Summary

Previous studies have demonstrated that cell-permeable cytoplasmic tail (CT) αIIβ peptides can modulate the activation of αIIbb3.As αV CT contains an αIIβ homologous region, a series of cell-permeable αV and αIIb peptides were generated to determine if αV CT can modulate the activation of β3 integrins in comparison to αIIb, and to identify the minimal bioactive sequences in αV CT.Using NMR structures and molecular models as guides, the initial peptides for study encompassed the αIIβ homologous sequences of αV CT (αV(987–1006); V-1), its amino-terminus (αV(987–993);V-2), a turn motif (αV(993–1001);V-3), the carboxyl- terminus (αV(999–1006); V-4), and corresponding homologous αIIb peptides.Treatment of platelets and αVβ3-expressing cells with the peptides revealed that IIb-1 inhibited αIIbβ3 activation and V-1 inhibited αVβ3 activation, but not vice versa.The inhibitory capacity of these peptides was mapped to the central turn-motif region which was encompassed by V-3, but only partially by IIb-3.V-2 and IIb-2 activated both β3 integrins, while V-4 and IIb-4 were inactive.The use of truncation and mutant peptides confirmed the importance of the turn motif for inhibitory activity and identified the side-chain of αV(Q1001) as a critical inhibitory residue. The difference in the integrin inhibitory capacity of αV and αIIb peptides and their capacity to influence the assembly of kinases with integrin CTs, reveals a possible divergence in the regulatory control of the two β3 integrins.