Abstract
SummaryIn addition to its role as an electron transporter, mitochondrial nicotinamide adenine dinucleotide (NAD+) is an important co-factor for enzymatic reactions, including ADP-ribosylation. Although mitochondria harbor the most intra-cellular NAD+, mitochondrial ADP-ribosylation remains poorly understood. Here we provide evidence for mitochondrial ADP-ribosylation, which was identified using various methodologies including immunofluorescence, western blot, and mass spectrometry. We show that mitochondrial ADP-ribosylation reversibly increases in response to respiratory chain inhibition. Conversely, H2O2-induced oxidative stress reciprocally induces nuclear and reduces mitochondrial ADP-ribosylation. Elevated mitochondrial ADP-ribosylation, in turn, dampens H2O2-triggered nuclear ADP-ribosylation and increases MMS-induced ARTD1 chromatin retention. Interestingly, co-treatment of cells with the mitochondrial uncoupler FCCP decreases PARP inhibitor efficacy. Together, our results suggest that mitochondrial ADP-ribosylation is a dynamic cellular process that impacts nuclear ADP-ribosylation and provide evidence for a NAD+-mediated mitochondrial-nuclear crosstalk.
Highlights
Nicotinamide adenine dinucleotide (NAD+) is an essential small molecule that functions as an important redox equivalent and as a co-factor for various enzymes (Chiarugi et al, 2012; Katsyuba and Auwerx, 2017)
When tested in combination with different organelle markers, we observed a distinct overlap between the ADP-ribosylation signal and a mitochondrial marker, which suggested that mitochondria contain ADP-ribosylated proteins (Figure 1B)
To further exclude that the detected mitochondrial signal is catalyzed by SelO, which has recently been shown to AMPylate a subset of mitochondrial redox proteins (Sreelatha et al, 2018), we knocked down SelO with two independent siRNAs (Figure S1F)
Summary
Nicotinamide adenine dinucleotide (NAD+) is an essential small molecule that functions as an important redox equivalent and as a co-factor for various enzymes (Chiarugi et al, 2012; Katsyuba and Auwerx, 2017). The NAD+ concentration is high within mitochondria ($400 mM, 40%–70% of the total cellular NAD+ pool) (Alano et al, 2007; Di Lisa et al, 2001), intermediate in the nucleus and cytosol ($100 mM), and low (< 1 mM) in extracellular spaces (Cambronne et al, 2016; Sallin et al, 2018). These concentrations vary considerably depending on the cell type, metabolic condition, stress, and redox status (Koch-Nolte et al, 2011). Mitochondriaderived ROS (mROS) were initially thought to exclusively cause cellular damage, but we understand that mROS are
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