Proteolysis of platelet cortactin by calpain.
Cortactin, a substrate of pp60(c-)src and a potent filamentous actin binding and cross-linking protein, is abundant in circulating platelets. After stimulation of platelet aggregation with collagen, cortactin undergoes a dramatic increase in tyrosine phosphorylation followed by a rapid degradation. The cleavage of platelet cortactin was detected in lysates prepared using either Triton-containing buffer or SDS-sample buffer. However, the degradation of cortactin was not observed in platelets derived from a Glanzmann's patient, who lacked functional integrin alphaIIbbeta3 (GPIIb-IIIa). In addition, the proteolysis of cortactin was abolished by treating platelets before but not after collagen stimulation with EGTA or calpeptin. Furthermore, recombinant cortactin was digested by mu-calpain in vitro in a dose-dependent manner, indicating that cortactin is a substrate for calpain. We also observed that the calpain-mediated digestion in vitro is dependent on the presence of a sequence containing a proline-rich region and multiple tyrosine residues that are phosphorylated by pp60(c-)src. Tyrosine phosphorylation by pp60(c-)src up-regulates the activity of calpain toward cortactin. Our data suggest that the calpain-mediated proteolysis of tyrosine-phosphorylated cortactin may provide a mechanism to remodel irreversibly the cytoskeleton in response to platelet agonists.
Huang
C
C
Department of Experimental Pathology, The Holland Laboratory, American Red Cross, Rockville, MD 20855, USA.
Tandon
N N
NN
Greco
N J
NJ
Ni
Y
Y
Wang
T
T
Zhan
X
X
D001792:Blood Platelets / Q000378:metabolism*; D002154:Calpain / Q000502:physiology*; D003094:Collagen / Q000494:pharmacology; D051356:Cortactin; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism*; D010766:Phosphorylation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000502:physiology; D014443:Tyrosine / Q000378:metabolism
C495868:CTTN protein, human; D051356:Cortactin; D008840:Microfilament Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014443:Tyrosine; D003094:Collagen; D016392:Proto-Oncogene Proteins pp60(c-src); D002154:Calpain