Pomerance Martine, Carapau Daniel, Chantoux Françoise, Mockey Michaël, Correze Claude, Francon Jacques, Blondeau Jean-Paul
Unité 486, Institut National de la Santé et de la Recherche Médicale-Paris XI, Faculté de Pharmacie, 5 rue Jean-Baptiste Clément, 92296 Châtenay-Malabry Cédex, France.
Mol Endocrinol. 2003 Nov;17(11):2283-94. doi: 10.1210/me.2002-0400. Epub 2003 Aug 7.
The cAMP pathway activates p38-MAPKs in the FRTL-5 rat thyroid cell line, contributing to the increased expression of the Na+/I- symporter (NIS) mRNA. This study investigates the cAMP-dependent expression and transcriptional activity of the p38-MAPK substrate CCAAT/enhancer-binding protein-homologous protein (CHOP). CHOP is expressed in the rat thyroid gland and in confluent PCCL3 and FRTL-5 cells. In FRTL-5 cells, TSH withdrawal induced a rapid down-regulation of CHOP that could be prevented by forskolin (Fk). Moreover, TSH and Fk were able to reinduce CHOP expression. The use of pharmacological inhibitors indicated that cAMP-induced CHOP expression was dependent on protein kinase A (PKA), mammalian target of rapamycin pathway, and reactive oxygen species. Transfection of a CHOP trans- reporting system revealed strong stimulation of the transcriptional activity of CHOP by Fk, by chlorophenylthio-cAMP, and by the catalytic subunit of PKA. CHOP transcriptional activity was significantly reduced by the p38-MAPK inhibitor SB203580, by transfection of a dominant-negative variant of p38alpha-MAPK, or by mutation of two serine residues in CHOP targeted by p38-MAPKs. Finally, cAMP-induced NIS mRNA expression was higher in FRTL-5 cells stably transfected with CHOP cDNA than in control cells. Likewise, the activity of the NIS promoter was higher in cells overexpressing CHOP than in control cells. These findings suggest that the stimulation of CHOP expression and transcriptional activity by the cAMP pathway may contribute to the regulation of genes involved in thyroid cell differentiation.
环磷酸腺苷（cAMP）信号通路可激活FRTL-5大鼠甲状腺细胞系中的p38丝裂原活化蛋白激酶（p38-MAPKs），促使钠/碘同向转运体（NIS）mRNA表达增加。本研究探讨了p38-MAPK底物CCAAT/增强子结合蛋白同源蛋白（CHOP）的cAMP依赖性表达及转录活性。CHOP在大鼠甲状腺、汇合的PCCL3细胞和FRTL-5细胞中均有表达。在FRTL-5细胞中，促甲状腺激素（TSH）撤除可导致CHOP迅速下调，而福斯可林（Fk）可阻止这种下调。此外，TSH和Fk能够重新诱导CHOP表达。药理学抑制剂的使用表明，cAMP诱导的CHOP表达依赖于蛋白激酶A（PKA）、雷帕霉素哺乳动物靶标信号通路和活性氧。CHOP反式报告系统的转染显示，Fk、氯苯硫代环磷酸腺苷（chlorophenylthio-cAMP）和PKA催化亚基可强烈刺激CHOP的转录活性。p38-MAPK抑制剂SB203580、转染p38α-MAPK的显性负变体或突变CHOP中被p38-MAPKs靶向的两个丝氨酸残基，均可显著降低CHOP的转录活性。最后，稳定转染CHOP cDNA的FRTL-5细胞中，cAMP诱导的NIS mRNA表达高于对照细胞。同样，过表达CHOP的细胞中NIS启动子的活性也高于对照细胞。这些发现表明，cAMP信号通路对CHOP表达和转录活性的刺激可能有助于调节参与甲状腺细胞分化的基因。
