Via its Untranslated Regions

Background: The hepatic secretion of apolipoprotein B (apoB), containing lipoproteins, is known to be regulated by insu-lin, and the overproduction of these atherogenic lipoproteins occurs in insulin-resistant states. Protein tyrosine phosphatase 1B (PTP-1B) is a key regulator of hepatic insulin signaling and is also upregulated in insulin resistance. We aimed to inves-tigate the role of PTP-1B in regulating apoB mRNA translational efficiency mediated by 5’/3 ’ untranslated regions (UTRs) under conditions of insulin stimulation. Methods: Human hepatoma HepG2 cells were transfected with a vector carrying the firefly luciferase reporter gene and either a chimeric apoB mRNA encoding the 5’/3 ’ untranslated region (5’LUC3’-pGL3) or a null sequence of length equiva-lent to apoB 5 ’ UTR (LUC-pGL3). The transfected cells were then infected with adenovirus carrying the mouse PTP-1B gene (AdPTP1B) in the absence or presence of insulin, and the cellular luciferase activity was determined. The RNA extracts from cells were transfected with constructs carrying 5’/3 ’ apoB UTR, or a null sequence was also translated in vitro in a rabbit reticulocyte translation system. Results: The luciferase activity of the cells transfected with constructs containing the apoB UTR sequences (5’LUC3’) was significantly higher than that of the control constructs carrying a null sequence (p<0.01, n=12). Similar results were ob-served following in vitro translation studies showing a significantly higher expression of the 5’/3 ’ UTR constructs (p<0.001