Suppression of melanotroph carcinogenesis leads to accelerated progression of pituitary anterior lobe tumors and medullary thyroid carcinomas in Rb+/- mice.

Mice with a single copy of the retinoblastoma gene (Rb(+/-)) develop a syndrome of multiple neuroendocrine neoplasia. They usually succumb to fast-growing, Rb-deficient melanotroph tumors of the pituitary intermediate lobe, which are extremely rare in humans. Thus, full assessment of Rb role in other, more relevant to human pathology, neoplasms is complicated. To prevent melanotroph neoplasia while preserving spontaneous carcinogenesis in other types of cells, we have prepared transgenic mice in which 770-bp fragment of pro-opiomelanocortin promoter directs expression of the human RB gene to melanotrophs (TgPOMC-RB). In three independent lines, transgenic mice crossed to Rb(+/-) background are devoid of melanotroph tumors but develop the usual spectrum of other neoplasms. Interestingly, abrogation of melanotroph carcinogenesis results in accelerated progression of pituitary anterior lobe tumors and medullary thyroid carcinomas. A combination of immunologic tests, cell culture studies, and tumorigenicity assays indicates that alpha-melanocyte-stimulating hormone, which is overproduced by melanotroph tumors, attenuates neoplastic progression by decreasing cell proliferation and inducing apoptosis. Taken together, we show that cell lineage-specific complementation of Rb function can be successfully used for refining available models of stochastic carcinogenesis and identify alpha-melanocyte-stimulating hormone as a potential attenuating factor during progression of neuroendocrine neoplasms.

Induction of carcinogenesis by concurrent inactivation of p53 and Rb1 in the mouse ovarian surface epithelium.

Alterations in p53 and Rb pathways are observed frequently in epithelial ovarian cancer (EOC).However, their roles in EOC initiation remain uncertain. Using a single intrabursal administration of recombinant adenovirus expressing Cre, we demonstrate that concurrent inactivation of p53 and Rb1 is sufficient for reproducible induction of ovarian epithelial carcinogenesis in mice homozygous for conditional gene alleles. Similarly to progression of disease in women, ovarian neoplasms spread i.p., forming ascites, and metastasize to the contralateral ovary, the lung, and the liver. These results establish critical interactions between p53 and Rb1 pathways in EOC pathogenesis, and provide a genetically defined immunocompetent mouse model of sporadic EOC.