CHARACTERIZATION OF A CD43 LEUKOSIALIN-MEDIATED PATHWAY FOR INDUCING APOPTOSIS IN HUMAN T-LYMPHOBLASTOID CELLS/

The monoclonal antibody (mAb) J393 induces apoptosis in Jurkat T-cells , NH2-terminal amino acid sequence analysis identified the 140-kDa sur face antigen for mAb J393 as CD43/leukosialin, the major sialoglycopro tein of leukocytes, While Jurkat cells co-expressed two discrete cell- surface isoforms of CD43, recognized by mAb J393 and mAb G10-2, respec tively, only J393/CD43 signaled apoptosis. J393/CD43 was found to be h yposialylated, bearing predominantly O-linked monosaccharide glycans, whereas G10-2/CD43 bore complex sialylated tetra- and hexasaccharide c hains, Treatment with soluble, bivalent mAb J393 killed 25-50% of the cell population, while concomitant engagement of either the CD3 . TcR complex or the integrins CD18 and CD29 significantly potentiated this effect, Treatment of Jurkat cells with mAb J393 induced tyrosine phosp horylation of specific protein substrates that underwent hyperphosphor ylation upon antigen receptor costimulation. Tyrosine kinase inhibitio n by herbimycin A diminished J393/CD43-mediated apoptosis, whereas inh ibition of phosphotyrosine phosphatase activity by bis(maltolato) oxov anadium-IV enhanced cell death, Signal transduction through tyrosine k inase activation may lead to altered gene expression, as J393/CD43 lig ation prompted decreases ill the nuclear Localization of the transcrip tional regulatory protein NF-kappa B and proteins binding the interfer on-inducible regulatory element, Since peripheral blood T-lymphocytes express cryptic epitopes for mAb J393, these findings demonstrate the existence of a tightly regulated CD43-mediated pathway for inducing ap optosis in human T-cell lineages.