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

Individuals with germ line mutations in the p53 gene, such as Li-Fraumeni syndrome (LFS), have an increased occurrence of many types of cancer, including an unusually high incidence of breast cancer. This report documents that normal breast epithelial cells obtained from a patient with LFS (with a mutation at codon 133 of the p53 gene) spontaneously immortalized in cell culture while the breast stromal fibroblasts from this same patient did not. Spontaneous immortalization of human cells in vitro is an extremely rare event. This is the first documented case of the spontaneous immortalization of breast epithelial cells from a patient with LFS in culture. LFS patient breast stromal fibroblasts infected with a retroviral vector containing human papillomavirus type 16 E7 alone were able to immortalize, whereas stromal cells obtained from patients with wild-type p53, similarly infected with human papillomavirus type 16 E7, did not. The present results indicate a protective role of normal pRb-like functions in breast stromal fibroblasts but not in breast epithelial cells and reinforces an important role of wild-type p53 in the regulation of the normal growth and development of breast epithelial tissue.
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PMID:Spontaneous in vitro immortalization of breast epithelial cells from a patient with Li-Fraumeni syndrome. 779 51

The growth suppressing activity of the retinoblastoma suspectibility gene product, pRb, is down regulated by cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) whose kinase activity is negatively regulated by CDK inhibitors of the p16 family. We have examined the genomic status of two recently isolated p16-related CDK inhibitors, p15 and p18, in 15 normal and 73 tumor-derived cell lines established from 23 different tissues, as well as 26 invasive primary breast cancers and 20 acute myelogenous leukemias. p15 was found to be homozygously deleted in 22% of the tumor derived cell lines, but no point mutations were found in either the cultured cells or the two types of primary tumors. With the exception of one breast cancer cell line, no deletions or mutations were found in the p18 gene in either cultured cell lines or primary tumors. These results indicate that mutation of the p18 gene occurs rarely in human tumors. Thus, while they share a very similar biochemical mechanism of inhibiting the kinase activity of CDK4 and CDK6, members of the p16 gene family play different roles in controlling cell proliferation and suppressing tumor growth.
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PMID:Mutational analysis of the p16 family cyclin-dependent kinase inhibitors p15INK4b and p18INK4c in tumor-derived cell lines and primary tumors. 857 Feb 24

The sequential transcriptional activation of cyclins, the regulatory subunits of cell cycle specific kinases, regulates progress through the cell cycle. In mitogen-stimulated cells cyclin D1 induction in early G1 is followed by induction of cyclin E, activation of the cyclin-dependent kinase Cdk2, and hyperphosphorylation of the retinoblastoma gene product (pRB) in mid-to-late G1 phase. T-47D breast cancer cells expressing cyclin D1 under the control of a metal-responsive metallothionein promoter were used to determine whether Cdk2 activation and pRB hyperphosphorylation are consequences of cyclin D1 induction. A 4-5-fold increase in cyclin D1 protein abundance was followed by approximately 2-fold increases in cyclin E protein abundance and Cdk2 activity and by hyperphosphorylation of pRB. These responses were apparent approximately 3 h after the increase in cyclin D1 protein, and approximately 3 h prior to the entry of cyclin D1-stimulated cells into S phase 12 h after zinc treatment. Cyclin D1 immunoprecipitates contained Cdk4 but no detectable Cdk2 and displayed pRb but not histone H1 kinase activity. Cdk2 activation was therefore likely to be due to increased abundance of cyclin E/Cdk2 complexes rather than formation of active cyclin D1/Cdk2 complexes. The sequence of events following zinc induction of cyclin D1 thus mimicked that following mitogen induction of cyclin D1. These data show that cyclin D1 induction is sufficient for Cdk2 activation and pRB hyperphosphorylation in T-47D human breast cancer cells, providing evidence that cyclin D1 induction is a critical event in G1 phase progression.
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PMID:Inducible expression of cyclin D1 in T-47D human breast cancer cells is sufficient for Cdk2 activation and pRB hyperphosphorylation. 886 12

Cyclin E is an important regulator of cell cycle progression that together with cyclin-dependent kinase (cdk) 2 is crucial for the G1/S transition during the mammalian cell cycle. Previously, we showed that severe overexpression of cyclin E protein in tumor cells and tissues results in the appearance of lower molecular weight isoforms of cyclin E, which together with cdk2 can form a kinase complex active throughout the cell cycle. In this study, we report that one of the substrates of this constitutively active cyclin E/cdk2 complex is retinoblastoma susceptibility gene product (pRb) in populations of breast cancer cells and tissues that also overexpress p16. In these tumor cells and tissues, we show that the expression of p16 and pRb is not mutually exclusive. Overexpression of p16 in these cells results in sequestering of cdk4 and cdk6, rendering cyclin D1/cdk complexes inactive. However, pRb appears to be phosphorylated throughout the cell cycle following an initial lag, revealing a time course similar to phosphorylation of glutathione S-transferase retinoblastoma by cyclin E immunoprecipitates prepared from these synchronized cells. Hence, cyclin E kinase complexes can function redundantly and replace the loss of cyclin D-dependent kinase complexes that functionally inactivate pRb. In addition, the constitutively overexpressed cyclin E is also the predominant cyclin found in p107/E2F complexes throughout the tumor, but not the normal, cell cycle. These observations suggest that overexpression of cyclin E in tumor cells, which also overexpress p16, can bypass the cyclin D/cdk4-cdk6/p16/pRb feedback loop, providing yet another mechanism by which tumors can gain a growth advantage.
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PMID:Cyclin E, a redundant cyclin in breast cancer. 898 90

The ability of mammalian cells to respond to extrinsic mitogens is downregulated in response to proliferative aging (senescence), and it is now likely that at least a subset of such lifespan checkpoints is triggered by a biological "clock" based on erosion of chromosome telomeres. This review outlines the intrinsic inhibitory signal pathways that link this clock to cell cycle arrest, focussing on the role of tumour suppressor gene products, particularly the p53 and pRb proteins. Emphasis is placed on cell-type specific differences in the timing of lifespan checkpoints, and the "choice" of the underlying inhibitory signal pathway. It is argued that such diversity may explain many differences between cell types in the selection of tumour suppressor gene mutations, providing for example a novel explanation for the difference in molecular pathology and clinical behaviour between two important subsets of human breast cancer.
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PMID:Telomeres, p53 and cellular senescence. 911 31

Somatostatin (SST) analogs inhibit tumor cell growth by exerting direct anti-proliferative effects with cytostatic (growth arrest) or cytotoxic (apoptosis) consequences. The SST analog SMS 201-995 (octreotide, OCT) inhibits growth of MCF-7 human breast adenocarcinoma cells, which express multiple SSTRs. Its action has been reported to result in either apoptosis or growth arrest, but the underlying mechanisms have not been elucidated in this tumor cell model. Here, we report that OCT elicits cytotoxic response in these cells, leading to apoptosis, which is associated with a rapid, time-dependent induction of wild-type p53 and an increase in Bax. There was no G1 cell-cycle arrest in these cells during OCT treatment as suggested by the decrease in G1/S ratio and the lack of induction of pRb and p21. Additionally, we demonstrate that OCT-induced DNA fragmentation in this cell line is due to selective activation of a cation-insensitive acidic endonuclease. Our data provide a rationale for utilizing SST analogs to treat SSTR-positive breast cancer cells expressing wild-type p53.
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PMID:Induction of wild-type p53, Bax, and acidic endonuclease during somatostatin-signaled apoptosis in MCF-7 human breast cancer cells. 953 89

To explore the regulation and function of D-type cyclins in breast cancer cells, the mouse mammary hyperplastic epithelial cell line TM2H was treated with 5 mM hexamethylenebisacetamide (HMBA), a polar differentiation factor. The resulting growth-inhibitory effect of HMBA was completely reversible and was analyzed in terms of percent cells in G1; association of D-type cyclins with cyclin-dependent kinase (cdk) 4 and cdk6; G1 kinase activity; association of retinoblastoma protein (pRb) and phosphorylated pRb with D-type cyclins; and association of p16INK4a, p15INK4b, and p27Kip1 with cdk4 and cdk6. Synchronized TM2H cells were examined at 0, 3, 5, 9, 12, and 24 h after exposure to 5 mM HMBA. Inhibition of DNA synthesis, as measured by thymidine uptake, was first observed at 5 h (40%) and peaked at 24 h (80%). Flow cytometry at 9 h showed treated cells to be in G1 arrest. Western blot analysis showed weakly detectable cyclin D1 but readily detectable cyclin D2 and D3 proteins at 0 h; thereafter, cyclin D2 and D3 protein levels remained higher while cyclin D1 levels declined significantly in treated versus untreated cells. By 5 h (early G1), HMBA had markedly inhibited cdk4 and cdk6 kinase activity (67% and 75%, respectively) in treated versus untreated cells. By 9 and 12 h, pRb levels had increased 3.4-fold in treated versus untreated cells. At 5 h, cyclin D-associated pRb was totally hypophosphorylated in treated cells and hyperphosphorylated in untreated cells. The levels of pRb associated with cyclin D2 and D3 increased 2.89-fold and 4.6-fold, respectively, in treated versus untreated cells. At 5 h, treated cells showed a fivefold increase in cdk4-associated p27Kip1 and, at 9 h, a fourfold increase in cdk6-associated p27Kip1 over control levels. In confirmation of these data, HMBA was found to inhibit the growth of Rb-positive Du/145Rb cells but not their Rb-negative parental Du/145 cells. The data suggest that HMBA-induced growth inhibition is due to multifactorial mechanisms involving decreases in total cyclin D1 and inhibition of cdk4 and cdk6 kinase activities through elevation of levels of cdk4- and cdk6-associated p27Kip1 and concomitant increases in hypophosphorylated pRb and stable cyclin D2/pRb and cyclin D3/pRb complexes that help maintain pRb in a functional state.
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PMID:Interaction of retinoblastoma protein and D cyclins during cell-growth inhibition by hexamethylenebisacetamide in TM2H mouse epithelial cells. 965 57

Navelbine (NVB, vinorelbine ditartrate, KW-2307), a new vinca alkaloid analogue, has been shown to be clinically effective against advanced breast cancer. In this report, the combined effect of NVB with medroxyprogesterone acetate (MPA), a synthetic progesterone derivative, was examined in vitro against human breast carcinoma MCF-7 cells. The combined effect was demonstrated to be synergistic using the isobologram and median-effect plot analyses. To elucidate the mechanism of action, we further examined effects of both drugs on cell cycle distribution of the cells in combination and/or alone. NVB at 2 nM induced apparent G1-phase accumulation as well as the induction of cyclin-dependent kinase (CDK) inhibitor p21(WAF1/CIP1) protein and the dephosphorylated form of retinoblastoma protein (pRb). In contrast, MPA at 0.1 microM also induced G1-phase accumulation as well as the reduced expression of cyclin D1 protein. In addition, the combination of both drugs induced augmented G1-phase accumulation, which occurred along with p21(WAF1/CIP1) protein induction, cyclin D1 protein reduction and pRb dephosphorylation. These results demonstrate that the synergistic combined effect of NVB with MPA was mediated through enhancement of G1-phase accumulation that resulted from the different action point(s) of each drug. Furthermore, the synergistic combined effect of NVB with MPA was also observed in other human breast carcinoma cell lines, such as T-47D and ZR-75-1. These results suggest that combination therapy of NVB with MPA in breast cancer might be effective in clinical studies.
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PMID:Combined effect of navelbine with medroxyprogesterone acetate against human breast carcinoma MCF-7 cells in vitro. 966 41

Pulmonary metastases are the main cause of death of patients with several types of cancer, including osteosarcoma, renal cell carcinoma, malignant melanoma, and breast cancer. Previously, we demonstrated that intralesional injection of the recombinant adenovirus (Ad) vector containing the herpes simplex virus thymidine kinase (TK) gene driven by an osteocalcin (OC) promoter (Ad-OC-TK) effectively suppressed the growth of osteosarcoma cells in vitro and tumors in vivo in a tumor-specific manner when supplemented with the prodrug acyclovir (ACV). In this communication, we studied the potential efficacy of the treatment of osteosarcoma pulmonary metastases with a systemic delivery route of Ad-OC-TK supplemented with ACV. We established osteosarcoma lung metastases in nude mice by the intravenous injection of rat osteosarcoma cells, ROS 17/2.8. These cells colonized and formed tumor nodules within 1 week in the lungs of nude mice. Whereas systemic delivery of a recombinant Ad vector containing the Escherichia coli beta-galactosidase (beta-gal) gene driven by a Rous sarcoma virus universal promoter (Ad-RSV-beta-gal) resulted in the nonspecific expression of beta-gal activity in the lung parenchyma, Ad-OC-beta-gal administration resulted in specific beta-gal expression in tumor cells deposited in the lung. When nude mice bearing ROS 17/2.8 lung tumors were treated with systemic Ad-OC-TK through tail vein administration, subsequent intraperitoneal ACV treatment significantly decreased the number of tumor nodules (P < .0001) and the net lung wet weight (P = .0005) while significantly increasing (.005 < P < .01) the survival of animals, when compared with untreated and Ad-OC-TK- or ACV-treated control groups. These results suggest that Ad-OC-TK/ACV may be used as a systemic therapy for the treatment of osteosarcoma lung metastasis.
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PMID:In vivo suppression of osteosarcoma pulmonary metastasis with intravenous osteocalcin promoter-based toxic gene therapy. 982 46

The p16-pRb pathway represents a vital cell-cycle checkpoint. In the present study we investigated the alterations of this G1-phase protein pathway using immunohistochemical and molecular methods in a series of 55 breast carcinomas and correlated the findings with clinicopathological features of the patients. Furthermore, we examined its relationship with the status of the chromosomal region 9p21-22 performing a deletion map analysis because there are indications that, in addition to CDKN2 and MTS2/p15(INK4B) tumor suppressor genes (TSGs), this area harbors other TSG(s). Aberrant expression (Ab) of p16 and pRb was observed in 26 (47%) and 16 (29%) of the carcinomas, respectively. A statistical trend pointing out an inverse relationship between p16 and pRb expression was found (p = 0.079). Analysis of the region that encodes for p16 by deletion mapping, a PCR-based methylation assay and PCR-SSCP, revealed that deletions and transcriptional silencing by methylation might represent the main mechanisms of CDKN2/p16(INK4A) inactivation in breast carcinomas. The results of deletion mapping also suggest that another TSG(s) may reside at the 9p21-22 area particularly at the D9S162 loci and that co-deletion of this putative gene with CDKN2/p16(INK4A) may play a role in breast carcinogenesis. In addition, microsatellite instability (MI), a marker of replication error phenotype (RER+), was observed with a frequency of 16% in the area examined and was inversely related with loss of heterozygosity (LOH). Interestingly, most cases with MI at the region encoding for p16 were aggregated in a subgroup of breast carcinomas with no other obvious genetic and/or epigenetic CDKN2/p16(INK4A) alterations. We speculate that there is an additional mechanism of CDKN2/p16(INK4A) inactivation. The relationship of p16 protein level pRb, status, the p16-pRb combined immunoprofiles, and the microsatellite alterations detected at the 9p21-22 locus with the patients' clinicopathological parameters revealed two significant correlations: one between normal pRb expression and lymph node involvement (p = 0.0263), and the other between microsatellite alterations (LOH and or MI) and tumor size (p = 9.2 x 10(-3)). In view of the heterogenous nature of breast cancer, we suggest that in a significant proportion of breast carcinomas, deregulation of the p16-pRb pathway in association with another, as-yet unidentified, TSG(s) of the 9p21-22 region may play a role in initiating or progressing the oncogenic procedure, while in other subgroups, alternative molecules may play this role.
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PMID:Alterations of p16-pRb pathway and chromosome locus 9p21-22 in sporadic invasive breast carcinomas. 999 Aug 66


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