title: Transcription-independent ARF regulation in oncogenic stress-mediated p53 responses.
abstract: The tumour suppressor ARF is specifically required for p53 activation under oncogenic stress. Recent studies showed that p53 activation mediated by ARF, but not that induced by DNA damage, acts as a major protection against tumorigenesis in vivo under certain biological settings, suggesting that the ARF-p53 axis has more fundamental functions in tumour suppression than originally thought. Because ARF is a very stable protein in most human cell lines, it has been widely assumed that ARF induction is mediated mainly at the transcriptional level and that activation of the ARF-p53 pathway by oncogenes is a much slower and largely irreversible process by comparison with p53 activation after DNA damage. Here we report that ARF is very unstable in normal human cells but that its degradation is inhibited in cancerous cells. Through biochemical purification, we identified a specific ubiquitin ligase for ARF and named it ULF. ULF interacts with ARF both in vitro and in vivo and promotes the lysine-independent ubiquitylation and degradation of ARF. ULF knockdown stabilizes ARF in normal human cells, triggering ARF-dependent, p53-mediated growth arrest. Moreover, nucleophosmin (NPM) and c-Myc, both of which are commonly overexpressed in cancer cells, are capable of abrogating ULF-mediated ARF ubiquitylation through distinct mechanisms, and thereby promote ARF stabilization in cancer cells. These findings reveal the dynamic feature of the ARF-p53 pathway and suggest that transcription-independent mechanisms are critically involved in ARF regulation during responses to oncogenic stress.
authors.affiliation: Institute for Cancer Genetics, and Department of Pathology and Cell Biology College of Physicians & Surgeons, Columbia University, 1130 St Nicholas Avenue, New York, New York 10032, USA.
authors.forename: Delin
authors.initials: D
authors.lastname: Chen
authors.forename: Jing
authors.initials: J
authors.lastname: Shan
authors.forename: Wei-Guo
authors.initials: WG
authors.lastname: Zhu
authors.forename: Jun
authors.initials: J
authors.lastname: Qin
authors.forename: Wei
authors.initials: W
authors.lastname: Gu
mesh_terms: D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D002460:Cell Line; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D000090243:Nucleophosmin; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D013312:Stress, Physiological / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D020298:U937 Cells; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination
chemical_list: C489427:MYC protein, human; C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D016271:Proto-Oncogene Proteins c-myc; D016159:Tumor Suppressor Protein p53; D000090243:Nucleophosmin; D044767:Ubiquitin-Protein Ligases; D020727:ADP-Ribosylation Factors