Transactivation activity of LBP-1 proteins and their dimerization in living cells.
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.
Katsura
Ayako
A
Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.
Kimura
Kota
K
Hosoi
Kentaro
K
Tomokuni
Yosuke
Y
Nesori
Masanori
M
Goryo
Kenji
K
Numayama-Tsuruta
Keiko
K
Torii
Satoru
S
Yasumoto
Ken-Ichi
K
Gotoh
Osamu
O
Takada
Mamiko
M
Fukumura
Hiroshi
H
Sogawa
Kazuhiro
K
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D024202:Electrophoretic Mobility Shift Assay; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D020014:K562 Cells; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals / Q000235:genetics; D010802:Phylogeny; D011485:Protein Binding; D055503:Protein Multimerization; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; D019913:Nuclear Localization Signals; C501906:TFCP2 protein, human; D014157:Transcription Factors; C085968:UBP1 protein, human