Polymorphisms/mutations of TCR-zeta-chain promoter and 3 ' untranslated region and selective expression of TCR zeta-chain with an alternatively spliced 3 ' untranslated region in patients with systemic lupus erythematosus

A vast majority of systemic lupus erythematosus (SLE) patients display decr eased expression of TCR zeta -chain mRNA, a critical signaling molecule imp licated in the selection of the TCR repertoire and in the prevention of aut oimmunity. To identify the molecular mechanisms involved in the downregulat ion of TCR zeta -chain transcripts in SLE T cells, we investigated the poss ibility of polymorphisms/mutations in the promoter and the 3' untranslated region. PCR, cloning and sequence analysis of the promoter region from the genomic DNA showed significantly higher number of polymorphisms in SLE T ce lls compared to non-SLE control subjects (P=0.044). Promoter sequence was a lso analysed from granulocytes to delineate the possibility of somatic muta tions in activated SLE T cells. Promoter polymorphisms were significantly h igher in granulocytes of SLE patients compared to non-SLE controls (P=0.048 ), suggesting that these polymorphisms were of genomic origin. Nucleotide a nalysis of the promoter sequence revealed a -76T insertion compared to the published sequence; in all of the SLE samples and controls. RT-PCR analysis of the TCR zeta -chain 3' untranslated region showed a 344 bp product in a ddition to the expected 906 bp product. Cloning and sequence analysis of th e 344 bp product indicated that it is an alternatively spliced form with bo th splicing donor and acceptor sites, resulting in deletion of nucleotides 672-1233 of TCR zeta -chain mRNA. Unlike the nomal TCR zeta -chain, the exp ression of TCR zeta -chain with the alternatively spliced 344 bp 3' untrans lated region was higher in SLE T cells compared to non-SLE controls. The nu mber of mutations/polymorphisms in the 906 bp TCR zeta -chain 3' untranslat ed region were significantly higher in SLE T cells compared to non-SLE subj ects (P=0.032). Frequent mutations/polymorphisms and aberrant splicing of t he downstream 3' untranslated region may affect the stability and/or transp ort of TCR zeta -chain mRNA, leading to its downregulation in SLE T cells. (C) 2001 Academic Press.