IDENTIFICATION OF A CALCIUM-INDUCIBLE, EPIDERMAL-SPECIFIC REGULATORY ELEMENT IN THE 3'-FLANKING REGION OF THE HUMAN KERATIN-1 GENE

Previous studies have shown that the process of epidermal differentiation is profoundly influenced by the level of intracellular calcium within keratinocytes. In this study we have identified a 249-bp region, located 7.9 kb downstream from the promoter of the human keratin 1 (HK1) gene, that is able to activate a SV40 minimal promoter chloramphenicol acetyl transferase (CAT) construct in transfected murine keratinocytes. This activity was potentiated by increased levels of calcium and was independent of the position and orientation of the 249-bp fragment. The 249-bp fragment demonstrated a marked specificity for epidermal keratinocytes and was not active in fibroblasts or in a breast epithelial cell line. Moreover, this fragment could activate CAT expression in a construct driven by the HK1 promoter, which alone had no intrinsic CAT activity. A 102-bp fragment derived from the 249-bp fragment was still responsive to calcium but no longer retained cell-type specificity. An AP-1 site at position +7903 and encoded by both the 249-bp and 102-bp fragments is implicated as the cis-element that mediates the calcium response. Taken collectively, these data identify and characterize a regulatory element that is able to activate both heterologous or homologous promoters in response to increased levels of intracellular calcium in keratinocytes.