title: Characterization of calcium- and integrin-binding protein 1 (CIB1) knockout platelets: potential compensation by CIB family members.
abstract: Platelet aggregation requires activation of the alphaIIbbeta3 integrin, an event regulated by the integrin cytoplasmic tails. CIB1 binds to the cytoplasmic tail of the integrin alphaIIb subunit. Previous over-expression and knockdown studies in murine megakaryocytes demonstrated that CIB1 inhibits integrin alphaIIbbeta3 activation. Here we analyzed Cib1(-/-) mice to determine the function of CIB1 in platelets in vitro and in vivo. We found that although these mice had no overt platelet phenotype, mRNA level of CIB1 homolog CIB3 was increased in Cib1(-/-) megakaryocytes. In vitro binding experiments showed that recombinant CIB1, -2 and -3 bound specifically to an alphaIIb cytoplasmic tail peptide. Subsequent protein modeling experiments indicated that CIBs 1-3 each have a highly conserved hydrophobic binding pocket. Therefore, the potential exists for compensation for the loss of CIB1 by these CIB family members, thereby preventing pathologic thrombus formation in Cib1(-/-) mice.
authors.affiliation: Curriculum in Genetics and Molecular Biology, The University of North Carolina, Chapel Hill, NC 27599, USA.
authors.forename: Jan C
authors.initials: JC
authors.lastname: Denofrio
authors.forename: Weiping
authors.initials: W
authors.lastname: Yuan
authors.forename: Brenda R
authors.initials: BR
authors.lastname: Temple
authors.forename: Holly R
authors.initials: HR
authors.lastname: Gentry
authors.forename: Leslie V
authors.initials: LV
authors.lastname: Parise
mesh_terms: D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002712:Chlorides; D004195:Disease Models, Animal; D005290:Ferric Compounds; D057927:Hydrophobic and Hydrophilic Interactions; D008533:Megakaryocytes / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008958:Models, Molecular; D010641:Phenotype; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D040201:Platelet Membrane Glycoprotein IIb / Q000378:metabolism; D011487:Protein Conformation; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013927:Thrombosis / Q000097:blood / Q000139:chemically induced; D013997:Time Factors
chemical_list: D002135:Calcium-Binding Proteins; D002712:Chlorides; C491605:Cib1 protein, mouse; D005290:Ferric Compounds; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D040201:Platelet Membrane Glycoprotein IIb; D012333:RNA, Messenger; D011994:Recombinant Proteins; C024555:ferric chloride