The detection and significance of cystic fibrosis transmembrane conductance regulator gene promoter mutations in Chinese patients with congenital bilateral absence of the vas deferens

Abstract

Objective: Mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR) gene can be involved in the development of congenital bilateral absence of the vas deferens (CBAVD). This study was aimed at investigating mutations in the promoter region of the CFTR gene and its associated effects on CFTR transcription in Chinese patients with CBAVD.

Methods: To identify CFTR promoter region mutations in Chinese CBAVD patients, fragments 1.4 kb upstream of the ATG start codon of the CFTR gene were sequenced in 66 Chinese patients with CBAVD and compared to the corresponding sequences from 60 healthy subjects and sequence data present in the NCBI database. The relationship between the mutations and gene regulation was explored using Transfac analysis and a phylogenetic footprint method. Plasmids were constructed by incorporating statistically significant variant sequences. The effects of the mutations on CFTR transcription were investigated using a dual luciferase reporter gene assay.

Results: a total of six point mutations, which included c.-150G > T, c.-205 T > C, c.-245C > T, c.-871G > T, c.-966 T > G and c.-1062G > C, and one deletion mutation, namely c.-861delT, were identified in the promoter region of the CFTR gene in Chinese CBAVD patients. Among them, c.-966 T > G had the highest frequency and presented in either a homozygous or heterozygous mutation state. The frequency of G/G genotype in the CBAVD group was 33/66 (50.00%), while the T/G and T/T genotypes had frequencies of 18/66 (27.27%) and 15/66 (22.73%), respectively. A significant difference was found between the CBAVD and control group (P < 0.01). The locus for this variant was found in a conserved sequence. The Transfac tool showed that transcription factors EHF and STAT3, which are closely associated with reproduction, can bind to the sequence containing the variant locus. Two types of plasmid vectors, one carrying the G/G variant and the other the wild type T/T sequences, were constructed and respectively transfected into human cervical cancer cells (HeLa), human renal epithelial cells (HEK-293), and human colon cancer cells (SW480). It was found that the homozygous c.-966 T > G mutation significantly reduced CFTR transcription efficiency by 18.75%-35.50%.

Conclusion: Mutations in the promoter region of the CFTR gene in Chinese CBAVD patients are different from those found in comparable Caucasian patients. The homozygous c.-966 T > G mutation state had the highest frequency, which reduced the CFTR transcriptional level and showed significant tissue-specificity.

Keywords: Intron; Luciferase reporter gene; Non-coding region; Promoter; Sequencing.