The GC box at the proximal enhancer of the Hdc gene is critical for Hdc gene transcription and histamine-mediated anaphylaxis
Background: Histamine is a critical mediator of anaphylaxis, a neurotransmitter, and a regulator of gastric acid secretion. Histidine decarboxylase is a rate-limiting enzyme for histamine synthesis. However, in vivo regulation of Hdc, the gene that encodes histidine decarboxylase is poorly understood. Objective: We sought to investigate how enhancers regulate Hdc gene transcription and histamine synthesis in resting conditions and in a mouse model of anaphylaxis. Methods: H3K27 acetylation histone modification and chromatin accessibility were used to identify candidate enhancers; The enhancer activity of candidate enhancers was measured in a reporter gene assay; and the function enhancers were validated using CRISPR deletion. Results: Deletion of the GC box, which binds to zinc finger transcription factors, in the proximal Hdc enhancer, reduced Hdc gene transcription and histamine synthesis in the mouse and human mast cell lines. Mast cells, basophils, brain cells, and stomach cells from GC box-deficient mice transcribed the Hdc gene much less than similar cells from wild-type mice and Hdc GC box-deficient mice failed to develop anaphylaxis. Conclusion: Our results demonstrate that the HDC GC box within the proximal enhancer in the mouse and human HDC gene is essential for Hdc gene transcription, histamine synthesis, and histamine-mediated anaphylaxis in vitro and in vivo. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC="FIGDIR/small/495950v3_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@106f99org.highwire.dtl.DTLVardef@10ec8b8org.highwire.dtl.DTLVardef@19bb1ceorg.highwire.dtl.DTLVardef@b663cd_HPS_FORMAT_FIGEXP M_FIG C_FIG Key messages: O_LIThe HDC GC box within the proximal enhancer of the mouse and human HDC gene is essential for Hdc gene transcription and histamine synthesis in mouse and human mast cells. C_LIO_LIThe mouse Hdc GC box is required for histamine-mediated anaphylaxis in vivo. C_LI Capsule summary Our results demonstrate that the Hdc GC box within the proximal enhancer of the mouse and human HDC gene is essential for Hdc gene transcription and histamine synthesis in mast cells. The mouse Hdc GC box is required for histamine-mediated anaphylaxis in the mouse model of anaphylaxis.