International Immunology Advance Access originally published online on June 5, 2009
International Immunology 2009 21(7):803-816; doi:10.1093/intimm/dxp048
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Roles of PU.1 in monocyte- and mast cell-specific gene regulation: PU.1 transactivates CIITA pIV in cooperation with IFN-
1 Atopy (Allergy) Research Center, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan
2 Department of Dermatology, Tokyo Medical University, 6-7-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo 160-0023, Japan
3 Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
4 Department of Immunology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan
5 Department of Ophthalmology, Tokyo Medical University, 6-7-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo 160-0023, Japan
Correspondence to: C. Nishiyama; E-mail: chinishi{at}juntendo.ac.jp
Over-expression of PU.1, a myeloid- and lymphoid-specific transcription factor belonging to the Ets family, induces monocyte-specific gene expression in mast cells. However, the effects of PU.1 on each target gene and the involvement of cytokine signaling in PU.1-mediated gene expression are largely unknown. In the present study, PU.1 was over-expressed in two different types of bone marrow-derived cultured mast cells (BMMCs): BMMCs cultured with IL-3 plus stem cell factor (SCF) and BMMCs cultured with pokeweed mitogen-stimulated spleen-conditioned medium (PWM-SCM). PU.1 over-expression induced expression of MHC class II, CD11b, CD11c and F4/80 on PWM-SCM-cultured BMMCs, whereas IL-3/SCF-cultured BMMCs expressed CD11b and F4/80, but not MHC class II or CD11c. When IFN-
was added to the IL-3/SCF-based medium, PU.1 transfectant acquired MHC class II expression, which was abolished by antibody neutralization or in Ifngr–/– BMMCs, through the induction of expression of the MHC class II transactivator, CIITA. Real-time PCR detected CIITA mRNA driven by the fourth promoter, pIV, and chromatin immunoprecipitation indicated direct binding of PU.1 to pIV in PU.1-over-expressing BMMCs. PU.1-over-expressing cells showed a marked increase in IL-6 production in response to LPS stimulation in both IL-3/SCF and PWM-SCM cultures. These results suggest that PU.1 overproduction alone is sufficient for both expression of CD11b and F4/80 and for amplification of LPS-induced IL-6 production. However, IFN- stimulation is essential for PU.1-mediated transactivation of CIITA pIV. Reduced expression of mast cell-related molecules and transcription factors GATA-1/2 and up-regulation of C/EBP
in PU.1 transfectants indicate that enforced PU.1 suppresses mast cell-specific gene expression through these transcription factors.
Transmitting editor: S. Koyasu
Received 29 November 2007, accepted 28 April 2009.