CXCR4 and prostate cancer: Consistent with earlier experiments which showed that FOXO3a-dependent gene expression is inhibited in the CD44+/CD133+ prostate cancer progenitors versus CD44−/CD133− cells [5], we found that the FACS purified CXCR4+ PC3 cell population showed decreased expression levels of FOXO3A responsive genes such as p21, GADD45, p130, BIM1, and CyclinG2 compared to CXCR4− cells, suggesting that increased expression of CXCR4 is associated with PI3K activation (Figure 4A).