Gont Alexander, Daneshmand Manijeh, Woulfe John, Lavictoire Sylvie J, Lorimer Ian A J
Cancer Therapeutics Program, Ottawa Hospital Research Institute, Ottawa, Canada.
Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada.
Oncotarget. 2017 Jan 31;8(5):8559-8573. doi: 10.18632/oncotarget.14348.
A defining feature of the brain cancer glioblastoma is its highly invasive nature. When glioblastoma cells are isolated from patients using serum free conditions, they accurately recapitulate this invasive behaviour in animal models. The Rac subclass of Rho GTPases has been shown to promote invasive behaviour in glioblastoma cells isolated in this manner. However the guanine nucleotide exchange factors responsible for activating Rac in this context have not been characterized previously. PREX1 is a Rac guanine nucleotide exchange factor that is synergistically activated by binding of G protein αγ subunits and the phosphoinositide 3-kinase pathway second messenger phosphatidylinositol 3,4,5 trisphosphate. This makes it of particular interest in glioblastoma, as the phosphoinositide 3-kinase pathway is aberrantly activated by mutation in almost all cases. We show that PREX1 is expressed in glioblastoma cells isolated under serum-free conditions and in patient biopsies. PREX1 promotes the motility and invasion of glioblastoma cells, promoting Rac-mediated activation of p21-associated kinases and atypical PKC, which have established roles in cell motility. Glioblastoma cell motility was inhibited by either inhibition of phosphoinositide 3-kinase or inhibition of G protein βγ subunits. Motility was also inhibited by the generic dopamine receptor inhibitor haloperidol or a combination of the selective dopamine receptor D2 and D4 inhibitors L-741,626 and L-745,870. This establishes a role for dopamine receptor signaling via G protein βγ subunits in glioblastoma invasion and shows that phosphoinositide 3-kinase mutations in glioblastoma require a context of basal G protein-coupled receptor activity in order to promote this invasion.
脑癌胶质母细胞瘤的一个显著特征是其高度侵袭性。当在无血清条件下从患者体内分离出胶质母细胞瘤细胞时，它们能在动物模型中准确重现这种侵袭行为。已证明Rho GTPases的Rac亚类可促进以这种方式分离出的胶质母细胞瘤细胞的侵袭行为。然而，此前尚未对在此背景下负责激活Rac的鸟嘌呤核苷酸交换因子进行表征。PREX1是一种Rac鸟嘌呤核苷酸交换因子，通过与G蛋白αγ亚基和磷脂酰肌醇3-激酶途径的第二信使磷脂酰肌醇3,4,5-三磷酸结合而协同激活。这使其在胶质母细胞瘤中特别受关注，因为几乎在所有病例中磷脂酰肌醇3-激酶途径都因突变而异常激活。我们发现，PREX1在无血清条件下分离出的胶质母细胞瘤细胞以及患者活检样本中均有表达。PREX1促进胶质母细胞瘤细胞的运动和侵袭，促进Rac介导的p21相关激酶和非典型蛋白激酶C的激活，这些激酶在细胞运动中已明确发挥作用。抑制磷脂酰肌醇3-激酶或抑制G蛋白βγ亚基均可抑制胶质母细胞瘤细胞的运动。通用的多巴胺受体抑制剂氟哌啶醇或选择性多巴胺受体D2和D4抑制剂L-741,626与L-745,870的组合也可抑制运动。这确立了多巴胺受体通过G蛋白βγ亚基信号传导在胶质母细胞瘤侵袭中的作用，并表明胶质母细胞瘤中的磷脂酰肌醇3-激酶突变需要基础G蛋白偶联受体活性的背景才能促进这种侵袭。
