Identification of activators of methionine sulfoxide reductases A and B.

The methionine sulfoxide reductase (Msr) family of enzymes has been shown to protect cells against oxidative damage. The two major Msr enzymes, MsrA and MsrB, can repair oxidative damage to proteins due to reactive oxygen species, by reducing the methionine sulfoxide in proteins back to methionine. A role of MsrA in animal aging was first demonstrated in Drosophila melanogaster where transgenic flies over-expressing recombinant bovine MsrA had a markedly extended life span.

Studies on the metabolism and biological activity of the epimers of sulindac.

Sulindac is a nonsteroidal, anti-inflammatory drug (NSAID) that has also been studied for its anticancer activity. Recent studies suggest that sulindac and its metabolites act by sensitizing cancer cells to oxidizing agents and drugs that affect mitochondrial function, resulting in the production of reactive oxygen species and death by apoptosis. In contrast, normal cells are not killed under these conditions and, in some instances, are protected against oxidative stress.

Studies on the reducing systems for plant and animal thioredoxin-independent methionine sulfoxide reductases B.

Two distinct stereospecific methionine sulfoxide reductases (Msr), MsrA and MsrB reduce the oxidized methionine (Met), methionine sulfoxide [Met(O)], back to Met. In this report, we examined the reducing systems required for the activities of two chloroplastic MsrB enzymes (NtMsrB1 and NtMsrB2) from tobacco (Nicotiana tabacum). We found that NtMrsB1, but not NtMsrB2, could use dithiothreitol as an efficient hydrogen donor.

Selenocompounds can serve as oxidoreductants with the methionine sulfoxide reductase enzymes.

In a recent study on the reducing requirement for the methionine sulfoxide reductases (Msr) (Sagher, D., Brunell, D., Hejtmancik, J.

Thionein can serve as a reducing agent for the methionine sulfoxide reductases.

It has been generally accepted, primarily from studies on methionine sulfoxide reductase (Msr) A, that the biological reducing agent for the members of the Msr family is reduced thioredoxin (Trx), although high levels of DTT can be used as the reductant in vitro. Preliminary experiments using both human recombinant MsrB2 (hMsrB2) and MsrB3 (hMsrB3) showed that although DTT can function in vitro as the reducing agent, Trx works very poorly, prompting a more careful comparison of the ability of DTT and Trx to function as reducing agents with the various members of the Msr family. Escherichia coli MsrA and MsrB and bovine MsrA efficiently use either Trx or DTT as reducing agents.

Gene structure, localization and role in oxidative stress of methionine sulfoxide reductase A (MSRA) in the monkey retina.

MSRA (EC 1.8.4.

Methionine sulfoxide reductases B1, B2, and B3 are present in the human lens and confer oxidative stress resistance to lens cells.

Purpose: Methionine-sulfoxide reductases are unique, in that their ability to repair oxidized proteins and MsrA, which reduces S-methionine sulfoxide, can protect lens cells against oxidative stress damage. To date, the roles of MsrB1, -B2 and -B3 which reduce R-methionine sulfoxide have not been established for any mammalian system. The present study was undertaken to identify those MsrBs expressed by the lens and to evaluate the enzyme activities, expression patterns, and abilities of the identified genes to defend lens cells against oxidative stress damage.

Reduction of Sulindac to its active metabolite, sulindac sulfide: assay and role of the methionine sulfoxide reductase system.

Sulindac is a known anti-inflammatory drug that functions by inhibition of cyclooxygenases 1 and 2 (COX). There has been recent interest in Sulindac and other non-steroidal anti-inflammatory drugs (NSAID) because of their anti-tumor activity against colorectal cancer. Studies with sulindac have indicated that it may also function as an anti-tumor agent by stimulating apoptosis.

alpha-bungarotoxin receptors contain alpha7 subunits in two different disulfide-bonded conformations.

Neuronal nicotinic alpha7 subunits assemble into cell-surface complexes that neither function nor bind alpha-bungarotoxin when expressed in tsA201 cells. Functional alpha-bungarotoxin receptors are expressed if the membrane-spanning and cytoplasmic domains of the alpha7 subunit are replaced by the homologous regions of the serotonin-3 receptor subunit. Bgt-binding surface receptors assembled from chimeric alpha7/serotonin-3 subunits contain subunits in two different conformations as shown by differences in redox state and other features of the subunits.

Stabilization of the intermediate in frameshift mutation.

A mismatch repair, proofreading deficient mutant of Escherichia coli lost a C from a C8 run at a rate 10 times higher than the loss of A from an A8 sequence in the same double mutant. This greater frameshift instability of a homopolymeric run of C's may be due to stabilization of a stacked intermediate. Gain of a (CA) unit in a similarly constructed (CA)15 sequence occurred at a rate about 1/3 that previously reported for a (CA)14 construct losing a (CA) repeat unit.

Role of proofreading and mismatch repair in maintaining the stability of nucleotide repeats in DNA.

The role of the proofreading exonuclease in maintaining the stability of multiply repeated units in DNA was studied in Escherichia coli. Reversion of plasmids in which the beta-galactosidase alpha complementing sequence was moved +2 out of frame by inserts containing (CA)14, (CA)5, (CA)2 or (TA)6 or +1 by creating a run of 8 C was compared in mutS and mutSdnaQ strains. Proofreading corrects at least half of the frameshift errors for all the plasmids and at least 99% of the errors in the (CA)2 plasmid.

Production of UV-induced frameshift mutations in vitro by DNA polymerases deficient in 3'-->5' exonuclease activity.

In order to study the conversion of UV lesions into frameshift and base substitution mutations, M13mp2 phage DNA was altered by the addition of extra pyrimidines, or by construction of a nonsense codon preceded by a run of pyrimidines within the beta-galactosidase complementing region. The normal sequence 5' GTC GTT TTA CAA 3' was changed to GTC GTT T TTA CAA (MIDT) or GTC GTT C TTA CAA (MIDC) to study frameshifts and to GTC GTT CTT TAA (OCHRE) to study reversion of the ochre (TAA) codon. Escherichia coli pol I Kf and T7 DNA polymerase mutant enzymes devoid of 3'-->5' exonuclease activity produced UV-induced revertants at higher frequency than did their exonuclease proficient counterparts.

Heterogeneity of O6-alkylguanine-DNA alkyltransferase activity in peripheral blood lymphocytes: relationship between this activity in lymphocytes and in lymphoblastoid lines from normal controls and from patients with Hodgkin's disease or non-Hodgkin's lymphoma.

We determined O6-alkylguanine-DNA alkyltransferase (AGT) activity in the peripheral blood lymphocytes (PBLs) of normal controls and patients with Hodgkin's disease or non-Hodgkin's lymphoma and compared these values with those of Epstein-Barr virus (EBV)-transformed cell lines prepared from the same PBL samples. PBLs have an AGT level characteristic of the individual from whom the cells were obtained. The AGT activity of lymphoblastoid cell lines obtained from a control group of PBLs was significantly correlated with the activity of the PBLs from which they were derived (r = 0.

The relationship between O6-alkylguanine alkyltransferase activity and sensitivity to alkylation-induced sister chromatid exchanges in human lymphoblastoid cell lines.

We investigated the relationship between the ability to repair the O6-alkylguanine lesions and sister chromatid exchange (SCE) induction. Six human lymphoblastoid cell lines, with O6-alkylguanine alkyltransferase (AGT) activities ranging from 0 to 13.2 fmol/micrograms DNA, were tested for their sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-, methyl methanesulfonate (MMS)- and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)-induced SCEs.

Chromosomal sensitivity of lymphocytes from individuals with therapy-related acute nonlymphocytic leukemia.

A small fraction of those individuals exposed to cytotoxic chemotherapy or radiation for the treatment of a primary malignant disease will develop a second malignancy some time later. Although exposure to the cytotoxic agents is believed to be the causative factor, the reason only certain individuals develop the second malignancy is unknown. Some studies have suggested that these individuals might be predisposed to cancer because of an inherent sensitivity to the alkylating agents used in cancer therapy.

Low O6-alkylguanine DNA alkyltransferase activity in the peripheral blood lymphocytes of patients with therapy-related acute nonlymphocytic leukemia.

Chemotherapeutic agents such as procarbazine, which produce methylated bases in DNA, are used to treat many Hodgkin's disease (HD) and non-Hodgkin's lymphoma (NHL) patients. A small proportion of such patients develop secondary malignancy. We examined the possibility that those patients who develop secondary malignancy have low endogenous levels of O6-alkylguanine DNA alkyltransferase (AGT) activity and are therefore more sensitive to the mutagenic and carcinogenic effects of their treatment.

Abasic sites from cytosine as termination signals for DNA synthesis.

DNA with abasic sites has been prepared by deamination of cytosine followed by treatment of the product with uracil N-glycosylase. Termination in vitro on such templates does not occur until treatment with uracil N-glycosylase. DNA terminated one base before abasic sites created from C's has been used as a template in "second stage" reactions.

In vitro models of mutagenesis.

The bypass of lesions in DNA with insertion of nucleotides opposite damaged bases has been studied as a model for mutagenesis in an in vitro system. Lesions introduced by dimethyl sulfate at adenines and by ultraviolet light at pyrimidine dimers act as termination sites on both double- and single-stranded DNA templates. Base selection opposite noninformational lesions is, in part, a property of the polymerases: different polymerases have different selectivities although all polymerases tested seem to prefer purines.

Insertion of nucleotides opposite apurinic/apyrimidinic sites in deoxyribonucleic acid during in vitro synthesis: uniqueness of adenine nucleotides.

M13 DNA containing 20-30 apurinic/apyrimidinic (AP) sites per intact circular molecule was prepared by growing phage on an ung- dut- Escherichia coli mutant and treating the DNA with uracil N-glycosylase. AP sites obstruct in vitro DNA synthesis catalyzed by E. coli pol I.