Up-regulation of mouse mast cell protease-6 gene by transforming growth factor-β and activin in mast cell progenitors

Previous studies have revealed that members of the transforming growth factor-β (TGF-β) including TGF-β1 and activin A modulate the function of mast cells. Here we show the up-regulation of mouse mast cell protease-6 (mMCP-6), which is expressed in differentiated mast cells, by TGF-β1 and activin A in bone marrow-derived cultured mast cell progenitors (BMCMCs). Quantitative real time RT-PCR analyses revealed that the mRNA level of mMCP-6 was slightly but reproducibly increased by treatment with TGF-β1 or activin A, which was regulated at the transcription level. Reporter assays showed that Smad3, a signal mediator of the TGF-β/activin pathway, was responsible for the transcription. The TGF-β response element is located at −153 bp relative to the transcription initiation site, CAGA. Microphthalmia-associated transcription factor (MITF), a tissue-specific transcription factor predominantly expressed in mast cells, melanocytes, the heart and skeletal muscle, also stimulated the transcription of mMCP-6. The region at −166 bp, GACCTG, was responsible for MITF-induced transcription. Mutations of the CAGA motif and the MITF responsive site indicated that the MITF site of mMCP-6 promoter is indispensable for the transcriptional activation by a constitutively active TGF-β receptor (ALK5-TD), whereas the CAGA motif is dispensable for transcription by MITF. Transcriptional activation of mMCP-6 by the TGF-β pathway was differently interacted with that by MITF isoform; ALK5-TD further enhanced MITF-E-induced transcription, whereas MITF-M-induced transcription abolished responsiveness to ALK5-TD. The positive regulation of mMCP-6 by the TGF-β/activin pathway and the differential regulation by the MITF isoform suggest a rigorous regulation of mast cell function as effector cells of immune response.