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信号通路涉及后期促进复合体（APC）的激活，APC是一种多亚基泛素蛋白连接酶，它反过来促进转录共抑制因子SnoN的破坏，从而介导tgf - β应答基因的反激活，负责细胞周期阻滞。APC似乎与其他片段（包括Cdh1和Smad2/Smad3）一起起作用，但其被tgf - β信号激活的机制尚不清楚。本研究的目的是阐明这一机制，并进一步验证tgf - β激活的APC在人类乳腺肿瘤异种移植小鼠模型中抑制肿瘤形成的作用。我们最近获得的证据表明，APC的一个关键亚基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tgf - β通过一个涉及Cdc27磷酸化和Smad2/Smad3募集Cdh1的过程激活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确定负责Cdc27磷酸化的激酶；(2)表征激酶与APC之间相互作用的性质及其生物学后果（SnoN破坏和细胞周期阻滞）；(3)在人乳腺肿瘤异种移植小鼠模型中验证TGFbeta激活APC在抑制肿瘤进展中的作用。了解通过APC参与tgf - β信号传导的生物学机制，并验证APC作为tgf - β效应物在抑制乳腺肿瘤进展中的作用，对于寻求确定信号受损如何促进肿瘤发生以及确定治疗干预的潜在靶点的未来研究至关重要。

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.