Haizhong Feng1, Yanxin Li1, Yuhua Yin1, Weiwei Zhang1, Yanli Hou1, Lei Zhang1, Zuoqing Li1, Baoshu Xie1, Wei-Qiang Gao1, Jann N Sarkaria1, Jeffery J Raizer1, C David James1, Andrew T Parsa1, Bo Hu1, Shi-Yuan Cheng1. 1. State Key Laboratory of Oncogenes and Related Genes, Renji-Med X Clinical Stem Cell Research Center, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China (H.F., W.Z., Y.H., L.Z., Z.L., W.-Q.G., S.-Y.C.); Department of Neurology, Northwestern Brain Tumor Institute, Center for Genetic Medicine, The Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois (H.F., J.J.R., B.H., S.-Y.C.); Key Laboratory of Pediatric Hematology and Oncology Ministry of Health, Pediatric Translational Medicine Institute, Shanghai Children's Medical Center, School of Medicine, Shanghai Jiao Tong University, Shanghai, China (Y.L.); Department of Neurological Surgery (Y.Y., B.X.); Department of Radiotherapy, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China (Y.H.); Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota (J.N.S.); Department of Neurological Surgery, Northwestern Brain Tumor Institute, The Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois (C.D.J., A.T.P.).
Abstract
BACKGROUND: Dedicator of cytokinesis 1 (Dock1 or Dock180), a bipartite guanine nucleotide exchange factor for Rac1, plays critical roles in receptor tyrosine kinase-stimulated cancer growth and invasion. Dock180 activity is required in cell migration cancer tumorigenesis promoted by platelet derived growth factor receptor (PDGFR) and epidermal growth factor receptor. METHODS: To demonstrate whether PDGFRα promotes tumor malignant behavior through protein kinase A (PKA)-dependent serine phosphorylation of Dock180, we performed cell proliferation, viability, migration, immunoprecipitation, immunoblotting, colony formation, and in vivo tumorigenesis assays using established and short-term explant cultures of glioblastoma cell lines. RESULTS: Stimulation of PDGFRα results in phosphorylation of Dock180 at serine residue 1250 (S1250), whereas PKA inhibitors H-89 and KT5720 oppose this phosphorylation. S1250 locates within the Rac1-binding Dock homology region 2 domain of Dock180, and its phosphorylation activates Rac1, p-Akt, and phosphorylated extracellular signal-regulated kinase 1/2, while promoting cell migration, in vitro. By expressing RNA interference (RNAi)-resistant wild-type Dock180, but not mutant Dock180 S1250L, we were able to rescue PDGFRα-associated signaling and biological activities in cultured glioblastoma multiforme (GBM) cells that had been treated with RNAi for suppression of endogenous Dock180. In addition, expression of the same RNAi-resistant Dock180 rescued an invasive phenotype of GBM cells following intracranial engraftment in immunocompromised mice. CONCLUSION: These data describe an important mechanism by which PDGFRα promotes glioma malignant phenotypes through PKA-dependent serine phosphorylation of Dock180, and the data thereby support targeting the PDGFRα-PKA-Dock180-Rac1 axis for treating GBM with molecular profiles indicating PDGFRα signaling dependency.
BACKGROUND: Dedicator of cytokinesis 1 (Dock1 or Dock180), a bipartite guanine nucleotide exchange factor for Rac1, plays critical roles in receptor tyrosine kinase-stimulated cancer growth and invasion. Dock180 activity is required in cell migration cancer tumorigenesis promoted by platelet derived growth factor receptor (PDGFR) and epidermal growth factor receptor. METHODS: To demonstrate whether PDGFRα promotes tumor malignant behavior through protein kinase A (PKA)-dependent serine phosphorylation of Dock180, we performed cell proliferation, viability, migration, immunoprecipitation, immunoblotting, colony formation, and in vivo tumorigenesis assays using established and short-term explant cultures of glioblastoma cell lines. RESULTS: Stimulation of PDGFRα results in phosphorylation of Dock180 at serine residue 1250 (S1250), whereas PKA inhibitors H-89 and KT5720 oppose this phosphorylation. S1250 locates within the Rac1-binding Dock homology region 2 domain of Dock180, and its phosphorylation activates Rac1, p-Akt, and phosphorylated extracellular signal-regulated kinase 1/2, while promoting cell migration, in vitro. By expressing RNA interference (RNAi)-resistant wild-type Dock180, but not mutant Dock180S1250L, we were able to rescue PDGFRα-associated signaling and biological activities in cultured glioblastoma multiforme (GBM) cells that had been treated with RNAi for suppression of endogenous Dock180. In addition, expression of the same RNAi-resistant Dock180 rescued an invasive phenotype of GBM cells following intracranial engraftment in immunocompromised mice. CONCLUSION: These data describe an important mechanism by which PDGFRα promotes glioma malignant phenotypes through PKA-dependent serine phosphorylation of Dock180, and the data thereby support targeting the PDGFRα-PKA-Dock180-Rac1 axis for treating GBM with molecular profiles indicating PDGFRα signaling dependency.
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