H2O2 signals 5-HT-induced ERK MAP kinase activation and mitogenesis of smooth muscle cells

Our previous studies have shown that 5-hydroxytryptamine (5-HT) induces cellular hyperplasia/hypertrophy through protein tyrosine phosphorylation, rapid formation of superoxide (O-2(-)), and extracellular signal-regulated kinase (ERK)1/ERK2 mitogen-activated protein (MAP) kinase activation. Intracellularly released O-2(-) is rapidly dismuted by superoxide dismutase (SOD) to H2O2, another possible cellular growth mediator. In the present study, we assessed whether H2O2 participates in 5-HT-induced mitogenic signaling. Inactivation of cellular Cu/Zn SOD by copper-chelating agents inhibited 5-HT-induced DNA synthesis of bovine pulmonary artery smooth muscle cells (BPASMCs). Infection of BPASMCs with an adenovirus containing catalase inhibited both ERK1/ ERK2 MAP kinase activation and DNA synthesis induced by 5-HT. Although we could not find evidence of p38 MAP kinase activation by 5-HT, SB-203580 and SB-202190, reported inhibitors of p38 MAP kinase, inhibited the 5-HT-induced growth of BPASMCs. However, these inhibitors also inhibited 5-HT-induced O-2(-) release. Thus quenching of O-2(-) may be their mechanism for inhibition of cellular growth unrelated to p38 MAP kinase inhibition. These data indicate that generation of O-2(-) in BPASMCs in response to 5-HT is followed by an increase in intracellular H2O2 that mediates 5-HT-induced mitogenesis through activation of ERK1/ERK2 but not of p38 MAP kinase.