p70 lupus autoantigen binds the enhancer of the T-cell receptor β-chain gene

Abstract

The p70 (Ku) autoantigen has been described as a nonhistone nuclear protein recognized by antibodies from lupus patients. In our studies on the regulation of T-cell receptor (TCR) β-chain gene expression we have identified the p70 lupus autoantigen as a DNA-binding protein that binds the enhancer of the TCR β-chain gene. This enhancer is essential for expression of the TCR β gene. The core TCR β enhancer contains the E3 motif, which we show here is essential for enhancer activity. The protection of the E3 motif in T cells and the marked reduction in enhancer activity when the E3 motif is mutated underline its physiological importance in regulating β enhancer activity. The p70 lupus autoantigen gene was identified by screening T-cell λgt11 libraries with an E3 probe. The gene encodes a protein which binds the E3 motif in a sequence-specific manner. The identification of a 70-kDa protein as a major E3-binding protein by UV crosslinking is consistent with the conclusion that the p70 lupus autoantigen binds the β enhancer. Finally, we have shown that T-cell nuclear proteins which bind the E3 motif bear p70 (Ku) lupus autoantigenic determinants. Together these data suggest that the p70 autoantigen binds a critical motif in the β enhancer and probably regulates TCR β gene expression.