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.
Matsuuchi
L
L
Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448.
Gold
M R
MR
Travis
A
A
Grosschedl
R
R
DeFranco
A L
AL
Kelly
R B
RB
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