The Role of Rb Dephosphorylation in Apoptosis

描述（由申请人提供）：许多控制细胞分裂的蛋白质参与了癌症的发展。视网膜母细胞瘤蛋白（Rb）的磷酸化状态调节该蛋白控制细胞增殖的能力。Rb的磷酸化刺激细胞周期的进展，而Rb的去磷酸化抑制细胞周期的进展。几乎在所有类型的癌症中都观察到Rb通路的改变导致Rb过度磷酸化。在本提案中，我们提出证据表明Rb的磷酸化状态在凋亡细胞死亡中起重要作用。事实上，在癌细胞中观察到的Rb磷酸化升高可能不仅导致增殖优势，而且可能导致细胞凋亡的抵抗。在这项工作中，我们将验证Rb某些氨基酸的去磷酸化导致caspase介导的Rb c端切割，从而引发Rb降解和细胞凋亡的假设。我们将在正常细胞和癌细胞中确定Rb磷酸化状态和Rb切割之间的功能联系。我们将探讨几种细胞凋亡诱导剂的作用机制中Rb切割的必要性。最后，我们将探讨转录因子E2F1是否在Rb切割诱导的细胞凋亡中起关键作用。这些研究将阐明Rb磷酸化、Rb切割和E2F1在肿瘤细胞凋亡中的重要性。

DESCRIPTION (provided by applicant): Many proteins that control cell division are involved in cancer development. The phosphorylation state of the Retinoblastoma protein (Rb) regulates the ability of this protein to control cell proliferation. Phosphorylation of Rb stimulates cell cycle progression, whereas dephosphorylation of Rb inhibits progression through the cell cycle. Alterations in the Rb pathway that lead to excessive phosphorylation of Rb have been observed in almost all types of cancer. In this proposal we present evidence that the phosphorylation state of Rb plays an important role in apoptotic cell death. In fact, it may be that elevated phosphorylation of Rb observed in cancer cells may not only cause a proliferation advantage but resistance to apoptosis. In this work we will test the hypothesis that dephosphorylation of certain amino acids of Rb leads to the caspase-mediated c-terminal cleavage of Rb, which triggers degradation of Rb and apoptosis. We will determine the functional connection between Rb phosphorylation state and Rb cleavage in normal and cancer cells. The requirement for Rb cleavage in the mechanism of action of several apoptosis-inducing agents will be examined. Finally we will investigate whether the transcription factor E2F1 plays a critical role in apoptosis induced by the cleavage of Rb. The proposed studies will elucidate the importance of Rb phosphorylation, Rb cleavage and E2F1 in apoptosis in cancer. PUBLIC HEALTH RELEVANCE: In cancer, cells divide and proliferate in an uncontrolled manner. Thus, the investigation of the molecules that control cell division may lead to information needed to understand cancer cell development and growth. This project is designed to study the function of a protein called Retinoblastoma which is implicated in many types of cancer.