Role of Circadian Deadenylase Nocturnin in the Mitochondria

Abstract

The circadian rhythm is an evolutionarily conserved process that drives rhythmic behavior and physiology with a period of approximately 24 hours. Circadian rhythms are generated by the heterodimeric transcription factors CLOCK/BMAL1. CLOCK/BMAL1 binds to E‐boxes across the genome and drives the transcription of many genes, including their own repressors Per and Cry. Transcription activation by CLOCK/BMAL1 and its inhibitory feedback loop generated by PER/CRY result in the rhythmic expression of thousands of clock‐controlled genes. Nocturnin (mNOC) is among those genes regulated by CLOCK/BMAL1. mNOC is highly expressed in the liver, where its expression is at maximum in the evening and minimum in the morning. Compared to WT mice, mNOC KO mice exhibit a resistance to high‐fat diet (HFD) induced obesity. Protein sequence analysis reveals that mNOC contains an EEP domain that is conserved in the CCR4 family, whose members function as deadenylases. Interestingly, mNOC also contains a putative mitochondrial targeting signal (MTS) in between two translation initiation sites. To investigate if mNOC does localize to the mitochondria, we performed immunocytochemistry in HEK293 cells overexpressing mNOC that does or does not code for the MTS; and performed a mitochondrial fractionation followed by proteinase k protection assay. To examine mNOC's function in the mitochondria, we overexpressed mNOC in HEK293 cells and performed RT‐qPCR to examine mitochondrial RNA stability. We found that mNOC is able to localize to the mitochondria, but we did not see changes in mitochondrial RNA levels. Further experiments will help conclude if mNOC is targeting mitochondrial translation.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.