title: Overexpression of PRAS40(T246A) in the Proliferative Compartment Suppresses mTORC1 Signaling, Keratinocyte Migration, and Skin Tumor Development.
abstract: The proline-rich Akt (v-akt murine thymoma viral oncogene homolog 1) substrate of 40 kDa (PRAS40), an inhibitory component of the mTORC1 complex, was identified as an Akt substrate through phosphorylation at Thr246. Phosphorylation at this site releases PRAS40 from the mammalian/mechanistic target of rapamycin complex 1 (mTORC1) complex allowing increased activity. Targeted expression of a mutant form of PRAS40 (PRAS40(T246A)) in basal keratinocytes of mouse epidermis (BK5.PRAS40(T246A) mice) has allowed further examination of mTORC1-specific signaling in epithelial carcinogenesis. BK5.PRAS40(T246A) mice were resistant to 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced epidermal hyperproliferation and skin tumor development. In transgenic mice, PRAS40(T246A) remained bound to raptor in keratinocytes even after treatment with TPA, consistent with reduced mTORC1 signaling and altered levels of cell cycle proteins. BK5.PRAS40(T246A) mice also displayed attenuated skin inflammation in response to TPA. Inhibition of mTORC1 in keratinocytes significantly inhibited their migration in vitro and, in addition, inhibited 12-O-tetradecanoylphorbol-13-acetate-induced proliferation and migration of bulge-region stem cells in vivo. Furthermore, targeted inhibition of mTORC1 in BK5.PRAS40(T246A) mice resulted in delayed wound healing. Decreased keratinocyte migration and impaired wound healing correlated with altered expression of epithelial-mesenchymal transition (EMT) markers and reduced smad signaling. Collectively, the current data using this unique mouse model provide further evidence that mTORC1 signaling in keratinocytes regulates key events in keratinocyte function and epithelial cancer development.
authors.affiliation: Division of Pharmacology and Toxicology, The University of Texas at Austin, Austin, Texas, USA.
authors.forename: Okkyung
authors.initials: O
authors.lastname: Rho
authors.affiliation: Division of Pharmacology and Toxicology, The University of Texas at Austin, Austin, Texas, USA.
authors.forename: Jaya
authors.initials: J
authors.lastname: Srivastava
authors.affiliation: Division of Pharmacology and Toxicology, The University of Texas at Austin, Austin, Texas, USA.
authors.forename: Jiyoon
authors.initials: J
authors.lastname: Cho
authors.affiliation: Division of Pharmacology and Toxicology, The University of Texas at Austin, Austin, Texas, USA; Department of Nutritional Science, The University of Texas at Austin, Austin, Texas, USA. Electronic address: john.digiovanni@austin.utexas.edu.
authors.forename: John
authors.initials: J
authors.lastname: DiGiovanni
mesh_terms: D000818:Animals; D002465:Cell Movement / Q000235:genetics; D049109:Cell Proliferation; D058750:Epithelial-Mesenchymal Transition / Q000235:genetics; D005260:Female; D015603:Keratinocytes / Q000378:metabolism*; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008822:Mice, Transgenic; D046912:Multiprotein Complexes / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics; D012878:Skin Neoplasms / Q000235:genetics / Q000473:pathology*; D051785:Smad Proteins / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity; D014945:Wound Healing / Q000235:genetics
chemical_list: D046912:Multiprotein Complexes; D010750:Phosphoproteins; D051785:Smad Proteins; C508191:proline-rich Akt substrate, 40 kDa protein, mouse; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D013755:Tetradecanoylphorbol Acetate