High HLJ1 expression reduces lung cancer cells' ability to move through the cell cycle via the STAT1/p21 pathway (Tsai et al. 2006).

Breast cancer cells treated with DNAJB6 have been demonstrated to have decreased malignant activity and exhibit partial reversal of the mesenchymal phenotype (Mitra et al. 2010). The downregulation of DNAJB4 showed an increase in the growth of breast cancer cells and malignant melanoma (Mitra et al. 2008). More expression of DNAJB6 diminished the migration, proliferation, invasion, motility, and malignancy of cancer cells in the breast cancer model of orthotopic nude mice (Menezes et al. 2012). Despite being present in the cytoplasm of the liver, DNAJC25's countenance is noticeably downregulated in case of cancer (Liu et al. 2012c).

Diagnostic and biomarker applications

Cancers of the stomach, colon, cervix, and lungs all have overexpression of many HSP40 family proteins (Castle et al. 2005). Due to its high expression in acute lymphoblastic leukaemia (ALL) cells of the B-lineage, HDJ-2 (DNAJA1) has been discovered as a diagnostic biomarker for monitoring minimum residual illness. Colon, lung, breast, and ovarian tumour tissues express low levels of Tid1 (Wang et al. 2014). In paediatric rhabdomyosarcoma, DNAJA4 is hypermethylated, which suggests that the methylation of DNA profiles of DNAJA4 might be helpful in risk prediction diagnosis and therapeutic target (Mahoney et al. 2012). The expression of JDP, also known as DNAJC12, is increased in breast cancers with estrogen receptors. A protein called JDP1 that targets estrogens could be utilized to identify the estrogen receptors’ transactivation. Compared to normal breast cells, aggressive breast cancer cells have much-reduced levels of DNAJB6 expression(Mitra et al. 2008).

Treatment and therapeutics

HSP40 proteins mediate the actions of chemotherapy drugs. BMS-690514 and KNK437 are human VEGFR /EGF receptor (HER) inhibitors that exert their anti-apoptotic actions in NSCLC (non-small-cell lung cancer) cells. The cytotoxicity of carboplatin and 5-FU counter to hepatoma cells was enhanced by HSP40 protein inhibition (Sharma et al. 2009). In human breast cancer cells, tipifarnib constrains the survival, growth of tumours, and angiogenesis by inhibiting the HSP 40. R115777 upregulates RhoB, a Ras homolog gene family member that also inhibits the activity of VEGF, MMP1, and HDJ-2. R115777 also decreases the amount of the phosphorylated AKT, p-ERK enhanced, MEK, and fibrosarcoma 1 (RAF-1) (Izbicka et al. 2005). Additionally, R115777 in glioblastoma multiforme increases radio-sensitization by targeting HDJ-2 (Wang et al. 2006). Scientists at the University of Bristol in the UK have shown that knocking out an essential gene in DNAJB1 increased the sensitivity of gefitinib (Inhibitor of epidermal growth factor receptor) against lung cancer by upregulating mitogen-inducible gene 6. By activating HLJ1, the turmeric spice's curcumin ingredient prevented lung cancer cells from migrating, invading, and metastasizing (Chen et al. 2008).

HSP60 and cancer

Known initially as chaperonin, HSP60 is mainly found in the mitochondria of eukaryotes, where it interacts with mitochondrial HSP70 (mortalin) and HSP10. Hsp60 and Hsp10 combine to produce an efficient Chaperonin that regulates the protein folding and assembly of proteins in mitochondria (Shi et al. 2016). HSP60 has also been discovered to be present in peripheral blood, the cell surface, extracellular space, and cytosol (Wadhwa et al. 2005). On chromosome 2, the human HSP60 and ten genes are situated next to one another and share a bidirectional promoter (Cappello et al. 2013). The apical, middle, and equatorial domains of HSP60 make up its three primary structural units (Sigler et al. 1998). HSP60 binds to Toll-like receptors and an antigen for T and B lymphocytes, indicating that it also functions in the body's immune system (Liffers et al. 2011; Lv et al. 2012).

Cancer development

Cancer cells actively release HSP60, which aids in angiogenesis, metastasis, and transformation (Tsai et al. 2008). HSP60 can boost anti-apoptotic actions and has cytoprotective properties against cell stresses such as chemotherapeutic drugs (Pace et al. 2013). Investigations have been made into several molecular pathways that underlie HSP60's pro-carcinogenesis abilities. By interacting with and suppressing the intracellular proteins clusterin and cyclophilin D, HSP60 enhances the survival of cancer cells by inhibiting apoptosis which is shown in Fig. 4 (Chaiwatanasirikul and Sala 2011). HSP60 inhibition results in cyclophilin D-dependent mitochondrial permeability transition, caspase-dependent apoptosis, and inhibition of tumour development (Ghosh et al. 2010). An essential molecule after HSP 60 is IGF-binding protein 7, when HSP 60 is downregulated, IGFBP7 plays an important role in increasing the cancer cells’ growth of colorectal cancer (Ruan et al. 2010). Cytosolic HSP60 participates in the protein NF-kB-dependent endurance of cancer cells. Along with the interaction, they also regulate activity like IkB kinase (KK) seen in human cervical carcinoma cells (Chun et al. 2010). Tsai et al.claim that both in vitro and in vivo, overexpression of HSP 60 led to the development of metastatic features in several malignancies (Tsai et al. 2009).

Fig. 4.

Model for HSP60's Control of Tumour Cell Apoptosis

Survivin (SVV) is a member of the inhibitor of the apoptosis family, which prevents the activation of caspases and apoptosis. HSP60 forms a complex with p53 that promotes p53 stability and prevents p53 from acting as a pro-apoptotic factor in tumour cells, in addition to maintaining mitochondrial survivin. The HSP 60 protein also modulates the stability of the mitochondrial SVV to regulate apoptosis.

Biomarker applications and diagnostic

Heat shock protein 60 could be used as a biomarker to identify and predict cancer. A poor prognosis and high levels of HSP60 expression are linked to cancer development. In the case of neck and head cancer, gastric, lung, prostate, colorectal, bronchial, and neuroblastoma cancer the HSP 60 is overexpressed (Abu-Hadid et al. 1997; Kang et al. 2009; Chatterjee and Burns 2017).

Treatment and therapeutics

A gene-coded for HSP60, which contributes to drug resistance in some cancer cell types, is a potential therapeutic target to fight cancer. The degree of resistance to platinum analogues is associated with higher HSP 60 expressions in human bladder and ovarian cancer cells (Abu-Hadid et al. 1997; Yun et al. 2020). In an ovarian cancer model of mice, the proteasome inhibitor bortezomib increases the levels of HSP90 and 60 on the surface of cancer cells and stimulates dendritic cells to engage in phagocytosis (Liu et al. 2012b).

HSP70 and cancer

The HSPA genes code for 13 diverse members of the HSP70 family in humans. ~ 18 kDa substrate-binding domain, ~ 44 kDa N-terminal ATPase domain, and the ~ 10 kDa C-terminal domain are three domains that make up the highly conserved domain structure of HSP70 proteins (Wang et al. 2014). Bcl-2 (present at the c terminal of HSP70 interacting protein-CHIP) along with athanogene (belonging to HSP 40) control the activity of HSP70 (Wu et al. 2017). The HSP70 gene family has a close connection to cancer. Protein folding and maintaining protein homeostasis are critical functions of HSPA70 proteins. Additionally, they improve cell survival under several stressors, such as physiological or environmental challenges.

Cancer development

HSP70s are frequently expressed at unusually high levels and play crucial roles in cancer genesis. HSP70s are survival factors contributing to cancer development because of their expression in tumours and anti-apoptotic properties. The HSP 70 is involved in cancer progression in multiple ways.

In cervical squamous carcinoma cells that have had HSP72 knocked down show increased apoptosis rather than enhanced cell proliferation, migration, or invasion, it is believed that HSP72 (HSPA1) directly contributes to malignancy (Li et al. 2011). HSP 72 and transcription factor 5 (ATF 5) aid in the survival of glioblastoma cells by preventing the breakdow n (Gabai et al. 2009). Additionally, HSP72 suppresses p53-independent (by Ras/ERK) or p53-dependent (through PI3K) oncogene-induced senescence pathways in breast, colon, lung, ovarian, and pancreatic cancer cells (Nylandsted et al. 2004). Further research into HSP72's involvement in autophagy and cancer by the Jaattela group revealed that it serves as a survival protein in cancer cells by stabilizing lysosomes (Khalouei et al. 2014). The various mechanisms of HSP 70 are described in Fig. 5.

Fig. 5.

HSP70 Proteins: Possible Functions in Cancer Progression Management and as Promising Pharmacological Strategies for Cancer Drugs

HSP70 with 71 kDa molecular weight is encoded in the human genome's HSPA6 gene, which is found on chromosome 1q(rat and mouse genomes do not have this gene) (Leung et al. 1990; Radons 2016). Under normal physiological conditions, the HSPA6 expression is less untraceable, but stress significantly increases its induction in most cells and tissues (Ramirez et al. 2015). HSPA6 may be implicated in TNF-mediated inflammation and apoptosis, according to Ramirez and colleagues' discovery that overexpression of TNIP1 lowered the production of heat shock proteins such as HSP72, HSP40, and HSPA6 in human epidermal keratinocytes (Regeling et al. 2016). In DLD-1 human intestinal epithelial cells, the cigarette smoke extract enhanced the expression of HSPA6. In DLD-1 cells, HSPA6 interacts with and stabilizes the BCL-XL, the anti-apoptotic protein, indicating that HSPA6 has an anti-apoptotic function (Helmbrecht and Rensing 1999; Regeling et al. 2016). Compared to differentiated cells, the amount of HSC70 in rat C6 glioma cells is much more significant throughout proliferation, especially in S-phase, indicating that HSC70 may boost cell proliferation (Helmbrecht and Rensing 1999). On human chromosome 5q31 lies the HSPA9 (mortalin) gene. It participates in myeloid cancers and is often eliminated in MDS (Myelodysplastic syndromes) and AML (acute myeloid leukemia) patients (Gestl and Anne Böttger 2012). Mortalin (HSPA9) (HSPA9) prevents the translocation of p53 into the nucleus by binding to and sequestering it in the cytoplasm. It appears to have a part in controlling the cell cycle and apoptosis in human colorectal cancer cells. The inhibition of mortalin results in the apoptosis of hematopoietic progenitor cells (Starenki et al. 2015). By turning on the MAPK/MEK/ERK pathways, Mortalin aids in cancer development. ERK pathway is majorly seen in medullary thyroid and ovarian cancer cells (Murphy 2013).

HSP70 inhibits the intrinsic and extrinsic mechanisms leading to apoptosis (A). HSP70 prevents apoptosis by (i) preventing the transport of APAF-1 to the apoptosome, (ii) preventing the recruitment of kinases involved in stress signalling, (iii) binding to and inhibiting the activity of these kinases, and (iv) binding to and impairing the function of AIF. It also prevents the translocation of BAX from the cytosol to the mitochondria. (B). HSP70 regulates the senescence of cells. Through (i) disrupting p53-dependent regulation and (ii) antagonizing p53-independent regulation, HSP70 prevents cell senescence. (C). HSP70 regulates autophagy and stabilizes lysosome activity. HSP70 aids in cellular survival by (i) stabilizing lysosomes by binding to endolysosomal lipid bisphosphate, (ii) inhibiting lysosomal membrane permeabilization, and (iii) triggering autophagy. (D). HSP70 manages HSP90 client proteins. HSP70 acts as a co-chaperone for HSP90 by facilitating the transport of client proteins to HSP90. c-RAF, HER2, CDK4, and AKT are the HSP70-delivered HSP90 client proteins.

Diagnostic and biomarker applications

Numerous malignancies have elevated levels of HSP72, which are associated with worse prognoses and tumour grades. Among various malignancies, melanoma, lung cancer, uterine cervical cancer, and prostate, oral, liver, and colorectal cancer showed the overexpression of HSP72 (Cai et al. 2012). In a study, the tumour tissues were collected from 507 nasopharyngeal cancer patients. Upon examination, it is found that HSP 72 is dominant in 2 regions i.e., cytoplasm and nucleus. The increased levels of HSP72 in the cytoplasm resulted in increased drug resistance. In contrast, increased HSP72 in nuclei was linked to decreased survival (Wang et al. 2010). According to research by Wang and colleagues, distant metastasis was substantially correlated with the expression of heat shock protein 72 in the cytoplasm of oesophagal cancer cells (Yang et al. 2015). In individuals with early-stage hepatocellular carcinoma caused by the hepatitis B virus (HBV), expression of HSPA6 is greater in cancer tissues of the liver than in normal tissues, stating there might be a role of HSPA6 in cancer progression.

Treatment and therapeutics

The expression of HSP70 proteins is rapidly increasing in various malignancies. In cancer treatment, HSP70 proteins are vital in mediating drug resistance (Murphy 2013). The HSP70 molecular chaperones, particularly GRP78 and HSP72, are attractive therapeutic targets for cancer treatment due to their significant involvement in cancer biology. As a result, there is considerable interest in the discovery, characterization, and development of HSP70 inhibitors. Some substances specifically target and block the members of the HSP70 family (Kumar et al. 2016).

Fisetin, an inhibitor of HSP 70, the flavonoid, can induce cell death in colon cancer cells. It reduces the levels of the proteins BCL-2, and MCL-1, in myeloid cell leukaemia and increases the risk of death (Yoshidomi et al. 2014). Fisetin induces apoptosis of cancer cells by inhibiting HSF1 activity by blocking its binding to the HSP70 promoter.

Some cancer medications use HSP72 as their therapeutic target, which also controls drug resistance. For instance, in cervical cancer, reduction of HSP72 increases susceptibility to cisplatin therapy (Takahashi et al. 2016). HSP72 shields human gastric cancer cells from oxaliplatin-induced apoptosis (Howe et al. 2014). HSP72 overexpression results in resistance to Bortezomib. Inhibition of HSP72 increases cancer cell death by reducing the extent of drug resistance. HS-72 was recognized by Howe et al. as an allosterically selective inhibitor of heat shock protein-72. In the animal model of HER2⁺ breast cancer, HSP-72 lowers the HSP72 ATP-binding affinity, slows tumour development, and lengthens the longevity of tumour-bearing mice (Kuballa et al. 2015).

Anticancer medications can increase HSPA6 expression. The proteasome inhibitor MG-132 is used to treat multiple myeloma and lymphoma, and it also promotes the expression of HSPA6 on the surface of human colon cancer cell lines CRL-1809 and HT-29. Whereas the MCF-7 breast cancer cells, the inhibitors of HSP90 viz, radicicol and tanespimycin dramatically increased the expression of HSPA6, indicating that HSPA6 could be the distinctive marker for inhibiting the HSP90 (Prodromou and Pearl 2003).

HSP90 and cancer

HSP90 is one of the most intensively explored HSP proteins and preferred target as they play a major role in cancer progression (Kampinga et al. 2009).

The HSP90 family contains five members, and they are encompassed with HSPC1 through HSPC5 genes (Kampinga et al. 2009). HSP90 is predominantly found in the cytoplasm. The N-terminal domain of HSP90 is ~ 25 kDa, the middle domain is ~ 40 kDa, and the C-terminal domain is ~ 12 kDa. HSP90 may form flexible homodimers. The N-terminal domain exhibits similarity with DNA gyrase, MutL (GHKL), and histidine kinase (Prodromou and Pearl 2003). Bergerat fold, an ATP-binding pocket seen in the N-terminal region of HSP90, acts as a binding site for nucleotides and medications like tanespimycin (17-allylamino, 17-demethoxygel- danamycin, 17-AAG) and GA (Geldanamycin). The catalytic loop is located in the middle domain and has three regions—a three-turn helix with asymmetric loops, a six-turn helix, and a three-layer sandwich, which binds to the g-phosphate from HSP90 client proteins and GA. The C-terminal domain of the HSP90 protein makes protein trafficking, folding, and maturation easier. HSP90 is involved in signalling pathways such as the IL-6 receptor, PI3K/AKT pathway, NG-KB, cyclin-dependent kinase, and BCR-ABL (Whitesell and Lindquist 2005).

Development of cancer

HSP90 plays a significant role in cancer development by controlling tumour development, metastasis, angiogenesis, apoptosis, and invasion. ILK (interleukins) and FAK (Focal adhesion kinase) are crucial agents that increase cell attachment. Inhibition of HSP90 promotes FAK and ILK degradation by proteases(Aoyagi et al. 2005). By triggering a downstream tyrosine kinase signalling cascade, HGF promotes angiogenesis and cell motility. Inhibition of HSP90 reduces angiogenesis and cell motility in T24 bladder cancer cells of humans through impairing HIF activity(Tsutsumi et al. 2008). By preventing activation in colorectal cancer cells and VEGF (Vascular endothelial growth factor) receptor expression, inhibitors of HSP90 also reduce angiogenesis. HIF-1/ and NF-kB are downregulated when HSP90 is inhibited, preventing colorectal cancer cells from moving, migrating, and becoming invasive. When a cell is under stress, inositol hexakisphosphate kinase-2 (IP6K2) mediates the apoptosis. Physically attaching to IP6K2, HSP90 prevents apoptosis by blocking the enzyme's catalytic activity. As a result, cancer cells die when the HSP90-IP6K2 connection is inhibited(Nagaraju et al. 2015).

Diagnostic and biomarker applications

Multiple myeloma, oropharyngeal squamous cell carcinoma, breast, ovarian, lung, endometrial malignancies, and breast are among the tumours where HSP90 is overexpressed (Shi et al. 2014). In oesophagal, lung, melanoma, bladder, and blood cancer, the highest expression of HSP90 was discovered as a sign of a deprived prognosis (Zackova et al. 2013).

Treatment and therapeutics

The possible therapeutic target to stop the growth and spread of tumours is HSP-90 due to its critical function in cancer biology. Several HSP90 inhibitors have been put through clinical studies and a few inhibitors which are used in cancer therapy are mentioned in Table 1 (Miyata et al. 2012). HSP90 inhibitors offer several benefits as anticancer medications: Because many signalling pathways are HSP90 client proteins, (i) HSP90 inhibitors can concurrently aim many signalling pathways. As a result, anti-HSP90 treatment is less likely to cause tumour cells to survive than single-target therapy. (ii)The inhibitors of HSP-90 can increase site-specific damage in tumour tissues while causing the least harm to healthy tissues. (iii) When HSP90 and proteasome inhibitors are used together, unfolded proteins accumulate that are hazardous to cancer and soluble (Lu et al. 2012).

Table 1.

Development of HSP90 Inhibitors for Cancer

SL.NO	Drug Name	Molecular Mechanism	References
1	2-Amino-7-[4-fluoro-2-(3-pyridyl)phenyl]-4-methyl-7,8 dihydro-6H-quinazolin-5-one oxime	Targets N-terminal ATPase site	Amici et al. (2014)
2	Onalespib	Induces senescence	Chan et al. (2013)
3	BJ-B11	Induces apoptosis	Ju et al. (2011)
4	Celastrol	Depletes BCR–ABL and induces apoptosis	Lu et al. (2010)
5	CH5164840	Induces oncogenic client protein degradation	Ono et al. (2012)
6	CUDC-305	induces apoptosis	Bao et al. (2009)
7	3,4-Diarylpyrazole	Inhibits ATPase activity	Cheung et al. (2005)
8	DMAG-N-oxide	Inhibits migration and integrin	Tsutsumi et al. (2008)
9	(-)-Epigallocatechinssgallate (EGCG)	Binds to HSP90 C-n terminus	Moses et al. (2015)
10	HSP990	Enhances PI3K inhibition	Wachsberger et al. (2014)

The first HSP90 inhibitor to be studied as an anticancer drug was GA, a benzoquinone ansamycin antibiotic. In animal experiments, it displayed significant hepatotoxicity but high anticancer efficacy (Rober et al 1995). GA binds to HSP90 and prevents glioma cells from migrating when HIF-1 is downregulated and FAK is phosphorylated. Caspase-3 triggers the apoptosis-inducing factor (AIF) and cytochrome C; also causes caspase-dependent apoptosis in mitochondrial glial cells (Nomura et al. 2004). In individuals suffering from resistant solid tumours and hematologic malignancies, PF-04929113 (SNX-5422, orally accessible selective HSP90 inhibitor) via oral treatment demonstrated better tolerability and promising anti-neoplastic efficacy (Rajan et al. 2011).

Individuals with non-Hodgkin lymphoma and lung cancer are now being investigated in clinical studies using the HSP90 inhibitor NVP-AUY922 (Seggewiss-Bernhardt et al. 2015). Thyroid, lung, colorectal, adrenocortical multiple myeloma, neuroendocrine carcinoid, CML cancer cells, and adult T-cells leukemia-lymphoma all experience cell death. It decreased the size and quantity of C666-1 tumours in mice in vivo (Chan et al. 2013).

Cancer and large HSPs

Two essential proteins make up the big HSP family, i.e., GRP170, which is kept in the endoplasmic reticulum and is most probably persuaded by glucose scarcity, and heat shock protein110 (also called HSP105), which is mainly brought by heat shock (Wang and Subjeck 2013). HSP110 also interacts with HSPs like HSP70 and 27. HSP110 is a far more effective chaperone than HSP70 at maintaining denatured proteins in a soluble, foldable form. This capacity is part of its chaperone action. In vivo thermotolerance in mammalian cells and the major protection/repair route for denaturing proteins contain HSP110. One of their remarkable cancer-related characteristics is the potential of big HSPs (HSP110 and GRP170) to stimulate the immune system and increase the immunogenicity of protein antigens. Large HSPs may boost the efficiency of antigen-targeted cancer vaccines by binding to and targeting the antigen protein for dendritic cell-mediated cross-presentation(Zuo et al. 2016).

Cancer development

siRNA produced synthetically aiming heat shock protein-110 to bring upon apoptosis in a wide variety of cancer cells and also critical for the organogenesis via improvement during the progress of embryo. This siRNA-induced apoptosis was mediated through caspases, but not the p53 tumour suppressor protein, even though the HSP105 protein was bound to wild-type p53 protein in HCT116 cells (Hosaka et al. 2006).

Biomarker and diagnostic applications

The noteworthy potential exists for HSP110 in the detection and prognosis of cancer. It is overexpressed in several malignancies, including oesophagal cancer, thyroid cancer, lung cancer, prolactinoma, melanoma, pituitary adenoma, and cancers of the breast, colorectal, pancreas, thyroid, and pituitary glands. Patients with melanoma or tongue squamous cell carcinoma have a terrible prognosis when HSP110 is highly expressed (Chengetayi Muchemwa et al. 2008).

Treatment and therapeutics

HSP 110 might be a target for treating colorectal, melanoma, and non-Hodgkin lymphoma. Immunization with dendritic cells pulsed with HSP110 led to tumour growth constraining and tumour denial in an intestinal adenoma model of mice. An HSP vaccine for stage IV or stage IIIB/C advanced melanoma has received the investigational new drug (IND) designation from FDA (Wang and Subjeck 2013).

Conclusion

The potential of HSPs in the context of cancer research is both promising and multifaceted. These molecular chaperones serve as not only clinical indicators but also pivotal players in the intricate landscape of carcinogenesis. Triggered by cellular stress, HSPs spring into action, with HSP90 and GRP78 emerging as prime targets for innovative anticancer therapies. While the development of HSP inhibitors remains a work in progress, it's crucial to recognize that HSPs are essential for the fundamental functioning of both normal and malignant cells. Their collaborative network ensures the smooth conduct of vital cellular processes. Interestingly, inhibiting one HSP may lead to the overexpression of others, highlighting the need for a comprehensive approach to target this intricate web of proteins. Small-molecule HSP inhibitors hold the potential to enhance the efficacy and specificity of cancer treatments significantly. Additionally, cutting-edge technologies like siRNA and CRISPR/Cas9 offer the means to target specific HSP molecules, thereby increasing precision in malignancy therapy. Furthermore, the utilization of nanoparticles containing HSP inhibitors may revolutionize drug delivery, ensuring that medications reach their intended cells or tissues with pinpoint accuracy. The roles of HSP 27, 40, 60, 70, and 90 in promoting metastasis, angiogenesis, and cell growth underscore their significance in cancer progression. Consequently, inhibitors targeting these HSP proteins may prove to be potent allies in the fight against cancer by curbing metastasis and angiogenesis, bringing us closer to more effective anticancer therapies.

Author contributions

YMT, DT, TES, VJ, AHR, SKM, AB, and AB made significant contribution to the work reported, whether that is in the conception, execution, or the acquisition, analysis, or interpretation of data, or all the areas; took part in drafting, revising, or critically reviewing the article; and gave final approval of the version to be published. All have read and agreed to the published version of the manuscript.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

The data that support the findings of this study are available in standard research databases such as PubMed, Science Direct, or Google Scholar, and/or on public domains that can be searched with either key words or DOI numbers.

Declarations

Conflict of interest

The authors declare that there is no conflict of interest.

Research involving human participants and/or animals

Not involved human participants and/or animals.

Informed consent

Not involved human participants so not applicable.