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

We have studied the role of autocrine transforming growth factor-beta (TGF-beta) signaling on antiestrogen-mediated growth inhibition of hormone-dependent T47D and MCF-7 human breast carcinoma cells. Tamoxifen treatment increased the secretion of TGF-beta activity into serum-free cell medium and the cellular content of affinity cross-linked type I and III TGF-beta receptors in both cell lines. Anti-pan-TGF-beta antibodies did not block anti-estrogen-induced recruitment in G1 and inhibition of anchorage-dependent and -independent growth of both cell lines. Early passage MCF-7 cells, which exhibit detectable type II TGF-beta receptors at the cell surface and exquisite sensitivity to exogenous TGF-beta1, were transfected with a tetracycline-controllable dominant-negative TGF-betaRII (DeltaRII) construct. Although the TGF-beta1 response was blocked by removal of tetracycline in MCF-7/DeltaRII cells, tamoxifen-mediated suppression of Rb phosphorylation, recruitment in G1, and inhibition of cell proliferation were identical in the presence and absence of tetracycline. TGF-beta1 treatment up-regulated the Cdk inhibitor p21 and induced its association with Cdk2 in MCF-7 cells; these responses were blocked by the DeltaRII transgene product. In MCF-7 cells with a functional TGF-beta signaling pathway, tamoxifen did not up-regulate p21 nor did it induce association of p21 with Cdk2, suggesting alternative mechanisms for antiestrogen-mediated cytostasis. Finally, transfection of late-passage, TGF-beta1 unresponsive MCF-7 cells with high levels of TGF-betaRII restored TGF-beta1-induced growth inhibition but did not enhance tamoxifen response in culture. Taken together these data strongly argue against any role for TGF-beta signaling on tamoxifen-mediated growth inhibition of hormone-dependent breast cancer cells.
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PMID:Blockade of transforming growth factor-beta signaling does not abrogate antiestrogen-induced growth inhibition of human breast carcinoma cells. 907 51

Estrogens induce cell proliferation in target tissues by stimulating progression through G1 phase of the cell cycle, but the underlying molecular targets remain undefined. To determine the role of the cyclin/cyclin-dependent kinase (CDK)/retinoblastoma protein (pRB) pathway in this response we treated MCF-7 breast cancer cells with the pure estrogen antagonist ICI 182780 to inhibit estrogen-induced gene expression and induce G1 phase arrest. Subsequent treatment with 17beta-estradiol resulted in the synchronous entry of cells into S phase commencing at 12 h. The proportion of cells in S phase reached a maximum of 60% at 21-24 h. Cells subsequently completed mitosis and entered a second semisynchronous round of replication. Entry into S phase was preceded by increased activity of both Cdk4 and cyclin E-Cdk2 and hyperphosphorylation of pRB, all within the first 3-6 h of estradiol treatment. The increase in Cdk4 activity was accompanied by increases in cyclin D1 mRNA and protein, indicating that an initiating event in the activation of Cdk4 was increased cyclin D1 gene expression. In contrast, the levels of Cdk2 and the CDK inhibitors p21 (WAF1/CIP1/SDI1) and p27 (KIP1) in total cell lysates and in cyclin E immunoprecipitates were unaltered at these early time points. However, an inhibitory activity was present in antiestrogen-pretreated cell lysates toward recombinant cyclin E-Cdk2 and was relieved by estradiol treatment. This activity was attributable predominantly to p21. These apparently conflicting data were resolved by performing gel filtration chromatography, which revealed that only a minority of cyclin E-Cdk2 complexes were active following estradiol treatment. Active complexes eluted at a higher molecular weight than inactive complexes, were relatively deficient in both p21 and p27, and contained Cdk2 with increased threonine 160 phosphorylation, consistent with a mechanism of activation of cyclin E-Cdk2 involving both reduced CDK inhibitor association and CDK-activating kinase-mediated phosphorylation of Cdk2. These results provide an explanation for the early activation of both cyclin D1-Cdk4 and cyclin E-Cdk2 complexes that accompany G1-S phase progression in response to estradiol.
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PMID:Estrogen-induced activation of Cdk4 and Cdk2 during G1-S phase progression is accompanied by increased cyclin D1 expression and decreased cyclin-dependent kinase inhibitor association with cyclin E-Cdk2. 909 45

In a recently developed human breast cancer model, treatment of tumor cells in a 3-dimensional culture with inhibitory beta1-integrin antibody or its Fab fragments led to a striking morphological and functional reversion to a normal phenotype. A stimulatory beta1-integrin antibody proved to be ineffective. The newly formed reverted acini re-assembled a basement membrane and re-established E-cadherin-catenin complexes, and re-organized their cytoskeletons. At the same time they downregulated cyclin D1, upregulated p21(cip,wat-1), and stopped growing. Tumor cells treated with the same antibody and injected into nude mice had significantly reduced number and size of tumors in nude mice. The tissue distribution of other integrins was also normalized, suggesting the existence of intimate interactions between the different integrin pathways as well as adherens junctions. On the other hand, nonmalignant cells when treated with either alpha6 or beta4 function altering antibodies continued to grow, and had disorganized colony morphologies resembling the untreated tumor colonies. This shows a significant role of the alpha6/beta4 heterodimer in directing polarity and tissue structure. The observed phenotypes were reversible when the cells were disassociated and the antibodies removed. Our results illustrate that the extracellular matrix and its receptors dictate the phenotype of mammary epithelial cells, and thus in this model system the tissue phenotype is dominant over the cellular genotype.
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PMID:Reversion of the malignant phenotype of human breast cells in three-dimensional culture and in vivo by integrin blocking antibodies. 910 51

Basic fibroblast growth factor (bFGF), a classical mitogen in fibroblasts and endothelial cells, inhibits the proliferation of MCF-7 and other human breast cancer cell lines. To explain this paradoxic effect, we investigated the effects of bFGF on cyclins and protein members of cyclin complexes that exert positive and negative control on the progression of cells through the G1 phase of the cell cycle. bFGF induced an increase in cyclin D1, cyclin E, and cyclin-dependent kinase 4 (cdk4) protein levels in a bFGF dose-dependent manner. However, bFGF also induced a heat-stable, transferable cytoplasmic factor in MCF-7 cells that inhibited the histone H1 kinase activity of reconstituted cyclin E-cdk2 and cyclin A-cdk2 complexes from Mv1Lu mink lung epithelial cells. The appearance of this inhibitor correlated with a bFGF dose- and time-dependent increase in the levels of cdk inhibitor p21(WAF1/CIP1) mRNA and protein. The increase in the level of p21(WAF1/CIP1) was associated with the disappearance of the rapidly migrating, activated form of cdk2 from cell lysates, dephosphorylation of the retinoblastoma protein (Rb), and a decrease in cyclin A levels. These changes were represented in the cyclin D1 and E complexes by an increased association with p21(WAF1/CIP1), proliferating cell nuclear antigen (PCNA), and the inactive form of cdk2, without an absolute change in cellular PCNA levels and by a switch in the association of cyclin D1 complexes with the hyperphosphorylated form to the dephosphorylated form of Rb. These experiments demonstrate that stimulation of MCF-7 cells with bFGF, although resulting in up-regulation of G1 proteins responsible for mitogenic events, also induces a concomitant decrease in cyclin A levels and an increase in p21(WAF1/CIP1) mRNA and protein and results in inactivation of cdk2, dephosphorylation of Rb, and a segregation of PCNA to the G1 cyclin complexes. The dual, conflicting signaling by bFGF results in a net inhibitory phenotype in these cells. These experiments suggest a pleiotropic role for bFGF in breast cancer.
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PMID:Basic fibroblast growth factor causes growth arrest in MCF-7 human breast cancer cells while inducing both mitogenic and inhibitory G1 events. 913 19

p21/Cip1/Waf1 (wild-type p53 activated fragment 1/cyclin-dependent kinase [Cdk]-interacting protein 1) is a prominent Cdk inhibitor and has been shown to be a downstream mediator of p53. In this study, we sought to clarify the clinical significance of Waf1 and the relationship between Waf1 and p53 in breast cancer. For this purpose, the expressions of Waf1 and p53 were evaluated immunohistochemically in a series of 104 patients. Waf1 was expressed in 51 (49%) of 104 tumors tested, and p53 in 33 tumors (32%). Inverse expression of these two proteins was seen in 76 cases (73%); 47 were Waf1-positive and p53-negative, and 29 were Waf1-negative and p53-positive. A comparison with clinicopathologic parameters showed that Waf1 expression correlated with negative lymph nodes (P<.01), a low histologic grade (P<.0001), and positive estrogen receptor status (P<.01). Recurrence-free survival was lower for patients with Waf1-negative tumors than for those with Waf1-positive tumors (P<.0001). In multivariate analysis, Waf1 expression and low histologic grade (1 or 2) tumors had an independent prognostic significance for recurrence-free survival. These results suggest that Waf1 is induced mainly by a p53-dependent pathway and could be a reliable indicator of recurrence in breast cancer.
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PMID:p21(Waf1/Cip1) and p53 protein expression in breast cancer. 916 66

Retinoids mediate the normal growth of a variety of epithelial cells and may play an important role in the chemoprevention of certain malignancies. Loss of retinoic acid (RA) receptor-beta function may be an important event in mammary carcinogenesis, because the majority of breast cancers, in contrast to normal mammary epithelial cells, fail to express this receptor. We previously reported that all-trans-RA mediates G1 arrest as well as apoptosis in certain RAR beta-transduced breast cancer cell lines. We now report the effect of RA on normal human mammary epithelial cells (HMECs), which express functionally active retinoid receptors. We observe that RA induces growth suppression and G1 arrest of these HMECs but find no evidence that RA mediates apoptosis in these normal cell strains. This RA-induced G1 arrest is temporally associated with decreased levels of hyperphosphorylated retinoblastoma protein without any significant changes in c-myc, p53, p21, or p27 expression. Expression of cyclin D1, cyclin-dependent kinase 4, and cyclin E proteins, however, decreased in association with RA-mediated G1 arrest. Our studies suggest that growth inhibition, rather than apoptosis, may be a mechanism by which RA and RA receptors act to prevent the malignant transformation of normal mammary epithelial cells. The molecular target(s) of the activated RA receptors that mediate this G1 arrest in HMECs appear to be associated with a retinoblastoma-dependent pathway.
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PMID:All-trans-retinoic acid mediates G1 arrest but not apoptosis of normal human mammary epithelial cells. 918 97

In order to elucidate the mechanisms by which estrogens and antiestrogens modulate the growth of breast cancer cells, we have characterized the changes induced by estradiol that occur during the G1 phase of the cell cycle of MCF-7 human mammary carcinoma cells. Addition of estradiol relieves the cell cycle block created by tamoxifen treatment, leading to marked activation of cyclin E-cdk2 complexes and phosphorylation of the retinoblastoma protein within 6 h. Cyclin D1 levels increase significantly while the levels of cyclin E, cdk2, and the p21 and p27 cdk inhibitors are relatively constant. However, the p21 cdk inhibitor shifts from its association with cyclin E-cdk2 to cyclin D1-cdk4, providing an explanation for the observed activation of the cyclin E-cdk2 complexes. These results support the notion that cyclin D1 has an important role in steroid-dependent cell proliferation and that estrogen, by regulating the activities of G1 cyclin-dependent kinases, can control the proliferation of breast cancer cells.
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PMID:Estrogen-dependent cyclin E-cdk2 activation through p21 redistribution. 919 41

Retinoic acid (RA) inhibition of breast cancer cell growth is associated with an accumulation of cells in G1 phase of the cell cycle. We have investigated the effects of RA on the expression and activity of cell cycle-regulatory proteins in MCF-7 human breast cancer cells. Flow cytometry analysis of MCF-7 cells treated with RA revealed a decrease in the percentage of cells in S phase by 48 h, which was maximal by 72 h. Phosphorylation of the retinoblastoma protein (pRb) was partially reduced in RA-treated cells accompanied by a decrease in the level of retinoblastoma protein. Expression of the cyclin D1 transcript was reduced by 48 h and cyclin-dependent kinase 2 (cdk2) mRNA levels declined within 8 h posttreatment followed by a decrease in cyclin D1 and cdk2 protein levels. Message and protein levels of cdk4 and cdc2 were not affected by RA. While cdk4 activity was similar in control and RA-treated cells, cdk2 activity began to decrease within 48 h of exposure to RA and was profoundly reduced after 72 h. This reduced activity was associated with decreased phosphorylation of cdk2. The decrease in cdk2 activity occurred in the absence of RA-mediated increases in the levels of the cdk inhibitors p21 and p27. However, assays of cdk2 from pooled lysates from RA-treated and control cells showed that RA-treated cells contain a cdk2-inhibitory activity. Our results show that RA inhibits cell cycle progression of MCF-7 cells by inhibiting cdk2 mRNA and protein production and by decreasing cdk2 activity.
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PMID:CDK2 is a target for retinoic acid-mediated growth inhibition in MCF-7 human breast cancer cells. 925 11

The p53 tumour-suppressor gene is important in the regulation of cell growth and apoptosis, and loss of functional wild-type activity may be associated with tumour formation and resistance to therapy. Differentiation of functionally normal wild-type protein from mutant or abnormal protein remains difficult using either immunohistochemical assays or mutational DNA sequencing. p21(WAF1/CIP1) (p21) is induced by wild type p53 and plays an important role in promoting cell cycle arrest. To test the hypothesis that p21 protein expression may act as a downstream marker of tumours from patients with locally advanced breast cancer before treatment with doxorubicin, pretreatment p53 status had been characterized in 63 tumours by p53 protein immunostaining and DNA mutational analysis. There was a significant association between immunostaining for p53 and the presence of p53 mutations (P = 0.01). Of 56 patients available for determination of p21, 31 (55%) expressed p21 protein. Twenty-eight out of 31 patients (90%) positive for p21 had low negative p53 protein expression, whereas only 3 of 13 patients (23%) with high p53 expressed p21 (P = 0.009). No association was seen between p21 protein expression and p53 mutations (P = 0.24). The combination of p53 and p21 immunostaining results improved the specificity of the immunostaining but at a cost of significant reduction in sensitivity. Immunohistochemical assessment of p21 protein expression is inversely associated with abnormal p53 protein in human breast cancer. The detection of p21 protein expression in combination with p53 protein expression did not improve the ability of immunohistochemistry (IHC) to differentiate between normal and mutant p53 protein.
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PMID:Absence of p21 expression is associated with abnormal p53 in human breast carcinomas. 927 25

Much of the predisposition to hereditary breast and ovarian cancer has been attributed to inherited defects in the BRCA1 tumour-suppressor gene. The nuclear protein BRCA1 has the properties of a transcription factor, and can interact with the recombination and repair protein RAD51. Young women with germline alterations in BRCA1 develop breast cancer at rates 100-fold higher than the general population, and BRCA1-null mice die before day 8 of development. However, the mechanisms of BRCA1-mediated growth regulation and tumour suppression remain unknown. Here we show that BRCA1 transactivates expression of the cyclin-dependent kinase inhibitor p21WAF1/CIP1 in a p53-independent manner, and that BRCA1 inhibits cell-cycle progression into the S-phase following its transfection into human cancer cells. BRCA1 does not inhibit S-phase progression in p21-/- cells, unlike p21+/+ cells, and tumour-associated, transactivation-deficient mutants of BRCA1 are defective in both transactivation of p21 and cell-cycle inhibition. These data suggest that one mechanism by which BRCA1 contributes to cell-cycle arrest and growth suppression is through the induction of p21.
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PMID:Arrest of the cell cycle by the tumour-suppressor BRCA1 requires the CDK-inhibitor p21WAF1/CiP1. 929 97


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