title: Caspase-12: a developmental link between G-protein-coupled receptors and integrin alphaIIbbeta3 activation.
abstract: Fibrinogen binding by integrin alphaIIbbeta3 is promoted by platelet agonists that increase the affinity and avidity of alphaIIbbeta3 for fibrinogen through a process called "inside-out" signaling. Having previously demonstrated that inside-out activation of alphaIIbbeta3 is defective in murine megakaryocytes that lack the transcription factor NF-E2, we screened for NF-E2-regulated genes that affect alphaIIbbeta3 activation. Caspase-12 is the most down-regulated gene we identified in NF-E2(-/-) megakaryocytes. Therefore, the role of this protein in alphaIIbbeta3 activation was determined using platelets from caspase-12(-/-) mice. Despite wild-type levels of alphaIIbbeta3, caspase-12(-/-) platelets exhibit reduced fibrinogen binding to alphaIIbbeta3 following stimulation by adenosine diphosphate (ADP) or protease-activated receptor 4 (PAR4) receptor-activating peptide. The defect in alphaIIbbeta3 activation is associated with decreased cytosolic free calcium and inositol triphosphate levels, and with reduced aggregation, despite wild-type phospholipase Cbeta expression levels. In contrast, agonist-induced surface expression of P-selectin, suppression of cAMP levels following ADP stimulation, and spreading on immobilized fibrinogen are unimpaired. Moreover, although caspase-12 is highly expressed in mature megakaryocytes, it is undetectable in platelets. Taken together, these studies establish that caspase-12 expression in murine megakaryocytes is regulated, directly or indirectly, by NF-E2, and suggest that caspase-12 participates in the development of fully functional signaling pathways linking some G-protein-coupled receptors to alphaIIbbeta3 activation.
authors.affiliation: Department of Laboratory Medicine, University of California-San Francisco, 513 Parnassus Ave, Rm S-577, San Francisco, CA 94143-0100, USA.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Kerrigan
authors.forename: Meenakshi
authors.initials: M
authors.lastname: Gaur
authors.forename: Ronan P
authors.initials: RP
authors.lastname: Murphy
authors.forename: Sanford J
authors.initials: SJ
authors.lastname: Shattil
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Leavitt
mesh_terms: D000527:Alprostadil / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D053454:Caspase 12; D020169:Caspases / Q000235:genetics* / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D050981:Erythroid-Specific DNA-Binding Factors; D015971:Gene Expression Regulation, Enzymologic; D008533:Megakaryocytes / Q000502:physiology; D051379:Mice; D008817:Mice, Mutant Strains; D050983:NF-E2 Transcription Factor; D050984:NF-E2 Transcription Factor, p45 Subunit; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D034061:Thrombopoiesis / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D050981:Erythroid-Specific DNA-Binding Factors; D050983:NF-E2 Transcription Factor; D050984:NF-E2 Transcription Factor, p45 Subunit; C494693:Nfe2 protein, mouse; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D043562:Receptors, G-Protein-Coupled; D014157:Transcription Factors; D000242:Cyclic AMP; C506440:Casp12 protein, mouse; D053454:Caspase 12; D020169:Caspases; D000527:Alprostadil; D002118:Calcium