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.
Highlights
P73 is a new member of the p53 gene family [1]
Isolation of MM1 as a p73␣-binding Protein in a Two-hybrid Screen—To isolate one or more cellular proteins that could interact with the unique COOH-terminal region of p73␣ and regulate its activity, we used a yeast-based two-hybrid system to screen a human fetal brain cDNA library with a “bait” plasmid encoding the extreme COOHterminal portion of p73␣ (Fig. 1A)
Of a total of 1 ϫ 106 primary transformants, 34 colonies grew on the selection medium lacking tryptophan, leucine, and histidine, and 10 out of the 34 His-positive transformants formed blue colonies. Plasmids carrying these 10 positive candidates were rescued into E. coli, and their nucleotide sequences were determined
Summary
P73 is a new member of the p53 gene family [1]. Like p53, p73 is a nuclear transcription factor, which carries an NH2-terminal transactivation domain, sequence-specific DNA-binding domain, and oligomerization domain. The ability of p73 to inhibit cell growth in p53-deficient cells was stronger than p73␣ [3] These observations suggest that the COOH-terminal region of p73 may possess a regulatory role, which modulates its transactivation ability as well as its biological activity. Of note, ⌬Np73 was predominantly expressed in the developing brain and sympathetic neurons, and inhibited the pro-apoptotic function of p53 by hetero-oligomerization [29] These homotypic and heterotypic interactions among p53 family members give a complexity to the understanding of the p73 signaling in vivo. Like p53, the COOH-terminal deletion of p73␣ caused the significant increase in its DNA-binding and transactivation activities [8, 25, 40] These observations suggest that the p73-DNA crystal structure might be similar to that of p53, the COOH-terminal region of p73 does not share amino acid sequence similarity with that of p53
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
