title: A specific isoform of poly(ADP-ribose) glycohydrolase is targeted to the mitochondrial matrix by a N-terminal mitochondrial targeting sequence.
abstract: Poly(ADP-ribose) polymerases (PARPs) convert NAD to polymers of ADP-ribose that are converted to free ADP-ribose by poly(ADP-ribose) glycohydrolase (PARG). The activation of the nuclear enzyme PARP-1 following genotoxic stress has been linked to release of apoptosis inducing factor from the mitochondria, but the mechanisms by which signals are transmitted between nuclear and mitochondrial compartments are not well understood. The study reported here has examined the relationship between PARG and mitochondria in HeLa cells. Endogenous PARG associated with the mitochondrial fraction migrated in the range of 60 kDa. Transient transfection of cells with PARG expression constructs with amino acids encoded by exon 4 at the N-terminus was targeted to the mitochondria as demonstrated by subcellular fractionation and immunofluorescence microscopy of whole cells. Deletion and missense mutants allowed identification of a canonical N-terminal mitochondrial targeting sequence consisting of the first 16 amino acids encoded by PARG exon 4. Sub-mitochondrial localization experiments indicate that this mitochondrial PARG isoform is targeted to the mitochondrial matrix. The identification of a PARG isoform as a component of the mitochondrial matrix raises several interesting possibilities concerning mechanisms of nuclear-mitochondrial cross talk involved in regulation of cell death pathways.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, Arizona Cancer Center, University of Arizona, Tucson, AZ 85728, USA.
authors.forename: Clifford J
authors.initials: CJ
authors.lastname: Whatcott
authors.forename: Mirella L
authors.initials: ML
authors.lastname: Meyer-Ficca
authors.forename: Ralph G
authors.initials: RG
authors.lastname: Meyer
authors.forename: Myron K
authors.initials: MK
authors.lastname: Jacobson
mesh_terms: D019943:Amino Acid Substitution / Q000502:physiology; D000596:Amino Acids / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D018834:Chaperonin 60 / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D019286:Endopeptidase K / Q000378:metabolism; D005091:Exons / Q000235:genetics; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D021382:Protein Sorting Signals / Q000502:physiology*; D021381:Protein Transport; D017384:Sequence Deletion / Q000502:physiology; D014162:Transfection
chemical_list: D000596:Amino Acids; D051017:Apoptosis Regulatory Proteins; D018834:Chaperonin 60; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D024101:Mitochondrial Proteins; D021382:Protein Sorting Signals; D006026:Glycoside Hydrolases; C022407:poly ADP-ribose glycohydrolase; D019286:Endopeptidase K; D004072:Digitonin