VEGF receptor expression and signaling in human bladder tumors.
Overexpression of vascular endothelial growth factor receptors (VEGFRs) has been reported in a variety of tumor types. Here we find that 11 out of the 14 bladder tumor cell lines examined express one or more VEGF receptors. Analysis of the T24 bladder tumor cell line reveals a functional autocrine loop involving VEGF and the Flk-1 receptor. Blocking VEGF expression in T24 cells results in a decrease in DNA synthesis. The Flk-1 receptor in T24 cells is phosphorylated in response to VEGF-121 or VEGF-165, and an Flk-1 inhibitor blocks VEGF to ERK signaling. We report that VEGF stimulation of T24 cells results in activation of H- and N-Ras and this is dependent on cellular sphingosine kinase 1 (SPK1) activity. Previously, we found VEGF-induced activation of Ras appears to be independent of a Ras-guanine nucleotide exchange factors (GEFs). Here we report that sphingosine can stimulate Ras-GTPase activating protein (GAP) activity in vitro, and sphingosine-1-phosphate (SPP) can block the stimulatory effects of sphingosine. We present a model where the balance between sphingosine and SPP regulates Ras-GAP activity such that stimulation of SPK1 favors downregulation of Ras-GAP and thereby the activation of Ras proteins. These data highlight a VEGF pathway that may be involved in the survival and proliferation of bladder tumor cells as well as other tumor cell types.
Wu
Weicheng
W
Department of Biochemistry and Molecular Biology, Norris Comprehensive Cancer Center, Keck School of Medicine at the University of Southern California, CA 90089, USA.
Shu
Xiaodong
X
Hovsepyan
Harut
H
Mosteller
Raymond D
RD
Broek
Daniel
D
D043925:Angiogenesis Inducing Agents / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D066298:In Vitro Techniques; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D040262:Receptors, Vascular Endothelial Growth Factor / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D013107:Sphingolipids / Q000378:metabolism; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D020703:ras GTPase-Activating Proteins / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism; D000099157:Sphingosine Kinase
D043925:Angiogenesis Inducing Agents; D004247:DNA; D017853:Phosphotransferases (Alcohol Group Acceptor); D011493:Protein Kinase C; D040262:Receptors, Vascular Endothelial Growth Factor; D013107:Sphingolipids; D042461:Vascular Endothelial Growth Factor A; D020744:rac GTP-Binding Proteins; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins; D000099157:Sphingosine Kinase; C467484:VEGFA protein, human