Portal de Periódicos da CAPES

The requirement of light chain for the surface deposition of the heavy chain of immunoglobulin M.

1983; Elsevier BV; Volume: 258; Issue: 8 Linguagem: Inglês

10.1016/s0021-9258(18)32532-8

1083-351X

Paul E. Mains, Carol Hopkins Sibley,

Glycosylation and Glycoproteins Research

The murine tumor line 702/3 resembles a pre-B lymphocyte in containig the heavy chain of IgM &) as a cytoplasmic protein in the apparent absence of light chain (L).However, these cells can be induced by lipopolysaccharide to differentiate into a B lymphocytelike state, containing pZLz tetramers as membranebound molecules.This is accompanied by an increase in p synthesis, the acquisition of complex carbohydrate by p, and the induction of L chain.We wished to determine which of these events is critical for membrane deposition of p.We found that uninduced 702/3 cells, as well as lipopolysaccharide-uninducible variants, contained a low, constitutive level of membrane bound p, all of which was found as p2L2.Dextran sulfate, another inducing agent, apparently caused a redistribution of this pre-existing surface p without altering the pattern of p synthesis or processing.One lipopolysaccharide-uninducible variant showed a small subset of surface ppositive cells, and the proportion of these cells increased with a prolonged induction period.The increase in p synthesis was nearly normal, but p did not acquire complex carbohydrate.However, the delayed appearance of surface p-positive cells was paralleled by a delayed increase in L chain, which occurred only in those cells with p on their membrane.We concluded that L chain signals the transport of p to the cell surface.The immunoglobulin IgM is an excellent system for determining the mechanism used by a cell to alter the intracellular localization of a particular protein during development.This antibody has been intensively studied at both the genetic and structural levels, and the ontogeny of the immunoglobulinproducing cells, the B lymphocytes, has been well characterized.During the differentiation of these cells, IgM is successively located in three cellular compartments: intracellular, external membrane, and secreted.It is our interest to define the biochemical signal(s) responsible for bringing about these changes.IgM is a disulfide-bonded tetrameric protein consisting of two heavy chains and two light chains (1).The frst type of heavy chain expressed during development is always that of