title: Id1 regulation of cellular senescence through transcriptional repression of p16/Ink4a.
abstract: The Id family of helix-loop-helix (HLH) transcriptional regulatory proteins does not possess a basic DNA-binding domain and functions as a negative regulator of basic HLH transcription factors. Id proteins coordinate cell growth and differentiation pathways within mammalian cells and have been shown to regulate G(1)-S cell-cycle transitions. Although much recent data has implicated Id1 in playing a critical role in modulating cellular senescence, no direct genetic evidence has been reported to substantiate such work. Here we show that Id1-null primary mouse embryo fibroblasts undergo premature senescence despite normal growth profiles at early passage. These cells possess increased expression of the tumor-suppressor protein p16/Ink4a but not p19/ARF, and have decreased cyclin-dependent kinase (cdk) 2 and cdk4 kinase activity. We also show that Id1 is able to directly inhibit p16/Ink4a but not p19/ARF promoter activity via its HLH domain, and that Id1 inhibits transcriptional activation at E-boxes within the p16/Ink4a promoter. Our data provide, to our knowledge, the first genetic evidence for a role for Id1 as an inhibitor of cellular senescence and suggest that Id1 functions to delay cellular senescence through repression of p16/Ink4a. Because epigenetic and genetic abrogation of p16/Ink4a function has been implicated in the evolution of several human malignancies, we propose that transcriptional regulation of p16/Ink4a may also provide a mechanism for the dysregulation of normal cellular growth controls during the evolution of human malignancies.
authors: Oncology Center, Johns Hopkins University School of Medicine, Bunting-Blaustein Cancer Research Building, 1650 Orleans Street, Room 336, Baltimore, MD 21231-1000, USA. ralani@jhmi.edu
authors: R M
authors: RM
authors: Alani
authors: A Z
authors: AZ
authors: Young
authors: C B
authors: CB
authors: Shifflett
mesh_terms: D000818:Animals; D002460:Cell Line; D016922:Cellular Senescence / Q000235:genetics*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D005786:Gene Expression Regulation; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1; D051379:Mice; D012097:Repressor Proteins; D015398:Signal Transduction / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; C497453:ID1 protein, human; C497455:Idb1 protein, mouse; D051798:Inhibitor of Differentiation Protein 1; D012097:Repressor Proteins; D014157:Transcription Factors