Coronavirus infection and PARP expression dysregulate the NAD metabolome: An actionable component of innate immunity

Abstract

Poly-ADP-ribose polymerase (PARP) superfamily members covalently link either a single ADP-ribose (ADPR) or a chain of ADPR units to proteins using nicotinamide adenine dinucleotide (NAD) as the source of ADPR. While the well-known poly-ADP-ribosylating (PARylating) PARPs primarily function in the DNA damage response, many non-canonical mono-ADP-ribosylating (MARylating) PARPs are associated with cellular antiviral responses. We recently demonstrated robust upregulation of several PARPs following infection with Murine Hepatitis Virus (MHV), a model coronavirus. Here we show that SARS-CoV-2 infection strikingly upregulates MARylating PARPs and induces the expression of genes encoding enzymes for salvage NAD synthesis from nicotinamide (NAM) and nicotinamide riboside (NR), while downregulating other NAD biosynthetic pathways. We show that overexpression of PARP10 is sufficient to depress cellular NAD and that the activities of the transcriptionally induced enzymes PARP7, PARP10, PARP12 and PARP14 are limited by cellular NAD and can be enhanced by pharmacological activation of NAD synthesis. We further demonstrate that infection with MHV induces a severe attack on host cell NAD+ and NADP+. Finally, we show that NAMPT activation, NAM and NR dramatically decrease the replication of an MHV virus that is sensitive to PARP activity. These data suggest that the antiviral activities of noncanonical PARP isozyme activities are limited by the availability of NAD, and that nutritional and pharmacological interventions to enhance NAD levels may boost innate immunity to coronaviruses.

Uncovering the Invisible: Mono-ADP-ribosylation Moved into the Spotlight

“…This possibility is in agreement with recent reports, suggesting that even upon DNA damage, ARTD1 predominantly catalyzes protein MARylation rather than PARylation [148]. Interestingly, overexpression of ARTD10 that led to enhanced mono-ADP-ribosylation was sufficient to repress cellular NAD + levels and, consequently, the MARylating activities of ARTD14, ARTD10, ARTD12 and ARTD8 [107]. The effect could be reversed by stimulating NAD + synthesis via pharmacologically activating NAMPT [107,149].…”

“…Ferrets infected with severe acute respiratory syndrome coronavirus (SARS-CoV)-2 showed elevated expression of intracellular mono-ARTs as well, suggesting that this phenomenon is also relevant in vivo [106]. Specifically, ARTD4/PARP4, ARTD5(6)/PARP5, ARTD14, ARTD9, ARTD11, ARTD13, ARTD8 and ARTD7/PARP15 were all significantly induced [107]. Other reports linked ARTD10 and ARTD12 to NF-κB signaling [108,109].…”

“…Interestingly, overexpression of ARTD10 that led to enhanced mono-ADP-ribosylation was sufficient to repress cellular NAD + levels and, consequently, the MARylating activities of ARTD14, ARTD10, ARTD12 and ARTD8 [107]. The effect could be reversed by stimulating NAD + synthesis via pharmacologically activating NAMPT [107,149].…”

The SARS-CoV-2 Conserved Macrodomain Is a Mono-ADP-Ribosylhydrolase

“…PARP10 CD is a standard substrate that has been used extensively in the field to analyze the activity of macrodomains (16,18,26,27). PARP10 is highly upregulated upon CoV infection (23,35) and is known to primarily auto-MARylate itself on acidic residues, which are the targets on November 24, 2020 by guest http://jvi.asm.org/ Downloaded from of the MacroD2 class of macrodomains (27). We then tested a panel of anti-MAR, anti-PAR, or both anti-MAR and anti-PAR binding reagents/antibodies for the ability to detect MARylated PARP10 by immunoblot.…”

The PARP Way to Epigenetic Changes

“…The AhR regulates PARP1 gene expression, implying that upregulation of PARP1 is likely to result from coronavirus infection [22]. Activation of PARP1 leads to cell death by consuming large amounts of NAD + and ATP; this is even more likely to happen during an infected state [104]. In this state of depleted nutrients, cell death leads to further recruitment and activation of immune cells.…”