Diagnostic efficacy of three-dimensional images by helical CT for lesions in the maxillofacial region

The purpose of this study was to evaluate the efficacy of three-dimensional (3-D) images produced with a helical CT for the diagnosis of lesions occurring in the maxillofacial region. Thirty-four patients, who had lesions in the maxillofacial region, were examined by plain radiography (intra and extraoral) and the helical CT. Further, 3-D images were reconstructed from the data provided by the helical CT using the volume rendering method. These images were compared with plain radiographic images and conventional two-dimensional (2-D) CT images in terms of the information they provided for diagnosis. Using the 3-D images for tumors, bone destruction, inner components, extent of the lesion,the relationship between the lesion and surrounding anatomical landmarks, and the roots of the adjacent teeth were observed in overall views. We conclude that 3-D images produced by helical CT may provide useful information for the diagnosis of lesions.

Expression of mitochondrial thioredoxin-dependent antioxidant protein, SP-22, in normal human and inflammatory mouse placentae

The aim of this study was to elucidate whether a novel mitochondrial antioxidant protein, SP-22, is localized in placenta and whether its expression is induced in placenta of lipopolysaccharide (LPS)-exposed mouse. Western blot analysis of normal human placenta indicated that the SP-22 protein was located in the mitochondrial fraction. Immunohistochemical analysis of SP-22 in normal placenta showed that immunoreactive SP-22 was distributed mostly in cytotrophoblastic cells but with almost no signal in syncytiotrophoblasts. The positive signals were also detected in the decidual cells and stromal cells in stem villi of normal placenta. We also examined LPS-mediated inflammatory placenta on day 13 of pregnancy at various time points after LPS injection (50 microg/kg, intraperitoneally). Western blot analysis indicated that LPS approximately quadrupled the expression of SP-22 in placenta of LPS-exposed mouse. When the SP-22 protein was localized immunohistochemically, the decidua and the diploid trophoblasts in the basal zone were intensively stained in placenta of LPS-exposed mouse compared to the control. The localization and inducible expression of SP-22 protein in placenta suggest a possible role in antioxidant system in mitochondria of normal and inflammatory placentae.

Novel control system for blood glucose using a model predictive method

We developed a novel blood glucose control system, using a model predictive method, to achieve optimal control of the blood glucose level in severely diabetic or pancreatectomized patients. This system is designed to predict glucose level changes in advance, considering delayed response time and the administered doses of insulin. This method is also designed to calculate the most appropriate insulin infusion rate by considering differences in individual response to insulin. In this study, we compared our system with a conventional proportional and differential controller (PD controller) to determine whether the new system could regulate the glucose level efficiently in pancreatectomized dogs. The model predictive control method resulted in a significant reduction of mean insulin infusion rate compared with the conventional PD controller (0.71 mU/kg per min vs. 1.81 mU/kg per min, p = 0.0005), when the glucose level in both methods reached the planned target level (100 mg/dl). The new system also tended to have a reduced mean glucose infusion rate for compensating for overshooting of the glucose level compared with the PD controller (0.7 mg/kg per min vs. 1.1 mg/kg per min, p = 0.16). These results indicate that the new system should be a useful tool for regulating the glucose level in severely diabetic patients.

Endothelin-1 as a protective factor against beta-adrenergic agonist-induced apoptosis in cardiac myocytes

OBJECTIVES

The purpose of this study was to investigate the regulation of beta-adrenergic agonist-induced apoptosis by endothelin-1 (ET-1) in cardiac myocytes.

BACKGROUND

Numerous hormonal factors including norepinephrine and ET-1 are activated in patients with heart failure. These factors may be involved in the positive and negative regulation of myocardial cell apoptosis observed in failing hearts. Recently, it has been shown that norepinephrine can induce myocardial cell apoptosis via a beta-adrenergic receptor-dependent pathway.

METHODS

Primary cardiac myocytes were prepared from neonatal rats. These cells were stimulated with the beta-adrenergic agonist isoproterenol (ISO) in the presence or absence of ET-1.

RESULTS

The administration of 10(-7) mol/liter of ET-1 completely blocked Iso-induced apoptosis. An endothelin type A receptor antagonist, FR139317, negated the inhibitory effect of ET-1 on apoptosis, while the endothelin type B receptor antagonist BQ788 did not show such a negation. Endothelin-1 also inhibited apoptosis induced by a membrane-permeable cAMP analogue (8-Br-cAMP), which bypassed Gi. The effect of ET-1 was neutralized by an MEK-1-specific inhibitor (PD098059), a phosphatidylinositol 3'-kinase inhibitor (wortmannin) and its downstream pp70 S6-kinase inhibitor, rapamycin.

CONCLUSIONS

These findings suggest that ET-1 represents a protective factor against myocardial cell apoptosis in heart failure and that this effect is mediated mainly through endothelin type A receptor-dependent pathways involving multiple downstream signalings in cardiac myocytes.

Spiny keratoderma of the palms and soles - report of two cases

We report two patients with spiny keratoderma of the palms and soles characterized by multiple tiny keratotic plugs on the palms and soles. This disease was reported to be possibly associated with internal malignancies. We found a tumor from the esophagus to cardia in one patient. Another had no tumor but the lesion occurred soon after a severe bronchial asthma attack. Causal relation between spiny keratoderma of the palms and soles and bronchial asthma is obscure. Since this disease has been under-diagnosed and under-reported, it is important for dermatologists to keep spiny keratoderma of the palms and soles in mind in daily clinical examinations.

Characteristics of Nonafluorobutyl Methyl Ether (NFE) Adsorption onto Activated Carbon Fibers and Different-Size-Activated Carbon Particles

The characteristics of adsorption of 1,1,1,2,2,3,3,4,4-nonafluorobutyl methyl ether (NFE), a chlorofluorocarbon (CFC) replacement, onto six different activated carbon; preparations (three activated carbon fibers and three different-sized activated carbon particles) were investigated to evaluate the interaction between activated carbon surfaces and NFE. The amount of NFE adsorbed onto the three activated carbon fibers increased with increasing specific surface area and pore volume. The amount of NFE adsorbed onto the three different-sized-activated carbon particles increased with an increase in the particle diameter of the granular activated carbon. The differential heat of the NFE adsorption onto three activated carbon fibers depended on the porosity structure of the activated carbon fibers. The adsorption rate of NFE was also investigated in order to evaluate the efficiency of NFE recovery by the activated carbon surface. The Sameshima equation was used to obtain the isotherms of NFE adsorption onto the activated carbon fibers and different-sized-activated carbon particles. The rate constant k for NFE adsorption onto activated carbon fibers was larger for increased specific surface area and pore volume. The rate of NFE adsorption on activated carbons of three different particle sizes decreased with increasing particle diameter at a low initial pressure. The adsorption isotherms of NFE for the six activated carbons conformed to the Dubinin-Radushkevich equation; the constants BE(0) (the affinity between adsorbate and adsorbent) and W(0) (the adsorption capacity) were calculated. These results indicated that the interaction between the activated carbon and NFE was larger with the smaller specific surface area of the activated carbon fibers and with the smaller particle diameter of the different-sized-activated carbon particles. The degree of packing of NFE in the pores of the activated carbon fibers was greater than that in the pores of the granular activated carbons. Copyright 2000 Academic Press.

An expanded histatin gene polymorphism and test of a possible disease resistant phenotype

Histatins are small molecular weight salivary proteins that are important in the non-immune host defense system. Two frequent cis-linked coding-change mutations were previously described in exon 5 of the HIS2 gene of Blacks. The polymorphic mutant allele was termed HIS2(2) and the wild-type allele HIS2(1). We here describe two new non-coding change polymorphisms of the HIS2 gene: a deletion in intron 5 (7183-7198 del) and a C-->T mutation in exon 5 [C-->T (7104)] that characterize two new HIS2 alleles, HIS2(3) and HIS2(4) respectively. Both mutations occur on a HIS2(1) background. The HIS2(3) allele occurred only in Afro-Americans, but not in 67 Japanese, 51 Chinese and 50 Whites. Among 66 random DNA samples from Afro-Americans, frequencies of HIS2(1), HIS2(2), HIS2(3) and HIS2(4) were 0.67, 0.22, 0.05 and 0.07 respectively, with a heterozygosity of 0.45. The frequencies of the HIS2(4) allele in 50 Whites and 50 Chinese were 0.06, and 0.1 respectively. In a comparison of 60 matched saliva and DNA samples from the Afro-American population, the DNA-based mutation analysis reliably identified salivary histatin phenotypes. The salivary histatin polymorphism (inferred from PCR analysis) was used to test a biologically plausible hypothesis, that the mutant histatin phenotype (coded by the HIS2(2) allele) confers relative resistance to severe and fatal malaria. In a study of 185 Black Tanzanian subjects, there were no significant differences in HIS2(2) allelic frequencies between the various test groups: for 86 cerebral malaria subjects, 54 uncomplicated malaria subjects, and 45 combined asymptomatic parasitemia and health controls, HIS2(2) frequencies were 0.16, 0.17 and 0.17 respectively. Thus, there was no support for the hypothesis in this population.

Human villous macrophage-conditioned media enhance human trophoblast growth and differentiation in vitro

In human chorionic villi, numerous macrophages, so-called Hofbauer cells, are located adjacent to trophoblasts. To determine the role of the macrophages in the proliferation and differentiation of trophoblasts, cytotrophoblast cells were cultured in serum-free culture-conditioned media of villous macrophages (VMCM), peritoneal macrophages (PMCM), and villous fibroblasts (VFCM). In VMCM, proliferation of cytotrophoblast cells was detected at 24 h by immunocytochemistry with Ki-67-antibody. A large number (P < 0.001) of multinucleated syncytia was formed in VMCM. In VMCM, cytotrophoblast cell fusion was completed by 96 h, which coincided with the peak of hCG secretion and initiation of human placental lactogen (hPL) release. Levels of hCG (P < 0.001) and hPL (P < 0. 001) secretion from syncytial cells were significantly higher in VMCM than in PMCM or in VFCM. Concentrations of macrophage colony-stimulating factor (M-CSF) and vascular endothelial growth factor (VEGF) analyzed by ELISA were greater in VMCM than in PMCM or in VFCM, whereas monocyte chemoattractant protein-1 (MCP-1) concentration was high in PMCM. The expression patterns of M-CSF, VEGF, and MCP-1 in villous macrophages and peritoneal macrophages by reverse transcriptase-polymerase chain reaction were similar to their secretion patterns. Thus, villous macrophages have a greater ability to stimulate hCG and hPL secretion than do peritoneal macrophages. This study suggests that macrophages within the villous stroma may stimulate the growth and differentiation of trophoblasts through their secreted substances.

The effect of the atrioventricular interval during atrioventricular sequential pacing on the hemodynamics in dynamic obstruction of the left ventricular outflow tract in dogs

The present study was performed to clarify the mechanism involved in the reduction of the pressure gradient in the left ventricular outflow tract of patients with hypertrophic obstructive cardiomyopathy when treated with atrioventricular (AV) sequential pacing. The effect of AV sequential pacing with variable AV intervals on the hemodynamics and dyssynchronous wall motion was experimentally studied using echocardiography in the dynamic obstruction of the left ventricular outflow tract created by dobutamine infusion in 17 dogs. The pressure gradient of the left ventricular outflow tract decreased with shortening of the AV interval during AV sequential pacing. Also, the dyssynchrony time, defined as the difference in the time between the intraventricular septum and posterior wall during the systolic phase recorded with M-mode echocardiography, increased with shortening of the AV interval during AV sequential pacing. However, very short AV intervals produced a significant decrease in the aortic pressure and increase in the pulmonary capillary wedge pressure. The dyssynchrony time showed a positive liner correlation with the percentage reduction in the pressure gradient of the left ventricular outflow tract (R=0.794, p<0.0001). It was concluded that dyssynchronous wall motion in the left ventricle was produced by pacing from the right ventricular apex and resulted in a reduction in the pressure gradient of the left ventricular outflow tract. Optimization of the AV interval during AV sequential pacing may play an important role in improving the hemodynamics in dynamic obstruction of the left ventricular outflow tract.

Reconstitution of damage DNA excision reaction from SV40 minichromosomes with purified nucleotide excision repair proteins

We previously constructed the cell-free nucleotide excision repair (NER) assay system with UV-irradiated SV40 minichromosomes to analyze the mechanism of NER reaction on chromatin DNA. Here we investigate the factor that acts especially on nucleosomal DNA during the damage excision reaction, and reconstitute the damage excision reaction on SV40 minichromosomes. NER-proficient HeLa whole cell extracts were fractionated, and the amounts of known NER factors involved in the column fractions were determined by immunoblot analyses. The column fractions were quantitatively and systematically replaced by highly purified NER factors. Finally, damage DNA excision reaction on SV40 minichromosomes was reconstituted with six highly purified NER factors, XPA, XPC-HR23B, XPF-ERCC1, XPG, RPA and TFIIH, as those essential for the reaction with naked DNA. Further analysis showed that the damages on chromosomal DNA were excised as the same efficiency as those on naked DNA for short incubation. At longer incubation time, however, the damage excision efficiency on nucleosomal DNA was decreased whereas naked DNA was still vigorously repaired. These observations suggest that although the six purified NER factors have a potential to eliminate the damage DNA from SV40 minichromosomes, the chromatin structure may still have some repressive effects on NER.

Nitric oxide inhibition improved myocardial metabolism independent of tissue perfusion during ischemia but not during reperfusion

Nitric oxide (NO) is one of the important regulators of cardiac metabolism and function as well as of tissue perfusion. Myocardial NO formation is increased during ischemia and reperfusion. We investigated the roles of endogenous NO in myocardial metabolism during ischemia and reperfusion independent of tissue perfusion changes. In an open-chest pig model, a bolus infusion of 20 mg/kg of N(G)-nitro l -arginine methyl ester (l -NAME), a NO synthase inhibitor, did not alter the regional myocardial perfusion compared with a control saline injection, as measured by colored microsphares. Using(31)P-nuclear magnetic resonance spectroscopy, we showed that the tissue levels of pH and adenosine triphosphate (ATP) but not those of creatine phosphate were significantly preserved in the l -NAME group compared with the placebo group during the subsequent 15-min regional ischemia. Thus, l -NAME reduced myocardial ATP utilization during ischemia, and the mechanism underlying these effects is independent of tissue perfusion changes. However, l -NAME did not accelerate the recovery of ATP levels following reperfusion, suggesting distinct roles of endogenous NO during reperfusion.

Role of E-selectin in bleomycin induced lung fibrosis in mice

BACKGROUND

Bleomycin (BLM), a well known anti-cancer drug, often causes acute lung injury and fibrosis by mechanisms that are not well understood. It is suspected that some proteases and active oxygen species generated from inflammatory cells cause the lung injury and subsequent lung fibrosis. It was therefore hypothesised that inhibition of adhesion of inflammatory cells to the endothelium might prevent these developments.

METHODS

BLM (100 mg/kg) was injected into the tail veins of ICR mice to evaluate the induction of E-selectin, an adhesion molecule known to induce neutrophil attachment on endothelial cells. E-selectin mRNA induction was detected by reverse transcriptase polymerase chain reaction (RT-PCR). The myeloperoxidase (MPO) activities in the lung tissues of BLM treated and control mice were compared to evaluate neutrophil infiltration. Pathological changes in the lungs of soluble E-selectin transgenic mice (TG) and their TG negative (non-TG) littermates after BLM treatment were also compared. Serum samples of TG mice and non-TG mice were tested for their ability to block the binding of sialyl Lewis(x) to recombinant E-selectin in vitro.

RESULTS

E-selectin mRNA was maximally induced at six hours after BLM treatment in the ICR mice. The soluble form of E-selectin which can competitively inhibit the binding of sialylated antigens on inflammatory cells to E- and P-selectins on the endothelium was detected in the serum of TG mice. BLM induced lung fibrosis occurred in non-TG mice but not in TG mice. This result confirms the finding that the serum of TG mice inhibits the binding of sialyl Lewis(x) to E-selectin in vitro.

CONCLUSION

E-selectin plays an essential role in BLM induced lung fibrosis through the induction of neutrophil and other inflammatory cell accumulation, and soluble E-selectin may be of use in the prophylactic treatment of lung fibrosis.

The molar vesicle fluid contains the beta-core fragment of human chorionic gonadotropin

The human chorionic gonadotropin (hCG) beta-core fragment (beta-CF) is a major molecular form of hCG beta subunit (hCGbeta) immunoreactivity in the urine of pregnant women and patients with trophoblastic disease. The majority of evidence supports the fact that the beta-CF is a degradative product of intact hCG and free hCGbeta in the kidneys. We found a beta-CF-like substance in the fluid of molar vesicles from a patient with complete hydatidiform mole. The molar fluid beta-CF (mbeta-CF) was indistinguishable from the beta-CF in the patient's urine (ubeta-CF) by immunoreactivity and by elution profile on gel chromatography. The binding study to lectins, however, showed that mbeta-CF contains a carbohydrate moiety that differs from that of ubeta-CF. Immunohistochemistry with anti-beta-CF antibody demonstrated a strong immunoreactivity in a large number of macrophages in the molar villous stroma. In vitro incubation of intact hCG with peritoneal macrophages showed a slow increase of intact hCG in the cell cytosol with the appearance of beta-CF-like substance in the cell supernatant. In conclusion, the source of beta-CF in molar fluid is likely to be macrophages existing in the villous stroma. Thus macrophages may ingest intact hCG and act as a local regulator of gonadotropic hormones.

Mutant mice lacking Crk-II caused by the gene trap insertional mutagenesis: Crk-II is not essential for embryonic development

Crk family adapter proteins including Crk-II, Crk-I, and Crk-L consist mostly of SH2 and SH3 domains. Through the interactions between SH2 domain and phosphotyrosine residues and/or between SH3 domain and proline-rich motifs, they are involved in a variety of signaling cascades. Despite their essential roles in the signal transductions, knock-out mice of these molecules have not been reported yet. We performed the gene trap insertional mutagenesis with a trap vector, pU-Hachi, and generated a mutant mice line, Ayu 8104, in which the trap vector was inserted into the c-crk gene. Homozygous Ayu 8104 mice lacked Crk-II and Crk-I transcripts but expressed the truncated Crk proteins retaining one SH2 and one SH3 domain. Since the structure of the truncated proteins was similar to that of Crk-I, the insertion was considered to cause Crk-II-specific disruption. Homozygous mutant mice, however, did not exhibit any obvious abnormalities, suggesting that Crk-family adapters, Crk-II, Crk-I, and Crk-L would redundantly function in the signaling cascades and Crk-II was not apparently essential for embryonic development.

Clinical application of a blood pressure autoregulation system during hypotensive anesthesia

A blood pressure autoregulation system based on the state-predictive control method was developed to minimize intraoperative blood loss and hence avoid blood transfusion. In this report, the system is further improved by incorporating fuzzy logic with a fail-safe function and an individual parameter-identifying function. The safety and stability of this system had been confirmed by preclinical experiments with dogs. Thereafter clinical application with 17 patients was conducted to maintain their mean arterial pressure at around 60 mmHg during major surgery. The use of this system resulted in decreased blood loss and more speedy and accurate surgery due to a clearer surgical field. Unwanted effects of hypotension were not observed clinically or in laboratory tests. This system is therefore safe, stable, and effective in reducing the blood loss during major surgery that otherwise might cause substantial blood loss.

Activation pattern of Langerhans cells in the afferent and efferent phases of contact hypersensitivity

Langerhans cells are MHC class II (Ia) positive antigen-presenting cells that play a crucial role in the induction of contact hypersensitivity (CHS). The topical application of a hapten modifies the cell surface moieties of Langerhans cells, and activates Langerhans cells to increase their size and Ia intensity. The haptenated and activated Langerhans cells emigrate from the epidermis and thus the in situ density of Langerhans cells usually decreases during 24-48 h after the hapten application in CHS. To determine whether the early activation pattern of Langerhans cells is different between the afferent phase and the efferent phase of CHS, we compared the density and morphologic changes of Langerhans cells in CHS to trinitrochlorobenzene using nonsensitized and sensitized mice. We found that the application of a hapten induces more significant enlargement of Langerhans cell size in the afferent phase than in the efferent phase, whereas the reduction of Langerhans cell density is more marked in the efferent than in the afferent phase of CHS. Moreover, topical immunosuppressive drugs inhibit the in situ activation of Langerhans cells.

[The detection of apoptosis cells by TUNEL stain in peripheral blood smears]

We have determined the fixative conditions for TUNEL stain in peripheral blood smears. Murine IL-3 dependent B cell line (BAF-3) was used as positive control. The intensity of fixing solutions effected on the positivity/negativity for TUNEL stain. Alive cells showed positivity for TUNEL stain (false positive), when 70% methyl alcohol, acetone or carnoy fluid was used. In contrast to the strong fixation by high concentrated glutaraldehyde and the phosphate buffer, denatured cells showed to be negative (false negative). The fixation by 0.4% glutaraldehyde and 70% methyl alcohol for 15 min at room temperature, followed by the treatment by 20 micrograms/ml proteinase K for 15 min at 37 degrees C was most suitable for TUNEL stain to detect the apoptotic cells in peripheral blood smears. The frequency of TUNEL positive cells increased significantly in peripheral blood cells treated by apoptosis induced reagents, or infected by CMV. This is a new approach for the techniques to detect the apoptotic cells in peripheral blood smears.

alpha- and beta-adrenergic pathways differentially regulate cell type-specific apoptosis in rat cardiac myocytes

BACKGROUND

The apoptosis of cardiac myocytes may play a role in the development of heart failure. Norepinephrine is one of the factors activated in heart failure and can induce myocardial cell apoptosis in culture. However, it is unknown if alpha- and beta-adrenergic pathways coordinately or differentially regulate apoptosis and if this apoptotic pathway uses common or cell type-specific apoptotic signals.

METHODS AND RESULTS

We stimulated cultured neonatal rat cardiac myocytes with an alpha(1)-adrenergic agonist (PE, phenylephrine), a beta-adrenergic agonist (isoproterenol [Iso]) or a membrane-permeable cAMP analogue (8-Br-cAMP) in serum-free conditions for 48 hours. Iso and 8-Br-cAMP markedly increased the number of TUNEL-positive cells (%TUNEL-positive nuclei >40%) compared with saline stimulation (<10%). DNA fragmentation was also confirmed by ladder formation in agarose gels. Apoptotic myocytes were characterized by cell shrinkage and nuclear condensation, consistent with morphological features of apoptosis. The Iso-induced apoptosis was almost completely inhibited by the protein kinase A-specific inhibitor KT5720. In contrast, PE inhibited 8-Br-cAMP-induced myocardial cell apoptosis. The apoptosis-inhibitory effect by PE was negated by the alpha(1)-adrenergic receptor antagonist prazosin and the MEK-1-specific inhibitor PD098059. Interestingly, although 8-Br-cAMP markedly induced apoptosis in cardiac myocytes, it completely blocked serum depletion-induced apoptosis in PC12 cells, a rat pheochromocytoma cell line.

CONCLUSIONS

These findings indicate that alpha- and beta-adrenergic pathways differentially regulate myocardial cell apoptosis. The results also suggest that a cAMP- protein kinase A pathway is necessary and sufficient for beta-adrenergic agonist-induced apoptosis and that this apoptotic pathway is not functional in other cell types, for example, PC12 cells.

Exchangeable gene trap using the Cre/mutated lox system

The gene trap technique is a powerful approach for characterizing and mutating genes involved in mouse development. However, one shortcoming of gene trapping is the relative inability to induce subtle mutations. This problem can be overcome by introducing a knock-in system into the gene trap strategy. Here, we have constructed a new gene trap vector, pU-Hachi, employing the Cre-mutated lox system (Araki et al., 1997), in which a pair of mutant lox, lox71 and lox66, was used to promote targeted integrative reaction by Cre recombinase. The pU-Hachi carries splicing acceptor (SA)-lox71-internal ribosomal entry site (IRES)-beta-geo-pA-loxP-pA-pUC. By using this vector, we can carry out random insertional mutagenesis as the first step, and then we can replace the beta-geo gene with any gene of interest through Cre-mediated integration. We have isolated 109 trap clones electroporated with pU-Hachi, and analyzed their integration patterns by Southern blotting to select those carrying a single copy of the trap vector. By use of some of these clones, we have succeeded in exchanging the reporter gene at high efficiency, ranging between 20-80%. This integration system is also quite useful for plasmid rescue to recover flanking genomic sequences, because a plasmid vector sequence can be introduced even when the pUC sequence of the trap vector is lost through integration into the genome. Thus, this method, termed exchangeable gene trapping, has many advantages as the trapped clones can be utilized to express genes with any type of mutation.

The XPV (xeroderma pigmentosum variant) gene encodes human DNA polymerase eta

Xeroderma pigmentosum variant (XP-V) is an inherited disorder which is associated with increased incidence of sunlight-induced skin cancers. Unlike other xeroderma pigmentosum cells (belonging to groups XP-A to XP-G), XP-V cells carry out normal nucleotide-excision repair processes but are defective in their replication of ultraviolet-damaged DNA. It has been suspected for some time that the XPV gene encodes a protein that is involved in trans-lesion DNA synthesis, but the gene product has never been isolated. Using an improved cell-free assay for trans-lesion DNA synthesis, we have recently isolated a DNA polymerase from HeLa cells that continues replication on damaged DNA by bypassing ultraviolet-induced thymine dimers in XP-V cell extracts. Here we show that this polymerase is a human homologue of the yeast Rad30 protein, recently identified as DNA polymerase eta. This polymerase and yeast Rad30 are members of a family of damage-bypass replication proteins which comprises the Escherichia coli proteins UmuC and DinB and the yeast Rev1 protein. We found that all XP-V cells examined carry mutations in their DNA polymerase eta gene. Recombinant human DNA polymerase eta corrects the inability of XP-V cell extracts to carry out DNA replication by bypassing thymine dimers on damaged DNA. Together, these results indicate that DNA polymerase eta could be the XPV gene product.

Xeroderma pigmentosum variant (XP-V) correcting protein from HeLa cells has a thymine dimer bypass DNA polymerase activity

Xeroderma pigmentosum variant (XP-V) represents one of the most common forms of this cancer-prone DNA repair syndrome. Unlike classical XP cells, XP-V cells are normal in nucleotide excision repair but defective in post-replication repair. The precise molecular defect in XP-V is currently unknown, but it appears to be a protein involved in translesion synthesis. Here we established a sensitive assay system using an SV40 origin-based plasmid to detect XP-V complementation activity. Using this system, we isolated a protein from HeLa cells capable of complementing the defects in XP-V cell extracts. The protein displays novel DNA polymerase activity which replicates cyclobutane pyrimidine dimer-containing DNA templates. The XPV polymerase activity was dependent on MgCl2, sensitive to NEM, moderately sensitive to KCl, resistant to both aphidicolin and ddTTP, and not stimulated by PCNA. In glycerol density gradients, the activity co-sedimented with a 54 kDa polypeptide at 3.5S, indicating that the monomeric form of this polypeptide was responsible for the activity. The protein factor corrected the translesion defects of extracts from three XPV cell strains. Bypass DNA synthesis by the XP-V polymerase occurred only in the presence of dATP, indicating that it can incorporate only dATP to bypass a di-thymine lesion.