Regulatory Control of Breast Tumor Cell Poly (ADP-Ribose) Polymerase

Abstract

Abstract : We have previously isolated an intact, stable, and fully functional multiprotein DNA replication complex (designated the DNA synthesome) from a variety of non-malignant and malignant tumor cells and tissues including breast cancer cells. We have also shown that poly(ADP-ribose) polymerase (PARP) is among the components of the DNA synthesome. The transformation of a non-malignant human cell to a malignant state is accompanied by a significant alteration in the mobility of specific components of the DNA synthesome, (such as PCNA) following 2D-PAGE analysis of the DNA synthesome, together with a 4-6-fold decrease in the replication fidelity of the replication complex. In order to establish whether the malignant transformation process is accompanied by an alteration in PARP, we purified PARP from malignant and non-malignant breast cells using phosphocellulose and hydroxylapatite chromatography. When analyzed by 2D SDS-PAGE, PARP isolated from the two cell lines showed a difference in the electrophoretic migration pattern. The enzyme present in non-malignant breast cells had a basic pI and was resolved as a single spot; however, malignant breast cell PARP appeared as a basic spot in addition to less abundant species having less basic pI values. The altered PARP isoforms were detected both in estrogen-dependent (MCF-7) and non-estrogen-dependent (MDA MB-468) cells. In addition, these isoforms were detected in ovarian cancer cell line PA-1. We have also found that PARP from malignant breast cells has different kinetic properties (Km and Vmax) than those of non-malignant PARP. Moreover, nuclear proteins in malignant and non-malignant breast cells are differentially poly(ADP-ribosylated). The results presented in this report suggest that PARP might have a different role during malignancy.