Nuclear localization of coactivator RAC3 is mediated by a bipartite NLS and importin alpha3.
The nuclear receptor coactivator RAC3 (also known as SRC-3/ACTR/AIB1/p/CIP/TRAM-1) belongs to the p160 coactivator family, which are involved in several physiological processes and diseases. Here we have investigated how RAC3 is translocated into the nucleus and show that it is mediated through a bipartite NLS and importin alpha3. This bipartite NLS is located within the conserved bHLH domain, and its mutation abolished nuclear localization. The NLS is also sufficient to cause nuclear import of EGFP, and the activity requires basic amino acids within the NLS. RAC3 binds strongly to importin alpha3, which also depends on the basic amino acids. Functionally, RAC3 cytoplasmic mutant loses its ability to enhance transcription, suggesting that nuclear localization is essential for coactivator function. Together, these results reveal a previous unknown mechanism for nuclear translocation of p160 coactivators and a critical function of the conserved bHLH within the coactivator.
Yeung
Percy Luk
PL
Department of Pharmacology, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, NJ, USA.
Zhang
Aihua
A
Chen
J Don
JD
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D006801:Humans; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000378:metabolism*; D056921:Nuclear Receptor Coactivator 3; D011485:Protein Binding; D016415:Sequence Alignment; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D028901:alpha Karyopherins / Q000378:metabolism*
C106259:KPNA4 protein, human; D019913:Nuclear Localization Signals; D014157:Transcription Factors; D028901:alpha Karyopherins; D056921:Nuclear Receptor Coactivator 3