title: Impact of mTORC1 inhibition on keratinocyte proliferation during skin tumor promotion in wild-type and BK5.AktWT mice.
abstract: In this study, we examined the impact of rapamycin on mTORC1 signaling during 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced keratinocyte proliferation and skin tumor promotion in both wild-type (FVB/N) and BK5.Akt(WT) mice. TPA activated mTORC1 signaling in a time-dependent manner in cultured primary mouse keratinocytes and a mouse keratinocyte cell line. Early activation (15-30 min) of mTORC1 signaling induced by TPA was mediated in part by PKC activation, whereas later activation (2-4 h) was mediated by activation of EGFR and Akt. BK5.Akt(WT) transgenic mice, where Akt1 is overexpressed in basal epidermis, are highly sensitive to TPA-induced epidermal proliferation and two-stage skin carcinogenesis. Targeting mTORC1 with rapamycin effectively inhibited TPA-induced epidermal hyperplasia and hyperproliferation as well as tumor promotion in a dose-dependent manner in both wild-type and BK5.Akt(WT) mice. A significant expansion (∼threefold) of the label retaining cell (LRC) population per hair follicle was observed in BK5.Akt(WT) mice compared to FVB/N mice. There was also a significant increase in K15 expressing cells in the hair follicle of transgenic mice that coincided with expression of phospho-Akt, phospho-S6K, and phospho-PRAS40, suggesting an important role of mTORC1 signaling in bulge-region keratinocyte stem cell (KSC) homeostasis. After 2 weeks of TPA treatment, LRCs had moved upward into the interfollicular epidermis from the bulge region of both wild-type and BK5.Akt(WT) mice. TPA-mediated LRC proliferation and migration was significantly inhibited by rapamycin. Collectively, the current data indicate that signaling through mTORC1 contributes significantly to the process of skin tumor promotion through effects on proliferation of the target cells for tumor development.
authors.affiliation: Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Dell Pediatric Research Institute, Austin, Texas.
authors.forename: Okkyung
authors.initials: O
authors.lastname: Rho
authors.forename: Kaoru
authors.initials: K
authors.lastname: Kiguchi
authors.forename: Guiyu
authors.initials: G
authors.lastname: Jiang
authors.forename: John
authors.initials: J
authors.lastname: DiGiovanni
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002460:Cell Line; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced*; D002867:Chromones / Q000494:pharmacology; D066246:ErbB Receptors / Q000096:biosynthesis; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D018859:Hair Follicle / Q000378:metabolism; D006965:Hyperplasia / Q000139:chemically induced / Q000517:prevention & control; D015603:Keratinocytes / Q000166:cytology*; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008813:Mice, Inbred ICR; D008822:Mice, Transgenic; D009025:Morpholines / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000096:biosynthesis; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D012878:Skin Neoplasms / Q000139:chemically induced / Q000473:pathology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D013755:Tetradecanoylphorbol Acetate / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C554292:12-O-tetradecanoylphorbol-1,3-acetate; D000903:Antibiotics, Antineoplastic; D002867:Chromones; D005419:Flavonoids; D009025:Morpholines; D046912:Multiprotein Complexes; D000081082:Phosphoinositide-3 Kinase Inhibitors; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C541485:EGFR protein, mouse; D066246:ErbB Receptors; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D013755:Tetradecanoylphorbol Acetate; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus
keywords: Akt; TPA; bulge-region stem cell; mTOR; rapamycin; tumor promotion