In this study, we screen a total of 243 DEGs, comprising 143 upregulated genes and 100 downregulated genes. After this screening with the PPI network and a Random Forest model, we selected KRT20 as a potentially key gene related to HNSCC’s LM and prognosis. Our analysis of HNSCC tissue microarrays was consistent with the results of our bioinformatics analysis, both indicating that KRT20 is highly expressed in N1+ HNSCC patients and predicts a poor prognosis.
Cytokeratins are filament cytoskeleton proteins that are found in all cells. Keratins are the most prevalent intermediate filament category found in epithelial cells, and they are expressed differently depending on the cell type. Tonofilaments made of keratin filaments braid the nucleus, span the cytoplasm, and adhere to the cytoplasmic plaques of epithelial cell-cell junctions (desmosomes) in epithelia. Keratins are an integral part of the stability continuum from single cells through tissue formation, and they play a key role in the integrity and mechanical stability of both single epithelial cells and epithelial tissues. . Several types of cytokeratins have been described in both normal urothelium and neoplastic urothelium .
KRT20, also known as keratin 20, is a low-molecular-weight cytokeratin encoded by the KRT20 gene, and it is located on chromosome 17q21.2. KRT20 is expressed differently in tumors. In the context of urothelial bladder cancer, strong evidence has suggested KRT20’s diagnostic and prognostic value. Moreover, molecular techniques have demonstrated higher KRT20 expression levels in bladder cancer samples compared to non-neoplastic bladder tissue . In 2010, Ye et al. found that KRT20’s staining intensity in cancer tissues significantly correlated with bladder carcinoma grades, distant metastasis, and TNM grades . Moreover, a previous study suggested similar results for colorectal tumors. KRT20 expression levels were significantly higher in colorectal tumors than in normal mucosa. Furthermore, KRT20 expression was associated with colorectal cancer recurrence and median survival rates among that study’s patient population . Yet, there are also several studies indicated different roles of KRT20 in tumor progression. Researchers found that tumors characterized by the complete absence of KRT20 expression were very poorly differentiated and contained high percentages of Ki67+ cells. More research was required to learn about KRT20.
KRT20’s role in HNSCC remains unclear—especially in the LM context. Through genome-wide co-expression analysis, we found that KRT20 may participate in drug metabolism cytochrome P450, glycerophospholipid metabolism, glutathione metabolism, retinol metabolism, lysine degradation, valine leucine and isoleucine degradation, and steroid hormone biosynthesis. Cytochrome P450s’ major function is the metabolism of foreign compounds. Previous studies have demonstrated cytochromes involvement in different tumors’ development and drug resistance. Furthermore, CYP1A1, a member of the cytochromes family, is regarded as a typical lung cancer biomarker . CYP1A1 is also thought to play a role in the pathophysiology of inflammatory illnesses by acting as an oxygenase in eicosanoid metabolism, according to recent research . The relationship between inflammation and malignancies has been well-studied. Chemokines, prostaglandins, and cytokines, all of which have been demonstrated to inhibit CYP enzyme function, are components of cancer inflammation . The proinflammatory cytokines IL-6, INF-, TNF-, and IL-1 are thought to be the most powerful mediators of cytochrome activity and expression reduction. Eicosanoids generated from cytochromes are affected by cancer-related inflammation .
Glycerophospholipid metabolism plays an important role in tumor cell survival, and it affects fundamental cellular processes—including signal transduction and gene expression. Highly proliferating cancer cells require the synthesis of new fatty acids to provide a constant glycerophospholipids supply. New fatty acids are needed to continuously provide glycerophospholipids for membrane production. Therefore, unlike normal tissues, endogenously synthesized fatty acids are primarily esterified to phospholipids—rather than triacylglycerols—from phosphatidic acid in membrane production . Glutathione (GSH) is the most common antioxidant in living creatures, and it has a variety of roles, the majority of which are related to maintaining the redox equilibrium of cells. Glutamyl transferase (GGT) is a membrane-bound enzyme that catalyzes the breakdown of extracellular GSH, allowing the creation of the constituent glutamate and cysteine required for intracellular GSH synthesis to take place. Under oxidative stress, GGT levels are considerably increased, particularly in highly metabolic cancer cells. A considerable glutathione route and dipeptide metabolites have been linked to stage IV clear-cell renal cell carcinoma, according to metabolomic analysis .
The results of the current study indicated that KRT20 is highly expressed among patients with N1+ HNSCC. Moreover, KRT20 overexpression was found to relate to poorer overall survival rates among patients with HNSCC. These results were verified in our clinical samples database. The research also showed the overexpression of KRT20 promoted migration and invasion in HNSCC cell lines. Accordingly, we propose that KRT20 is a potential biomarker involved in the LM of HNSCC.
However, this study entailed several limitations. First, it was based on the TCGA. Although the results were verified in our clinical samples containing 68 HNSCC patients, the sample size was insufficient. Importantly, this study’s results must be validated using external databases. Secondly, our study was verified in cell experiments but not in in vivo experiments. Besides, proposed molecular mechanism and its genotype–phenotype correlation were not investigated in corresponding in vitro and in vivo experiments. KRT20’s molecular mechanism in the LM of HNSCC remains unclear, and further studies are needed to elucidate this mechanism.