Abstract
The ABCC1 gene is structurally and functionally related to the cystic fibrosis transmembrane conductance regulator gene (CFTR). Upregulation of ABCC1 is thought to improve lung function in patients with cystic fibrosis (CF); the mechanism underlying this effect is unknown. We analyzed the ABCC1 promoter single nucleotide polymorphism (SNP rs504348), plasma-induced ABCC1 mRNA expression levels, and ABCC1 methylation status and their correlation with clinical variables among CF subjects with differing CFTR mutations. We assigned 93 CF subjects into disease severity groups and genotyped SNP rs504348. For 23 CF subjects and 7 healthy controls, donor peripheral blood mononuclear cells (PBMCs) stimulated with plasma underwent gene expression analysis via qRT-PCR. ABCC1 promoter methylation was analyzed in the same 23 CF subjects. No significant correlation was observed between rs504348 genotypes and CF disease severity, but pancreatic insufficient CF subjects showed increased colonization with any form of Pseudomonas aeruginosa (OR = 3.125, 95% CI: 1.192–8.190) and mucoid P. aeruginosa (OR = 5.075, 95% CI: 1.307–28.620) compared to the pancreatic sufficient group. A significantly higher expression of ABCC1 mRNA was induced by CF plasma compared to healthy control plasma (p < 0.001). CF subjects with rs504348 (CC/CG) also had higher mRNA expression compared to those with the ancestral GG genotype (p < 0.005). ABCC1 promoter was completely unmethylated; therefore, we did not detect any association between methylation and CF disease severity. In silico predictions suggested that histone modifications are crucial for regulating ABCC1 expression in PBMCs. Our results suggest that ABCC1 expression has a role in CFTR activity thereby increasing our understanding of the molecular underpinnings of the clinical heterogeneity in CF.
Highlights
Cystic fibrosis (CF) is a heritable multisystem disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene [1,2]
We investigated the ABCC1 promoter single nucleotide polymorphism (SNP) rs504348 by measuring plasma-induced ABCC1 mRNA expression levels, and rs504348 ABCC1 promoter methylation in CF subjects with differing CFTR genotypes
We correlated these molecular measures with clinical status to better understand the molecular mechanisms linking increased expression of ABCC1 and improved lung function observed in CF patients
Summary
Cystic fibrosis (CF) is a heritable multisystem disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene [1,2]. Modifier genes that may impact CF disease severity are emerging keys to deciphering clinical heterogeneity [4,5,6,7]. The gene encoding the multidrug resistance-associated protein 1, ABCC1/MRP1, is a candidate for further molecular investigation based on its structural and functional association with CFTR [8,9]. ABCC1, as well as CFTR (ABCC7) and 11 other genes associated with multidrug resistance, are subfamily C members of the ATP-binding cassette (ABC) transporter genes [10]. CFTR is unique among the ABC subfamily C members of transporters due to its intrinsic ability to conduct chloride ions at a fast rate [12,13,14], but it shares its closest homology with ABCC1 [9,15,16]
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