Nugent P, Potchinsky M, Lafferty C, Greene R M
Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Exp Cell Res. 1995 Oct;220(2):495-500. doi: 10.1006/excr.1995.1341.
We have previously shown that both transforming growth factor-beta (TGF-beta) and retinoic acid (RA) regulate the expression of cellular retinoic acid binding proteins (CRABP) I and II and TGF-beta 3 mRNAs in primary cultures of murine embryonic palate mesenchymal (MEPM) cells. We now describe additional cross-talk between the RA and TGF-beta signal transduction pathways--the ability of TGF-beta, including the endogenous form(s), to modulate the expression of the nuclear retinoic acid receptor-beta (RAR-beta). Northern blot hybridization revealed that RA induced the expression of RAR-beta mRNA, there being little or no detectable expression in untreated MEPM cells. Induction by 3.3 microM RA was abrogated by simultaneous treatment with TGF-beta 1 (5 ng/ml). TGF-beta 1 alone had no effect on RAR-beta mRNA expression. Determination of RAR-beta mRNA half-life by treatment with actinomycin D indicated that TGF-beta 1 did not alter the stability of RAR-beta mRNA. Conditioned medium (CM) from MEPM cells contained little active TGF-beta protein; heat treatment of the CM dramatically increased the amount of active TGF-beta as assessed by the mink lung epithelial cell bioassay. Furthermore, heat- or acid-activated CM also inhibited CRABP-I and RA-induced RAR-beta expression. The effect of heat-activated conditioned medium could be abrogated with panspecific neutralizing antibodies to TGF-beta, confirming that endogenous TGF-beta is the biologically active factor in heat-activated CM. These results provide evidence for complex interactions between TGF-beta and RA in the regulation of gene expression in embryonic palatal cells and suggest a role for endogenous TGF-beta in the regulation of expression of genes encoding elements of the RA signal transduction pathway.
我们先前已经表明，转化生长因子-β（TGF-β）和视黄酸（RA）均可调节小鼠胚胎腭间充质（MEPM）细胞原代培养物中细胞视黄酸结合蛋白（CRABP）I和II以及TGF-β3 mRNA的表达。我们现在描述RA和TGF-β信号转导途径之间的额外相互作用——TGF-β（包括内源性形式）调节核视黄酸受体-β（RAR-β）表达的能力。Northern印迹杂交显示，RA诱导RAR-β mRNA的表达，在未处理的MEPM细胞中几乎没有可检测到的表达。同时用TGF-β1（5 ng/ml）处理可消除3.3 μM RA的诱导作用。单独的TGF-β1对RAR-β mRNA表达没有影响。用放线菌素D处理测定RAR-β mRNA半衰期表明，TGF-β1不会改变RAR-β mRNA的稳定性。MEPM细胞的条件培养基（CM）中含有少量活性TGF-β蛋白；通过貂肺上皮细胞生物测定法评估，CM的热处理显著增加了活性TGF-β的量。此外，热激活或酸激活的CM也抑制CRABP-I和RA诱导的RAR-β表达。热激活条件培养基的作用可用TGF-β的泛特异性中和抗体消除，证实内源性TGF-β是热激活CM中的生物活性因子。这些结果为TGF-β和RA在胚胎腭细胞基因表达调节中的复杂相互作用提供了证据，并表明内源性TGF-β在调节RA信号转导途径元件编码基因的表达中起作用。
