title: Modulation of replicative senescence of diploid human cells by nuclear ERK signaling.
abstract: Normal somatic cells have a limited replicative lifespan, and serial subcultivation ultimately results in senescence. Senescent cells are irreversibly growth-arrested and show impaired responses to mitogens. Activation of the ERK signaling pathway, an absolute requirement for cell proliferation, results in nuclear relocalization of active ERKs, an event impaired in senescent fibroblasts. This impairment coincides with increased activity of the nuclear ERK phosphatase MKP2. Here we show that replicative lifespan can be altered by changes in nuclear ERK activity. Ectopic expression of MKP2 results in premature senescence. In contrast, knock-down of MKP2 expression, through transduction of MKP2 sequence-specific short hairpin RNA, or expression of the phosphatase resistant ERK2(D319N) mutant, abrogates the effects of increased endogenous MKP2 levels and senescence is postponed. Nuclear targeting of ERK2(D319N) significantly augments its effects and the transduced cultures show higher than 60% increase in replicative lifespan compared with cultures transduced with wt ERK2. Long-lived cultures senesce with altered molecular characteristics and retain the ability to express c-fos, and Rb is maintained in its inactive form. Our results support that MKP2-mediated inactivation of nuclear ERK2 represents a key event in the establishment of replicative senescence. Although it is evident that senescence can be imposed through multiple mechanisms, restoration of nuclear ERK activity can bypass a critical senescence checkpoint and, thus, extend replicative lifespan.
authors.affiliation: Lankenau Institute for Medical Research, Wynnewood, Pennsylvania 19096, USA. tresini@netscape.net
authors.forename: Maria
authors.initials: M
authors.lastname: Tresini
authors.forename: Antonello
authors.initials: A
authors.lastname: Lorenzini
authors.forename: Claudio
authors.initials: C
authors.lastname: Torres
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Cristofalo
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology* / Q000235:genetics; D049109:Cell Proliferation; D016922:Cellular Senescence / Q000235:genetics; D004171:Diploidy; D054637:Dual-Specificity Phosphatases; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D006131:Growth Inhibitors / Q000502:physiology; D006801:Humans; D020935:MAP Kinase Signaling System / Q000235:genetics; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000502:physiology; D054639:Mitogen-Activated Protein Kinase Phosphatases; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
chemical_list: D006131:Growth Inhibitors; D048049:Extracellular Signal-Regulated MAP Kinases; D019950:Mitogen-Activated Protein Kinase 1; D054639:Mitogen-Activated Protein Kinase Phosphatases; C490583:DUSP4 protein, human; D054637:Dual-Specificity Phosphatases; D017027:Protein Tyrosine Phosphatases