The Impact of Hydrogen Sulfide Regulatory Gene Alterations on Head and neck squamous cell carcinoma prognosis and tumor microenvironment

Abstract Background Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer globally, with high morbidity and mortality due to late-stage diagnoses, treatment resistance, and recurrence. Hydrogen sulfide (H 2 S) metabolism, primarily regulated by cystathionine gamma-lyase ( CTH ) and cystathionine beta-synthase ( CBS ), plays a crucial role in cancer biology by promoting tumour proliferation and survival. This study investigates the expression and methylation patterns of H 2 S regulatory genes [ CTH , CBS , catalase ( CAT ), D-amino acid oxidase ( DAO ), mercaptopyruvate sulfurtransferase ( MPST ), and sulfide quinone reductase-like protein ( SQRDL )] in HNSCC, aiming to understand their role in cancer progression and prognosis. Materials and methods Gene expression and promoter methylation data were analysed using GEPIA2 and UALCAN. Kaplan–Meier survival analysis assessed prognostic relevance. Functional enrichment and protein–protein interaction (PPI) networks were examined using ShinyGO, STRING, and GeneMANIA. Single-cell RNA sequencing from the TISCH2 database provided insights into tumour microenvironment (TME) dynamics. Results CTH , CBS , and SQRDL were significantly upregulated in HNSCC tissues, while DAO remained unchanged. Promoter methylation analysis revealed hypomethylation of CTH and SQRDL , suggesting increased expression, while CBS , MPST , and DAO showed hypermethylation, indicating repression. Kaplan–Meier analysis linked high CTH and CAT expression and low DAO expression to poor overall survival. Functional enrichment highlighted roles in cysteine biosynthesis, sulfur metabolism, and oxidative stress. PPI networks interacted with tumour-related proteins, implicating H 2 S genes in tumour progression. Single-cell RNA sequencing confirmed differential expression across TME cell types, indicating a role in immune modulation. Conclusion H 2 S regulatory genes play a significant role in HNSCC progression through altered expression and epigenetic regulation. Their association with patient survival and involvement in critical metabolic pathways, suggest potential as prognostic biomarkers and therapeutic targets. Further clinical validation is needed to explore their utility in personalised HNSCC treatment.