CYTOPLASMIC TAIL DELETION OF T-CELL RECEPTOR (TCR) BETA-CHAIN RESULTSIN ITS SURFACE EXPRESSION AS GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED POLYPEPTIDE ON MATURE T-CELLS IN THE ABSENCE OF TCR-ALPHA

Surface expression of the T cell antigen receptor (TCR) in mature T ce lls requires the association of a variable heterodimer (alpha.beta or gamma.delta) with six invariant CD3 polypeptides (gamma, delta, epsilo n-epsilon, zeta-zeta, or zeta-eta). We describe here that deletion of the cytoplasmic tail polypeptide sequence (Lys-Lys-Lys-Asn-Ser) of TCR beta-chain (beta(CT)) results in expression of the truncated beta-cha in on the surface of a mature T cell hybridoma line, in the absence of TCR-alpha, as a glycophosphatidylinositol (GPI)-anchored monomeric po lypeptide. The GPI-anchored TCR-beta(CT) is not associated with CD3-ep silon and is incapable of conventional signal transduction. Associatio n with TCR-alpha prevents beta(CT) from GPI-linkage formation. The alp ha beta(CT) heterodimer binds the CD3 polypeptides, and the resultant TCR alpha beta(CT)/CD3 complex is capable of signal transduction. Our data show that a signal sequence for GPI-linkage formation is present in TCR-beta, and this alternative membrane anchoring mechanism can be utilized by beta-chain polypeptide lacking the CT sequence. We conclud e therefore that in the absence of TCR-alpha expression, the beta-chai n CT sequence plays an essential function in hindering GPI-Linkage for mation, thereby preventing escape of incompletely assembled TCR beta-c hain to the cell surface of mature T cells.