Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism of growth control in estrogen-dependent and -independent human breast cancer is not completely understood. We have used both hormonally responsive and unresponsive breast cancer cells in culture to study the role of estrogens, oncogenes, and growth factors in their malignant transformation. MCF-7, an estrogen-receptor containing cell line, requires estradiol for tumor formation in vivo and is growth stimulated by estradiol and growth inhibited by antiestrogens in vitro. The growth regulation of MCF-7 cells by estrogens and antiestrogens may be linked to changes in several growth-related enzymes and polypeptide growth factors. Growth-acting polypeptides that are estradiol-inducible include IGF-I, TGF-alpha, and PDGF. Induction of at least two growth-related enzymes, thymidine kinase and dihydrofolate reductase is by transcriptional regulation of their mRNAs. To understand the natural progression of human breast cancer, we have experimentally constructed a hormone-independent fully tumorigenic cell line from the non-tumorigenic MCF-7 cells by introduction of an activated oncogene, v-rasH, into these cells by DNA-mediated gene transfer. Acquisition of the activated ras gene confers hormone autonomy on the previously hormone-dependent tumorigenicity and results in upregulation in secretion of some of the growth factors in amounts compared to estradiol stimulation. The transfected cells also become refractory to growth regulation by estradiol and antiestrogens in culture, although estrogen responses persist. Hormone-independent breast cancer cells in culture show high constitutive growth factor secretion. Direct infusion of some of the authentic growth factors and medium conditioned by estrogen-independent cells into athymic ovariectomized mice suggests a direct involvement of some of the polypeptides in the in vivo progression of tumors by these cells. Thus, aberrant production of growth factors, triggered either by activated oncogenes and estrogen stimulation in hormone-dependent cells, or by increased constitutive production in hormone-independent cells may in an autocrine, paracrine, or endocrine manner be associated with neoplastic growth of breast cancer.
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PMID:Estrogen and oncogene mediated growth regulation of human breast cancer cells. 350 Oct 40

The kidney epithelial cell line (MDBK) secretes primarily insulin-like growth factor binding protein (IGFBP)-2 under basal conditions, but exposure to forskolin decreases the synthesis of and induces IGFBP-3. Since IGFBP-3 has been shown to both potentiate and inhibit insulin-like growth factor (IGF) bioactivity, MDBK cells were transfected with an expression vector containing bovine IGFBP-3 cDNA and the dihydrofolate reductase (DHFR) gene as a selectable marker, with the goal of obtaining an epithelial cell line which constitutively secreted IGFBP-3. Stable clones which secreted greater than 100 ng/ml of IGFBP-3 were obtained and designated MDBKpMONBP-3. Northern blotting indicated that endogenous IGFBP-3 mRNA, which was undetectable in wild-type (WT) MDBK cells, was expressed in MDBKpMONBP-3 cells while the IGFBP-3 transgene did not appear to be expressed. DHFR mRNA transcripts were also expressed by MDBKp-MONBP-3 cells, whereas these transcripts were not detected in WT MDBK cells, suggesting that gene amplification of DHFR may have allowed cells to survive in methotrexate (MTX) without taking up the expression vector. In addition to the altered pattern of IGFBP-3 secretion, a marked alteration in cell morphology was observed. MDBKpMONBP-3 cells grew in distinct islands and exhibited dome formation (a characteristic of differentiated epithelial cells) whereas the WT cells did not. The alterations in morphology and IGFBP-3 expression were irreversible, since MDBKpMONBP-3 cells failed to revert to the WT phenotype upon removal of MTX and dialyzed serum. Since vectorial secretion of proteins is often associated with epithelial cell differentiation, cells were plated on tissue culture inserts which allowed conditioned media (CM) to be collected from both the apical and basal surfaces of confluent monolayers. Release of IGFBP-2 was approximately equal from apical and basal surfaces in WT MDBK cells. In contrast, release of both IGFBP-2 and IGFBP-3 was greater (3.1-fold and 3.5-fold, respectively) from basal as compared to apical surfaces of the MDBKpMONBP-3 cells. To determine if cells which were secreting IGFBP-3 had altered growth responses to IGF-I, cells were grown in serum-free media in the presence of IGF-I (0 to 100 ng/ml). Treatment of MDBKpMONBP-3 cells with 100 ng/ml of IGF-I increased cell number 138 +/- 37% above serum-free controls compared to 73 +/- 10% in WT MDBK cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Enhanced expression of dihydrofolate reductase by bovine kidney epithelial cells results in altered cell morphology, IGF-I responsiveness, and IGF binding protein-3 expression. 752 25

IGF-I rescues diabetic heart defects and oxidative stress, although the underlying mechanism of action remains poorly understood. This study was designed to delineate the beneficial effects of IGF-I with a focus on RhoA, Akt, and eNOS coupling. Echocardiography was performed in normal or diabetic Friend Virus-B type (FVB) and IGF-I transgenic mice. Cardiomyocyte contractile properties were evaluated using peak shortening (PS), time-to-90% relengthening (TR90), and intracellular Ca2+ rise and decay. Diabetes reduced fraction shortening, PS, and intracellular Ca2+; it increased chamber size, prolonged TR90, and intracellular Ca2+ decay. Levels of RhoA mRNA, active RhoA, and O2(-) were elevated, whereas nitric oxide (NO) levels were reduced in diabetes. Diabetes-induced O2(-) accumulation was ablated by the NO synthase (NOS) inhibitor nitro-L-arginine methyl ester (L-NAME), indicating endothelial NOS (eNOS) uncoupling, all of which except heart size were negated by IGF-I. The IGF-I-elicited beneficial effects were mimicked by the Rho kinase inhibitor Y27632 and BH4. Diabetes depressed expression of Kv1.2 and dihydrofolate reductase (DHFR), increased beta-myosin heavy-chain expression, stimulated p38 MAPK, and reduced levels of total Akt and phosphorylated Akt/eNOS, all of which with the exception of myosin heavy chain were attenuated by IGF-I. In addition, Y27632 and the eNOS coupler folate abrogated glucose toxicity-induced PS decline, TR90 prolongation, while it increased O2(-) and decreased NO and Kv1.2 levels. The DHFR inhibitor methotrexate impaired myocyte function, NO/O2(-) balance, and rescued Y27632-induced cardiac protection. These results revealed that IGF-I benefits diabetic hearts via Rho inhibition and antagonism of diabetes-induced decrease in pAkt, eNOS uncoupling, and K+ channel expression.
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PMID:IGF-I alleviates diabetes-induced RhoA activation, eNOS uncoupling, and myocardial dysfunction. 1819 85

Chimeric genes were constructed by fusing of human GH (hGH) cDNA to one, two, or three cassettes of the carboxyl-terminal peptide (CTP) of human chorionic gonadotropin (hCG)-beta-subunit. hGH variant genes were inserted into the pCI-DHFR plasmid, transfected into DG44 cells, and stable clones were selected. Bioactivity and pharmacokinetic studies were performed in hypophysectomized Sprague Dawley derived male rats. The results indicated that sc injections of GH-wild-type (WT), Biotropin (commercial), GH-CTP, or CTP-GH (0.6 mg/kg) once every 5 d for 11 d (total dose of 1.2 mg/kg) resulted in an increased weight gain by 4, 4.9, 5.1, and 7 g, respectively. Treatment with CTP-GH-CTP-CTP (GH-LA) or CTP-GH-CTP (0.6 mg/kg) once every 5 d for 11 d or with Biotropin (0.12 mg/kg) daily for 11 d (total dose 1.2 mg/kg) resulted in a dramatic increase in weight gain of 16.5, 16.8, and 17 g, respectively. Repeated injections with different doses of GH-LA, 0.6, 1.8 mg/kg every 4 d or daily injection of 0.12 mg/kg of Biotropin increased the weight gain by 16, 28, and 18 gr, respectively. In addition, the cumulative serum levels of IGF-I after injection of GH-LA was significantly higher than that detected after injection of Biotropin. Pharmacokinetic studies indicated that the half-life, mean residence time, area under the curve, time of maximal plasma concentration, and maximal plasma concentration of GH-LA are dramatically increased compared with Biotropin. This may suggest that the mechanism of GH metabolic clearance is affected by the presence of CTP. These data establish a rationale for using this chimera as a long-acting GH analog.
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PMID:Designing a long-acting human growth hormone (hGH) by fusing the carboxyl-terminal peptide of human chorionic gonadotropin beta-subunit to the coding sequence of hGH. 2066 71