Alkaline intracellular pH (pHi) increases PI3K activity to promote mTORC1 and mTORC2 signaling and function during growth factor limitation.

The conserved protein kinase mTOR (mechanistic target of rapamycin) responds to diverse environmental cues to control cell metabolism and promote cell growth, proliferation, and survival as part of two multiprotein complexes, mTOR complex 1 (mTORC1) and mTORC2. Our prior work demonstrated that an alkaline intracellular pH (pHi) increases mTORC2 activity and cell survival in complete media in part by activating AMP-activated protein kinase, a kinase best known to sense energetic stress. It is important to note that an alkaline pHi represents an underappreciated hallmark of cancer cells that promotes their oncogenic behaviors. In addition, mechanisms that control mTORC1 and mTORC2 signaling and function remain incompletely defined, particularly in response to stress conditions. Here, we demonstrate that an alkaline pHi increases phosphatidylinositide 3-kinase (PI3K) activity to promote mTORC1 and mTORC2 signaling in the absence of serum growth factors. Alkaline pHi increases mTORC1 activity through PI3K-Akt signaling, which mediates inhibitory phosphorylation of the upstream proteins tuberous sclerosis complex 2 and proline-rich Akt substrate of 40 kDa and dissociates tuberous sclerosis complex from lysosomal membranes, thus enabling Rheb-mediated activation of mTORC1. Thus, alkaline pHi mimics growth factor-PI3K signaling. Functionally, we also demonstrate that an alkaline pHi increases cap-dependent protein synthesis through inhibitory phosphorylation of eIF4E binding protein 1 and suppresses apoptosis in a PI3K- and mTOR-dependent manner. We speculate that an alkaline pHi promotes a low basal level of cell metabolism (e.g., protein synthesis) that enables cancer cells within growing tumors to proliferate and survive despite limiting growth factors and nutrients, in part through elevated PI3K-mTORC1 and/or PI3K-mTORC2 signaling.

Kazyken D ，Lentz SI ，Wadley M ，Fingar DC ... -  《-》

TSC/mTORC1 mediates mTORC2/AKT1 signaling in c-MYC-induced murine hepatocarcinogenesis via centromere protein M.

Zhou Y ，Zhang S ，Qiu G ，Wang X ，Yonemura A ，Xu H ，Cui G ，Deng S ，Chun J ，Chen N ，Xu M ，Song X ，Wang J ，Xu Z ，Deng Y ，Evert M ，Calvisi DF ，Lin S ，Wang H ，Chen X ... -  《-》

Discrete Mechanistic Target of Rapamycin Signaling Pathways, Stem Cells, and Therapeutic Targets.

Jhanwar-Uniyal M ，Zeller SL ，Spirollari E ，Das M ，Hanft SJ ，Gandhi CD ... -  《Cells》

RhoA modulates signaling through the mechanistic target of rapamycin complex 1 (mTORC1) in mammalian cells.

The mechanistic target of rapamycin (mTOR) in complex 1 (mTORC1) pathway integrates signals generated by hormones and nutrients to control cell growth and metabolism. The activation state of mTORC1 is regulated by a variety of GTPases including Rheb and Rags. Recently, Rho1, the yeast ortholog of RhoA, was shown to interact directly with TORC1 and repress its activation state in yeast. Thus, the purpose of the present study was to test the hypothesis that the RhoA GTPase modulates signaling through mTORC1 in mammalian cells. In support of this hypothesis, exogenous overexpression of either wild type or constitutively active (ca)RhoA repressed mTORC1 signaling as assessed by phosphorylation of p70S6K1 (Thr389), 4E-BP1 (Ser65) and ULK1 (Ser757). Additionally, RhoA·GTP repressed phosphorylation of mTORC1-associated mTOR (Ser2481). The RhoA·GTP mediated repression of mTORC1 signaling occurred independent of insulin or leucine induced stimulation. In contrast to the action of Rho1 in yeast, no evidence was found to support a direct interaction of RhoA·GTP with mTORC1. Instead, expression of caRheb, but not caRags, was able to rescue the RhoA·GTP mediated repression of mTORC1 suggesting RhoA functions upstream of Rheb to repress mTORC1 activity. Consistent with this suggestion, RhoA·GTP repressed phosphorylation of TSC2 (Ser939), PRAS40 (Thr246), Akt (Ser473), and mTORC2-associated mTOR (Ser2481). Overall, the results support a model in which RhoA·GTP represses mTORC1 signaling upstream of Akt and mTORC2.

Gordon BS ，Kazi AA ，Coleman CS ，Dennis MD ，Chau V ，Jefferson LS ，Kimball SR ... -  《-》

Receptor-recognized α₂-macroglobulin binds to cell surface-associated GRP78 and activates mTORC1 and mTORC2 signaling in prostate cancer cells.

Misra UK ，Pizzo SV 《PLoS One》