TGF-alpha is a member of the EGF family of cytokines that are synthesized as transmembrane precursors with soluble forms released by proteolytic cleavage. Membrane-bound proTGF-alpha is biologically active and plays a role in mediation of cell-cell adhesion and in juxtacrine stimulation of adjacent cells. Expression of TGF-alpha is widespread in tumors and transformed cells. TGF-alpha is also expressed in normal tissues during embryogenesis and in adult tissues, including pituitary, brain, keratinocytes and macrophages. TGF-alpha binds and activates the EGF receptor. It induces fibroblast proliferation, epithelial development, keratinocyte migration, and angiogenesis.