Papel de los genes Rb11 y E2F1 en las alteraciones epidérmicas asociadas a la pérdida del gen Rb1 en ratones modificados

Resumen

The retinoblastoma gene (RB1), a member of the pocket protein family with p107 and p130, was the first known tumor suppressor identified and cloned. It is believed to be absent, deregulated or functionally inactivated in about 90% of human tumors. So it can be considered an ideal target to study the molecular basis of cancer. pRb negatively regulates cell cycle progression in part by binding to and inhibiting E2F transcription factors. The major aim of this project is to elucidate the role of the retinoblastoma family members and family members of E2F factors in skin homeostasis and epidermal carcinogenesis through mouse genetic manipulation techniques to generate inducible knock out models. After adjusting the experimental conditions using a reporter strain, Rosa26Ind, to fix inducible cre-mediated recombination, we generated a new mouse model in which the Rb1 gene deletion is induced and takes place specifically in epidermis after topical application of tamoxifen, in a temporary controlled manner thus mimicking, in a more accurate way, human sporadic tumors. Using this system we generated the following mouse strains: RbInd (pRb deletion is induced in basal layers of epidermis), RbInd;p107-/ - (pRb deletion is induced in basal layers of epidermis of p107 deficient mice ) and RbInd;E2F1-/- (pRb deletion is induced in basal layers of epidermis in E2F1 deficient mice). RbInd mice show an epidermal phenotype consisting on hyperplasia and hyperproliferation, but they do not develop spontaneous tumors, even after injury stimuli. All the RbInd;p107-/- mice, by two months after induction of Rb loss, show a characteristic phenotype with tumoral and pretumoral lesions in the oral and perioral areas associated with increased Akt/mTOR activity and reduced Pten expression as demonstrated by phosphoproteomic and genomic analyses. These data support a tumor suppressor role for p107 in epidermis in the absence of pRb. On the other hand, in RbInd;E2F1- /- mice, the epidermal phenotype due to pRb ablation is aggravated by E2F1 loss indicating that pRb functions in epidermis are not solely dependent on E2F1. In addition, a large proportion of mice develop spontaneous skin tumors six months after treatment. Skin tumors observed in this mouse model are non-invasive, well differentiated in situ carcinomas with induced p53 expression. Based on genomic data we find that Wnt/ß-catenin is among the major molecular mechanisms underlying such spontaneous tumorigenesis. Based on functional comparative genomics of human cancer datasets it is conceivable that this models can be considered a suitable representation of several tumors where loss of p53 may lead to malignancy.