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J Biol Chem. 1995 Nov 3;270(44):26146-51.

Calpain cleavage of the cytoplasmic domain of the integrin beta 3 subunit.

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Department of Vascular Biology, Scripps Research Institute, La Jolla, California 92037, USA.


The cytoplasmic domains of integrin beta subunits are involved in bidirectional transmembrane signaling. We report that the cytoplasmic domain of the integrin beta 3 subunit undergoes limited proteolysis by calpain, an intracellular calcium-dependent protease. Calpain cleavage occurs during platelet aggregation induced by agonists such as thrombin. Five cleavage sites have been identified. Four of these sites (C-terminal to Thr741, Tyr747, Phe754, and Tyr759) are utilized in intact platelets and flank two NXXY motifs (Asn744-Pro-Leu-Tyr747 and Asn756-Ile-Thr-Tyr759). The fifth site (Ala735) is accessible to calpain after EDTA treatment of the alpha IIb beta 3 heterodimer. The NXXY motif is critical to the bidirectional signaling functions of beta 3 integrins and their association with the cytoskeleton. Thus, calpain cleavage of the beta 3 cytoplasmic domain may provide a means to regulate integrin signaling functions.

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