Induction of expression of the cystic fibrosis transmembrane conductance regulator.

The cystic fibrosis transmembrane conductance regulator (CFTR) was studied in HT-29 human colonic carcinoma cells with the aim of assessing possible mechanisms of up-regulation of its expression. CFTR was identified and quantified in total cell extracts by Western immunoblots using a monoclonal anti-CFTR antibody and was functionally assessed by tracer Cl-efflux from intact cells. It was found that various stimuli that lead to a sustained (greater than or equal to 8 h) elevation of intracellular cyclic AMP elicited a marked and specific increase in CFTR expression in cell membranes and concomitant activation of Cl- secretion. Further activation of Cl- secretion was obtained by additional short term activation by cyclic AMP analogues or cyclic AMP-inducing agents. Blockers of transcription or translation largely depressed the cAMP-mediated induction of CFTR levels and associated function, indicating that the inductive phenomenon was at the transcriptional level. The results imply the involvement of putative cyclic AMP responsive (and related) elements that are present in the CFTR gene promoter and that are known to modulate eukaryotic gene expression. Activation of these elements by various stimuli might provide pharmacological tools for up-regulation of CFTR expression at both biochemical and physiological levels.