Abstract:

Objective To analyze the expression， clinical significance， and relationship with tumor immune infiltration of serine/arginine-rich splicing factor 9 （SRSF9） in head and neck squamous cell carcinoma （HNSCC） by bioinformatics methods， and to discuss its mechanism. Methods The expression of SRSF9 in HNSCC and its relationship with clinical pathologic characteristics and prognosis of the patients were analyzed by The Cancer Genome Atlas （TCGA） Database， GSE30784 and GSE13601 datasets in Gene Expression Omnibus （GEO） Database， Clinical Proteomic Tumor Analysis Consortium （CPTAC） Database， Gene Expression Profiling Interactive Analysis （GEPIA） Database， and Kaplan-Meier plotter Database；the variations of SRSF9 gene were examined through cBioPortal Database； ESTIMATE algorithm and The Tumor Immune Estimation Resource （TIMER） Database were used to assess the correlation between SRSF9 expression and tumor microenvironment， as well as tumor immune cell infiltration； LinkedOmics Database was used to analyze the SRSF9 co-expressed genes and their regulatory pathways in the HNSCC；the TCGA SpliceSeq Database was used to analyze the variable splicing events regulated by SRSF9 in the HNSCC；Gene Ontology （GO） functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes （KEGG） signaling pathway enrichment analysis were conducted on the target genes. Results The analysis results from TCGA Database and GSE30784 and GSE13601 datasets in GEO Database showed that the expression level of SRSF9 mRNA in the HNSCC tissue was significantly higher than that in adjacent normal tissue （P<0.01）.The CPTAC Database analysis results showed that compared with normal tissue， the expression level of SRSF9 protein in the HNSCC tissue was significantly increased （P<0.001）.The SRSF9 mRNA expression was associated with pathological grading （P=0.004） and HPV infection （P=0.031） in the patients with HNSCC according to TCGA Database analysis. The GEPIA and Kaplan-Meier plotter Database analysis results showed that high expression of SRSF9 mRNA in the HNSCC tissue was correlated with poorer overall survival （OS） of the patients ［hazard ratio （HR） = 1.40， P=0.019； HR=1.55， P=0.003］. The cBioPortal Database analysis results showed that copy number variation （CNV） of SRSF9 gene occurred in 26.85% in HNSCC， and CNV was positively correlated with SRSF9 mRNA expression levels （r=0.44， P<0.001）. The ESTIMATE algorithm analysis results showed that high expression of SRSF9 mRNA group had lower stromal and immune score， and higher tumor purity than those in low expression of SRSF9 mRNA group（P<0.001）. The TIMER Database analysis results showed there was a positive correlation between the expression of SRSF9 mRNA and CD4+ T lymphocyte infiltration （r=0.186， P<0.001）， and there were negative correlations between the expression level SRSF9 mRNA and B lymphocyte， CD8+ T lymphocyte， and dendritic cell infiltrations （r=－0.269， P<0.001； r=－0.353， P<0.001； r=－0.304， P<0.001）. The co-expressed gene enrichment analysis results showed upregulation of genes related to ribosomes， spliceosomes， and metabolic pathways， and downregulation of genes associated with focal adhesions， cytokines， and cell adhesion molecules. The main pathways involved in SRSF9-related variable splicing target genes were lipid metabolism， glucagon， and tight junctions. Conclusion SRSF9 is highly expressed in HNSCC and is associated with poor prognosis and tumor microenvironment immune cell infiltration， suggesting its potential as a molecular target for the diagnosis， prognosis assessment， and treatment of HNSCC.

Key words: Head and neck, Squamous cell carcinoma, Serine/arginine-rich splicing factor 9, Alternative splicing, Tumor immunity, Bioinformatics