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 retinoblastoma tumor suppressor gene product (pRb) is involved in controlling cell cycle progression from G1 into S. pRb functions, in part, by regulating the activities of several transcription factors, making pRb involved in the transcriptional control of cellular genes. Transient-transfection assays have implicated pRb in the transcription of several genes, including c-fos, the interleukin-6 gene, c-myc, cdc-2, c-neu, and the transforming growth factor beta2 gene. However, these assays place the promoter in an artificial context and exclude the effects of far 5' upstream regions and chromosomal architecture on gene transcription. In these experiments, we have studied the role of pRb in the control of cell cycle-related genes within a chromosomal context and within the context of the G1 phase of the cell cycle. We have used adenovirus vectors to overexpress pRb in human osteosarcoma cells and breast cells synchronized in early G1. By RNase protection assays, we have assayed the effects of this virus-produced pRb on gene expression in these cells. These results indicate that pRb is involved in the transcriptional downregulation of the E2F-1, E2F-2, dihydrofolate reductase, thymidine kinase, c-myc, proliferating-cell nuclear antigen, p107, and p21/Cip1 genes. However, it has no effect on the transcription of the E2F-3, E2F-4, E2F-5, DP-1, DP-2, or p16/Ink4 genes. The results are consistent with the notion that pRb controls the transcription of genes involved in S-phase promotion. They also suggest that pRb negatively regulates the transcription of two of the transcription factors whose activity it also represses, E2F-1 and E2F-2, and that it plays a role in downregulating the immediate-early gene response to serum stimulation.
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PMID:Regulation of cellular genes in a chromosomal context by the retinoblastoma tumor suppressor protein. 967 66

Epigenetic marks that specify silent heterochromatic domains in eucaryotic genomes include methylation of histone H3 lysine 9. Strikingly, active loci in the vicinity of silent domains are sometimes characterized by acetylation of histone H3 lysine 9, suggesting that the balance between these two competitive modifications is important for the establishment of specific chromatin structures. Some euchromatic genes, targeted by the retinoblastoma protein Rb, are also believed to be regulated by histone H3 lysine 9 methylation. Here, we study the dihydrofolate reductase promoter, which is repressed in G0 and at the beginning of G1 by p107 or p130, two Rb-related proteins. We found that these two pocket proteins share with Rb the ability to associate with the histone methyl transferase SUV39H1. SUV39H1 can be recruited to the E2F transcription factor and functions as a transcriptional corepressor. With ChIP assays followed by real-time PCR, we showed that K9 of histone H3 evolves from a hypermethylated state in G0 to a hyperacetylated state at the G1/S transition. Taken together, these results indicate that the temporal regulation of euchromatic promoters may involve controlling the balance between methylation and acetylation of histone H3 lysine 9, a feature previously described for the spatial regulation of chromatin function.
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PMID:Balance between acetylation and methylation of histone H3 lysine 9 on the E2F-responsive dihydrofolate reductase promoter. 1258 81

The SWI/SNF chromatin remodeling complex plays a critical role in the coordination of gene expression with physiological stimuli. The synthetic enzymes ribonucleotide reductase, dihydrofolate reductase, and thymidylate synthase are coordinately regulated to ensure appropriate deoxyribonucleotide triphosphate levels. Particularly, these enzymes are actively repressed as cells exit the cell cycle through the action of E2F transcription factors and the retinoblastoma tumor suppressor/p107/p130 family of pocket proteins. This process is found to be highly dependent on SWI/SNF activity as cells deficient in BRG-1 and Brm subunits fail to repress these genes with activation of pocket proteins, and this deficit in repression can be complemented, via the ectopic expression of BRG-1. The failure to repress transcription does not involve a blockade in the association of E2F or pocket proteins p107 and p130 with promoter elements. Rather, the deficit in repression is due to a failure to mediate histone deacetylation of ribonucleotide reductase, dihydrofolate reductase, and thymidylate synthase promoters in the absence of SWI/SNF activity. The basis for this is found to be a failure to recruit mSin3B and histone deacetylase proteins to promoters. Thus, the coordinate repression of deoxyribonucleotide triphosphate metabolic enzymes is dependent on the action of SWI/SNF in facilitating the assembly of repressor complexes at the promoter.
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PMID:SWI/SNF activity is required for the repression of deoxyribonucleotide triphosphate metabolic enzymes via the recruitment of mSin3B. 1751 60

High-risk types of HPV express the oncoproteins, E6 and E7, that can inactivate TP53 and RB1, respectively, and thus take control of both cell cycle and apoptosis. Herein, the mRNA expression profiles of 24 G1/S checkpoint genes were analysed in cancer and squamous intraepithelial lesions (SIL) of the uterine cervix. In total 35 squamous cervical carcinomas, 26 high-grade SIL (HSIL), 33 low-grade SIL (LSIL) tissues, and 28 normal uterine cervix specimens as controls were assessed by RT-PCR. Five genes were found to be upregulated only in tumours, RBL2, E2F2, CDK6, CCNE1 and MYC; eight in tumours and HSILs, E2F1, E2F3, E2F5, CCND1, CDK2, CDKN1B, PCNA and POLA, and five in tumours, HSILs and LSILs, TP53, E2F4, CDKN1A, CDKN2A and DHFR. MDM2 was found to be upregulated in SIL, while RBL1 was found to be downregulated in all three groups of cases. TP73 exhibited lower levels in carcinomas; however, its exon 13-containing isoforms were increased and exon 2-containing isoforms were reduced in both cancer and HSIL. Three genes, RB1, CDK4 and CDKN2D, did not exhibit any significant alteration in gene expression. Hierarchical clustering revealed that this set of G1/S checkpoint genes was able to discriminate the total 122 samples into groups of disease and non-disease with only 8 exceptions (6.6%). Our data suggest that deregulation of G1/S phase transition in cervical carcinogenesis is a progressive process. Certain clusters of genes are activated very early in pre-cancerous SILs while others are activated later, during malignant transformation. The ability of this array of markers to identify disease status suggests that it could be used for diagnostic purposes.
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PMID:Deregulation of the G1/S phase transition in cancer and squamous intraepithelial lesions of the uterine cervix: a case control study. 1881 14

Cell proliferation and differentiation are closely coupled. However, we previously showed that overexpression of cyclin-dependent kinase (Cdk6) blocks chondrocyte differentiation without affecting cell-cycle progression in vitro. To investigate whether Cdk6 inhibits chondrocyte differentiation in vivo, we generated chondrocyte-specific Cdk6 transgenic mice using Col2a1 promoter. Unexpectedly, differentiation and cell-cycle progression of chondrocytes in the Cdk6 transgenic mice were similar to those in wild-type mice. Then, we generated chondrocyte-specific Ccnd1 transgenic mice and Cdk6/Ccnd1 double transgenic mice to investigate the possibility that Cdk6 inhibits chondrocyte differentiation through E2f activation. Bromodeoxyuridine (BrdU)-positive chondrocytes and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive chondrocytes were increased in number, and chondrocyte maturation was inhibited only in Cdk6/Ccnd1 transgenic mice (K6(H)/D1(H) mice), which showed dwarfism. Retinoblastoma protein (pRb) was highly phosphorylated but p107 was upregulated, and the expression of E2f target genes was dysregulated as shown by upregulation of Cdc6 but downregulation of cyclin E, dihydrofolate reductase (dhfr), Cdc25a and B-Myb in chondrocytes of K6(H)/D1(H) mice. Similarly, overexpression of Cdk6/Ccnd1 in a chondrogenic cell line ATDC5 highly phosphorylated pRb, upregulated p107, induced apoptosis, upregulated Cdc6 and downregulated cyclin E, dhfr and B-Myb and p107 small interfering RNA reversed the expression of downregulated genes. Further, introduction of kinase-negative Cdk6 and cyclin D1 abolished all effects by Cdk6/cyclin D1 in ATDC5 cells, indicating the requirement of the kinase activity on these effects. p53 deletion partially restored the size of the skeleton and almost completely rescued chondrocyte apoptosis, but failed to enhance chondrocyte proliferation in K6(H)/D1(H) mice. These findings indicated that Cdk6/Ccnd1 overexpression inhibited chondrocyte maturation and enhanced G1/S cell-cycle transition by phosphorylating pRb, but the chondrocytes failed to accomplish the cell cycle, and underwent p53-dependent apoptosis probably due to the dysregulation of E2f target genes. Our findings also indicated that p53 deletion in addition to the inactivation of Rb was not sufficient to accelerate chondrocyte proliferation, suggesting the resistance of chondrocytes to sarcomagenesis.
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PMID:Overexpression of Cdk6 and Ccnd1 in chondrocytes inhibited chondrocyte maturation and caused p53-dependent apoptosis without enhancing proliferation. 2362 20


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