Masking of the CD3γ di-Leucine-based Motif by ζ is Required for Efficient T-Cell Receptor Expression


Dr. Carsten Geisler,


The T-cell receptor (TCR) is a multimeric receptor composed of the Tiαβ heterodimer and the noncovalently associated CD3γδε and ζ2 chains. All of the TCR chains are required for efficient cell surface expression of the TCR. Previous studies on chimeric molecules containing the di-leucine-based endocytosis motif of the TCR subunit CD3γ have indicated that the ζ chain can mask this motif. In this study, we show that successive truncations of the cytoplasmic tail of ζ led to reduced surface expression levels of completely assembled TCR complexes. The reduced TCR expression levels were caused by an increase in the TCR endocytic rate constant in combination with an unaffected exocytic rate constant. Furthermore, the TCR degradation rate constant was increased in cells with truncated ζ. Introduction of a CD3γ chain with a disrupted di-leucine-based endocytosis motif partially restored TCR expression in cells with truncated ζ chains, indicating that the ζ chain masks the endocytosis motif in CD3γ and thereby stabilizes TCR cell surface expression.