Characterization of human B creatine kinase gene regulation in the heart in vitro and in vivo

During cardiogenesis, genes indicative of the adult phenotype are transcriptionally activated while genes characteristic of the embryonic phenotype are down-regulated. The regulation of embryonic genes such as the brain isoform of creatine kinase (BCK) during cardiac development has not been characterized. Accordingly, the transcriptional regulation of BCK in the developing heart was determined. In vitro and in vivo promoter analyses of the human BCK gene identified an element between +25 and +57 that functioned as an enhancer. Electromobility shift assays using adult and neonatal nuclear extracts identified a specific complex binding this element, the abundance of which correlated with the developmental level of endogenous cardiac BCK expression. Mutations at +47 and +53 led to a loss of activity in transfected cells and obviated binding in electromobility shift assays. These data show that a nuclear factor in cardiocytes interacts with an enhancer element (+25 and +57), via nucleotides +47 and +53, to drive BCK expression in the heart and suggest that developmental BCK expression is via abundance of this factor. The nuclear factor has not been identified but as described previously binding sites are not present in the enhancer, it is either a known factor interacting with a new recognition site or a new factor.