The T-cell receptor (TCR) Ç-chain is a vital T-cell signaling molecule that is considered the limiting factor among the eight subunits of the TCR in receptor assembly, transport, and surface expression and is crucial to receptor signaling function (1,2). The Ç-chain transcript is generated as the spliced product of eight exons separated by distances of 0.7 to more than 8 kb (3).
The Ç-chain exists in multiple forms and membrane fractions with distinct functions in antigen (Ag)-mediated signaling process. In addition to the soluble 16-kDa unphosphorylated form, the detergent-soluble fraction of TCR Ç-chain includes the phosphorylated p21- and p23-kDa forms and mono- and polyubiquitinated forms. The detergent-insoluble membrane fraction includes the actin cytoskeleton-bound form and lipid raft-associated forms of the TCR Ç-chain. Systemic lupus erythematosus (SLE) T cells display low levels of p16, p21, and 23-kDa and detergent-insoluble membrane-bound forms of the TCR Ç-chain. In contrast, ubiquitinated forms of the Ç-chain are high in SLE T cells.
We reported that the levels of residual TCR Ç-chain associated with lipid rafts and the membrane clustering of the TCR Ç-chain are significantly increased in SLE T cells. A majority of patients with SLE also display decreased expression of TCR Ç-chain messenger RNA (mRNA) (4,5).
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