(PQA1) Regulation of Metformin Response by Breast Cancer Associated Gene 2 (BCA2)

描述(申请人提供)：乳腺癌相关基因2(BCA2)是一种新的环指泛素E3连接酶，在50%的乳腺肿瘤中过表达。AMPK是细胞能量稳态的主要调节者，最近成为治疗乳腺癌和其他癌症的有希望的分子靶点。尽管FDA批准的激活AMPK的抗糖尿病药物二甲双胍处于第三阶段临床试验，但由于缺乏详细的机制研究，AMPK激活在各种癌症类型中的益处仍然存在争议。我们发现，二甲双胍处理乳腺癌细胞诱导BCA2的表达，然后反馈抑制诱导的AMPK激活。我们这一新的BCA2-AMPK调控通路的发现可以解释为什么患者对二甲双胍治疗有不同的反应，并表明二甲双胍联合BCA2抑制剂可能是一种比单独应用二甲双胍更有效的乳腺癌治疗策略。我 在目前的研究中，我们假设：(I)二甲双胍介导的AMPK在人乳腺癌细胞中的激活触发了两条相互冲突的信号通路：已知的通过mTOR抑制的癌症预防/肿瘤抑制信号和鲜为人知的通过诱导E3连接酶BCA2活性导致潜在的AMPK激活激酶降解的癌症生存反馈通路；(Ii)抑制BCA2介导的反馈环将增加二甲双胍预防乳腺癌的效果。为了验证我们的假设，我们建议研究BCA2在二甲双胍诱导的、AMPK介导的乳腺癌细胞生存反馈环中的作用(目标1)，确定潜在的AMPK激活激酶BCA2底物，并研究其在二甲双胍诱导的生存反馈环(目标2)中的功能，最后，确定抑制BCA2活性是否可以增加二甲双胍预防小鼠乳腺癌的效果(目标3)。 该项目的成功完成将显著提高对临床二甲双胍疗效分子机制的理解，有助于解释现有的关于二甲双胍在不同癌症患者中疗效的临床数据，并为临床治疗提供科学依据 设计合理的二甲双胍防癌临床试验。我们的研究可以使二甲双胍的研究超越目前的相关阶段，并首次建立详细的、机械的途径，将肿瘤组织BCA2状态与二甲双胍的疗效和改变癌症发病率的变化联系起来。 这一创新建议将：(I)研究二甲双胍诱导的癌细胞生存反馈环路中一个以前未知的关键成分，即导致潜在的肿瘤抑制AMPK激活激酶降解的E3连接酶BCA2；(Ii)通过将二甲双胍与BCA2或AKT的抑制剂结合以提高含有高水平BCA2介导的AMPK抑制信号的乳腺癌细胞的疗效的新的理论和方法，寻求改变目前二甲双胍研究及其临床应用的范式。

DESCRIPTION (provided by applicant): Breast Cancer Associated Gene 2 (BCA2) is a novel RING-finger ubiquitin E3 ligase that is overexpressed in >50% of breast tumors. AMPK is the master regulator of cellular energy homeostasis that has recently emerged as a promising molecular target in the treatment of breast and other cancers. Although the FDA- approved, AMPK activating, anti-diabetic drug metformin is in Phase III clinical trials, the benefit of AMPK activation remains controversial in various cancer types, due to lack of detailed mechanistic studies. We have found that metformin treatment of breast cancer cells induces BCA2 expression that then feedback inhibits the induced AMPK activation. Our discovery of this novel BCA2-AMPK regulatory pathway could explain why patients have various responses to metformin therapies, and suggests that metformin therapy when combined with a BCA2 inhibitor may be a more effective breast cancer treatment strategy than metformin alone. I In the current study, we hypothesize: (i) Metformin-mediated AMPK activation in human breast cancer cells triggers two conflicting signaling pathways: the well-known cancer-preventive/ tumor-suppressing signal via mTOR inhibition and the less-known cancer-survival feedback pathway via induction of the E3 ligase BCA2 activity that leads to degradation of a potential AMPK-activating kinase; (ii) Inhibition of BCA2-mediated feedback loop will increase the breast cancer-preventive effect of metformin. To test our hypotheses, we propose to study the role of BCA2 in metformin-induced, AMPK-mediated survival feedback loop in breast cancer cells (Aim 1), to identify the BCA2 substrate, a potential AMPK-activating kinase, and to study its function in metformin-induced survival feedback loop (Aim 2), and finally, to determine whether inhibition of BCA2 activity could increase breast cancer-preventive effect of metformin in mice (Aim 3). The successful completion of this project will significantly improve understanding of the molecular mechanisms of clinical metformin efficacy, help interpret the existing clinical data about various metformin efficacies in different cancer patients, and provide a scientific basis for designing rationalized metformin-based cancer prevention clinical trials. Our study could move the metformin research beyond the current correlative stages and establish, for the first time, detailed, mechanistic pathways that link tumor tissue BCA2 status to metformin efficacy and to changes that alter cancer incidence. This innovative proposal will: (i) study a previously unknown key component involved in the metformin- induced cancer cell survival feedback loop, the E3 ligase BCA2 that causes degradation of a potential tumor- suppressing AMPK-activating kinase; (ii) seek to shift the paradigms of current metformin research and its clinical use by means of a novel rationale and methodology for combining metformin with an inhibitor of BCA2 or AKT to increase the efficacy of metformin in breast cancer cells containing high levels of BCA2-mediated AMPK-inhibitory signal.