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

描述（由申请人提供）：乳腺癌相关基因2（BCA 2）是一种新型环指泛素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因子，最近已成为治疗乳腺癌和其他癌症的有前途的分子靶点。尽管FDA批准的AMPK激活抗糖尿病药物二甲双胍处于III期临床试验中，但由于缺乏详细的机制研究，AMPK激活的益处在各种癌症类型中仍然存在争议。我们发现，二甲双胍治疗乳腺癌细胞诱导BCA 2表达，然后反馈抑制诱导的AMPK激活。我们发现这种新的BCA 2-AMPK调节途径可以解释为什么患者对二甲双胍治疗有不同的反应，并表明二甲双胍与BCA 2抑制剂联合治疗可能是比二甲双胍单独治疗更有效的乳腺癌治疗策略。 我 在本研究中，我们假设：（i）二甲双胍介导的人类乳腺癌细胞中AMPK活化触发两种相互冲突的信号传导途径：众所周知的通过mTOR抑制的癌症预防/肿瘤抑制信号和不太为人所知的通过诱导E3连接酶BCA 2活性的癌症存活反馈途径，该活性导致潜在的AMPK活化激酶降解;（ii）抑制BCA 2介导的反馈回路将增加二甲双胍的乳腺癌预防作用。为了验证我们的假设，我们建议研究BCA 2在二甲双胍诱导的乳腺癌细胞中AMPK介导的生存反馈回路中的作用（目的1），鉴定BCA 2底物，一种潜在的AMPK激活激酶，并研究其在二甲双胍诱导的生存反馈回路中的功能（目的2），最后，以确定抑制BCA 2活性是否可以增加二甲双胍在小鼠中的乳腺癌预防效果（目的3）。 该项目的成功完成将显著提高对二甲双胍临床疗效的分子机制的理解，有助于解释现有二甲双胍在不同癌症患者中各种疗效的临床数据，并为以下方面提供科学依据： 设计合理的二甲双胍为基础的癌症预防临床试验。我们的研究可以使二甲双胍研究超越当前的相关阶段，并首次建立详细的机制途径，将肿瘤组织BCA 2状态与二甲双胍疗效和改变癌症发病率的变化联系起来。 这一创新提案将：（i）研究涉及二甲双胍诱导的癌细胞存活反馈环的先前未知的关键组分，E3连接酶BCA 2，其引起潜在的肿瘤抑制AMPK活化激酶的降解;（二）寻求通过将二甲双胍与BCA 2或AKT抑制剂联合使用以提高二甲双胍疗效的新原理和方法来改变目前二甲双胍研究及其临床应用的范式。二甲双胍在含有高水平BCA 2介导的AMPK抑制信号的乳腺癌细胞中的作用。

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.