Pearson D, Sasse J
Shriners Hospital for Crippled Children, Tampa Unit, Florida 33612-9499.
J Biol Chem. 1992 Dec 15;267(35):25364-70.
The small, leucine-rich proteoglycans, decorin and biglycan, are prominent components of many extracellular matrices and are differentially regulated in various tissues. We have examined the effects of retinoic acid (RA) on the expression of biglycan and decorin at the protein and mRNA levels in cultured bovine articular chondrocytes. Biglycan protein expression is rapidly turned off after 1-2 days of treatment with RA. In contrast, decorin protein expression is increased 12-18-fold following 3 days of RA treatment. The level of biglycan mRNA was also rapidly reduced upon RA treatment, mirroring the protein expression. The reduction was apparent by 6 h, and, by 4 days, the levels were nearly undetectable. In contrast, decorin mRNA was induced upon treatment with RA. The increase in decorin message levels was first apparent by 24 h, reaching maximum by 2 days, and remained constant through 4 days. The repression of biglycan mRNA displayed equal sensitivity to RA concentrations from 10(-5) to 10(-9) M. Decorin mRNA was induced in a dose-dependent fashion by RA. Retinoic acid at a concentration of 10(-5) M, the highest dose examined, resulted in maximal induction of the message, and control levels were obtained with 10(-8) M. The protein synthesis inhibitor cycloheximide inhibited the induction of decorin mRNA, indicating that the induction by RA was a secondary event. In contrast, the repression of biglycan by RA was not significantly altered by cycloheximide, showing that the repression was a direct effect. Actinomycin D inhibited the induction of decorin mRNA, indicating that transcription was required for the induction. Nuclear run-on assays confirmed that RA was regulating biglycan mRNA expression at the transcription level. A 24-h RA treatment decreased the level of transcription of the biglycan gene 5-fold. In contrast, no increase in transcription from the decorin gene could be detected by nuclear run-on assays. Therefore, the elevation in decorin mRNA levels observed after RA treatment was the result of a post-transcriptional event, most likely the consequence of stabilization of the message. This study demonstrates that the genes for these two similar proteoglycans are under very different forms of regulation by RA in chondrocytes. The pattern of differential expression of biglycan and decorin could serve as an additional marker for indicating changes of the cartilage phenotype.
富含亮氨酸的小分子蛋白聚糖核心蛋白聚糖和双糖链蛋白聚糖是许多细胞外基质的重要组成部分，在不同组织中受到不同的调控。我们研究了视黄酸（RA）对培养的牛关节软骨细胞中双糖链蛋白聚糖和核心蛋白聚糖在蛋白质和mRNA水平表达的影响。用RA处理1 - 2天后，双糖链蛋白聚糖的蛋白质表达迅速关闭。相反，经RA处理3天后，核心蛋白聚糖的蛋白质表达增加了12 - 18倍。RA处理后，双糖链蛋白聚糖mRNA水平也迅速降低，与蛋白质表达情况一致。6小时时这种降低就很明显，到4天时，其水平几乎检测不到。相比之下，RA处理可诱导核心蛋白聚糖mRNA表达。核心蛋白聚糖mRNA水平的增加在24小时时首次明显出现，2天时达到最大值，并在4天内保持稳定。双糖链蛋白聚糖mRNA的抑制对10(-5)至10(-9) M的RA浓度表现出相同的敏感性。RA以剂量依赖的方式诱导核心蛋白聚糖mRNA表达。浓度为10(-5) M（所检测的最高剂量）的视黄酸导致该mRNA的最大诱导，而10(-8) M时获得对照水平。蛋白质合成抑制剂放线菌酮抑制了核心蛋白聚糖mRNA的诱导，表明RA的诱导是一个次级事件。相反，放线菌酮对RA抑制双糖链蛋白聚糖的作用没有显著改变，表明这种抑制是直接作用。放线菌素D抑制了核心蛋白聚糖mRNA的诱导，表明诱导需要转录。核转录分析证实RA在转录水平调控双糖链蛋白聚糖mRNA表达。24小时的RA处理使双糖链蛋白聚糖基因的转录水平降低了5倍。相反，通过核转录分析未检测到核心蛋白聚糖基因转录增加。因此，RA处理后观察到的核心蛋白聚糖mRNA水平升高是转录后事件的结果，很可能是mRNA稳定化的结果。这项研究表明，在软骨细胞中，这两种相似的蛋白聚糖的基因受到RA非常不同形式的调控。双糖链蛋白聚糖和核心蛋白聚糖的差异表达模式可作为指示软骨表型变化的另一个标志物。
