Insulin Modulates Intracellular Apolipoprotein B mRNA Traffic into RNA Granules/Cytoplasmic P Bodies: Implications in Translational Control

Apolipoprotein B (ApoB) synthesis is partially regulated at the translational level; however, the molecular mechanisms that govern translational control of apoB mRNA remains largely unknown. We imaged intracellular apoB mRNA traffic and determined whether insulin silences apoB mRNA translation by trafficking into translationally-silenced cytoplasmic RNA granules called Processing Bodies (PBS). ApoB mRNA was visualized by using a strong interaction between the bacteriophage MS2 protein and a specific phage RNA sequence that binds MS2 protein. We observed a statistically significant increase in the localization of apoB mRNA into PBs, 4h, 8h, and 16h after insulin treatment. Conversely, acute insulin treatment (1h) did not show any significant effect. Insulin was also found to reduce polysomal association of apoB mRNA 4h and 16h post treatment in HepG2 cells. Overall, our data suggest that chronic insulin treatment silences apoB translation in HepG2 cells by localizing apoB mRNA into PBs and reducing translationally-competent mRNA pools.MAS