Cortactin localization in actin-containing adult and fetal tissues.

Cortactin is a tyrosine kinase substrate that binds to filamentous actin. It represents a highly conserved family of perimembrane signaling proteins. The human homologue of cortactin is encoded by gene EMS1, which is amplified in some human breast, head, and neck carcinomas. This study shows that cortactin is preferentially localized to the apical surfaces of the polarized epithelium, specifically, to the terminal web of small bowel epithelium and to apical surfaces of the proximal renal tubules, thyroid follicles, and bronchiolar epithelium. Cortactin is also seen in cell and tissue types with actin-based contractile capacities, including smooth and striated muscle and myoepithelium.