A calcium responsive element that regulates expression of two calcium binding proteins in Purkinje cells

Calbindin D28 encodes a calcium binding protein that is expressed in the cerebellum exclusively in Purkinje cells. We have used biolistic transfection of organotypic slices of P12 cerebellum to identify a 40-bp element from the calbindin promoter that is necessary and sufficient for Purkinje fell specific expression in this transient ipl situ assay, This element (PCE1) is also present in the calmodulin TI promoter, which regulates expression of a second Purkinje cell Ca2+ binding protein, Expression of high levels of exogenous calbindin or calretinin decreased transcription mediated by PCE1 in Purkinje cells 2.5- to 3-fold, whereas the presence of 1 mu M ionomycin in the extracellular medium increased expression, These results demonstrate that PCE1 is a component of a cell-specific and Ca2+-sensitive transcriptional regulatory mechanism that may play a key role in setting the Ca2+ buffering capacity of Purkinje cells.