Insulin-like growth factor 1 specifically up-regulates expression of modifier subunit of glutamate-cysteine ligase and enhances glutathione synthesis in SH-SY5Y cells

Abstract

Glutathione is a key regulator of oxidative balance in all mammals, especially in the central nervous system. The first step of glutathione synthesis is catalyzed by glutamate-cysteine ligase (GCL), which is composed of catalytic and modifier subunits (GCLC and GCLM, respectively). In non-neural cells and tissues, insulin and insulin-like growth factor 1 (IGF-1) have been found to stimulate transcription of GCLC gene. Here we found that treatment of human neuroblastoma SH-SY5Y cells with insulin or IGF-1 increased mRNA level of GCLM, but not of GCLC, in a concentration- and time-dependent manner. In contrast, insulin did not increase GCL expression in rat C6 glioma cells. We also confirmed that IGF-1 increased protein level of GCLM and cellular glutathione content in SH-SY5Y cells. In addition, IGF-1 increased nuclear factor erythroid 2-related factor 2 (Nrf2) protein in the nuclear fraction of SH-SY5Y cells. siRNA-mediated knockdown of Nrf2 protein expression abrogated IGF-1-induced up-regulation of GCLM mRNA expression. Finally, IGF-1-induced increase in nuclear Nrf2 protein and GCLM mRNA expression was abolished by LY294002, a phosphoinositide 3-kinase inhibitor. These results indicate that insulin and IGF-1 have the ability to enhance glutathione biosynthesis in neuronal cells via specific up-regulation of GCLM expression.