Transactivation activity of LBP-1 proteins and their dimerization in living cells

Genes Cells. 2009 Oct;14(10):1183-96. doi: 10.1111/j.1365-2443.2009.01344.x. Epub 2009 Sep 14.


LBP-1 proteins form dimers and act as transcription factors that activate a number of genes related to cell growth and differentiation. LBP-1a and LBP-1c are localized in the cytoplasm when transiently expressed in cultured cells, but translocated into the nucleus after forming heterodimers with LBP-1b, which is a splicing variant of LBP-1a with an intrinsic nuclear localization signal (NLS). Here, we report that LBP-1b showed potent transactivation activity, and that forcibly expressed LBP-1a and LBP-1c in the nucleus essentially exhibited very little or no transactivation activity. Mutations in the NLS that abolished the NLS activity of LBP-1b also abrogated the transactivation activity. We have found that LBP-1 proteins contain a putative sterile alpha motif domain indispensable for their dimerization capability in the C-terminal region. To demonstrate whether homo- and heterodimers composed of LBP-1a and/or LBP-1c are generated in the nucleus, we applied the FLIM-based fluorescence resonance energy transfer imaging technique to living cells. It revealed that dimers composed of LBP-1a and LBP-1c were re-formed probably by a partner-exchange of LBP-1b-containing heterodimers.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alternative Splicing
  • Amino Acid Sequence
  • Animals
  • Blotting, Western
  • COS Cells
  • Cell Line
  • Cell Line, Tumor
  • Cell Nucleus / metabolism
  • Chlorocebus aethiops
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Electrophoretic Mobility Shift Assay
  • Fluorescence Resonance Energy Transfer
  • Humans
  • K562 Cells
  • Microscopy, Fluorescence
  • Molecular Sequence Data
  • Mutation
  • Nuclear Localization Signals / genetics
  • Phylogeny
  • Protein Binding
  • Protein Multimerization
  • Sequence Homology, Amino Acid
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcriptional Activation*


  • DNA-Binding Proteins
  • Nuclear Localization Signals
  • TFCP2 protein, human
  • Transcription Factors
  • UBP1 protein, human