HPF1 and nucleosomes mediate a dramatic switch in activity of PARP1 from polymerase to hydrolase

Abstract

Poly(ADP-ribose) polymerase 1 (PARP1) is an important player in the response to DNA damage. Recently, histone PARylation factor (HPF1) was shown to be a critical modulator of the activity of PARP1 by facilitating PARylation of histones and redirecting the target amino acid specificity from acidic to serine residues. Here we investigate the mechanism and specific consequences of HPF1-mediated PARylation using nucleosomes as both activators and substrates for PARP1. HPF1 provides that catalytic base Glu284 to substantially redirect PARylation by PARP1 such that the histones in nucleosomes become the primary recipients of PAR chains. Surprisingly, HPF1 partitions most of the reaction product to free ADPR, resulting in much shorter PAR chains compared to reactions in the absence of HPF1. This HPF1-mediated switch from polymerase to hydrolase has important implications for the PARP1-mediated response to DNA damage and raises interesting new questions about the role of intracellular ADPR and depletion of NAD+.

Why structure and chain length matter: on the biological significance underlying the structural heterogeneity of poly(ADP-ribose)

“…In accordance, using novel HPLC assays quantifying ADP-ribose, NAD + and nicotinamide, Rudolph et al. could recently show that the presence of HPF1 leads to the release of ADP-ribose, resulting in distinctly shorter PAR chains ( 60 ). Additionally, activation of PARP1 by the Y-box-binding protein 1 (YB-1) has been shown to increase total protein PARylation but at the same time decrease the length of PAR ( 108 ).…”

NAD+ Degrading Enzymes, Evidence for Roles During Infection

“…As an example, the important recent discovery surrounding PARP-1 molecular functions have revealed that it can switch between PARylating and PAR hydrolysis activity via a HPF-1dependent mechanism (Rudolph et al, 2021). Importantly, both of these processes readily consume NAD + , exemplifying potential importance for our conception of PARPs as pure NAD + consumers and indicates a more sophisticated model of PARylation and its biological roles.…”

“…Parthanatos, a cell death pathway dependent upon PAR chain formation, works independent of caspase activity and has been attributed to PARPmediated NAD + depletion (reviewed in David et al, 2009 andRobinson et al, 2019). Recently, the histone PARylation factor 1 (HPF-1) has been identified as an integral modulator of PARP-1 PARylating activity as part of the DNA damage response (Gibbs-Seymour et al, 2016;Suskiewicz et al, 2020;Rudolph et al, 2021). Such work has provided novel insights into the factors that modulate rates of NAD + degradation by PARP-1 and has implications for the future development of PARP inhibition as a clinical strategy.…”

Chemical synthesis of linear ADP-ribose oligomers up to pentamer and their binding to the oncogenic helicase ALC1

“…Moreover, exciting recent work indicates that factors such as HPF1 can switch the in vitro activity of PARP1 from a polymerase to hydrolase. 36 One impact of this is that the average length of the ADPr oligomer is severely reduced, potentially down to mono-ADP-ribosylation in combination with PARG activity. 37 Based on our current and previous data, 5 we can propose that ALC1 activity would be exquisitely sensitive to all cellular events that result in dynamic changes to the balance of mono-, di-, oligo-and poly-ADPr on chromatin.…”