C-erbB-2 gene product, a membrane protein commonly expressed on human fetal epithelial cells.

C-erbB-2 is a human proto-oncogene which has homologies with the well known proto-oncogene c-erbB. The c-erbB-2 gene is amplified and overexpressed in some human adenocarcinomas. Its expression, in terms of RNA levels in normal human fetal kidney, lung and liver, has also been reported. In the present study, various fetal tissues from three human abortuses obtained at 9, 14 and 24 weeks of gestation, were studied immunohistologically by the ABC method and immunochemically by Western blot analysis for the distribution of c-erbB-2 gene product at the protein level. A polyclonal antibody raised in rabbit by immunization with a synthetic polypeptide corresponding to part of the predicted intracytoplasmic domain was used. Strong immunoreactivity was observed on the membrane of most of the epithelial cells examined, including transitional cells of the renal pelvis and ureter, glandular cells of the gastrointestinal tract, renal tubuli, bronchi and pancreas, and stratified epithelium of the oral cavity, trachea and esophagus in this gestational period. A much more intense reaction was observed on the basolateral sides than on the apical side of these cells. No immunoreactivity was found in the liver, adrenal gland, striated and smooth muscles, brain, endothelium or fibroblasts. Western blot analysis confirmed increased expression of the c-erbB-2 gene product in fetal kidney and intestine but not in the brain. As the protein seems to be poorly expressed in normal adult epithelial cells except for renal tubuli, the present results suggest that the protein is a membrane-associated receptor protein which controls some specific reaction of fetal epithelium.