Identification and characterization of a nuclear localization signal of TRIM28 that overlaps with the HP1 box

Tripartite motif-containing 28 (TRIM28) is a transcription regulator, which forms a repressor complex containing heterochromatin protein 1 (HPI). Here, we report identification of a nuclear localization signal (NLS) within the 462-494 amino acid region of TRIM28 that overlaps with its HP1 binding site, HP1 box. GST-pulldown experiments revealed the interaction of the arginine-rich TRIM28 NLS with various importin alpha subtypes (alpha 1, alpha 2 and alpha 4). In vitro transport assay demonstrated that nuclear localization of GFP-TRIM28 NLS is mediated by importin alpha s, in conjunction with importin beta 1 and Ran. Further, we demonstrated that HP1 and importin as compete for binding to TRIM28. Together, our findings suggest that importin a has an essential role in the nuclear delivery and preferential HP1 interaction of TRIM28. (C) 2015 Elsevier Inc. All rights reserved.