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

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 ADP-ribose (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+.

Rudolph J ，Roberts G ，Muthurajan UM ，Luger K ... -  《eLife》

Dual function of HPF1 in the modulation of PARP1 and PARP2 activities.

Poly(ADP-ribosyl)ation catalyzed by poly(ADP-ribose) polymerases (PARPs) is one of the immediate cellular responses to DNA damage. The histone PARylation factor 1 (HPF1) discovered recently to form a joint active site with PARP1 and PARP2 was shown to limit the PARylation activity of PARPs and stimulate their NAD+-hydrolase activity. Here we demonstrate that HPF1 can stimulate the DNA-dependent and DNA-independent autoPARylation of PARP1 and PARP2 as well as the heteroPARylation of histones in the complex with nucleosome. The stimulatory action is detected in a defined range of HPF1 and NAD+ concentrations at which no HPF1-dependent enhancement in the hydrolytic NAD+ consumption occurs. PARP2, comparing with PARP1, is more efficiently stimulated by HPF1 in the autoPARylation reaction and is more active in the heteroPARylation of histones than in the automodification, suggesting a specific role of PARP2 in the ADP-ribosylation-dependent modulation of chromatin structure. Possible role of the dual function of HPF1 in the maintaining PARP activity is discussed.

Kurgina TA ，Moor NA ，Kutuzov MM ，Naumenko KN ，Ukraintsev AA ，Lavrik OI ... -  《Communications Biology》

[Poly(ADP-Ribose) Polymerases 1 and 2: Classical Functions and Interaction with New Histone Poly(ADP-Ribosyl)ation Factor HPF1].

Kurgina TA ，Lavrik OI 《-》

HPF1 remodels the active site of PARP1 to enable the serine ADP-ribosylation of histones.

Sun FH ，Zhao P ，Zhang N ，Kong LL ，Wong CCL ，Yun CH ... -  《Nature Communications》

Dispensability of HPF1 for cellular removal of DNA single-strand breaks.

In response to DNA damage, the histone PARylation factor 1 (HPF1) regulates PARP1/2 activity, facilitating serine ADP-ribosylation of chromatin-associated factors. While PARP1/2 are known for their role in DNA single-strand break repair (SSBR), the significance of HPF1 in this process remains unclear. Here, we investigated the impact of HPF1 deficiency on cellular survival and SSBR following exposure to various genotoxins. We found that HPF1 loss did not generally increase cellular sensitivity to agents that typically induce DNA single-strand breaks (SSBs) repaired by PARP1. SSBR kinetics in HPF1-deficient cells were largely unaffected, though its absence partially influenced the accumulation of SSB intermediates after exposure to specific genotoxins in certain cell lines, likely due to altered ADP-ribosylation of chromatin. Despite reduced serine mono-ADP-ribosylation, HPF1-deficient cells maintained robust poly-ADP-ribosylation at SSB sites, possibly reflecting PARP1 auto-poly-ADP-ribosylation at non-serine residues. Notably, poly-ADP-ribose chains were sufficient to recruit the DNA repair factor XRCC1, which may explain the relatively normal SSBR capacity in HPF1-deficient cells. These findings suggest that HPF1 and histone serine ADP-ribosylation are largely dispensable for PARP1-dependent SSBR in response to genotoxic stress, highlighting the complexity of mechanisms that maintain genomic stability and chromatin remodeling.

Hrychova K ，Burdova K ，Polackova Z ，Giamaki D ，Valtorta B ，Brazina J ，Krejcikova K ，Kuttichova B ，Caldecott KW ，Hanzlikova H ... -  《-》