CRM1 Mediates the Export of ADAR1 through a Nuclear Export Signal within the Z-DNA Binding Domain

Abstract

RNA editing of specific residues by adenosine deamination is a nuclear process catalyzed by adenosine deaminases acting on RNA (ADAR). Different promoters in the ADAR1 gene give rise to two forms of the protein: a constitutive promoter expresses a transcript encoding (c)ADAR1, and an interferon-induced promoter expresses a transcript encoding an N-terminally extended form, (i)ADAR1. Here we show that (c)ADAR1 is primarily nuclear whereas (i)ADAR1 encompasses a functional nuclear export signal in the N-terminal part and is a nucleocytoplasmic shuttle protein. Mutation of the nuclear export signal or treatment with the CRM1-specific drug leptomycin B induces nuclear accumulation of (i)ADAR1 fused to the green fluorescent protein and increases the nuclear editing activity. In concurrence, CRM1 and RanGTP interact specifically with the (i)ADAR1 nuclear export signal to form a tripartite export complex in vitro. Furthermore, our data imply that nuclear import of (i)ADAR1 is mediated by at least two nuclear localization sequences. These results suggest that the nuclear editing activity of (i)ADAR1 is modulated by nuclear export.

ACKNOWLEDGMENTS

H.P. and J.N. contributed equally to this work.

We thank Marie Öhman, Brenda L. Bass, and Herbert L. Ley III for the ADAR1-specific antibody, Just Justesen for the eRF3a-specific antibody, André Gerber and Walter Keller for the ADAR1 plasmid, Iain W. Mattaj for the CRM1 plasmid, Dirk Görlich for the Ran and Rna1p plasmids, Trine E. Larsen for the R2L R/G editing construct, and Minoru Yoshida for a generous supply of LMB. We are grateful to Ray Brown for critical reading of the manuscript. Finally, we are indebted to Rita Rosendahl for excellent technical assistance.

The work was supported in part by grants from the Danish National Science and Medical Research Councils, The Carlsberg Foundation, Novo Nordisk Foundation, and Karen Elise Jensen Foundation. H.P., J.N., and C.K.D. were supported by the University of Aarhus.