Critical Roles for PU.1, GATA1, and GATA2 in the Expression of Human FcεRI on Mast Cells: PU.1 and GATA1 Transactivate FCER1A, and GATA2 Transactivates FCER1A and MS4A2

The high-affinity IgE receptor, FceRI, which is composed of α-, β-, and γ-chains, plays an important role in IgE-mediated allergic responses. In the current study, involvement of the transcription factors, PU.1, GATA1, and GATA2, in the expression of FceRI on human mast cells was investigated. Transfection of small interfering RNAs (siRNAs) against PU.1, GATA1, and GATA2 into the human mast cell line, LAD2, caused significant downregulation of cell surface expression of FceRI. Quantification of the mRNA levels revealed that PU.1, GATA1, and GATA2 siRNAs suppressed the α transcript, whereas the amount of β mRNA was reduced in only GATA2 siRNA transfectants. In contrast, γ mRNA levels were not affected by any of the knockdowns. Chromatin immunoprecipitation assay showed that significant amounts of PU.1, GATA1, and GATA2 bind to the promoter region of FCER1A (encoding FceRIα) and that GATA2 binds to the promoter of MS4A2 (encoding FceRIβ). Luciferase assay and EMSA showed that GATA2 transactivates the MS4A2 promoter via direct binding. These knockdowns of transcription factors also suppressed the IgE-mediated degranulation activity of LAD2. Similarly, all three knockdowns suppressed FceRI expression in primary mast cells, especially PU.1 siRNA and GATA2 siRNA, which target FceRIα and FceRIβ, respectively. From these results, we conclude that PU.1 and GATA1 are involved in FceRIα transcription through recruitment to its promoter, whereas GATA2 positively regulates FceRIβ transcription. Suppression of these transcription factors leads to downregulation of FceRI expression and IgE-mediated degranulation activity. Our findings will contribute to the development of new therapeutic approaches for FceRI-mediated allergic diseases.