title: Allelic effects on gene regulation at the autoimmunity-predisposing CTLA4 locus: a re-evaluation of the 3' +6230G>A polymorphism.
abstract: Genetic variation at a linkage disequilibrium block encompassing the cytotoxic T-lymphocyte antigen-4 (CTLA4) gene influences susceptibility to autoimmunity, but identifying the polymorphism(s) responsible for this effect has been challenging. Recently, a single-nucleotide polymorphism (SNP) located 3' to the known polyadenylation site of CTLA4 (+6230G>A) and strongly associated with autoimmune disease was reported to regulate levels of soluble CTLA4 isoform (sCTLA4) but not the full-length isoform. The purpose of the present study is to define the mechanistic effect of the 3'SNP on the isoforms of CTLA4 (alternative splicing vs polyadenylation vs effects on RNA stability). However, using allele-specific single-nucleotide primer extension, we found no difference between mRNA transcripts derived from either +6230G>A allele in 11 heterozygous individuals, in either of the two known CTLA4 isoforms. We also found no effect of this polymorphism on ICOS (inducible costimulator), a putative downstream target. In addition, repeated attempts at 3' RACE (3'rapid amplification of cDNA ends) were unsuccessful in amplifying any contiguous sequence past the known CTLA4 polyadenylation site and no such sequence was found in the EST databases. We conclude that the mechanism of the observed association of the +6230 SNP with autoimmune disease remains to be determined, but does not involve modulation of steady-state mRNA of any known CTLA4 isoform.
authors.affiliation: Endocrine Genetics Laboratory, Department of Pediatrics, Division of Pediatric Endocrinology, The McGill University Health Center (Montreal Children's Hospital), Montréal, Québec, Canada.
authors.forename: S M
authors.initials: SM
authors.lastname: Anjos
authors.forename: W
authors.initials: W
authors.lastname: Shao
authors.forename: L
authors.initials: L
authors.lastname: Marchand
authors.forename: C
authors.initials: C
authors.lastname: Polychronakos
mesh_terms: D024509:3' Flanking Region / Q000235:genetics*; D000483:Alleles; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000235:genetics*; D015551:Autoimmunity / Q000235:genetics*; D060908:CTLA-4 Antigen; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics; D020022:Genetic Predisposition to Disease; D006801:Humans; D015810:Linkage Disequilibrium; D008297:Male; D020641:Polymorphism, Single Nucleotide; D020033:Protein Isoforms / Q000235:genetics; D039104:RNA 3' Polyadenylation Signals / Q000235:genetics
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D020033:Protein Isoforms