title: Twist1 regulates keratinocyte proliferation and skin tumor promotion.
abstract: In the present study, we evaluated the effect of deleting Twist1 on keratinocyte proliferation and on skin tumor development using the two-stage chemical carcinogenesis model. BK5.Cre × Twist1(flox/flox) mice, which have a keratinocyte-specific Twist1 knockout (Twist1 KO), developed significantly reduced numbers of papilloma (70% reduction) and squamous cell carcinoma (75% reduction) as well as delayed tumor latency compared to wild-type (WT) mice. Interestingly, knockdown of Twist1 in primary keratinocytes impeded cell cycle progression at the G1/S transition that coincided with reduced levels of the cell cycle proteins c-Myc, Cyclin E1, and E2F1 and increased levels of p53 and p21. Furthermore, ChIP analyses revealed that Twist1 bound to the promoter regions of Cyclin E1, E2F1, and c-Myc at the canonical E-box binding motif suggesting a direct transcriptional regulation. Further analyses of Twist1 KO mice revealed a significant reduction in the number of label-retaining cells as well as the number of α6-integrin(+) /CD34(+) cells in the hair follicles of untreated mice compared to WT mice. These mice also exhibited significantly reduced epidermal proliferation in response to TPA treatment that again correlated with reduced levels of cell cycle regulators and increased levels of p53 and p21. Finally, Twist1 deficiency in keratinocytes led to an upregulation of p53 via its stabilization and nuclear localization, which is responsible for the increased expression of p21 in these cells. Collectively, these findings indicate that Twist1 has a novel role in epithelial carcinogenesis by regulating proliferation of keratinocytes, including keratinocyte stem cells during tumor promotion.
authors.affiliation: Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, Texas.
authors.forename: Jaya
authors.initials: J
authors.lastname: Srivastava
authors.affiliation: Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, Texas.
authors.forename: Okkyung
authors.initials: O
authors.lastname: Rho
authors.affiliation: Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, Texas.
authors.forename: Ronnie M
authors.initials: RM
authors.lastname: Youssef
authors.affiliation: Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, Texas.|Department of Nutritional Sciences, College of Natural Sciences, The University of Texas at Austin, Austin, Texas.
authors.forename: John
authors.initials: J
authors.lastname: DiGiovanni
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene / Q000633:toxicity; D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D049109:Cell Proliferation; D015972:Gene Expression Regulation, Neoplastic; D055786:Gene Knockout Techniques; D015603:Keratinocytes / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012878:Skin Neoplasms / Q000139:chemically induced* / Q000235:genetics / Q000473:pathology*; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity; D051879:Twist-Related Protein 1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D009687:Nuclear Proteins; D051879:Twist-Related Protein 1; C067250:Twist1 protein, mouse; D015127:9,10-Dimethyl-1,2-benzanthracene; D013755:Tetradecanoylphorbol Acetate
keywords: Twist1; cell cycle; keratinocyte stem cells; skin carcinogenesis