5-Aminoimidazole-4-carboxamide ribonucleoside stabilizes low density lipoprotein receptor mRNA in hepatocytes via ERK-dependent HuR binding to an AU-rich element

Abstract

Objective5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR) has pleiotropic and beneficial effects on metabolic disorders. However, the effects of AICAR on low density lipoprotein (LDL) metabolism are poorly understood. Methods and resultsAICAR induces increased LDLR mRNA levels and increased LDLR protein production in hepatocytes. The AICAR-dependent LDLR mRNA increase was partially mediated by mRNA stabilization in an extracellular signal-regulated kinase1/2 (ERK1/2)-dependent manner, but not by the AMP-activated protein kinase (AMPK) activation. Reporter assays using a variety of constructs harboring the 3′-untranslated region (UTR) of human LDLR mRNA revealed that the most upstream AU-rich element (ARE) was critical for these AICAR effects. Using UV cross-linking assays, we found increased binding of three cytoplasmic proteins to this ARE region in response to AICAR and identified a 35-kDa protein as Human antigen R (HuR). Blocking ERK signaling pathway activation resulted in attenuated HuR binding. Silencing HuR expression by RNA interference hindered AICAR-induced LDLR mRNA stability, whereas its overexpression stabilized this mRNA. ConclusionsAICAR-dependent LDLR mRNA stabilization is mediated, at least in part, by HuR binding to the ARE1 region. Given that AICAR enhanced LDL uptake in hepatocytes, our findings warrant further studies using animal models to develop a novel LDL-cholesterol lowering agent as a possible strategy to treat atherosclerosis-related cardiovascular diseases.