LSP1 regulates anti-IgM induced apoptosis in WEHI-231 cells and normal immature B-cells.
Expression of LSP1, a 330 amino acid intracellular phosphoprotein, is restricted to lymphocytes, macrophages and neutrophils. In B-lymphoma cell lines LSP1 co-caps with membrane IgM after stimulation with anti-IgM. We used the LSP1+ B-lymphoma cell line WEHI-231/89 and normal lipopolysaccharide treated immature B-cells from Lsp1-/- and wild type mice to determine a role for LSP1 in signaling through membrane IgM. WEHI-231/89 cells were transfected with a truncated LSP1 protein containing the COOH-terminal residues 179-330. The three transfectants expressing the LSP1 truncate were significantly more susceptible to anti-IgM induced apoptosis than the parental cells or G418r control cell lines, while anti-IgM induced growth arrest was not affected. Expression of the LSP1 truncate increased the extent of anti-IgM induced loss of mitochondrial membrane potential, delta(psi)m indicating that LSP1 acts at a early stage in BCR mediated apoptosis. Expression of the LSP1 truncate in WEHI-231/89 cells increased susceptibility to ionomycin induced apoptosis but had no effect on apoptosis induced by nocodazole, sorbitol, C2-ceramide or H2O2. A role for LSP1 in anti-IgM induced apoptosis was confirmed using normal immature B-cells from 129/SvJ-Lsp1-/- mice which were less susceptible to anti-IgM induced apoptosis than those isolated from wild-type 129/SvJ mice. These results suggest that LSP1 regulates a Ca2+-dependent step in the induction phase of anti-IgM mediated apoptosis.
Jongstra-Bilen
J
J
University of Toronto Arthritis Centre of Excellence at the Toronto Hospital, Department of Immunology, University of Toronto, Ontario, Canada.
Wielowieyski
A
A
Misener
V
V
Jongstra
J
J
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000096:biosynthesis / Q000276:immunology*; D017209:Apoptosis; D001402:B-Lymphocytes / Q000473:pathology*; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D002478:Cells, Cultured; D005260:Female; D005434:Flow Cytometry; D051379:Mice; D008840:Microfilament Proteins; D010446:Peptide Fragments / Q000096:biosynthesis / Q000235:genetics; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D011994:Recombinant Proteins / Q000096:biosynthesis
D000888:Antibodies, Anti-Idiotypic; D002135:Calcium-Binding Proteins; C057701:Lsp1 protein, mouse; D008840:Microfilament Proteins; D010446:Peptide Fragments; D010750:Phosphoproteins; D011994:Recombinant Proteins; C044203:anti-IgM; D002118:Calcium