Distinct Domains of IκBα Regulate c-Rel in the Cytoplasm and in the Nucleus

ABSTRACT

IκBα is a critical regulator of Rel/NF-κB-mediated gene activation. It controls the induction of NF-κB factors by retaining them in the cytoplasm and also functions in the nucleus to terminate the induction process. In this study, we show that IκBα regulates the transcriptional activity of c-Rel in the nuclear compartment. We also demonstrate that discrete functional domains of IκBα are responsible for the cytoplasmic and nuclear regulation of c-Rel. We show that the determinants for the cytoplasmic regulation of c-Rel reside in the N-terminal and central ankyrin regions of IκBα and that the N-terminal domain of IκBα is required to mask the c-Rel nuclear localization signal. Importantly, IκBα sequences necessary to regulate c-Rel in the nucleus map to its central ankyrin domain and to a few negatively charged amino acids that immediately follow in the C-terminal IκBα PEST domain. The mapping of the IκBα determinants that control the cytoplasmic and nuclear activities of c-Rel to specific regions of the molecule suggests that IκBα inhibitors could be designed to antagonize Rel/NF-κB activity in different subcellular compartments or at defined stages of activation.

ACKNOWLEDGMENTS

We thank N. Rice (ABL-NCI, Frederick, Md.) for the generous gift of antibody Ab1507 against c-Rel, H. Bose (University of Texas, Austin) for an iκbα cDNA clone and antibodies against the chicken IκBα protein, T. Gilmore (Boston University, Boston, Mass.) for a chicken c-rel cDNA clone, and K. Nakayama (Kanazawa University, Kanazawa, Japan) for the pIL6CAT plasmid. We are grateful to S. Crespo for expert assistance with the construction and characterization of some IκBα mutants. We thank F. Agnès, J. Bash, C. Chen, and W.-X. Zong for fruitful discussions during the course of this work. We also thank J. Bash, C. Chen, I. Martı́nez-Férez, A. Rabson, and W.-X. Zong for helpful comments on the manuscript and N. Rice for sharing results prior to publication.

This work was supported by a grant from the National Institutes of Health (CA54999) and by the New Jersey Commission on Science and Technology (C.G.). I.L. was supported by postdoctoral fellowships from Ministerio de Educación y Ciencia (Spain)/Fulbright Program and from the International Human Frontier Science Program.