TFEC is a macrophage-restricted member of the microphthalmia-TFE subfamilyof basic helix-loop-helix leucine zipper transcription factors

The murine homologue of the TFEC was cloned as part of an analysis of the e xpression of the microphthalmia-TFE (MiT) subfamily of transcription factor s in macrophages. TFEC, which most likely acts as a transcriptional repress or in heterodimers with other MiT family members, was identified in cells o f the mononuclear phagocyte lineage, coexpressed,vith all other known MiT s ubfamily members (Mitf, TFE3, TFEB), Northern blot analysis of several diff erent cell lineages indicated that the expression of murine TFEC (mTFEC) wa s restricted to macrophages. A 600-bp fragment of the TATA-less putative pr oximal promoter of TFEC shares features with many known macrophage-specific promoters and preferentially directs luciferase expression in the RAW264.7 macrophage cell line in transient transfection assays. Five of six putativ e Ets motifs identified in the TFEC promoter bind the macrophage-restricted transcription factor PU,I under in vitro conditions and in transfected 3T3 fibroblasts; the minimal luciferase activity of the TFEC promoter could be induced by coexpression of PU.1 or the related transcription factor Ets-2. The functional importance of the tissue-restricted expression of TFEC and a possible role in macrophage-specific gene regulation require further inve stigation, but are likely to be linked to the role of the other MiT family members in this lineage.