Detection of a biomarker for the cancer status of ovarian epithelial cells

Abstract

A screen of ovarian and breast non-malignant and malignant samples was conducted using a novel antiserum against the proliferating cell nuclear antigen (PCNA) to assess the status of the PCNA protein in the samples. The novel antiserum, called “B1 antiserum”, was generated against a synthetic peptide representing a binding domain of the PCNA protein. Protein extracts from primary cultures of non-malignant ovarian surface epithelial cells, ovarian cancer cell lines, non-malignant ovarian tissue samples and ovarian tumours were prepared and resolved by 2 D gel electrophoresis, transferred to membranes and blotted with the B1 antiserum. The antiserum detected a novel protein, as well as PCNA, in the non-malignant samples but the novel protein was absent in the malignant samples. The novel protein was detected at a molecular weight of about 45 kD and an isoelectric point (pI) of approximately 5.5 vs. a molecular weight of 36 kD and pI of 4.6 for PCNA. We refer to the novel protein as the B1 protein. A panel of PCNA antibodies to different epitopes of the protein did not detect the novel B1 protein in Western blots, making it unlikely that the B1 protein is a modified form of PCNA. The B1 protein has not been observed in other cell types such as fibroblasts or smooth muscle cells nor in malignant ovarian epithelial cell lines or tumor samples. Interestingly, the B1 protein does occur in the ovarian cancer line PA-1, which is not of epithelial origin. These observations indicate that B1 could be tumor suppressor associated with epithelial cell types. Support from the Northern Ontario School of Medicine and U.S. D.O.D.