Pratt M A, Crippen C, Hubbard K, Menard M
Department of Pharmacology, University of Ottawa, Ontario, Canada.
Cell Growth Differ. 1998 Sep;9(9):713-22.
We have studied the expression of the retinoid X receptor (RXR) family of receptors during the DMSO-induced differentiation of P19 murine embryonal carcinoma cells into mesoderm and muscle. RXR-alpha protein is weakly detectable in untreated P19 cells and in a mutant line of P19 cells (D3) that are resistant to DMSO-induced differentiation but begins to increase by day 3 and continues to rise gradually thereafter, whereas RXR-gamma protein is readily detected in P19 cells and decreases over the course of differentiation. Protein expression is uncoupled from mRNA levels, because DMSO induces a rapid, aggregation-independent, transient increase in RXR-alpha mRNA that diminishes by day 3 of differentiation. Thus, the expression of RXR-alpha protein is prevented at early times during DMSO-induced differentiation. Stable P19 cell clones that constitutively express RXR-alpha protein [P19(RXR-alpha)] are resistant to DMSO-induced differentiation associated with increased levels of oligonucleosomal-length DNA fragmentation. Loss of RXR-alpha expression after multiple passages results in a reversion to a DMSO-responsive phenotype. Id1 transcripts are present in P19 cells and are transiently decreased on day 2 of DMSO differentiation but remain elevated in DMSO-treated P19(RXR-alpha) and in P19 cells treated simultaneously with retinoic acid and DMSO. The mRNA for the mesoderm inducer protein Brachyury T was also deregulated in P19(RXR-alpha) cells and D3 cells compared with that of wild-type P19 cells. Together, these results show that expression of the RXR-alpha mRNA and protein in P19 cells is tightly regulated during the mesodermal/muscle differentiation of P19 cells, and that ectopic expression of the RXR-alpha protein prevents differentiation associated with increased cell death, prolonged expression of Brachyury T, and constitutive expression of Id1.
我们研究了维甲酸X受体（RXR）家族受体在二甲基亚砜（DMSO）诱导P19小鼠胚胎癌细胞分化为中胚层和肌肉过程中的表达情况。在未处理的P19细胞以及对DMSO诱导分化具有抗性的P19细胞突变系（D3）中，RXR-α蛋白的表达水平很低，几乎检测不到，但在第3天开始增加，此后继续逐渐上升；而RXR-γ蛋白在P19细胞中很容易检测到，并且在分化过程中表达量下降。蛋白表达与mRNA水平不一致，因为DMSO会诱导RXR-α mRNA快速、不依赖聚集且短暂地增加，这种增加在分化第3天时就会减弱。因此，在DMSO诱导分化的早期阶段，RXR-α蛋白的表达受到抑制。持续表达RXR-α蛋白的稳定P19细胞克隆[P19（RXR-α）]对DMSO诱导的分化具有抗性，且这种抗性与寡核小体长度的DNA片段化水平增加有关。多次传代后RXR-α表达缺失会导致细胞恢复到对DMSO敏感的表型。Id-1转录本存在于P19细胞中，在DMSO分化第2天时短暂减少，但在经DMSO处理的P19（RXR-α）细胞以及同时用视黄酸和DMSO处理的P19细胞中仍保持较高水平。与野生型P19细胞相比，中胚层诱导蛋白Brachyury T的mRNA在P19（RXR-α）细胞和D3细胞中也出现了表达失调。总之，这些结果表明，在P19细胞向中胚层/肌肉分化的过程中，P19细胞中RXR-α mRNA和蛋白的表达受到严格调控，并且RXR-α蛋白的异位表达可阻止与细胞死亡增加、Brachyury T延长表达以及Id1组成型表达相关的分化。
