Müller F U, Bokník P, Knapp J, Neumann J, Vahlensieck U, Oetjen E, Scheld H H, Schmitz W
Institut für Pharmakologie und Toxikologie, Universität Münster, Germany.
FASEB J. 1998 Sep;12(12):1191-9. doi: 10.1096/fasebj.12.12.1191.
In end-stage human heart failure, excessive beta-adrenergic stimulation of the cAMP-dependent signaling pathway due to enhanced endogenous catecholamines is hypothesized to contribute to expressional alterations of myocardial regulatory proteins. The cAMP response element modulator (CREM) regulates the transcription of cAMP-responsive genes and might be involved in the regulation of cardiac gene expression. Using the reverse transcription polymerase chain reaction, we identified a novel CREM mRNA, CREM-Ib deltaC-X, in the human heart. Overexpression of CREM-Ib deltaC-X decreased cAMP response element (CRE) -mediated gene transcription in HIT-T15 cells, and this activity was assigned to the part of the sequence encoding putative internally translated proteins. Two of three possible internally translated proteins were immunologically identified in cells overexpressing CREM-Ib deltaC-X tagged with the hemagglutinin epitope of the influenza virus. Both proteins were expressed in bacteria and showed CRE-specific DNA binding, formation of heterodimers with the cAMP response element binding protein (CREB), and inhibition of CREB's binding to the CRE. CREM expression was detected on the mRNA and protein levels in the human heart. We conclude that CREM-Ib deltaC-X generates internally translated repressors of CRE-mediated gene transcription, suggesting the first example for the existence and function of human cardiac CREM.
在终末期人类心力衰竭中，由于内源性儿茶酚胺增加，β-肾上腺素能对cAMP依赖性信号通路的过度刺激被认为会导致心肌调节蛋白的表达改变。cAMP反应元件调节剂（CREM）调节cAMP反应基因的转录，可能参与心脏基因表达的调控。利用逆转录聚合酶链反应，我们在人类心脏中鉴定出一种新的CREM mRNA，即CREM-Ib deltaC-X。CREM-Ib deltaC-X的过表达降低了HIT-T15细胞中cAMP反应元件（CRE）介导的基因转录，并且这种活性归因于编码推定的内部翻译蛋白的序列部分。在过表达带有流感病毒血凝素表位标签的CREM-Ib deltaC-X的细胞中，通过免疫鉴定出三种可能的内部翻译蛋白中的两种。这两种蛋白都在细菌中表达，并表现出CRE特异性DNA结合、与cAMP反应元件结合蛋白（CREB）形成异二聚体以及抑制CREB与CRE的结合。在人类心脏的mRNA和蛋白水平上均检测到了CREM的表达。我们得出结论，CREM-Ib deltaC-X产生CRE介导的基因转录的内部翻译阻遏物，这提示了人类心脏CREM存在及其功能的首个实例。
