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Arterioscler Thromb Vasc Biol. 2012 Feb;32(2):434-41. doi: 10.1161/ATVBAHA.111.239194. Epub 2011 Nov 10.

Rap1-Rac1 circuits potentiate platelet activation.

Author information

1
Dept. of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, 98 Manning Drive, 306a Mary Ellen Jones Building, Chapel Hill, NC 27599, USA.

Abstract

OBJECTIVE:

The goal of this study was to investigate the potential crosstalk between Rap1 and Rac1, 2 small GTPases central to platelet activation, particularly downstream of the collagen receptor GPVI.

METHODS AND RESULTS:

We compared the activation response of platelets with impaired Rap signaling (double knock-out; deficient in both the guanine nucleotide exchange factor, CalDAG-GEFI, and the Gi-coupled receptor for ADP, P2Y12), to that of wild-type platelets treated with a small-molecule Rac inhibitor, EHT 1864 (wild-type /EHT). We found that Rac1 is sequentially activated downstream of Rap1 on stimulation via GPVI. In return, Rac1 provides important feedback for both CalDAG-GEFI- and P2Y12-dependent activation of Rap1. When analyzing platelet responses controlled by Rac1, we observed (1) impaired lamellipodia formation, clot retraction, and granule release in both double knock-out and EHT 1864-treated wild-type platelets; and (2) reduced calcium store release in EHT 1864-treated wild-type but not double knock-out platelets. Consistent with the latter finding, we identified 2 pools of Rac1, one activated immediately downstream of GPVI and 1 activated downstream of Rap1.

CONCLUSIONS:

We demonstrate important crosstalk between Rap1 and Rac1 downstream of GPVI. Whereas Rap1 signaling directly controls sustained Rac1 activation, Rac1 affects CalDAG-GEFI- and P2Y12-dependent Rap1 activation via its role in calcium mobilization and granule/ADP release, respectively.

PMID:
22075250
PMCID:
PMC3262085
DOI:
10.1161/ATVBAHA.111.239194
[Indexed for MEDLINE]
Free PMC Article

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