Association of B lymphocyte antigen receptor polypeptides with multiple chaperone proteins.
The B cell antigen receptor (BCR) is comprised of four different polypeptides, immunoglobulin (Ig) heavy chain, Ig light chain, and the two signaling subunits of this receptor, Ig-alpha and Ig-beta. These four chains must assemble correctly in the endoplasmic reticulum (ER) before the BCR can be transported to the cell surface. The roles of the different chaperone proteins in mediating the assembly of mIg with the Ig-alpha/beta are not fully understood. To gain insights into the roles of chaperone proteins in BCR assembly, we have generated transfected non-lymphoid cell lines that express various intermediate assembled forms of the BCR and used them to examine the interactions of chaperone proteins with subunits of the BCR. We examined the interactions of BiP (GRP78), GRP94 and calnexin with the mu heavy chain, lambda light chain, Ig-alpha and Ig-beta. We report for the first time that Ig-alpha associates with GRP94 and that this interaction increases dramatically when other BCR chains are co-expressed. In contrast, the mu heavy chain interacts strongly with BiP (GRP78) when expressed by itself but this interaction is reduced when the lambda light chain is expressed, with the resulting mu(lambda) complexes interacting with GRP94 and calnexin. Thus, our data are consistent with the idea that there is an ordered association of BCR components with different protein chaperones during BCR assembly.
Foy
S P
SP
Department of Zoology (Cell Biology Group), The University of British Columbia, 6270 University Blvd., BC, V6T 1Z4, Vancouver, Canada.
Matsuuchi
L
L
D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D037281:Calnexin; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins; D007143:Immunoglobulin Heavy Chains / Q000235:genetics / Q000378:metabolism; D007137:Immunoglobulin alpha-Chains / Q000235:genetics / Q000378:metabolism; D007146:Immunoglobulin lambda-Chains / Q000235:genetics / Q000378:metabolism; D007148:Immunoglobulin mu-Chains / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D025941:Protein Interaction Mapping / Q000379:methods; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D007143:Immunoglobulin Heavy Chains; D007137:Immunoglobulin alpha-Chains; D007146:Immunoglobulin lambda-Chains; D007148:Immunoglobulin mu-Chains; D008565:Membrane Proteins; D018832:Molecular Chaperones; D010455:Peptides; D011947:Receptors, Antigen, B-Cell; C018551:glucose-regulated proteins; D037281:Calnexin