Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Agonist and antagonist activities have been reported for several catechol estrogens given exogenously. Since the metabolic clearance rate for catechol estrogens in the body is very rapid, catechol estrogens produced at other tissues will have minimal effect on breast tissue. Information of the extent of catechol estrogen formation within cells is critical in assessing the overall importance of these estrogen metabolites. Investigations of the conversion of estrogens to catechol estrogens were performed in the MCF-7 human mammary carcinoma cell culture system. Reverse-phase high-performance liquid chromatography (HPLC) analysis demonstrated that very little metabolism of estradiol occurs after 48 h, with only small amounts of estrone, 2-hydroxyestradiol, 2-hydroxyestrone, and estriol being observed. The total amount of 2-hydroxyestrogen products formed from 1 microM estradiol was 406.2 pmol (SD = 60.9) per 3 x 10(7) cells in 48 h. Similar results were obtained using the simpler radiometric assay for estrogen 2-hydroxylase, which measures the release of 3H2O from [2(-3)H]estradiol. The effects of inhibitors of estrogen 2-hydroxylase were also examined in MCF-7 cells. 2-Bromoestradiol, 4-bromoestradiol, and 2,4-dibromoestradiol effectively block estrogen 2-hydroxylase in a dose-dependent manner in MCF-7 cultures, with ED50 of approximately 1 microM for each inhibitor. Furthermore, these bromoestrogens bind poorly to estrogen receptors in MCF-7 cells and do not alter cell growth. Thus, in MCF-7 mammary cell cultures, metabolism of estradiol occurs to only a minor degree, and it is unlikely that the levels of catechol estrogens would reach physiologically relevant concentrations in the intact breast cancer cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Endocrinol 1989 Jul
PMID:Catechol estrogen formation in MCF-7 cell culture and effects of bromoestrogen inhibitors. 255 56

Insulin-like growth factor-II (IGF-II) is a potent mitogen for several types of cultured cells and tissues. We have studied the interaction of IGF-II with a panel of cultured human breast cancer cell lines, examining the possibility that these cells synthesize and secrete IGF-II activity which could have autocrine/paracrine functions. Synthetic IGF-II was mitogenic in five of seven cell lines tested, including the estrogen receptor-positive lines MCF-7L, ZR75-1, and T47D and the estrogen receptor (ER)-negative lines Hs578T and MDA-231. IGF-II was slightly less potent than IGF-I in stimulating DNA synthesis in MCF-71 cells, an effect that paralleled its ability to compete for [125I]IGF-I binding in these cells. Affinity labeling studies revealed that IGF-II could also compete for binding to the 130,000 mol wt alpha-subunit of the IGF-I receptor. A monoclonal antibody to the IGF-I receptor inhibited the mitogenic effects of IGF-II in MCF-7L and MDA-231 cells, suggesting that this receptor mediates the growth effects of IGF-II in these breast cancer cells. Using a RIA and a RRA, IGF-II-like activity was detected in conditioned medium extracts processed to remove IGF-binding proteins from several breast cancer cell lines, with the highest levels found in conditioned medium from MCF-7L and T47D cell lines. IGF-II mRNA transcripts in MCF-7L and T47D cells were identified by Northern blot analysis and were confirmed by RNase protection assay. IGF-II mRNA was increased by estrogen in MCF-7L cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1989 Nov
PMID:Insulin-like growth factor-II (IGF-II): a potential autocrine/paracrine growth factor for human breast cancer acting via the IGF-I receptor. 255 2

Phenothiazines and structurally related compounds inhibit cellular proliferation and sensitize multidrug-resistant (MDR) cells to chemotherapeutic agents. To identify more potent pharmaceuticals, we studied the structure-activity relationships of 30 phenothiazines and related compounds on cellular proliferation and MDR in sensitive MCF-7 and resistant MCF-7/DOX human breast cancer cells. Substitutions on the phenothiazine ring that increased hydrophobicity increased antiproliferative and anti-MDR activities. For example, -Cl and -CF3 groups increased whereas -OH groups decreased potency. Modifying the length of the alkyl bridge and the type of amino side chain also influenced potency. Compounds with increased activity against cellular proliferation and MDR possessed a four-carbon bridge rather than a three- or two-carbon bridge and a piperazinyl amine rather than a noncyclic amino group. Compounds with tertiary amines were better anti-MDR agents than those with secondary or primary amines but were equipotent antiproliferative agents. The effects of these substituents were unrelated to hydrophobicity. The structure-activity relationships suggest that an ideal phenothiazine structure for reversing MDR has a hydrophobic nucleus with a -CF3 ring substitution at position 2, connected by a four-carbon alkyl bridge to a para-methyl-substituted piperazinyl amine. We subsequently studied related compounds having certain of these properties. Substitution of a carbon for a nitrogen at position 10 of the tricyclic ring, with a double bond to the side chain (thioxanthene), further increased activity against MDR. For example, (trans)-flupenthixol, the most potent of these compounds, increased the potency of doxorubicin against MDR cells by 15-fold, as compared with its stereoisomer (cis)-flupenthixol (5-fold) or its phenothiazine homolog fluphenazine (3-fold). (cis)- and (trans)-flupenthixol were equipotent antiproliferative agents. (trans)-flupenthixol was not accumulated more than (cis)-flupenthixol in MDR cells, implying that their stereospecific anti-MDR effects were not the result of selective differences in the access of the drugs to intracellular targets. Both drugs increased the accumulation of doxorubicin in MDR cells, but not in sensitive cells, suggesting that they modulate MDR by interacting with a uniquely overexpressed cellular target in these resistant cells. The apparent lack of clinical toxicity of (trans)-flupenthixol makes it an attractive drug for further investigation.
Mol Pharmacol 1989 Jan
PMID:Structural features determining activity of phenothiazines and related drugs for inhibition of cell growth and reversal of multidrug resistance. 256 2

In order to study the mechanism of etoposide (VP-16) resistance in human tumor cells and to assess the role of P-170 glycoprotein in VP-16 accumulation, we have examined the uptake and efflux of VP-16 in both sensitive and multidrug-resistant MCF-7 human breast and HL60 human promyelocytic leukemia cells. The drug-resistant cells, MCF-7/ADR and HL60/ADR, were selected for resistance to adriamycin and were 200- to 250-fold resistant to VP-16. Whereas MCF-7/ADR cells overexpress the P-170 glycoprotein and show the multidrug-resistant phenotype, HL60/ADR cells do not overexpress the P-170 glycoprotein. Although there was a 2-fold decrease in accumulation of VP-16 in MCF-7/ADR cells, this decrease did not correlate with a 250-fold resistance to the drug. VP-16 efflux was rapid and almost complete from MCF-7 cell lines and it was decreased at 4 degrees. Further, there was a significant increase in VP-16 accumulation in the MCF-7/ADR cells in the presence of glucose-free medium supplemented with sodium azide. However, no change in the pattern of VP-16 efflux was observed. Under these conditions, addition of glucose caused release of VP-16 from MCF-7/ADR cells, suggesting energy-dependent modifications in the drug binding. Coincubation of vincristine with VP-16 also increased the drug accumulation and decreased the rate of efflux of VP-16 in both sensitive and resistant MCF-7 cells, suggesting that vincristine and VP-16 may compete for similar binding and efflux mechanisms in these cell lines. In contrast, daunorubicin increased VP-16 accumulation only in the sensitive MCF-7 cell line, whereas the efflux rate of VP-16 was not significantly changed in either cell line. HL60 sensitive cells accumulated 4- to 5-fold more VP-16 than the resistant subline. Both sensitive and resistant cells showed an important noneffluxable pool of the drug, 3-fold larger for sensitive cells (79 +/- 12 versus 25 +/- 2 pmol of VP-16/mg of protein, for sensitive and resistant cells, respectively). The efflux of VP-16 was temperature dependent only in sensitive cells. VP-16 accumulation in HL60/ADR cells was increased in glucose-free medium supplemented with sodium azide; however, the noneffluxable pool of VP-16 was not significantly changed. In contrast, although these conditions had no effect on the drug accumulation in the parental line, they caused a decrease in the noneffluxable pool of VP-16, suggesting an energy-dependent binding and retention of VP-16.(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Pharmacol 1989 Mar
PMID:Role of differential drug uptake, efflux, and binding of etoposide in sensitive and resistant human tumor cell lines: implications for the mechanisms of drug resistance. 256 28

Human MCF-7 breast cancer cells have been studied to determine their suitability as an autocrine model for the synthesis, secretion and action of insulin-like growth factor-I (IGF-I). Secretion of immunoreactive (ir-) IGF-I into serum-free medium was very low (less than 500 pg/10(6) cells per day). Northern blot hybridization detected at least two IGF-I messenger RNA transcripts (approximately 4.6 and approximately 1.8 kb) which were similar in size to those reported in other human and rat tissues. IGF-II mRNA was also detected but at low abundance. Cell proliferation was stimulated in a dose-responsive manner by exogenous IGF-I (10-30 ng/ml). Addition of a monoclonal antibody against IGF-I to MCF-7 cells in serum-free medium caused an inhibition of cell proliferation, suggesting that endogenous locally produced IGF-I does play an autocrine/paracrine role in MCF-7 cell growth. Proliferation of MCF-7 cells was sensitive to oestradiol (10 nM) in the absence but not in the presence of the weakly oestrogenic pH indicator phenol red. Neither IGF-I secretion nor IGF-I mRNA synthesis, however, was affected by addition of oestradiol. Similarly, GH, dexamethasone or dexamethasone plus oestradiol had no effect on either parameter. These data indicate that MCF-7 cells synthesize, secrete and respond to IGF-I. The very low levels of ir-IGF-I produced and their apparent lack of hormonal modulation suggest, however, that further studies are required to establish whether IGF-I plays a major physiological role in growth and development of MCF-7 cells.
J Mol Endocrinol 1989 Nov
PMID:Insulin-like growth factor-I and its autocrine role in growth of MCF-7 human breast cancer cells in culture. 259 Mar 82

We have previously demonstrated that regulation of estrogen receptor (ER) expression in MCF-7 breast cancer cells is a complex process involving transcriptional and posttranscriptional regulation by estradiol. Treatment of MCF-7 cells with estradiol results in the down-regulation of receptor expression; posttranscriptional suppression of receptor mRNA appears to be the predominant mechanism. To determine whether posttranscriptional regulation of ER gene expression is mediated by an ER-dependent mechanism independent of protein synthesis, we have used the competitive estrogen antagonist, 4-hydroxytamoxifen, and the inhibitor of protein synthesis, cycloheximide, to study regulation of ER mRNA by estradiol. 4-Hydroxytamoxifen had no effect on the steady-state level of receptor mRNA and effectively blocked the suppression of ER mRNA by estradiol. The metabolic inhibitor, cycloheximide, was unable to prevent the estrogen induced decrease in ER mRNA. These data provide evidence that the posttranscriptional suppression of ER expression through estradiol is mediated through the ER independent of protein synthesis. A study of the effects of estradiol on the steady-state levels of nuclear and cytoplasmic receptor mRNA suggest that posttranscriptional suppression is a nuclear event.
Mol Endocrinol 1989 Nov
PMID:Role of an estrogen receptor-dependent mechanism in the regulation of estrogen receptor mRNA in MCF-7 cells. 260 58

The aim of this work was to determine whether dexamethasone (Dex), a synthetic glucocorticoid, counteracts the stimulatory effects of estradiol (E2) on MCF-7 cells. We have shown that Dex inhibits in a dose-dependent fashion the estradiol-stimulated cell proliferation. This inhibition (ID50 congruent to 5-10 nM), which is complete at 100 nM Dex, is prevented by the antiglucocorticoid RU 486 and is clearly different from that found with trans-4-OH-tamoxifen because the inhibition due to a fixed concentration of Dex is not abolished by a high concentration of estradiol. This inhibitory effect displays some degree of specificity. Progesterone and the progestins R 5020 and ORG 2058 are without effect and Dex does not alter the triiodo-L-thyronine-stimulated cell growth. To characterize further the antiestrogenic action of Dex, the effects of this drug on specific responses to estradiol were studied. (1) Among the positive responses to estradiol two are prevented by Dex (the increase of concentration of progestin receptors and that of immunoreactive insulin-like growth factor I, IR-IGF-I, in conditioned medium) and two are insensitive to Dex (the enhancement of the secretion of 52,000 and 160,000 Mr proteins). (2) A negative response to estradiol (the down-regulation of estrogen receptor) is not prevented but rather accentuated by Dex. Thus, Dex counteracts the stimulatory effects of estradiol on the proliferation of MCF-7 cell variants characterized by progestin insensitivity. This non-classical antiestrogenic effect could be due in part to the attenuation of the E2-induced IR-IGF-I secretion and, less probably, to the accentuation of the down-regulation of E2 receptors. It could account for certain therapeutic and/or side effects of glucocorticoids on estrogen target cells.
Mol Cell Endocrinol 1989 Oct
PMID:Non-classical antiestrogenic actions of dexamethasone in variant MCF-7 human breast cancer cells in culture. 261 31

Non-steroidal antioestrogens, such as tamoxifen, inhibit the growth of human breast cancer cells. The experiments described here compare and contrast the efficacy of tamoxifen and the 'pure' antioestrogen, ICI 164384, on the inhibition of proliferation of MCF-7 cells. Previous studies have shown that ICI 164384 has a greater maximal inhibitory effect than conventional antioestrogens on the growth of MCF-7 cells. Both types of compound block progression of cells through the cell cycle in the early G1 phase. These studies have been extended to measure the population distribution of antioestrogen-treated cells by the use of two-parameter flow cytometry. ICI 164384 proved to be more effective than tamoxifen in decreasing the proportion of actively growing cells in an asynchronous population. In cells grown in the complete absence of exogenous oestrogens, growth was stimulated by oestradiol, insulin, insulin-like growth factor-I (IGF-I) or transforming growth factor-alpha (TGF-alpha). The potent metabolite of tamoxifen, trans 4'-hydroxytamoxifen (4'-OHT), alone also stimulated growth, whereas ICI 164384 did not. Oestradiol and insulin added together demonstrated a clear synergistic enhancement of cell growth. Correspondingly, the stimulatory effect of 4'-OHT on growth was magnified in the presence of insulin, and a combination of ICI 164384 with insulin revealed a much weaker stimulatory action of the 'pure' antagonist. For both compounds the interaction with insulin was complex and characterized by a bell-shaped dose-response curve. However, for 4'-OHT at all concentrations in the range 1 pM-1 microM in the presence of insulin, cell numbers were greater than in cultures exposed to insulin alone. This was not the case for ICI 164384 which suggested that differences in efficacy may be due to interactions between oestrogen and growth factor-mediated mechanisms. Furthermore, ICI 164384 was more effective in inhibiting the action of IGF-I and TGF-alpha alone or in combination, although both antioestrogens produced a partial blockade of growth factor responses in the complete absence of oestradiol. It is concluded that the difference in efficacy between partial agonist and 'pure' antagonist antioestrogens to inhibit growth in vitro is consistent with the difference in the pharmacological profile of these compounds. The absence of stimulatory activity of ICI 164384 is of particular significance in reducing to a minimum the synergistic interaction between oestrogens and insulin.(ABSTRACT TRUNCATED AT 400 WORDS)
J Mol Endocrinol 1989 May
PMID:Effects of antioestrogens on the proliferation of MCF-7 human breast cancer cells. 266 80

It has been suggested that transforming growth factor-alpha (TGF-alpha) is a mitogenic autocrine growth factor for human breast cancer cells, responsible for mediating the mitogenic effects of 17 beta-estradiol (E2) in responsive cells. To test this hypothesis we have introduced eukaryotic expression vectors directing the expression of TGF-alpha mRNA into E2-responsive MCF-7 human breast cancer cells. Transfected cells produce levels of TGF-alpha equivalent to or greater than those produced by both E2-stimulated MCF-7 cells and hormone-independent MDA-MB-231 cells. One transfected clone (H8) secretes sufficient TGF-alpha to fully down-regulate EGF-R expression. However, both of the transfected clones that constitutively secrete elevated levels of TGF-alpha (A8 and H8) respond to E2 stimulation in vitro by increasing the rate of cellular proliferation and inducing PGR synthesis. The basal proliferative capacity of H8 and A8 cells is equivalent to that of the parental cells and to cells transfected only with the G418 (neomycin) resistance gene. Furthermore, the TGF-alpha cDNA-transfected clones do not form tumors in ovariectomized athymic nude mice without E2 supplementation. Thus, the precise role of TGF-alpha in mediating either the in vivo or the in vitro mitogenic effects of E2 in MCF-7 human breast cancer cells remains unclear. While TGF-alpha expression may be essential, it is not sufficient alone to induce the fully E2-independent phenotype. Thus, TGF-alpha may function in combination with other E2-induced growth factors to control breast cancer proliferation and tumorigenesis.
Mol Endocrinol 1989 Feb
PMID:The effects of a constitutive expression of transforming growth factor-alpha on the growth of MCF-7 human breast cancer cells in vitro and in vivo. 271 Jan 38

In two sublines of the estrogen receptor-positive human breast cancer cell line, MCF-7, propagated with 0.5% fetal calf serum (FCS) (subline 0.5) and without serum (subline 9), respectively, addition of 10% newborn calf serum (NCS) inhibits cell proliferation and stimulates the secretion of a 42 kDa protein. Both with and without NCS, estradiol (E2) stimulates the secretion of a 61 kDa and a 52 kDa protein in subline 9, and an additional third protein (66 kDa) is stimulated in subline 0.5. E2 inhibits the synthesis of the 42 kDa protein in both sublines. Different cell proliferation rates of MCF-7 cells can be established in cultures with 10% NCS and varying concentrations of E2. In such experiments final cell number after 6 days is positively correlated to the relative amount of the 66 kDa, the 61 kDa and the 52 kDa proteins, whereas the relative amount of the 42 kDa protein is negatively correlated to the final cell number. These results indicate that the 52 kDa, the 61 kDa and the 66 kDa proteins may act as positive growth factors, whereas the 42 kDa protein may act as a negative growth factor. The 42 kDa, the 52 kDa and the 61 kDa proteins are apparently glycoproteins, and the 66 kDa protein is not glycosylated. The 61 kDa protein is immunoreactive with antitrypsin antibodies.
Mol Cell Endocrinol 1989 Apr
PMID:Regulation of the secretion of proteins synthesized by the human breast cancer cell line, MCF-7. 274 30


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