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Query: UMLS:C0006142 (breast cancer)
 160,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recent advances in defining the molecular mechanisms of cell cycle control in eukaryotes provide a basis for better understanding the hormonal control of cell proliferation in normal and neoplastic breast epithelium. It is now clear that a number of critical steps in cell cycle progression are controlled by families of serine/threonine kinases, the cdks. These kinases are activated by interactions with various cyclin gene products which form the regulatory subunits of the kinase complexes. Several families of cyclins control cell cycle progression in G1 phase, cyclins C, D and E, or in S, G2 and mitosis, cyclins A and B. Recent studies have defined the expression and regulation of cyclin genes in normal breast epithelial cells and in breast cancer cell lines. Following growth arrest of T-47D breast cancer cells by serum deprivation restimulation with insulin results in sequential induction of cyclin genes. Cyclin D1 mRNA increases within 1 h of mitogenic stimulation and is followed by increased expression of cyclins D3 and E in G1 phase, cyclin A in late G1/early S phase and cyclin B1 in G2. Similar results were observed following epidermal growth factor stimulation of normal breast epithelial cells. Other hormones--oestrogens and progestins--and growth factors--insulin-like growth factor-I and basic fibroblast growth factor--with actions in G1 were also investigated for their effects on G1 cyclin gene expression. In all cases there was an excellent correlation between the induction of cyclin D1 mRNA and subsequent entry into S phase. Furthermore, growth inhibition by antioestrogens and concurrent G1 arrest were preceded by an acute decrease in cyclin D1 gene expression. These observations suggest a likely role for cyclin D1 in mediating many of the known hormonal effects on cell proliferation in breast epithelial cells.
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PMID:Cyclin gene expression and growth control in normal and neoplastic human breast epithelium. 827 47

Recent studies have identified a family of proteins called cyclins that control cell cycle. Among these proteins, cyclin B synthesis and degradation are necessary and sufficient to cause a Xenopus egg cell-free system to oscillate between S and M. To understand the link between hormonal regulation of cell growth and the expression of B-type cyclins, we studied the effect of estradiol on cyclin B1 mRNA in a hormone-responsive breast cancer cell line, MCF-7. Cells were synchronized at G1 by isoleucine starvation, and estradiol was added along with the removal of cell cycle block. Flow cytometric analysis showed 81 +/- 7% cells in G1 after 30 h of isoleucine starvation. Significant population of cells progressed to S by 16 h after the addition of estradiol, whereas a comparable transition occurred in control cells by 36 h only. In cells progressing from G1-->S-->G2-->M under the influence of estradiol, there was a significant increase in cyclin B1 mRNA at 30 and 36 h, consistent with the accumulation of this cyclin in G2/M. In addition, we found that cyclin B1 mRNA degradation occurred early in G1, and this process was accelerated by estradiol. At 2 h after removal of the isoleucine block, there was a 40% reduction in the level of cyclin B1 mRNA in estradiol-treated cells compared to untreated controls. Cyclin B1 protein degradation followed a similar pattern, as determined by Western blots using a monoclonal anti-cyclin B1 antibody. Since previous studies suggested a polyamine pathway in the mechanism of action of estradiol, we questioned whether polyamines are important in controlling the level of cyclin B1 mRNA. Treatment of synchronized cells with the polyamine biosynthetic inhibitor, difluoromethylornithine attenuated cyclin B1 mRNA degradation in the presence of estradiol. This process was mostly reversed by exogenous putrescine and spermidine but not by putrescine homologues. Collectively, these data suggest that the mechanism of cell growth regulation by estradiol in MCF-7 cells includes alterations in cyclin B1 mRNA. Our data also indicate molecular pathways for the action of polyamines in estrogenic control of cell cycle.
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PMID:Regulation of cyclin B1 by estradiol and polyamines in MCF-7 breast cancer cells. 831 64

If exposure to xenoestrogens or electromagnetic fields (EMFs) such as 60 Hz contributes to the etiology of breast cancer, it is likely that they must stimulate the growth of breast cells, damage genetic material or enhance the effects of other mitogenic or mutagenic agents (co-promotion). Therefore, the ability of xenoestrogens or exposure to 60-Hz fields to stimulate the entry of growth-arrested human breast cancer cells into the cell cycle was determined using cyclin-dependent kinase 2 (Cdk2) activity, synthesis of cyclin D1 and cdc2 activity. Exposure of estrogen receptor-positive MCF-7 or T-47D cells to estrogen and xenoestrogens (DDT and Red No. 3) increased Cdk2 and cyclin B1-cdc2 activity and cyclin D1 synthesis. Exposure of breast cancer cells to 12 mG or 1 or 9 G electromagnetic fields at 60 Hz failed to stimulate Cdk2 or cyclin B1-cdc2 activity or cyclin D1 synthesis. Simultaneous co-exposure of cells to 60-Hz fields and chemical promoters did not enhance Cdk2 activation above the levels produced by the chemical promoter alone. Estrogen and xenoestrogens also stimulated binding of the estrogen receptor to the estrogen receptor element but the EMF did not. Phorbol 12-myristate 13-acetate (PMA) induced phosphorylation of p53 and pRb1O5 in MCF-7 cells, but EMF exposure had no effect. DNA-damaging chemotherapeutic agents and Red Dye No. 3 were found to increase p53 site-specific DNA binding in breast cancer cells, but EMF exposure did not. Differential display analysis failed to detect any effect of EMF exposure on gene expression in MCF-7 cells, whereas the effects of estradiol were detected. These studies suggest that estrogen and xenoestrogens stimulate growth-arrested breast cancer cells to enter the growth cycle, but EMF exposure does not. Site-specific p53-DNA binding was increased in MC F-7 cells treated with DNA-damaging agents, but not by EMF exposure. EMF exposure does not appear to act as a promoter or DNA-damaging agent for human breast cancer cells in vitro.
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PMID:Effects of 60-Hz fields, estradiol and xenoestrogens on human breast cancer cells. 892 16

We investigated the in vivo expression of cyclin B1 and Cdc2 (key molecules for G2-M transition during the cell cycle) in nonmalignant and cancerous human breast lesions using immunohistochemistry and quantitative proliferative index (PI) analysis. Breast epithelial cells co-expressed cyclin B1 and Cdc2 in their cytoplasm in the G2 phase and in their nuclei in the M phase. Cyclin B1, but not Cdc2, immunostaining rapidly disappeared from the nuclei during the mitotic metaphase to anaphase transition. Static image analysis revealed the mean proliferative index for cyclin B1/cdc2 for each type of lesion to be as follows: normal glands (n = 20), 2.0/2.5%; benign lesions, including typical ductal hyperplasia (n = 76), 2.5/5.8%; atypical ductal hyperplasia (n = 21), 3.0/6.6%; carcinomas in situ (n = 70), 7.4/14.0%; and invasive carcinomas (n = 58), 10.0/22.9%. Proliferative index data for atypical hyperplasia were virtually identical to those for benign lesions and were significantly lower than those for breast cancer, suggesting that expression levels of cyclin B1 and Cdc2 may be used to distinguish premalignant human breast lesions from advanced disease. Furthermore, the proliferative index for cyclin B1 for comedo-type ductal carcinomas in situ agreed with that for invasive ductal carcinomas (mean, 10.1% versus 9.5%), apparently explaining the clinicopathological aggressiveness of this tumor at the molecular level.
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PMID:Expression of the G2-M checkpoint regulators cyclin B1 and cdc2 in nonmalignant and malignant human breast lesions: immunocytochemical and quantitative image analyses. 900 17

Tyrphostins are a group of compounds specifically targeted for the inhibition of tyrosine phosphorylation in signal transduction pathways. We studied the effects of a tyrphostin, 3,4-dihydroxy-alpha-cyanothiocinnamamide (tyrphostin-47), on hormone-responsive MCF-7 and hormone-unresponsive MCF-7-5C cell growth by DNA analysis for a period of 10 days. The growth of both cell lines was inhibited by this drug at 50 and 100 microM concentrations. Flow cytometric analysis showed that tyrphostin treatment caused a significant delay in the progression of MCF-7 cells through G1 and S phases of the cell cycle. The level of cyclin B1, a component of the mitosis promoting factor (MPF), was reduced by 90% in the presence of 100 microM tyrphostin. The other component of MPF, p34cdc2 kinase, was not affected; however, its functional activity was dramatically reduced, as determined by histone H1 phosphorylation assay. In contrast, G1 cyclins (D1 and E) and tyrosine kinase activity were not markedly affected by tyrphostin-47, as determined by Western immunoblot detection with specific antibodies. Our results suggest that a possible mechanism of tyrphostin action in breast cancer cells might involve the suppression of cyclin B1 and inhibition of the functional activity of cyclin B1/p34cdc2 complex. Our data indicate that the cell cycle machinery might be a target for developing novel drugs for breast cancer.
Breast Cancer Res Treat 1997 May
PMID:Mechanism of action of a tyrphostin, 3,4-dihydroxy-alpha-cyanothiocinnamamide, in breast cancer cell growth inhibition involves the suppression of cyclin B1 and the functional activity of cyclin B1/p34cdc2 complex. 916 77

In order to elucidate the biochemical mechanisms by which the universal cyclin kinase inhibitor p27Kip1 regulates cell cycle progression in human breast cancer cells, a recombinant adenovirus expressing human p27 was constructed (Adp27). Upon infection of human breast cancer cells MDA-MB-231 and MCF-7 with Adp27, a high level of p27 expression was observed, and this resulted in a marked decrease in the proportion of cells in S-phase. In multiple cell lines, comparison of the cytotoxicity of Adp27 with another adenovirus vector expressing the related universal cyclin kinase inhibitor WAF1/Cip1 (AdWAF1), showed Adp27 to be markedly more (up to 56-fold) toxic than AdWAF1. DNA histograms showed Adp27 to cause a G1/S arrest at lower viral doses than AdWAF1. Analysis of cyclin dependent kinase activity following Adp27 infections showed decreased Cdk2 and cyclin B1-Cdc2 activity at lower viral doses when compared with AdWAF1. Adp27 is therefore potentially useful for studies of growth regulation and for gene therapy when growth inhibition is desired.
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PMID:A recombinant adenovirus expressing p27Kip1 induces cell cycle arrest and loss of cyclin-Cdk activity in human breast cancer cells. 917 4

BRCA1, a familial breast and ovarian cancer susceptibility gene encodes nuclear phosphoproteins that function as tumor suppressors in human breast cancer cells. Previously, we have shown that overexpression of a BRCA1 splice variant BRCA1a accelerates apoptosis in human breast cancer cells. In an attempt to determine whether the subcellular localization of BRCA1 is cell cycle regulated, we have studied the subcellular distribution of BRCA1 in asynchronous and growth arrested normal, breast and ovarian cancer cells using different BRCA1 antibodies by immunofluorescence and immunohistochemical staining. Upon serum starvation of NIH3T3, some breast and ovarian cancer cells, most of the BRCA1 protein redistributed to the nucleus revealing a new type of regulation that may modulate the activity of BRCA1 gene. We have also characterized two new variant BRCA1 proteins (BRCA1a/p110 and BRCA1b/ p100) which are phosphoproteins containing phosphotyrosine. Immunofluorescence and Western blotting analysis indicate cytoplasmic and nuclear localization of BRCA1a and BRCA1b proteins. To elucidate the biological function of BRCA1, we created a bacterial fusion protein of glutathione-transferase (GST) and BRCA1 zinc finger domain and detected two cellular proteins with molecular weights of approximately 32 and 65 kD, one of which contains phosphotyrosine designated p32 and p65 BRCA1 interacting proteins (BIP) that specifically interact with BRCA1. Western blot analysis of BIP with cyclins/CDKs and E2F antisera indicated association with cdc2, cdk2, cdk4, cyclin B, cyclin D, cyclin A and E2F-4 but not with cdk3, cdk5, cdk6, E2F-1, E2F-2, E2F-3, E2F-5 and cyclin E. Furthermore, we have also demonstrated a direct interaction of in vitro translated BRCA1a and BRCA1b proteins with recombinant cyclin A, cyclin B1, cyclin D1, cdc2, cdk2 and E2F fusion proteins in vitro. Taken together these results seem to suggest that BRCA1 could be an important negative regulator of cell cycle that functions through interaction with E2F transcriptional factors and phosphorylation by cyclins/cdk complexes with the zinc ring finger functioning as a major protein-protein interaction domain. If the interactions we observe in vitro is also seen in vivo then it may be possible that lack or impaired binding of the disrupted BRCA1 proteins to E2F, cyclins/CDKs in patients with mutations in the zinc finger domain could deprive the cell of an important mechanism for braking cell proliferation leading to the development of breast and ovarian cancers.
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PMID:BRCA1 proteins are transported to the nucleus in the absence of serum and splice variants BRCA1a, BRCA1b are tyrosine phosphoproteins that associate with E2F, cyclins and cyclin dependent kinases. 924 50

p27Kip1, a cyclin-dependent kinase inhibitor, is recognized as a negative regulator of the cell cycle. In this paper, we report that overexpression of p27Kip1 triggers apoptosis in several different human cancer cell lines. Using a recombinant adenoviral vector that expresses p27Kip1 (Adp27), we found that overexpression of p27Kip1 in MDA-MB-231 breast cancer cells induces apoptosis that was seen by a number of different techniques, including flow cytometry and in situ terminal deoxynucleotidyl transferase-mediated nick end labeling, flow cytometric assay for sub-G1 population, and 4',6-diamindino-2-phenylindole staining. Cleavage of poly(ADP-ribose) polymerase and degradation of cyclin B1, events that are known to be associated with apoptosis, were also observed following overexpression of p27Kip1. This is the first report indicating a role for p27Kip1 in induction of apoptosis.
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PMID:Promoting apoptosis: a novel activity associated with the cyclin-dependent kinase inhibitor p27. 940 46

The cytotoxicity of a recombinant adenovirus expressing the wild type tumor suppressor gene p53 (AdWTp53) was studied in two human breast cancer MCF-7 sublines selected for resistance to adriamycin (MCF-Adr) and mitoxantrone (MCF-Mito). Although the levels of wild type p53 protein following infection with AdWTp53 are comparable in all cell lines, the two drug-resistant MCF-7 sublines were 300- and 18-fold more sensitive to killing by AdWTp53 compared with the drug-sensitive parental MCF-7 cell lines. In each cell line, AdWTp53 infection led to cell cycle arrest, and reduction of Cdk2 and cyclin B1-Cdc2 activity. Nucleosomal DNA fragmentation analysis (as a function of apoptosis) following AdWTp53 infection revealed that, while the parental MCF-7 cells failed to undergo apoptosis, both drug-resistant cell lines showed distinct DNA laddering. In MCF-Adr cells, a combination treatment of AdWTp53 and adriamycin was much more toxic than either of the reagents used individually. Finally, exposure of a mixed population of MCF-Adr and CD34+ cells to AdWTp53 selectively prevented MCF-Adr cell colony formation, while there was no inhibition of CFU-GM colony formation from CD34+ cells. These findings suggest that some drug-resistant human breast cancers may be effectively treated with adenovirus expressing wild type p53.
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PMID:A recombinant adenovirus expressing wild type p53 induces apoptosis in drug-resistant human breast cancer cells: a gene therapy approach for drug-resistant cancers. 940 9

The eukaryotic cell cycle is regulated by a highly conserved family of protein kinases, the cyclin-dependent kinases (CDKs). Monomeric free CDKs do not possess enzymatic activity, largely due to the steric hindrance caused by the T-loop at the entrance of the catalytic cleft, making ATP inaccessible to the substrate. Binding of a cyclin, primarily to the NH2-terminal lobe of the CDK that surrounds the PSTAIRE helix, induces a large conformational change in the PSTAIRE helix of the CDK and also causes the T-loop to move out of the way of the catalytic cleft. We identified from breast cancer tissues a novel variant of human CDC2, termed CDC2deltaT, that lacks 171 nucleotides corresponding to 57 amino acids, which compose most of the T-loop. CDC2deltaT was detected in 10 of 14 breast cancer tissues analyzed, whereas it was not detectable in diploid human fibroblast cell lines or in interleukin 2-stimulated normal human lymphocytes. CDC2deltaT protein is unable to complex with cyclin B1 and lacks histone H1 kinase activity. CDC2deltaT also fails to bind to the CDK inhibitor p21. These results indicate that the T-loop not only plays a key role in keeping a free CDK in its inactive state but also in facilitating CDK activation by promoting cyclin binding.
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PMID:T-loop deletion of CDC2 from breast cancer tissues eliminates binding to cyclin B1 and cyclin-dependent kinase inhibitor p21. 951 86


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