Adrenomedullin regulates cellular glutathione content via modulation of γ-glutamate-cysteine ligase catalytic subunit expression

Abstract

Adrenomedullin (AM) participates in a wide range of physiological and pathological processes including vasorelaxation, angiogenesis, cancer promotion, and apoptosis. Recently, it has been reported that AM protects a variety of cells against oxidative stress induced by stressors such as hypoxia, ischemia/reperfusion, and hydrogen peroxide through the phosphatidylinositol 3-kinase (PI3K)-dependent pathway. However, the molecular mechanisms underlying the pathway of cell survival against hypoxic injury are largely unknown. In an effort to investigate the survival mechanism against hypoxic injury, we studied the effects of AM on cellular levels of reactive oxygen species, well-known mediators of cell death after oxidative stress, and the mechanism involved in the regulation of reactive oxygen species levels. Here, we show that AM increases γ-glutamate-cysteine ligase (γ-GCL) activity under both hypoxic and normoxic conditions, resulting in an up-regulation of cellular glutathione levels to more than 2-fold higher than basal expression. In addition, we demonstrate that AM induces concentration-dependent expression of the catalytic subunit of γ-GCL (γ-GCLC) at the mRNA and protein levels through the activation of the γ-GCLC promoter fragment sequence from -597 to -320. However, when treated with the PI3K inhibitors, the effects of AM on γ-GCLC expression were completely abrogated, suggesting that a PI3K pathway linked AM with the transcriptional activation of the γ-GCLC promoter. Taken together, our data suggests that AM participates in the regulation of cellular redox status via glutathione synthesis. These results may explain, in part, the mechanism by which AM protects cells against oxidative stress. Copyright © 2006 by The Endocrine Society.