Transcriptional regulator that acts as a repressor or an activator. Acts as a transcriptional transactivator on the proximal promoter region of the tartrate-resistant acid phosphatase (TRAP) E-box containing promoter. Collaborates with MITF in target gene activation. Acts as a transcriptional repressor on minimal promoter containing element F (that includes an E-box sequence) (By similarity). Binds to element F in an E-box sequence-specific manner (By similarity). Acts as a transcriptional repressor on minimal promoter containing mu E3 enhancer sequence (By similarity). Binds to mu E3 DNA sequence of the immunoglobulin heavy-chain gene enhancer (By similarity). Binds DNA in a homo- or heterodimeric form. Homodimer. Forms heterodimers with MITF. Interacts with MITF. Forms heterodimers with TFE3 (By similarity). Expressed in osteoclast-like cells (at protein level). Expressed in cells of the mononuclear phagocyte lineage. Expressed in macrophages and in osteoclast-like cells. Expressed in the early developing retinal pigmented epithelium and in the peripheral retina. Up-regulated in bone marrow-derived macrophages by Th2 cytokines, IL-4, IL-13 and LPS. Contains an activation domain in the C-terminal region. Belongs to the MiT/TFE family.