Alteration of poly(ADP-ribose) glycohydrolase nucleocytoplasmic shuttling characteristics upon cleavage by apoptotic proteases.
Poly(ADP-ribosyl)ation is an important post-translational modification which mostly affects nuclear proteins. The major roles of poly(ADP-ribose) synthesis are assigned to DNA damage signalling during base excision repair, apoptosis and excitotoxicity. The transient nature and modulation of poly(ADP-ribose) levels depend mainly on the activity of poly(ADP-ribose) polymerase-1 (PARP-1) and poly(ADP-ribose) glycohydrolase (PARG), the key catabolic enzyme of poly(ADP-ribose). Given the fact that PARG substrate, poly(ADP-ribose), is found almost exclusively in the nucleus and that PARG is mainly localized in the cytoplasm, we wanted to have a closer look at PARG subcellular localization in order to better understand the mechanism by which PARG regulates intracellular poly(ADP-ribose) levels. We examined the subcellular distribution of PARG and of its two enzymatically active C-terminal apoptotic fragments both biochemically and by fluorescence microscopy. Green fluorescent protein (GFP) fusion proteins were constructed for PARG (GFP-PARG), its 74 kDa (GFP-74) and 85 kDa (GFP-85) apoptotic fragments and transiently expressed in COS-7 cells. Localization experiments reveal that all three fusion proteins localize predominantly to the cytoplasm and that a fraction also co-localizes with the Golgi marker FTCD. Moreover, leptomycin B, a drug that specifically inhibits nuclear export signal (NES)-dependent nuclear export, induces a redistribution of GFP-PARG from the cytoplasm to the nucleus and this nuclear accumulation is even more pronounced for the GFP-74 and GFP-85 apoptotic fragments. This observation confirms our hypothesis for the presence of important regions in the PARG sequence that would allow the protein to engage in CRM1-dependent nuclear export. Moreover, the altered nuclear import kinetics found for the apoptotic fragments highlights the importance of PARG N-terminal sequence in modulating PARG nucleocytoplasmic trafficking properties.
Bonicalzi
Marie-Eve
ME
Health and Environment Unit, Laval University Hospital Research Centre, CHUQ, Faculty of Medicine, Laval University, Québec, G1V 4G2, Canada.
Vodenicharov
Momchil
M
Coulombe
Miryan
M
Gagné
Jean-Philippe
JP
Poirier
Guy G
GG
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D019556:COS Cells; D020169:Caspases / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D005231:Fatty Acids, Unsaturated; D008164:Luminescent Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D006026:Glycoside Hydrolases; C022407:poly ADP-ribose glycohydrolase; D020169:Caspases; C038753:leptomycin B