Synthesis, Assembly, and Secretion of Gamma Globulin by Mouse Myeloma Cells

Abstract

The synthesis, assembly, and secretion of the three major subclasses of mouse IgG has been examined in 14 myeloma tumors and two cultured cell lines as well as in the cells from the popliteal lymph nodes of immunized mice. The total amount of IgG synthesized was between 15 and 43% of the cytoplasmic proteins made during a 15 min period. H2 and H2L were the major precursors of IgG2a and IgG1 but, in all of the tumors, HL was also an intermediate. In contrast, HL was a major precursor of IgG2b. Most of the noncovalent and covalent assembly of IgG occurred after release of the newly synthesized H and L chains from the polyribosomes and assembly was not completed until 10 min or more after the synthesis of the polypeptide chains.

Composition, Assembly, and Trafficking of a Wheat Xylan Synthase Complex

“…Although the exact mechanism of assemblydependent trafficking of wheat XSC assembly has not yet been fully elucidated, it is tempting to propose that the assembly of GTs into complexes, such as wheat XSC and HA synthase, occurs through a coupled folding and binding mechanism described for the assembly of IgG subclasses (Baumal et al, 1971;Dyson and Wright 2002), which involves chaperones to ensure that only specific combinations of heavy chains and two identical light chains are correctly associated and functional (Mains and Sibley, 1983). The assembly of IgGs starts with the formation of heavy chain homodimers that are actively retained in the ER unless they associate with light chains, which can exit the ER alone.…”

“…Such an assemblydependent trafficking mechanism has been described in several membrane multiprotein complexes in mammalian and yeast cells and appears to involve a "quality control" step regulating the assembly of functional complexes before exiting the ER. For example, ATPsensitive potassium channels in animal cells need to assemble into complexes containing specific numbers and correct subunits before exiting the ER (Zerangue et al, 1999), as do G-protein-coupled g-aminobutyric acid receptors (Margeta-Mitrovic et al, 2000), invariant chain of the major histo-compatibility complex class II (Khalil et al, 2003), and IgG antibodies in animal blood cells (Baumal et al, 1971;Mains and Sibley, 1983). In all these cases, unassembled subunits or partial complexes are retained in the ER.…”

IgG2a-producing variants of an IgG2b-producing mouse myeloma cell line.

“…The major pathway used by any mouse myeloma tumor for the assembly of H2L2 from newly synthesized heavy and light chains depends on the subclass of the heavy chain that it makes (27). For example, T 2b producing tumors assemble their immunoglobulin mainly via H + L --, HL + HL --~ H2L2, while the major pathway in theT2a producing tumors is H + H ---, H2 + L -* H2L + L ~ H2L2 (27).…”

“…The major pathway used by any mouse myeloma tumor for the assembly of H2L2 from newly synthesized heavy and light chains depends on the subclass of the heavy chain that it makes (27). For example, T 2b producing tumors assemble their immunoglobulin mainly via H + L --, HL + HL --~ H2L2, while the major pathway in theT2a producing tumors is H + H ---, H2 + L -* H2L + L ~ H2L2 (27). Our studies on the short heavy chain producing variants further supported the idea that the structure of the heavy chain dictates the assembly pattern: variants synthesizing heavy chains of 50,000 mol wt fail to assemble past the HL stage, while those synthesizing heavy chains of 40,000 mol wt secrete both H2I¢ and HL (5).…”

Similarity of Casein- and Endotoxin-Induced, Myeloma-Associated and Aged SJL/J Amyloid in Various Strains of Mice

“…Casein-induced amyloidosis in ex perimental animals has proven to be a good model for studying secondary human amy loidosis because constant antigenic stimula tion is common to both, and amyloid isolat ed from experimental animals (including 1 Supported by the Canadian Arthritis and Rheu matism Society. guinea pigs and mice) is structurally similar to human protein A [17,18].…”