CD44 and renal cell carcinoma: Therefore, to preliminarily investigate the function and mechanism of the RSK4, CD44 and MMP-9 proteins in RCC, up- and downregulation of RSK4 were performed by lipofectamine-mediated gene transfection in ACHN cell lines, and the expression of CD44, MMP-9, rpS6, p-rpS6, GSK3β, pGSK-3βSer9 and β-catenin levels in the RSK4-overexpressing ACHN cell line was studied by western blot.