CXCR4 and renal cell carcinoma: Recently, Micucci et al. showed that the enhanced self-renewal activity of the CXCR4+ spheres was preceded by the upregulation of hypoxia-inducible factor 2α (HIF2α) in the RCC cell lines Caki-1, Caki-2, 786-O, and 769-P [44].