title: Dominant negative c-jun inhibits activation of the cyclin D1 and cyclin E kinase complexes.
abstract: The AP-1 transcription factor is activated by oncogenic signal transduction cascades and its function is critical for both mitogenesis and carcinogenesis. To define the role of AP-1 in the context of a human fibrosarcoma cell line, HT1080, we expressed a dominant negative c-jun mutant fused to the green fluorescent protein in an ecdysone-inducible system. We demonstrated that high levels of this mutant, GFP-TAM67, inhibit AP-1 activity and arrest cells predominantly in the G1 phase of the cell cycle. This arrest is reversible and occurs only above a threshold concentration; low to moderate levels of GFP-TAM67 are insufficient for growth arrest. Contrary to expectations based on the literature, GFP-TAM67 does not inhibit expression of cyclin D1, cyclin E, or their respective cyclin-dependent kinases. However, pRB is hypophosphorylated in GFP-TAM67-arrested cells and the activity of both the cyclin D1:cdk and the cyclin E:cdk complexes are impaired. Both of these complexes show an increased association with p21(CIP1/WAF1), concomitantly with induction of the p21 mRNA by GFP-TAM67. These results suggest a novel function of AP-1 in the activation of the G1 cyclin:cdk complexes in human tumor cells by regulating the expression of the p21(CIP1/WAF1) gene.
authors.affiliation: Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0521, USA. Robert.Hennigan@uc.edu
authors.forename: R F
authors.initials: RF
authors.lastname: Hennigan
authors.forename: P J
authors.initials: PJ
authors.lastname: Stambrook
mesh_terms: D002453:Cell Cycle / Q000502:physiology; D019938:Cyclin D1 / Q000378:metabolism*; D019927:Cyclin E / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D004440:Ecdysone / Q000031:analogs & derivatives / Q000235:genetics; D004791:Enzyme Inhibitors / Q000378:metabolism; D005434:Flow Cytometry; D017930:Genes, Reporter; D006801:Humans; D015151:Immunoblotting; D018613:Microscopy, Confocal; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: C493956:CDKN1A protein, human; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D016755:Proto-Oncogene Proteins c-jun; D011993:Recombinant Fusion Proteins; D018808:Transcription Factor AP-1; D019938:Cyclin D1; D004440:Ecdysone; D018844:Cyclin-Dependent Kinases