Abstract
PARP1 and PARP2 produce poly(ADP-ribose) in response to DNA breaks. HPF1 regulates PARP1/2 catalytic output, most notably permitting serine modification with ADP-ribose. However, PARP1 is substantially more abundant in cells than HPF1, challenging whether HPF1 can pervasively modulate PARP1. Here, we show biochemically that HPF1 efficiently regulates PARP1/2 catalytic output at sub-stoichiometric ratios matching their relative cellular abundances. HPF1 rapidly associates/dissociates from multiple PARP1 molecules, initiating serine modification before modification initiates on glutamate/aspartate, and accelerating initiation to be more comparable to elongation reactions forming poly(ADP-ribose). This “hit and run” mechanism ensures HPF1 contributions to PARP1/2 during initiation do not persist and interfere with PAR chain elongation. We provide structural insights into HPF1/PARP1 assembled on a DNA break, and assess HPF1 impact on PARP1 retention on DNA. Our data support the prevalence of serine-ADP-ribose modification in cells and the efficiency of serine-ADP-ribose modification required for an acute DNA damage response.
Highlights
PARP1 and PARP2 produce poly(ADP-ribose) in response to DNA breaks
Histone PARylation Factor 1 (HPF1) adapts the catalytic output of PARP1 and PARP2 such that ADP-ribose is linked to Ser residues rather than Glu/Asp residues[18]
Whereas the ester bond of PAR linked to Glu/Asp residues is sensitive to hydroxylamine treatment and reverses the PARP1/2 migration shift, the ether bond of PAR linked to Ser residues, due to the presence of HPF1, is resistant to hydroxylamine treatment (Fig. 1c)[18]
Summary
PARP1 and PARP2 produce poly(ADP-ribose) in response to DNA breaks. HPF1 regulates PARP1/2 catalytic output, most notably permitting serine modification with ADP-ribose. HPF1 rapidly associates/dissociates from multiple PARP1 molecules, initiating serine modification before modification initiates on glutamate/aspartate, and accelerating initiation to be more comparable to elongation reactions forming poly(ADP-ribose). This “hit and run” mechanism ensures HPF1 contributions to PARP1/2 during initiation do not persist and interfere with PAR chain elongation. PARP1/2/3 modify themselves with ADP-ribose at multiple sites, a process termed auto-modification, and they modify a variety of other proteins including histones, other DNA repair factors, and certain DNA structures[4,5,6]. HPF1 switches the amino acid specificity of PARP1 and PARP2 modifications from Glu/Asp to Ser ADP-ribosylation[18]
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