Characterization of a cell surface glycoprotein IPO-3, expressed on activated human B and T lymphocytes.
We characterize the expression, biochemical structure, and function of a novel glycoprotein, IPO-3, up-regulated on activated human lymphocytes. IPO-3 is found on activated B cells, B cell lines, and hairy cell leukemias but is not expressed on T cell or nonlymphoid cell lines. IPO-3 is not B cell-specific as it is detected at low levels on CD45RO+ CD45RA- peripheral blood T cells and CD4+CD8+CD45RO+ CD45RA- thymocytes. The IPO-3 Ag is a single-chain heavily N-glycosylated phosphoglycoprotein approximately 75 to 95 kDa in size with a 42-kDa protein core. In vitro kinase assays revealed that IPO-3 has a protein kinase activity associated with it that is maintained even in Nonidet P-40 lysates. IPO-3 is up-regulated on resting B cells within 16 h after activation with different signals including anti-IgM, IL-4, or mAb to CD40, CD20, or Bgp95. It could also be induced on T cells via CD3-cross-linking, but the kinetics of IPO-3 induction was slower on T cells than on B cells. Cross-linking IPO-3 on B cells with mAb did not induce proliferation alone but did augment proliferation promoted by IL-4 and anti-CD40 and did trigger increases in [Ca2+]i in resting B cells. Binding of IPO-3 could not be inhibited by a variety of mAb to previously identified activation markers. Thus, the IPO-3 glycoprotein appears to be a novel marker of activated B and T lymphocytes, which may play a role in the regulation of lymphocyte activation.
Sidorenko
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SP
Regional Primate Research Center, University of Washington School of Medicine, Seattle 98195.
Clark
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EA
D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D000954:Antigens, Surface / Q000032:analysis* / Q000502:physiology; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D015703:Antigens, CD; D000954:Antigens, Surface; D008562:Membrane Glycoproteins; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium