Retrodifferentiation and rejuvenation of senescent monocytic cells requires PARP-1

• Published in: Experimental gerontology Vol. 42; no. 6; pp. 554 - 562
• Main Authors: Selle, Astrid, Ullrich, Oliver, Harnacke, Katja, Hass, Ralf
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 01.06.2007
• Subjects: Aging; Apoptosis - drug effects; Apoptosis - physiology; Benzamides - pharmacology; Cell Differentiation - drug effects; Cell Differentiation - physiology; Cell Proliferation - drug effects; Cellular Senescence - drug effects; Cellular Senescence - physiology; DNA, Antisense - genetics; Growth control; Humans; Leukemia, Myeloid - enzymology; Leukemia, Myeloid - pathology; Leukemic cells; Leupeptins - pharmacology; Monocytes - cytology; Monocytes - drug effects; Monocytes - enzymology; PARP-1; Phenotype; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases - genetics; Poly(ADP-ribose) Polymerases - metabolism; Proteasome Endopeptidase Complex - metabolism; Rejuvenation; Retrodifferentiation; Tetradecanoylphorbol Acetate - pharmacology; Tumor development; U937 Cells; Retrodifferentiation; Growth control; Rejuvenation; Aging; Leukemic cells; PARP-1; Tumor development
• ISSN: 0531-5565; 1873-6815
• DOI: 10.1016/j.exger.2006.12.004

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.