title: Stimulation of tyrosine phosphorylation without inositol lipid hydrolysis in human B lymphocytes on engaging CD72.
abstract: Occupancy of CD72 on resting tonsillar B cells by monoclonal antibodies (mAb) promotes entry into the G1 phase of the cell cycle with an accompanying increase in MHC Class II expression and provides a co-stimulus to immobilized anti-mu for driving DNA synthesis. We now report that engagement of CD72 by mAb stimulates tyrosine phosphorylation in B cells with a peak of activity seen at 5-10 min. Two major substrates of 29 and 57 kDa showed a basal level of phosphorylation which increased with time, while a 40 kDa protein and several other minor components were phosphorylated de novo on the addition of mAb to CD72. Inositol lipid hydrolysis was found to be unperturbed, although a shallow rise in the basal level of intracellular free Ca2+ was provoked on engaging CD72. Receptor cross-linking was not a requirement for signaling human B cells through CD72: simple occupancy by univalent antibody was sufficient both to trigger the rise in basal [Ca2+]i and to promote DNA synthesis.
authors.affiliation: Department of Immunology, University of Birmingham, UK.
authors.forename: M
authors.initials: M
authors.lastname: Kamal
authors.forename: K
authors.initials: K
authors.lastname: Knox
authors.forename: M
authors.initials: M
authors.lastname: Finney
authors.forename: R H
authors.initials: RH
authors.lastname: Michell
authors.forename: M J
authors.initials: MJ
authors.lastname: Holder
authors.forename: J
authors.initials: J
authors.lastname: Gordon
mesh_terms: D015703:Antigens, CD / Q000378:metabolism*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism*; D001402:B-Lymphocytes / Q000276:immunology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism*; D008970:Molecular Weight; D010716:Phosphatidylinositols / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D019000:Phosphotyrosine; D015398:Signal Transduction; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C064228:CD72 protein, human; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D010750:Phosphoproteins; D019000:Phosphotyrosine; D014443:Tyrosine; D002118:Calcium