HNSCC is the dominant subtype of head and neck cancer, representing over 90% of all cases1. Despite its high incidence and metastatic potential, early diagnosis remains challenging, and treatment options like immunotherapy lack consistent efficacy5. In light of these limitations, comprehensive research endeavors are crucial. In recent years, bioinformatics has offered a faster and more efficient approach to analyzing biological datasets, paving the way for novel insights18. In this study, we employed bioinformatics to analyze gene expression profiles from three datasets GSE6791 (42 HNSCC, 14 healthy controls), GSE29330 (13 HNSCC, 12 healthy controls), and GSE58911 (15 HNSCC, 15 healthy controls). Our analysis identified 28 co-DEGS in HNSCC, comprising eight up-regulated and 20 down-regulated genes. Furthermore, eight hub genes were identified, four up-regulated and four down-regulated. Notably, among the hub genes, up-regulated SPP1 and downregulated KRT78 expression significantly correlated with tumor grade, individual cancer stages, and poor survival in HNSCC patients.
GO analysis revealed that co-DEGs were primarily enriched in terms related to ECM organization, proteolysis, collagen catabolic process, and ECM disassembly. KEGG pathway analysis further highlighted significant enrichment in ECM-receptor interaction, rheumatoid arthritis, and the IL-17 signaling pathway. This finding aligns with existing evidence associating ECM with tumor development and progression19–21. Li et al. reported that proteolytic ECM degradation, driven by elevated plasminogen activator urokinase levels, contributes significantly to HNSCC metastasis22. Similarly, Tanis et al. observed increased expression of ECM-related genes like MMPs, laminin, and collagen in oral squamous cell carcinoma (OSCC), another major HNSCC subtype, linking these genes to OSCC metastasis23. Notably, MMPs, known for their role in ECM degradation and protein up-regulation across various cancers24, have been shown to accelerate tumor metastasis and invasion in nasopharyngeal carcinoma, another HNSCC type, through activity regulation25. Regarding ECM formation, overexpression of ECM-composing proteins like collagen and hyaluronic acid has been linked to increased matrix stiffness in the tumor microenvironment26. This aligns with our GO analysis suggesting abnormal ECM organization and catabolic reactions might contribute to cancer progression.
Our KEGG analysis further strengthens this notion by highlighting enrichment in ECM-receptor interaction consistent with Huang et al.’s findings emphasizing the crucial role of membrane receptors in recognizing ECM components in cancer26. Additionally, the enrichment in the rheumatoid arthritis pathway aligns with studies demonstrating enhanced immune response to Epstein-Barr virus (EBV) infection in rheumatoid arthritis patients compared to healthy controls27. Given the association of EBV with both rheumatoid arthritis and HNSCC, potential similarities in immune responses between these diseases cannot be ruled out28. Further, clinical studies in OSCC have reported a higher frequency of TH17 cells and a positive correlation between IL-17 expression and tumor budding29,30.
Through PPI network analysis, we identified four up-regulated hub genes (MMP1, MMP3, MMP12, and SSP1) and four down-regulated genes (CRNN, KRT4, KRT78, and SCEL). To determine their role in HNSCC, we conducted several analyses focusing on the relationship between hub gene expression and the disease. Our analysis of the TCGA HNSCC database revealed significantly elevated expression of MMP1, MMP3, MMP12, and SPP1 in tumor tissues compared to normal tissues. This finding aligns with established knowledge in several other cancers, where MMPs have been implicated in poor prognosis. For example, Zhang et al. observed increased MMP1 genes and protein expression in HNSCC, with over-expression positively correlating with advanced tumor size and metastasis. Similar findings have been reported for MMP1 in colorectal cancer, where knockdown experiments confirmed its pro-tumorigenic role31,32. Additionally, a bioinformatic study mirrored our results by demonstrating MMP1, MMP3, and MMP12 up-regulation in colorectal cancer, highlighting the potential universal relevance of these MMPs in tumor progression33. This up-regulation might be related to the general tendencies of MMPs in cancer, where MMP1 is significantly and almost universally upregulated, and MMP3 and MMP12 show significant upregulation in at least 10 types of cancer34.
Conversely, our analysis revealed significantly reduced expression of CRNN, KRT4, KRT78, and SCEL in HNSCC. Notably, this pattern was consistent across protein expression pattern data from both the CPTAC and HPA databases, further substantiating their potential involvement in the disease. CRNN, known for its tumor-suppressive functions in cell cycle regulation, is also down-regulated in other squamous cell carcinoma types, suggesting its broader role in epithelial malignancies35–37. Interestingly, CRNN down-regulation might contribute to KRT4 down-regulation, as CRNN acts as a keratinocyte proliferation marker38. Therefore, the co-downregulation of CRNN and KRT4 might synergistically promote the progression of squamous cell carcinomas like HNSCC. Regarding SCEL, identified as a precursor of the cornified envelope in keratinizing tissues, our finding of its down-regulation in HSCC aligns with observations in melanoma, where lower expression correlated with poor overall survival39,40. However, it’s worth noting that SCEL expression seems to vary depending on cancer type, as it has been found in gallbladder and pancreatic cancers41,42. Therefore, further investigations are needed to elucidate the context-specific roles of SCEL in different malignancies.
Among the up-regulated hub genes, SPP1, also known as OSTEOPONTIN, stood out for its strong association with tumor grade progression, particularly grade 2 (G2). This aligns with its established role in promoting tumor development and metastasis43. Feng et al. demonstrated that high SPP1 expression in HNSCC patients correlated with lymph node metastasis and macrophage infiltration, both of which contribute to cell proliferation and invasion of tumor44. Similarly, Cho et al., showed that silencing SPP1 in non-small cell lung cancer decreased protein levels and inhibited tumor growth45. Notably, elevated SPP1 is also observed in colon, gastric, and lung cancers43,46,47. It's worth noting that tumor G2, characterized by intermediate growth and limited spread, might represent a tipping point for metastasis48,49. While both grade 1 and G2 are typically curable with treatment, targeting SPP1, specifically at G2, could offer an effective therapeutic or diagnostic strategy.
Among the down-regulated hub genes, KRT78 expression displayed a significant association with individual cancer stages. These findings resonate with the established function of keratins, the intermediate filament proteins forming the cytoskeleton. Keratins are categorized into types 1 and 2, based on their characteristics, with KRT78 classified as type 2, alongside KRT450. Several studies have linked abnormal keratin expression to cancer progression51, in line with our GO analysis showing enriched keratinization in HNSCC co-DEGs. For instance, clinical studies report decreased keratin levels during the transition from normal to invasive HNSCC52, and down-regulation of both KRT4 and KRT13 in OSCC53. Additionally, co-expression of KRT4, KRT13, and KRT78 in the epithelium basal layer has been established54, further supporting our findings of co-downregulation of KRT4 and KRT78 in HNSCC. Interestingly Fortier et al. showed that loss of KRT8 and KRT18 in epithelial cells correlated with increased MMP2 and MMP9 activity, promoting collective cancer cell migration55. This parallels our observation of decreased KRT4 and KRT78 alongside increased MMP1, MMP3, and MMP12 expression in HNSCC.