Abstract 562: Targeting TMEPAI in breast cancer therapy and prevention
Authors: Singha Prajjal Kanti , Pandeswara Srilakshmi , Venkatachalam Manjeri A. , Saikumar Pothana 
Published: August 2012

We earlier identified that TMEPAI (Transmembrane prostate androgen induced) as a novel TGF-β inducible gene that converts tumor suppressive TGF-β into a tumor promoter in breast cancer. The objective of the present study was to assess the role of TMEPAI in the regulation of TGF-β mediated canonical and non-canonical signaling pathways and evaluate the effect of novel drugs, which block TMEPAI expression, in controlling breast tumor progression. Knockdown of endogenous TMEPAI expression was achieved by Lentiviral shRNA expression vectors. DNA transfections, luciferase assays, cell culture, cell proliferation, immunoblotting, immunohistochemistry and in vivo tumor studies using nude mice were done using standard methods. Here, we show that TMEPAI knock-down in MDA-MB-231 triple negative breast cancer cells increased TGF-β mediated Smad signaling with prolonged activation of Smad2 and Smad3 proteins measured by their phosphorylation and Smad-driven luciferase reporter activity. In contrast, exogenous expression of TMEPAI in normal human mammary epithelial cells (HMEC) or TMEPAI-deficient MDA-MB-231cells reduced Smad signaling. While proliferation of HMEC is inhibited by TGF-β, MDA-MB-231 cells showed a biphasic growth response to TGF-β, which is blocked by TMEPAI-deficiency. This led us to test the role of TMEPAI in regulating the canonical and non-canonical pathways of TGF- ≤ signaling. Our studies identified that TMEPAI subverts tumor suppressive TGF-β mediated Smad signaling into tumor promotive non-Smad signaling through stimulation of all three groups of mammalian mitogen-activated protein kinase (MAPK) pathways and Akt pathway. TMEPAI-deficiency prevented the activation of these MAPKs in breast cancer cells. Importantly, TMEPAI-deficiency increased PTEN and reduced pAkt levels in MDA-MB-231 cells. Furthermore, evaluation of TMEPAI as a prognostic biomarker by immunohistochemistry (IHC) revealed high TMEPAI expression in several aggressive human breast tumor samples but not in the matched normal human breast specimens. In addition, drug screening identified a terpenoid derivative (TD) that blocked the expression of TMEPAI and inhibited the proliferation, migration and invasion of MDA-MB-231 cells. Notably, TD did not block the growth of normal human mammary epithelial cells. In addition, TD enhanced TGF-β-mediated Smad signaling but inhibited growth promoting activation of MAPKs and Akt in MDA-MB-231 cells. Importantly, administration of TD (at 2mg/Kg body weight by i.p.) markedly reduced the mass of tumors in mice harboring MDA-MB-231-derived xenograft tumors. Our findings suggest that TMEPAI is a novel biomarker and a therapeutic target for TGF-β dependent aggressive breast cancers. In addition to reducing the tumor mass, drugs that block TMEPAI expression may also prevent nascent tumor formation by their ability to stimulate growth suppressive TGF-β signaling and inhibit growth promoting signaling.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 562. doi:1538-7445.AM2012-562