Elucidating the mechanisms by mTORC2 that regulates metabolism and fuel utilization.

MARTINEZ CALEJMAN, C; LI, HUAWEI; GUERTIN, DAVID

Whistler

Congreso; Keystone Symposia-Tumor Metabolism; 2017

Keystone Symposia

mTORC2 is a serine/threonine kinase complex that phosphorylates AKT1 on S473 and AKT2 on S474 and is important in cancer and diabetes. Using brown adipose tissue as a model because of its remarkable and dynamic metabolic properties, we recently discovered an essential role for mTORC2 in controlling de novo lipogenesis and thermogenesis in mature brown adipocytes. In addition, brown preadipocytes require mTORC2 to differentiate in vitro and they have a mild glucose uptake defect. Interestingly, genetic loss-of-function data suggests these functions of mTORC2 may be independent of classic AKT signaling, which is supported by both targeted and unbiased phospho-proteomics. This led us to hypothesize (1) that the failure of mTORC2-deficient cells to differentiate results from the inefficient production of a bioactive metabolite produced from glucose, the precursor for de novo lipogenesis, and (2) that this metabolic circuit is either controlled by a unique mTORC2-dependent AKT pathway or an AKT-independent pathway downstream of mTORC2. In support, we find that supplementing acetate (which is converted in cells to acetyl-CoA by Acss2), but not pyruvate or citrate, into the medium is sufficient to rescue differentiation in the absence of mTORC2. This suggests a key function of mTORC2 may be to regulate acetyl-CoA production and/or utilization. Indeed, metabolite profiling indicates a marked decrease in acetylcarnitine (a metabolite in equilibrium with acetyl-CoA) in mTORC2-deficient cells. Moreover, the phosphorylation of ATP-citrate lyase (ACLY) on S455 (a proposed AKT phosphorylation site) is also decreased, and expressing recombinant phosphomimetics versions of AKT1 (S473D) or ACLY (S455A) also rescues differentiation. These data support a model in which ACLY may be a unique AKT substrate that requires mTORC2, and that mTORC2 promotes brown adipocyte differentiation by regulating acetyl-coA metabolism. I will use these findings and their broader implications in understanding cancer cell metabolism.