title: B4B, a novel growth-arrest gene, is expressed by a subset of progenitor/pre-B lymphocytes negative for cytoplasmic mu-chain.
abstract: We subjected PBMC of normal adults to density fractionation to enrich for an immunoblast fraction that would include early immune lineage precursors. Differential display PCR experiments identified one transcript that is expressed specifically in this immunoblast fraction. This cDNA, designated B4B, encodes a novel gene product containing four putative transmembrane-spanning domains. B4B+ cells, detected with anti-B4B Ig, were found at very low frequency in PBMC (0.01%) and were enriched significantly in intermediate density fractions (0.1-1.0%). B4B+ cells were shown to be CD19+CD45+HLA-DR+ and negative for CD20, cytoplasmic mu-chain, CD3, CD16, CD56, CD34, and CD68 (monocyte), consistent with a progenitor/pre-B lymphocyte subset that does not express cytoplasmic mu-chain and thus may lack productive Ig rearrangement. This phenotypic description of the B4B+ subset agrees with our finding that the frequency of B4B+ cells was greatly increased in bone marrow (3-10%) as compared with PBMC (0.01%). The B4B polypeptide sequence exhibits significant homology to only one known protein, PMP-22/gas-3, a Schwann cell-specific protein that induces cell growth arrest. Transient expression of B4B specifically inhibited cellular proliferation by more than 50%. Based on its antiproliferative effect and pattern of expression restricted to a subpopulation of immature B cells, the B4B gene product may be involved in the elimination of B cells before productive VDJC rearrangement of Ig loci or, alternatively, in the growth arrest of transformed progenitor B cells.
authors.affiliation: Department of Molecular Immunology, Activated Cell Therapy, Mountain View, CA 94043, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Ruegg
authors.forename: H Y
authors.initials: HY
authors.lastname: Wu
authors.forename: F F
authors.initials: FF
authors.lastname: Fagnoni
authors.forename: E G
authors.initials: EG
authors.lastname: Engleman
authors.forename: R
authors.initials: R
authors.lastname: Laus
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000737:chemistry; D016175:B-Lymphocyte Subsets / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism*; D001483:Base Sequence; D015152:Blotting, Northern; D002454:Cell Differentiation / Q000235:genetics; D002455:Cell Division / Q000235:genetics; D002469:Cell Separation; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000302:isolation & purification; D005434:Flow Cytometry; D018507:Gene Expression Regulation, Developmental; D006131:Growth Inhibitors / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D006801:Humans; D007106:Immune Sera / Q000096:biosynthesis; D007148:Immunoglobulin mu-Chains / Q000096:biosynthesis*; D007150:Immunohistochemistry; D016130:Immunophenotyping; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins; D010446:Peptide Fragments / Q000276:immunology; D016133:Polymerase Chain Reaction; D011956:Receptors, Cell Surface; D014162:Transfection
chemical_list: D000954:Antigens, Surface; D018076:DNA, Complementary; D006131:Growth Inhibitors; D007106:Immune Sera; D007148:Immunoglobulin mu-Chains; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D010446:Peptide Fragments; D011956:Receptors, Cell Surface; C097051:epithelial membrane protein-1