Abstract
In the heart of adult animals, the hyperpolarization-activated cation channel (HCN4) is exclusively expressed in the pacemaker cells. HCN4 is expressed in the ventricle of fetal heart, and is re-expressed in the ventricle of hypertrophied heart. In order to clarify the transcriptional mechanisms of HCN4 gene, promoter activity was explored using luciferase reporter assay in primary cultured myocytes isolated form embryonic (E12.5) or neonatal (P1-2) rat heart. The hypertrophic stimuli with phenylephrine (50 μM) and endothelin-1 (50 nM) were applied to neonatal myocytes. The promoter deletion analysis showed that proximal –847 bp fragment acted as a minimal promoter both in fetal and neonatal myocytes. The activity of the minimal promoter was significantly higher in embryonic myocyte than in neonatal myocyte, and was insensitive to hypertrophic stimuli. The first intron of hcn4 possesses NRSE, a cis-acting element of neuron-restrictive silencing factor (NRSF). When ~3 kb intron fragment containing NRSE was fused to the minimal promoter of HCN4, promoter activity was highly repressed in neonatal myocytes, whereas the repression was much weaker in fetal myocytes. The hypertrophic stimuli reversed the transcriptional suppression by NRSE-NRSF system. We concluded that multiple cis-acting elements were involved in the transcription of HCN4, and they play different roles in the development and in hypertrophic stimuli. [Jpn J Physiol 54 Suppl:S100 (2004)]
