¹Cellular Organization and Signaling, National Centre for Biological Sciences, TIFR, Bangalore-560065, Karnataka, India

Correspondence: A Sarin, Cellular Organization and Signaling, National Centre for Biological Sciences, Bellary Road, Bangalore, 560065, India. Tel: +91 80 23666080; Fax: +91 80 23636462; E-mail: sarina@ncbs.res.in or apurva.sarin@gmail.com

Received 3 November 2008; Revised 5 January 2009; Accepted 6 February 2009; Published online 6 March 2009.

Abstract

The regulation of cellular metabolism and survival by trophic factors is not completely understood. Here, we describe a signaling cascade activated by the developmental regulator Notch, which inhibits apoptosis triggered by neglect in mammalian cells. In this pathway, the Notch intracellular domain (NIC), which is released after interaction with ligand, converges on the kinase mammalian target of rapamycin (mTOR) and the substrate-defining protein rapamycin independent companion of mTOR (Rictor), culminating in the activation of the kinase Akt/PKB. Biochemical and molecular approaches using site-directed mutants identified AktS473 as a key downstream target in the antiapoptotic pathway activated by NIC. Despite the demonstrated requirement for Notch processing and its predominant nuclear localization, NIC function was independent of CBF1/RBP-J, an essential DNA-binding component required for canonical signaling. In experiments that placed spatial constraints on NIC, enforced nuclear retention abrogated antiapoptotic activity and a membrane-anchored form of NIC-blocked apoptosis through mTOR, Rictor and Akt-dependent signaling. We show that the NIC-mTORC2-Akt cascade blocks the apoptotic response triggered by removal of medium or serum deprivation. Consistently, membrane-tethered NIC, and AktS473 inhibited apoptosis triggered by cytokine deprivation in activated T cells. Thus, this study identifies a non-canonical signaling cascade wherein NIC integrates with multiple pathways to regulate cell survival.