PAK4与MORC2相互作用下调E-cadherin在乳腺癌细胞EMT及转移中的作用机制

PAK4, a serine/threonine protein kinase, has involved in a variety of cellular activities including regulation of cytoskeletal reorganization, cell proliferation, oncogenic transformation. MORC2 is a member of the MORC protein family. The biological functions and mechanisms of MORC2 remain poorly understood till now. We found that MORC2 is a new binding protein of PAK4.Our previous work showed that the overexpression of both PAK4 and MORC2 down-regulated E-cadherin expression, silencing of MORC2 led to a transition to epithelial morphology in the mesenchymal-like MDA-MB-231 breast cancer cells, upregulation of E-cadherin and down-regulation of N-cadherin and Vimentin protein expression, indicating that MORC2 promoted EMT of breast cancer cells. PAK4 and MORC2 inhibited E-cadherin promoter activity independently and cumulatively in MCF-7 cells, the promoter activity of E-cadherin was associated with MORC2 and HDACs. The aim of this program is to demonstrate the mechanisms of E-cadherin down-regulation through the binding and phosphorylation of MORC2 by PAK4, and the effect of PAK4 and MORC2 interaction on breast cancer cells EMT, cell migration, invasion and tumor development in orthotopic mouse model, and also the relationship between PAK4, MORC2 expression and breast cancer metastasis, prognosis using breast cancer specimens.This program will provide novel envidence for the targets of breast cancer therapy.

PAK4是一种丝/苏氨酸激酶，参与调节细胞骨架重组、细胞增殖、恶性转化等多种细胞活动。MORC2是MORC蛋白家族成员之一，其生物学功能及机制目前报道甚少。我们发现MORC2是PAK4新的结合蛋白。前期工作表明PAK4或MORC2过表达均下调E-cadherin表达，MORC2沉默导致MDA-MB-231细胞形态由间质细胞表型向上皮细胞表型转变，并上调E-cad下调N-cad和Vimentin 蛋白表达，提示MORC2促进乳腺癌细胞EMT。MCF-7细胞中PAK4和MORC2以独立的和累加的方式下调E-cad启动子活性，且E-cad启动子活性与MORC2和HDACs相关。本课题旨在阐明PAK4结合或磷酸化MORC2下调E-cad表达的机制，及对乳腺癌细胞EMT、迁移侵袭和裸鼠成瘤的影响；结合乳腺癌标本阐明PAK4和MORC2的表达与乳腺癌转移和预后的关系，为寻找乳腺癌治疗靶点提供理论依据。

MORC2是MORC蛋白家族成员，参与染色质重塑，抑制基因转录并促进脂肪生成。但MORC2在结直肠癌中的作用及机制还不清楚。NDRG1是潜在的转移抑制子，在结直肠癌细胞中，NDRG1通过维持E-cadherin和β-catenin黏附复合体，促进细胞黏附，抑制EMT和转移。我们的结果表明，MORC2下调NDRG1的mRNA、蛋白表达水平，并结合到NDRG1启动子上抑制NDRG1启动子活性。MORC2招募组蛋白去乙酰化酶SIRT1，共同抑制NDRG1转录。MORC2过表达促进SIRT1的核易位。MORC2通过抑制NDRG1促进结肠癌细胞的迁移和侵袭以及体内结肠癌细胞的转移。在临床结直肠癌样本中，MORC2过表达，而NDRG1低表达。以上结果提示MORC2是结直肠癌潜在的治疗靶点。PAK5是丝/苏氨酸激酶，调节细胞骨架重组，细胞运动和细胞凋亡；转录因子GATA1在乳腺癌中发挥着关键的抗凋亡作用，但PAK5和GATA1在乳腺癌转移中的作用尚不明确。我们发现，作为一个新的E-cadherin抑制子，GATA1促进乳腺癌细胞EMT。GATA1是PAK5的新底物，PAK5磷酸化GATA1的161位和187位丝氨酸。GATA1结合到E-cadherin启动子上，下调E-cadherin表达，干扰细胞连接并促进乳腺癌细胞在体内的转移。GATA1招募HDAC3/4到E-cadherin启动子处，而GATA1的突变体GATA1S161AS187A则招募得较少。这些结果提示，磷酸化的GATA1招募更多的HDAC3/4，从而促进E-cadherin的转录抑制，导致乳腺癌细胞EMT。我们的结果揭示了GATA1的新功能，有助于更好地阐明EMT的机制，表明GATA1和PAK5对它的磷酸化可能在乳腺癌转移中发挥重要的作用。此外，我们阐明了MORC2下调ArgBP2的机制并发现，在胃癌中ArgBP2低表达；ArgBP2抑制胃癌细胞的增殖、迁移和侵袭。我们的结果为进一步阐明ArgBP2的转录调控机制奠定了基础，并提示ArgBP2是胃癌治疗的潜在靶点。另外，我们发现PAK4通过增强p53的泛素化降解增强G6PD活性，促进葡萄糖摄取，从而促进结肠癌细胞增殖。我们的结果揭示了PAK4促进结肠癌细胞生长的葡萄糖代谢相关的新机制，提示阻遏PAK4和/或G6PD是治疗结肠癌的潜在策略。