Abstract
Signaling pathways mediating the antiangiogenic action of 16K human (h)PRL include inhibition of vascular endothelial growth factor (VEGF)-induced activation of the mitogen-activated protein kinases (MAPK). To determine at which step 16K hPRL acts to inhibit VEGF-induced MAPK activation, we assessed more proximal events in the signaling cascade. 16K hPRL treatment blocked VEGF-induced Raf-1 activation as well as its translocation to the plasma membrane. 16K hPRL indirectly increased cAMP levels; however, the blockade of Raf-1 activation was not dependent on the stimulation of cAMP-dependent protein kinase (PKA), but rather on the inhibition of the GTP-bound Ras. The VEGF-induced tyrosine phosphorylation of the VEGF receptor, Flk-1, and its association with the Shc/Grb2/Ras-GAP (guanosine triphosphatase-activating protein) complex were unaffected by 16K hPRL treatment. In contrast, 16K hPRL prevented the VEGF-induced phosphorylation and dissociation of Sos from Grb2 at 5 min, consistent with inhibition by 16K hPRL of the MEK/MAPK feedback on Sos. The inhibition of Ras activation was paralleled by the increased phosphorylation of 120 kDa proteins comigrating with Ras-GAP. Taken together, these findings show that 16K hPRL inhibits the VEGF-induced Ras activation; this antagonism represents a novel and potentially important mechanism for the control of angiogenesis.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Biological Transport
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Cyclic AMP / metabolism
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Cyclic AMP-Dependent Protein Kinases / metabolism
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Endothelial Growth Factors / metabolism*
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Endothelial Growth Factors / pharmacology
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Endothelium, Vascular / drug effects
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Endothelium, Vascular / metabolism*
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Enzyme Activation / drug effects
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GRB10 Adaptor Protein
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GTPase-Activating Proteins
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Genes, ras*
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Humans
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Lymphokines / metabolism*
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Lymphokines / pharmacology
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Membrane Proteins / metabolism
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Peptide Fragments / metabolism
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Peptide Fragments / pharmacology
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Prolactin / metabolism*
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Prolactin / pharmacology
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Proteins / metabolism
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Proto-Oncogene Proteins c-raf / drug effects
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Proto-Oncogene Proteins c-raf / metabolism
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Receptor Protein-Tyrosine Kinases / drug effects
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Receptor Protein-Tyrosine Kinases / metabolism
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Receptors, Growth Factor / drug effects
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Receptors, Growth Factor / metabolism
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Receptors, Vascular Endothelial Growth Factor
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Signal Transduction
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Son of Sevenless Proteins
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Vascular Endothelial Growth Factor A
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Vascular Endothelial Growth Factors
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ras GTPase-Activating Proteins
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ras Proteins / metabolism
Substances
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Endothelial Growth Factors
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GTPase-Activating Proteins
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Lymphokines
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Membrane Proteins
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Peptide Fragments
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Proteins
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Receptors, Growth Factor
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Son of Sevenless Proteins
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Vascular Endothelial Growth Factor A
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Vascular Endothelial Growth Factors
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ras GTPase-Activating Proteins
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GRB10 Adaptor Protein
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Prolactin
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Cyclic AMP
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Receptor Protein-Tyrosine Kinases
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Receptors, Vascular Endothelial Growth Factor
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Proto-Oncogene Proteins c-raf
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Cyclic AMP-Dependent Protein Kinases
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ras Proteins