Gαi-PSD95信号复合物在恶性胶质瘤中的表达及生物学功能研究

The prognosis of patients with glioblastoma multiforme (GBM) using the current standard of care is still poor despite aggressive surgery, radiation, and chemotherapies. One key hurdle is the molecular heterogeneity of GBM. In GBM, receptor tyrosine kinases (RTKs) including epidermal growth factor receptor (EGFR), vascular endothelial growth factor receptor (VEGFR) and brain-derived neurotrophic factor (BDNF) receptor Trk-B are often over-expressed and/or constitutively-activated to promote tumor progression. Results from clinical trials of anti-RTK agents have been disappointing, mainly due to fact that multiple RTKs signaling are co-activated in GBM, while most of these agents only target one single RTK, or one single pathway. Our preliminary studies have indentified two new adaptor proteins for RTKs: namely inhibitory heterotrimeric G proteins α subunit (Gαi proteins) and postsynaptic density protein-95 (PSD95). We found that Gαi proteins form a complex with PSD95, and were important for EGFR, VEGR and Trk-B induced activation of multiple downstream signals including PI3K/Akt/mTOR, CaMKII and/or mitogen-activated protein kinase (MAPK). Meanwhile, just like RTKs, Gαi-PSD95 signal complex was found to be over-expressed in GBM tissues. We propose here that Gαi-PSD95 adaptor complex associates with multiple RTKs to mediate downstream signal transduction, and eventually promotes GMB cell survival, proliferation, migration and new blood vessel formation. This study suggests that Gαi-PSD95 signal complex might be as a novel biomarker and an efficient drug target for better anti-GBM therapy.

EGFR、Trk-B、VEGFR等受体酪氨酸激酶(RTKs)家族在恶性胶质瘤(GBM)组织中同时过度活化，促进GMB发生、发展。目前抗RTK药物仅能干扰单个RTK通路，效果一般。申请者前期研究发现RTKs通路2个新中间蛋白：Gαi（G蛋白抑制性α亚单位）和PSD95（突触后致密蛋白95）,介导下游信号转导。预实验结果显示：Gαi、PSD95在人GMB组织中高表达，两者结合形成信号复合物，并和多个RTKs耦联。本项目中，申请者将系统观察该信号复合物在人胶质瘤中表达水平，分析其与肿瘤种类、分级等临床指标的相关性。重点阐明Gαi-PSD95介导RTKs信号转导的机制。并利用多种生物学方法，从分子，细胞及整体水平研究Gαi-PSD95信号复合物在GMB细胞存活、增殖、迁移中的作用，以及对VEGF诱导的血管内皮细胞增殖的影响。拟证实Gαi-PSD95是多个RTKs共用中间蛋白和GMB诊治新靶点。

EGFR、PDGFR、FGFR、VEGFR等受体酪氨酸激酶（RTKs）家族在胶质瘤（GBM）组织中过表达且过度活化，促进GMB发生、发展。目前抗RTK药物仅能干扰单个RTK通路，效果一般。本项目中，申请者研究证实RTK通路中新的衔接蛋白（adaptor proteins）：G蛋白抑制性α亚单位（Gαi蛋白）和突触后致密蛋白95（PSD95）。研究结果显示：Gαi-PSD95在人GMB组织及细胞中高表达，并和多个RTKs耦联。此外，两者介导EGF、FGF、VEGF等诱导的Akt-mTOR信号通路的活化。而敲减、突变或敲除Gαi-PSD95则抑制GMB细胞存活、增值。研究结论，Gαi-PSD95是多个RTKs共用中间蛋白，介导下游Akt-mTOR等信号活化，促进GMB细胞存活、增值。本项目Gαi-PSD95很有可能是GMB的诊治新的有效靶点。