Post‐Translational Fate of Variant MOPC 315 λ Chains in Xenopus Oocytes and Mouse Myeloma Cells

Publisher Website
Google Scholar
Abstract
The post‐translational fates of three immunoglubulin λ chain variants of MOPC 315 were investigated in mouse plasmactyoma cell lines and in mRNA‐microinjected Xenopus oocytes.Quite unexpectedly we found that one non‐secretory variant chain (λ‐43) underwent extensive post‐translational N‐glycosylation; however the presence of the oligosaccharide moiety did not account for the non‐secretory phenotype nor did it affect the rate of degradation of this λ chain. Another variant chain (λ‐47) at first believed to be non‐secretory, was found to be secreted from oocytes at a very low level, but mostly as a λ‐λ dimer. In myeloma cells a low level of λ‐47 chain was secreted and again λ‐λ dimers were the favoured secretory form. The secretory λ‐48 chain also formed λ‐λ dimers, whereas λ‐43, which was never secreted, was only found as a monomeric λ chain in both oocytes and myeloma cells.A similar relationship between assembly and secretion was found when oocytes were coinjected with MOPC 21 heavy (γ1) chain mRNA and MOPC 315 λ chain mRNAs. The wild type λ chain (λ‐48) was able to assemble with the γ chain in a covalently bound tetramer (γγλλ). The variant λ‐47 chain was also able to form γγλλ tetramers, whereas the λ‐43 was nott, even when glycosylation was prevented by tunicamycin. Both types of tetramer were secreted.These data reinforce the idea that conformational changes play a major role in the routing of secretory proteins and that the cellular mechanisms by which these changes are recognized are not cell‐type specific.