Abstract 4677: Slug is a potential target to restore transforming growth factor-β mediated apoptosis in lung cancer cells

Abstract

Abstract Transforming growth factor-β (TGFβ) inhibits carcinogenesis at early stages by inhibiting cell growth and inducing apoptosis. Cancer cells acquire resistance to TGFβ induced apoptosis and divert the TGF-β signaling to stimulate tumor promoting processes such as Epithelial-Mesenchymal-Transition (EMT), immunosuppression and angiogenesis. Hence, the identification of molecular targets/ pathways enabling cancer cells to overcome TGFβ-mediated apoptosis is critical for exploiting tumor suppressive functions of TGFβ for therapy. We have identified slug (snai2), a zinc-finger transcription factor, as a critical regulator of TGF-β mediated apoptosis in lung cancer cells. In EMT models of lung cancer slug is up-regulated by several fold upon TGFβ treatment. Knock down of Smad 3 or Smad 4, but not Smad 2, completely abrogated the TGF-β induced up-regulation of Slug. Chromatin immunoprecipitation analysis revealed increased occupancy of Smad 3 to the slug promoter on TGFβ treatment indicating slug might be a direct target gene of Smad 3. Slug is often described as a potent E-cadherin suppressor and an important regulator of EMT along with other E-box proteins. In contrast siRNA knock-down of slug (slug KD) in lung cancer cells did not prevent TGFβ induced E-cadherin suppression or acquisition of mesenchymal markers such as N-cadherin, vimentin and fibronectin; instead lead to increased cell death. Slug KD cells on TGFβ treatment underwent apoptosis through the typical apoptosis cascade characterized by increased annexin-v staining and caspase-3 activation. This apoptotic cell death is abrogated by inhibitors of caspase-3 and caspase-9. Inhibition of caspase-8, an initiator of extrinsic apoptotic pathway or siRNA knockdown of RIP1 that promotes necroptosis did not inhibit the death of TGFβ treated slug KD cells. Together these finding suggests slug KD results in cell death via intrinsic apoptosis pathway in response to TGFβ. This study indicates slug induction during EMT allows cancer cells to escape from apoptotic functions of TGFβ and might function as a critical regulatory switch to shift TGFβ role from tumor suppressor to tumor promoter. Thus slug inhibition might serve as a potential mechanism to reinstate the apoptotic functions of TGFβ in lung cancer cells. 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 4677. doi:1538-7445.AM2012-4677