Identification and characterization of c-erbB-2 proteins in serum, breast tumor tissue, and SK-BR-3 cell line.

We have identified and characterized c-erbB-2 protein molecules in sera from patients with carcinomas, in both cytosol and cell membrane extract from breast tumor tissue and in both the culture medium and cell extract of the SK-BR-3 cell line. These proteins were characterized by various chromatographic techniques and identified by the use of two immunoassays; one measures both the c-erbB-2 oncoprotein (p185) and its ectodomain (p120), and the other in-house assay reacts specifically for p185. We found that the majority of the immunoreactivity detected in the serum, tumor tissue cytosol, and conditioned cell medium was derived from the ectodomain molecule (p120) of the c-erbB-2 oncoprotein (p185), whereas only p185 was detected in the extracts from cell membrane of both tumor tissue and the SK-BR-3 cell line. The ectodomain molecules (p120) found in the serum, cytosol, and cell medium were very similar in terms of molecular size and charge property. The molecular weight was determined to be 120 kDa by the size exclusion HPLC method. Both p120 and p185 are glycoproteins and were retained by the ConA Sepharose column. Both molecules are also heterogeneous in charge and multiple peaks could be identified in the elution profiles of anion exchange HPLC and chromatofocusing. This information should not only facilitate the isolation of these molecules, but also improve preparation of specific antibodies, preparation of calibrators, and development of improved assays for these proteins.