title: Physical interaction of p73 with c-Myc and MM1, a c-Myc-binding protein, and modulation of the p73 function.
abstract: p73 shares high sequence homology with the tumor suppressor p53. Like p53, ectopic overexpression of p73 induces cell cycle arrest and/or apoptosis, and these biological activities are linked to its sequence-specific transactivation function. The COOH-terminal region of p73 is unique and has a function to modulate DNA-binding ability and transactivation activity. To identify and characterize cellular proteins that interact with the COOH-terminal region of p73 alpha and regulate its activity, we employed a yeast-based two-hybrid screen with a human fetal brain cDNA library. We found MM1, a nuclear c-Myc-binding protein, was associated with p73 alpha in both yeast two-hybrid and in vitro pull-down assays. In mammalian cells, MM1 co-immunoprecipitated with p73 alpha, whereas p73 beta and tumor suppressor p53 did not interact with MM1. Overexpression of MM1 in p53-deficient osteosarcoma SAOS-2 cells enhanced the p73 alpha-dependent transcription from the p53/p73-responsive Bax and PG13 promoters, whereas p73 beta- and p53-mediated transcriptional activation was unaffected in the presence of MM1. MM1 also stimulated the p73 alpha-mediated growth suppression in SAOS-2 cells. More importantly, we found that c-Myc was physically associated with p73 alpha and significantly impaired the transcriptional activity of p73 alpha on Bax and p21(waf1) promoters. Expression of MM1 strongly reduced the c-Myc-mediated inhibitory activity on p73 alpha. These results suggest that MM1 may act as a molecular partner for p73 to prevent the c-Myc-mediated inhibitory effect on its activity.
authors.affiliation: Division of Biochemistry, Chiba Cancer Center Research Institute, Chiba 260-8717, Japan.
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Watanabe
authors.forename: Toshinori
authors.initials: T
authors.lastname: Ozaki
authors.forename: Takahito
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Kou
authors.initials: K
authors.lastname: Miyazaki
authors.forename: Masato
authors.initials: M
authors.lastname: Takahashi
authors.forename: Mitsuchika
authors.initials: M
authors.lastname: Hosoda
authors.forename: Syunji
authors.initials: S
authors.lastname: Hayashi
authors.forename: Satoru
authors.initials: S
authors.lastname: Todo
authors.forename: Akira
authors.initials: A
authors.lastname: Nakagawara
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D016147:Genes, Tumor Suppressor; D006801:Humans; D007150:Immunohistochemistry; D009687:Nuclear Proteins / Q000378:metabolism* / Q000502:physiology; D011233:Precipitin Tests; D011485:Protein Binding; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins; D020798:Two-Hybrid System Techniques
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016271:Proto-Oncogene Proteins c-myc; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins