[Effect of the defect of integrin alpha II b beta 3 on the inside-out signal transduction in platelets]

To investigate the effect of the defect of integrin alpha II b beta 3 on the inside-out signal transduction in platelets.

The transfected cDNA, its expression and the ability of cells binding to PAC-1 and fibrinogen were investigated by RT-PCR, DNA sequence analysis, flow cytometry and Western blotting.

The integrin alpha II b beta 3 level in the patients with Glanzmann's thrombasthenia was significantly lower than that of the normal subjects and the platelets of the patients failed to bind PAC-1 activated by ADP. There were both C3077G and G3078C mutations in exon 30 of mutant alpha II bR995A beta 3 cDNA, which resulted in an amino acid substitution arginine (R) 995 to alanine (A). CHO cells transfected with wild-type alpha II b beta 3 or mutant alpha II bR995A beta 3 cDNA respectively expressed normal alpha II b beta 3 and mutant alpha II bR995A beta 3. When cells were not activated, wild-type alpha II b beta 3 CHO cells failed to bind PAC-1, but could adhere to fibrinogen, but mutant chimera alpha II bR995A beta 3 CHO cells were able to bind PAC-1 and exhibited high affinity binding fibrinogen.

The point mutation in integrin alpha II bR995A can induce the inside-out signal transduction in platelets, and have integrin alpha II bR995A beta 3 locked into an activation state; the defect of alpha II b beta 3 in patients with GT impairs the inside-out signal transduction mediated by alpha II b beta 3 in platelets and the adhesive functions of platelets.