Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0006142 (breast cancer)
 160,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Specific activity of 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) was measured in 48 tissue specimens of human female breast cancer and, in addition, 48 nonmalignant tissue specimens obtained in each case from the same cancer-bearing breast. In all cases the nonmalignant tissue showed greater conversion of estradiol-17 beta into estrone than the neoplastic tissues. In normal human breast tissue of premenopausal women specific enzyme activity depended on the phase of the MENSTRUAL CYCLE: the highest values of 17 beta-HSD activity were found in the early secretory phase. To determine the intracellular distribution of the 17 beta-HSD, purified microsomes, mitochondria, peroxysomes, lysosomes, nuclei and cytosol fractions were prepared. The purity of each fraction was monitored by marker enzymes. It was found that the 17 beta-HSD was mainly located in mitochondria and microsomes. Furthermore it could be demonstrated that the microsomal enzyme was bound tightly to the membranes of the endoplasmic reticulum, while the mitochondrial 17 beta-HSD was mainly associated with the outer membranes of the organelle. Kinetic parameters (Km-values, coenzyme requirements and maximal velocities) of a cytoplasmic, nuclear, mitochondrial and microsomal 17 beta-HSD of normal and neoplastic human mammary tissue were compared. Maximal velocity was highest in enzyme preparations of normal mammary tissue obtained from premenopausal women in the early secretory phase. Km-values wrere nearly identical in normal and neoplastic mammary tissue preparations (approx. 1 X 10(-6) M). NAD was more efficient than NADP as a cofactor. For the conversion of estradiol to estrone the optimum temperature was approximately 40 degrees C and the optimum pH 9.5. For the reduction of estrone the optimum pH was 6.5. Sulphydryl groups were shown to be essential for catalysis.
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PMID:Comparison of the in vitro conversion of estradiol-17 beta to estrone of normal and neoplastic human breast tissue. 1 41

Activities of glucosephosphate isomerase, lactate dehydrogenase, and NADP-isocitrate dehydrogenase were significantly elevated in breast cancer specimens from patients who responded favorably to combination cytotoxic chemotherapy regimens compared with those in carcinomas from patients failing to respond to the same chemotherapy. Presence of estrogen receptors and clinical response to hormonal therapy were also evaluated in neoplasms from these patients. The data suggest that measurement of the enzyme profile, along with estrogen receptor levels, may be useful in selecting a mode of therapy for patients with advanced disease.
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PMID:Relationship of glycolytic enzyme activities and response of breast cancer patients to chemotherapy: A preliminary report. 97 90

The kinetic mechanism of the cytosolic NADP(+)-dependent malic enzyme from cultured human breast cancer cell line was studied by steady-state kinetics. In the direction of oxidative decarboxylation, the initial-velocity and product-inhibition studies indicate that the enzyme reaction follows a sequential ordered Bi-Ter kinetic mechanism with NADP+ as the leading substrate followed by L-malate. The products are released in the order of CO2, pyruvate, and NADPH. The enzyme is unstable at high salt concentration and elevated temperature. However, it is stable for at least 20 min under the assay conditions. Tartronate (2-hydroxymalonate) was found to be a noncompetitive inhibitor for the enzyme with respect to L-malate. The kinetic mechanism of the cytosolic tumor malic enzyme is similar to that for the pigeon liver cytosolic malic enzyme but different from those for the mitochondrial enzyme from various sources.
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PMID:Kinetic mechanism of the cytosolic malic enzyme from human breast cancer cell line. 163 39

Cytosolic NADP(+)-dependent malic enzyme from a cultured human breast cancer cell line was purified to near homogeneity by two highly efficient chromatography systems: Pharmacia-LKB Q-Sepharose anion-exchange chromatography and adenosine-2',5'-bisphosphate-agarose affinity chromatography. The overall yield was 27%. The enzyme is presumably a tetramer composed of four probably identical subunits of Mr 65,000, which is similar to the enzyme from other sources. The pI and optimum reaction pH values for the tumor malic enzyme are 5.5 and 7.2, respectively. At pH 6.9, most of the enzyme exists as monomers. Activation energy for the enzyme-catalyzed oxidative-decarboxylation reaction is 57.4 kJ/mol. The enzyme is strictly NADP+ dependent, as NAD+ cannot support the oxidative-decarboxylation reaction. ATP at low concentration inhibits the enzyme activity. Fumarate at concentrations up to 5 mM does not affect the enzymatic reaction rate. Therefore the tumor cytosolic malic enzyme, unlike the mitochondrial malic enzyme, is not an allosteric regulatory enzyme.
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PMID:Purification and characterization of the cytosolic NADP(+)-dependent malic enzyme from human breast cancer cell line. 176 Oct 63

The identification of several steroid-transforming enzymes within human breast cancers has led to speculation that the growth of some hormone-responsive tumors might be mediated in part by intracellularly derived estrogens. Reports that MCF-7 human breast cancer cells can transform both estrone (E1)1 to estradiol (E2) and dehydroepiandrosterone (DHEA) to the estrogenic steroid 5-androstenediol (AED), have prompted us to investigate the 17-ketosteroid reductase activities (17-KSR's) which mediate these potentially important reactions. Enzyme assays were performed by quantifying the amounts of [3H]AED or [3H]E2 former from [3H]DHEA or [3H]E1, respectively, by various subcellular preparations from MCF-7 cells under a variety of experimental conditions. DHEA 17-KSR was found to be localized exclusively within cytosol, whereas the E1 17-KSR activity appeared to be nearly equally divided between the soluble and particulate cytoplasmic subfractions. The particulate E1 17-KSR appeared capable of utilizing NADH or NADPH, whereas both the cytosolic form of this enzyme and the soluble DHEA 17-KSR activity showed a strict requirement for NADPH. Although both of the soluble 17-KSR's also showed similar pH optima, several other features suggested that they are different enzymes in MCF-7. E1 did not inhibit the conversion of DHEA to AED, and DHEA did not interfere with the transformation of E1 to E2, indicating that major differences in substrate specificity exist between the two cytosolic activities. Furthermore, DHEA 17-KSR activity within cytosol stored at -20 degrees C deteriorated almost completely over twelve weeks of storage, whereas E1 17-KSR activity remained stable. Finally, although both enzymes were found to be subject to product inhibition, AED inhibited DHEA 17-KSR competitively, whereas cytosolic E1 17-KSR activity was inhibited by E2 in noncompetitive fashion. Studies of the oxidation of E2 to E1 by MCF-7 cells showed that this transformation is catalyzed by both soluble and particulate 17-hydroxysteroid oxidases which utilize either NAD or NADP as cofactor. Having previously reported the presence of a particulate NADP(H)-linked androstenedione (AE) 17-ketosteroid oxidoreductase in MCF-7, we now suggest that at least three different enzymes, one particulate and two soluble forms, participate in the conversion of 17-ketosteroids to their hormonally active 17-hydroxysteroid derivatives within this cell line. The restricted substrate requirements of each enzyme provide a rationale for developing selective enzyme inhibitors which could provide important investigational tools and potentially effective therapeutic agents.
Breast Cancer Res Treat 1990 Oct
PMID:Dehydroepiandrosterone and estrone 17-ketosteroid reductases in MCF-7 human breast cancer cells. 196 14

We found that Adriamycin increased the pentose phosphate shunt activity in both Adriamycin-sensitive (WT) and Adriamycin-resistant (ADRR) human breast cancer MCF-7 cells. In contrast, hydrogen peroxide and cumene hydroperoxide markedly stimulated pentose-shunt activity in ADRR but only moderately increased the activity in WT cells. Furthermore, the altered oxidation-reduction regulation is associated with changes intrinsic to the key enzymes of the pentose-shunt pathway, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase and with glutathione peroxidase. We found the Vmax values for glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were 50- and 4-fold lower, respectively, in ADRR than WT cells and the Kms of NADP+ were 10-fold lower in ADRR than WT. The activity of glutathione reductase in ADRR is 42% of that in WT. In spite of these changes, the response of the cells to both hydrogen peroxide and organic peroxide is not limited by either the capacity of the pentose shunt or glutathione reductase, but is determined by the activity of glutathione peroxidase and a glutathione transferase which possess peroxidase activity. The kinetic properties of the glucose-6-phosphate dehydrogenase in ADRR may, however, seriously limit the activity of cytochrome P-450 reductase, a major enzyme of Adriamycin conversion to a free radical.
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PMID:Adriamycin resistance in human tumor cells associated with marked alteration in the regulation of the hexose monophosphate shunt and its response to oxidant stress. 366 3

The kinetic properties of oestradiol 17 beta-dehydrogenase have been studied in the MCF-7 human breast cancer cell line. The activity of the enzyme was found to be linear with respect to time for at least 2 h and with respect to protein concentrations over the range 40-300 micrograms protein per tube. The enzyme was able to utilize both NAD and NADP as cofactors but at higher concentrations NAD was the more effective. The apparent Km was estimated to be 13.4 microM which is approximately two-fold higher than found for breast tumour tissue.
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PMID:Kinetic studies of oestradiol 17 beta-hydroxysteroid dehydrogenase in MCF-7 mammary cancer cells. 386 10

A cDNA coding for human breast cancer cell cytosolic NADP(+)-dependent malic enzyme was obtained. This cDNA is composed of a length of 2084 base pairs, with 1698 base pairs coding for 565 amino acid residues and a length of 386 base pairs representing a 3'-noncoding region. Comparing this nucleotide sequence with that from the normal human tissue [Loeber, G., Dworkin, M. B., Infante, A., and Ahorn, H. (1994), FEBS Lett. 344, 181-186] reveals that three nucleotides in the open reading frame and the length of 3'-noncoding region of the cDNA are different. One of the changes results in a substitution of serine at position 438 for proline, which, however, may not cause significant changes in the predicted secondary structure. A partial cDNA lacking the first 84 nucleotides in the open reading frame was successfully cloned and expressed functionally in Escherichia coli cells. Its Km value for L-malate (1.21 +/- 0.11 mM) is four times higher than that for the natural human breast cancer cell malic enzyme (0.29 +/- 0.04 mM) but similar to that for the full-length recombinant enzyme (1.06 +/- 0.07 mM). The Km values for Mn2+ and NADP+ (0.26 +/- 0.03 and 0.97 +/- 0.4 microM, respectively) are similar to those for the natural enzyme (0.12 +/- 0.02 and 1.9 +/- 0.3 microM, respectively) or the recombinant wild-type enzyme (0.56 +/- 0.04 and 0.44 +/- 0.02 microM, respectively). A recombinant pigeon liver malic enzyme without the first 13 amino acid residues was used for comparison. The Km values for L-malate and Mn2+ of the truncated enzyme (11.2 +/- 0.9 mM and 61.2 +/- 4.6 microM, respectively) are over 40 times larger than those for the natural pigeon liver malic enzyme (0.21 +/- 0.02 mM and 1.06 +/- 0.08 microM, respectively) or the recombinant wild-type enzyme (0.25 +/- 0.01 mM and 1.48 +/- 0.05 microM, respectively). We suggest that the N-terminus of malic enzyme may be required for the substrate binding during the catalytic cycle.
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PMID:Nonidentity of the cDNA sequence of human breast cancer cell malic enzyme to that from the normal human cell. 880 75

Excess 17beta-estradiol (E2), the most potent of human estrogens, is known to act as a stimulus for the growth of breast tumors. Human estrogenic 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1), which catalyzes the reduction of inactive estrone (E1) to the active 17beta-estradiol in breast tissues, is a key enzyme responsible for elevated levels of E2 in breast tumor tissues. We present here the structure of the ternary complex of 17beta-HSD1 with the cofactor NADP+ and 3-hydroxyestra-1,3,5,7-tetraen-17-one (equilin), an equine estrogen used in estrogen replacement therapy. The ternary complex has been crystallized with a homodimer, the active form of the enzyme, in the asymmetric unit. Structural and kinetic data presented here show that the 17beta-HSD1-catalyzed reduction of E1 to E2 in vitro is specifically inhibited by equilin. The crystal structure determined at 3.0-A resolution reveals that the equilin molecule is bound at the active site in a mode similar to the binding of substrate. The orientation of the 17-keto group with respect to the nicotinamide ring of NADP+ and catalytic residues Tyr-155 and Ser-142 is different from that of E2 in the 17beta-HSD1-E2 complex. The ligand and substrate-entry loop densities are well defined in one subunit. The substrate-entry loop adopts a closed conformation in this subunit. The result demonstrates that binding of equilin at the active site of 17beta-HSD1 is the basis for inhibition of E1-to-E2 reduction by this equine estrogen in vitro. One possible outcome of estrogen replacement therapy in vivo could be reduction of E2 levels in breast tissues and hence the reduced risk of estrogen-dependent breast cancer.
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PMID:Structure of the ternary complex of human 17beta-hydroxysteroid dehydrogenase type 1 with 3-hydroxyestra-1,3,5,7-tetraen-17-one (equilin) and NADP+. 992 55

Human estrogenic 17beta-hydroxysteroid dehydrogenase (17beta-HSD1, EC1.1.1.62) is an important enzyme that catalyses the last step of active estrogen formation. 17Beta-HSD1 plays a key role in the proliferation of breast cancer cells. The three-dimensional structures of this enzyme and of the enzyme-estradiol complex have been solved (Zhu et al., 1993, J. Mol. Biol. 234:242; Ghosh et al., 1995, Structure 3:503; Azzi et al., 1996, Nature Struct. Biol. 3:665). The determination of the non-reactive ternary complex structure, which could mimic the transition state, constitutes a further critical step toward the rational design of inhibitors for this enzyme (Ghosh et al. 1995, Structure 3:503; Penning, 1996, Endocrine-Related Cancer, 3:41). To further study the transition state, two non-reactive ternary complexes, 17beta-HSD1-EM519-NADP+ and 17beta-HSD1-EM553-NADP+ were crystallized using combined methods of soaking and co-crystallization. Although they belong to the same C2 space group, they have different unit cells, with a = 155.59 A, b = 42.82 A, c = 121.15 A, beta = 128.5 degrees for 17beta-HSD1-EM519-NADP+, and a = 124.01 A, b = 45.16 A, c = 61.40 A, beta = 99.2 degrees for 17beta-HSD1-EM553-NADP+, respectively. Our preliminary results revealed that the inhibitors interact differently with the enzyme than do the natural substrates.
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PMID:Two non-reactive ternary complexes of estrogenic 17beta-hydroxysteroid dehydrogenase: crystallization and preliminary structural analysis. 1041 39


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