Heating events in the nascent solar system recorded by rare earth element isotopic fractionation in refractory inclusions

Equilibrium condensation of solar gas is often invoked to explain the abundance of refractory elements in planets and meteorites. This is partly motivated, by the observation that the depletions in both the least and most refractory rare earth elements (REEs) in meteoritic group II calcium-aluminum-rich inclusions (CAIs) can be reproduced by thermodynamic models of solar nebula condensation. We measured the isotopic compositions of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb in eight CAIs to test this scenario. Contrary to expectation for equilibrium condensation, we find light isotope enrichment for the most refractory REEs and more subdued isotopic variations for the least refractory REEs. This suggests that group II CAIs formed by a two-stage process involving fast evaporation of preexisting materials, followed by near-equilibrium recondensation. The calculated time scales are consistent with heating in events akin to FU Orionis- or EX Lupi-type outbursts of eruptive pre-main-sequence stars.

An exploratory analysis of factors associated with weight change in a 16-week trial of oral vs. orally disintegrating olanzapine: the PLATYPUS study

BACKGROUND

We conducted exploratory analyses of the data from a multinational, randomised study to identify factors associated with weight change after 16 weeks of treatment with standard olanzapine tablets (SOT) or sublingual orally disintegrating olanzapine (ODO).

METHODS

One hundred and forty nine outpatients who gained weight during prior SOT therapy were enrolled into the study and treated with ODO (N = 84) or SOT (N = 65). Exploratory analyses were conducted with the subset of compliant patients (ODO: n = 60; SOT: n = 47).

RESULTS

The decrease in the rate of weight gain at the end of study therapy (change from baseline) was greater in the ODO group than the SOT group (-0.59 kg/week vs. -0.38 kg/week, p = 0.0246). Age was negatively associated with weight change (p = 0.0203) in both treatment groups combined: patients gained 0.7 kg less for every 10 years of age. The least squares mean weight gain was lower with ODO than SOT in male patients (0.35 kg vs. 3.04 kg, p = 0.061), but not female patients and in American patients (0.55 kg vs. 6.21 kg, p < 0.0001), but not Canadian or Mexican patients.

CONCLUSIONS

Although not conclusive, these data suggest that ODO may be a reasonable treatment option for some patients who gain weight with SOT. Further research is required to confirm these findings.

Involvement of a cryptic ATPase activity of UvrB and its proteolysis product, UvrB* in DNA repair

The incision of damaged DNA by the Escherichia coli UvrABC endonuclease requires ATP hydrolysis. Although the deduced sequence of the UvrB protein suggests a putative ATP binding site, no nucleoside triphosphatase activity is demonstrable with the purified UvrB protein. The UvrB protein is specifically proteolyzed in E. coli cell extracts to yield a 70 kD fragment, referred to as UvrB*, which has been purified and is shown to possess a single-strand DNA dependent ATPase activity. Substrate specificity and kinetic analyses of UvrB* catalyzed nucleotide hydrolysis indicate that the stimulation in DNA dependent ATPase activity following formation of the UvrAB complex results from the activation of the normally sequestered UvrB associated ATPase. Using nucleotide analogues, it can be shown that this activity is essential to the DNA incision reaction carried out by the UvrABC complex.

Potential role of proteolysis in the control of UvrABC incision

UvrB is specifically proteolyzed in Escherichia coli cell extracts to UvrB*. UvrB* is capable of interacting with UvrA in an aparently similar manner to the UvrB, however UvrB* is defective in the DNA strand displacement activity normally displayed by UvrAB. Whereas the binding of UvrC to a UvrAB-DNA complex leads to DNA incision and persistence of a stable post-incision protein-DNA complex, the binding of UvrC to UvrAB* leads to dissociation of the protein complex and no DNA incision is seen. The factor which stimulates this proteolysis has been partially purified and its substrate specificity has been examined. The protease factor is induced by "stress" and is under control of the htpR gene. The potential role of this proteolysis in the regulation of levels of active repair enzymes in the cell is discussed.

A randomized controlled trial of the effect of sublingual orally disintegrating olanzapine versus oral olanzapine on body mass index: the PLATYPUS Study

BACKGROUND

Patients with schizophrenia and bipolar disorder have frequently reported weight gain during olanzapine treatment. Previous studies have observed a decrease in weight gain, or weight loss, in patients switching from standard olanzapine tablets (SOT) to orally disintegrating olanzapine (ODO) tablets. The primary objective of this study was to investigate the change in body mass index (BMI) in patients who had previously gained weight with SOT and continued with this therapy during the study period, compared with those patients who switched to ODO during the study period.

METHODS

This was a 16-week, multicentre, randomized, double-blind, double-dummy, study of outpatients diagnosed with schizophrenia, schizoaffective disorder, related psychotic disorder or bipolar disorder, who were taking 5-20 mg SOT daily. Patients continued treatment with 5-20 mg olanzapine in a flexible single daily dose, and were randomized to either receive sublingual ODO plus an oral placebo, or sublingual placebo plus SOT.

RESULTS

No statistically significant between group differences in mean change from baseline in BMI, weight or waist circumference were observed. Analysis of change in body weight from baseline, by pre-specified category (no change, loss of >or=1.5 kg, gain of >or=1.5 kg), revealed a significant difference between groups, favoring ODO patients, who also experienced a significant reduction in subjective appetite and better treatment compliance, compared to patients in the SOT group.

CONCLUSIONS

In this study, patients treated with ODO experienced a similar mean change in BMI and weight from baseline, to those patients treated with SOT.

XPD gene polymorphism and host characteristics in the association with cutaneous malignant melanoma risk

We recently reported an association between low DNA repair capacity, measured through the host-cell reactivation assay, and melanoma risk in subjects with dysplastic naevi or low tanning ability. We investigated the genetic basis for these findings by analysing the Asp312Asn and Lys751Gln polymorphisms of the XPD (ERCC2) DNA repair gene in the same subjects. Similar to our previous report, no significant association between XPD polymorphisms and melanoma risk was found in 176 melanoma cases and 177 controls (odds ratio (OR)=1.5, 95% confidence interval (CI)=0.9–2.5 for 312Asn; OR=1.3, 95% CI=0.8–2.1 for 751Gln, adjusted for age, gender, dysplastic naevi and pigmentation characteristics). However, XPD variants were associated with increased risk in older (>50 years) subjects (OR=3.4, 95% CI=1.6–7.3 for 312Asn; OR=2.3, 95% CI=1.1–4.9 for 751Gln). The 751Gln allele was associated with elevated melanoma risk among subjects without dysplastic naevi (OR=2.6, 95% CI=1.1–6.4). Subjects with low tanning ability and XPD variants exhibited a nonsignificant increase of melanoma risk (OR=2.3, 95% CI=0.7–7.0 for 312Asn; OR=3.0, 95% CI=1.0–8.8 for 751Gln). DNA repair capacity was slightly decreased in subjects carrying 751Gln alleles. XPD variants may modify melanoma risk in subjects with specific host characteristics, such as older age, lack of dysplastic naevi or low tanning ability.

Functional significance of XPD polymorphic variants: attenuated apoptosis in human lymphoblastoid cells with the XPD 312 Asp/Asp genotype

Recent molecular epidemiological studies have identified polymorphisms in the XPD gene that are associated with increased risk of brain gliomas and head, neck, lung, and skin cancers. However, the functional significance of these polymorphic variants in altering cell processes such as cell cycle checkpoints, DNA repair, and apoptosis is uncertain. We have cloned the XPD variants Lys751Gln, Asp312Asn, and Lys751Gln-Asp312Asn into a pcDNA-3.1-expression vector. Using these constructs, we did not find any detectable difference in either in vitro binding with wild-type p53 or in DNA repair proficiency as measured by host cell reactivation assay. We then genotyped 34 different lymphoblastoid cell lines from six Centre d'Etude du Polymorphisme Humaine (CEPH)/Utah pedigree families and a CEPH/French pedigree family for polymorphisms at codons 751 and 312 and assessed their apoptotic response after either UV or ionized radiation exposure. The lymphoblastoid cell lines with homozygous or heterozygous Asp at codon 312 have similar apoptotic rates, whereas cell lines with homozygous Asn at codon 312 showed a 2.5-fold increased response to UV (P = 0.005; Student's t test). This is the first report known to us of a functional polymorphism in a gene involved in DNA damage-induced apoptosis. However, the presence of Lys or Gln at codon 751 did not influence the apoptotic response to UV. The diminished apoptotic response of cells containing the 312 Asp allele could both allow the survival and selective clonal expansion of carcinogen-damaged cells and be a mechanistic explanation for the increased risk of cancer at diverse tissue sites.

Polymorphisms of the DNA repair gene XPD: correlations with risk of basal cell carcinoma revisited

The XPD gene product has a dual function in basal transcription and in nucleotide excision repair. We have previously reported that two polymorphisms in the gene, one silent mutation in codon 156 of exon 6 and one giving rise to a Lys-->Gln substitution in codon 751 of exon 23, showed signs of being associated with basal cell carcinoma in a Scandinavian study group of psoriasis patients and non-psoriatics with and without basal cell carcinoma [Dybdahl, Vogel, Frentz, Wallin and Nexø (1999) Cancer Epidemiol. Biomark. Prev., 8, 77-81]. In both polymorphisms, the CC genotype appeared to be protective against basal cell carcinoma. Here, we have genotyped an American study group of basal cell carcinoma patients and controls without skin cancer for the two polymorphisms. In addition, we studied an A-->G polymorphism in codon 312 of exon 10, which results in an Asp-->Asn substitution in a conserved region of XPD. In the whole study group, subjects carrying the AA and AC genotype in exon 6 were at 1.9-fold higher risk of basal cell carcinoma (P = 0.062, CI 0.96-3.75). If only subjects without a family history of non-melanoma skin cancer were included, subjects carrying AA or AC genotype were at 3.3-fold higher risk of basal cell carcinoma (P = 0.007, CI 1.35-8.18). Among subjects with a family history of non-melanoma skin cancer, subjects with an AG or AA genotype in codon 312 of exon 10 were at 5.25-fold increased risk of basal cell carcinoma (P = 0.027, CI 1.15-23.93). A protective effect of the CC genotype in exon 23 could not be confirmed. Cases with a family history of skin cancer had statistically significantly different allele frequencies of the polymorphisms in exon 6 and exon 10 from cases without family history of non-melanoma skin cancer. Our results indicate that the exon 6(A) allele is a risk factor in basal cell carcinoma.

A new xeroderma pigmentosum group C poly(AT) insertion/deletion polymorphism

We found a common biallelic polymorphism (PAT) in the xeroderma pigmentosum complementation group C (XPC) DNA repair gene consisting of an insertion of 83 bases of A and T [poly(AT)] and a 5 base deletion within intron 9. We developed a PCR assay to resolve the XPC PAT+ and PAT- alleles and found that the PAT+ allele frequency was 0.44 in 156 cancer-free donors from the Johns Hopkins School of Public Health, 0.41 in 263 cancer-free donors from the Baltimore Longitudinal Study of Aging and 0.36 in samples from 216 unselected donors from NIH. We also found a single nucleotide polymorphism in exon 15 of the XPC gene (A2920C, Lys939-->Gln) that creates a new enzyme restriction site. This XPC exon 15 single nucleotide polymorphism occurred at a frequency of 0.38 in 98 NIH donors and is in linkage disequilibrium with the PAT locus. We developed an allele-specific complementation assay utilizing post-UV host cell reactivation to assess DNA repair capacity of polymorphic alleles. We found similar DNA repair with XPC 2920A and XPC 2920C. These common polymorphisms in the XPC DNA repair gene may be useful for molecular epidemiological studies of cancer susceptibility.

Oligomerization of the UvrB nucleotide excision repair protein of Escherichia coli

A combination of hydrodynamic and cross-linking studies were used to investigate self-assembly of the Escherichia coli DNA repair protein UvrB. Though the procession of steps leading to incision of DNA at sites flanking damage requires that UvrB engage in an ordered series of complexes, successively with UvrA, DNA, and UvrC, the potential for self-association had not yet been reported. Gel permeation chromatography, nondenaturing polyacrylamide gel electrophoresis, and chemical cross-linking results combine to show that UvrB stably assembles as a dimer in solution at concentrations in the low micromolar range. Smaller populations of higher order oligomeric species are also observed. Unlike the dimerization of UvrA, an initial step promoted by ATP binding, the monomer-dimer equilibrium for UvrB is unaffected by the presence of ATP. The insensitivity of cross-linking efficiency to a 10-fold variation in salt concentration further suggests that UvrB self-assembly is driven largely by hydrophobic interactions. Self-assembly is significantly weakened by proteolytic removal of the carboxyl terminus of the protein (generating UvrB*), a domain also known to be required for the interaction with UvrC leading to the initial incision of damaged DNA. This suggests that the C terminus may be a multifunctional binding domain, with specificity regulated by protein conformation.

Enhanced repair of benzo(a)pyrene-induced DNA damage in human cells treated with thymidine dinucleotides

The small DNA fragment thymidine dinucleotide (pTpT) stimulates photoprotective responses in mammalian cells and intact skin. These responses include increased melanogenesis (tanning) and enhanced repair of DNA damage induced by ultraviolet (UV) light. Here we show that pTpT treatment of human keratinocytes enhances their repair of DNA damaged by the chemical carcinogen benzo(a)pyrene (BP), as determined by increased expression of a transfected BP-damaged reporter plasmid containing the chloramphenicol acetyltransferase (CAT) gene. The pTpT-enhanced repair of this BP-damaged plasmid is accomplished at least in part through activation of the p53 tumor suppressor protein and transcription factor, because p53-null H1299 cells showed enhanced repair only if previously transfected with a p53-expression vector. To elucidate the mechanism of this enhanced DNA repair, we examined the expression of p21 and proliferating cell nuclear antigen (PCNA), proteins known to be regulated by p53, as well as the XPA protein, which is mutated in the inherited repair-deficient disorder xeroderma pigmentosum (XP) group A and is necessary for the recognition of UV-induced DNA photoproducts. The p53, PCNA and XPA proteins were all up-regulated within 48 h after the addition of pTpT. Taken together, these data demonstrate that pTpT-enhanced repair of DNA damaged by either UV irradiation or chemical mutagens can be achieved in human cells by exposure to small DNA fragments at least in part through the activation of p53 and increased expression of p53-regulated genes.

Smoking behaviors of women whose children attend an urban pediatric primary care clinic

OBJECTIVE

To characterize smoking behaviors of caregivers whose children attend a large urban pediatric primary care center.

DESIGN

Descriptive survey. Women (n = 479) classified as smokers completed a questionnaire including demographics, smoking habits, measures of addiction, social reinforcers for smoking, attitudes and knowledge, other health and safety habits, and the pediatrician's role in smoking cessation counseling.

RESULTS

Of 1421 women surveyed, 36.6% (517) were classified as daily smokers. Four hundred and seventy-nine (93%) were enrolled in the study. Thirty-eight (7%) refused or were ineligible. Smokers differed significantly from non-smokers, with smokers more likely to have lower incomes (p<.03), lower educational attainment (p<.001), and were more likely to be white than non-smokers (p<.001). The average smoker smoked 14 cigarettes per day for 10 years. Half of the subjects had not considered quitting smoking in the near future. The majority of subjects (66%) lived with at least one other smoker, and reported that more than half of their friends smoked. Most (79%) participants agreed that pediatricians should give smoking cessation advice to parents of their patients. However, only 19% recalled being counseled to quit, and 55% recalled their child's doctor discussing the danger of environmental tobacco smoke.

CONCLUSION

The pediatric visit is an excellent opportunity for identifying women who smoke. Efforts to assist women with smoking cessation in similar settings will need to take into account their poverty and the high degree of social support for their continued smoking.

What the analyst does not hear

In the clinical situation, the analyst fails to hear more than he or she hears and spends much time working in the dark. The author raises questions about how we can take cognizance of that state of affairs in our thinking about analytic work. A clinical example illustrates how, in an analytic atmosphere, a patient will correct an analyst's failure to hear. Some ideas are offered about how to maximize the patient's participation in that effort. The author suggests that the problem may not fall precisely under the heading of technique so much as reflecting the analyst's attitude.

Accessibility of epitopes on UvrB protein in intermediates generated during incision of UV-irradiated DNA by the Escherichia coli Uvr(A)BC endonuclease

Structural intermediates generated during incision of damaged DNA by the Uvr(A)BC endonuclease were probed with monoclonal antibodies (mAbs) raised against the Escherichia coli UvrB protein. It was found that the epitope of B2C5 mAb, mapped at amino acids (aa) 171-278 of UvrB, is not accessible in any of the preformed Uvr intermediates. Preformed B2C5-UvrB immunocomplexes, however, inhibited formation of those intermediates. B2C5 mAb seems to interfere with the formation of the UvrA-UvrB complex due to overlapping of its epitope and the UvrA binding region of UvrB. Conversely, the epitope of B3C1 mAb (aa 1-7 and/or 62-170) was accessible in all Uvr intermediates. The epitope of B*2E3 mAb (aa 171-278) was not accessible in any of the nucleoprotein intermediates preceding UvrB-DNA preincision complex. However, B*2E3 was able to immunoprecipitate this complex and to inhibit overall incision. B2A1 mAb (aa 8-61) inhibited formation of those Uvr intermediates requiring ATP binding and/or hydrolysis by UvrB. B*2B9 mAb (aa 473-630) inhibited Uvr nucleoprotein complexes involving UvrB. B*2B9 seems to prevent the binding of the UvrA-UvrB complex to DNA. The epitope of the B*3E11 mAb (aa 379-472) was not accessible in Uvr complexes formed at damaged sites. These results are discussed in terms of structure-functional mapping of UvrB protein.

Introduction of a tryptophan reporter group into the ATP binding motif of the Escherichia coli UvrB protein for the study of nucleotide binding and conformational dynamics

The DNA-dependent ATPase activity of UvrB is required to support preincision steps in nucleotide excision repair in Escherichia coli. This activity is, however, cryptic. Elicited in nucleotide excision repair by association with the UvrA protein, it may also be unmasked by a specific proteolysis eliminating the C-terminal domain of UvrB (generating UvrB*). We introduced fluorescent reporter groups (tryptophan replacing Phe47 or Asn51) into the ATP binding motif of UvrB, without significant alteration of behavior, to study both nucleotide binding and those conformational changes expected to be essential to function. The inserted tryptophans occupy moderately hydrophobic, although potentially heterogeneous, environments as evidenced by fluorescence emission and time-resolved decay characteristics, yet are accessible to the diffusible quencher acrylamide. Activation, via specific proteolysis, is accompanied by conformational change at the ATP binding site, with multiple changes in emission spectra and a greater shielding of the tryptophans from diffusible quencher. Titration of tryptophan fluorescence with ATP has revealed that, although catalytically incompetent, UvrB can bind ATP and bind with an affinity equal to that of the active UvrB* form (Kd of approximately 1 mM). The ATP binding site of UvrB is therefore functional and accessible, suggesting that conformational change either brings amino acid residues into proper alignment for catalysis and/or enables response to effector DNA.

Selection of monoclonal antibodies for probing of functional intermediates in incision of UV-irradiated DNA by Uvr(A)BC endonuclease from Escherichia coli

Monoclonal antibodies (mAbs) were generated that recognize UvrA and UvrB proteins. These proteins are components of the Uvr(A)BC endonuclease, which initiates nucleotide excision repair in Escherichia coli. mAbs, which can be used for probing of structural intermediates of Uvr(A)BC endonuclease functioning, were selected for their ability to: (i) recognize different epitopes; (ii) have a high-affinity for native antigenic protein; (iii) preserve functionality of the Uvr protein in immunocomplex. The adherence of anti-Uvr mAbs with these criteria was verified by additivity and competition tests, and by their influence on the ATPase activities of UvrA and UvrB*, the functionally active proteolytic fragment of UvrB. Two out of twelve anti-UvrA and seven out of thirteen anti-UvrB/anti-UvrB* hybridoma lines were shown to satisfy these criteria. Recognition of UvrA and UvrB deletion mutant proteins by mAbs was used to map their epitopes. Epitopes of A2D1 and A2B1 mAbs were mapped to regions of amino acids 230-281 and 560-680 of UvrA, respectively. Epitopes of anti-UvrB/UvrB* mAbs were assigned to the following amino acid regions of UvrB: B2A1, 8-61; B2C5 and B*2E3, 171-278; B2E2, 631-673; B3C1, 1-7 and/or 62-170; B*2B9, 473-630; B*3E11, 379-472. The ability of selected mAbs to neutralize the incision function of Uvr(A)BC was analyzed. The results are discussed in terms of the applicability of these mAbs to probe the structures of intermediates in the functioning of Uvr(A)BC.

Transcription coupled nucleotide excision repair by isolated Escherichia coli membrane-associated nucleoids

One form of nucleotide excision repair (NER) is known to be functionally coupled to transcription, but the nature of this functional link in Escherichia coli is still unclear. Here we have employed the isolated membrane-associated nucleoids from E.coli to examine this issue. We show that the isolated nucleoid fraction is capable of excision of UV-induced pyrimidine dimers when reconstituted with a cytoplasmic fraction resolved by sucrose gradient fractionation. This excision activity by UvrABC is sensitive to rifampicin and is dependent on transcription. By using crosslinking and immunoprecipitation, the damage recognition protein, UvrA, was found to be specifically associated with the RNA polymerase beta subunit on the chromosomal DNA independent of DNA damage. It suggests that at least in one of the NER pathways the search for damage may be directly linked to RNA polymerase. In addition, the role of transcription in the unfolding of the nucleoid structure to allow repair enzymes to gain access to the damaged DNA is described. This study provides insight into the understanding of the transcription-repair coupling in vivo.

DNA damage-dependent recruitment of nucleotide excision repair and transcription proteins to Escherichia coli inner membranes

The entire process of nucleotide excision repair (NER) in Escherichia coli has been reconstituted in vitro from purified proteins and defined DNA substrates. However, how this system is organized in vivo in unclear. We report here the isolation and characterization of macromolecular assemblies containing NER and transcription proteins from E. coli. This ensemble consists of at least 17 proteins. They are recruited, as a consequence of DNA damage induced by UV irradiation, to the inner membrane. The UV-induced 6-4 photoproducts are also relocated to the inner membrane following UV-irradiation of the cells. This recruitment process is dependent on the uvrA, uvrC and recA gene products. These results suggest that at least part of the repair process may associate with the inner membrane and also provide insights into understanding the cellular organization of repair processes.

Epidemiology of ultraviolet-DNA repair capacity and human cancer

The following conclusions are derived from an epidemiological study. Reduced repair of ultraviolet (UV)-induced DNA damage contributes directly to basal cell carcinoma (BCC) in individuals with prior sunlight overexposure. A family history of BCC is a predictor of low DNA repair. Repair of UV-damaged DNA declines at a fixed rate of approximately 1% per annum in noncancerous controls. The DNA repair differences between young BCC cases and their controls disappear as they age. Hence, BCC, in terms of DNA repair, is a premature aging disease. The persistence of photochemical damage because of reduced repair results in point mutations in the p53 gene and allelic loss of the nevoid BCC gene (Gorlin's syndrome) located on chromosome 9q. The fact that environmental vulnerability is gender oriented implicates hormones in regulating DNA repair. Xeroderma pigmentosum appears to be a valid paradigm for the role of DNA repair in BCC in the general population.

The topodynamics of incision of UV-irradiated covalently closed DNA by the Escherichia coli Uvr(A)BC endonuclease

The Escherichia coli Uvr(A)BC endonuclease (Uvr(A)BC) initiates nucleotide excision repair of a large variety of DNA damages. The damage recognition and incision steps by the Uvr(A)BC is a complex process utilizing an ATP-dependent DNA helix-tracking activity associated with the UvrA2B1 complex. The latter activity leads to the generation of highly positively supercoiled DNA in the presence of E. coli topoisomerase I in vitro. Such highly positively supercoiled DNA, containing ultraviolet irradiation-induced photoproducts (uvDNA), is resistant to the incision by Uvr(A)BC, whereas the negatively supercoiled and relaxed forms of the uvDNA are effectively incised. The E. coli gyrase can contribute to the above reaction by abolishing the accumulation of highly positively supercoiled uvDNA thereby restoring Uvr(A)BC-catalyzed incision. Eukaryotic (calf thymus) topoisomerase I is able to substitute for gyrase in restoring this Uvr(A)BC-mediated incision reaction. The inability of Uvr(A)BC to incise highly positively supercoiled uvDNA results from the failure of the formation of UvrAB-dependent obligatory intermediates associated with the DNA conformational change. In contrast to Uvr(A)BC, the Micrococcus luteus UV endonuclease efficiently incises uvDNA regardless of its topological state. The in vitro topodynamic system proposed in this study may provide a simple model for studying a topological aspect of nucleotide excision repair and its interaction with other DNA topology-related processes in E. coli.

The effect of donor age on the processing of UV-damaged DNA by cultured human cells: reduced DNA repair capacity and increased DNA mutability

Aging in humans carries an increased risk of skin cancer, a disorder linked to somatic mutations in sun damaged skin. DNA repair plays a major role in protection against sun damage. We found an age-related decline in post-UV DNA repair capacity (measured by the ability to repair a UV-treated plasmid (pCMVcat)) of-0.6% per year (p = 0.0001) in cultured primary skin fibroblasts from normal donors from the first to the tenth decade of life. There was a corresponding age-related increase in post-UV mutability (measured as mutations introduced into a transfected, UV-treated plasmid (pSP189)) of +0.6% per year (p = 0.001) in lymphoblastoid cell lines from normal donors of the same age range. This study indicates that aging in humans is associated with decreasing ability to process new UV-induced DNA damage and this age-related reduction in DNA repair capacity and increase in DNA mutability is reflected in cultured skin and blood cells.

The analyst's influence

Analytic work involves a variety of influences the analyst brings to bear on the patient. Our emphasis on the centrality of interpretation tends to neglect consideration of the many ways in which the analyst influences the patient other than by the content of interpretation. The author considers the kinds of influence necessary to establish and maintain an analytic process and a therapeutic alliance. The nature and the role of the analyst's authority are discussed, along with the issue of how the analyst influences the patient to question the analyst's authority.

RNA polymerase signals UvrAB landing sites

Transcription when coupled to nucleotide excision repair specifies the location in active genes where preferential DNA repair is to take place. During DNA damage-induced recruitment of RNA polymerase (RNAP), there is a physical association of the beta subunit of Escherichia coli RNAP and the UvrA component of the repair apparatus (G. C. Lin and L. Grossman, submitted for publication). This molecular affinity is reflected in the ability of the RNAP to increase, in a promoter-dependent manner, DNA supercoiling by the UvrAB complex. In the presence of the RNAP, the UvrAB complex is able to bind to promoter regions and to translocate in a 5' to 3' direction along the non-transcribed strand. As a consequence of this helicase-catalyzed translocation, preferential incision of DNA damaged sites occurs downstream on the transcribed strand. Because of the helicase directionality, the initial binding of the UvrAB complex to the transcribed strand would inevitably lead to its collision with the RNAP. These results imply that the RNAP-induced DNA structure in the vicinity of the transcription start site signals a landing or entry site for the UvrAB complex on DNA.

The binding of UvrAB proteins to bubble and loop regions in duplex DNA

Based on the binding of the UvrAB complex to a promoter region in transcription open complexes (Ahn, B., and Grossman, L. (1996) J. Biol. Chem. 271, 21453-21461) and the requirement of a single-stranded region for UvrAB helicase activity, we examined the binding of UvrAB proteins to synthetic bubble or loop regions in duplex DNA and the role of these regions in translocation of the UvrAB complex as well as incision of DNA damage. We found that the UvrAB complex was able to bind to bubble and loop regions with an affinity similar to that for damaged DNA in the absence of RNAP. The preferential recognition and incision of damaged sites by the UvrAB complex was observed downstream of the bubble or loop region in the strand complementary to the strand along which the UvrAB complex translocates. These results imply that the bubble region generated in duplex DNA by RNAP serves as a preferred entry site for the translocation of the UvrAB complex, and that preferential binding and unidirectional translocation of the UvrAB complex predetermine where incision is to occur.

'Psychic reality' and reality testing in the analysis of perverse defences

The author considers that a large group of clinical phenomena, of which perversion is the most dramatic example, is characterised by the effort to disavow troubling perceptions of reality. In these cases, patients are sometimes characterised--erroneously, in his view-as living in a different 'psychic reality'. He suggests that patients who use perverse defences are able to distinguish fantasy from reality, but they are motivated to refrain from testing cherished fantasies against their own view of reality. Such patients are difficult to work with, because they dismiss painful realities in treatment as readily as any other unwanted perceptions. The author suggests that treatment must focus on the various disavowals of the patient's own perceptions of reality, to the extent that the analyst must be prepared to be a spokesperson for reality. Treatment in which the patient's 'psychic reality' is viewed as a 'kind' of reality rather than addressed as a fantasy can thus collude with perverse defences.

Measurement of DNA repair deficiency in workers exposed to benzene

We hypothesize that chronic exposure to environmental toxicants can induce genetic damage causing DNA repair deficiencies and leading to the postulated mutator phenotype of carcinogenesis. To test our hypothesis, a host cell reactivation (HCR) assay was used in which pCMVcat plasmids were damaged with UV light (175, 350 J/m2 UV light), inactivating the chloramphenicol acetyltransferase reporter gene, and then transfected into lymphocytes. Transfected lymphocytes were therefore challenged to repair the damaged plasmids, reactivating the reporter gene. Xeroderma pigmentosum (XP) and Gaucher cell lines were used as positive and negative controls for the HCR assay. The Gaucher cell line repaired normally but XP cell lines demonstrated lower repair activity. Additionally, the repair activity of the XP heterozygous cell line showed intermediate repair compared to the homozygous XP and Gaucher cells. We used HCR to measure the effects of benzene exposure on 12 exposed and 8 nonexposed workers from a local benzene plant. Plasmids 175 J/m2 and 350 J/m2 were repaired with a mean frequency of 66% and 58%, respectively, in control workers compared to 71% and 62% in exposed workers. Conversely, more of the exposed workers were grouped into the reduced repair category than controls. These differences in repair capacity between exposed and control workers were, however, not statistically significant. The lack of significant differences between the exposed and control groups may be due to extremely low exposure to benzene (< 0.3 ppm), small population size, or a lack of benzene genotoxicity at these concentrations. These results are consistent with a parallel hprt gene mutation assay.

The effect of epigastric vessel ligation on the vascular territories of the pig rectus muscle

In a pig model, unilateral ligation of the inferior epigastric vessels caused an initial decrease in normal vascularity, followed by an increase toward normal vascularity, in the inferior portion of the rectus muscle over 42 days. Ligation appeared to dilate the choke vessels between the superior and inferior arterial territories. The results indicate that by ligation of the inferior epigastric vessels, the vascular territory, which is normally tenuous, can undergo a transposition without vascular compromise.

DNA repair and epidemiology of basal cell carcinoma

In a molecular epidemiological study of DNA repair, host reactivation assay was used to measure the DNA repair capacity of cryopreserved lymphocytes from 88 primary basal cell carcinoma (BCC) patients and 135 cancer-free controls. In this study population, reduced repair of ultraviolet radiation-induced DNA damage contributed to the risk of sunlight-induced BCC. A family history of BCC is associated with low DNA repair. Repair of ultraviolet radiation-damaged DNA declines at a rate of approximately 1%/year in noncancerous controls. Reduced DNA repair is more likely seen in young BCC patients, indicating that BCC is a premature aging disease of the skin. The persistence of photochemical damage because of reduced repair results in point mutations in the p53 gene and allelic loss of the nevoid BCC gene located on chromosome 9q. Xeroderma pigmentosum appears to be a valid paradigm for the role of DNA repair in BCC in the general population.

DNA repair and epidemiology of basal cell carcinoma

In a molecular epidemiological study of DNA repair, host reactivation assay was used to measure the DNA repair capacity of cryopreserved lymphocytes from 88 primary basal cell carcinoma (BCC) patients and 135 cancer-free controls. In this study population, reduced repair of ultraviolet radiation-induced DNA damage contributed to the risk of sunlight-induced BCC. A family history of BCC is associated with low DNA repair. Repair of ultraviolet radiation-damaged DNA declines at a rate of approximately 1%/year in noncancerous controls. Reduced DNA repair is more likely seen in young BCC patients, indicating that BCC is a premature aging disease of the skin. The persistence of photochemical damage because of reduced repair results in point mutations in the p53 gene and allelic loss of the nevoid BCC gene located on chromosome 9q. Xeroderma pigmentosum appears to be a valid paradigm for the role of DNA repair in BCC in the general population.

DNA repair capacity for ultraviolet light-induced damage is reduced in peripheral lymphocytes from patients with basal cell carcinoma

Sunlight exposure and certain host factors such as red hair and fair skin are established risk factors for non-melanoma skin cancers. Because deficient DNA repair capacity has contributed to the development of skin cancers in a rare genetic disease, xeroderma pigmentosum, we explored this deficiency as an etiologic factor in a recent population study. We used a new DNA repair assay, the host-cell reactivation, in a clinic-based case-control study to test the hypothesis that reduced DNA repair is the underlying molecular mechanism for the development of sunlight-induced basal cell carcinoma. The peripheral lymphocytes from 88 patients with primary BCC and 135 cancer-free controls were tested for their capacity to repair ultraviolet light-induced DNA damage in a reporter gene, chloramphenicol acetyl transferase. All subjects were between the ages of 20 and 60 years and were frequency matched by age (+/- 5) and sex. Among those who reported frequent sunbathing, poor tanning ability, a history of multiple sunburns, exposure to chemicals, or multiple medical irradiations, the BCC patients had significantly lower DNA repair capacity than controls (p < 0.05). DNA repair capacity was also found substantially lower in the basal cell carcinoma patients who had red hair and light skin (type I). Compared to controls, basal cell carcinoma cases with selected risk factors had a relative decrease in DNA repair capacity of 10-28%. These findings provided evidence that reduced DNA repair capacity is one of the underlying molecular mechanisms for sunlight-induced skin carcinogenesis in the general population.

The use of monoclonal antibodies for studying intermediates in DNA repair by the Escherichia coli Uvr(A)BC endonuclease

The Escherichia coli Uvr(A)BC endonuclease acts in a progression of several distinct steps accompanied by changes in the conformation of macromolecular constituents, the overall architecture of the complex, and its stoichiometry. In order to probe these structural changes, we generated monoclonal antibodies (mAbs) to Uvr proteins. The anti-UvrA mAb, A2D1, recognizing the N-terminal zinc-finger region of UvrA, and the anti-UvrB mAb, B2E2, having an epitope within the 43 C-terminal amino acids of UvrB, were purified and further characterized. It was found that A2D1 mAb interacts in solution both with UvrA-UvrB and UvrA-DNA complexes in the presence of the requisite ATP. This implies that the N-terminal zinc-finger of UvrA doesn't play a direct role in its interactions with UvrB and DNA. On the other hand, A2D1 does inhibit formation of the UvrB-damaged DNA preincision complex, apparently by preventing UvrB delivery by UvrA. The interaction of B2E2 with UvrA-UvrB and nucleoprotein complexes, including UvrB, suggests that the highly hydrophobic C-terminal domain of UvrB (i) doesn't participate in its interaction with UvrA, (ii) is accessible to this mAb in an intermediate UvrA-UvrB DNA helix-tracking complex, and (iii) seems to be directly involved in the formation of the preincision complex. These conclusions are supported by the finding that the neutralizing effect of A2D1 and B2E2 on the Uvr(A)BC endonuclease is significantly decreased if the preincision complex is preformed prior to mAbs addition.

DNA repair and susceptibility to basal cell carcinoma: a case-control study

This study investigated the role of DNA repair in susceptibility to sunlight-induced basal cell carcinoma using a host cell reactivation assay in peripheral lymphocytes. The study included Maryland basal cell carcinoma patients and cancer-free dermatologic controls who had had noncancerous skin disorders diagnosed between 1987 and 1990. Logistic regression models were used to assess the independent effect of the selected variables stratified by DNA repair level, with adjustment for age and family history. Skin type, lifetime number of severe sunburns, and actinic elastosis were also selected as risk factors for basal cell carcinoma. Cryopreserved lymphocytes from 88 cases and 135 controls were used for the DNA repair assay. When data were stratified by DNA repair level and adjusted for age and family history of skin cancer, significantly increased odds ratios associated with lighter skin (odds ratio (OR) = 3.2, 95% confidence interval (CI) 1.5-7.3), six or more severe sunburns in a lifetime (OR = 4.2, 95% CI 1.6-10.7), and moderate or severe actinic elastosis (OR = 4.4, 95% CI 1.5-12.8) were observed in persons with low DNA repair but not in those with high DNA repair. These findings suggest that impaired DNA repair may be a susceptibility factor for sunlight-induced skin cancer in the general public, as it is in patients with xeroderma pigmentosum.

Vitamin supplementation and reduced risk of basal cell carcinoma

A clinic-based case-control study was conducted to determine the association between vitamin supplement use and risk of basal cell carcinoma (BCC) of the skin. The subjects were 131 patients with histopathologically confirmed primary BCC and 200 cancer-free controls with non-premalignant skin disorders. Use of any vitamins (mainly multivitamins and vitamins A, C, and E) was associated with reduced risk of BCC. After controlling for age, sex, cigarette smoking, number of lifetime severe sunburns, and skin actinic elastosis, regular vitamin supplementation was associated with a significantly reduced risk of BCC (odds ratio (OR) = 0.3; 95% confidence interval (CI) = 0.2-0.06). The ORs decreased as the regularity (p < 0.001) and daily doses of supplement used increased, especially for vitamins A (p < 0.005) and E (p < 0.005). Vitamin supplementation was not associated with alterations in cellular DNA repair. These results, however, cannot be considered conclusive because of the relatively low participation rates (131/830 for cases and 200/1406 for controls) due to the requirement of blood donation and more rigorous studies are needed to clarify the effect of supplemental vitamins, particularly of vitamins A and E, on the risk of BCC of the skin.