Signal Transduction by the Retinoblastoma Protein

描述(申请人提供)：癌细胞在细胞周期控制和分化方面表现出异常。这至少部分归因于这样一个事实，即大多数癌细胞含有损害视网膜母细胞瘤蛋白(PRB)功能的突变。PRB的靶标是E2F细胞周期调控转录因子家族的成员。不受pRb约束的E2F可以诱导细胞增殖，但也可以诱导细胞凋亡。E2F在S相被细胞周期蛋白NCDK2中和。阻断Cyclin A/CDK2与E2F相互作用的短肽(RXL肽)选择性地杀死转化的细胞，可能是因为与正常细胞相比，癌细胞具有高水平的E2F。具体目标1将是确认或驳斥RXL多肽通过阻止细胞周期蛋白A/CDK2中和E2F而杀死细胞的假设。PRb对G1/S转换的控制与其抑制E2F反应启动子的能力有关，而对分化的控制与此无关。另外两个PRB相互作用因子EID1和RBP2可能与分化控制有关。EID1抑制p300/CBP组蛋白乙酰酶活性，阻断分化，并在细胞退出细胞周期时迅速被泛素化。了解EID1周转的控制将是特定目标2的重点。初步数据表明，pRB和RBP2在依赖于分化的染色质重塑中发挥作用。PRB/RBP2相互作用的功能意义将在特定目标3和特定目标4中阐述，具体目标4将询问EID1和/或RBP2是否导致在RB-/-小鼠中观察到的发育异常。

DESCRIPTION (provided by applicant): Cancer cells exhibit abnormalities in cell-cycle control and in differentiation. This is due, at least partly, to the fact that most cancer cells harbor mutations that compromise the function of the retinoblastoma protein (pRB.) The best understood targets of pRB are members of the E2F cell-cycle regulatory transcription factor family. E2F, unfettered by pRB, can induce cellular proliferation but can also induce apoptosis. E2F is neutralized in S-phase by cyclin NCdk2. Short peptides ('RXL peptides') that block the interaction of cyclin A/cdk2 with E2F selectively kill transformed cells, perhaps due to the high levels of E2F that typify cancer cells compared to normal cells. Specific aim 1 will be to confirm or refute the hypothesis that RXL peptides kill cells by preventing the neutralization of E2F by cyclin A/cdk2. Control of the G1/S transition by pRB is linked to its ability to repress E2F-responsive promoters, whereas control of differentiation is not. Two additional pRB interactors, EID1 and RBP2, might be linked to differentiation control. EID1 inhibits p300/CBP histone acetylase activity, blocks differentiation, and is rapidly polyubiquitinated as cell exit the cell-cycle. Understanding the control of EID1 turnover will be the focus of Specific aim 2. Preliminary data suggests a role of pRB and RBP2 in differentiation-dependent chromatin remodeling. The functional significance of pRB/RBP2 interactions will be addressed in Specific aim 3 and specific aim 4 will ask whether EID1 and/or RBP2 contribute to the developmental abnormalities observed in RB-/- mice.