前列腺癌SPOP基因高频突变促进组蛋白甲基化酶GLP/G9a介导的细胞增殖和侵袭的分子机制研究

Characterization of the exome and genome of prostate cancers by next-generation sequencing has identified numerous genetic alternations. SPOP was identified as one of the most frequently affected genes by somatic point mutations in prostate cancer, suggesting SPOP is potentially a key driver for prostate cancer development and progression. However, how SPOP mutations contribute to prostate cancer remains to be elucidated. SPOP acts as an adaptor protein of the CUL3-RBX1 E3 ubiquitin ligase complex, selectively recruits substrates for their ubiquitination and subsequent degradation. GLP, a histone methyltransferase responsible for histone H3 lysine 9 (H3K9) mono- and dimethylation, has been observed to be upregulated in different types of cancer and its overexpression has been associated with poor prognosis. In this study, we identified GLP as a bona fide substrate for the SPOP-CUL3-RBX1 E3 ubiquitin ligase complex. SPOP triggers GLP degradation via the ubiquitin-proteasome pathway. Strikingly, prostate cancer-associated mutants of SPOP are defective in promoting GLP degradation. This study revealed novel molecular events underlying the regulation of GLP protein homeostasis, and provided insights in understanding the relationship between SPOP mutations and epigenetics dysregulation in prostate cancer.

最近几项高通量测序研究发现SPOP基因在前列腺癌样本中发生高频失活突变，但SPOP突变对于前列腺癌发生发展的生物学意义还未得到阐明。SPOP是Cullin3家族泛素E3连接酶复合体的一个底物识别亚基，介导底物的泛素化降解。组蛋白甲基化酶GLP和它的同源蛋白G9a形成二聚体，共同介导组蛋白H3K9的单、双甲基化修饰。GLP/G9a在多种肿瘤中上调表达，促进细胞的恶性增殖。我们通过酵母双杂交方法发现GLP是SPOP的互作蛋白，SPOP可促进GLP的泛素化降解。并且前列腺癌来源的SPOP突变体丧失了和GLP相互作用的能力。本项研究将在分子、细胞、模式动物和肿瘤样本等多个层次，深入阐明前列腺癌中SPOP突变导致的GLP蛋白异常积累所引起的表观遗传学效应和生物学表型，为SPOP突变诱发的前列腺癌提供一种新的机制解释，并为GLP蛋白抑制剂应用于前列腺癌的个性化治疗提供理论依据。

最近几项高通量测序研究发现SPOP基因在前列腺癌样本中发生高频失活突变，但SPOP突变对于前列腺癌发生发展的生物学意义还未得到阐明。SPOP是Cullin3家族泛素E3连接酶复合体的一个底物识别亚基，介导底物的泛素化降解。组蛋白甲基化酶GLP和它的同源蛋白G9a形成二聚体，共同介导组蛋白H3K9的单、双甲基化修饰。GLP/G9a在多种肿瘤中上调表达，促进细胞的恶性增殖。我们通过酵母双杂交方法发现GLP是SPOP的互作蛋白，SPOP可促进GLP的泛素化降解。并且前列腺癌来源的SPOP突变体丧失了和GLP相互作用的能力。在本项目的支持下，我们揭示了SPOP突变导致的基因组DNA甲基化水平的上升依赖于GLP/G9a招募DNMT1的作用，但和其组蛋白甲基化酶的活性无关。SPOP突变导致的GLP/G9a蛋白稳定使的肿瘤抑制基因GATA5、NDRG3和FOXO3等的启动子区甲基化水平上升，从而抑制其基因的表达。我们还发现DNA甲基化抑制剂5-氮杂胞苷(5-AzaC)能逆转SPOP突变的基因组高甲基化。这一研究结果对未来SPOP突变亚型的分子靶向治疗具有一定的应用价值。