新癌基因E3连接酶HECTD3表达调节机制的研究

Our recently study showed that E3 ligase HECTD3 frequently up-regulated in breast cancer. It ubiquitinates caspase-8 with K63-linked polyubiquitin chains that do not target caspase-8 for degradation but decrease the caspase-8 recruitment into the death inducing signaling complex (DISC) for activation. Therefore, inhibits cancer cells to chemotherapeutic drug (TRAIL and cisplatin) induced apoptosis. The aim of this project is indentified what transcription factor and miRNA are involved in regulation of HECTD3 expression. Our preliminary data had showed that insulin and EGF both up-regulate HECTD3 in MCF10A, however cisplatin down-regulates HECTD3 in MDA-MB-231. We previously analyze the promoter and 3'UTR of HECTD3 and found that there are STAT3 binding site in promoter of HECTD3 gene and targeting site in 3'UTR of HECTD3 mRNA. Importantly, transfecting siRNA targeting HECTD3 and miR-939 both decrease HECTD3 level in MDA-MB-231 cell. Therefore, we will indentify the transcription factor and miRNA regulating HECTD3 through pathway screening combining with regulation mechanism analysis and function study. At last, the STAT3 and miR-939 expressing are also analyzed in breast cancer samples. Success of the proposed aims will clarify the mechanism of regulation new oncogene, HECTD3, which could provide new strategies for screening of diagnosis biomarker and development of new anti-cancer therapy.

最新发现E3连接酶HECTD3在乳腺肿瘤中表达显著上调，并通过K63方式多聚泛素化其底物Casp8来抑制其活化，从而抑制凋亡，促进癌细胞生存并增加对抗肿瘤药物（TRAIL和顺铂）敏感性。本项目主要目的是确立调节HECTD3表达的转录因子和确立调节其表达的miRNA。前期研究表明胰岛素、EGF等在MCF10A中均可上调HECTD3，而顺铂则在MB-231中下调HECTD3。前期对HECTD3基因启动子区和mRNA的3'UTR区生物信息学分析，发现在启动子区含有STAT3的结合位点与3'UTR区具有miR-939靶位点，敲降STAT3和转染miR-939均可显著降低HECTD3水平。因此本课题通过调节信号通路筛选、调节机制和生物功能学分析，确立参与调节的转录因子和miRNA。最后对STAT3和miR-939在乳腺肿瘤中表达分析，阐明HECTD3表达调节分子机制，为以后临床应用提供理论指导作用。

肿瘤微环境中的炎症细胞在肿瘤的发生发展中起重要作用，其分泌的多种细胞因子可以促进恶性细胞的生长和存活。探索肿瘤微环境中的这些细胞因子如何调节肿瘤细胞内凋亡信号传导机制有助于为肿瘤的靶向治疗提供更多的靶点。这里我们发现，肿瘤微环境中的炎症细胞分泌的一种重要的细胞因子IL-6可以明显上调HECTD3的表达。而E3连接酶HECTD3在肿瘤细胞抵抗凋亡过程中起重要作用。此外，我们发现皮肤黑色素瘤中HECTD3上调的患者总生存期和无病生存期均低于其他患者。而在脑低级神经胶质瘤中HECTD3下调的患者总生存期和无病生存期均高于其他患者。而在细胞中HECTD3可以与凋亡起始因子caspase-9相互作用并可以促进其多聚泛素化来抑制其与Apaf-1相互作用和寡聚化的形成抑制caspase-9的活化，从而抑制细胞凋亡。另外，HECTD3的这种抑制凋亡的作用受到ERK激酶的磷酸化调节。因此，HECTD3可以成为预防和治疗肿瘤的一个潜在靶标。