title: Bmi-1 extends the life span of normal human oral keratinocytes by inhibiting the TGF-beta signaling.
abstract: We previously demonstrated that Bmi-1 extended the in vitro life span of normal human oral keratinocytes (NHOK). We now report that the prolonged life span of NHOK by Bmi-1 is, in part, due to inhibition of the TGF-beta signaling pathway. Serial subculture of NHOK resulted in replicative senescence and terminal differentiation and activation of TGF-beta signaling pathway. This was accompanied with enhanced intracellular and secreted TGF-beta1 levels, phosphorylation of Smad2/3, and increased expression of p15(INK4B) and p57(KIP2). An ectopic expression of Bmi-1 in NHOK (HOK/Bmi-1) decreased the level of intracellular and secreted TGF-beta1 induced dephosphorylation of Smad2/3, and diminished the level of p15(INK4B) and p57(KIP2). Moreover, Bmi-1 expression led to the inhibition of TGF-beta-responsive promoter activity in a dose-specific manner. Knockdown of Bmi-1 in rapidly proliferating HOK/Bmi-1 and cancer cells increased the level of phosphorylated Smad2/3, p15(INK4B), and p57(KIP2). In addition, an exposure of senescent NHOK to TGF-beta receptor I kinase inhibitor or anti-TGF-beta antibody resulted in enhanced replicative potential of cells. Taken together, these data suggest that Bmi-1 suppresses senescence of cells by inhibiting the TGF-beta signaling pathway in NHOK.
authors.affiliation: UCLA School of Dentistry, Center for the Health Sciences, Room 43-091, 10833 Le Conte Ave, Los Angeles, CA 90095, USA. rkim@dentistry.ucla.edu
authors.forename: Reuben H
authors.initials: RH
authors.lastname: Kim
authors.forename: Mark B
authors.initials: MB
authors.lastname: Lieberman
authors.forename: Rachel
authors.initials: R
authors.lastname: Lee
authors.forename: Ki-Hyuk
authors.initials: KH
authors.lastname: Shin
authors.forename: Shebli
authors.initials: S
authors.lastname: Mehrazarin
authors.forename: Ju-Eun
authors.initials: JE
authors.lastname: Oh
authors.forename: No-Hee
authors.initials: NH
authors.lastname: Park
authors.forename: Mo K
authors.initials: MK
authors.lastname: Kang
mesh_terms: D015153:Blotting, Western; D049109:Cell Proliferation; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D016922:Cellular Senescence; D050762:Cyclin-Dependent Kinase Inhibitor p15 / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D015870:Gene Expression / Q000502:physiology; D005822:Genetic Vectors; D006801:Humans; D015603:Keratinocytes / Q000166:cytology* / Q000378:metabolism; D009061:Mouth Mucosa / Q000166:cytology* / Q000378:metabolism; D009687:Nuclear Proteins / Q000502:physiology*; D010766:Phosphorylation; D063150:Polycomb Repressive Complex 1; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D012097:Repressor Proteins / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism; D014162:Transfection; D053773:Transforming Growth Factor beta1 / Q000037:antagonists & inhibitors*
chemical_list: C069077:BMI1 protein, human; C493956:CDKN1A protein, human; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050761:Cyclin-Dependent Kinase Inhibitor p57; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D053773:Transforming Growth Factor beta1; D063150:Polycomb Repressive Complex 1