Wan Y J, Wang L, Wu T C
Department of Pathology, Harbor-UCLA Medical Center, Torrance 90509.
Exp Cell Res. 1994 Jan;210(1):56-61. doi: 10.1006/excr.1994.1009.
Two classes of nuclear receptors for retinoic acid (RA) have been identified--retinoic acid receptor (RAR) and retinoid x receptor (RXR). Previously, we demonstrated that all-trans-retinoic acid (t-RA) differentially self-regulated the expression of RAR alpha, -beta, and -gamma transcripts. In the present study, we examined the effect of t-RA and 9-cis-RA (c-RA) on the expression of RXR genes in F9 cells by Northern blot analyses. The results showed that t-RA increased the levels of both the 5.6-kb RXR alpha and 3.8-kb RXR gamma mRNAs, decreased the amounts of 2.3-kb RXR gamma mRNA, but had no significant effect on the levels of RXR beta mRNA. Addition of a cyclic AMP analog along with t-RA further induced the differentiation of F9 cells to become parietal endodermal cells, but did not change the regulatory patterns of RXR mRNAs. The RNA synthesis inhibitor, actinomycin D, blocked the induction of 5.6-kb RXR alpha and 3.8-kb RXR gamma mRNA by t-RA, suggesting that the regulations at least in part were at the transcriptional levels. The protein synthesis inhibitor, cycloheximide, induced the expression of 5.6-kb RXR alpha mRNA and further enhanced the inductive effect of t-RA. In contrast, cycloheximide prevented the t-RA-regulated expression of both 3.8- and 2.3-kb RXR gamma mRNA, suggesting that ongoing protein synthesis was required for the regulation of RXR gamma gene. In addition, c-RA exerted effects similar to those of t-RA on RXR gene expression. A concentration of 10(-8) M was required for c-RA to regulate the expression of RXR genes, while 10(-9) M of t-RA was effective in regulating RXR genes. Addition of t-RA and c-RA simultaneously had neither synergistic nor additive effects in regulating RXR gene expression. These data suggest that RAR may play an important role in RA-regulated RXR gene expression.
现已确定两类视黄酸（RA）核受体——视黄酸受体（RAR）和视黄醇X受体（RXR）。此前，我们证明全反式视黄酸（t-RA）能以不同方式自我调节RARα、β和γ转录本的表达。在本研究中，我们通过Northern印迹分析检测了t-RA和9-顺式视黄酸（c-RA）对F9细胞中RXR基因表达的影响。结果显示，t-RA增加了5.6 kb的RXRα和3.8 kb的RXRγ mRNA水平，降低了2.3 kb的RXRγ mRNA量，但对RXRβ mRNA水平无显著影响。将环磷酸腺苷类似物与t-RA一起添加可进一步诱导F9细胞分化为壁内胚层细胞，但未改变RXR mRNA的调控模式。RNA合成抑制剂放线菌素D可阻断t-RA对5.6 kb的RXRα和3.8 kb的RXRγ mRNA的诱导，这表明至少部分调控发生在转录水平。蛋白质合成抑制剂环己酰亚胺可诱导5.6 kb的RXRα mRNA表达，并进一步增强t-RA的诱导作用。相反，环己酰亚胺可阻止t-RA对3.8 kb和2.3 kb的RXRγ mRNA的调控表达，这表明RXRγ基因的调控需要持续的蛋白质合成。此外，c-RA对RXR基因表达的影响与t-RA相似。c-RA调节RXR基因表达所需的浓度为10^(-8) M，而10^(-9) M的t-RA对调节RXR基因有效。同时添加t-RA和c-RA在调节RXR基因表达方面既无协同作用也无相加作用。这些数据表明RAR可能在RA调节的RXR基因表达中起重要作用。
