![]() ![]() The expression of the two topoisomerase II genes was apparently not co-ordinately regulated in these tissue samples. To assess the relationship between expression of topoisomerase II isoforms and established prognostic factors and pathological variables, 56 primary breast tumour samples were studied. The relative level of expression of the alpha and beta isoforms may contribute to the degree of tumour responsiveness to different chemotherapeutic agents. Two isoforms of topoisomerase II (alpha and beta) have been described in human cells which differ in their subcellular localisation, biochemical properties and susceptibility to inhibition by anti-cancer drugs. Topoisomerase II is a key target for several anti-cancer drugs used for breast cancer therapy, including doxorubicin, epirubicin and mitoxantrone. The association of exposure to topo II- reactive chemotherapy with 11q23 rearrangements involving the MLL gene in t-AML suggests that topo II may play a role in the aberrant recombination events that occur in this region both in AML de novo and in t-AML. Our study indicates that the MLL gene rearrangements are similar both in AML that develops de novo and in t-AML. Of the 5 patients lacking 11q23 rearrangements, some of whom had monoblastic features, none had an MLL rearrangement, although 4 had received topo II inhibitors. None of the patients who had not received topo II inhibitors showed an MLL rearrangement. Ten of the 12 t-AML patients had received topo II inhibitors and 9 of these, all with balanced translocations of 11q23, had MLL rearrangements on Southern blot analysis. We have studied 17 patients with t-MDS/t-AML, 12 of whom had cytogenetically detectable 11q23 rearrangements. We previously identified a gene, MLL (myeloid-lymphoid leukemia or mixed-lineage leukemia), at 11q23 that is involved in the de novo leukemias. These leukemias develop after a relatively short latent period and often follow the use of drugs that inhibit the activity of DNA-topoisomerase II (topo II). Five percent to 15% of patients treated with chemotherapy for a primary neoplasm develop therapy-related AML (t-AML) that may show rearrangements, usually translocations involving band 11q23 or, less often, 21q22. These proteins are distinct from the major nuclear matrix proteins and may be involved in mediating chromosome territory organization.Ĭhromosome band 11q23 is frequently involved in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) de novo, as well as in myelodysplastic syndromes (MDS) and lymphoma. A second treatment results in disruption of the chromosome territories in conjunction with the release of a small subset of acidic proteins. Based on these findings, we developed a fractionation strategy to release the bulk of nuclear matrix proteins under conditions where the chromosome territories are maintained intact. Identical results were obtained using eight different human chromosome paints. Correlative with territorial disruption is the formation of a faint DNA halo surrounding the nuclear lamina and a dispersive effect on the characteristically discrete DNA replication sites in the nuclear interior. In contrast, complete extraction of the internal nuclear matrix components with RNase treatment followed by 2 M NaCl results in the disruption of higher order chromosome territory architecture. We report for the first time that chromosome territories are maintained intact on the nuclear matrix. To study the possible role of the nuclear matrix in chromosome territory organization, normal human fibroblast cells are treated in situ via classic isolation procedures for nuclear matrix in the absence of nuclease (e.g., DNase I) digestion, followed by chromosome painting. Several MAR binding proteins have been identified in association with the nuclear matrix (von Kries et al., 1991 Romig et al., 1992 Dickinson et al., 1992 Dickinson et al.,, 1997 Tsutsui et al., 1993 Fackelmayer et al., 1994 Dickinson and Kohwi-Shigematsu, 1995 Wang et al., 1995 Liu et al., 1997 de Belle et al., 1998). These chromatin loops are believed to be anchored to components of the nuclear matrix or chromosome scaffold by S/MARs (scaffold/matrix attachment regions) 1, which presumably bind to specific components on the nuclear matrix/scaffold (Goldberg et al., 1983 Pienta and Coffey, 1984 Nelson and Coffey, 1987 Chai and Sandberg, 1988 Laemmli et al., 1992 Roberge et al., 1992 Hiraoka et al., 1993). While the question remains as to what mediates organization into chromosome territories, numerous studies have demonstrated that chromatin is arranged into repeating loop domains of 50–200 kb in the interphase nucleus and mitotic chromosomes (Cook and Brazell, 1975 Cook et al., 1976 Paulson and Laemmli, 1977 Pardoll et al., 1980 Vogelstein et al., 1980). ![]()
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