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)

Adenovirus E1A dependent trans-activation of transcription involves the utilization of cellular promoter specific transcription factors. One such factor termed E2F is important for the transcription of the viral E2 gene and appears to be a rate limiting component targeted during the trans-activation event. Since E2F is of cellular origin and likely to be involved in cellular gene control, we have identified E2F binding sites in cellular genes. Examples include the c-myc, c-myb and N-myc protoncogenes, the DHFR gene and the EGF receptor gene. The transcription of these genes is regulated by cell proliferation signals and each falls into the so-called immediate early class: genes that are activated independent of new protein synthesis. Because of these common properties of regulation, we have addressed the possible role of E2F in growth factor dependent activation of transcription. Expression of a c-myc promoter driven CAT gene, transfected into quiescent 3T3 cells, is stimulated by serum addition whereas an identical gene containing mutations in the E2F binding sites is not responsive. The DNA binding activity of E2F is increased 4-fold upon serum stimulation and the kinetics of activation parallel activation of c-myc transcription. Furthermore, this increase in E2F activity is independent of new protein synthesis indicating that serum stimulation results in an activation of a pre-existing factor. These results thus provide strong evidence linking E2F and proliferation dependent control of transcription. We also believe that the E2F transcription factor is the first example of a regulator of the class of immediate early genes that is slowly activated by stimulation of cell proliferation.
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PMID:A role for the adenovirus inducible E2F transcription factor in a proliferation dependent signal transduction pathway. 214 65

A 365-bp fragment from the 5' region of the human transferrin receptor gene has been subcloned and sequenced. This fragment contains 115 bp of flanking sequence, the first exon, and a portion of the first intron. It contains a TATA box, several GC-rich regions, and is able to efficiently promote expression of the bacterial CAT gene in mouse 3T3 cells. Sequence comparisons demonstrate that this DNA segment has homology to the promoter regions of the human dihydrofolate reductase gene and the mouse interleukin 3 gene, as well as to a monkey DNA sequence that has homology to the SV40 origin and promotes expression of an unidentified gene product. Several high molecular mass proteins that interact with the transferrin receptor gene promoter have been identified. The activity of these proteins is transiently increased in 3T3 cells that have been stimulated by serum addition. This increase precedes a rise in transferrin receptor mRNA levels in the cytoplasm, which in turn precedes entry of the cells into S phase. DNase I footprinting of the transferrin receptor promoter reveals several protein binding sites. Two of the sites are within the conserved GC-rich region of the promoter. One of these binding sites probably interacts with Spl, while the second interacts with an uncharacterized protein.
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PMID:Cell proliferation and expression of the transferrin receptor gene: promoter sequence homologies and protein interactions. 349 Oct 79

pPL608-TR1 is a high-copy plasmid that permits phenotypic expression of the mouse dihydrofolate reductase (DHFR) gene in Bacillus subtilis. A plasmid mutation has been identified that increases expression of mouse DHFR more than ten-fold. The mutation is located in a 0.2-kb segment that intervenes between the DHFR gene and the 0.3-kb promoter fragment needed for transcriptional activation of DHFR. Nucleotide sequence analysis suggests that the effect of the mutation is to facilitate translation, initiated within the promoter fragment, through the 0.2-kb segment to the site of insertion of the DHFR-containing fragment. Additional promoter-containing fragments selected by their ability to promote expression of a plasmid gene located downstream from DHFR, the CAT gene, promote either high, intermediate or no phenotypic expression of DHFR. The results indicate that promoter fragments that allow phenotypic expression of the mouse DHFR gene contain two regulatory signals. One signal is essential to transcription of both DHFR and CAT and therefore functions as a promoter. The second signal may be necessary for translation of that portion of the mRNA specifying mouse DHFR.
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PMID:Enhanced expression of mouse dihydrofolate reductase in Bacillus subtilis. 640

Two polymorphic dihydrofolate reductase (DHFR) alleles, termed 20 K and 21 K, exist in Chinese hamster lung cells. Three major transcripts of different lengths are transcribed from each allele, and the expression of these transcripts differs dramatically between the alleles as a result of differential utilization of three poly(A) sites. Transcripts from the 20 K allele are preferentially polyadenylated at the first poly(A) site, while those from the 21 K allele are preferentially polyadenylated at the third site. In this study, transient expression experiments were used to demonstrate that a 2.1 kb genomic fragment containing the three DHFR poly(A) sites is sufficient to reproduce the allele-specific polyadenylation pattern on transiently expressed CAT-DHFR transcripts in COS cells. Site-directed mutagenesis allowed identification of the sequence elements which are responsible for this allele-specific polyadenylation. These studies indicate that a single-base change in the third poly(A) signal sequence, which alters the consensus AAUAAA signal in the 21 K allele to a weak AAUAAU signal in the 20 K allele, is primarily responsible for the dramatic difference in polyadenylation between the two alleles. Thus, as a result of this single-base change in the third poly(A) signal sequence, utilization of the first poly(A) site, located 1.2 kb upstream, changes dramatically.
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PMID:A genetic polymorphism within the third poly(A) signal of the DHFR gene alters the polyadenylation pattern of DHFR transcripts in CHL cells. 804 33

We compared (i) the enhancer/promoter (mCMV promoter) from the murine cytomegalovirus (CMV) major immediate early gene,(ii) the enhancer/promoter from human CMV major immediate early gene, containing a short promoter (h1CMV) or a long stretch of 5' untranslated region (UTR) from the gene promoter (h2CMV) and (iii) the simian virus 40 (SV40) enhancer/early region promoter (SV2) for their ability to direct foreign gene expression in transiently transfected mammalian cell lines. Two series of recombinant plasmids containing the different viral promoters fused to the cat reporter gene and 3'-UTR for processing of transcripts from either the SV40 early region or the rabbit Beta 1-globin-encoding gene (Glb) were also analyzed for their effect on transient gene expression. The mCMV was the most active in dihydrofolate reductase-deficient Chinese hamster ovary (CHOdhfr-) cells and BALB/3T3 clone A31 mouse embryo cells. The h2CMV was more active than the other promoters in Bowes human melanoma cells and in Vero African green monkey kidney cells. In human hepatoma (Hep G2) cells, similar levels of CAT synthesis were observed with the h2CMV- and the mCMV-based vectors. In Hep G2 and Bowes cells, 3'-UTR from the SV40 early region resulted in consistently higher levels of cat expression, as compared to the rabbit beta 1-Glb gene, while the converse was true in BALB/3T3 clone A31 and Vero cells. SV40 early region and rabbit beta1-Glb gene 3'-UTR resulted in similar cat expression in CHOdhfr- cells.
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PMID:Efficiency of different viral promoters in directing gene expression in mammalian cells: effect of 3'-untranslated sequences. 865 43

Methotrexate (MTX; 4-amino-10-methylfolic acid) is a folic acid reductase inhibitor used to treat autoimmune diseases and certain types of cancer. Testicular toxicity resulting from MTX is a significant side effect that may cause subsequent infertility. The present study was conducted to examine the ameliorating effects of vitamin B17 (VitB17) against testicular toxicity induced by MTX in male rats. A total of 50 male albino rats were equally divided into five groups [control group; vitamin B17 group (VitB17) administered VitB17 only; methotrexate group administered MTX only; cotreated group, (VitB17+MTX) and posttreated group (MTX+VitB17)]. In methotrexate group (MTX), a significant decrease was observed in body weight and the testicular weight, as well as the levels of plasma testosterone, luteinizing hormone and follicle-stimulating hormone compared with control. The sperm count, viability, morphology index, total motility, and progressive motility also decreased in MTX rats compared with control. Furthermore, the levels of reduced glutathione, catalase, and superoxide dismutase, as well as proliferating cell nuclear antigen protein expression, in the testicular tissue decreased in MTX compared with control. In addition, MTX caused a significant increase in DNA and tissue damage compared with control. However, VitB17 ameliorated these effects, indicating that it has a preventative and curative effect against MTX-induced reproductive toxicity in male rats. The protective effect of VitB17 may be associated to its antioxidant properties as it possibly acts as a free-radical scavenger and lipid peroxidation inhibitor, as well as its protective effect on the levels of GSH, SOD, and CAT.
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PMID:Vitamin B17 Ameliorates Methotrexate-Induced Reproductive Toxicity, Oxidative Stress, and Testicular Injury in Male Rats. 3319 2