Molecular cloning and analysis of the human cardiac sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA2) gene promoter

The sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA2) plays a critical role in regulating Ca²⁺ movements in myocardium. In cardiac hypertrophy and human heart failure, the decrease in mRNA and protein levels of SERCA2 might account for the reduced diastolic Ca²⁺ re-uptake seen in these conditions. To investigate the regulation of human SERCA2 gene expression, an 18.6-kb human genomic clone that contains exons 1, 2 and 3 of the SERCA2 gene has been isolated, and 13 kb of 5' upstream flanking sequence of which the proximal 2.5 kb of the promoter have been sequenced. Similar to the rabbit gene, the human SERCA2 promoter possesses a TATA-like box (-25 bp), a CAAT-box (-78 bp) and a number of consensus cis-regulatory elements including three Sp1 sites, a CACCC-box, and an OTF-1 binding sequence. No CArG box (present in the rabbit SERCA2 promoter) was identified in the human proximal promoter. Two putative thyroid response elements (TRE) are also present, suggesting that the human SERCA2 gene is also regulated by thyroid hormone as are the rat and rabbit genes. To study transcriptional activity of the human SERCA2 promoter in vitro, luciferase reporter plasmids containing a series of 5' deleted promoter constructs from -2577 bp to +170 bp were transfected into neonatal rat cardiomyocytes and C2C12 myotubes. The results suggest that: (a) the sequences from the transcription start site to -263 bp are necessary to obtain maximal transcriptional activity; (b) sequences from the transcription start site to -125 bp are essential for basal transcriptional activity; (c) at least one positive regulatory element is located between -263 bp and -125 bp; and (d) at least one negative regulatory element is present between -1741 bp and -412 bp.