Modulation of DNA binding of glucocorticoid receptor by aurintricarboxylic acid

Effects of aurintricarboxylic acid (ATA) were examined on the DNA binding properties of rat liver glucocorticoid-receptor complex. The DNA-cellulose binding capacity of the glucocorticoid-receptor complex was completely abolished by a pretreatment of receptor preparation with 0.1-0.5 mM ATA at 4 degrees C. The half-maximal inhibition (i.d.50) in the DNA binding of [3H]triamcinolone acetonide-receptor complex [( 3H]TARc) was observed at 130- and 40 microM ATA depending upon whether the inhibitor was added prior to or following the receptor activation. The entire DNA-cellulose bound [3H]TARc could be extracted in a concentration-dependent manner by incubation with 2-100 microns ATA. The [3H]TARc remained intact under the above conditions, the receptor in both control and ATA-treated preparations sedimented in the same region in salt-containing 5-20% sucrose gradients. The action of ATA appeared to be on the receptor and not on DNA-cellulose. The DNA-binding capacity of ATA-treated receptor preparations could be recovered upon exhaustive dialysis. The treatment with ATA did not appear to change the ionic behavior of heat activated GRc; the receptor in both control and the ATA-treated preparations showed similar elution profiles. Therefore, ATA appears to alter the binding to and dissociation of glucocorticoid-receptor complex from DNA. The use of ATA should offer a good chemical probe for analysis of the DNA binding domain(s) of the glucocorticoid receptor.     

Regional immunotherapy has a detrimental effect on the response to combined irradiation and chemotherapy in locally advanced non-small cell bronchogenic carcinoma

Summary Twenty-one patients with stage III M₀ non-oat cell bronchogenic carcinoma confined to the thorax were randomized to receive either intrapleural BCG (10⁷ cfu, Tice strain) or intrapleural saline 3 weeks prior to beginning combined irradiation and chemotherapy. Radiation to the primary tumor and regional nodes was given at a dose of 3,000 rad in ten sessions and was followed in 7–14 days by CAMP chemotherapy (cyclophosphamide, adriamycin, methotrexate, and procarbazine) for a planned duration of 6 months. Isoniazid, 300 mg/day, was given to all patients for 3 months starting 1 week after intrapleural therapy. There were no significant differences in pretreatment prognostic factors or in response to radiation therapy. The patients receiving intrapleural BCG in addition to radiation and chemotherapy had a median survival of 18 weeks, significantly shorter than that for the patients receiving intrapleural saline (54 weeks, P=0.017).Presented in part at the 16th Annual Meeting of the American Society of Clinical Oncology, San Diego, California, May 27, 1980     

Mode of action of phosphonoformate as an anti-herpes simplex virus agent

Phosphonoformate inhibited the replication of Herpes simplex virus (HSV) type 1 and type 2 in culture. The concentration required to inhibit the replication of both types of virus by 2 logs at 28 h post-infection was approximately 150 microM. It was more potent than phosphonoacetate against the growth of both virus types. A virus mutant which is resistant to phosphonoacetate was cross-resistant to phosphonoformate. Arsonoacetate, at 300 microM, had no antivirus activity. Phosphonoformate also inhibited HeLa and KB cell growth; at a concentration of about 500 microM, cell growth was inhibited by 50%. The anti-cell growth effects of the drug were completely reversible. The antivirus effect of phosphonoformate was partially reversible, depending on the time and duration of exposure of infected cultures to the drug. To obtain the maximum antivirus effect, phosphonoformate had to be added within the first 3 h post-virus-infection and be continuously present for at least 18 h. Phosphonoformate, added at 0 h post-infection, suppressed the induction of virus-specific DNA polymerase and DNAase activities. dTMP incorporation into DNA was preferentially inhibited in nuclei isolated from infected cells compared to uninfected cells, and the degree of inhibition varied with the ionic strength of the assay. Phosphonoformate was a potent inhibitor of the purified HSV-1 and HSV-2 DNA polymerases, inhibiting DNA polymerase activity by 50% at a concentration of 3 microM and ionic strength of 0.2.     

Proteolytic degradation of the nuclear isoform of uracil-DNA glycosylase occurs during the S phase of the cell cycle

Uracil-DNA glycosylases are enzymes that remove uracil from DNA and initiate base-excision repair. These enzymes play a key role in maintaining genomic integrity by reducing the mutagenic events caused by G:C to A:T transition mutations. The recent finding that a family of RNA editing enzymes (APOBECs) can deaminate cytosine in DNA has raised the interest in these base-excision repair enzymes. This research focuses on the regulation of the nuclear isoform of uracil-DNA glycosylase, a 36000 Da protein that contains a unique 44 amino acid N-terminus. In synchronized HeLa cells, UDG1A protein levels decrease to barely detectable levels during the S phase of the cell cycle. Immunoblot analysis of immunoprecipitated or affinity-isolated UDG1A reveals ubiquitin-conjugated UDG1A when proteolysis is inhibited using N-acetyl-leu-leu-norleu-al or MG132, inhibitors of proteosomal dependent protein degradation. Transient transfection experiments, with histidine-tagged ubiquitin, were used to confirm that endogenous UDG1A is ubiquitinated in vivo. Addition of the nuclear export inhibitor, leptomycin B, prevents ubiquitination and degradation of UDG1A. This indicates that translocation from the nucleus may be a step in UDG1A turnover. Finally, UDG1A protein degradation is prevented when cells are incubated with the cyclin-dependent kinase inhibitor, roscovitine. These results suggest that protein phosphorylation and/or nuclear export participate in the post-translational regulation of UDG1A protein levels.     

X-ray absorption spectroscopic investigation of the resting ferrous and cosubstrate-bound active sites of phenylalanine hydroxylase

Previous studies of ferrous wild-type phenylalanine hydroxylase, [Fe(2+)]PAH(T)[], have shown the active site to be a six-coordinate distorted octahedral site. After the substrate and cofactor bind to the enzyme ([Fe(2+)]PAH(R)[L-Phe,5-deaza-6-MPH(4)]), the active site converts to a five-coordinate square pyramidal structure in which the identity of the missing ligand had not been previously determined. X-ray absorption spectroscopy (XAS) at the Fe K-edge further supports this coordination number change with the binding of both cosubstrates to the enzyme, and determines this to be due to the loss of a water ligand.     

Proliferation-dependent expression of nuclear uracil-DNA glycosylase is mediated in part by E2F-4

There are two isoforms of the prototypical human uracil-DNA glycosylase: one mitochondrial (UDG1) and one nuclear (UDG1A). Results presented here reveal a novel genetic organization of UDG1. Specifically, the UDG1 5' UTR is composed of two non-coding exons and the promoter region is located much farther upstream than previously recognized. We also examine the proliferation-dependent expression of UDG1A and demonstrate that the protein disappears rapidly as cells transit from the cell cycle into G0. Ribonuclease protection assays reveal that UDG1A mRNA levels are greatly reduced during G0 as well. To begin to characterize the mechanisms contributing to this regulation, we identified two overlapping candidate E2F binding sites (denoted A and B) in the UDG1A 5' UTR. EMSA analysis of this region shows a unique protein complex present only in extracts derived from G0 cells. In vitro studies using purified E2F-4 and mutant competitors demonstrate that binding occurs in a proliferation-dependent manner exclusively to E2F site A. Two approaches were then used to assess the in vivo role of the candidate E2F sites. First, chromatin immunoprecipitation (ChIP) analysis demonstrates that E2F-4 binds to the UDG1A 5' UTR exclusively in G0 cells. Secondly, using transient transfection analysis, we show that mutating these sites abolishes the proliferation-dependent response of UDG1A.