Constitutive activation of Stat3alpha in brain tumors: localization to tumor endothelial cells and activation by the endothelial tyrosine kinase receptor (VEGFR-2).
Members of the normally latent family of transcription factors signal/inducers and activators of transcription (Stat) are activated in a number of human tumors and tumor-derived cell lines. In the case of Stat3, it is believed that this activation leads to the induction of survival signals as well as increased proliferation. In this study, we demonstrate that Stat3 is constitutively activated in glioma and medulloblastoma tumors and that the activated protein localizes predominantly to the tumor endothelial cells in the highly vascularized glioma tumors. Our efforts to elucidate potential mechanism(s) for this activated protein have shown that coexpression of Stat3alpha and the vascular endothelial growth factor receptor-2 (VEGFR-2) result in ligand-independent activation of Stat3alpha tyrosine phosphorylation and subsequent transcriptional activation in non-endothelial cells. We also show that activated Stat3alpha can increase transcription from the vascular endothelial growth factor (VEGF) gene. Taken together, these results suggest that the activated Stat3alpha found in brain tumors may be due to the endothelial tyrosine kinase VEGFR-2 and that Stat3alpha may play a central role in autocrine VEGF activation.
Schaefer
Laura K
LK
Department of Neurosurgery, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, TX 77030, USA. tschaefe@mdanderson.org
Ren
Zhiyong
Z
Fuller
Gregory N
GN
Schaefer
Timothy S
TS
D016475:3T3 Cells; D000818:Animals; D001932:Brain Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D019556:COS Cells; D004268:DNA-Binding Proteins / Q000378:metabolism*; D024202:Electrophoretic Mobility Shift Assay; D004727:Endothelium / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D005910:Glioma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D008527:Medulloblastoma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D051379:Mice; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D017978:Receptors, Growth Factor / Q000378:metabolism*; D040262:Receptors, Vascular Endothelial Growth Factor; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D004268:DNA-Binding Proteins; D017978:Receptors, Growth Factor; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D019000:Phosphotyrosine; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor