Regulation of Histamine Synthesis and Tryptase Expression through Transcription Factors, Growth Factor Independent 1 (Gfi1) and Gfi1b, in Murine Cultured Mast Cells

Mast cells are involved in various immunological responses, although it remains unknown how their terminal differentiation is regulated. We previously established a culture model that mimics the process of mast cell maturation in the cutaneous tissue and found that growth factor independent 1 (Gfi1) was up-regulated whereas its paralogue Gfi1b down-regulated. Here we investigated the roles of Gfi1 and Gfi1b in the process of mast cell maturation using a murine mast cell line, MC9. Gfi1 and Gfi1b cDNAs were stably expressed in MC9 cells using the recombinant lentivirus. Histamine synthesis was significantly induced by stem cell factor (SCF) alone, whereas tryptase expression was significantly augmented in the presence of both SCF and Swiss 3T3 cells. Since exogenously expressed Gfi1 and Gfi1b might affect their expression levels in MC9 cells, we investigated the relationship between the expression profiles of Gfi1/Gfi1b proteins and maturation indices, such as histamine synthesis and tryptase expression. The comparison suggested that histamine synthesis during the co-culture period was positively regulated by Gfi1b while augmented expression of tryptase was abolished by one-sided expression of Gfi1/Gfi1b. Our findings indicated the involvement of Gfi1 and Gfi1b in the process of murine mast cell maturation.