Mammalian target of rapamycin complex (mTORC) regulates a variety of cellular responses including proliferation, growth, differentiation and cell migration. In this study, we show that mammalian target of rapamycin complex 2 (mTORC2) regulates invasive cancer cell migration through selective activation of Akt1. Insulin-like growth factor-1 (IGF-1)-induced SKOV-3 cell migration was completely abolished by phosphatidylinositol 3-kinase (PI3K) (LY294002, 10 lM) or Akt inhibitors (SH-5, 50 lM), whereas inhibition of extracellular-regulated kinase by an ERK inhibitor (PD98059, 10 lM) or inhibition of mammalian target of rapamycin complex 1 (mTORC1) by an mTORC1 inhibitor (Rapamycin, 100 nM) did not affect IGF-1-induced SKOV-3 cell migration. Inactivation of mTORC2 by silencing Rapamycin-insensitive companion of mTOR (Rictor), abolished IGF-1-induced SKOV-3 cell migration as well as activation of Akt. However, inactivation of mTORC1 by silencing of Raptor had no effect. Silencing of Akt1 but not Akt2 attenuated IGF-1-induced SKOV-3 cell migration. Rictor was preferentially associated with Akt1 rather than Akt2, and overexpression of Rictor facilitated IGF-1-induced Akt1 activation. Expression of PIP3-dependent Rac exchanger1 (P-Rex1), a Rac guanosine exchange factor and a component of the mTOR complex, strongly stimulated activation of Akt1. Furthermore, knockdown of P-Rex1 attenuated Akt activation as well as IGF-1-induced SKOV-3 cell migration. Silencing of Akt1 or P-Rex1 abolished IGF-1-induced SKOV-3 cell invasion. Finally, silencing of Akt1 blocked in vivo metastasis, whereas silencing of Akt2 did not. Given these results, we suggest that selective activation of Akt1 through mTORC2 and P-Rex1 regulates cancer cell migration, invasion and metastasis.

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Abbreviations: ALCP, ascites from liver cirrhosis patients; AOCP, ascites from ovarian cancer patients; GPCR, G protein coupled receptor; LPA, 1-or 2-acyl-sn-glycero-3-phosphate; MEF, mouse embryo fibroblast; mTOR, mammalian target of rapamycin; PI3K, phosphatidylinositol 3-kinase; P-Rex1, PIP3-dependent Rac exchanger1 AbstractAkt plays pivotal roles in many physiological responses including growth, proliferation, survival, metabolism, and migration. In the current studies, we have evaluated the isoform-specific role of akt in lysophosphatidic acid (

In this study, we investigated the role of Akt1 isoform in phenotypic change of vascular smooth muscle cells (VSMCs) and neointima formation. Laminin-induced conversion of synthetic VSMCs into contractile VSMCs was measured by expression of marker proteins for contractile VSMCs and collagen gel contraction assay. Culture of synthetic VSMCs on laminin-coated plates induced expression of marker proteins for contractile VSMCs and showed contraction in response to angiotensin II (AngII) stimulation. Silencing integrin-linked kinase attenuated activation of Akt and blocked phenotypic conversion of VSMCs resulting in the loss of AngII-dependent contraction. Laminin-induced phenotypic conversion of VSMCs was abrogated by phosphatidylinositol 3-kinase inhibitor or in cells silencing Akt1 but not Akt2. Proliferation of contractile VSMCs on laminin-coated plate was enhanced in cells silencing Akt1 whereas silencing Akt2 did not affect. Promoter activity of myocardin and SM22α was enhanced in contractile phenotype and overexpression of myocardin stimulated promoter activity of SM22α in synthetic phenotype. Promoter activity of myocardin and SM22α was reduced in cells silencing Akt1 and promoter activity of SM22α was restored by overexpression of myocardin in cells silencing Akt1. However, silencing of Akt2 affected neither promoter activity of myocardin nor SM22α. Finally, neointima formation in carotid artery ligation and high fat-diet-induced atherosclerosis was facilitated in mice lacking Akt1. This study demonstrates that Akt1 isoform stimulates laminin-induced phenotypic conversion of synthetic VSMCs by regulating the expression of myocardin. VSMCs become susceptible to shifting from contractile to synthetic phenotype by the loss of Akt1 in pathological conditions.

a b s t r a c tPhosphatidylinositol 3-kinase pathways play key regulatory roles in cell cycle progression into S phase. In this study, we demonstrated that Akt1/PKBa isoform plays an essential role in G 1 /S transition and proliferation. Cells lacking Akt1/PKBa showed an attenuated proliferation as well as G 1 /S transition, whereas cells lacking Akt2/PKBb showed normal proliferation and G 1 /S transition. The effect of Akt1/PKBa on cell proliferation and G 1 /S transition was completely abolished by swapping pleckstrin homology (PH) domain with that of Akt2/PKBb. Finally, full activation of Akt/PKB and cyclin D expression was achieved by the Akt1/PKBa or chimeric proteins containing the PH domain of Akt1/PKBa indicating that the PH domain of Akt1/PKBa provides full kinase activity and is necessary for the G 1 /S transition.

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