ADP-ribosylhydrolase 3 (ARH3), not poly(ADP-ribose) glycohydrolase (PARG) isoforms, is responsible for degradation of mitochondrial matrix-associated poly(ADP-ribose)

J Biol Chem. 2012 May 11;287(20):16088-102. doi: 10.1074/jbc.M112.349183. Epub 2012 Mar 20.


Important cellular processes are regulated by poly(ADP-ribosyl)ation. This protein modification is catalyzed mainly by nuclear poly(ADP-ribose) polymerase (PARP) 1 in response to DNA damage. Cytosolic PARP isoforms have been described, whereas the presence of poly(ADP-ribose) (PAR) metabolism in mitochondria is controversial. PAR is degraded by poly(ADP-ribose) glycohydrolase (PARG). Recently, ADP-ribosylhydrolase 3 (ARH3) was also shown to catalyze PAR-degradation in vitro. PARG is encoded by a single, essential gene. One nuclear and three cytosolic isoforms result from alternative splicing. The presence and origin of a mitochondrial PARG is still unresolved. We establish here the genetic background of a human mitochondrial PARG isoform and investigate the molecular basis for mitochondrial poly(ADP-ribose) degradation. In common with a cytosolic 60-kDa human PARG isoform, the mitochondrial protein did not catalyze PAR degradation because of the absence of exon 5-encoded residues. In mice, we identified a transcript encoding an inactive cytosolic 52-kDa PARG lacking the mitochondrial targeting sequence and a substantial portion of exon 5. Thus, mammalian PARG genes encode isoforms that do not catalyze PAR degradation. On the other hand, embryonic fibroblasts from ARH3(-/-) mice lack most of the mitochondrial PAR degrading activity detected in wild-type cells, demonstrating a potential involvement of ARH3 in PAR metabolism.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Animals
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism
  • Cytosol / metabolism
  • Embryo, Mammalian / cytology
  • Embryo, Mammalian / metabolism
  • Exons / physiology
  • GTPase-Activating Proteins / genetics
  • GTPase-Activating Proteins / metabolism*
  • Glycoside Hydrolases / genetics
  • Glycoside Hydrolases / metabolism*
  • HeLa Cells
  • Hep G2 Cells
  • Humans
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Mice
  • Mice, Inbred BALB C
  • Mice, Knockout
  • Mitochondria / genetics
  • Mitochondria / metabolism*
  • Poly Adenosine Diphosphate Ribose / genetics
  • Poly Adenosine Diphosphate Ribose / metabolism*


  • GTPase-Activating Proteins
  • Isoenzymes
  • Poly Adenosine Diphosphate Ribose
  • Glycoside Hydrolases
  • ADPRHL2 protein, human