The ligand-induced membrane IgM association with the cytoskeletal matrix of B cells is not mediated through the Ig alpha beta heterodimer.
The B cell Ag receptor complex consists of membrane-associated Ig (mIg), Ig alpha, and Ig beta, associated molecules that have been implicated in transducing the activation signal that occurs upon receptor cross-linking. The role of the Ig alpha beta heterodimer in mediating binding to the cytoskeleton is unknown. We studied the ligand-induced association of mIgM with the cytoskeleton following receptor cross-linking in mIgM-expressing B lymphoma lines by biochemical assays, FACS analysis, and electron microscopy. Cytoskeletal association is not detected in unstimulated cells, but occurs rapidly upon anti-IgM-mediated cross-linking. Ig alpha is absent from the cytoskeleton-mIgM complex. To further analyze the possible role of Ig alpha beta in cytoskeletal binding, a surface Ig alpha beta-negative plasmacytoma line was transfected with a mutant form of mIgM (IgM-MutA). IgM-MutA is expressed on the surface despite the lack of Ig alpha beta, and the cytoskeletal binding occurred to a similar extent as in Ig-alpha-positive cell lines. In another transfectant expressing a mutated form of human mIgM (YS:VV), which does not have the capacity to bind to Ig alpha beta, the association of the receptor with the cytoskeleton appeared to be more extensive (100%) and faster than with mouse mIgM. These data indicate that Ig-associated Ig alpha beta proteins are not required for mIgM association with the cytoskeleton.
Hartwig
J H
JH
Department of Immunology, University of Toronto, Ontario, Canada.
Jugloff
L S
LS
De Groot
N J
NJ
Grupp
S A
SA
Jongstra-Bilen
J
J
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D001666:Binding Sites, Antibody; D015153:Blotting, Western; D003598:Cytoskeletal Proteins / Q000276:immunology*; D006801:Humans; D007070:Immunoglobulin A / Q000378:metabolism; D007075:Immunoglobulin M / Q000276:immunology / Q000378:metabolism*; D007700:Kinetics; D016393:Lymphoma, B-Cell / Q000276:immunology; D046911:Macromolecular Substances; D051379:Mice; D011947:Receptors, Antigen, B-Cell / Q000276:immunology / Q000378:metabolism* / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D003598:Cytoskeletal Proteins; D007070:Immunoglobulin A; D007075:Immunoglobulin M; D046911:Macromolecular Substances; D011947:Receptors, Antigen, B-Cell