CXCR4 and prostate cancer: The chemokine receptor CXCR4, a direct transcriptional target of KLF5, is subsequently activated and binding of its ligand CXCL12 (CXCL12, also known as SDF-1α) underlies the preferential chemotactic migration of prostate cancer cells to organ sites with elevated levels of CXCL12, for example bone [104,105].