The Retinoblastoma Protein and Its Homolog p130 Regulate the G(1)/S Transition in Pancreatic β-Cells

OBJECTIVE: The retinoblastoma protein family (pRb, p130, p107) plays a central role in the regulation of cell cycle progression. Surprisingly, loss of pRb in the β-cell has no discernible effect on cell cycle control. Therefore, we explored the effects of individual loss of either p130 or p107 in addition to the simultaneous loss of both pRb/p130 on the β-cell. RESEARCH DESIGN AND METHODS: Adult mice deficient in either p130 or p107 or both pRb/p130 were examined for effects on β-cell replication, function, and survival. The Cre-Lox system was also used to inactivate pRb in wild-type and p130-deficient β-cells in vitro. RESULTS: In vivo loss of either p107 or p130 did not affect β-cell replication or function. Combined pRb/p130 loss, however, resulted in dramatically accelerated proliferation as well as apoptotic cell death. Pancreas and β-cell mass were significantly reduced in double mutants. Despite this, overall glucose tolerance was normal, except for mild postprandial hyperglycemia. Ex vivo, acute deletion of pRb in p130-deficient β-cells also caused a striking increase in proliferation. The combined deletion of pRb/p130 upregulated islet expression of E2F2 but not E2F1. CONCLUSIONS: These studies define an essential role for the pocket proteins in controlling the G(1)/S transition in β-cells. When deficient in both pRb and p130, β-cells undergo unrestrained cell cycle reentry and activation of apoptosis. These studies underscore the central role of the pRb pathway in controlling β-cell turnover and provide new cellular targets for β-cell regeneration.