Identification of nuclear matrix proteins crosslinked to DNA by cis-DDP in situ in human breast cancer cell lines

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Spencer, Virginia Ann
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The nuclear matrix (NM) plays an important role in the structural and functional organization of the cell nucleus. Human breast cancer is a disease that is thought to progress from a well-differentiated, hormone-dependent state to a poorly-differentiated, hormone-independent state. NM protein composition, and the interaction of NM proteins with intermediate filament proteins varies over human breast cancer progression, suggesting that NM proteins may be prognostic markers of cancer progression. Cell lines representing each stage of human breast cancer progression were treated with cis-diamminedichloroplatinum(II) to crosslink proteins to nuclear DNA in situ, and the DNA-bound proteins were isolated. Two-dimensional profiles of DNA-crosslinked proteins from the cell lines investigated showed a remarkable similarity to one another as well as to each cell line's respective NM profile. However, differences in the types of DNA-crosslinked proteins were observed between cell lines representative of each stage of disease progression, thus adding to the importance of the NM, and, more specifically, NM-DNA interactions in breast cancer development. As well, the association of some DNA-crosslinked proteins such as cytokeratins 8, 18 and 19 was dependent on estrogen in a hormone-depen ent human breast cancer cell line, but not in a hormone-independent human breast cancer cell line. Thus, the acquisition of a hormone-independent phenotype may interfere with the ability of estrogen to regulate intermediate filament-nuclear DNA interactions in human breast cancer cells. These findings suggest that some of the various cellular events leading to malignancy in human breast cancer involve the NM and the cytoskeleton (CSK). Furthermore, the characterization of NM proteins and proteins crosslinked to DNA by cis-DDP in situ, which are primarily NM proteins, are two complementary approaches to identify NM proteins that are informative in cancer diagnosis.