PRAS40 and PRR5-Like Protein Are New mTOR Interactors that Regulate Apoptosis

Abstract

TOR (Target of Rapamycin) is a highly conserved protein kinase and a central controller of cell growth. TOR is found in two functionally and structurally distinct multiprotein complexes termed TOR complex 1 (TORC1) and TOR complex 2 (TORC2). In the present study, we developed a two-dimensional liquid chromatography tandem mass spectrometry (2D LC-MS/MS) based proteomic strategy to identify new mammalian TOR (mTOR) binding proteins. We report the identification of Proline-rich Akt substrate (PRAS40) and the hypothetical protein Q6MZQ0/FLJ14213/CAE45978 as new mTOR binding proteins. PRAS40 binds mTORC1 via Raptor, and is an mTOR phosphorylation substrate. PRAS40 inhibits mTORC1 autophosphorylation and mTORC1 kinase activity toward eIF-4E binding protein (4E-BP) and PRAS40 itself. HeLa cells in which PRAS40 was knocked down were protected against induction of apoptosis by TNFα and cycloheximide. Rapamycin failed to mimic the pro-apoptotic effect of PRAS40, suggesting that PRAS40 mediates apoptosis independently of its inhibitory effect on mTORC1. Q6MZQ0 is structurally similar to proline rich protein 5 (PRR5) and was therefore named PRR5-Like (PRR5L). PRR5L binds specifically to mTORC2, via Rictor and/or SIN1. Unlike other mTORC2 members, PRR5L is not required for mTORC2 integrity or kinase activity, but dissociates from mTORC2 upon knock down of tuberous sclerosis complex 1 (TSC1) and TSC2. Hyperactivation of mTOR by TSC1/2 knock down enhanced apoptosis whereas PRR5L knock down reduced apoptosis. PRR5L knock down reduced apoptosis also in mTORC2 deficient cells. The above suggests that mTORC2-dissociated PRR5L may promote apoptosis when mTOR is hyperactive. Thus, PRAS40 and PRR5L are novel mTOR-associated proteins that control the balance between cell growth and cell death.

Mitochondria are required for pro‐ageing features of the senescent phenotype

“…Previous studies have suggested links between the DDR and the mTOR signalling pathway potentially via protein kinase B (PKB/Akt) phosphorylation: firstly, Akt has been shown to activate mTORC1 by directly phosphorylating the TSC1/TSC2 complex (Inoki et al , 2002) or by dissociation of PRAS40 from the essential mTORC1 component RAPTOR (Thedieck et al , 2007). Secondly, Akt has been shown to be a direct phosphorylation target of ATM, an upstream driver of the DDR (Viniegra et al , 2005).…”

Gene expression analysis of mTOR pathway: association with human longevity

“…Rictor, an important component of mTORC2, contributes to glucose homeostasis in murine muscle tissue (Kumar et al, 2008), TORC2 C. elegans mutants show modulation of lifespan by affecting feeding and metabolism of different diets (Soukas et al, 2009), TORC2 is a mediator of proliferative and survival signals in cancer cells (Fang et al, 2012) and a study in mouse embryonic fibroblasts showed that mTORC2 regulates the TLR-mediated inflammatory response via FoxO1 (Brown et al, 2011). In addition, PRR5L, which is part of mTORC2, has been suggested to play a role in apoptosis in HeLa cells, but whether it is pro-apoptotic or antiapoptotic remains unclear (Thedieck et al, 2007). Recently, Lamming et al showed that disruption of mTORC2 can result in glucose intolerance and insulin resistance in rodents and may be relevant in the pathogenesis of type 2 diabetes and metabolic syndrome (Lamming et al, 2012).…”

mTOR Signaling in Lymphangioleiomyomatosis

“…[38][39][40][41] PROTOR1, also known as PRR5, appears to regulate platelet-derived growth factor (PDGF) signaling and cellular apoptosis. [42][43][44] Both mTOR complexes contain mLST8 (originally termed GbL), which is essential for the function of mTORC2, and modulates mTORC1 activity in nutrient-sensitive manner. 45 …”

“…52,53 However, PRAS40 also constitutively binds and inhibits mTORC1, dissociating from the complex in cells exposed to insulin or nutrients. 43,54,55 The integral ER membrane protein FKBP38 constitutively inhibits mTORC1 activity by blocking the interaction between mTOR and Rheb. [56][57][58] FKBP38 dissociates from Rheb in cells exposed to mitogens, and thus facilitates the activation of mTOR.…”