The mitochondrial complex I activity is reduced in cells with impaired cystic fibrosis transmembrane conductance regulator (CFTR) function.

Cystic fibrosis (CF) is a frequent and lethal autosomal recessive disease. It results from different possible mutations in the CFTR gene, which encodes the CFTR chloride channel. We have previously studied the differential expression of genes in CF and CF corrected cell lines, and found a reduced expression of MTND4 in CF cells. MTND4 is a mitochondrial gene encoding the MTND4 subunit of the mitochondrial Complex I (mCx-I). Since this subunit is essential for the assembly and activity of mCx-I, we have now studied whether the activity of this complex was also affected in CF cells. By using Blue Native-PAGE, the in-gel activity (IGA) of the mCx-I was found reduced in CFDE and IB3-1 cells (CF cell lines) compared with CFDE/6RepCFTR and S9 cells, respectively (CFDE and IB3-1 cells ectopically expressing wild-type CFTR). Moreover, colon carcinoma T84 and Caco-2 cells, which express wt-CFTR, either treated with CFTR inhibitors (glibenclamide, CFTR(inh)-172 or GlyH101) or transfected with a CFTR-specific shRNAi, showed a significant reduction on the IGA of mCx-I. The reduction of the mCx-I activity caused by CFTR inhibition under physiological or pathological conditions may have a profound impact on mitochondrial functions of CF and non-CF cells.

CISD1 codifies a mitochondrial protein upregulated by the CFTR channel.

Cystic fibrosis (CF) is an autosomic recessive disease caused by mutations in the CFTR chloride channel, which indirectly affect the expression of a net of genes. Here we describe a new CFTR-dependent gene, CISD1, encoding for the first member of a family of proteins possessing a CDGSH signature. CISD1 mRNA is down-regulated in cystic fibrosis cells, and restored in the same cells ectopically expressing wt-CFTR (CFDE and CFDE/6RepCFTR; IB3-1 and S9 cells). Inhibition of CFTR chloride transport activity by using glibenclamide (50muM, 24h) or CFTR(inh)-172 (5muM, 24h), resulted in the down-regulation of CISD1 mRNA, and CFTR stimulation with cAMP/isoproterenol/IBMX upregulated its expression. As predicted by PSORT II, a CISD1-GFP chimera was found to be located into mitochondria, suggesting a possible role in the function/regulation of mitochondrial activity, in agreement with earlier observations of a possible mitochondrial failure in cystic fibrosis.