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Angiopoietin-1 activates both anti- and proapoptotic mitogen-activated protein kinases
Rania Harfouche1, Jean-Philippe Gratton, George D Yancopoulos
1Critical Care Division, Royal Victoria Hospital, 687 Ave. West, Montreal, Québec, Canada H3A 1A1.
Abstract:
In this study, we identified whether mitogen-activated protein kinases (MAPKs) mediate the effects of angiopoietin-1 (Ang-1) on endothelial cell apoptosis. Exposure of human umbilical vein endothelial cells to Ang-1 (300 ng/ml) evoked within 15-30 min a 15-fold and a 5-fold increase in phosphorylation of ERK1/2 and p38 MAPKs, respectively. Inhibitors of the PI-3 kinase pathway attenuated Ang-1-induced ERK1/2 phosphorylation at a level up-stream from Raf and MEK1/2, but these inhibitors augmented Ang-1-induced p38 phosphorylation. When serum and growth supplements were withdrawn, the percentage of endothelial apoptosis tripled over 24 h compared with control cells. The presence of Ang-1 (300 ng/ml) significantly attenuated endothelial cell apoptosis and inhibited caspase-9, -7, and -3 activation. These antiapoptotic effects were augmented when a p38 inhibitor was combined with Ang-1, whereas inhibition of ERK1/2 eliminated the antiapoptotic properties of Ang-1. We conclude that both anti- (ERK1/2) and pro- (p38) apoptotic members of MAPKs are simultaneously activated by Ang-1 in endothelial cells and that activation of ERK1/2 by Ang-1 is mediated through the PI-3 kinase pathway. The strong antiapoptotic effects of the ERK and the PI-3 kinase pathways mask the proapoptotic function of p38 MAPKs resulting in net attenuation of apoptosis by Ang-1.
Insights
Angiopoietin-1 (Ang-1) activates both pro- and anti-apoptotic pathways in endothelial cells via mitogen-activated protein kinases (MAPKs). The anti-apoptotic effects of ERK1/2, mediated by PI-3 kinase, dominate over the pro-apoptotic function of p38, leading to reduced cell death.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Endothelial cell apoptosis is critical in vascular homeostasis and disease.
- Angiopoietin-1 (Ang-1) is a key regulator of endothelial cell function.
- Mitogen-activated protein kinases (MAPKs) are involved in cellular signaling pathways.
Purpose of the Study:
- To investigate whether MAPKs mediate the anti-apoptotic effects of Ang-1 on endothelial cells.
- To elucidate the specific roles of ERK1/2 and p38 MAPK pathways in Ang-1 signaling.
- To determine the involvement of the PI-3 kinase pathway in Ang-1-induced MAPK activation.
Main Methods:
- Human umbilical vein endothelial cells were treated with Ang-1.
- Phosphorylation levels of ERK1/2 and p38 MAPKs were assessed.
- Inhibitors of PI-3 kinase, ERK1/2, and p38 pathways were used to study their roles in apoptosis and MAPK activation.
Main Results:
- Ang-1 significantly increased phosphorylation of ERK1/2 and p38 MAPKs.
- Ang-1 treatment attenuated endothelial cell apoptosis and inhibited caspase activation.
- Inhibition of ERK1/2 abolished Ang-1's anti-apoptotic effects, while p38 inhibition augmented them.
Conclusions:
- Ang-1 simultaneously activates both pro- (p38) and anti- (ERK1/2) apoptotic MAPK pathways in endothelial cells.
- Ang-1-induced ERK1/2 activation is mediated by the PI-3 kinase pathway.
- The dominant anti-apoptotic signaling of ERK1/2 and PI-3 kinase pathways masks the pro-apoptotic function of p38, resulting in net protection against apoptosis.