The Role of Rb Dephosphorylation in Apoptosis

描述(申请人提供)：许多控制细胞分裂的蛋白质参与癌症的发展。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。在几乎所有类型的癌症中都观察到了导致Rb过度磷酸化的Rb途径的改变。在这项提案中，我们提出了Rb的磷酸化状态在细胞凋亡中发挥重要作用的证据。事实上，在癌细胞中观察到的Rb磷酸化水平的升高可能不仅会导致增殖优势，还可能导致对凋亡的抵抗。在这项工作中，我们将检验这一假说，即Rb的某些氨基酸的去磷酸化导致Caspase介导的Rb的c-末端裂解，从而触发Rb的降解和细胞凋亡。我们将在正常细胞和癌细胞中确定Rb磷酸化状态和Rb裂解之间的功能联系。我们将研究几种诱导细胞凋亡剂的作用机制中对Rb裂解的要求。最后，我们将研究转录因子E2F1是否在Rb裂解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裂解和E2F1在肿瘤细胞凋亡中的重要性。 与公共卫生相关：在癌症中，细胞以不受控制的方式分裂和增殖。因此，对控制细胞分裂的分子的研究可能会带来了解癌细胞发育和生长所需的信息。该项目旨在研究一种名为视网膜母细胞瘤的蛋白质的功能，这种蛋白质与许多类型的癌症有关。

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.