Histone Deacetylase 4 Possesses Intrinsic Nuclear Import and Export Signals

Abstract

Nucleocytoplasmic trafficking of histone deacetylase 4 (HDAC4) plays an important role in regulating its function, and binding of 14-3-3 proteins is necessary for its cytoplasmic retention. Here, we report the identification of nuclear import and export sequences of HDAC4. While its N-terminal 118 residues modulate the nuclear localization, residues 244 to 279 constitute an authentic, strong nuclear localization signal. Mutational analysis of this signal revealed that three arginine-lysine clusters are necessary for its nuclear import activity. As for nuclear export, leucine-rich sequences located in the middle part of HDAC4 do not function as nuclear export signals. By contrast, a hydrophobic motif (MXXLXVXV) located at the C-terminal end serves as a nuclear export signal that is necessary for cytoplasmic retention of HDAC4. This motif is required for CRM1-mediated nuclear export of HDAC4. Furthermore, binding of 14-3-3 proteins promotes cytoplasmic localization of HDAC4 by both inhibiting its nuclear import and stimulating its nuclear export. Unlike wild-type HDAC4, a point mutant with abrogated MEF2-binding ability remains cytoplasmic upon exogenous expression of MEF2C, supporting the notion that direct MEF2 binding targets HDAC4 to the nucleus. Therefore, HDAC4 possesses intrinsic nuclear import and export signals for its dynamic nucleocytoplasmic shuttling, and association with 14-3-3 and MEF2 proteins affects such shuttling and thus directs HDAC4 to the cytoplasm and the nucleus, respectively.

ACKNOWLEDGMENTS

We thank S. Khochbin and E. N. Olson for sharing results about subcellular localization of HDAC4 and HDAC5, C. M. Grozinger and S. L. Schreiber for HDAC5 expression plasmids, M. Yoshida for leptomycin B, C. Dargemont and R. Lin for CRM1 cDNA, D. Gorlich for RanQ69L expression plasmid, J. Han for anti-MEF2C antibody, J. J. LeBrun for use of a FluoChem imaging system, and M. Park and S. Stifani for use of fluorescence microscopes. A.H.W. is the recipient of a Canadian Institutes of Health Research (CIHR) doctoral research award.

This work was supported by grants from the National Cancer Institute of Canada and a scholarship from the CIHR (to X.-J.Y.).