The expression of the cystic fibrosis transmembrane conductance regulator (CFTR) gene can be downregulated by inflammatory stimuli such as phorbol myristate acetate (PMA). Since the respiratory manifestations of cystic fibrosis (CF) are characterized by intense chronic airway inflammation very early in life, successful gene therapy for CF will require that expression of the transferred normal CFTR gene be resistant to down-regulation by inflammatory mediators. To evaluate the concept that a viral promoter- human CFTR cDNA unit would be resistant to this form of down-regulation, a retrovirus promoter (5′ long terminal repeat of the Moloney murine leukemia virus) - human CFTR cDNA unit was transferred to T84 human colon carcinoma cell line using a retrovirus vector. Exposure of the retrovirus-modified T84 cells to PMA resulted in down-regulation of the endogenous CFTR mRNA transcripts (6.5 kb), but did not affect the level of exogenous CFTR transcripts (8.0 kb). Importantly, in parallel with the persistence of the exogenous CFTR transcripts, the modified cells still maintained cAMP-regulated Cl- secretion in the presence of PMA. These in vitro data suggest that a constitutive viral promoter -CFTR cDNA unit should be resistant to modulation by inflammatory stimuli, a likely requirement for successful gene therapy for CF.
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