RNA binding proteins and liver metabolism

Abstract

The liver acts as an important integrator of glucose and lipid metabolism by transducing extracellular nutrient and hormonal signals to intracellular pathways that regulate gene expression to respond to physiological and metabolic stress stimuli. Posttranscriptional gene regulation (PTGR) is essential to sustain these pathways and its biological relevance has been demonstrated by poor correlations between transcript and protein pools in hepatocytes. PTR is governed by the formation of different ribonucleoprotein complexes with RNA binding proteins (RBPs) at their core. Through RNA-binding domains these proteins control processing, maturation, transport, stability and turnover of all classes of RNAs, both spacially and temporally. Hence aberrant RNA metabolism in hepatocytes may not only interfere with cellular responses required for normal glucose and lipid homeostasis, but it can also lead to metabolic diseases such as type 2 diabetes (T2D), as demonstrated by genome-wide association studies linking Insulin growth factor 2 mRNA-binding protein 2 (IGF2BP2) with T2D.

In my talk I will describe a method we have developed allowing us to identify the repertoire of active RBPs (called RNA interactome), as well as their binding sites, in organs of living animals using photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation techiques (parClip), thereby enabling mapping of ribonucleoprotein complexes at high resolution in physiological and disease states. I will further discuss in detail the RNA binding protein Vigilin, a highly conserved and the largest RBP of the KH domain family, in hepatic metabolism and disease. Vigilin is upregulated in livers of obese mice and in patients with fatty liver disease. By using in vivo, biochemical and genomic approaches, we demonstrate that vigilin controls VLDL secretion through the modulation of apolipoproteinB/Apob mRNA translation. Crosslinking studies reveal that vigilin binds to CU-rich regions in the mRNA coding sequence of Apob and other proatherogenic secreted proteins, including apolipoprotein C-III/Apoc3 and fibronectin/Fn1. Consequently, hepatic vigilin knockdown decreases VLDL/LDL levels and formation of atherosclerotic plaques in Ldlr^–/– mice. These studies uncover a role for vigilin as a key regulator of hepatic Apob translation and demonstrate the therapeutic potential of inhibiting vigilin for cardiovascular diseases.