Shock D D, Naik U P, Brittain J E, Alahari S K, Sondek J, Parise L V
Department of Pharmacology, The University of North Carolina at Chapel Hill, CB# 7365, Chapel Hill, NC 27599, USA.
Biochem J. 1999 Sep 15;342 Pt 3(Pt 3):729-35.
The alphaIIbbeta3 integrin receives signals in agonist-activated platelets, resulting in its conversion to an active conformation that binds fibrinogen, thereby mediating platelet aggregation. Fibrinogen binding to alphaIIbbeta3 subsequently induces a cascade of intracellular signalling events. The molecular mechanisms of this bi-directional alphaIIbbeta3-mediated signalling are unknown but may involve the binding of proteins to the integrin cytoplasmic domains. We reported previously the sequence of a novel 22-kDa, EF-hand-containing, protein termed CIB (calcium- and integrin-binding protein) that interacts specifically with the alphaIIb cytoplasmic domain in the yeast two-hybrid system. Further analysis of numerous tissues and cell lines indicated that CIB mRNA and protein are widely expressed. In addition, isothermal titration calorimetry indicated that CIB binds to an alphaIIb cytoplasmic-domain peptide in a Ca(2+)-dependent manner, with moderate affinity (K(d), 700 nM) and 1:1 stoichiometry. In aggregated platelets, endogenous CIB and alphaIIbbeta3 translocate to the Triton X-100-insoluble cytoskeleton in a parallel manner, demonstrating that the cellular localization of CIB is regulated, potentially by alphaIIbbeta3. Thus CIB may contribute to integrin-related functions by mechanisms involving Ca(2+)-modulated binding to the alphaIIb cytoplasmic domain and changes in intracellular distribution.
αIIbβ3整合素在激动剂激活的血小板中接收信号，导致其转变为与纤维蛋白原结合的活性构象，从而介导血小板聚集。纤维蛋白原与αIIbβ3的结合随后引发一系列细胞内信号事件。这种双向的αIIbβ3介导的信号传导的分子机制尚不清楚，但可能涉及蛋白质与整合素细胞质结构域的结合。我们之前报道了一种名为CIB（钙和整合素结合蛋白）的新型22 kDa含EF手型结构域的蛋白质序列，它在酵母双杂交系统中与αIIb细胞质结构域特异性相互作用。对众多组织和细胞系的进一步分析表明，CIB mRNA mRNAmRNA和蛋白质广泛表达。此外，等温滴定量热法表明，CIB以Ca(2+)依赖的方式与αIIb细胞质结构域肽结合，亲和力适中（解离常数K(d)为700 nM），化学计量比为1:1。在聚集的血小板中，内源性CIB和αIIbβ3以平行方式转运至Triton X-100不溶性细胞骨架，表明CIB的细胞定位受到调控，可能受αIIbβ3调控。因此，CIB可能通过涉及Ca(2+)调节与αIIb细胞质结构域结合以及细胞内分布变化的机制，对整合素相关功能发挥作用。
