KLF4 in cancer chemoresistance: molecular mechanisms and therapeutic implications

Abstract

Chemoresistance is a major obstacle in cancer treatment, and it often results in treatment failure and disease progression. Among the plethora of factors contributing to chemoresistance, the transcription factor Krüppel-like factor 4 (KLF4) has emerged as a pivotal player. This review discusses the role of KLF4 in orchestrating various mechanisms underlying cancer chemoresistance. KLF4, originally identified as a regulator of cell differentiation and proliferation, has recently gained attention for its role in modulating cellular responses to chemotherapeutic agents. Through complex regulatory networks, KLF4 modulates the process of drug efflux, DNA repair, apoptotic signaling, tumor heterogeneity, and cancer cell stemness, leading to the development of cancer chemoresistance. Additionally, tissue or cell types specific post-translational modification (PTM) of KLF4 plays a significant role in the development of cancer chemoresistance. The review explores emerging possibilities and available information that can be utilised to understand the mechanism of chemoresistance mediated by KLF4 in cancer. In conclusion, understanding the complex mechanisms through which KLF4 orchestrates cancer chemoresistance opens promising avenues for developing more effective therapeutic interventions to combat treatment-resistant cancers.

Introduction

Despite significant advancements in cancer treatment, chemoresistance remains a major challenge, limiting the effectiveness of standard chemotherapy regimens. The American Cancer Society estimated the 2,041,910 new cancer cases and 618,120 cancer deaths in the U.S. in 2025. Cancer mortality has steadily declined, preventing nearly 4.5 million deaths since 1991 due to reduced smoking, early detection, and improved treatments, although significant racial disparities persist. While cancer incidence has declined in men, it has risen in women, particularly in those under 50. Lung cancer rates in women under 65 have also surpassed those in men. Future progress in cancer control is threatened by racial disparities and increasing cases in younger adults, highlighting the need for equitable prevention and treatment efforts [1]. In India, the incidence of cancer cases is projected to rise by 12.8% in 2025 compared to 2020. Cancer chemoresistance is one of the major challenges in cancer therapeutics and contributes significantly to mortality. Ramos et al. reported the first evidence of cancer chemoresistance to nitrogen mustard in 1942 [2]. Since then, single or multidrug resistance has emerged with nearly all drugs used in cancer therapy. Drug resistance is responsible for approximately 80 to 90% of cancer patient mortality [3, 4]. Chemoresistance is either an inherent (intrinsic) or acquired characteristic of cancer cells to survive and proliferate in the presence of chemotherapeutic drugs that would normally induce cell death. Intrinsic chemoresistance can stem from (1) inherent genetic mutations, (2) tumor heterogeneity, or (3) activation of intrinsic pathways utilized as defense mechanisms against chemotherapeutic drugs or environmental toxins. Similarly, acquired resistance may develop because of: (1) activation of proto-oncogenes, (2) altered expression levels of drug targets, (3) alterations in the tumor microenvironment (TME) post-treatment, (4) development of cross cascade interactions of signaling pathways, (5) epigenetic alterations in genes taking part in carcinogenesis, (6) alterations in the cell cycle genes, (7) impairment of apoptosis mechanism, and (8) altered DNA repair pathways. Growing evidence also suggests that oncogenes have a direct or indirect effect on drug resistance in cancer cells [5]. Activation of a proto-oncogene to an oncogene promotes drug resistance, while the presence of a tumor suppressor gene enhances the sensitivity of cancer cells to chemotherapeutic agents [5].

Kruppel-like Factor 4 (KLF4) is a zinc finger transcription factor and a member of an evolutionarily conserved family. It was first identified by Shields et al. (1996) in mouse fibroblast cells and by Garrett-Sinha et al. (1996) in the small intestine of newborn mice [6, 7]. The human KLF4 gene, located on chromosome 9q31, was cloned and identified in human umbilical vein endothelial cells [8]. In a pioneering study published in 2006, KLF4 was found to be one of the four distinct transcription factors apart from Oct4, Sox2, and Nanog, that could transform adult mouse fibroblasts into embryonic stem cells [9]. KLF4 is involved in several other cellular physiological processes such as proliferation, apoptosis, and the pathogenesis of inflammation and tumorigenesis. In cancer, it is reported to function both as an oncogene and tumor suppressor. KLF4 has four distinct functional domains; an amino-terminal activation domain, a middle repression domain, a nuclear localization sequence, and a carboxyl-terminal DNA binding domain (DBD). The activation domain induces the expression, while the repression domain suppresses the expression of KLF4 target genes [10]. The presence of both activation and repression domains in KLF4 explains its tumor suppressor and oncogenic function in different cell and tissue types [11, 12]. KLF4 acts as an oncogene or tumor suppressor in a specific tissue or cell type and can also be established by assessing its role in either inducing chemoresistance or sensitizing cancer cells to chemotherapeutic agents. In Table 1, we have documented instances where KLF4 functions either as an oncogene or a tumor suppressor, contingent upon its role in either promoting chemoresistance or enhancing the sensitivity of cancer cells to chemotherapeutic agents. KLF4 protein directly or indirectly plays a role in the development of both intrinsic and acquired chemoresistance. Multiple factors such as altered KLF4 expression or sub-cellular localization enhance the effectiveness of chemotherapy drug treatment [13–15].

Table 1.

Reports highlighting KLF4’s role as either an oncogene or a tumor suppressor in the development of chemoresistance in cancer cells

S. no	Cancer type	Tumor-suppressor/oncogene	Tumor biopsy/cell line	KLF4 and chemoresistance	References
1	Colorectal cancer	Tumor-suppressor	HCT- 15	KLF4 protein Sensitise HCT- 15 cells to Cisplatin	[16]
		Oncogene	SW480	KLF4 protein desensitise SW480 cells to 5-FU	[17]
		Oncogene	Spheroid cells isolated from DLD- 1 cell line	KLF4 induces resistance to Chemotherapeutic agents in spheroid cells	[18]
		Tumor-suppressor	Colon cancer cell lines SW480, SW620, and HCT116	KLF4 induces sensitivity of colon cancer cells to 5-FU restrain autophagy pathway	[19]
2	Breast cancer	Tumor-suppressor	TNBC cell line MDA-MB- 231 and MDAMB- 468	High KLF4 expression sensitizes cancer cells to erlotinib	[20]
		Oncogene	MCF7; MDA-MB 231	KLF4 desensitises breast cancer cells to cisplatin	[21]
		Oncogene	HER2-amplified human BT474and M6 cell line	Knockdown of KLF4 sensitized the cells to lapatinib	[22]
		Oncogene	Primary biopsy tissues of human breast cancer	High KLF4 expression in breast cancer predicts lower pathological complete remission after neoadjuvant chemotherapy	[23]
3	Prostate cancer	Tumor- suppressor	Prostate cancer cell line PC- 3 and DU145	Cisplatin induced KLF4 promoted cell apoptosis in prostate cancer cells	[24]
		Tumor- suppressor	Prostate cancer cell line PC- 3 and DU145	non-protein coding RNA LINC00673 inhibits drug resistance by epigenetic reactivation of KLF4	[25]
4	Gastric cancer	Tumor-suppressor	Gastric cancer biopsy & cell lines (MKN45 and SNU1)	The loss of KLF4 leads to cisplatin resistance in H. pylori-positive gastric cancer	[26]
5	Lung Cancer	Tumor-suppressor	Human lung cancer cell lines A549 and A549, Cisplatin resistant cells	KLF 4 Enhances Sensitivity of Cisplatin to Lung Cancer Cells	[27]
		Oncogene	NSCLC patients tumor biopsy and cell line (H1993)	KLF4 enhances gefitinib resistance in lung cancer cells by promoting c-Met amplification	[28]
6	Hepatocellular carcinoma	Tumor-suppressor	Human Hepatocellular carcinoma cell line, Hep3B cells	DUB3 enzyme enhances the chemosensitivity by stabilizing the KLF4 protein in HCC cells	[29]
		Oncogene	Human Hepatocellular carcinoma cell lines Hep3B and Huh7	KLF4 induces the development of Sorafenib resistance in hepatocellular carcinoma cell lines	[30]
7	Osteosarcoma	Oncogene	Osteosarcoma cells line KHOS/NP, U2OS, and primary tumor cells MDOS- 20	KLF4 confers resistance to first-line chemotherapeutic drugs Adriamycin and Cisplatin	[31]
		Oncogene	Osteosarcoma cell lines (MG- 63, SaOS- 2 and U- 2 OS)	KLF4/HMGB1 interaction induced chemotherapy resistance in osteosarcoma cells	[32]
8	Ovarian cancer	Tumor suppressor	Ovarian cancer cell lines SKOV3 and OVCAR3	Increasing the levels of KLF4 through lentiviral transduction made ovarian cancer cells more responsive to the chemotherapy drugs paclitaxel and cisplatin	[33]

This review article aims to examine the role of Krüppel-like factor 4 (KLF4) in mediating cancer chemoresistance. The article will explore how KLF4 regulates key mechanisms such as drug efflux, DNA repair, apoptotic signaling, tumor heterogeneity, and cancer stemness, contributing to treatment failure and disease progression. It will also highlight the impact of post-translational modifications (PTMs) on KLF4’s function in a cancer type-specific manner. By analyzing currently available literature and online data, this review would suggest the potential therapeutic strategies that could counteract KLF4-driven chemoresistance, thereby improving cancer treatment outcomes. KLF4 functions as both a tumor suppressor and an oncogene in a tumor type-specific manner, resulting in contrasting effects on drug resistance. While addressing both aspects in a single manuscript is possible, it may overwhelm the reader. Focusing on one perspective often provides implicit insights into the other. While we briefly discuss KLF4’s tumor suppressor function, our primary focus is on KLF4 mediated molecular mechanisms and therapeutic implications in cancer chemoresistance, highlighting its oncogenic role in the development of cancer chemoresistance.

Analysis of KLF4 expression and its protein–protein interactions using online databases

Krüppel-like factor 4 (KLF4) modulates multiple signaling pathways, including mTORC1, p38 MAPK, and ERK/YAP, to enhance cancer cell survival, stemness, and chemoresistance. In ovarian cancer, KLF4 promotes cisplatin resistance via mTORC1 activation, enhancing cancer cell survival [34]. It also activates p38 MAPK by inducing MKK3/6, leading to HSP27 and ATF2 regulation, promoting epithelial-mesenchymal transition (EMT) and drug resistance [31]. In oral squamous cell carcinoma, KLF4 upregulation via the EphA2-ERK/YAP pathway enhances stemness and potential chemoresistance [35]. In colorectal cancer, KLF4 drives oxaliplatin resistance through PiHL–EZH2–HMGA2 signaling, promoting survival, self-renewal, and reduced apoptosis [36]. EGFR activation upregulates KLF4, which in turn enhances EGFR signaling, fostering cell survival and reducing sorafenib efficacy [30].

Further to explore the expression status of KLF4 and its involvement in other cellular processes and pathways, we did a pan-cancer analysis of the KLF4 gene across normal, tumor, and metastatic samples using TNMplot, which integrates TCGA, GTEx, and GEO datasets. Data processing and statistical analysis were performed using TNMplot’s built-in tools, and results were visualized through box plots. Our analysis revealed KLF4 downregulation in several cancers, while its overexpression was observed in AML, pancreatic, renal, and skin cancers (Fig. 1A).

Fig. 1.

A Pan-cancer analysis of KLF4 gene expression across various cancer types using TNMplot reveals KLF4 mRNA expression levels (Transcripts Per Million) in paired tumor and normal tissue samples. B PPI network analysis of KLF4 and its top 10 interacting genes identified using the STRING database. C and D. GO and KEGG pathway analysis of KLF4 and its interacting genes using the DAVID database highlights their key regulatory roles in cancer-associated pathways. *Indicates that the difference is statistically significant (p < 0.05)

Additionally, we performed protein–protein interaction (PPI) network analysis of KLF4 using STRING v12.0 (https://string-db.org/), identifying the top 10 interacting genes, including SOX2, NANOG, TP53, MYC, CTNNB1, and EP300, which are involved in stem cell maintenance and cancer-related pathways (Fig. 1B). Further, we did GO and KEGG analyses using DAVID database (https://david.ncifcrf.gov/). GO enrichment analysis revealed that KLF4 is significantly involved in biological processes (BP) such as stem cell population maintenance, cell fate commitment, and regulation of telomerase activity. Cellular component (CC) analysis associated KLF4 with transcription regulator complexes and many more, while molecular function (MF) analysis highlighted its roles in DNA binding, histone deacetylase binding, and RNA polymerase III transcription factor activity and many more (Fig. 1C). KEGG pathway analysis linked KLF4 to key signaling pathways, including Wnt signaling, cell cycle regulation, and various cancer-associated pathways (colorectal, thyroid, and endometrial cancers), supporting its diverse role in several cancer related pathways (Fig. 1D). P-values ≤ 0.05 were considered significant.

Molecular mechanisms of KLF4-mediated chemoresistance in cancer cells

KLF4 regulates several molecular mechanisms involved in developing cancer chemoresistance, such as drug efflux, drug metabolism, DNA damage response, apoptosis, and development of tumor heterogeneity.

Role of KLF4-mediated drug efflux in cancer chemoresistance

Drug efflux is a key factor in cancer chemoresistance, primarily mediated by a family of membrane proteins known as ATP-binding cassette (ABC) transporters, although the other drug efflux protein also has been reported such as P-glycoprotein [37]. These transporters actively pump chemotherapeutic drugs out of cancer cells, decreasing intracellular drug concentrations and diminishing their cytotoxic effects. Overexpression of ATP-binding cassette (ABC) transporters specifically, ABCB1, ABCG2, and ABCC1 mediate drug efflux and is the known cause of cancer chemoresistance. Duz et al. reported that ABC transporters expression was increased significantly as the Hep- 2 cells developed resistance to higher doses of Fluorouracil (5 FU), a chemotherapy drug [38]. KLF4 is known to regulate the expression of ABC transporter proteins. Knockdown of KLF4 in thyroid cancer cells decreases the resistance to doxorubicin and paclitaxel, by reducing the expression of ABC transporter proteins [39]. The same study reported overexpression of KLF4 increases the promoter activity of the ABCG2 gene [39]. Both KLF4 and ABC transporter proteins are suggested to be crucial contributors to chemoresistance in Laryngeal squamous cell carcinoma. In human acute myeloid leukemia cells expressing dominant-negative c-Jun, the efflux activity of multidrug transporter proteins is inhibited, resulting in enhanced sensitivity to chemotherapeutic drugs [40]. KLF4 represses the gene encoding the mitogen-activated protein kinase kinase MAP2 K7. Activated MAP2 K7 is a “kinase kinase” and is a known downstream activator of c-Jun NH₂-terminal kinase (JNK), c-Jun. This suggests KLF4 might induce the expression of multidrug transporter protein by inhibiting the expression of c-Jun.

Role of KLF4 mediated DNA damage response and endoplasmic reticulum stress resistance in cancer chemoresistance

Chemotherapy induces substantial DNA damage in cancer cells, typically through the formation of double-strand breaks, cross-linking, or base modifications. The DNA damage response is a complex cellular intrinsic mechanism to detect and repair such damage, maintaining genomic stability. After chemotherapy, cancer cells activate DNA damage response pathways to repair the damage and prevent cell death.

KLF4 is associated with the initiation of DNA damage response pathways, enhancing DNA repair and cell viability after exposure to chemotherapy-induced DNA damage, as seen in breast and several other cancers [41]. KLF4 was detected in chemotherapy-treated non-stem gastric cancer cells supporting the idea that DNA damage-induced expression of KLF4 in cancer cells plays a role in chemoresistance [42]. Concordant to this, recently Lu et al. also showed that KLF4 was detected in chemotherapy-treated non-stem gastric cancer cells but not in the control cells supporting the idea of DNA damage-induced expression of KLF4 in cancer cells [42]. Another clue pointing to KLF4’s role in chemoresistance involves the RAS gene, which is frequently mutated in cancers. Interestingly, the ectopic expression of the oncogenic RASV12 mutant allele does not result in the transformation of primary fibroblasts. Instead, it induces a senescence-like cell cycle arrest, prompting researchers to investigate factors responsible for RASV12-mediated transformation in mouse embryonic fibroblasts. KLF4 was identified as a crucial factor that bypassed RASV12-induced senescence and contributed to resistance against DNA-damage-induced apoptosis by suppressing p53 expression [43] (Fig. 2).

Fig. 2.

Schematic representation of KLF4 mediated signalling in tissue/cell type where KLF4 acts as an oncogene. The chemotherapeutic drugs used to treat cancer can cause significant DNA damage in cancer cells leading to increased level of KLF4. DNA damage induced KLF4 promotes the cancer cell survival and chemoresistance by inducing DNA repair pathway (via inducing p53 dependent and independent expression of p21, and its PARylation), inhibiting apoptosis (via inhibition of p53 and activation of anti-apoptotic gene MCL and BCL-XL), inducing ER stress resistance, and inducing the chemotherapeutic drug efflux. Figure was prepared using BioRender

KLF4 triggers p53-dependent G1/S cell cycle arrest in response to DNA damage caused by chemotherapy [44]. Another report indicates that KLF4 plays a crucial role as a mediator of p53 in driving the transcriptional activation of p21. The upregulation of p21 plays a crucial role in cell cycle arrest, allowing for DNA repair and contributing to the maintenance of genomic stability [45]. P53 independent upregulation of P21 also has been reported previously [46, 47]. Thus, the upregulation of p21, either p53 dependent [45] or independent [46, 47], plays a crucial role in cell cycle arrest, allowing for DNA repair and contributing to the maintenance of genomic stability.

The extent of DNA damage to cells (mild or severe) also affects the response of KLF4 to DNA damage. Zhou et al. observed an inverse relationship between KLF4 expression levels and the degree of DNA damage. P53 induces KLF4 activation in response to mild DNA damage. However, in the case of severe DNA damage, KLF4 is strongly suppressed due to increased mRNA degradation, which pushes cells toward irreversible apoptosis [48]. It is also evident that KLF4 suppresses the expression of p53, by directly acting on its promoter, resulting in a diminished level of apoptosis and resistance to DNA-damage-induced cell death [43]. KLF4 deficient cells had reduced expression of the anti-apoptotic proteins MCL1 and BCL-XL, and MCL1 was upregulated by lapatinib in a KLF4-dependent manner. Restoring MCL1 expression in KLF4 deficient cells re-established drug resistance [22] (Fig. 2).

Klf4-overexpression in KLF4 knockout mouse embryonic fibroblast cells exhibited a more robust DNA damage repair response [49]. This suggests that KLF4 enhances the ability of cancer cells to withstand the toxic effects of chemotherapy in certain types of cancer. Post-translational modification of KLF4 such as PARylation triggered by DNA damage, enhances its ability to bind to the p21 promoters on chromatin. This binding leads to cell cycle arrest and subsequent repair of damaged DNA. Such DNA repair processes promote cell survival and reduce the sensitivity of cells (chemo-resistant cells) to DNA-damaging chemotherapeutic drugs [41]. Authors also demonstrated increased sensitivity to PARP inhibitors upon KLF4 depletion or inhibition of its PARylation in cultured cell models of Triple-Negative Breast Cancer (TNBC). It is worth mentioning that PARP inhibitors like Olaparib, and Rucaparib are commonly used chemotherapeutic agents in cancer treatment. Silencing KLF4 enhanced the responsiveness of HER2-overexpressing cells to the chemotherapeutic drug lapatinib in human breast cancer cells [22]. Additionally, KLF4 selectively activates DNA repair pathways in a human oesophageal cancer cell line [50]. KLF4 overexpression also correlates with chemoresistance and poor prognostic in B-cell non-Hodgkin Lymphoma [51]. Ovarian cancer cell lines with the acquired resistance to cisplatin showed significantly higher expression of KLF4 compared to cisplatin-sensitive cells [52]. These cells also showed higher resistance to apoptosis and sub-G1 arrest. In osteosarcoma cells, expression of KLF4 was significantly induced after chemotherapeutic drugs (cisplatin, methotrexate, and doxorubicin treatment) treatment, and its knockdown induced apoptosis and drug sensitivity [32].

Tumor cells invading or metastasizing to distant sites often encounter stressors like hypoxia, oxidative stress, and glucose deprivation, which disrupt the protein-folding process in the endoplasmic reticulum (ER). These challenges lead to an accumulation of misfolded proteins in the ER, triggering ER stress and activating the unfolded protein response (UPR). Cancer cells are particularly prone to ER stress, and hyperactivation of the UPR is well-documented in numerous solid and hematologic malignancies. Furthermore, adaptation to ER stress plays a critical role in the development of chemoresistance. Elevated KLF4 levels have been shown to enhance ER stress resistance in melanoma by upregulating the transcription of NCUB2. [53]. Elevated NUCB2 has been shown to play a critical role in suppressing ER stress-induced apoptosis and facilitating cell metastasis in melanoma. This suggests that KLF4-mediated ER stress resistance enables cancer cells to evade apoptosis, thereby promoting cell survival [54].

Thus, KLF4 acts as a doorkeeper against genomic instability triggered by chemotherapeutic agents, subsequently inducing cell survival and chemoresistance in certain cancer types. Its intricate network of actions, from promoting DNA repair pathways to governing cell cycle progression and mitigating oxidative stress, collectively safeguards the cellular genome from various sources of DNA damage including chemotherapy. Hence targeting KLF4 in conditions where DNA damage or ER resistance underlies disease progression can be a promising specific target to combat cancer chemoresistance.

Role of KLF4 mediated tumor heterogeneity in cancer chemoresistance

Tumour heterogeneity refers to the existence of cells within the tumor, with distinct genotypes and/or phenotypes. During cancer progression, it generally becomes more heterogeneous. Such differences at the cellular level between the cells within a tumor may impose additional challenges for how a cancer can be diagnosed and treated. Two models are being used to explain the tumor heterogeneity, (1) the cancer stem cell model and, (2) the clonal evolution model [55]. Both models contribute to heterogeneity at varying extents in a tumor.

The Cancer Stem Cell (CSC) model of tumor heterogeneity is a concept that suggests tumors are composed of a hierarchical organization of cells with different abilities to proliferate and differentiate. According to this model, a specific group of cancer cells within the tumor, referred to as cancer stem cells, exhibit properties similar to those of stem cells. These cells are believed to drive tumor growth, metastasis, and recurrence due to their ability to self-renew and differentiate into various cell types that constitute the tumor mass. CSCs and heterogeneity raised due to it is a major contribution to tumor relapses and chemoresistance [56]. CSCs originate either from differentiated cells or pre-existing stem cells [57]. Unlike conventional stem cells, CSCs have deregulated self-renewal properties [58]. Chemotherapy induces the enrichment of cancer stem cell population in a tumor [59] including breast cancer [60–62], lung cancer [63], ovarian cancer [64], and prostate cancer [65]. In another report, authors showed that cisplatin treatment induces cancer stem cell enrichment in platinum-resistant ovarian cancer cells through NF-κB-TNFα-PIK3 CA signaling axis [64].

KLF4 is key to maintaining cancer cell stemness, crucial for the pluripotency and self-renewal of adult and embryonic stem cells, and influences their chemotherapy response. It has been used to generate induced pluripotent stem cells (iPS) from somatic fibroblasts [9]. KLF4 promotes stem cell-like traits in cancers such as osteosarcoma [31], colon [18, 66], and breast cancer [67–70]. It is highly expressed in cancer stem cell-enriched populations in mouse mammary tumors and breast cancer cell lines [68]. In glioblastoma [71] and colorectal cancer [66], KLF4 upregulates stem cell markers like OCT4, NANOG, and CD133. Karagonlar et al. showed that KLF4 overexpression in non-stem cells enabled tumor-forming ability similar to stem cells, suggesting its role in enhancing cancer stem cell enrichment or boosting stemness within tumors [72].

Two FDA-approved iron chelators, Deferoxamine (DFO) and Deferasirox (DFX) show promise as cancer therapies by inhibiting stemness markers such as KLF4, Nanog, c-Myc, SOX2, and OCT3/4, reducing chemoresistance and tumor progression [73–75]. Studies also found that DFO and DFX decrease stemness markers in esophageal cancer cells, unlike cisplatin [76]. Combining iron chelators with traditional chemotherapy could improve outcomes. Additionally, elevated levels of EGFR and KLF4 were linked to sorafenib resistance in hepatocellular carcinoma, and targeting EGFR with Erlotinib or Icotinib, while downregulating KLF4, restored sorafenib sensitivity [30]. These findings emphasize the potential of targeting KLF4 and related pathways to combat chemoresistance.

The clonal evolution model of tumor heterogeneity describes how cancer progresses through the accumulation of genetic mutations within tumor cells over time. This model suggests that tumors originate from a single cell that undergoes genetic changes, leading to the formation of a population of genetically diverse cells that are more resistant to cancer therapies. Clonal evolution leads emergence of multiple clonal lineages from a common ancestor cell in parallel leading to heterogeneity. These clonal lineages provide a selective advantage when exposed to chemo-therapeutic agents and radiations. Although the role of KLF4 in clonal evolution is not fully established, it plays a significant role in transforming mature, differentiated cells into immature, undifferentiated ones [77] a process heavily influenced by KLF4 [9]. Further, Damaghi et al. have reported that the harshest tumor microenvironmental conditions in ductal carcinoma in situ result in the clonal selection of cells with Warburg effect phenotype, and these cells showed increased nuclear KLF4 expression [78]. Thus, more investigation is needed to establish its role, but available information to date suggests that KLF4 may have a significant role in contributing to tumor heterogeneity by clonal evolution.

KLF4-mediated alterations in the tumor microenvironment contribute to chemoresistance

The tumor microenvironment (TME) consists of cancerous and non-cancerous cells in constant interaction, driving cancer progression and metastasis. Key non-cancerous components include cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), T cells, NK cells, B cells, endothelial cells, and pericytes. These cells shape tumor behavior and serve as valuable indicators for predicting therapeutic effectiveness [79]. These genomically stable yet adaptable TME cells have transcriptomes and phenotypes shaped by interactions with cancer cells and other TME components. For instance, fibroblasts can reprogram into various cancer-associated fibroblast (CAF) subtypes, including myofibroblastic, immune-regulatory, and antigen-presenting CAFs [80]. These subpopulations uniquely contribute to ECM production, adhesion, and immune regulation [81, 82]. Perivascular cell phenotypic switching in the pre-metastatic lung, driven by the expression of KLF4 and PDGFRα, is triggered by a growing primary tumor or tumor-secreted factors. Targeted inhibition of KLF4 expression in perivascular cells disrupts this phenotypic shift and significantly reduces metastatic spread [83]. In the same report, authors emphasize that therapies targeting KLF4 could prove beneficial when used in conjunction with chemotherapy. This combination could enhance the overall effectiveness of the treatment by addressing different aspects of tumor growth and spread. Further, studies have also identified that KLF 4 mediates infiltration and polarization of tumor-associated macrophages in the tumor microenvironment. Chen et al. demonstrated that increased KLF4 expression is associated with higher levels of CD8⁺ T cells and macrophage infiltration in Hepatocellular carcinoma [84]. In another recent report, Aurora et al. has shown that KLF4 induces the M2-type tumor microphase polarization which is associated with induced tumorigenesis [85]. In support of this Mantovani et al. reviewed that M2-type macrophages can induce chemoresistance by secreting growth factors and inhibiting cell death which leads to protection from the cytotoxic effects of chemotherapy [86]. M2 macrophages contribute to chemoresistance in colorectal cancer by reducing the apoptosis induced by 5-Fluorouracil (5-FU), a therapeutic drug used to treat various neoplasms [87]. Further, M2-type tumor-associated macrophages confer chemoresistance in peritoneally disseminated pancreatic cancer by inducing epithelial-to-mesenchymal transition [88]. Thus, KLF4 is implicated in the phenotypic switching of perivascular cells and macrophage polarization, which contributes to metastasis and chemoresistance. Targeting KLF4, particularly in combination with chemotherapy, could improve treatment outcomes by addressing both tumor growth and resistance mechanisms.

The role of post-translational modifications (PTMs) of KLF4 in the development of chemoresistance and its potential as a therapeutic target

KLFs are primarily regulated through post-translational modifications, notably phosphorylation, and acetylation, which influence their DNA-binding ability, protein interactions, and stability. KLF4 contains both transcriptional activation and repression domains, allowing it to regulate tumorigenesis and other diseases in a bidirectional manner. The coactivator p300/CBP, related to CREB-binding protein, interacts with KLF4 at its activation domain and acetylates lysine residues K225 and K229 on its repression domain [89]. CBP/p300 mediated acetylation of these lysine residues is required for the transcriptional activation of KLF4 target genes [89]. CBP/p300 contains an acetyl-lysine-specific protein interaction domain known as the ‘bromodomain,’ which plays a crucial role in regulating gene transcription. Bromodomains are present in several acetyltransferase proteins too, where they function as acetyl-lysine binding domains, as it has intrinsic property to bind with acetylated lysine [90]. This indicates that under specific conditions, the bromodomain may interact with acetylated lysine residues K225 and K229 in the repression domain of KLF4, leading to the transcriptional inactivation of KLF4 target genes. Previous studies in colon cancer cells have shown that this transcriptional inactivation of KLF4 results in chemoresistance [16]. CBP/p300 bromodomain inhibition declines the expression of several ABC transporter proteins, leading to increased multidrug sensitivity in breast cancer cells [91]. A potential explanation for the role of KLF4 in cancer progression and the development of chemoresistance can be outlined as follows: The CBP/p300 complex interacts with the activation domain of KLF4, which promotes the acetylation of two lysine residues (K225 and K229) situated within the repressor domain of KLF4. This acetylation process enhances KLF4’s transcriptional activity, leading to the activation of genes (e.g., ABC transporter) involved in promoting chemotherapy resistance (Fig. 3A). Although the tumor suppressor function of KLF4 is not within the scope of this review, one can speculate that the CBP/p300 complex interacts with the activation domain of KLF4, leading to the acetylation of two lysine residues in its repression domain, which may facilitate subsequent interactions as well, leading to the reduced transcription of genes (e.g., ABC transporter) involved in promoting chemotherapy resistance (Fig. 3B). Hence, the combination of chemotherapeutic drug treatment and CBP/p300 bromodomain inhibitors may reduce chemoresistance in cancer cells.

Fig. 3.

Post-translational modification (PTM) of KLF4 in the development of chemoresistance in cancer cells: The N-terminus of KLF4 contains an activation domain (1–157 amino acids) followed by a repression domain (158–385 amino acids). The activation domain interacts with p300/CBP, leading to transcriptional activation and acetylation of lysine residues (K225 and K229) in the repression domain. A PEST sequence rich in proline (P), glutamic acid (E), serine (S), and threonine (T) is located between these two domains, serving as a signal for protein degradation. The C-terminus features a DNA binding domain with three Zinc fingers (ZnF1, ZnF2, and ZnF3) that recognize and bind to specific DNA sequences in the nucleus. A nuclear localization signal between the Repression and DNA binding domains guides the transportation of KLF4 into the nucleus. Please note that the size of each domain may vary across studies and is not necessarily proportional in length. A Tissue/cells where KLF4 acts as an oncogene, p300/CBP acetylate lysine residues in the repression domain but do not interact with it, likely due to the presence of specific factors in the tissue. This result in transcription of genes that promote chemoresistance, such as ABC transporters, resulting in the development of chemoresistance. Treatment with bromodomain inhibitors during chemotherapy may enhance the sensitivity of cancer cells to treatment. B Tissue/cells where KLF4 acts as a tumor suppressor, p300/CBP acetylate lysine residues in the repression domain and also interact with it, resulting in reduced transcription of genes (e.g., ABC transporters) involved in promoting chemoresistance

Clinical implications

KLF4 plays a crucial role in mediating resistance to chemotherapy through mechanisms such as drug efflux, enhanced DNA repair, and tumor heterogeneity. Therapeutic strategies targeting KLF4 could help sensitize cancer cells to chemotherapy, improving treatment efficacy, particularly when combined with ABC transporter inhibitors. Additionally, KLF4 contributes to cancer stem cell maintenance and tumor relapse, suggesting that its inhibition may help prevent recurrence. Given its dual role as an oncogene or tumor suppressor, personalized treatment strategies targeting KLF4-specific pathways are essential. Monitoring KLF4 levels may help predict patient response to chemotherapy and guide personalized treatment strategies. Further, we suggest that KLF4-targeted therapies could be integrated into existing precision oncology strategies.

Future perspective

The exploration of KLF4 as a key architect of cancer chemoresistance opens several promising avenues for future research and therapeutic development. One significant direction is the detailed investigation of KLF4’s dual role as an oncogene and tumor suppressor in different cancer types, which could suggest personalized therapeutic strategies based on the cancer’s specific KLF4 profile. Understanding the post-translational modifications of KLF4 can further aid in combating chemoresistance in cancer patients. It is also important to know other factors than CBP/p300 that decide the oncogenic or tumor suppressor role of KLF4 in chemoresistance. More research is needed to understand KLF4’s interaction with the tumor microenvironment in patients who respond well to conventional therapy and those who do not. Future studies could focus on combinatory treatments that target KLF4 alongside conventional chemotherapy to overcome resistance and improve patient outcomes. Ultimately, the insights gained from this review suggest that targeting KLF4 could revolutionize the management of chemoresistant cancers, making it a crucial focus of oncological research.

Limitation of the study

As discussed previously, KLF4 exhibits a dual role as both an oncogene and a tumor suppressor. However, in this review, we have primarily focused on its oncogenic function to maintain clarity and prevent overwhelming the readers.

Abbreviations

ABC

ATP-binding cassette

BP

Biological process

CAF

Cancer-associated fibroblast

CC

Cellular component

CSC

Cancer stem cell

DBD

DNA-binding domain

DFO

Deferoxamine

DFX

Deferasirox

EGFR

Epidermal growth factor receptor

EMT

Epithelial-mesenchymal transition

ER

Endoplasmic reticulum

FDA

Food and Drug Administration

GO

Gene ontology

HCC

Hepatocellular carcinoma

HMGB

High-mobility group box

KEGG

Kyoto encyclopedia of genes and genomes

MF

Molecular function

mTORC1

Mechanistic target of rapamycin complex 1

NLS

Nuclear localization signal

NSCLC

Non-small-cell lung cancer

PARP

Poly (ADP-ribose) polymerase

PC

Prostate cancer

PEST

Proline, glutamic acid, serine, threonine

PPI

Protein–protein interaction

PTM

Post-translational modification

RCC

Renal cell carcinoma

TAM

Tumor-associated macrophage

TME

Tumor microenvironment

TNBC

Triple-negative breast cancer

UPR

Unfolded protein response

ZnF

Zinc finger

Author contributions

SSY was responsible for conceptualizing, designing, and editing the review and drafting the manuscript. PK and NK contributed by drafting the review's figures, tables, and sections. SS, ST, and SK updated the reference lists and screened potential studies for inclusion in the review. RRN interpreted the information, prepared and finalized the figures, edited the manuscript, and provided critical feedback throughout the drafting process.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.