Characterization of the cardiac KCNE1 gene promoter

KCNE1 encodes an essential cardiac slow delayed-rectifier potassium current (I(Ks)) beta-subunit (minK). Varying minK expression is important in disease-related remodeling and species-dependent expression. This study addressed 5'-regulatory elements that potentially control KCNE1 transcription.

The transcriptional start site of human KCNE1 (HKCNE1) was determined with 5'RACE. Of four isoforms, the putative promoter driving the isoforms constituting >80% expression in human hearts was further analyzed. A 1625-bp region 5' to the transcriptional start site was subcloned into luciferase-reporter plasmid (PGL3-Basic). The full promoter sequence increased luciferase expression 31-fold in neonatal rat cardiomyocytes (NRMs). A much smaller 327-bp core promoter maintained activity 21-29 fold. The core promoter conferred cardiomyocyte-preferential expression, with an activity in NRMs 4.9-fold greater than in Chinese Hamster Ovary cells (CHOs), compared to approximately 2.0 for the full-length promoter. Site-directed mutagenesis of all three GATA elements in the core promoter reduced its activity by >50% and attenuated cardiomyocyte-preferential expression. Mutagenesis of the second GATA element alone decreased promoter activity by approximately 50%. GATA4 knockdown with siRNA inhibited approximately 40% of core promoter activity in NRMs. Angiotensin-II increased HKCNE1 promoter activity, but only in the presence of intact GATA elements. The typically low-level I(Ks) expression in mouse and rabbit is related to low minK expression. Cloning of the mouse KCNE1 (MKCNE1) 5'-regulatory region showed approximately 50% sequence identity to human. MKCNE1 had only 1 GATA element in the region corresponding to the human core promoter and had less promoter activity (11.7 vs 29.0-fold PGL3-Basic for human).

Promoter elements in the HKCNE1 5'-end, particularly GATA binding sites, may be important in tissue, disease and species-related transcriptional regulation of I(Ks).