PMID:11799106

Citation	Chang, NS (2002) The non-ankyrin C terminus of Ikappa Balpha physically interacts with p53 in vivo and dissociates in response to apoptotic stress, hypoxia, DNA damage, and transforming growth factor-beta 1-mediated growth suppression. J. Biol. Chem. 277:10323-31
Abstract	Transforming growth factor beta (TGF-beta1) suppresses the growth of mink lung Mv1Lu epithelial cells, whereas testicular hyaluronidase abolishes the growth inhibition. Exposure of Mv1Lu cells to TGF-beta1 rapidly resulted in down-regulation of cytosolic IkappaBalpha and hyaluronidase prevented this effect, suggesting a possible role of IkappaBalpha in the growth regulation. Ectopic expression of wild-type and dominant negative IkappaBalpha prevented TGF-beta1-mediated growth suppression. Nonetheless, the blocking effect of IkappaBalpha is not related to regulation of NF-kappaB function by its N-terminal ankyrin-repeat region (amino acids 1-243). Removal of the PEST (proline-glutamic acid-serine-threonine) domain-containing C terminus (amino acids 244-314) abolished the IkappaBalpha function, and the C terminus alone blocked the TGF-beta1 growth-inhibitory effect. Co-immunoprecipitation by anti-p53 antibody using Mv1Lu and other types of cells, as well as rat liver and spleen, revealed that a portion of cytosolic IkappaBalpha physically interacted with p53. In contrast, Mdm2, an inhibitor of p53, was barely detectable in the immunoprecipitates. The cytosolic p53 x IkappaBalpha complex rapidly dissociated in response to apoptotic stress, etoposide- and UV-mediated DNA damage, hypoxia, and TGF-beta1-mediated growth suppression. Also, a rapid increase in the formation of the nuclear p53 x IkappaBalpha complex was observed during exposure to etoposide and UV. In contrast, TGF-beta1-mediated promotion of fibroblast growth failed to mediate p53 x IkappaBalpha dissociation. Mapping by yeast two-hybrid showed that the non-ankyrin C terminus of IkappaBalpha physically interacted with the proline-rich region and a phosphorylation site, serine 46, in p53. Deletion of serine 46 or alteration of serine 46 to glycine abolished the p53 x IkappaBalpha interaction. Alteration to threonine retained the binding interaction, suggesting that serine 46 phosphorylation is involved in the p53 x IkappaBalpha complex formation. Functionally, enhancement of p53 apoptosis was observed when p53 and IkappaBalpha were transiently co-expressed in cells. Together, the IkappaBalpha x p53 complex plays an important role in responses involving growth regulation, apoptosis, and hypoxic stress.
Links	PubMed Online version:10.1074/jbc.M106607200
Keywords	Animals; Ankyrins/metabolism; Anoxia; Apoptosis; COS Cells; Cell Division; Cell Line; Cell Nucleus/metabolism; Cytosol/metabolism; DNA Damage; DNA-Binding Proteins/chemistry; DNA-Binding Proteins/metabolism; Dose-Response Relationship, Drug; Down-Regulation; Etoposide/pharmacology; Genes, Dominant; Humans; Hyaluronoglucosaminidase/metabolism; I-kappa B Proteins; Liver/metabolism; Mice; Microscopy, Fluorescence; Mutagenesis, Site-Directed; Phosphorylation; Precipitin Tests; Proline/metabolism; Protein Binding; Protein Structure, Tertiary; Rats; Recombinant Proteins/metabolism; Serine/chemistry; Spleen/metabolism; Staurosporine/pharmacology; Threonine/metabolism; Time Factors; Transfection; Transforming Growth Factor beta/metabolism; Transforming Growth Factor beta1; Tumor Cells, Cultured; Tumor Suppressor Protein p53/metabolism; Ultraviolet Rays
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