Albert Smolenski

Jan Schultess

Meike Hoffmeister

Olga Neumüller

Oliver Danielewski

Pavel Riha

BMC Pharmacology

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cGMP-dependent protein kinase regulates Rap1 signaling in platelets

BioMed Central
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BMC Pharmacology
Open AccessPoster presentation
cGMP-dependent protein kinase regulates Rap1 signaling in 
platelets
Albert Smolenski*, Meike Hoffmeister, Pavel Riha, Olga Neumüller, 
Oliver Danielewski and Jan Schultess
Address: Institute for Biochemistry II, University of Frankfurt Medical School, 60590 Frankfurt, Germany
Email: Albert Smolenski* - smolenski@biochem2.de
* Corresponding author    
cGMP- and cAMP-dependent protein kinases (cGK and
cAK) mediate the inhibitory effects of endothelium-
derived messenger molecules nitric oxide and prostacyclin
on platelets. To understand the mechanisms involved in
platelet inhibition we searched for new substrates of cGK
and cAK. We identified Rap1GAP2, the only GTPase-acti-
vating protein of Rap1 in platelets. Rap1 is a guanine-
nucleotide binding protein that controls integrin activity,
platelet adhesion and aggregation. Rap1GAP2 is required
to turn over Rap1-GTP to Rap1-GDP resulting in the inac-
tivation of integrins and reduced cellular adhesion. Using
phospho-specific antibodies we demonstrate phosphor-
ylation of endogenous Rap1GAP2 on serine 7 by cGK and
cAK in intact platelets. Yeast-two-hybrid screening
revealed an interaction of the phosphoserine/-threonine
binding adapter protein 14-3-3 with Rap1GAP2, and we
mapped the 14-3-3 binding site to the N-terminus of
Rap1GAP2 close to the cGK/cAK phosphorylation site. We
could show that 14-3-3 binding to Rap1GAP2 requires
phosphorylation of serine 9. Platelet activation by ADP
and thrombin treatment induces Rap1GAP2 serine 9
phosphorylation and enhances the attachment of 14-3-3
to Rap1GAP2. In contrast, phosphorylation of serine 7 by
cGK/cAK leads to the detachment of 14-3-3. Furthermore,
Rap1GAP2 serine 7 phosphorylation correlates with the
inhibition of Rap1-GTP formation by cGMP and cAMP in
platelets. Cell adhesion experiments provide additional
evidence that Rap1GAP2 is activated by the detachment of
14-3-3. Point mutants of Rap1GAP2 deficient in 14-3-3
binding inhibit Rap1-mediated cell adhesion significantly
stronger than a Rap1GAP2 mutant that binds 14-3-3 con-
stitutively. Our findings define a novel regulatory mecha-
nism that might contribute to both platelet activation and
endothelial inhibition of platelet adhesion and aggrega-
tion.
from 3rd International Conference on cGMP Generators, Effectors and Therapeutic Implications
Dresden, Germany. 15–17 June 2007
Published: 25 July 2007
BMC Pharmacology 2007, 7(Suppl 1):P56 doi:10.1186/1471-2210-7-S1-P56
<supplement> <title> <p>3<sup>rd </sup>International Conference on cGMP Generators, Effectors and Therapeutic Implications</p> </title> <note>Meeting abstracts – A single PDF containing all abstracts in this Supplement is available <a href="http://www.biomedcentral.com/content/files/pdf/1471-2210-7-S1-full.pdf">here</a>.</note> </supplement>
This abstract is available from: http://www.biomedcentral.com/1471-2210/7/S1/P56
© 2007 Smolenski et al; licensee BioMed Central Ltd. 


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cGMP-dependent protein kinase regulates Rap1 signaling in platelets

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