CX3CL1/fractalkine enhances prostate cancer spinal metastasis by activating the Src/FAK pathway

Chemokines serve important roles in the development of cancer. C-X3-C motif chemokine ligand 1 (CX3CL1) has been demonstrated to promote metastases in different types of tumors. The authors' previous studies demonstrated that the CX3CL1 (also termed fractalkine)/steroid receptor coactivator (Src)/focal adhesion kinase (FAK) signaling pathway is associated with spinal metastasis. In the present study, it was observed that CX3CL1/C-X3-C motif chemokine receptor 1 (CX3CR1) was overexpressed in prostate cancer tissues with spinal metastasis compared with primary tumors. Overexpression of CX3CR1 induced cell proliferation, migration and invasion, and inhibited cellular apoptosis. However, repression of CX3CR1 reduced cell proliferation, migration and invasion, and increased cellular apoptosis. In addition, the Src/FAK pathway was activated by CX3CL1, which depends on the Tyr992 residue of epidermal growth factor receptor (EGFR) for phosphorylation. The inhibitors of these kinases repressed the cell migration induced by CX3CL1 or CX3CR1 overexpression. Furthermore, overexpression of CX3CR1 induced the spinal metastasis of prostate cancer in an in vivo mouse model. Therefore, CX3CL1 and its regulation of the EGFR, Src and FAK pathways may be potential targets for the early prevention of spinal metastasis in prostate cancer.