CFTR mRNA expression is regulated by an upstream open reading frame and RNA secondary structure in its 5′ untranslated region

Post-transcriptional regulation of gene expression through 5' untranslated region (5' UTR)-encoded cis-acting elements is an important mechanism for the control of protein expression levels. Through controlling specific aspects of translation initiation, expression can be tightly regulated while remaining responsive to cellular requirements. With respect to cystic fibrosis (CF), the overexpression of cystic fibrosis transmembrane conductance regulator (CFTR) protein trafficking mutants, such as delta-F508, is of great biological and clinical interest. By understanding the post-transcriptional mechanisms that regulate CFTR expression, new procedures can be developed to enhanceCFTRexpression inhomozygous delta-F508 CFpatients. Wehave identified the keyelements ofacomplex negative regulatorymechanismthat isencodedwithin thehumanCFTR5' UTRand show how these elements act in combination to restrict CFTR gene expression to a consistently low level in a transcript-specific manner. This study shows, for the first time, that endogenous human CFTR expression is post-transcriptionally regulated through a 5' UTR-mediated mechanism. We show that the very low levels of endogenous CFTR expression, compared with other low expression genes, are maintained through the cooperative inhibitory effects of an upstream open reading frame and a thermodynamically stable RNA secondary structure.