Table 2.
Studies Investigating Mechanisms of Oral Microbiome-Induced Carcinogenesis.
| Author | Year | Cancer Type | Study Design | Sample Type | Number of Samples | Major Findings |
|---|---|---|---|---|---|---|
| Kostic et al. | 2013 | CRC | In vitro, animal model | In vitro cancer progression model | Samples from adenoma (n = 32) and carcinoma (n = 27) cases | In ApcMin/+ mouse model, F. nucleatum increases tumor multiplicity and selectively recruits tumor-infiltrating myeloid cells, which can promote tumor progression. Tumors from ApcMin/+ mice exposed to Fusobacterium nucleatum exhibit a proinflammatory expression signature that is shared with human fusobacteria-positive CRC. |
| Gur et al. | 2015 | CRC | In vitro | Cell lines | Cells | F. nucleatum specifically targets the inhibitory receptor TIGIT, via its Fap2 protein, to inhibit immune cell activities. NK cell killing of tumors is inhibited by hemagglutinating F. nucleatum strains. |
| Abed et al. | 2016 | CRC | In vitro, animal model | Human CRC samples, orthotopic mouse CRC model | CRC metastases from 5 frozen and 7 formalin-fixed, paraffin-embedded blocks, 7 tumor-free samples | Fusobacterial Fap2 and host Gal-GalNAc are involved in fusobacterial CRC localization and enrichment. |
| Proenca et al. | 2018 | CRC | In vitro | Clinical specimens | Diseased and adjacent normal tissues of 27 CRA and 43 CRC patients. | mRNA expression of IL-1B, IL-6, IL-8, and miR-22 was positively correlated with F. nucleatum quantification in CRC tumors. mRNA expression of miR-135b and TNF was inversely correlated. The miRNA/mRNA interaction network suggested that the upregulation of miR-34a in CRC proceeds via aTLR2/TLR4-dependent response to F. nucleatum. KRAS mutations were more frequently observed in CRC samples infected with F. nucleatum and were associated with greater expression of miR-21 in CRA, while IL-8 was upregulated in MSI-high CRC. |
| Wu, Wu, et al. | 2018 | CRC | In vitro, animal model | Animal specimens | C57BL/6-ApcMin/+ | F. nucleatum and antibiotics treatment altered gut microbial structures in mice. F. nucleatum invaded intestinal mucosa in large amounts but were less abundant in the feces ofF. nucleatum–fed mice. The average number and size of intestinal tumors in F. nucleatum groups were increased compared to control groups in ApcMin/+ mice. The expression of TLR4, PAK1, p-PAK1, p-β-catenin S675, and cyclin D1 was increased in F. nucleatum groups compared to the controls. TAK-242 decreased number and size of tumors compared to F. nucleatum groups. p-PAK1, p-β-catenin S675, and cyclin D1 expression was decreased in the TAK-242-treated group compared to F. nucleatum groups. |
| Rubinstein et al. | 2019 | CRC | In vitro, animal model | Cancer progression model | 18 CRC cases, ApcMin/+ mouse model | Annexin A1 is specifically expressed in proliferating colorectal cancer cells and involved in activation of cyclin D1. Its expression level in colon cancer is a predictor of poor prognosis independent of cancer stage, grade, age, and sex. The FadA adhesin from F. nucleatum upregulates annexin A1 expression through E-cadherin. A positive feedback loop between FadA and annexin A1 is identified in the cancerous cells, absent in the noncancerous cells. |
| Martilla et al. | 2013 | HNSCC | Clinical | Microbial samples taken from the mucosa using filter paper | 30 OSCC; 30 oral lichenoid disease; 30 controls | The majority (68%) of cultures produced carcinogenic levels of acetaldehyde (>100 mM) when incubated with ethanol (22 mM). The mean acetaldehyde production by microbes cultured from smoker samples was significantly higher (213 mM) than from nonsmoker samples (141 mM). |
| Moritani et al. | 2015 | HNSCC | Clinical | Saliva, bacterial strains | 28 species; 166 orally healthy subjects | All Neisseria species tested produced conspicuous amounts of ACH from ethanol, and Rothia mucilaginosa, Streptococcus mitis, and Prevotella histicola exhibited the ability to produce ACH. In addition, xylitol and sorbitol inhibited ACH production by Neisseria mucosa by more than 90%. |
| Gallimidi et al. | 2015 | HNSCC | In vitro, animal model | Mouse tongue | n = 14 mice | Porphyromonas gingivalis and F. nucleatum stimulate tumorigenesis via direct interaction with oral epithelial cells through Toll-like receptors. |
| Sztutskowa et al. | 2016 | HNSCC | In vitro | Human TIGKs | Cells infected withP. gingivalis, Streptococcus gordonii, and F. nucleatum | P. gingivalis induced expression and nuclear localization of the ZEB1 transcription factor, which controls epithelial-mesenchymal transition. P. gingivalis also caused an increase in ZEB1 expression as a dual-species community with F. nucleatum or S. gordonii. Increased ZEB1 expression was associated with elevated ZEB1 promoter activity. P. gingivalis strains lacking the FimA fimbrial protein were attenuated in their ability to induce ZEB1 expression. ZEB1 levels correlated with an increase in expression of mesenchymal markers, including vimentin and MMP-9, and with enhanced migration of epithelial cells. Knockdown of ZEB1 with siRNA prevented the P. gingivalis–induced increase in mesenchymal markers and epithelial cell migration. Oral infection of mice byP. gingivalis increased ZEB1 levels in gingival tissues, and intracellular P. gingivalis was detected by antibody staining in biopsy samples from OSCC. |
| Groenger et al. | 2017 | HNSCC | In vitro | Cell lines | PHGK and SCC-25 cells infected withP. gingivalis | After infection with P. gingivalis membranes, the RNA of 16 to 33 of 84 key genes involved in the antibacterial immune response was upregulated; among them were IKBKB (NF-κB signaling pathway), IRF5 (TLR signaling), and JUN, MAP2K4, MAPK14, and MAPK8 (MAPK pathway) in SCC-25 cells and IKBKB, IRF5, JUN, MAP2K4, MAPK14, and MAPK8 in PHGK. Significant upregulation of IKBKB, MAP2K4, MAPK14, and IRF5 was demonstrated in SCC-25 cells and IKBKB, MAP2K4, MAPK 14, IRF5, and JUN in PHGK. P. gingivalis membrane upregulated the expression of genes involved in downstream TLR, NF-κB, and MAPK signaling pathways involved in the proinflammatory immune response in primary and malignant oral epithelial cells. |
| Geng et al. | 2017 | HNSCC | In vitro | HIOECs | P. gingivalis–infected HIOECs | Persistent exposure to P. gingivalis caused cell morphological changes, increased proliferation ability with higher S phase fraction in the cell cycle, and promoted cell migratory and invasive properties. Tumor-related genes such as NNMT, FLI1, GAS6, lncRNACCAT1, PDCD1LG2, and CD274 may be considered the key regulators in tumor-like transformation in response to long-time exposure of P. gingivalis. |
| Woo et al. | 2017 | HNSCC | In vitro | OSCC cell line (OSC-20) | P. gingivalis–infected OSC-20 | Sustained infection with P. gingivalis could modify the response of OSCC cells to chemotherapeutic agents and their metastatic capability in vivo. Tumor xenografts composed of P. gingivalis–infected OSCC cells demonstrated a higher resistance to Taxol through Notch1 activation, as compared with uninfected cells. P. gingivalis–infected OSCC cells formed more metastatic foci in the lung than uninfected cells. |
| Wu, Zheng, et al. | 2018 | HNSCC | In vitro, animal model | Wild-type C57BL/6 mice |
4NQO-induced oral carcinoma andP. gingivalis–induced chronic periodontitis model | P. gingivalis infection increased the tongue lesion size and multiplicity of each mouse and promoted oral cancer development. P. gingivalis treatment significantly increased the level of free fatty acids and altered the fatty acid profile in tongue tissues and the serum of mice. P. gingivalis induced the formation of fatty liver of the mice. Expression of fatty acid synthase and acetyl-CoA carboxylase 1 were increased in the tongue and liver tissues of 4NQO-treated mice infected with P. gingivalis. |
| Yost et al. | 2018 | HNSCC | In vitro | community-wide metatranscriptome | Oral swab samples from OSCC tumor (n = 4), a healthy adjacent site (n = 4), matching sites (n = 4), and buccal mucosa (n = 3) from healthy subjects (n = 4) | Fusobacteria showed a higher number of transcripts at tumor sites and tumor-adjacent sites of cancer patients compared to the healthy controls. Specific metabolic signatures were consistently found in disease. Activities such as iron ion transport, tryptophanase activity, peptidase activities, and superoxide dismutase were overrepresented in tumor and tumor-adjacent samples when compared to the healthy controls. OSCC-oral communities showed that activities related to capsule biosynthesis, flagellum synthesis and assembly, chemotaxis, iron transport, hemolysins, and adhesins were upregulated at tumor sites. Activities associated with protection against reactive nitrogen intermediates, chemotaxis, and flagellar and capsule biosynthesis were also upregulated in nontumor sites of cancer patients. |
| Abdulkareem et al. | 2018 | HNSCC | In vitro | OSCC cell line (H400) | Cells were treated separately with heat-killed periodontal pathogensF. nucleatum, P. gingivalis, or Escherichia coli LPS | Upregulation after 1, 5, and 8 d in transcription of mesenchymal markers and downregulation of epithelial ones compared with unstimulated controls. Periodontal pathogens caused increase in level of all cytokines investigated, which could be involved in EMT induction and Snail activation. Exposure of cells to the bacteria increased migration and the rate of wound closure. Downregulation of epithelial markers also resulted in decrease in impedance resistance of cell monolayers to passage of electrical current. |
| Song et al. | 2019 | HNSCC | In vitro, animal model | OSC-20 cell line, BALB/c mice | BALB/c mice grafted with OSC-20 and treated with P. gingivalis | Compared with uninfected mice, the mice that were chronically administered P. gingivalis showed increased resistance to paclitaxel and a decreased tumor growth rate. P. gingivalis–treated mice exhibited higher serum IL-6 than uninfected mice. The sensitivity of tumor xenografts to paclitaxel in mice administered P. gingivalis was increased when the mice were administered ibuprofen. |
| Ohshima et al. | 2019 | HNSCC | In vitro | Human TIGKs, OKF6/TERT2 keratinocytes, SCC9 and HeLa cells | Cells infected with P. gingivalis, S. gordonii, Streptococcus sanguinis, Streptococcus cristatus, and F. nucleatum | P. gingivalis can upregulate expression of ZEB2, a transcription factor that controls epithelial-mesenchymal transition and inflammatory responses. ZEB2 regulation by P. gingivalis was mediated through pathways involving β-catenin and FOXO1. S. gordonii was capable of antagonizing ZEB2 expression. S. gordonii suppressed FOXO1 by activating the TAK1-NLK negative regulatory pathway, even in the presence of P. gingivalis. |
| Stashenko et al. | 2019 | HNSCC | In vitro, animal model | 4NQO-induced model of OSCC in gnotobiotic mice | Microbiome inocula from healthy mice and mice with 4NQO-induced tumor, 16S rRNA gene sequencing, and metatranscriptomic | Mice colonized with different oral microbiomes and exposed to 4NQO had increased tumor numbers and sizes compared to controls exposed to 4NQO but lacking a microbiome. In the 2 groups that were inoculated with OSCC-associated microbiome, opposite profiles of abundance in Parabacteroides and Corynebacterium were observed. While the percentage of Parabacteroides bacteria decreased in the control group, it increased in the OSCC group, and the opposite was observed for Corynebacterium. The metatranscriptomic analysis revealed overexpression of the same metabolic signatures associated with OSCC regardless of the community profile. These included nitrogen transport, response to stress, interspecies interactions, Wnt pathway modulation, and amino acid and lipid biosynthesis. |
ACH, acetaldehyde; CRA, colorectal adenoma; CRC, colorectal carcinoma; EMT, epithelial-mesenchymal transition; HIOEC, human immortalized oral epithelial cell; HNSCC, head and neck squamous cell carcinomas; IL, interleukin; miRNA, microRNA; mRNA, messenger RNA; MSI, microsatellite instability; NK, natural killer; OSCC, oral squamous cell carcinoma; rRNA, ribosomal RNA; siRNA, small interfering RNA; TIGK, telomerase immortalized gingival keratinocyte; TNF, tumor necrosis factor; 4NQO, 4-nitroquinoline-1-oxide.