Using our antibodies directed against amphiregulin, we have studied the in vivo expression and localization of amphiregulin in normal human colon, human colon carcinomas and normal human placenta. In all normal colon specimens, amphiregulin was detected and localized to the terminally-differentiated, nonproliferative epithelial cells of mucosal surface. In 18 of 36 cancers, amphiregulin was detected in the proliferative malignant epithelial cells of the tumors and was more commonly detected in the well-differentiated carcinomas (71%). Amphiregulin was detected in the terminally-differentiated syncytiotrophoblasts of human placenta but was not detectable after 18 weeks of gestation. In all three instances , amphiregulin was detected in the nucleus as well as cytoplasm of the cells in vivo. Thus, amphiregulin expression in normal tissues is related to differentiation, but amphiregulin may function as autocrine growth stimulator in colonic carcinomas. An evaluation of the mechanism of action of amphiregulin in a human colon carcinoma cell line reveals that the cells secrete amphiregulin and that it acts via an extracellular autocrine loop to drive the proliferation of the cells. The data suggests that amphiregulin acts through the EGF receptor. Expression of the cDNA for various oncogenes result in the transformation of normal human mammary epithelial cells and the concomitant elevated expression of amphiregulin mRNA and protein, suggesting that amphiregulin may be a key intermediate in oncogene-mediated malignant transformation.
