Epithelial Cl- channels mediate Cl- and fluid secretion in the lung. In cystic fibrosis, aberrant Cl- secretion is one of the major causes for lung fluid imbalance. Regulation of Cl- channels is therefore an important issue in the lung. IFN-gamma regulates Na+ and Cl- channels and fluid transport in the lung, but the mechanisms involved in these regulations are not clear. In expression studies, we found that IFN-gamma increased ClC-2 transcripts in Calu-3 cells. Studies of the promoter identified a minimal promoter Which interacts with transcription factors Sp1 and Sp3. However, reporter gene assays showed that IFN-gamma did not activate the promoter. Instead, IFN-gamma significantly increased ClC-2 transcript stability. Using Ussing chamber experiments, we demonstrate that IFN-gamma activates a pH-regulated and Cd2+-sensitive short circuit current, characteristic properties of the ClC-2 Cl- channel. These data suggest that IFN-gamma activates ClC-2 channel activity in lung epithelial cells via mRNA stabilization. (C) 2004 Elsevier Inc. All rights reserved.