T cells from patients with systemic lupus erythematosus (SLE) display antigen receptor-mediated signaling aberrations associated with defective T cell receptor (TCR) zeta chain protein and messenger RNA (mRNA) expression. This study was undertaken to explore the possibility that coding-region mutations/polymorphisms of the TCR zeta chain could account for its decreased expression and altered signaling in SLE T cells.
TCR zeta chain mRNA from 48 SLE patients, 18 disease controls, and 21 healthy volunteers was reverse transcribed, amplified by polymerase chain reaction, and cloned, and complementary DNA (cDNA) was sequenced. DNA sequences from multiple clones were analyzed for silent single-nucleotide polymorphisms, mutations, and splice variations, to promote the identification of heterozygosity.
DNA sequence analysis revealed several widely distributed missense mutations and silent polymorphisms in the coding region of the TCR zeta chain, which were more frequent in SLE patients than in patients with other rheumatic diseases or healthy controls (P < 0.0001). Several of the missense mutations were located in the 3 immunoreceptor tyrosine activation motifs or the GTP binding domain, and this could lead to functional alterations in the TCR zeta chain. A splice variant of the TCR zeta chain with a codon CAG (glutamine) insertion between exons IV and V was found in half of the SLE and control samples. Two larger spliced isoforms of the TCR zeta chain, with an insertion of 145 bases and 93 bases between exons I and II, were found only in SLE T cells. We also identified various alternatively spliced forms of the TCR zeta chain resulting from the deletion of individual exons II, VI, or VII, or a combined deletion of exons V and VI; VI and VII; II, III, and IV; or V, VI, and VII in SLE T cells. The frequency of the deletion splice variants was significantly higher in SLE than in control samples (P = 0.004). These variations were observed in cDNA and may not reflect the status of the genomic DNA.
These findings demonstrate that heterogeneous mutations/polymorphisms and alternative splicing of TCR zeta chain cDNA are more frequent in SLE T cells than in T cells from non-SLE subjects and may underlie the molecular basis of known T cell signaling abnormalities in this disease.