Carbonic anhydrases in human keratinocytes and their regulation by all-trans retinoic acid and 1α,25-dihydroxyvitamin D₃

Carbonic anhydrases (CAs) are ubiquitously expressed enzymes and catalyse an important physiological reaction of interconverting the hydration of carbon dioxide to bicarbonates, which is crucial for maintaining acid/base equilibrium in certain tissues. While 15 different isoforms of CAs are present in various cell types in human tissues, their expression pattern in the epidermis remains to be investigated. Here, we report the expression of 5 CA isoforms (CAII, CAIX, CAXI, CAXII and CAXIII) in human primary keratinocytes. Further, we demonstrate that the expression of CAII and CAIX in these cells is significantly up-regulated by the biologically active metabolites of vitamin A (all-trans retinoic acid) and vitamin D (1α,25-dihydroxyvitamin D₃), respectively. Taken together, apart from providing new information on the expression of CAs in the skin, our results highlight a previously undisclosed connection between vitamin A and CAII expression and vitamin D and CAIX expression.