Abstract
The monoclonal antibody (mAb) J393 induces apoptosis in Jurkat T-cells. NH2-terminal amino acid sequence analysis identified the 140-kDa surface antigen for mAb J393 as CD43/leukosialin, the major sialoglycoprotein of leukocytes. While Jurkat cells co-expressed two discrete cell-surface isoforms of CD43, recognized by mAb J393 and mAb G10-2, respectively, only J393/CD43 signaled apoptosis. J393/CD43 was found to be hyposialylated, bearing predominantly O-linked monosaccharide glycans, whereas G10-2/CD43 bore complex sialylated tetra- and hexasaccharide chains. 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 phosphorylation of specific protein substrates that underwent hyperphosphorylation upon antigen receptor costimulation. Tyrosine kinase inhibition by herbimycin A diminished J393/CD43-mediated apoptosis, whereas inhibition of phosphotyrosine phosphatase activity by bis(maltolato)oxovanadium-IV enhanced cell death. Signal transduction through tyrosine kinase activation may lead to altered gene expression, as J393/CD43 ligation prompted decreases in the nuclear localization of the transcriptional regulatory protein NF-kappaB and proteins binding the interferon-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 apoptosis in human T-cell lineages.
Highlights
In T-lymphocytes CD43/leukosialin, the major sialoglycoprotein of leukocytes [1, 2], is thought to serve a dual role in regulating cellular immune responses
We found the carbohydrate structure of J393/CD43 in Jurkat cells to be deficient in oligosaccharide complexity and sialic acid content when compared with that of the G10-2/CD43 isoform expressed in HPBALL cells
The majority of serine/threonine residues in the extracellular portion of the J393 antigen contained only terminal GalNAc monosaccharides, similar to the Tn antigen-bearing CD43 molecule expressed in Jurkat cells [50]
Summary
In T-lymphocytes CD43/leukosialin, the major sialoglycoprotein of leukocytes [1, 2], is thought to serve a dual role in regulating cellular immune responses. Treatment of Jurkat cells with mAb J393 induces apoptosis in a CD43 isoform-specific manner.
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