title: Inhibition of lens fiber cell morphogenesis by expression of a mutant SV40 large T antigen that binds CREB-binding protein/p300 but not pRb.
abstract: Simian virus (SV) 40 large T antigen can both induce tumors and inhibit cellular differentiation. It is not clear whether these cellular changes are synonymous, sequential, or distinct responses to the protein. T antigen is known to bind to p53, to the retinoblastoma (Rb) family of tumor suppressor proteins, and to other cellular proteins such as p300 family members. To test whether SV40 large T antigen inhibits cellular differentiation in vivo in the absence of cell cycle induction, we generated transgenic mice that express in the lens a mutant version of the early region of SV40. This mutant, which we term E107KDelta, has a deletion that eliminates synthesis of small t antigen and a point mutation (E107K) that results in loss of the ability to bind to Rb family members. At embryonic day 15.5 (E15.5), the transgenic lenses show dramatic defects in lens fiber cell differentiation. The fiber cells become post-mitotic, but do not elongate properly. The cells show a dramatic reduction in expression of their beta- and gamma-crystallins. Because CBP and p300 are co-activators for crystallin gene expression, we assayed for interactions between E107KDelta and CBP/p300. Our studies demonstrate that cellular differentiation can be inhibited by SV40 large T antigen in the absence of pRb inactivation, and that interaction of large T antigen with CBP/p300 may be enhanced by a mutation that eliminates the binding to pRb.
authors.affiliation: Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Qin
authors.initials: Q
authors.lastname: Chen
authors.forename: Dongcai
authors.initials: D
authors.lastname: Liang
authors.forename: Larry D
authors.initials: LD
authors.lastname: Fromm
authors.forename: Paul A
authors.initials: PA
authors.lastname: Overbeek
mesh_terms: D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics*; D017209:Apoptosis; D015153:Blotting, Western; D001973:Bromodeoxyuridine / Q000494:pharmacology; D050882:CREB-Binding Protein; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D004247:DNA / Q000737:chemistry; D053938:DNA Fragmentation; D004268:DNA-Binding Proteins / Q000378:metabolism; D050684:E2F Transcription Factors; D005838:Genotype; D007150:Immunohistochemistry; D007908:Lens, Crystalline / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D051739:Microphthalmia-Associated Transcription Factor; D008856:Microscopy, Fluorescence; D008938:Mitosis; D008957:Models, Genetic; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051257:Proto-Oncogene Proteins c-maf; D016160:Retinoblastoma Protein / Q000378:metabolism*; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D019076:Transgenes; D038204:beta-Crystallins / Q000096:biosynthesis; D038222:gamma-Crystallins / Q000096:biosynthesis
chemical_list: D000952:Antigens, Polyomavirus Transforming; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; C495608:Maf protein, mouse; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D051257:Proto-Oncogene Proteins c-maf; D016160:Retinoblastoma Protein; D015534:Trans-Activators; D014157:Transcription Factors; D038204:beta-Crystallins; D038222:gamma-Crystallins; D004247:DNA; D050882:CREB-Binding Protein; C494364:Crebbp protein, mouse; D001973:Bromodeoxyuridine