ID3 and breast carcinoma: Inhibitors of DNA binding proteins 1 may regulate antifibrotic effects independent of E-box promoter regulators.34,48,74 Apart from their role of inhibiting and regulating gene transcription, ID1 also binds to estrogen receptor β (ERβ) and inhibits breast cancer cell proliferation.46 Due to their varied cellular functions in different cell types, ID1 and ID3 proteins are localized in the nucleus as well as in the cytoplasm of cells.48,75 Our studies demonstrated a similar pattern of expression of ID1 and ID3 proteins in the primary human TM cells.