I?B kinase (IKK), the pivotal kinase in signal-dependent activation of nuclear factor-?B (NF-?B), is composed of multiple protein components, including IKK ?/?/? core subunits. To investigate the regulation of the IKK complex, we immunoaffinity purified the IKK complex, and by MALDI-TOF mass spectrometry identified a splice variant of zinc finger protein 268 (ZNF268) as a novel IKK-interacting protein. Both the full-length and the spliced form of the ZNF268 protein were detected in a variety of mammalian tissues and cell lines. The genes were cloned and expressed by in vitro transcription/translation. Several deletion derivatives, such as KRAB domain (KRAB) on its own, the KRAB/spacer/4-zinc fingers (zF4), and the spacer/ 4-zinc fingers (zS4), were ectopically expressed in mammalian cells and exhibited had different subcellular locations. The KRAB-containing mutants were restricted to the nucleus, while zS4 was localized in the cytosol. TNF-?-induced NF-?B activation was examined using these mutants and only zS4 was found to stimulate activation. Collectively, the results indicate that a spliced form of ZNF268 lacking the KRAB domain is located in the cytosol, where it seems to play a role in TNF-?-induced NF-?B activation by interacting with the IKK complex.

Keywords: C2H2-type zinc finger protein, I kappa B kinase, KRAB, NF-kappa B, TNF-alpha, ZNF268,