Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To test the feasibility of using the human epidermal growth factor receptor (EGFR) as a model for growth factor receptor action in human hematopoietic cells, we infected Burkitt lymphoma cells (Namalwa) with a recombinant amphotrophic retrovirus containing a thymidine kinase promoter-driven human EGFR complementary DNA and the neomycin resistance gene. Neomycin-resistant cells expressing surface EGFR were selected by cell sorting using anti-EGFR monoclonal antibody 225. The selected cells expressed a Mr 170,000 protein immunoprecipitated by monoclonal antibody 225 and apparently identical to EGFR from A431 carcinoma cells. Infected Namalwa cells expressed 42,000 epidermal growth factor (EGF) binding sites/cell, and Scatchard analysis showed two affinities (Kd approximately 5 nM and approximately 0.5 nM). EGFR autophosphorylation was detected using antiphosphotyrosine antibodies after 5 min exposure to EGF. EGF binding induced rapid EGFR internalization (t1/2 = 9 min) and mobilization of transferrin receptors to the cell surface within 1 min. In fetal bovine serum-containing and serum-free cultures, EGF did not stimulate Namalwa cell proliferation. However, in the presence of 1.25% dimethyl sulfoxide (DMSO), EGF caused a dose-dependent increase in DNA synthesis. DMSO induced a cell cycle block in G1, which was partially reversed by EGF. DMSO induced changes in some B-cell markers suggesting cellular differentiation and increased surface EGF receptor number. Cells grown in DMSO and EGF were established as an EGF-dependent cell line for greater than 12 weeks, whereas cells grown in DMSO without EGF died within 1-2 weeks. Namalwa cells expressing EGFR demonstrated more rapid tumor growth in athymic mice. These studies demonstrate expression of functional EGFR mediating early biochemical and growth responses in a human hematopoietic cell, and indicate that EGFR can be used as an effective model in human hematopoietic cells. Results using DMSO are consistent with studies in other human leukemia cells indicating that agents inducing differentiation can restore growth factor dependence in previously factor-independent leukemia cells.
...
PMID:Expression of functional epidermal growth factor receptors in a human hematopoietic cell line. 170 31

Serum-free mouse embryo (SFME) cells, derived in medium supplemented with insulin, transferrin, high density lipoprotein, epidermal growth factor, and fibronectin, do not undergo crisis, maintain a predominantly diploid karyotype with no detectable chromosomal abnormalities for well over 100 population doublings in vitro, and are growth inhibited by concentrations of serum that are growth-stimulatory for most cell lines in culture. Serum inhibition of SFME cell proliferation was reversible and was not prevented by addition of the supplements of the serum-free medium, even when added repeatedly during the culture period. The serum effect on SFME cell proliferation could be detected after incubation in serum-containing medium for as little as 8 h. SFME cells in serum-containing medium were arrested in the G1 phase of the cell cycle with a greatly reduced rate of incorporation of precursors into DNA and thymidine kinase activity, while a reduction in rate of incorporation of amino acids into protein was not observed. SFME cultures maintained for extended periods in serum-containing medium underwent a crisis-like period followed by the appearance of variant cells capable of growing in serum-supplemented medium. These cells exhibited abnormal karyotype and were resistant to several inhibitors of proliferation active on the parent SFME cell type.
...
PMID:Serum inhibition of proliferation of serum-free mouse embryo cells. 189 91

Overexpression of the p185 product of the c-erb B2/neu gene is correlated with cell transformation and tumorigenesis. To study expression of this gene, a 1548-base pair fragment (-1571 to -24 bp relative to the ATG initiator codon) of the human c-erb B2/neu 5'-noncoding region was isolated, sequenced, and analyzed with respect to basal and inducible activity using the luciferase expression vector pSVOAL delta 5'. This fragment contained an Alu repetitive element which was confirmed in two independent clones. Basal activity of the 1548-base pair fragment was equivalent to the epidermal growth factor receptor promoter region and 32 and 16% as active as the Herpes simplex thymidine kinase and Rous sarcoma virus promoters, respectively. Induction of luciferase activity was observed in response to epidermal growth factor, 12-O-tetradecanoylphorbol-13-acetate, dibutyryl cAMP, and retinoic acid. Additive and synergistic responses with more than 30-fold increases were observed after treatment with combinations of inducing agents, indicating complex regulation of this gene. These results show that the promoter region of the c-erb B2/neu gene contains sequences that dictate regulatory responses to several environmental signals.
...
PMID:Structure and inducible regulation of the human c-erb B2/neu promoter. 196 58

The transcriptionally active RVL3-VL30 element contains a triple repeat of TGACTCC, a sequence nearly identical to the AP-1 binding site. However, 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulation was unable to elicit chloramphenicol acetyltransferase (CAT) expression from a construct containing these AP-1-like sequences upstream of the thymidine kinase promoter present in pTES. Endothelin, which activates protein kinase C (pkC) and elevates intracellular Ca2+ in Rat-1 cells, was effective in stimulating CAT expression from the VL30-pTES construct. We attempted to assess the relative importance of these second messenger systems by stimulating each pathway separately with exogenous agonists. We determined that neither stimulation of pkC by the tumor promoter TPA nor elevation of intracellular Ca2+ by the tumor promoter thapsigargin was sufficient to stimulate CAT expression from the VL30-pTES vector. When combined, the two tumor promoters induced a synergistic increase in CAT expression. Our data indicate that elevation of intracellular Ca2+ by thapsigargin was not required for full activation of pkC by TPA. First, TPA was able to stimulate expression of other genes in Rat-1 cells, indicating full activation of pkC. Second, thapsigargin synergized effectively with epidermal growth factor to stimulate CAT activity from the VL30-pTES construct in cells depleted of pkC activity by chronic TPA treatment. The permissive effects of thapsigargin on gene expression were also observed for an endogenous gene, transin/stromelysin. The permissive effects of elevated intracellular Ca2+ levels may represent a general mechanism for the stimulation of some genes by pkC-mediated pathways.
...
PMID:Two tumor promoters, 12-O-tetradecanoylphorbol-13-acetate and thapsigargin, act synergistically via distinct signaling pathways to stimulate gene expression. 212 50

The ability of an upstream element of the rat PRL gene to permit transcriptional regulation in response to several different hormones has been examined. To test the ability of specific DNA sequences to mediate hormone responsiveness, DNA fragments were subcloned upstream of a thymidine kinase-chloramphenicol acetyltransferase fusion gene and transferred into GH3 pituitary tumor cells. Initially, fragments representing a distal enhancer element (positions -1713 to -1495) and a more proximal element (positions -292 to -38) were tested. The results demonstrate that the distal enhancer permits cAMP, TRH, epidermal growth factor (EGF), and estradiol to stimulate expression of the thymidine kinase-chloramphenicol acetyltransferase gene. The proximal element permitted fusion gene regulation in response to cAMP, TRH, EGF, and phorbol esters. For the cAMP, TRH, and EGF responses, the distal element permitted responses approximately equal to or greater than responses conferred by the proximal PRL gene fragment. The response of the distal element to cAMP and TRH was more than additive with the response to estradiol, suggesting that the estrogen response element is distinct but may interact cooperatively with the other hormone response elements. Mutation of the estrogen-responsive element abolished both the response to estrogen and the cooperative response with cAMP, but not the response to cAMP itself. Mutation of a sequence involved in basal enhancer activity of the distal element reduced both basal transcription and the response to cAMP. These results suggest that the distal enhancer sequence of the PRL gene contains, in addition to an estrogen response element, elements that confer responsiveness to cAMP, TRH, and EGF.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:The distal enhancer region of the rat prolactin gene contains elements conferring response to multiple hormones. 253 91

The present investigation examines the responsiveness of the gastric mucosa to the growth-promoting action of epidermal growth factor (EGF) during advancing age. Two sets of experiments were performed. In the first set of experiments, groups of 4-, 8-, 16-, and 24-mo-old Fischer 344 rats were injected subcutaneously at 12-h intervals for 2 days with either EGF (10 micrograms/kg) in gelatin or the vehicle only (controls). The animals were killed 16-18 h after the last injection. The oxyntic gland mucosa was assayed for thymidine kinase and the rate of DNA synthesis in vitro (indicators of proliferative activity) as well as for tyrosine kinase (Tyr-k) activity. In control rats, the rate of DNA synthesis and thymidine kinase activity rose steadily between 4 and 24 mo of age. However, whereas Tyr-k activity in the gastric mucosal cytosol changed only marginally with age, activity of the enzyme in the membrane fraction rose steadily between 4 and 16 mo and then increased abruptly. EGF stimulated gastric mucosal DNA synthesis and thymidine kinase activity in 4- to 16-mo-old rats compared with the corresponding controls, but in the 24-mo-old animals, it caused a significant 40-50% inhibition. EGF had no demonstrable effect on Tyr-k activity in either cytosolic or membrane fraction. We postulated that Tyr-k activity might have returned to basal level 16-18 h after the last EGF injection.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Aging: altered responsiveness of gastric mucosa to epidermal growth factor. 280 40

The steady-state levels of calcyclin mRNA are regulated by growth factors. Using deletion mutants of the 5'-flanking region and a linked reporter (the bacterial chloroamphenicol transferase gene), we have investigated the elements of the calcyclin gene's promoter that respond to growth factors. By a transient expression assay after transfection in BALB/c/3T3 cells, we have been able to show that the serum-inducible sequences are contained in a 164-base pair fragment just upstream of the cap site. This fragment also contains an enhancer, and responds to platelet-derived growth factor as well as to serum. The sequences from -1371 to -1194 upstream of the cap site contain an element which is negatively regulated by epidermal growth factor. These findings have been confirmed in hamster cell lines in which the deletion mutants of the calcyclin promoter controlled the expression of the cDNA for human thymidine kinase. These results indicate that, like in other growth-regulated genes the activity of the calcyclin promoter is modulated by both positive and negative elements. Even more intriguing, though, is the finding that some of these negative elements may be influenced by growth factors in the environment.
...
PMID:Growth factor regulation of the promoter for calcyclin, a growth-regulated gene. 283 6

To understand the mechanisms of oncogenesis by human T-cell leukemia virus type I, we have investigated the ability of the tax1, protein to modulate transcription of protooncogenes. By using a transient cotransfection assay, we report that the protooncogene fos promoter is transactivated by tax1 in a variety of cell types. Two regions containing upstream sequences between positions -362/-324 and -323/-276 of the c-fos promoter responded to this activation and also conferred tax1 responsiveness to the heterologous herpesvirus thymidine kinase promoter. These two sequences include elements mediating the induction by v-sis-conditioned medium and serum, phorbol ester, or epidermal growth factor, respectively. Furthermore, expression of the endogenous c-fos gene was activated by tax1 in human T-cell leukemia virus type I-infected cell lines. In contrast, no trans-activation of the c-myc or c-Ha-ras promoter was observed.
...
PMID:c-fos promoter trans-activation by the tax1 protein of human T-cell leukemia virus type I. 284 64

The enzymes of the DNA synthesizing machinery constitute a group of gene products that are generally expressed co-ordinately at the G1/S boundary of the cell cycle. We have investigated how growth factors regulate the steady-state mRNA levels of two of these genes, the PCNA (proliferating cell nuclear antigen)/cyclin and the thymidine kinase genes. To detect the PCNA/cyclin mRNA, we isolated a cDNA clone from a human library. Two different cell lines were used for these studies: BALB/c3T3 cells, which are exquisitely sensitive to growth factors, and ts13 cells, a temperature-sensitive (ts) mutant of the cell cycle, which arrests in G1 at the restrictive temperature. The steady-state levels of the RNAs for these two genes under different growth conditions were also compared with the levels of histone H3 RNA which are good indicators of the fraction of cells in S phase. Both PCNA/cyclin and thymidine kinase genes share two fundamental characteristics, i.e. they are not inducible in a G1-specific ts mutant of the cell cycle at the restrictive temperature and their expression is inhibited by cycloheximide, indicating that unlike early growth-regulated genes, they require the previous expression of other growth-regulated genes. However, the two genes also show differences, the most notable being that PCNA/cyclin is inducible by epidermal growth factor alone, while thymidine kinase is not.
...
PMID:Regulation of the proliferating cell nuclear antigen cyclin and thymidine kinase mRNA levels by growth factors. 289 75

MM14 mouse myoblasts withdraw irreversibly from the cell cycle and become postmitotic within a few hours of being deprived of fibroblast growth factor (Clegg, C. H., T. A. Linkhart, B. B. Olwin, and S. D. Hauschka, 1987, J. Cell Biol., 105:949-956). To examine the mechanisms that may regulate this developmental state of skeletal muscle, we tested the mitogen responsiveness of various cell types after their polyethylene glycol-mediated fusion with post-mitotic myocytes. Heterokaryons containing myocytes and quiescent nonmyogenic cells such as 3T3, L cell, and a differentiation-defective myoblast line (DD-1) responded to mitogen-rich medium by initiating DNA synthesis. Myonuclei replicated DNA and reexpressed thymidine kinase. In contrast, (myocyte x G1 myoblast) heterokaryons failed to replicate DNA in mitogen-rich medium and became postmitotic. This included cells with a nuclear ratio of three myoblasts to one myocyte. Proliferation dominance in (myocyte x 3T3 cell) and (myocyte x DD-1) heterokaryons was conditionally regulated by the timing of mitogen treatment; such cells became postmitotic when mitogen exposure was delayed for as little as 6 h after cell fusion. In addition, (myocyte x DD-1) heterokaryons expressed a muscle-specific trait and lost epidermal growth factor receptors when they became postmitotic. These results demonstrate that DNA synthesis is not irreversibly blocked in skeletal muscle; myonuclei readily express proliferation-related functions when provided with a mitogenic signal. Rather, myocyte-specific repression of DNA synthesis in heterokaryons argues that the postmitotic state of skeletal muscle is regulated by diffusible factors that inhibit processes of cellular mitogenesis.
...
PMID:Heterokaryon analysis of muscle differentiation: regulation of the postmitotic state. 362 12


1 2 3 Next >>

---