title: Fate of surrogate light chains in B lineage cells.
abstract: Biosynthesis of the immunoglobulin (Ig) receptor components and their assembly were examined in cell lines representative of early stages in human B lineage development. In pro-B cells, the nascent surrogate light chain proteins form a complex that transiently associates in the endoplasmic reticulum with a spectrum of unidentified proteins (40, 60, and 98 kD) and Bip, a heat shock protein family member. Lacking companion heavy chains, the surrogate light chains in pro-B cells do not associate with either the Ig(alpha) or Ig(beta) signal transduction units, undergo rapid degradation, and fail to reach the pro-B cell surface. In pre-B cells, by contrast, a significant portion of the surrogate light chain proteins associate with mu heavy chains, Ig(alpha), and Ig(beta) to form a stable receptor complex with a relatively long half-life. Early in this assembly process, Bip/GRP78, calnexin, GRP94, and a protein of approximately 17 kD differentially bind to the nascent mu heavy chains. The 17-kD intermediate is gradually replaced by the surrogate light chain protein complex, and the Ig(alpha) and Ig(beta) chains bind progressively to the mu heavy chains during the complex and relatively inefficient process of pre-B receptor assembly. The results suggest that, in humans, heavy chain association is essential for surrogate light chain survival and transport to the cell surface as an integral receptor component.
authors.affiliation: Department of Medicine, University of Alabama at Birmingham, 35294, USA.
authors.forename: K
authors.initials: K
authors.lastname: Lassoued
authors.forename: H
authors.initials: H
authors.lastname: Illges
authors.forename: K
authors.initials: K
authors.lastname: Benlagha
authors.forename: M D
authors.initials: MD
authors.lastname: Cooper
mesh_terms: D015703:Antigens, CD / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology*; D051925:CD79 Antigens; D002135:Calcium-Binding Proteins / Q000378:metabolism; D037281:Calnexin; D002352:Carrier Proteins / Q000378:metabolism; D002451:Cell Compartmentation; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins; D006412:Hematopoietic Stem Cells / Q000276:immunology*; D006801:Humans; D007147:Immunoglobulin Light Chains; D054444:Immunoglobulin Light Chains, Surrogate; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D011485:Protein Binding; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D051925:CD79 Antigens; C497881:CD79A protein, human; C497883:CD79B protein, human; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D007147:Immunoglobulin Light Chains; D054444:Immunoglobulin Light Chains, Surrogate; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D011947:Receptors, Antigen, B-Cell; C018551:glucose-regulated proteins; D037281:Calnexin