CD44 Is a Prognostic Biomarker Correlated With Immune Infiltrates and Metastasis in Clear Cell Renal Cell Carcinoma

Background/Aim: CD44 is a critical cell-surface glycoprotein. However, its prognostic significance and correlation with tumor-infiltrating lymphocytes in clear cell renal cell carcinoma (ccRCC) are not well-understood. Materials and Methods: The mRNA and protein levels of CD44 in ccRCC were assessed. The prognostic value of CD44 was analyzed in the TCGA and PrognoScan databases. The functional enrichment and immune infiltrates analyses were conducted. The STRING database was used to analyze the protein interactions of CD44. Tissue array, western blot, qRTPCR, and transwell assay were performed to determine the expression and biological function of CD44 in ccRCC cells. Results: CD44 was highly expressed in ccRCC and correlated with poor prognosis. CD44 mRNA and protein expression was associated with TNM stage, pathologic stage, and histologic grade. Functional enrichment analyses revealed CD44 is involved in extracellular matrix organization, metastasis, IL6/JAK/STAT3 signaling and so on. Moreover, CD44 expression was positively correlated with infiltrating levels of macrophages, Th2 cells and Th1 cells in ccRCC. Combining the immune infiltration analysis and immunohistochemistry, the SPP1/CD44 axis might participate in immune escape through regulating PD-L2 expression. Experiments indicated that CD44 was increased in ccRCC and inhibition of CD44 could suppress the migration of ccRCC cells. Conclusion: High expression of CD44 in ccRCC was associated with metastasis, poor prognosis, and high infiltrating levels of macrophages. The SPP1/CD44 axis potentially contributes to the regulation of PD-L2. These results demonstrated that targeting the SPP1/CD44 axis or inhibiting CD44 expression may be a new therapy to suppress ccRCC progression.