CXCR4 and renal cell carcinoma: To eliminate endogenous CXCR4 activity and better assess the role of CXCR4 nuclear localization in RCC, we knocked down endogenous CXCR4 with a lentiviral-based shRNA (Supplementary Figure 1A) and then ectopically expressed either recombinant CXCR4 or CXCR4-mNLS with the indicated synonymous mutation to avoid the shRNA target sequence (Fig. 2b).