title: Retrodifferentiation and rejuvenation of senescent monocytic cells requires PARP-1.
abstract: Long-term culture of phorbol ester (TPA)-differentiated and growth-arrested human U937 leukemia cells was associated with expression of c-jun transcription factors and vimentin intermediate filaments until the cells entered a retrodifferentiation program. This retrodifferentiation process revealed a reversion of the senecent differentiated cells back to undifferentiated and proliferative active young cells. A significant protein ubiquitination was detectable before retrodifferentiation and rejuvenation indicating a proteolytic down-modulation of differentiation markers. Thus, proteolytic activity significantly increased during retrodifferentiation, however, proteasomal protein expression remained unaltered. In order to investigate proteasomal associates, (ADP-ribose)polymerase-1 (PARP-1) expression progressively increased to maximal levels at the time of retrodifferentiation suggesting a possible regulatory association. Indeed, PARP-1 immunoprecipitations demonstrated a co-immunoprecipitation of proteolytically active 20S proteasome with maximal levels during retrodifferentiation. Inhibition of PARP and the proteasome by 3-aminobenzamide and MG-132, respectively, revealed about 90% of apoptotic cells by cell cycle analysis at the time of retrodifferentiation whereas control cells doubled. In contrast, a similar PARP and proteasome inhibition within 5d after TPA-induced differentiation demonstrated little if any apoptotic effects. More specifically, down-modulation of PARP-1 by an antisense PARP-1 vector construct underwent a rapid differentiation and aging and revealed no detectable retrodifferentiation in contrast to control vector-transfected U937 cells. In conclusion, retrodifferentiation of growth-arrested U937 monocytic cells requires proteasomal protein degradation and activity of PARP-1.
authors.affiliation: Department of Cell Biology and Neurobiology, Institute of Anatomy, Medical Faculty Charité, Humboldt University Berlin, Germany.
authors.forename: Astrid
authors.initials: A
authors.lastname: Selle
authors.forename: Oliver
authors.initials: O
authors.lastname: Ullrich
authors.forename: Katja
authors.initials: K
authors.lastname: Harnacke
authors.forename: Ralf
authors.initials: R
authors.lastname: Hass
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001549:Benzamides / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D049109:Cell Proliferation / Q000187:drug effects; D016922:Cellular Senescence / Q000187:drug effects / Q000502:physiology*; D016373:DNA, Antisense / Q000235:genetics; D006801:Humans; D007951:Leukemia, Myeloid / Q000201:enzymology / Q000473:pathology; D007976:Leupeptins / Q000494:pharmacology; D009000:Monocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D010641:Phenotype; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D020298:U937 Cells
chemical_list: D001549:Benzamides; D016373:DNA, Antisense; D007976:Leupeptins; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C025160:3-aminobenzamide; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D046988:Proteasome Endopeptidase Complex; D013755:Tetradecanoylphorbol Acetate; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde