title: Plasmacytic transcription factor Blimp-1 is repressed by Bach2 in B cells.
abstract: Bach2 is a B cell-specific transcription repressor whose deficiency in mice causes a reduced class switch recombination and a reduced somatic hypermutation of immunoglobulin genes. Little is known about the direct target genes of Bach2 in B cells. By analyzing various B cell and plasma cell lines, we showed that the expression patterns of Bach2 and Blimp-1 (B lymphocyte-induced maturation protein 1), a master regulator of plasma cell differentiation, are mutually exclusive. The reporter gene of the Blimp-1 gene (Prdm1) was repressed by the overexpression of Bach2 in B cell lines. The heterodimer of Bach2/MafK bound to the Maf recognition element located upstream of the Prdm1 promoter in an electrophoretic mobility shift assay. The binding of MafK in B cells to the Prdm1 Maf recognition element was confirmed by chromatin immunoprecipitation assays. When MafK was purified from the BAL17 B cell line, a significant portion of it was present as a heterodimer with Bach2, with no apparent formation of MafK homodimer. These results strongly suggest that Bach2 represses the expression of Blimp-1 together with MafK in B cells prior to plasma cell differentiation. Accordingly, the knockdown of Bach2 mRNA using short hairpin RNA in BAL17 cells resulted in higher levels of Prdm1 expression after the stimulation of B cell receptor by surface IgM cross-linking. Induction of Prdm1 was more robust and faster in primary Bach2-deficient B cells than in wild-type control B cells upon lipopolysaccharide stimulation. Therefore, the Prdm1 regulation in B cells involves the repression by Bach2, which may be cancelled upon terminal plasma cell differentiation.
authors.affiliation: Department of Biochemistry, Tohoku University Graduate School of Medicine, Seiryo-machi 2-1, Sendai 980-8575, Japan.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Ochiai
authors.forename: Yasutake
authors.initials: Y
authors.lastname: Katoh
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Ikura
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Hoshikawa
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Noda
authors.forename: Hajime
authors.initials: H
authors.lastname: Karasuyama
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tashiro
authors.forename: Akihiko
authors.initials: A
authors.lastname: Muto
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Igarashi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D017931:DNA Primers; D019281:Dimerization; D051379:Mice; D008969:Molecular Sequence Data; D000074462:Positive Regulatory Domain I-Binding Factor 1; D012333:RNA, Messenger / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
chemical_list: C102109:Bach2 protein, mouse; D050976:Basic-Leucine Zipper Transcription Factors; D017931:DNA Primers; C513258:Prdm1 protein, mouse; D012333:RNA, Messenger; D012097:Repressor Proteins; D014157:Transcription Factors; D000074462:Positive Regulatory Domain I-Binding Factor 1