Date of Award

Spring 5-21-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Science

First Advisor

Shafiq A. Khan, Ph.D.

Second Advisor

Jaideep Chaudary, Ph.D.

Third Advisor

Nathan Bowen, Ph.D.

Abstract

Transforming growth factor -β (TGF-β) plays an important role in the progression of prostate cancer. It acts as a tumor suppressor in normal epithelial cells but as a tumor promoter in advanced prostate cancer cells. The PI3-kinase pathway has been shown to play integral roles in many cellular processes including cell proliferation, survival, and cell migration in many cell types. PI3-kinase pathway mediates TGF-β effects on prostate cancer cell migration and invasion. Phosphatase and tensin homolog (PTEN), a tumor suppressor gene, inhibits PI3-kinase pathway and is frequently mutated in prostate cancers. In this present study, we investigated possible roles of PTEN in TGF-β effects on proliferation, migration, and the activation of PI3-kinase/AKT pathway in prostate cancer cells. PTEN was expressed in DU145 cells; however PC3 cells lack PTEN expression. TGF-β1 and TGF-β3 had no effect on PTEN mRNA levels but both isoforms increased PTEN protein levels in DU145 and RWPE1 cells, suggesting that TGF-β may mediate regulation of PTEN protein stability. TGF-β1 and TGF-β3 increased PTEN protein levels even in the presence of cycloheximide, a protein synthesis inhibitor, in DU145 cells. In addition, TGF-β upregulated phosphorylation of PTEN, stabilizing PTEN protein. Increase of PTEN protein levels in these cells may also indicate that PTEN may mediate TGF-β effects on cell proliferation. Knockdown of PTEN in DU145 cells resulted in significant increase in cell proliferation which was no longer affected by TGF-β isoforms. PTEN overexpression in PC3 cells inhibited cell proliferation. Knockdown of endogenous PTEN enhanced cell migration in DU145 cells, whereas PTEN overexpression reduced migration in PC3 cells and reduced phosphorylation of AKT in response to TGF-β. Based on these results, we conclude that PTEN plays a role in inhibitory effects of TGF-β on cell proliferation whereas its absence may enhance TGF-β effects on activation of PI3-kinase pathway and cell migration.

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