Expression of TGFB isoforms and their effects on migratory and invasive behavior of prostate cancer cells: involvement of PI3-KINASE/AKT Signaling pathway

摘要

Transforming growth factor-β (TGFβ) is a secreted protein that is involved in the regulation of many cellular processes and has been implicated as a factor in cancer cell invasion and metastasis. Studies have indicated that different TGFβ isoforms may exert differential effects on cancer cells during different stages of the disease, however very little is known about the expression patterns of the 3 isoforms in prostate cancer. Non traditional signaling pathways including P13-kinase have been associated with TGFβ- mediated effects on cancer cell invasion and metastasis. Whether or not TGFβ isoforms play a differential role in migration and invasion of prostate cancer, and act through P13 - Kinase, has not been investigated. In the present study, we have carried out expression analysis of TGFβ isoforms and signaling components in cell line models representing different stages of prostate cancer and studied the differential effects of specific isoforms on migratory, invasive behavior and induction of the P13-Kinase and MAP-Kinase/ERK pathways. TGFβ1 and TGFβ3 were expressed in all prostate cell lines, with TGFβ3 increasing in metastatic DU145, PC3 and PC3M cell lines. TGFI31 and TGFI33 induced motility and invasive behavior in PC3 cells, with TGFβ3 being more potent in inducing invasive behavior. TGFβ3 caused a significant increase in the phosphorylation of AKT (pAKT^473), a downstream target of P13-Kinase, in PC3 cells. LY294002, a P13-kinase inhibitor, blocked this induced migration and phosphorylation of AKT. Inhibitors of TGFβRI (SB43 1524) and Smad3 (SIS3) blocked TGFβ isoform induced motility and TGFβ isoform induced pAKT^473. There was no differential isoform effect on the phosphorylation of ERK (pERK). PD98059, a MEK inhibitor of MAP-Kinase/ERK, did inhibit TGFβ isoform induced migration and pERK, but did not affect isoform induced pAK^T473. Furthermore, TGFβ isoforms phosphorylate both Smad2 and Smad3 in a similar manner in PC3 cells. Based on these results, we conclude that TGFβ3 is expressed in metastatic prostate cancer cell lines and is involved in induction of invasive behavior in these cells. Furthermore, these effects of TGFβ3 are mediated via the P13- Kinase pathway and are TGFβRI and Smad3 dependent.