THE RAT T-CELL SURFACE PROTEIN RT6 IS ASSOCIATED WITH SRC FAMILY TYROSINE KINASES AND GENERATES AN ACTIVATION SIGNAL

RT6 is a glycosyl-phosphatidylinositol-linked surface molecule present on most mature rat T-cells. RT6(+) T-cells can prevent the expression of autoimmune diabetes in the BB rat, but the mechanism is unknown. B ecause cross-linking of other glycosyl-phosphatidylinositol-linked T-c ell proteins is known to activate T-cells, we investigated the signali ng properties of RT6. Antibody cross-linking of RT6 enhanced expressio n of the alpha subunit of the interleukin-2 (IL-2) receptor and potent iated the proliferation of rat T-cells cultured in the presence of pho rbol ester plus recombinant IL-2 (rIL-2) and/or rIL-4. RT6 was found t o coimmunoprecipitate with five tyrosine phosphorylated proteins inclu ding p60(fyn) and p56(lck), members of the src tyrosine kinase family. Pretreatment of T-cells with phorbol ester increased the phosphorylat ion of proteins that coimmunoprecipitated with RT6, altered the electr ophoretic mobility of several of these coimmunoprecipitated phosphopro teins, and increased the amount of p60(fyn) and p56(lck) coimmunopreci pitated with RT6. These data indicate that RTB-mediated signaling even ts may prime T-cells to respond to exogenous cytokines, suggesting a p ossible mechanism by which surface RT6 may influence T-cell function.