CXCR4 and malignant colon neoplasm: While these papers do not directly show a role for Ca2+ in CXCR4 signaling, Chao et al. [47] found that CAFs had elevated expression of SDF-1 and that exogenous SDF-1 activates a Ca2+ response and increases anchorage-independent growth in CD133+/CXCR4+ colon cancer cells.