Analysis of polypeptide expression in benign and malignant human breast lesions: down-regulation of cytokeratins

Abstract

Summary Malignant progression of tumour cells is caused by the accumulation of genetic defects, which when combined will generate a large phenotypic diversity. Simultaneous quantitation of a large number of gene products in tumour cells is desirable, but difficult to achieve. We have here quantitated the levels of a number of abundant polypeptides in human breast carcinoma cells using two-dimensional gel electrophoresis (2-DE; PDQUEST). For this purpose, tumour cells were prepared from the tissue of 17 breast carcinomas. Fibroadenoma tissue was used as reference for benign cells. An increase of the spot density of the PCNA polypeptide was observed in rapidly proliferating tumour cells, confirming the validity of the procedures used. In the set of 24 polypeptide spots with known identity, decreases in cytokeratin and tropomyosin levels were observed. The levels of all cytokeratin forms resolved (CK7, CK8, CK15 and CK18) were significantly lower in carcinomas than in fibroadenomas. The levels of tropomyosin 2 and 3 were lower in carcinomas than in fibroadenomas. In contrast, the levels of some members of the stress protein family (pHSP60, HSP90 and calreticulin) were higher in carcinomas. Furthermore, changes in the expression of lactate dehydrogenase and GT-i, but not in nm23, were observed. We conclude that simultaneous analysis of multiple polypeptides in human carcinomas can be achieved by 2-DE and may be useful in prognostic studies, and that malignant progression of breast carcinomas results in the decreased expression of cytokeratin polypeptides. This phenomenon must be considered in studies where cytokeratins are used as markers to identify the epithelial cell compartment in breast carcinomas.Keywords: two-dimensional gel electrophoresis; human breast tumour; cytokeratin Breast cancer is both biologically and clinically a heterogeneous disease. Although presenting without evidence of disseminating cancer, a proportion of women will die rapidly in metastatic disease. In spite of enormous efforts in breast cancer research, three main problems remain: (1) to objectively and reliably select those premalignant lesions which, if untreated, will progress to invasive malignancy; (2) to objectively and reliably determine the aggressiveness of an individual tumour and (3) to analyse cellular properties which allow highly individualised tumour-specific treatment.Two-dimensional gel electrophoresis (2-DE) is a technique which can be used to obtain qualitative and quantitative information on protein expression in cells. In a recent update of the two-dimensional protein database, 1082 proteins were reported to be identified by name (Celis et al., 1995). Identification is aided by recent progress in microsequencing, including mass spectrophotometry. We have here explored 2-DE to characterise polypeptide profiles in human breast carcinomas. Major polypeptides in the gel profiles were identified (mostly cytoskeletal and stress-related proteins) and quantified. We describe alterations in the expression of some of these poly...

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