Signaling mechanisms coupled to CXCL12/CXCR4-mediated cellular proliferation are PTEN-dependent.

A key difference between normal and malignant prostate cells in vitro and in vivo is that both alleles of PTEN are largely intact in normal benign prostate glands and cultured epithelial cells, whereas one or both alleles of PTEN are mutant or deleted in the majority of prostate tumors and malignant prostate cancer cell lines. Intact PTEN suppresses phosphorylation of Akt downstream of PI3K activation in non-transformed cells whereas Akt phosphorylation is unimpeded in malignant cells that are often PTEN-deficient. We have previously shown that activation of the CXCL12/CXCR4 axis transactivates the EGFR to promote pro-proliferative signaling preferentially through the Raf/MEK/Erk pathway in benign prostate epithelial cells. These cells demonstrate little basal pAkt and these levels do not increase with CXCL12 stimulation because PTEN is intact and fully functional. Thus, inactivation of PTEN may be the critical factor that modulates downstream signaling and the specific CXCL12-stimulated proliferative responses of non-transformed and transformed prostate epithelial cells. Based on these data, we hypothesize that the CXCL12/CXCR4-mediated activation of downstream pro-proliferative signaling through the Raf/MEK/Erk or PI3K/Akt pathways is modulated by PTEN status.