Epiregulin acts as a local signal mediator and shows dual biological activity, stimulating the proliferation of fibroblasts, hepatocytes, smooth muscle cells, and keratinocytes while also inhibiting the growth of several tumor-derived epithelial cell lines. Epiregulin was first identified in NIH 3T3 cell conditioned medium, and is one of the seven known ligands for the epidermal growth factor receptor (EGFR). Epiregulin is synthesized as a transmembrane precursor before being proteolytically cleaved to release a 46-amino-acid active protein. Epiregulin also shows more potent bioactivity in vitro than other EGF-like growth factors