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Aberrant Trafficking of the B Cell Receptor Ig-ß Subunit in a B Lymphoma Cell Line¹

Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada

The B cell Ag receptor (BCR) has two important functions: first, it binds and takes up Ag for presentation to T lymphocytes; and second, it transmits signals that regulate B cell development. Normal expression of the BCR requires the association of the Ag binding subunit, membrane IgM (mIgM), with the signaling component, the Ig-ß heterodimer. After assembly in the endoplasmic reticulum, the intact BCR travels through the secretory pathway to the cell surface. In this paper, we report two variants of the B lymphoma cell lines, WEHI 279 and WEHI 231, that have both lost the ability to express µ heavy chain and consequently do not express mIgM. However, these variants do express the Ig-ß heterodimer. In one variant, WEHI 279*, the Ig-ß remained trapped intracellularly in the absence of mIgM. The other variant, 303.1.5.LM, expressed an aberrantly glycosylated Ig-ß on the cell surface that was capable of signaling after cross-linking with anti-Ig-ß Abs. Further characterization uncovered a point mutation in the 303.1.5.LM mb1 gene that would change a proline for a leucine in the extracellular domain of Ig-. The 303.1.5.LM Ig-ß could not associate with a wild-type mIgM after µ heavy chain was reconstituted by DNA transfection. Thus, this mutation could define a region of the Ig- polypeptide that is important for recognition by the endoplasmic reticulum quality control system, for association with glycosylating enzymes, and for the association of Ig-ß subunits with mIgM subunits to create a complete BCR complex.

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				L. D. Wang, J. Lopes, A. B. Cooper, M. Dang-Lawson, L. Matsuuchi, and M. R. Clark Selection of B lymphocytes in the periphery is determined by the functional capacity of the B cell antigen receptor PNAS, January 27, 2004; 101(4): 1027 - 1032. [Abstract] [Full Text] [PDF]