Activation of the Mouse Ig Germline ε Promoter by IL-4 Is Dependent on AP-1 Transcription Factors

Abstract

Induction of germline (GL) ε transcripts, an essential step preceding Ig isotype switching to IgE, requires activation of transcription factors by IL-4 and a B cell activator, e.g., CD40 ligand or LPS. We demonstrate that AP-1 (Fos and Jun), induced transiently by CD40 ligand or LPS, binds a DNA element in the mouse GL ε promoter. AP-1 synergizes with Stat6 to activate both the intact GL ε promoter and a minimal heterologous promoter driven by the AP-1 and Stat6 sites of the mouse GL ε promoter. By contrast, C/EBPβ, which trans-activates the human GL ε promoter, inhibits IL-4 induction of the mouse promoter, probably by attenuating the synergistic interaction between AP-1 and Stat6. Furthermore, AP-1 does not trans-activate the human GL ε promoter. Thus, induction of GL ε transcripts in mice and humans may be regulated differently. In addition, although mouse GL ε transcripts have a half-life of ∼100 min, the RNA level continues to increase for up to 24 h, and the promoter appears to be active for at least 2 days after B cell activation. Altogether, these data suggest that induction of AP-1 activity, although transient, is required for activation of the mouse GL ε promoter by IL-4-induced Stat6.

CD40 Induces Interleukin-6 Gene Transcription in Dendritic Cells

“…Engagement and Fra1 at either the mRNA or protein level (41)(42)(43). However, few studies have investigated CD40 mediated induction of AP-1 activity or Jun and Fos protein family expression in monocytes or DCs.…”

Differential Regulation of Mouse Germline Ig γ1 and ε Promoters by IL-4 and CD40

“…CD40L or Ab to CD40 synergizes with IL-4 to further induce GL ⑀ and mouse ␥1 transcripts in cultured mouse splenic B cells (28 -32). In the absence of IL-4, CD40 signaling induces modest levels of GL ␥1 and ⑀ transcripts, but ␥1 transcripts appear to be more inducible than ⑀ transcripts (18,31,32).…”

“…1B presents the sequence of the IL-4-responsive region of the GL ⑀ promoter. If either the Stat6 or AP-1 element is mutated, IL-4 induction is completely eliminated (32,36,38). Furthermore, cotransfection of various AP-1 proteins along with the ⑀ reporter plasmid into the I.29 B cell line greatly activates the promoter in IL-4-treated cells (32).…”

“…The eukaryotic expression plasmids, cloned in pcDNA3, expressing CEBP␤, C/EBP␥, c-Fos, JunB, or c-Jun were described previously (32). Expression plasmids pcDNA3-ATF2 and the dominant-negative pcDNA3-ATF2dn were provided by Phyllis LuValle (University of Calgary, AB, Canada) (43).…”

Serum Response Factor Contributes Selectively to Lymphocyte Development

“…Induction of activator protein-1 is required for activation of the germline ⑀ promoter. This represents an essential step preceding immunoglobulin (Ig) isotype switching to IgE (38) and plays a central role in the regulation of promoter activity for interleu-kin-2 (IL-2) and interferon-␥ in T cells (25). The immediate early gene egr-1 has been shown to play a role in limiting the number of T cell precursors and in the efficient differentiation and survival of thymocytes during the process of positive selection (39).…”