Up-regulation of CXCR4 expression in PC-3 cells by stromal-derived factor-1α (CXCL12) increases endothelial adhesion and transendothelial migration:: Role of MEK-ERK signaling pathway-dependent NF-κB activation

The chemokine stromal-derived factor-lot (SDF-1 alpha/CXCL-12) and its receptor, CXCR4, play a crucial role in adhesion and transendothelium migration (TEM) of prostate cancer cells. We tested the hypothesis that enhanced expression of CXCR4 in prostate cancer cells is dependent upon SDF-1 alpha-mediated activation of nuclear factor-kappa B (NF-kappa B). SDF-1 alpha increased the CXCR4 mRNA and protein expression in PC-3 cells but not in LNCaP cells. Similarly, SDF-1 alpha enhanced the NF-kappa B-dependent transcriptional activity in PC-3 cells but not in LNCaP cells. SDF-1 alpha increased PC-3 cell adhesion to the human umbilical vein endothelial cell monolayer and enhanced TEM, which was abrogated with anti-CXCR4 monoclonal antibody (mAb). Suppression of NF-kappa B activity in PC-3 cells by a mutant I kappa B alpha super-repressor adenoviral vector decreased the CXCR4 mRNA expression and inhibited adhesion and TEM. Transient overexpression of p65 subunit of NF-kappa B in PC-3 cells up-regulated CXCR4 receptor expression and increased the adhesion and TEM of these cells in response to SDF-1 alpha gradient. Treatment of PC-3 cells with SDF-1 alpha leads to nuclear translocation of NF-kappa B protein within 15 to 30 minutes, which correlated with I kappa B alpha phosphorylation. A p42/44 mitogen-activated protein kinase [MAPK, extracellular signal regulated kinase-1/2 (ERK-1/2)] biphasic activation pattern was observed in these cells at 15 minutes and 3 hours after SDF-1 alpha treatment. Phosphorylation of I kappa B kinase alpha was observed within 30 minutes, which was blocked by PD98059 [MAPK kinase (MEK) inhibitor]. PD98059 cotreatment significantly inhibited SDF-1 alpha-induced NF-kappa B reporter activity and CXCR4 receptor expression as shown by flow cytometry. These data suggest that SDF-1 alpha-induced expression of CXCR4 in PC-3 cells is dependent on MEK/ERK signaling cascade and NF-kappa B activation.