Stimulation of tyrosine phosphorylation without inositol lipid hydrolysis in human B lymphocytes on engaging CD72.
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.
Kamal
M
M
Department of Immunology, University of Birmingham, UK.
Knox
K
K
Finney
M
M
Michell
R H
RH
Holder
M J
MJ
Gordon
J
J
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
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