Tetradis S, Nervina J M, Nemoto K, Kream B E
Department of Oral Diagnosis, School of Dental Medicine, The University of Connecticut Health Center, Farmington, Connecticut, USA.
J Bone Miner Res. 1998 Dec;13(12):1846-51. doi: 10.1359/jbmr.1998.13.12.1846.
Parathyroid hormone (PTH) regulates gene expression in skeletal osteoblasts mainly through the cAMP-protein kinase A (PKA) pathway. In neuroendocrine cells, activation of the cAMP-PKA signaling pathway leads to induction of the inducible cAMP early repressor (ICER), which is transcribed from an intronic promoter of the CREM gene and acts as a transcriptional repressor. To investigate whether PTH induces ICER expression in osteoblastic cells, RNA from MC3T3-E1 cells was subjected to reverse transcriptase-polymerase chain reaction using primers spanning the ICER sequence. Amplified products were subcloned, sequenced, and used as a probe for Northern blot analysis. In MC3T3-E1 cells, PTH induced ICER mRNA levels, which peaked at 2 h and declined to baseline by 8 h. Cycloheximide caused superinduction of ICER mRNA in response to PTH. In cultured mouse calvariae, PTH also induced ICER mRNA accumulation, which peaked at 2 h and returned almost to baseline by 10 h. Overexpression of ICER IIgamma decreased both baseline and PTH-stimulated prostaglandin G/H synthase 2 promoter activity in MC3T3-E1 cells. The induction of ICER represents a novel mechanism by which PTH regulates gene expression in osteoblastic cells.
甲状旁腺激素（PTH）主要通过环磷酸腺苷 - 蛋白激酶A（PKA）途径调节骨骼成骨细胞中的基因表达。在神经内分泌细胞中，环磷酸腺苷 - PKA信号通路的激活会导致诱导型环磷酸腺苷早期阻遏物（ICER）的诱导，ICER由CREM基因的内含子启动子转录而来，并作为转录阻遏物发挥作用。为了研究PTH是否在成骨细胞中诱导ICER表达，使用跨越ICER序列的引物对MC3T3 - E1细胞的RNA进行逆转录 - 聚合酶链反应。扩增产物被亚克隆、测序，并用作Northern印迹分析的探针。在MC3T3 - E1细胞中，PTH诱导ICER mRNA水平升高，在2小时达到峰值，并在8小时降至基线水平。放线菌酮导致ICER mRNA对PTH的超诱导。在培养的小鼠颅骨中，PTH也诱导ICER mRNA积累，在2小时达到峰值，并在10小时几乎恢复到基线水平。ICER IIγ的过表达降低了MC3T3 - E1细胞中基线和PTH刺激的前列腺素G/H合酶2启动子活性。ICER的诱导代表了PTH调节成骨细胞中基因表达的一种新机制。
