The membrane IgM-associated proteins MB-1 and Ig-beta are sufficient to promote surface expression of a partially functional B-cell antigen receptor in a nonlymphoid cell line.
The B-cell antigen receptors consist of membrane immunoglobulins (mIgs) noncovalently associated with two accessory proteins, MB-1 and Ig-beta. We used transfection into a nonlymphoid cell line to test whether MB-1 and Ig-beta were sufficient to promote cell surface expression of mIgM capable of signal transduction. Expression of MB-1 and Ig-beta, but not MB-1 alone, allowed high-level surface expression of mIgM in the AtT20 endocrine cell line, which presumably lacks other B-cell-specific components. The reconstituted antigen receptor was capable of mediating some of the signaling reactions characteristic of mIgM in B lymphocytes. Crosslinking mIgM on transfected AtT20 cells stimulated tyrosine phosphorylation of MB-1 and Ig-beta and also increased the amount of phosphatidylinositol 3-kinase activity that could be precipitated with anti-phosphotyrosine antibodies. When total cell lysates were analyzed by anti-phosphotyrosine immunoblotting, however, no induced phosphorylation of more abundant proteins was detected. Moreover, crosslinking of the receptor in AtT20 cells did not stimulate inositol phospholipid breakdown. Thus, the transfected B-cell antigen receptor could initiate some signal transduction events but AtT20 cells may lack components required for other signaling events associated with mIgM.
Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448.
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L
Matsuuchi
M R
MR
Gold
A
A
Travis
R
R
Grosschedl
A L
AL
DeFranco
R B
RB
Kelly
D000818:Animals; D015703:Antigens, CD; D051925:CD79 Antigens; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D007148:Immunoglobulin mu-Chains / Q000235:genetics / Q000276:immunology; D007295:Inositol Phosphates / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology*; D008970:Molecular Weight; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000235:genetics / Q000276:immunology*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000235:genetics* / Q000378:metabolism; D015183:Restriction Mapping; D015398:Signal Transduction; D014162:Transfection; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
D015703:Antigens, CD; D051925:CD79 Antigens; D007148:Immunoglobulin mu-Chains; D007295:Inositol Phosphates; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell; D019000:Phosphotyrosine; D014443:Tyrosine; D010770:Phosphotransferases; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases