Alternatively spliced forms of Igalpha and Igbeta prevent B cell receptor expression on the cell surface.
The B cell antigen receptor (BCR) includes an Igalpha/Igbeta heterodimer non-covalently associated with surface immunoglobulin. Recently, variant Igalpha and Igbeta transcripts, arising from alternative mRNA splicing, have been reported. The present study examined the function of the potential products of these transcripts, by utilizing cDNA expression plasmids to reconstitute human BCR expression in transfected 293T cells. Spliced transcripts produced truncated proteins (deltaIgalpha and deltaIgbeta), that failed to form heterodimers with their full-length counterparts, and did not mediate transport of IgM to the cell surface. When overexpressed, both deltaIgalpha and deltaIgbeta acted as competitors of Igalpha and Igbeta, leading to down-modulated surface IgM expression, and retention of IgM in the endoplasmic reticulum. These findings document a possible novel mechanism for controlling BCR expression in B cells, based on up-regulated synthesis of components devoid of transport function.
Department of Oncology and Surgical Sciences, Interuniversity Center for Research on Cancer, University of Padova, Padova, Italy. stefano.indraccolo@unipd.it
Stefano
S
Indraccolo
Sonia
S
Minuzzo
Rita
R
Zamarchi
Francesca
F
Calderazzo
Erich
E
Piovan
Alberto
A
Amadori
D017398:Alternative Splicing; D002460:Cell Line; D019281:Dimerization; D006801:Humans; D007075:Immunoglobulin M / Q000032:analysis; D014176:Protein Biosynthesis; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics
D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell