We explored transcriptional regulation of mouse mast cell protease-9 (mMCP-9), which is implicated in inflammation of the jejunum during helminth infections and tissue remodeling of the uterus during pregnancy. Transcription was positively regulated by microphthalmia-associated transcription factor (MITF), a member of the basic helix-loop-helix-leucine zipper family that binds to the E-box, a CANNTG sequence. The most significant segment for positive regulation by MITF was nt - 183 to - 177 of the mMCP-9 promoter, CATCATG, which bound MITF-M. In addition, not only other MITF isoforms but also TFE3, another member of the family, activated mMCP-9 transcription through this nucleotide sequence inserted one base within the E-box. (C) 2003 Elsevier Inc. All rights reserved.