Alternative splicing of intron 23 of the human cystic fibrosis transmembrane conductance regulator gene resulting in a novel exon and transcript coding for a shortened intracytoplasmic C terminus.

K Yoshimura,C.S Chu,R.G Crystal

doi:10.1016/s0021-9258(18)54206-x

Abstract

The cystic fibrosis transmembrane conductance regulator (CFTR) gene, the gene responsible for the lethal hereditary disorder cystic fibrosis, codes for a membrane protein functioning as a cAMP-regulated Cl- channel. Evaluation of human CFTR mRNA transcripts from epithelial and nonepithelial cells demonstrated a CFTR cDNA containing a 260-base pair (bp) insertion between the known CFTR exons 23 and 24, introducing a premature stop codon that would result in a CFTR protein shortened by 61 amino acids at the carboxyl terminus compared to that expected from the normal reported human CFTR coding sequences. Sequence analysis of intron 23 of the CFTR gene demonstrated that the 260-bp insertion (named exon 24a), a part of the reported intron 23 and located consecutive to exon 24, is likely generated by an alternative splice acceptor site. The exon 24a+ CFTR mRNA transcripts represented 3-16% of the total CFTR transcripts in epithelial and nonepithelial cells. These observations suggest an unexpected plasticity of expression of the CFTR gene, where alternative splicing of precursor CFTR mRNA transcripts permits the use of an alternative exon derived from a genomic segment previously believed to function as an intron.

Highlights

The cystic fibrosis transmembrane conductanceregulator (CFTR) gene, the gene responsible for the lethal hereditary disorder cystic fibrosis, codes for a membrane protein functioning as aCAMP-regulated C1channel
The 5”flanking region has the characteristics of a promoter of a housekeeping gene supporting a relatively low rate of transcription [14, 19], but transcription can be regulated [14, 17, 18].CFTR mRNA transcripts have a half-life of 13-19 h, and CFTR mRNA stability can be altered [17].’
The present study demonstrates additional, unexpected flexibility in CFTR gene expression: the alternative use of previously reported intron sequences as coding sequences to generate a novel exon and CFTR mRNA transcripts coding for a CFTR protein with all putative functional domains intact, but acarboxyl-terminal intracytoplasmic tail with a novel sequence, that is 4.1% shorter than CFTR protein predicted by the previously described 27exon CFTR mRNA [3]

Summary

THEJOURNALOF BIOCLHOEGMICIASTLRY

Vol 268, Nofo. 1, Issue January 5, pp. 686690,1993 Printed in U.S.A. Alternative Splicing of Intron 23 of the Human Cystic Fibrosis Transmembrane Conductance Regulator Gene Resultingin a Novel Exon and Transcript Codingfor a Shortened IntracytoplasmicC Terminus*. The present study demonstrates additional, unexpected flexibility in CFTR gene expression: the alternative use of previously reported intron sequences as coding sequences to generate a novel exon (referred to as “exon 24a”) and CFTR mRNA transcripts coding for a CFTR protein with all putative functional domains intact, but acarboxyl-terminal intracytoplasmic tail with a novel sequence, that is 4.1% shorter than CFTR protein predicted by the previously described 27exon CFTR mRNA [3]. Cystic fibrosis (CF),’ a common fatal hereditary disorder in Europe and North America, manifests mainly on the epithelial surfaces of the lung, pancreas, and gastrointestinal tract [1].The disorder is caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, a gene composed of exons and 26 intronsspanninga 250-kb segment of chromosome 7 at q31 [2,3,4]. ‘The abbreviations usedare: CF, cystic fibrosis; CFTR, cystic fibrosis transmembrane conductance regulator; PCR, polymerase chain reaction; bp, base pair(s); kb, kilobase(s)

MATERIALS AND METHODS

RESULTS

DISCUSSION