Regulation of platelet membrane levels of glycoprotein VI by a platelet-derived metalloproteinase.
Thrombosis can be initiated when activated platelets adhere to injured blood vessels via the interaction of subendothelial collagen with its platelet receptor, glycoprotein (GP) VI. Here we observed that incubation of platelets with convulxin, collagen, or collagen-related peptide (CRP) resulted in GPVI signaling-dependent loss of surface GPVI and the appearance of an approximately 55-kDa soluble fragment of GPVI as revealed by immunoblotting. Ethylenediaminetetraacetic acid (EDTA) or GM6001 (a metalloproteinase inhibitor with broad specificity) prevented this loss. In other receptor systems, calmodulin binding to membrane-proximal cytoplasmic sequences regulates metalloproteinase-mediated ectodomain shedding. In this regard, we have previously shown that calmodulin binds to a positively charged, membrane-proximal sequence within the cytoplasmic tail of GPVI. Incubation of platelets with calmodulin inhibitor W7 (150 microM) resulted in a time-dependent loss of GPVI from the platelet surface. Both EDTA and GM6001 prevented this loss. Surface plasmon resonance demonstrated that W7 specifically blocked the association of calmodulin with an immobilized synthetic peptide corresponding to the calmodulin-binding sequence of GPVI. These findings suggest that disruption of calmodulin binding to receptor cytoplasmic tails by agonist binding to the receptor triggers metalloproteinase-mediated loss of GPVI from the platelet surface. This process may represent a potential mechanism to regulate GPVI-dependent platelet adhesion.
Gardiner
Elizabeth E
EE
Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia, 3800. elizabeth.gardiner@med.monash.edu.au
Arthur
Jane F
JF
Kahn
Mark L
ML
Berndt
Michael C
MC
Andrews
Robert K
RK
D000595:Amino Acid Sequence; D001665:Binding Sites; D001792:Blood Platelets / Q000201:enzymology / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D006801:Humans; D045726:Metalloproteases / Q000502:physiology*; D010446:Peptide Fragments / Q000032:analysis; D015539:Platelet Activation; D010980:Platelet Membrane Glycoproteins / Q000032:analysis / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D020349:Surface Plasmon Resonance
D002147:Calmodulin; D010446:Peptide Fragments; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D045726:Metalloproteases