Cbl-b is a novel physiologic regulator of glycoprotein VI-dependent platelet activation.
Cbl-b, a member of the Cbl family of E3 ubiquitin ligases, plays an important role in the activation of lymphocytes. However, its function in platelets remains unknown. We show that Cbl-b is expressed in human platelets along with c-Cbl, but in contrast to c-Cbl, it is not tyrosine-phosphorylated upon glycoprotein VI (GPVI) stimulation. Cbl-b, unlike c-Cbl, is not required for Syk ubiquitylation downstream of GPVI activation. Phospholipase Cgamma2 (PLCgamma2) and Bruton's tyrosine kinase (BTK) are constituently associated with Cbl-b. Cbl-b-deficient (Cbl-b(-/-)) platelets display an inhibition in the concentration-response curve for GPVI-specific agonist-induced aggregation, secretion, and Ca(2+) mobilization. A parallel inhibition is found for activation of PLCgamma2 and BTK. However, Syk activation is not affected by the absence of Cbl-b, indicating that Cbl-b acts downstream of Syk but upstream of BTK and PLCgamma2. When Cbl-b(-/-) mice were tested in the ferric chloride thrombosis model, occlusion time was increased and clot stability was reduced compared with wild type controls. These data indicate that Cbl-b plays a positive modulatory role in GPVI-dependent platelet signaling, which translates to an important regulatory role in hemostasis and thrombosis in vivo.
Daniel
James L
JL
Department of Anatomy, Sol Sherry Thrombosis Research Center, Temple University, Philadelphia, Pennsylvania 19140, USA. james.daniel@temple.edu
Dangelmaier
Carol A
CA
Mada
Sripal
S
Buitrago
Lorena
L
Jin
Jianguo
J
Langdon
Wallace Y
WY
Tsygankov
Alexander Y
AY
Kunapuli
Satya P
SP
Sanjay
Archana
A
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D051966:Phospholipase C gamma / Q000378:metabolism; D015539:Platelet Activation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C118387:Cblb protein, mouse; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; C492211:CBLB protein, human; D050721:Proto-Oncogene Proteins c-cbl; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C000625951:Btk protein, mouse; D051966:Phospholipase C gamma
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