蛋白修饰导致SH3BGRL在肿瘤中表达上调及在肿瘤发生、转移中的机理

So far, there is rare report on physiological effects of SH3 domain-binding glutamic acid-rich-like protein (SH3BGRL) in tumorigenesis worldwide. Our group characterized murine SH3BGRL as a tumorigenic and metastatic gene for the first time, which can specifically bind the inactive form of c-Src to get it activated, and subsequently triggered the FAK-mediated downstream signaling of MAPK and AKT. Unexpectedly, human SH3BGRL (hSH3BGRL) in turn suppressed tumorigenesis and metastasis in nature, and its somatic mutation, such as R76C can similarly act as murine SH3BGRL to facilitate tumorigenesis and metastasis. However, the mutation frequency of SH3BGRL in human tumors is very low, less than 3% in all tumors. In contrast, our clinical analyses showed that SH3BGRL is upregulated in various tumors, up to 40-45% of total checked samples. Molecularly, the upregulation of SH3BGRL is not resulted from transcriptional regulation. Our further study by 2-dimensional electrophoresis indicated that the molecular weight and biochemical feathers of SH3BGRL in normal tissues are evidently different from those in tumor samples, suggesting that protein modification of SH3BGRL should be existed, which leads to the protein stability increase and consequently promote tumor formation and metastasis. Based on the above preliminary data, we would like to further confirm this hypothesis if SH3BGRL is indeed modified and what kind modification is involved. Meanwhile, factors participated in the process will also be uncovered, which will be additionally validated in the in vivo tumor xenograft model. To further confirm the results in clinical relevance, SH3BGRL protein modification status and the critical enzymes or other factors would be checked on both transcriptional and protein levels and analyzed by correlation simulation to clinical prognosis and survival. In summary, our study will definitely shed lights on the mechanism of SH3BGRL in tumorigenesis and metastasis, and also provide experimental bases for the diagnosis and prognosis of tumors induced by SH3BGRL aberrant expression, while disclose some potential novel therapeutical targets to cancer diagnosis and therapy.

目前关于SH3BGRL在肿瘤发生和转移方面鲜有研究。我们首次报道了鼠类SH3BGRL可通过结合c-Src并活化其与FAK及下游MAPK和PI3K-AKT通路导致肿瘤发生转移；而人SH3BGRL却是一个肿瘤抑制基因，当其发生突变时就可转换为致瘤、促转移基因。但大量临床病样分析表明人SH3BGRL的突变率极低；我们前期结果也已表明它在肿瘤样品中普遍表达上调，却在基因转录水平未有变化；蛋白组学分析显示它在肿瘤和正常组织中的分子量及理化性质均不相同，由此猜测SH3BGRL蛋白修饰可能导致其在肿瘤组织中积累并促进肿瘤发生转移。本研究拟在此基础上深入探讨SH3BGRL蛋白修饰种类及导致其表达上调并促进肿瘤发生、转移的分子机理；发现导致其蛋白修饰的重要靶标分子；结合小鼠肿瘤模型和临床病样分析验证该蛋白修饰和相关修饰酶类在肿瘤发生和转移中的作用，为全面诊断治疗由它表达失调导致的癌症患者提供理论和实践基础。

肿瘤相关疾病是导致人类死亡的主要原因之一，但是目前关于肿瘤发生和肿瘤转移的机制仍然不明确。我们前期研究发现，小分子连接蛋白SH3BGRL具有双面性，我们首次报道了鼠类SH3BGRL可通过结合c-Src并活化其与FAK及下游MAPK和PI3K-AKT通路导致肿瘤发生转移；而人SH3BGRL却是一个肿瘤抑制基因，当其发生突变时就可转换为致瘤、促转移基因。但大量临床病样分析表明人SH3BGRL的突变率极低，但其在乳腺癌中却普遍上调表达，而在其它肿瘤中的表达尚不明确。由此我们在当时已有的前期结果基础上发现，SH3BGRL可能存在蛋白修饰，这种修饰就可以导致其在肿瘤中特异的结合某些蛋白因子，从而影响肿瘤发生转移。由此，我们们利用蛋白组学方法，在乳腺癌中发现了SH3BGRL特异性结合的蛋白因子，包括HER2、PFN1以及核糖体亚基蛋白。在这些发现基础上，我们进一步发现SH3BGRL结合HER2后，稳定HER2在细胞膜上，从而延迟其内吞作用，并可以特异性活化HER2 Y1196位磷酸化，从而导致下游PI3K-AKT和MAPK持续活化，导致对HER2靶向治疗的Herceptin和Laptinib抗药性；同时，还发现SH3BGRL可以通过结合核糖体从而在蛋白翻译水平促进泛素化E3连接酶STUB1翻译，从而促进PFN1的降解，而促进乳腺癌的转移；同样的SH3BGRL还可以在翻译水平上促进PIK3C3的翻译水平，促进乳腺癌细胞的自噬水平，而导致乳腺癌出现对doxorubicin等化疗药物出现抗性。上述结果充分表明SH3BGRL可以作为乳腺癌诊断、治疗和预后的分子靶点和标记，将为乳腺癌的有效精准治疗奠定理论基础。 同时，我们在AML型白血病中发现，SH3BGRL却有抑制肿瘤发生的作用，其表达与病人的良好预后相关，揭示了SH3BGRL的细胞和肿瘤特异性，同时表明SH3BGRL可以作为一个诊断和良好预后的分子标记。同时受本项目部分资助，我们还合成、研究了可以克服紫杉醇抗性的第二代紫杉醇化合的作用机制，为新药开发奠定了前期基础。