INTERACTION OF AN ADENOVIRUS E3 14.7-KILODALTON PROTEIN WITH A NOVEL TUMOR-NECROSIS-FACTOR ALPHA-INDUCIBLE CELLULAR PROTEIN CONTAINING LEUCINE-ZIPPER DOMAINS

Early region 3 (E3) of group C human adenoviruses (Ad) encodes several inhibitors of tumor necrosis factor alpha (TNF-alpha) cytolysis, incl uding an E3 14.7-kDa protein (E3-14.7K) and a heterodimer containing t wo polypeptides of 10.4 and 14.5 kDa, To understand the mechanism by w hich the viral proteins inhibit TNF-alpha functions, the E3-14.7K prot ein was used to screen a HeLa cell cDNA library to search for interact ing proteins in the yeast two-hybrid system. A novel protein containin g multiple leucine zipper domains without any significant homology wit h any known protein was identified and has been named FIP-2 (for 14.7K -interacting protein), FIP-2 interacted with E3-14.7K both in vitro an d in vivo, It colocalized with Ad E3-14.7K in the cytoplasm, especiall y near the nuclear membrane, and caused redistribution of the viral pr otein. FIP-2 by itself does not cause cell death; however, it can reve rse the protective effect of E3-14.7K on cell killing induced by overe xpression of the intracellular domain of the 55-kDa TNF receptor or by RIP, a death protein involved in the TNF-alpha and Fas apoptosis path ways, Deletion analysis indicates that the reversal effect of FIP-2 de pends on its interaction with E3-14.7K. Three major mRNA forms of FIP- 2 have been detected in multiple human tissues, and expression of the transcripts was induced by TNF-alpha treatment in a time-dependent man ner in two different cell lines. FIP-2 has consensus sequences for sev eral potential posttranslational modifications, These data suggest tha t FIP-2 is one of the cellular targets for Ad E3-14.7K and that its me chanism of affecting cell death involves the TNF receptor, RIP, or a d ownstream molecule affected by either of these two molecules.