Abstract LB-3: The recruitment of PP2A by TGF-β receptors mediates the response to TGF-β-induced activation of ERK in prostate cancer
Authors: Zhang Qiang , Chen Lin , Helfand Brian , Kozlowski James , Brendler Charles B , Kuzel Timothy M. , Lee Chung 
Published: August 2014

Introduction and Objective: We recently demonstrated that TGF-β mediated phosphorylation of extra-cellular signal-regulated kinase (ERK) activation results in the prostate cancer (CaP) progression and metastasis. Serine/threonine protein phosphatases 2, PP2A (including subunit −A, −B and −C) are well known to be involved in the dephosphorylation and inactivation of ERK. In this study, we determined the association between the recruitment of PP2A by TGF-β receptors (TβRI and TβRII) and activation of ERK under the treatment of TGF-β.

Methods: The human CaP cell lines PC-3 with different capability of aggressive (PC-3, PC-3M, PC-3M-Pro and PC-3M-LN4), and benign prostate epithelial cell line BPH-1 were used for these studies. Cells were treated with TGF-β (10ng/mL) for 24 minutes. The expression of phospho-ERK (p-ERK), total-ERK (t-ERK), TβRs was evaluated by quantitative western blot analyses. The conjugation of PP2A (−A, −B and −C) and TβRI and TβRII were elucidated using western blot following immunoprecipitation (IP, Pierce Crosslink kit) with TβRI and TβRII as the precipitant respectively. Briefly, precleared lysate was immunopreciptated by the crosslinked TβRI or TβRII antibody (5 μg) and agarose mixture for overnight on 4°C. Control agarose resin in the kit was used as a negative control when western-blot for PP2A was conducted. The recruitment of PP2A by TβRs was correlated with the expression of p-ERK and TβRs.

Results: TGF-ß treatment resulted in an increase in p-Erk expression (4-fold) in all PC-3 cell lines in a time dependent manner post TGF-ß exposure. In addition, the expressions of TßRI and TßRII were suppressed by 46% and 29% respectively. IP studies revealed recruitment of PP2A conjugated with TßRI and TßRII. In contrast, the expression of p-Erk was dramatically inhibited in BPH-1 by TGF-ß exposure. Although there is no significant change on the expression of TßRs, the ratio of PP2A versus TßRII was significantly increased from 2.08 to 3.12, which suggests that the recruitment of PP2A was relatively increased in BPH-1 cells under the treatment of TGF-ß. Finally, there was a reverse correlation between recruited PP2A and activation of p-ERK in both PC-3 cell lines, and BPH-1 cells.

Conclusion: Taken together the results suggest that TGF-β suppresses the recruitment of PP2A by TGF-β receptors in CaP cells in contrast to benign prostate cells, which results in relatively increased activation of ERK and the subsequent tumor progression. The identification of the recruitment of PP2A by TβRs represents a new focus to elucidate in part how TGF-β plays a different, or even a contrary role in CaP and benign cell respectively. PP2A may be a potential new target for CaP therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-3. doi:10.1158/1538-7445.AM2011-LB-3