Phosphorylated retinoid X receptor α loses its heterodimeric activity with retinoic acid receptor β
Phosphorylated retinoid X receptor α loses its heterodimeric activity with retinoic acid receptor β
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DOI：
10.1111/j.1349-7006.2007.00621.x
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发表时间：
2007-12
期刊：
影响因子：
5.7
通讯作者：
K. Yoshimura;Y. Muto;M. Shimizu;R. Matsushima-Nishiwaki;M. Okuno;Y. Takano;H. Tsurumi;S. Kojima;Y. Okano;H. Moriwaki
中科院分区：
文献类型：
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作者：
K. Yoshimura;Y. Muto;M. Shimizu;R. Matsushima-Nishiwaki;M. Okuno;Y. Takano;H. Tsurumi;S. Kojima;Y. Okano;H. Moriwaki
维甲酸X受体（RXR）α磷酸化引起的功能障碍与肝细胞癌的发生有关。然而，磷酸化RXRα失去其生理功能的确切机制仍不清楚。在本研究中，我们研究了RXRα的磷酸化是否影响其二聚体活性。荧光共振能量转移研究和免疫沉淀试验表明，当293 T细胞转染磷酸化模拟突变体RXRα（T82 D/S260 D）时，RXRα和视黄酸受体β之间的物理相互作用受损，而当细胞转染未磷酸化的突变体RXRα（T82 A/S260 A）时，这种相互作用以与野生型RXRα转染细胞相似的水平被激活。用类维生素A处理T82 A/S260 A转染的细胞导致视黄酸受体应答元件和RXR应答元件启动子的转录活性显著增加，而这些转录活性在T82 D/S260 D转染的细胞中没有增加。用T82 A/S260 A转染增强了类维生素A引起的细胞生长抑制和细胞凋亡诱导，尽管T82 D/S260 D转染的细胞失去了对类维生素A的反应性。此外，用T82 A/S260 A转染导致HuH 7人肝细胞癌细胞在软琼脂中的细胞生长抑制和集落形成能力降低。这些发现表明，RXRα的磷酸化消除了其与RXR和视黄酸受体β形成同源二聚体和异源二聚体的能力，从而导致细胞生长控制的丧失和癌症发展的加速。因此，抑制RXRα磷酸化并恢复其作为核受体主要调节剂的原始功能可能是控制癌细胞生长的有效策略。（Cancer Sci 2007; 98：1868-1874）
A malfunction in retinoid X receptor (RXR) α due to phosphorylation is associated with the development of hepatocellular carcinoma. However, the precise mechanisms by which phosphorylated RXRα loses its physiological function remain unclear. In the present study we examined whether phosphorylation of RXRα affects its dimeric activity. Fluorescence resonance energy transfer studies and immunoprecipitation assays showed that the physical interaction between RXRα and retinoic acid receptor β was impaired when 293T cells were transfected with phosphomimic mutant RXRα (T82D/S260D), whereas this interaction was activated at a level similar to wild‐type RXRα‐transfected cells when the cells were transfected with an unphosphorylated mutant RXRα (T82A/S260A). Treating the T82A/S260A‐transfected cells with retinoid resulted in a significant increase in the transcriptional activities of the retinoic acid receptor responsive element and RXR responsive element promoters, whereas these transcriptional activities did not increase in the T82D/S260D‐transfected cells. Transfection with T82A/S260A enhanced both the inhibition of cell growth and the induction of apoptosis caused by retinoid, although the T82D/S260D‐transfected cells lost their responsiveness to retinoid. Moreover, transfection with T82A/S260A caused an inhibition of cell growth and a reduction of colony‐forming ability in soft agar in HuH7 human hepatocellular carcinoma cells. These findings suggest that phosphorylation of RXRα abolishes its ability to form homodimers and heterodimers with RXR and retinoic acid receptor β, thus resulting in the loss of cell growth control and the acceleration of cancer development. In conclusion, the inhibition of RXRα phosphorylation and the restoration of its original function as a master regulator of nuclear receptors might therefore be an effective strategy for controlling cancer cell growth. (Cancer Sci 2007; 98: 1868–1874)