CD44 Is Associated with Poor Prognosis of ccRCC and Facilitates ccRCC Cell Migration and Invasion through HAS1/MMP9

Background: In many solid tumors, CD44 has been identified as a cancer stem cell marker as well as an important molecular in cancer progression and metastasis, making it attractive for potential therapeutic applications. However, our knowledge of the biological function and mechanism of CD44 in clear cell renal cell carcinoma (ccRCC) is limited. Methods: In this study, the expression, prognostic values and functional enrichment analysis of CD44 in ccRCC were analyzed using public databases. Quantitative real-time PCR (qRT-PCR), Western blotting, and immunohistochemical (IHC) assays were taken to detect CD44 expression in ccRCC tissues. The effects of CD44 on the proliferation, migration and invasion of ccRCC cells were investigated by gain-of-function and loss-of-function experiments. Subcutaneous models further confirmed the role of CD44 in tumor growth. The relationship between CD44, HAS1 and MMP9 was investigated to uncover the regulatory mechanism of CD44 in ccRCC. Results: CD44 was significantly upregulated in ccRCC and associated with poor overall survival (OS). Based on the functional enrichment analysis and PPI network, we found that CD44 had associations with ECM interaction and focal adhesion pathway. Clinical ccRCC sample validation revealed that CD44 mRNA and protein expression were significantly increased in ccRCC tissues, and strong CD44 staining was observed in four metastatic ccRCC cases. In vitro experiments showed that CD44 overexpression promoted cell proliferation, migration and invasion. In vivo experiments also demonstrated that CD44 overexpression accelerated tumor formation in mice. Finally, we found that CD44 regulates the expression of HAS1 in ccRCC, which is essential for the secretion of MMP9 and cell migratory ability. Conclusion: The upregulation of CD44 mRNA and protein expressions in ccRCC is indicative of unfavorable clinical prognoses. The CD44/HAS1/MMP9 axis is believed to exert a significant influence on the regulation of ECM degradation and ccRCC metastasis.