Cellular mechanisms for the formation of a soluble form derivative of TCRa chain by suppressor t cells

Upon stimulation with anti-CD3, suppressor T cell (Ts) hybridomas and homologous transfectants or TCRa cDNA in the Ts cells produced a 55 kDa, TCRa chain derivative which has both the antigenic determinant of glycosylation inhibiting factor (GIF) and TCRa-determinant. Evidence was obtained that the TCRa derivative was synthesized by the transfectant after stimulation with anti-CDS, and not derived from TCR present on the cell surface. Stimulation of the homologous stable transfectants with anti-CD3 induced translocation of the 13 kDa GIF peptide into endoplasmic reticulum. When helper T cell hybridoma or transfectants of the same TCRa cDNA in helper cell-derived TCRa clone were stimulated with anti-CD3, translocation of GIF peptide was not detected and these cells failed to secrete a TCRa derivative. However, further transfection of a chimeric cDNA encoding a procalcitonin-GIF fusion protein into the helper cell-derived stable transfectant of TCRa cDNA facilitated translocation of the fusion protein and formation of the 55 kDa GIF. The results indicated that translocation of GIF peptide into endoplasmic reticulum is unique for Ts cells, and essential for the formation/secretion of a soluble form derivative of TCRa chain.