TY - JOUR
T1 - Crkl is constitutively tyrosine phosphorylated in platelets from chronic myelogenous leukemia patients and inducibly phosphorylated in normal platelets stimulated by thrombopoietin
AU - Oda, Atsushi
AU - Miyakawa, Yoshitaka
AU - Druker, Brian J.
AU - Ishida, Akaru
AU - Ozaki, Katsutoshi
AU - Ohashi, Hideya
AU - Wakui, Masatoshi
AU - Handa, Makoto
AU - Watanabe, Kiyoaki
AU - Okamoto, Shinichiro
AU - Ikeda, Yasuo
PY - 1996/12/1
Y1 - 1996/12/1
N2 - Platelet functions such as aggregation and clot retraction are often abnormal in chronic myelogenous leukemia (CML) patients. However, the molecular mechanisms of these altered functions are unknown. As expression of the p210(bcr-abl) oncogene product, a constitutively active tyrosine kinase, is known to have an essential role in the pathogenesis of CML and tyrosine phosphorylation is intimately involved in various aspects of platelet activation, we examined the pattern of protein tyrosine phosphorylation in platelets from 15 CML patients by immunoblotting with a monoclonal antiphosphotyrosine antibody (4G10). Before and after stimulation with thrombin, the only consistent difference between normal and CML platelets was the presence of a tyrosine phosphorylated protein with a relative molecular weight of 39 kD. This tyrosine phosphorylated protein was identified as crkl, an SH2, SH3 containing adapter protein. Thus, as previously demonstrated for neutrophils from CML patients, tyrosine phosphorylation of p39crkl persists in mature platelets. No tyrosine phosphorylation of crkl was detected following stimulation with thrombin in normal platelets. However, crkl became incorporated into the Triton X-100 insoluble residue following thrombin stimulation in a manner dependent on platelet aggregation. Further, we found that crkl is an endogenous substrate for calpain, a protease that may be involved in postaggregation signaling processes. This suggests that crkl may be involved in the reorganization of the cytoskeleton during normal platelet aggregation and its tyrosine phosphorylation in CML platelets may contribute to the abnormal platelet function in CML patients. Finally, we found that thrombopoietin induces tyrosine phosphorylation of crkl in normal platelets and FDCP cells genetically engineered to express human c-Mpl. This suggests that crkl can be phosphorylated by a kinase other than p210(bcr-abl) and that crkl may have a role in signaling by thrombopoietin.
AB - Platelet functions such as aggregation and clot retraction are often abnormal in chronic myelogenous leukemia (CML) patients. However, the molecular mechanisms of these altered functions are unknown. As expression of the p210(bcr-abl) oncogene product, a constitutively active tyrosine kinase, is known to have an essential role in the pathogenesis of CML and tyrosine phosphorylation is intimately involved in various aspects of platelet activation, we examined the pattern of protein tyrosine phosphorylation in platelets from 15 CML patients by immunoblotting with a monoclonal antiphosphotyrosine antibody (4G10). Before and after stimulation with thrombin, the only consistent difference between normal and CML platelets was the presence of a tyrosine phosphorylated protein with a relative molecular weight of 39 kD. This tyrosine phosphorylated protein was identified as crkl, an SH2, SH3 containing adapter protein. Thus, as previously demonstrated for neutrophils from CML patients, tyrosine phosphorylation of p39crkl persists in mature platelets. No tyrosine phosphorylation of crkl was detected following stimulation with thrombin in normal platelets. However, crkl became incorporated into the Triton X-100 insoluble residue following thrombin stimulation in a manner dependent on platelet aggregation. Further, we found that crkl is an endogenous substrate for calpain, a protease that may be involved in postaggregation signaling processes. This suggests that crkl may be involved in the reorganization of the cytoskeleton during normal platelet aggregation and its tyrosine phosphorylation in CML platelets may contribute to the abnormal platelet function in CML patients. Finally, we found that thrombopoietin induces tyrosine phosphorylation of crkl in normal platelets and FDCP cells genetically engineered to express human c-Mpl. This suggests that crkl can be phosphorylated by a kinase other than p210(bcr-abl) and that crkl may have a role in signaling by thrombopoietin.
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U2 - 10.1182/blood.v88.11.4304.4304
DO - 10.1182/blood.v88.11.4304.4304
M3 - Article
C2 - 8943867
AN - SCOPUS:10544225380
SN - 0006-4971
VL - 88
SP - 4304
EP - 4313
JO - Blood
JF - Blood
IS - 11
ER -