The G protein-coupled 5-HT_(1A) receptor causes suppression of caspase-3 through MAPK and protein kinase C_α

摘要

The 5-HT_(1A) agonist 8-hydroxy-2 (di-n-propylamino) tetralin (8-OH-DPAT) causes inhibition of caspase-3 and apoptosis via the extracellular signal-regulated kinases (ERK1/2) in hippocampal HN2-5 cells. Two 5-HT_(1A) agonists, Repinotan hydrochloride (BAY * 3702) and 8-OH-DPAT, block caspase-3 activation and apoptosis caused by anoxia/reoxygenation and H_2O_2 treatment. This is reversed upon transient expression of dominant negative Ras (N17Ras) and Raf-1 (Raf301), confirming the involvement of Ras and Raf-1 in this 5-HT_(1A)-R→ERK1/2→caspase-3 pathway. A selective inhibitor of phospholipase Cβ(PLCβ) (U73122) but not a general protein kinase C(PKC) inhibitor (GFX) reversed the 5-HT_(1A)-R-mediated ERK1/2 stimulation. However, both GFX and the PKCα and PKCβ_1 inhibitor Go6976 reversed the ERK1/2-mediated inhibition of caspase-3, ERK-dependent activation of only PKCα was observed in immunoprecipitates obtained from 5-HT_(1A) agonist-treated HN2-5 cells. Finally, transient expression of kinase-negative PKCα eliminated the 8-OH-DPAT-evoked block on the H_2O_2-triggered caspase-3 stimulation, establishing PKCα as a link between ERK and caspase-3 (5-HT_(1A)-R→PLC→ERK1/2→PKCα→caspase-3). Our results elucidate a novel yet general, neuroprotective pathway through which G protein-coupled receptors could cause inhibition of effector caspases, such as caspase-3.