Coordinating Etk/Bmx activation and VEGF upregulation to promote cell survival and proliferation.
Etk/Bmx, a member of the Tec family of non-receptor tyrosine kinase, is characterized by an N-terminal PH domain and has recently been shown to be involved in the regulation of various cellular processes, including proliferation, differentiation, motility and apoptosis. Since VEGF and the activation of its signaling pathway have been implicated in modulating a variety of biological responses, we characterized the role of Etk-dependent signaling pathways involved in the upregulation of VEGF expression, and explored the functional implications of this enhancement in sustaining cell proliferation and survival. Using Northern and Western analyses, transient transfections, and pharmacological agents, we demonstrate that Etk activation alone is sufficient to transcriptionally induce VEGF expression, independent of the previously identified hypoxia response element (HRE), in both Pa-4 epithelial and TR-BBB endothelial cells under normoxia. In addition, Etk utilizes both MEK/ERK and PI3-K/Pak1 signaling pathways in concert to activate VEGF transcription. Functionally, Etk activation elicits a profound stimulatory effect on TR-BBB cell proliferation and formation of capillary-like networks in Matrigel containing reduced levels of growth factors. Finally, antisense oligonucleotides against either endogenous VEGF or Etk abrogate the proliferation of Etk-activated TR-BBB cells, and exogenous VEGF treatment stimulates endogenous Etk tyrosine phosphorylation in HUVECs. Taken together, these results indicate that VEGF is both an Etk downstream target gene and an Etk upstream activator, constituting a reciprocal Etk-VEGF autoregulatory loop. These findings, to our knowledge, are the first delineation of a network of positive feedforward signaling pathways that converge on the Etk-VEGF axis, causally associating Etk-mediation of VEGF induction with enhanced cellular processes in both epithelial and endothelial cells.
Chau
Cindy H
CH
Department of Molecular Pharmacology and Toxicology, University of Southern California, Los Angeles, California, CA 90033, USA.
Chen
Kai-Yun
KY
Deng
Hong-Tao
HT
Kim
Kwang-Jin
KJ
Hosoya
Ken-ichi
K
Terasaki
Tetsuya
T
Shih
Hsiu-Ming
HM
Ann
David K
DK
D000818:Animals; D002455:Cell Division / Q000235:genetics*; D002460:Cell Line; D002470:Cell Survival / Q000235:genetics*; D016228:Endothelial Growth Factors / Q000235:genetics*; D004742:Enhancer Elements, Genetic; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics*; D008222:Lymphokines / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011505:Protein-Tyrosine Kinases / Q000235:genetics*; D051381:Rats; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; C492365:Bmx protein, rat; D011505:Protein-Tyrosine Kinases