|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1994 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1993 : ¥1,400,000 (Direct Cost : ¥1,400,000)
Phosphoinositide-specific phospholipase C (PI-PLC) is a key signal transgducing enzyme generating two second messengers, inositol triphosphate and diacyglycerol. There are three types (beta, gamma, delta) containing nine distinct subtypes. We have been shown in human platelets that multiple forms of PI-PLC are present in cytosol and membrane fractions containing PLC-beta2, -beta3, -gamma1, -gamma2. We have purified the membrane-associated PI-PLCs (150 kDa and 100kDa) that were activated by G-protein betagamma subunits and demonstrated that truncation of the PI-PLC (150kDa) by mu-calpain much enhanced its activation by G-protein betagamma subunits. Treatment of human platelets with A23187 and natural agonists, thrombin and collagen, caused decrease of PLC-beta3 (155 and 140kDa) and concomitant increase of 100-kDa product of cleavage on immunoblots with the antibody to internal sequences of PLC-beta3. The cleavage of these PLC-beta3 enzymes was completely blocked by calpain inhibitor, calpeptin, indicating that the PLC-beta3modification of calpain. This is the first demonstration that PLC-beta3 is indeed cleavaged by calpain upon platelet activation by physiological agonists. The cleavage correlated with irreversible aggregation, suggesting that the PLC-beta3 modification may play a role in secondary irreversible aggregation in agonist-stimulated human platelets.