The cytoplasmic tail of the T cell receptor ζ chain is dispensable for antigen‐mediated T cell activation

Abstract

The T cell antigen receptor consists of an antigen-binding alpha beta heterodimer and a group of invariant polypeptides denoted CD3-gamma, CD3-delta, CD3-epsilon and CD3-zeta. Whether antigen responsiveness is dependent on the expression of functional CD3-zeta subunit remains controversial. For instance, transfection of a zeta-/eta- variant of the 2B4.11. T cell hybridoma with mutated zeta cDNA that encoded a zeta protein truncated at residue 108, restored the surface expression of T cell antigen receptor complexes with, however, impaired antigen responsiveness [Frank, S. J., Niklinska, B. B., Orloff, D. G., Mercep, M., Ashwell, J. D. and Klausner, R. D., Science 1990. 249: 174.]. In marked contrast, BW5147 transfectants that expressed T cell antigen receptors devoid of functional zeta subunits were still able to trigger the production of interleukin-2 in response to antigen [Wegener, A.-M. K., Letourneur, F., Hoeveler, A., Brocker, T., Luton, F. and Malissen, B., Cell 1992. 68: 83.]. To assess if the above discrepancies may have resulted from the use of different recipient T cells, we transfected a zeta/eta-deficient variant of 2B4.11 (MA5.8) with the very same truncated zeta cDNA we previously used in BW5147. Consistent with our initial observations in BW5147, the cytoplasmic tail of the zeta polypeptide was found dispensable for antigenic responsiveness. Furthermore, a difference between the two recipient T cells was detected when cells were challenged via the Thy-1 and Ly-6 molecules. Once expressed in MA5.8, but not in BW5147, T cell antigen receptor complexes devoid of functional zeta subunits were able to sustain activation initiated via Thy-1 and Ly-6 molecules.

Regulation of Constitutive TCR Internalization by the ζ-Chain

“…Analysis of chimeric receptors containing internalization signals from the cytoplasmic domains of CD3␥ and CD3␦ have shed light on a possible role for whereby it masks internalization signals present in the TCR complex from the cellular endocytic machinery (28,34). Consistent with this masking role, reports on the ability of C-terminal deletion or internal deletion mutants of in cell lines and transgenic mice to support TCR expression have indicated that the extent of deletions of the native sequence correlates with reduced ability to support surface expression (7,(35)(36)(37).…”

T cells with two functional antigen-specific receptors.

“…Moreover, the transgene-encoded TCR does not provide for the alloreactivity of the T cells that bear it; alloreactivity comes instead from receptors selected on the H-2b background in this case, and these are likely to be both self-MHC-restricted and alloreactive, as is true of several other TCR that have been shown to have similar dual specificity. Studies using clonotypic antibodies to block a given TCR (11,12) as well as transfection data (13)(14)(15)(16)) have yet to reveal cells that have two TCRs that mediate recognition of antigen and self-MHC separately from recognition of non-self-MHC. Indeed, it appears from these studies that, in each case, alloreactivity involves cross-reactions of TCR specific for a foreign antigenic peptide bound to self-MHC molecules.…”

“…To further examine the development of T cells with two TCRs, we have analyzed CD4+ T cells in mice transgenic for the rearranged genes encoding the a and 13 chains of an autoreactive TCR specific for myelin basic protein (MBP) and the MHC class II molecule I-Au (3). This system has allowed us to examine the expression of TCRs of two different types on a single cell and to ask directly whether T cells having two different TCRs are required for the development of autoimmunity.…”

CD3 gamma contains a phosphoserine-dependent di-leucine motif involved in down-regulation of the T cell receptor.

“…The disulfide-linked ca3 heterodimer is responsible for antigen recognition (Dembic et al, 1986;Saito et al, 1987b) and the activation signals are delivered through the associated CD3 chains (Malissen and Schmitt-Verhulst, 1993). Recent studies have provided definitive evidence for a signal transduction function of the CD3E and r chains Romeo and Seed, 1991;Letourneur and Klausner, 1992a;Wegener et al, 1992;Hermans and Malissen, 1993); however, the specific role of the CD3-y and 6 chains in TCR function is still unknown. After TCR stimulation, a number of cellular proteins become phosphorylated on tyrosine residues, among them being r (Baniyash et al, 1988), ZAP-70 (Chan et al, 1991), the proto-oncogene vav (Margolis et al, 1992) and phospholipase C-yl (PLC'yl) (Park et al, 1991;Secrist et al, 1991;Weiss et al, 1991).…”