Activation of APC by TGF-beta Suppresses Breast Cancer

描述(申请人提供)：失去转化生长因子-β生长抑制是许多人类肿瘤的标志。转化生长因子-β信号通路涉及后期促进复合体(APC)的激活，这是一种多亚基泛素蛋白连接酶，进而促进转录共抑制因子SnoN的破坏，从而介导导致细胞周期停滞的转化生长因子-β反应基因的反式激活。APC似乎与其他部分一起作用，包括CDH1和Smad2/Smad3，但它被转化生长因子-β信号激活的机制尚不清楚。目前的建议的目的是阐明这一机制，并进一步验证转化生长因子-β激活的APC在利用小鼠人乳腺肿瘤异种移植瘤抑制肿瘤形成中的作用。我们最近获得的证据表明，APC的关键亚基CDc27在激活过程中被磷酸化，并且有证据表明负责的酶可能是酪蛋白激酶II。基于这些和其他数据，我们假设转化生长因子-β通过一个涉及CDc27磷酸化和CDH1的Smad2/Smad3募集的过程来激活APC。我们的具体目标将是(1)通过确认酪蛋白激酶II的作用和/或确定其他候选激酶的作用来确定负责CDC27磷酸化的激酶；(2)表征该激酶和APC之间相互作用的性质及其生物学后果(SnoN破坏和细胞周期停滞)；以及(3)验证TGFbeta激活APC在抑制人乳腺癌移植瘤小鼠模型中的肿瘤进展中的作用。了解APC介导的转化生长因子-β信号转导的生物学机制，并确认APC作为转化生长因子-β效应因子在抑制乳腺肿瘤进展中的作用，对于进一步研究信号转导受损与肿瘤发生的关系以及确定治疗干预的潜在靶点具有重要意义。

DESCRIPTION (provided by applicant): Loss of TGF-beta growth inhibition is a hallmark of many human tumors. The TGF-beta signaling pathway involves the activation of anaphase-promoting complex (APC), a multisubunit ubiquitin protein ligase, which in turn facilitates the destruction of SnoN, a transcriptional co-suppressor, thereby mediating the transactivation of TGF-beta responsive genes responsible for cell cycle arrest. APC appears to act in conjunction with other moieties, including Cdh1 and Smad2/Smad3, but the mechanism by which it is activated by TGF-beta signaling is poorly understood. The objectives of the current proposal are to elucidate that mechanism and further validate the role of TGF-beta activated APC in suppressing tumor formation using human, breast tumor xenografts in a mouse model. We have recently obtained evidence implicating the phosphorylation of Cdc27, a key subunit of APC, in the process of activation, as well as evidence suggesting that the responsible enzyme may be casein kinase II. Based on these and other data, we hypothesize that TGF-beta activates APC through a process that involves Cdc27 phosphorylation and Smad2/Smad3 recruitment of Cdh1. Our specific aims will be (1) to identify the kinase responsible for phosphorylation of Cdc27 by confirming the role of casein kinase II and/or determining a role for other candidate kinases; (2) to characterize the nature of the interactions between the kinase and APC and their biological consequences (SnoN destruction and cell cycle arrest); and (3) to validate the role of activation of APC by TGFbeta in suppressing tumor progression in a human, breast tumor xenograft mouse model. Understanding the biological mechanisms involved in TGF-beta signaling via APC and validating the role of APC as a TGF-beta effecter in the inhibition of breast tumor progression will be important for future studies that seek to determine how impaired signaling contributes to oncogenesis and for identification of potential targets for therapeutic intervention.