Conditional Deletion of Rb Causes Early Stage Prostate Cancer

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Abstract
Prostate cancer remains the second leading cause of cancer-related death for men in the United States. Mutations in tumor suppressor genes including retinoblastoma (Rb), p53, and PTEN have been linked to the development of prostate cancer in man and mouse models, and loss of heterozygosity of the Rb locus has been observed in up to 60% of clinical cases. In this study we demonstrate that conditional somatic deletion of even a single Rb allele in the epithelial cells of the mouse prostate causes focal hyperplasia, thereby establishing a causal relationship between Rb loss and development of early stage prostate cancer. As a consequence of Rb ablation we observed increased expression of E2F target genes and a concomitant increase in proliferation in the epithelial compartment. However, by 52 weeks of age these lesions had not become malignant and represent an early stage of the disease. Nevertheless, the multifocal nature of the phenotype in the mice closely resembled multifocality of clinical disease. Taken together, our data demonstrated that loss of pRB-mediated cell cycle control directly caused the initiation of proliferative prostate disease but was insufficient to cause malignancy. Establishment of this early initiation model will aid efforts to thoroughly characterize early prostate disease as well as the elucidation of molecular mechanisms that cooperate with Rb loss to facilitate progression and metastasis.