Transactivation activity of LBP-1 proteins and their dimerization in living cells
Transactivation activity of LBP-1 proteins and their dimerization in living cells
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DOI：
10.1111/j.1365-2443.2009.01344.x
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发表时间：
2009-10-01
期刊：
影响因子：
2.1
通讯作者：
Sogawa, Kazuhiro
中科院分区：
文献类型：
--
作者：
Katsura, Ayako;Kimura, Kota;Sogawa, Kazuhiro
LBP-1 蛋白形成二聚体并充当转录因子，激活许多与细胞生长和分化相关的基因。 LBP-1a和LBP-1c在培养细胞中瞬时表达时定位于细胞质中，但在与LBP-1b形成异二聚体后易位到细胞核中，LBP-1b是LBP-1a的剪接变体，具有内在核定位信号(NLS)。在这里，我们报告LBP-1b显示出有效的反式激活活性，而在细胞核中强制表达LBP-1a和LBP-1c的则基本上表现出很少或没有反式激活活性。 NLS 中的突变消除了 LBP-1b 的 NLS 活性，也消除了反式激活活性。我们发现 LBP-1 蛋白含有一个推定的无菌 α 基序结构域，这对于它们在 C 端区域的二聚化能力是必不可少的。为了证明由 LBP-1a 和/或 LBP-1c 组成的同二聚体和异二聚体是否在细胞核中产生，我们将基于 FLIM 的荧光共振能量转移成像技术应用于活细胞。结果表明，由 LBP-1a 和 LBP-1c 组成的二聚体可能是通过含有 LBP-1b 的异二聚体的伴侣交换而重新形成的。
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.