title: Regulation of telomerase activity and anti-apoptotic function by protein-protein interaction and phosphorylation.
abstract: The enzyme telomerase is necessary for the synthesis and maintenance of telomere length. The catalytic subunit, telomerase reverse transcriptase (TERT), is regulated by interaction with the 90 kDa heat shock protein (HSP90) and by Akt-dependent phosphorylation. Here, we demonstrate that HSP90 and Akt physically interact with TERT. Treatment of cells with novobiocin, which blocks C-terminal interaction of HSP90, disrupted HSP90 binding to Akt, induced Akt dephosphorylation and significantly reduced telomerase activity. The reduction of TERT activity by novobiocin was associated with an increase in apoptosis. Likewise, the induction of Akt dephosphorylation by protein phosphatase 2A (PP2A) reduced telomerase activity. HSP90 is known to prevent PP2A-mediated dephosphorylation of Akt. To investigate whether the effect of novobiocin is due to the reduction of Akt or TERT phosphorylation, we overexpressed a phospho-mimetic, active Akt (T308D/S473D). Akt (T308D/S473D) prevented novobiocin-induced reduction of telomerase activity and the stimulation of apoptosis. Moreover, overexpression of a dominant negative PP2A construct (PP2A(L199P)) as well as incubation with the PP2A inhibitor okadaic acid blocked the inhibition of telomerase activity by novobiocin. These data suggest that the association between HSP90, Akt and TERT in concert with the phosphorylation of TERT is necessary for maintaining telomerase activity and inhibition of apoptosis.
authors.affiliation: Molecular Cardiology, Department of Internal Medicine IV, University of Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt, Germany.
authors.forename: Judith
authors.initials: J
authors.lastname: Haendeler
authors.forename: Jörg
authors.initials: J
authors.lastname: Hoffmann
authors.forename: Sandy
authors.initials: S
authors.lastname: Rahman
authors.forename: Andreas M
authors.initials: AM
authors.lastname: Zeiher
authors.forename: Stefanie
authors.initials: S
authors.lastname: Dimmeler
mesh_terms: D017209:Apoptosis; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D009675:Novobiocin / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000502:physiology; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism* / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D019098:Telomerase / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D018841:HSP90 Heat-Shock Proteins; D011518:Proto-Oncogene Proteins; D009675:Novobiocin; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C509186:TERT protein, human; D019098:Telomerase; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D020169:Caspases