title: PTEN loss promotes rasHa-mediated papillomatogenesis via dual up-regulation of AKT activity and cell cycle deregulation but malignant conversion proceeds via PTEN-associated pathways.
abstract: PTEN tumor suppressor gene failure in ras(Ha)-activated skin carcinogenesis was investigated by mating exon 5 floxed-PTEN (Delta5PTEN) mice to HK1.ras mice that expressed a RU486-inducible cre recombinase (K14.creP). PTEN inactivation in K14.cre/PTEN(flx/flx) keratinocytes resulted in epidermal hyperplasia/hyperkeratosis and novel 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted papillomas, whereas HK1.ras/K14.cre/PTEN(flx/flx) cohorts displayed a rapid onset of papillomatogenesis due to a synergism of increased AKT activity and extracellular signal-regulated kinase (ERK) elevation. High 5-bromo-4-deoxyuridine labeling in Delta5PTEN papillomas showed that a second promotion mechanism centered on failures in cell cycle control. Elevated cyclin D1 was associated with both HK1.ras/ERK- and Delta5PTEN-mediated AKT signaling, whereas cyclin E2 overexpression seemed dependent on PTEN loss. Spontaneous HK1.ras/Delta5PTEN malignant conversion was rare, whereas TPA promotion resulted in conversion with high frequency. On comparison with all previous HK1.ras carcinomas, such TPA-induced carcinomas expressed atypical retention of keratin K1 and lack of K13, a unique marker profile exhibited by TPA-induced K14.cre/PTEN(flx/flx) papillomas that also lacked endogenous c-ras(Ha) activation. Moreover, in all PTEN-null tumors, levels of ras(Ha)-associated total ERK protein became reduced, whereas phosphorylated ERK and cyclin D1 were lowered in late-stage papillomas returning to elevated levels, alongside increased cyclin E2 expression, in TPA-derived carcinomas. Thus, during early papillomatogenesis, PTEN loss promotes ras(Ha) initiation via elevation of AKT activity and synergistic failures in cyclin regulation. However, in progression, reduced ras(Ha)-associated ERK protein and activity, increased Delta5PTEN-associated cyclin E2 expression, and unique K1/K13 profiles following TPA treatment suggest that PTEN loss, rather than ras(Ha) activation, gives rise to a population of cells with greater malignant potential.
authors.affiliation: Section of Squamous Cell Biology and Dermatology, Division of Cancer Sciences and Molecular Pathology, Glasgow University, Glasgow G11 6NU, Scotland, UK.
authors.forename: Denggao
authors.initials: D
authors.lastname: Yao
authors.forename: Claire L
authors.initials: CL
authors.lastname: Alexander
authors.forename: Jean A
authors.initials: JA
authors.lastname: Quinn
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Porter
authors.forename: Hong
authors.initials: H
authors.lastname: Wu
authors.forename: David A
authors.initials: DA
authors.lastname: Greenhalgh
mesh_terms: D000818:Animals; D002273:Carcinogens; D002454:Cell Differentiation / Q000502:physiology; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D053535:Keratin-13; D007633:Keratins / Q000096:biosynthesis; D020935:MAP Kinase Signaling System; D051379:Mice; D008822:Mice, Transgenic; D015735:Mifepristone / Q000494:pharmacology; D051058:Oncogene Protein v-akt / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D010212:Papilloma / Q000139:chemically induced / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D012878:Skin Neoplasms / Q000139:chemically induced / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D013755:Tetradecanoylphorbol Acetate; D015854:Up-Regulation; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D002273:Carcinogens; D053535:Keratin-13; C507427:Krt13 protein, mouse; D015735:Mifepristone; D007633:Keratins; D051058:Oncogene Protein v-akt; D051059:PTEN Phosphohydrolase; D018631:ras Proteins; D013755:Tetradecanoylphorbol Acetate