Activation of APC by TGF-beta Suppresses Breast Cancer

描述（由申请人提供）：TGF-β生长抑制的丧失是许多人类肿瘤的标志。TGF-β信号传导途径涉及后期促进复合物（APC）（一种多亚基泛素蛋白连接酶）的活化，其进而促进SnoN（一种转录共抑制因子）的破坏，从而介导负责细胞周期停滞的TGF-β响应基因的反式激活。APC似乎与其他部分（包括Cdh 1和Smad 2/Smad 3）一起起作用，但其被TGF-β信号激活的机制尚不清楚。目前的建议的目的是阐明该机制，并进一步验证TGF-β激活的APC在小鼠模型中使用人乳腺肿瘤异种移植物抑制肿瘤形成中的作用。我们最近获得的证据表明，磷酸化Cdc 27，APC的关键亚基，在激活过程中，以及证据表明，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TGF-β通过Cdc 27磷酸化和Cdh 1的Smad 2/Smad 3募集过程激活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鉴定负责Cdc 27磷酸化的激酶;（2）表征激酶和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）;和（3）验证TGF β激活APC在人乳腺肿瘤异种移植小鼠模型中抑制肿瘤进展的作用。了解TGF-β信号通过APC的生物学机制，并验证APC作为TGF-β效应器在抑制乳腺肿瘤进展中的作用，对于未来的研究将是重要的，这些研究旨在确定受损的信号如何有助于肿瘤发生，并确定治疗干预的潜在靶点。

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.