Studies on tongue cancer are severely lacking; with no clear marker genes, prognosis and progression are difficult to predict, and low drug sensitivity during treatment is a challenge. Prior research addressing the role of single transcripts in the treatment of OTSCC has failed to elucidate how their effects at the genetic level. Reviews examining the relationship between clinical phenotype and tumor have also been unsuccessful at answering this question (14–17). Although the incidence of this cancer is increasing each year among young people (1–4), the reason for the increase remains unclear. No credible association between smoking and OTSCC has been found among young or old patients (18, 19).
Here, we demonstrated the MAPK cascade involvement of all target genes corresponding to mutant methylation promoters simultaneously present in the tumors of five patients with OTSCC. Thus far, no other studies have found abnormalities in the expression of MAPK cascade pathways in OTSCC tissues. The MAPK pathway mediates cell proliferation, differentiation, and chemotaxis. Its negative feedback regulation of the MAPK cascade in cancer cells reduces the sensitivity and efficacy of cancer therapeutic agents (20, 21). Moreover, the pathway influences important physiological processes (e.g., neuronal function, immune response, and embryonic development) through regulating gene expression, cytoskeletal protein dynamics, and cell proliferation or apoptosis pathways (22, 23). Based on our findings and previous reports, we put forward a preliminary hypothesis that the MAPK cascade is deeply involved in the biological variation of oral cancer development, migration, and drug resistance. The results of this study suggest that mutation of methylated promoters triggers aberrant expression of mRNA transcripts, ultimately activating the MAPK cascade. Therefore, if we can target and block specific methylated promoter mutations and the resulting MAPK cascade, we may be able to reduce the likelihood of adverse events in OTSCC.
The occurrence of extracellular matrix heterogeneity is inextricably linked to tumors. The precipitation and mechanical sclerosis of the extracellular matrix are considered key factors leading to tumor infiltration and metastasis (24–27). Here, we confirmed that in tumor samples of patients with OTSCC, an abnormal extracellular matrix is associated with cancer progression. Recent research suggests that activation of the PI3K-Akt signaling pathway promotes epithelial-mesenchymal transition (EMT), ultimately resulting in tumor invasion, metastasis, and drug resistance (28). Studies have also confirmed that some specific inhibitors of the PI3K-Akt signaling pathway (e.g., marine drugs) can reverse EMT and thus reduce the degree of drug resistance in tumor tissue during treatment (29, 30). Similar to these previous results, we also noted activation of the PI3K-Akt signaling pathway in OTSCC. Thus, further investigation is needed to determine whether drugs that specifically act on this pathway can inhibit EMT and improve patient prognosis.
Human papillomavirus (HPV)-negative tumors are believed to be associated with the development of oral squamous cell carcinoma, including of the tongue, and are also predictive of poor prognosis and treatment resistance (31, 32). In our study, HPV infection was the KEGG pathway with the second-highest number of aberrantly expressed transcripts enriched in OTSCC tissue. Another pathway of importance was the calcium signaling pathway, which is involved in crosstalk with reactive oxygen species (ROS) signaling pathways leading to tumorigenesis (33, 34). Inhibition of calcium signaling can inhibit cancer cell proliferation and metastasis in some cancers (35). Consistent with previous findings, our study confirmed the activation of the calcium signaling pathway in OTSCC tissues.
Data from the TCGA-HNSCC cohort were used to verify whether our results aligned with the results of previous large sample analyses. Notably, the most differentially expressed transcripts in OTSCC were clearly correlated with prognosis in the TCGA-HNSCC cohort. Nevertheless, the potential heterogeneity between HNSCC and OTSCC, ethnic differences in the patients studied, and differences in sequencing methods can explain why some of our results are inconsistent with the results of the HNSCC cohort analysis. With a larger sample size in future research, the credibility of our findings will also increase.
It has been demonstrated that LINC00885 promotes tumor cell proliferation and invasion (36). Current research has focused on breast and cervical cancers, but its expression in OTSCC remains unclear (37, 38). Our findings revealed that LINC00885 was also upregulated in OTSCC tissues. The prognostic signature model based on the target gene of LINC00885 has high predictive efficacy in predicting the patients' prognosis after surgery or treatment. Notably, since both HNRNPH1 and WDR81 have risk coefficients less than 0 in the risk profile model, the patients’ risk scores are the absolute value of the actual risk score. In this study, the HNRNPH1 and WDR81 genes were highly expressed in OTSCC tumor samples and serve as protective genes for predicting prognosis. Compared to gene-based models, the combined clinical phenotype-gene model has a more reliable predictive efficacy, but more complex information needs to be collected.
Our study found no correlation between mutations occurring in the genome and differences in the transcriptome. However, this does not mean that genes are not mutated in OTSCC tissues or that gene mutations do not affect the transcriptome, thereby leading to functional changes. On the contrary, genomic sequencing of OTSCC tissue samples from five patients showed a large number of mutations in the genome of the tumor tissue compared to the paracancerous tissue samples.
Our study shows that two mC-, two mCG-, and one mCHH-type methylation mutations cause aberrant expression of the transcriptome in OTSCC. Mapping such molecular changes to cellular functions reveals differences in MAPK cascade pathways. Further, lncRNAs as well as their target genes in the variants were used to predict the prognostic risk of patients. Ultimately, such changes lead to cancer development, increased drug resistance, and suboptimal prognosis in patients with OTSCC. Analysis of transcripts showed that five patients with OTSCC had differential genes mainly clustered in pathways with multiple functions. These pathways include deposition and mechanical sclerosis of extracellular matrix tissue, PI3K-Akt signaling pathway leading to EMT, HPV infection, and interaction of calcium signaling with ROS signaling. In conclusion, this study can provide a theoretical basis for follow-up research on experimental etiology or interventions. Targeted blockade of specific methylated promoter mutations and the resulting MAPK cascade may be a new direction for reducing adverse events in OTSCC. The prognostic signature models constructed based on the WDR81 and HNRNPH1 genes and the combined clinical phenotype-gene prognostic signature models have shown high predictive efficacy and can be constructed to predict patient prognostic risk in the clinical setting.