Cullin3介导Beclin 1泛素化降解抑制自噬及其在肿瘤治疗中的作用

自噬在肿瘤发生发展中起重要作用，调控自噬的核心蛋白Beclin 1是一种抑癌因子，然而肿瘤细胞中Beclin 1蛋白低表达的原因还没有被完全阐明。我们研究发现泛素连接酶Cullin3可以与Beclin 1相互作用，敲低Cullin3可以引起Beclin 1的泛素化修饰降低、蛋白水平上调、自噬活性增加，且Cullin3在肿瘤组织中相对高表达。质谱与序列分析表明Beclin1 S249可能是IKKα磷酸化位点。本课题拟深入研究Cullin3通过介导Beclin 1发生泛素化降解，进而调控自噬的分子机制；研究IKKα磷酸化Beclin 1对其泛素化的促进作用；证明Cullin3促进Beclin 1降解，导致乳腺癌/卵巢癌恶性进展，并在临床样本中分析二者表达的相关性，评估对临床治疗的意义。本研究旨在深入理解Beclin 1在肿瘤中低表达的调控机制，有助于将自噬合理应用于临床开发肿瘤治疗的新策略。

Autophagy plays an important role during the development of human cancer. Many tumor cells downregulate the tumor suppressor Beclin 1, a core player in autophagy pathway. The underlying mechanism, however, remains elusive. In our preliminary study, we found that Cullin3, an E3 ubiquitin Ligase, could interact with Beclin 1 and promoted the ubiquitination and degradation of Beclin 1. Knocking down Cullin3 leaded to increase of the autophagy activity. More importantly, human tumor samples expressed high level of Cullin 3 compared to normal tissue. Our mass spectrometry data indicated potential phosphorylation of Beclin 1 by IKKα at Ser249. In this proposal, we will study the detailed mechanism by which Cullin3 promotes the ubiquitin-mediated degradation of Beclin 1 and regulates autophagy. Meanwhile, we will examine the role of IKKα-mediated phosphorylation of Beclin 1 in ubiquitination. Moreover, we want to explore the tumor-promoting effect of Cullin3 in human cancer and to investigate the efficacy of Cullin/IKK inhibitors for cancer treatment. We will intestigate the correlation between Cullin3 and Beclin 1 expression and their role in cancer progression, therapeutic sensitivity and prognosis in human samples. The study will reveal the underlying mechanism of the low expression of Beclin 1 in cancer cells, which will benefit novel therapeutics that apply autophagic regulation in combating cancer.