Lithium chloride inhibits the expression and secretion of insulin-like growth factor-binding protein-1

Abstract

Insulin-like growth factor-binding protein-1 (IGFBP-1) regulates IGF availability for glucose homeostasis. The IGFBP-1 promoter shares common regulatory response elements with phosphoenol pyruvate carboxykinase (PEPCK), the expression and activity of which is inhibited by lithium chloride, associated with an inhibition of glycogen synthase kinase (GSK)-3 activity, in the rat hepatoma cell line H4-II-E. We therefore determined the effect of lithium chloride on IGFBP-1 expression and secretion in H4-II-E cells. Lithium chloride inhibited IGFBP-1 secretion in a dose response and reversible manner by approx 80% during 5-h and 16-h incubations. An inhibitory effect on IGFBP-1 mRNA expression was observed at 2 h. The inhibitory effect of lithium and insulin were not additive when used alone, but inhibition by lithium occurred when insulin action was blocked by activating AMP-activated protein kinase with 5-aminoimidazole-4-carboxamide-riboside (AICAR). These findings suggest that GSK-3 inhibition, or another pathway activated by lithium, may be involved in a pathway controlling IGFBP-1, inhibiting synthesis when insulin activity is absent or impaired.