title: Reexpression of the retinoblastoma protein in tumor cells induces senescence and telomerase inhibition.
abstract: Normal human diploid cells senesce in vitro and in vivo after a limited number of cell divisions. This process known as cellular senescence is an underlying cause of aging and a critical barrier for development of human cancers. We demonstrate here that reexpression of functional pRB alone in RB/p53-defective tumor cells via a modified tetracycline-regulated gene expression system resulted in a stable growth arrest at the G0/G1 phase of the cell cycle, preventing tumor cells from entering S phase in response to a variety of mitogenic stimuli. These cells displayed multiple morphological changes consistent with cellular senescence and expressed a senescence-associated beta-galactosidase biomarker. Further studies indicated that telomerase activity, which was assumably essential for an extended proliferative life-span of neoplastic cells, was abrogated or repressed in the tumor cell lines after induction of pRB (but not p53) expression. Strikingly, when returned to an non-permissive medium for pRB expression, the pRB-induced senescent tumor cells resumed DNA synthesis, attempted to divide but most died in the process, a phenomenon similar to postsenescent crisis of SV40 T-antigen-transformed human diploid fibroblasts in late passage. These observations provide direct evidence that overexpression of pRB alone in RB/p53-defective tumor cells is sufficient to reverse their immortality and cause a phenotype that is, by all generally accepted criteria, indistinguishable from replicative senescence. The results suggest that pRB may play a causal role in the intrinsic cellular senescence program.
authors.affiliation: Department of Molecular Oncology, The University of Texas MD Anderson Cancer Center, The Woodlands 77381, USA.
authors.forename: H J
authors.initials: HJ
authors.lastname: Xu
authors.forename: Y
authors.initials: Y
authors.lastname: Zhou
authors.forename: W
authors.initials: W
authors.lastname: Ji
authors.forename: G S
authors.initials: GS
authors.lastname: Perng
authors.forename: R
authors.initials: R
authors.lastname: Kruzelock
authors.forename: C T
authors.initials: CT
authors.lastname: Kong
authors.forename: R C
authors.initials: RC
authors.lastname: Bast
authors.forename: G B
authors.initials: GB
authors.lastname: Mills
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: S X
authors.initials: SX
authors.lastname: Hu
mesh_terms: D016922:Cellular Senescence; D006801:Humans; D009369:Neoplasms / Q000473:pathology*; D016160:Retinoblastoma Protein / Q000502:physiology*; D019098:Telomerase / Q000037:antagonists & inhibitors*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology; D001616:beta-Galactosidase / Q000096:biosynthesis
chemical_list: D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D019098:Telomerase; D001616:beta-Galactosidase