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16K human prolactin inhibits vascular endothelial growth factor-induced activation of Ras in capillary endothelial
G D'Angelo1, J F Martini, T Iiri
1Department of Obstetrics, Gynecology and Reproductive Sciences, University of California School of Medicine, San Francisco 94143, USA. dangelo@ipmc.cnrs.fr
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.
Insights
16K human prolactin (hPRL) inhibits vascular endothelial growth factor (VEGF)-induced mitogen-activated protein kinases (MAPK) activation by blocking Ras activation. This novel antiangiogenic mechanism provides new insights into controlling blood vessel formation.
Area of Science:
- Molecular Biology
- Cell Signaling
- Angiogenesis Research
Background:
- 16K human prolactin (hPRL) exhibits antiangiogenic properties.
- Vascular Endothelial Growth Factor (VEGF) signaling pathways are crucial for angiogenesis.
- Mitogen-activated protein kinases (MAPK) are key mediators in VEGF signaling.
Purpose of the Study:
- To elucidate the precise step at which 16K hPRL inhibits VEGF-induced MAPK activation.
- To investigate the molecular mechanisms underlying 16K hPRL's antiangiogenic effects.
Main Methods:
- Assessment of proximal signaling events in the MAPK cascade following VEGF stimulation.
- Analysis of Raf-1 activation and translocation.
- Measurement of cAMP levels and protein kinase A (PKA) activity.
- Evaluation of Ras activation and its upstream regulators.
- Examination of VEGF receptor (Flk-1) phosphorylation and complex formation.
Main Results:
- 16K hPRL blocked VEGF-induced Raf-1 activation and plasma membrane translocation.
- The antiangiogenic effect was linked to the inhibition of GTP-bound Ras, not PKA stimulation.
- VEGF-induced Flk-1 phosphorylation and Shc/Grb2/Ras-GAP complex association were unaffected.
- 16K hPRL inhibited Sos phosphorylation and dissociation from Grb2, suggesting MEK/MAPK feedback inhibition.
- Increased phosphorylation of Ras-GAP associated proteins was observed.
Conclusions:
- 16K hPRL inhibits VEGF-induced Ras activation, representing a novel antiangiogenic mechanism.
- This inhibition of Ras activation is a key step in 16K hPRL's antiangiogenic action.
- The findings offer potential therapeutic targets for controlling angiogenesis.