Cyclic AMP and alkaline pH downregulate carbonic anhydrase 2 in mouse fibroblasts

Background: The hydration of CO2 catalyzed by the ubiquitous carbonic anhydrase 2 (Ca2) is central for bicarbonate transport, bone metabolism and acid-base homeostasis in metazoans. There is evidence that in some tissues Ca2 expression can be acutely induced by cAMP, whereas in other cell types it is unresponsive to cAMP-mediated transcriptional activation. Methods: We isolated fibroblasts from wild type and mice lacking the ubiquitous chloride/bicarbonate exchanger (Ae2(a,b)(-/-)mice). In these cells the regulation of carbonic anhydrase 2 by cAMP was studied. Results: We show that Ca2 expression is strongly inhibited by chronic incubation with dibutyryl-cAMP, forskolin or alkaline pH in cultured mouse fibroblasts. Furthermore, fibroblasts obtained from anion exchanger 2 deficient (Ae2(a,b)(-/-)) mice, which display intracellular alkalosis and increased cAMP production, express less than 10% of control Ca2 mRNA and protein. Surprisingly, inhibition of the bicarbonate-sensitive soluble adenylyl cyclase (SAC) was found to reduce CA2 expression instead of increasing it. Conclusions: CA2 expression is strongly regulated by intracellular pH and by cAMP, suggesting a role for soluble adenylyl cyclase. Regulation occurs in opposite directions which may be explained by an incoherent feedforward loop consisting of activation by pCREB and repression by ICER. (C) 2013 Elsevier B.V. All rights reserved.