Cyclic nucleotide-dependent protein kinases inhibit binding of 14-3-3 to the GTPase-activating protein Rap1GAP2 in platelets.
GTPase-activating proteins are required to terminate signaling by Rap1, a small guanine nucleotide-binding protein that controls integrin activity and cell adhesion. Recently, we identified Rap1GAP2, a GTPase-activating protein of Rap1 in platelets. Here we show that 14-3-3 proteins interact with phosphorylated serine 9 at the N terminus of Rap1GAP2. Platelet activation by ADP and thrombin enhances serine 9 phosphorylation and increases 14-3-3 binding to endogenous Rap1GAP2. Conversely, inhibition of platelets by endothelium-derived factors nitric oxide and prostacyclin disrupts 14-3-3 binding. These effects are mediated by cGMP- and cAMP-dependent protein kinases that phosphorylate Rap1GAP2 at serine 7, adjacent to the 14-3-3 binding site. 14-3-3 binding does not change the GTPase-activating function of Rap1GAP2 in vitro. However, 14-3-3 binding attenuates Rap1GAP2 mediated inhibition of cell adhesion. Our findings define a novel crossover point of activatory and inhibitory signaling pathways in platelets.
Institute of Biochemistry II, University of Frankfurt Medical School, 60590 Frankfurt, Germany.
Meike
M
Hoffmeister
Pavel
P
Riha
Olga
O
Neumüller
Oliver
O
Danielewski
Jan
J
Schultess
Albert P
AP
Smolenski
D048948:14-3-3 Proteins / Q000235:genetics / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D019556:COS Cells; D002522:Chlorocebus aethiops; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D011464:Epoprostenol / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013917:Thrombin / Q000378:metabolism / Q000494:pharmacology; D020827:rap1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
D048948:14-3-3 Proteins; D020690:GTPase-Activating Proteins; C500320:RAP1GAP2 protein, human; D009569:Nitric Oxide; D000244:Adenosine Diphosphate; D011464:Epoprostenol; D000242:Cyclic AMP; D013917:Thrombin; D020827:rap1 GTP-Binding Proteins; D006152:Cyclic GMP