CXCR4 and renal cell carcinoma: To investigate the mechanisms underlying notch regulation of chemotaxis of RCC CSCs, the notch1 overexpression RCC CSCs model (CSCs-Notch1) were successfully constructed and western blot analysis showed that overexpression of notch1 induced up-regulation of CXCR4 and SDF-1 (Fig. 6a and b).