Interaction between hnRNPA1 and IκBα Is Required for Maximal Activation of NF-κB-Dependent Transcription

Abstract

Transcriptional activation of NF-κB is mediated by signal-induced phosphorylation and degradation of its inhibitor, IκBα. NF-κB activation induces a rapid resynthesis of IκBα which is responsible for postinduction repression of transcription. Following resynthesis, IκBα translocates to the nucleus, removes template bound NF-κB, and exports NF-κB to the cytoplasm in a transcriptionally inactive form. Here we demonstrate that IκBα interacts directly with another nucleocytoplasmic shuttling protein, hnRNPA1, both in vivo and in vitro. This interaction requires one of the N-terminal RNA binding domains of hnRNPA1 and the C-terminal region of IκBα. Cells lacking hnRNPA1 are defective in NF-κB-dependent transcriptional activation, but the defect in these cells is complemented by ectopic expression of hnRNPA1. hnRNPA1 expression in these cells increased the amount of IκBα degradation, compared to that of the control cells, in response to activation by Epstein-Barr virus latent membrane protein 1. Thus in addition to regulating mRNA processing and transport, hnRNPA1 also contributes to the control of NF-κB-dependent transcription.

ACKNOWLEDGMENTS

We thank Alex Houston and Ellis Jaffray, University of St. Andrews, for DNA sequencing and purified GST fusion proteins. We are grateful to Gideon Dreyfuss, University of Pennsylvania, for supplying the 4B10 monoclonal antibody to hnRNPA1 and Yaacov Ben-David, Sunnybrook Health Science Centre, Toronto, Canada, for providing the CB3 cell line.

This work was funded by the BBSRC and supported in part by the European Union Concerted Action BIOMED II (ROCIO II project).