Abstract:

Objective To discuss the expression of apoptosis-related gene CD44 in the thyroid cancer （THCA） tissue and its relationships with the clinicopathological characteristics of the patients and tumor infiltrating leukocytes（TILs）， and to provide new research directions for the diagnosis and treatment of THCA. Methods The expression spectrum of differentially expressed genes （DEGs） related to THCA apoptosis were obtained from The Cancer Genome Atlas （TCGA） Database. The up-regulated CD44 gene was selected and the expression level of CD44 mRNA in THCA tissue and parancancerous tissue were detected； receiver operating characteristic （ROC） curve was used to identify the THCA tissue and paracancerous tissue； Gene Ontology （GO）， Kyoto Encyclopedia of Genes and Genomes （KEGG）， and Gene Set Enrichment Analysis （GSEA） were used to analyze the function and pathway enrichment of DEGs； the protein-protein interaction （PPI） network was established by using STRING Database and visualized by Cytoscape software； the relationship between the expression of CD44 mRNA in THCA tissue and the infiltration abundance of TILs was analyzed by TIMER Database； the relationships between expression of CD44 protein and immune checkpoints were analyzed by R software. A total of 110 samples of THCA patients were selected， the expressions of CD44 protein in THCA tissue and paracancerous tissue were detected by the immunohistochemical SABC method. Results The TCGA Database analysis results showed that compared with paracancerous tissue，the expression level of CD44 mRNA in THCA tissue was increased（P<0.05）； the ROC curve analysis results showed that when the critical value was 6.855， the sensitivity， specificity， and accuracy of CD44 were 89.71%，75.13%， and 72.91%， respectively. The GO and KEGG analysis results showed that the DEGs were mainly enriched in the apoptosis-related pathways； the GSEA analysis results showed that the DEGs were associated with degranulation response of the neutrophils.The TIMER Database analysis results showed that the expression level of CD44 mRNA in THCA tissue was positively correlated with the infiltration abundance of B cells， macrophages， CD4+T lymphocytes， dendritic cells， and neutrophils （partial.cor>0，P<0.01），and was negatively correlated with tumor purity and the infiltration adundance of CD8+ T lymphocytes（partial.cor≤0，P<0.01）；the expression of CD44 protein in THCA tissue was positively correlated with 9 immune checkpoint genes （P<0.01）， and negatively correlated with 1 immune checkpoint gene （P<0.01）； the immunohistochemical SABC results showed that the positive expression rate of CD44 protein in THCA tissue was higher than that in paracancerous tissue （P<0.01）； the expression of CD44 protein in THCA tissue was correlated with the tumor diameter and lymph node metastasis （P<0.05），and was not correlated with gender， age， and extra glandular invasion of the patients（P>0.05）. Conclusion High expression of CD44 in THCA tissue may be related to progression and multiple immune responses of tumor.

Key words: Thyroid carcinoma, Bioinformatics, Hyaluronic acid receptor protein, Tumor immune infiltration, Immune checkpoint