Gli1+-PDL Cells Contribute to Alveolar Bone Homeostasis and Regeneration

The periodontal ligament (PDL) contains mesenchymal stem cells (MSCs) that can differentiate into osteoblasts, cementoblasts, and fibroblasts. Nevertheless, the distribution and characteristics of these cells remain uncertain. Gli1, an essential hedgehog signaling transcription factor, functions in undifferentiated cells during embryogenesis. Therefore, in the present study, the differentiation ability of Gli1⁺ cells was examined using Gli1-CreERT2/ROSA26-loxP-stop-loxP-tdTomato (iGli1/Tomato) mice. In 4-wk-old iGli1/Tomato mice, Gli1/Tomato⁺ cells were only slightly detected in the PDL, around endomucin-expressing blood vessels. These cells had proliferated over time, localizing in the PDL as well as on the bone and cementum surfaces at day 28. However, in 8-wk-old iGli1/Tomato mice, Gli1/Tomato⁺ cells were quiescent, as most cells were not immunoreactive for Ki-67. These cells in 8-wk-old mice exhibited high colony-forming unit fibroblast activity and were capable of osteogenic, chondrogenic, and adipogenic differentiation in vitro. In addition, after transplantation of teeth of iGli1/Tomato mice into the hypodermis of wild-type mice, Tomato fluorescence indicating the progeny of Gli1⁺ cells was detected in the osteoblasts and osteocytes of the regenerated bone. These results demonstrate that Gli1⁺ cells in the PDL were MSCs and could contribute to the alveolar bone regeneration.

Intermediate length scale organisation in tin borophosphate glasses: new insights from high field correlation NMR

The structure of tin borophosphate glasses, considered for the development of low temperature sealing glasses or anode materials for Li-batteries, has been analysed at the intermediate length scale by a combination of high field standard and advanced 1D/2D nuclear magnetic resonance techniques. The nature and extent of B/P mixing were analysed using the (11)B((31)P) dipolar heteronuclear multiple quantum coherence NMR sequence and the data interpretation allowed (i) detecting the presence and analysing the nature of the B-O-P linkages, (ii) re-interpreting the 1D (31)P spectra and (iii) extracting the proportion of P connected to borate species. Interaction between the different borate species was analysed using the (11)B double quantum-simple quantum experiment to (i) investigate the presence and nature of the B-O-B linkage, (ii) assign the different borate species observed all along the composition line and (iii) monitor the borate network formation. In addition, (119)Sn static NMR was used to investigate the evolution of the chemical environment of the tin polyhedra. Altogether, the set of data allowed determining the structural units constituting the glass network and quantifying the extent of B/P mixing. The structural data were then used to explain the non-linear and unusual evolution of the glass transition temperature.

Development of a routine laboratory direct detection system of staphylococcal enterotoxin genes

A novel direct detection system has been developed for eight staphylococcal enterotoxin (SE)-encoding genes (sea, seb, sec, sed, see, seg, seh and sei) in milk. Specific detection by real-time PCR was successful for all SE-encoding genes in the reference strains. Furthermore, a novel DNA-preparation method with good reproducibility [coefficients of variation 0.31, 0.99 and 1.21 % at 10(6), 10(4) and 10(2) c.f.u. (ml milk sample)(-1), respectively] was developed to overcome PCR inhibition in the milk samples. The combination of this DNA-preparation method and real-time PCR resulted in high sensitivity [between 1.1 x 10(2) and 1.0 x 10(4) c.f.u. (ml milk sample)(-1)] and allowed the completion of the entire procedure within 4 h. Results of an evaluation of this method for the detection of SE-encoding genes using known outbreak milk samples produced results showing good correspondence with the reversed passive latex agglutination assay. In addition, this newly developed system can be applied to clinical samples such as faeces and vomit. Consequently, the system should be useful in the routine direct detection of SE-encoding genes in food-borne-poisoning samples.

Inhibition of X-ray and doxorubicin-induced apoptosis by butyrolactone I, a CDK-specific inhibitor, in human tumor cells

Cell-cycle progression is coordinately regulated by cyclin-dependent kinases (CDKs). The inhibition of CDKs by p21Waf1/Cip1/Sdi1 prevents the apoptosis of cells treated with DNA-damaging agents. In this study, we found that butyrolactone I, a specific inhibitor of CDC2 family kinases, blocks the X-ray- or doxorubicin-induced apoptosis of DLD1 (p21+/+) human colorectal carcinoma cells in a dose-dependent manner. We also found that butyrolactone I inhibits the CDK2 activity and enhances cell survival after an X-ray irradiation or doxorubicin treatment in both DLD1 (p21-/-) and DLD1 (p21+/+) cells. These findings suggest that butyrolactone I prevents apoptosis by the direct inhibition of CDK and also, possibly, by CDK-inhibition through p53-independent p21-induction. Our findings indicate that CDK activity is required for DNA-damaging agent-induced apoptosis.

Postlabelling analysis of DNA adducts formed in human hepatoma cells treated with 3-nitrobenzanthrone

3-Nitrobenzanthrone (NBA) is one of the most mutagenic nitroaromatic compounds that has been found recently in diesel exhaust and airborne particles. A [32P]-postlabelling analysis was carried out to examine the adducts in DNA from human hepatoma HepG2 cells treated with NBA. Two major and two minor adduct spots were obtained in the analysis. The structure of the compound obtained from one of the minor adduct spots was identified to be N-acetyl-3-amino-2-(2'-deoxyguanosin-3', 5'-bisphosphate-8-yl)-benzanthrone, based on identical mobility of the compound with that of synthetic standards in thin-layer chromatography and high performance liquid chromatography. This substance is the identical adduct found in our previous in vitro study. The yet-unidentified major adduct spots may be guanosin- and adenosin-benzanthrone adducts without the N-acetyl group.

Involvement of cyclin-dependent kinases in doxorubicin-induced apoptosis in human tumor cells

Apoptotic cell death caused by doxorubicin, a chemotherapeutic agent, is suppressed by expression of p21 (waf1/cip1/sdi1), a cyclin-dependent kinase (cdk) inhibitor. To examine cdk activity required for doxorubicin-induced apoptosis, we transfected p21-deficient human tumor DLD1(p21-/-) cells with plasmids carrying wild-type p21 and mutated p21 unable to bind to cdks or proliferating cell nuclear antigen. The apoptosis induced at the G(2)/M phase after doxorubicin treatment was suppressed by transient expression of the p21 with cdk-binding activity but not by the p21 lacking the activity. We also transfected cells with plasmids carrying wild-type, dominant negative and constitutively active mutants of cdk2 or cdk4. The apoptosis was suppressed by transient expression of dominant negative mutants of cdk2 or cdk4. These findings indicate that cdk is involved in the doxorubicin-induced apoptosis pathway.

[Bioethics in genetic diagnosis and therapy]

Human genetics, or medical genetics have been rarely taught in most of the medical schools in Japan, as there are only several medical schools with genetics departments among 80 medical schools in Japan. Bioethics has just been becoming an important issue in the medical community in Japan. People hate to be told of hereditary diseases, possibly due to the traditional concept of hereditary diseases as punishment for the evil acts of the ancestors. Recent rapid progress in genetic diagnosis and therapy, however, requires the medical community in Japan to consider the bioethical aspects related to human genetics. We need proper guidelines, and the efforts have been made by the government as well as by the Society for Familial Tumor to propose practical guidelines for human genetics. They may considerably be different from those in the Western countries.

Expression of a mammalian DNA photolyase confers light-dependent repair activity and reduces mutations of UV-irradiated shuttle vectors in xeroderma pigmentosum cells

Photoreactivation is one of the DNA repair mechanisms to remove UV lesions from cellular DNA with a function of the DNA photolyase and visible light. Two types of photolyase specific for cyclobutane pyrimidine dimers (CPD) and for pyrimidine (6-4) pyrimidones (6-4PD) are found in nature, but neither is present in cells from placental mammals. To investigate the effect of the CPD-specific photolyase on killing and mutations induced by UV, we expressed a marsupial DNA photolyase in DNA repair-deficient group A xeroderma pigmentosum (XP-A) cells. Expression of the photolyase and visible light irradiation removed CPD from cellular DNA and elevated survival of the UV-irradiated XP-A cells, and also reduced mutation frequencies of UV-irradiated shuttle vector plasmids replicating in XP-A cells. The survival of UV-irradiated cells and mutation frequencies of UV-irradiated plasmids were not completely restored to the unirradiated levels by the removal of CPD. These results suggest that both CPD and other UV damage, probably 6-4PD, can lead to cell killing and mutations.

Decreased host-cell reactivation of UV-irradiated adenovirus in human colon tumor cell lines that have normal post-UV survival

An ongoing study in our laboratories is to examine the relationship of DNA repair defects to human cancer. Our underlying hypothesis has been that human tumors may arise that lack interesting DNA repair pathways if these pathways are important in preventing cancer. In this study, we found that the UV-irradiated adenoviruses showed hypersensitivity when assayed on monolayers of certain human colon tumor cell lines, including three that are reported to have defects in long patch DNA mismatch repair genes and one with no reported defect in mismatch repair. The survival curves showed two components. The first sensitive component was characteristic of 77-95% of the infections depending upon the cell line and the experiment and had an average slope indicating 4.8-fold hypersensitivity to UV. The average of the second-component slopes indicated that the remainder of the infections was accompanied by near-normal repair. Although the value of the first component indicated that the colon tumor lines supported the growth of UV-damaged adenoviruses poorly, the cell lines themselves showed the same post-UV colony-forming ability as did normal human fibroblasts, and their ability to support the growth of N-methyl-N'-nitro-N-nitrosoguanidine-damaged adenoviruses was normal, i.e. it parallelled their ability to repair O6-methylguanine in vitro. We previously observed two-component survival curves when assaying UV-irradiated adenovirus on monolayers of all of seven strains of fibroblasts from Cockayne's syndrome patients. By contrast, single-component curves have been obtained using 21 strains of normal human fibroblasts and seven other tumor lines. We interpret the two-component survival curves in terms of the defective transcription-coupled repair of UV-induced DNA damage that is characteristic both of Cockayne's and certain colon tumor cell lines. In addition, four mismatch repair-deficient colon tumor lines were resistant to killing by elevated levels of dG.

Molecular analysis of mutations induced by a benzene metabolite, p-benzoquinone, in mouse cells using a novel shuttle vector plasmid

Human population has been continually exposed to benzene which is present in our environment as an essential component of petroleum. p-Benzoquinone (p-BQ) is one of the benzene metabolites and is thought to be an ultimate toxic or carcinogenic substance. For molecular analysis of carcinogen-induced mutations in mouse cells, we constructed a new shuttle vector plasmid pNY200 that has supF gene as a target of the mutations and replicates in mouse and in Escherichia coli cells. In p-BQ-treated pNY200 propagated in mouse cells, base substitutions were induced predominantly at G:C sites, and the major mutation was G:C-->A:T transition. Many tandem base substitutions were also induced at CC:GG sequences. By a postlabeling analysis and a polymerase stop assay, we confirmed that p-BQ adducts formed in DNA and mutation sites roughly correspond to the sites where the adducts were formed. Comparing data of pNY200 in mouse cells with those of the similar shuttle vector plasmid pMY189 in human cells should be important for extrapolation of data from mouse to human, because carcinogenicity of chemicals is tested in mice.

Trans-dominant inhibition of poly(ADP-ribosyl)ation potentiates alkylation-induced shuttle-vector mutagenesis in Chinese hamster cells

In most eukaryotic cells, the catalytic activation of poly(ADP-ribose) polymerase (PARP) represents one of the earliest cellular responses to the infliction of DNA damage. To study the biological function(s) of poly(ADP-ribosyl)ation, we have established stable transfectants (COM3 cells) of the SV40-transformed Chinese hamster cell line C060 which conditionally overexpress the PARP DNA-binding domain upon addition of dexamethasone. We could demonstrate that DNA-binding domain overexpression, which leads to trans-dominant inhibition of poly(ADP-ribosyl)ation, potentiates the cytotoxicity of alkylation treatment and of gamma-radiation. Likewise, carcinogen-induced gene amplification, viewed as a manifestation of genomic instability, was potentiated by the overexpression of the PARP DNA-binding domain. Recently, we studied the effect of trans-dominant PARP inhibition on mutagenesis by employing a shuttle-vector assay in which mutagen-exposed plasmid pYZ289 is electroporated into COM3 cells. We could show that dexamethasone-induced overexpression of the PARP DNA-binding domain in COM3 cells potentiates the mutagenicity of the alkylating agent N-methyl-N-nitrosourea, while no effect of dexamethasone treatment on mutation frequency was recorded in control cells lacking the PARP DNA-binding domain transgene. Taken together, our results further substantiate the role of poly(ADP-ribosyl)ation in the maintenance of genomic integrity and stability under conditions of genotoxic stress.

Long-term exposure to a magnetic field (5 mT at 60 Hz) increases X-ray-induced mutations

Exposure to extremely low frequency magnetic field (ELFMF) at 400 mT has been shown to induce mutations (Mutat. Res., 349: 109-114, 1996; Int. J. Radiat. Biol., 71: 75-79, 1997; and Biochem. Biophys. Res. Commun., 243: 579-584, 1998). However, whether ELFMF at low flux densities (under 1 mT) induces mutations is debatable. We investigated the effect of long-term exposure to 5 mT ELFMF at 60 Hz on mutant frequency. Chinese hamster ovary K1 (CHO-K1) cells were exposed or sham-exposed to 5 mT ELFMF for up to 6 weeks with or without X-irradiation (3 Gy), and the mutant frequency of the hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene was analyzed. Long-term exposure to 5 mT ELFMF did not increase mutations, suggesting a threshold for mutation induction greater than 115 mA/m2 or a magnetic density of 5 mT. However, enhancement of the X-ray-induced mutation rate was observed after treatment with X-irradiation followed by long-term exposure to 5 mT ELFMF. At little as a 1-week exposure to ELFMF after X-irradiation enhanced the mutation rate. We also found that 400 mT exposure enhanced the mutation rate induced by X-irradiation (Mutat. Res., 349: 109-114, 1996). These results suggest that exposure to more than 5 mT ELFMF may promote X-ray-induced mutations.

Phylogeny of Japanese papilionid butterflies inferred from nucleotide sequences of the mitochondrial ND5 gene

Phylogenetic relationships among the Japanese papilionid butterflies were analyzed by comparing 783 nucleotide sequences of the mitochondrial gene encoding NADH dehydrogenase subunit 5 (ND5). Phylogenetic trees of the representative species from each family in the superfamily Papilionoidea revealed that the species of the family Papilionidae and those of all other families formed distinct clusters, with a few species of the family Hesperiidae (Hesperioidea) as an outgroup. In the phylogenetic trees of most Japanese species of the family Papilionidae with Nymphalis xanthomelas (Nymphalidae) as an outgroup, the tribe Parnassiini (Parnassiinae) formed a cluster, and the rest formed the other cluster in which the tribe Zerynthiini (Parnassiinae) and the subfamily Papilioninae formed different subclusters. In the Papilioninae cluster, the tribes Troidini and Graphiini formed a subcluster, and the tribe Papilionini formed the other subcluster. These results generally agree with the traditional classification of the papilionid butterflies based on their morphological characteristics and support the proposed evolutionary genealogy of the butterflies based on their morphology, behavior, and larval host plants, except that the tribes Parnasiini and Zerynthiini (both Parnassiinae) are not in the same cluster.

Mutagenic specificity of a derivative of 3-nitrobenzanthrone in the supF shuttle vector plasmids

3-Nitrobenzanthrone (NBA) is a powerful bacterial mutagen and a suspected human carcinogen present in diesel exhaust and airborne particulates [Enya, T., et al. (1997) Environ. Sci. Technol. 31, 2772-2776]. In the accompanying paper [Enya, T., et al. (1998) Chem. Res. Toxcol. 11, 1460-1467], N-acetoxy-N-acetyl-3-aminobenzanthrone (N-Aco-N-Ac-ABA) was synthesized to yield the DNA adducts of NBA. In this work, to investigate the mutagenic specificity of NBA in human cells, we analyzed mutations induced by N-Aco-N-Ac-ABA using the supF shuttle vector plasmids. Base sequence analysis of 110 and 100 plasmids with mutations in the supF gene propagated in normal cells [WI38-VA13] and nucleotide excision repair deficient cells [XP2OS(SV)], respectively, revealed that the majority of the mutations were base substitutions (85 and 90%) and the rest were deletions and insertions (10 and 15%) in both cell lines. About half of the mutant plasmids had a single base substitution. Of the base substitutions, the most frequent mutation was G.C to T.A transversion (41 and 51%), followed by G.C to A.T transitions (18 and 24%) in either cell. The mutations were distributed not randomly but located at several hot spots, and almost all (nine of ten) hot spots were at the sites of G.C base pairs. The polymerase stop assay in the supF gene revealed that N-Aco-N-Ac-ABA preferentially bound to guanine residues, and mutation sites were generally consistent with the sites where the guanine adducts were formed.

Sensitivity of group F xeroderma pigmentosum cells to UV and mitomycin C relative to levels of XPF and ERCC1 overexpression

The XPF and ERCC1 proteins form a tight complex and function as an endonuclease to incise on the 5'-side of pyrimidine dimers in DNA. Levels of both proteins are extremely low in group F xeroderma pigmentosum (XP-F) cells. We transfected XP-F cells with the plasmids expressing XPF or ERCC1 and examined levels of both proteins in the cells. Although XP-F cells are sensitive to UV and mitomycin C (MMC), cells overexpressing XPF expressed ERCC1 as well and resistance to UV and MMC was restored to the normal level. In contrast, cells overexpressing ERCC1 did not express XPF and were still sensitive to UV and MMC. These results indicate that both the XPF and ERCC1 proteins are required to repair UV- and MMC-induced DNA damage. Even though a high level of ERCC1, which has been presumed to be a catalytic subunit of the endonuclease, is stably present in XP-F cells, ERCC1 protein alone cannot carry out excision repair completely.

Molecular analysis of mutations induced by acrolein in human fibroblast cells using supF shuttle vector plasmids

Types of mutations induced by acrolein in the supF gene on the shuttle vector plasmid pMY189 replicated in normal human fibroblast cells were examined. Base sequence analysis of 92 plasmids with mutations in the supF gene revealed that the majority of the mutations were base substitutions (76%) and the others were deletions and insertions (24%). Single base substitutions were most frequently found (46%), while multiple base substitutions were 18% and tandem (two adjacent) base substitutions were 12% of the mutations. Of the base substitution mutations, G:C to T:A transversions were 44% and G:C to A:T transitions were 24%. The mutations were distributed not randomly but located at several hotspots. Acrolein produced DNA intra-strand cross-links between guanine residues, which might be responsible for rather high induction of the tandem base substitution mutations.

Characterization of molecular defects in xeroderma pigmentosum group F in relation to its clinically mild symptoms

Xeroderma pigmentosum (XP) complementation group F was first reported in Japan and most XP-F patients reported to date are Japanese. The clinical features of XP-F patients are rather mild, including late onset of skin cancer. Recently a cDNA that corrects the repair deficiency of cultured XP-F cells was isolated. The XPF protein forms a tight complex with ERCC1 and this complex functions as a structure-specific endonuclease responsible for the 5' incision during DNA excision repair. Here we have identified XPF mRNA mutations and examined levels of the mRNA and protein expression in seven primary cell strains from Japanese XP-F patients. The XP-F cell strains were classified into three types in terms of the effect of the mutation on the predicted protein; (i) XPF proteins with amino acid substitutions; (ii) amino acid substituted and truncated XPF proteins; and (iii) truncated XPF protein only. A normal level of expression of XPF mRNA was observed in XP-F cells but XPF protein was extremely low. These results indicate that the detected mutations lead to unstable XPF protein, resulting in a decrease in formation of the ERCC1-XPF endonuclease complex. Slow excision repair of UV-induced DNA damage due to low residual endonuclease activity provides a plausible explanation for the typical mild phenotype of XP-F patients.

Enhanced NOR-1 gene expression by exposure of Chinese hamster cells to high-density 50 Hz magnetic fields

Enhanced expression of neuron derived orphan receptor (NOR-1) gene was observed by exposure of Chinese hamster ovary K1 (CHO-K1) cells to an extremely low frequency magnetic field (ELFMF) of 50 Hz at 400 mT, but not at 5 mT. The enhanced expression, reaching the maximum at 6 h, was transient and reduced to the control level after exposure to 400 mT ELFMF for 24 h. The NOR-1 expression induced by treatment with forskolin and TPA was further enhanced by the simultaneous treatment with 400 mT ELFMF, in which the maximum response was at 3 h. The NOR-1 expression by these treatments was induced more earlier than that by 400 mT ELFMF alone. When cells were treated with an inhibitor of the protein kinase C (calphostin C or crocetin) and Ca2+ entry blockers (nifedipin and dantrolen) during the 400 mT ELFMF exposure, the enhanced NOR-1 expression was not observed. Exposure of CHO-K1 cells to the high-density 400 mT ELFMF may affect the signal transduction in the cells, resulting in the enhanced NOR-1 gene expression.

Mutations of p16 and p15 tumor suppressor genes and replication errors contribute independently to the pathogenesis of sporadic malignant melanoma

Mutations of p16 and p15 suppressor oncogenes and the replication errors in six microsatellite loci in sporadic malignant melanomas were analyzed. Four (9.1%) homozygous deletions of both p16 and p15 genes and one point mutation (2.3%) in the p15 gene were detected among 44 primary melanoma samples. One mutation in each of the p16 and p15 genes was observed in ten metastatic lesions. Eight (18.2%) replication errors were detected in three microsatellite loci in the primary melanoma samples, but no replication error was detected in the metastatic samples. None of the samples showed the alteration of p16/p15 genes and the replication errors concomitantly. These results suggest that (1) the homozygous deletions of p16/p15 genes and the replication errors may occur in rather early stages of melanoma tumorigenesis, while the p16/p15 gene mutation may occur in later stages, and (2) the p16 and p15 gene mutations in sporadic malignant melanomas might not be induced by the defect in mismatch repair, implying that p16 as well as p15 gene alterations may play an important role in the pathogenesis of sporadic malignant melanomas.

Specific tandem GG to TT base substitutions induced by acetaldehyde are due to intra-strand crosslinks between adjacent guanine bases

Acetaldehyde is present in tobacco smoke and automotive exhaust gases, is produced by the oxidation of ethanol, and causes respiratory organ cancers in animals. We show both the types and spectra of acetaldehyde-induced mutations in supF genes in double- and single-stranded shuttle vector plasmids replicated in human cells. Of the 101 mutants obtained from the double-stranded plasmids, 63% had tandem base substitutions, of which the predominant type is GG to TT transversions. Of the 44 mutants obtained from the single-stranded plasmids, 39% had tandem mutations that are of a different type than the double-stranded ones. The GG to TT tandem substitutions could arise from intra-strand crosslinks. Our data indicate that acetaldehyde forms intra- as well as inter-strand crosslinks between adjacent two-guanine bases. Based upon the following observations: XP-A protein binds to acetaldehyde-treated DNA, DNA excision repair-deficient xeroderma pigmentosum (XP) cells were more sensitive to acetaldehyde than the repair-proficient normal cells, and a higher frequency of acetaldehyde-induced mutations of the shuttle vectors was found in XP cells than in normal cells, we propose that the DNA damage caused by acetaldehyde is removed by the nucleotide excision repair pathway. Since treatment with acetaldehyde yields very specific GG to TT tandem base substitutions in DNA, such changes can be used as a probe to identify acetaldehyde as the causal agent in human tumors.

Suppression of high-density magnetic field (400 mT at 50 Hz)-induced mutations by wild-type p53 expression in human osteosarcoma cells

Exposure of cultured human osteosarcoma cells (Saos-LP-12) to high-density (400 mT at 50 Hz) extremely low frequency magnetic fields (ELFMF) induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene. Saos-LP-12 cells, which are isolated from parental Saos-2 cells and have a deletion in the coding region of the p53 gene, are introduced to the wild-type (wt) p53 expression plasmid (pOPRSVp53). The mutation in Saos-LP-12 cells was suppressed by expression of the introduced wt p53 gene during 400 mT ELFMF exposure. No marked difference in the mutation spectrum was observed among the treatments of ELFMF [p53 (-)], ELFMF [p53 (+)], and sham exposures. Our findings suggest that wt p53 has a function in suppression of DNA replication errors and/or in maintenance of genomic stability after high-density ELFMF exposure.

Mutated p21(WAF1/CIP1/SDI1) lacking CDK-inhibitory activity fails to prevent apoptosis in human colorectal carcinoma cells

Human colorectal tumor cell lines were established which express wildtype p21 or p21 with a mutation at codon 46 (Cys) or 140 (Gly) on IPTG treatment (LacSwitch). The IPTG-induced wildtype p21 bound to CDK2 and PCNA and inhibited CDK activity in the cells and reduced cell growth rate; whereas, both IPTG-induced mutated p21 proteins neither bound to CDK2 nor affected the CDK activity but did bind to PCNA, and they did not affect the cell growth rate. Wildtype p21 suppressed apoptosis and enhanced survival of X-ray-irradiated or adriamycin-treated cells; but, mutated p21 neither suppressed apoptosis nor affected cell survival. When cells were treated with mimosine, a p53-independent p21-inducer, or butyrolactone I, a specific inhibitor of CDK, cellular endogenous p21 was induced and X-ray or adriamycin-induced apoptosis was blocked. These results suggest that CDK-binding or CDK-inhibitory activity of p21 is required to prevent apoptosis, i.e., CDK is required for apoptosis in human tumor cells.

Reduced UV-induced mutations in human osteosarcoma cells stably expressing transfected wild-type p53 cDNA

We constructed the plasmid which can express human wild-type p53 cDNA and introduced it into the human osteosarcoma cell line SAOS-2 that lacks the chromosomal p53 gene. A cell clone stably expressing p53 protein was isolated and UV sensitivity and UV-induced mutation frequencies of the clone were examined. The UV sensitivity of the clone was slightly higher and UV-induced hprt mutation frequencies of the clone were markedly lower than those of parental SAOS-2 cells. The capability to repair UV-induced DNA damage assessed by the amount of unscheduled DNA synthesis or DNA single strand breaks as well as cell cycle progression after UV irradiation were not different between the clone and SAOS-2 cells. These results indicate that wild-type p53 protein would be involved in the human DNA damage-processing pathway other than the genome-overall excision repair.

Complete restoration of normal DNA repair characteristics in group F xeroderma pigmentosum cells by over-expression of transfected XPF cDNA

XP-F cDNA was cloned into a mammalian expression vector plasmid, and introduced into group F xeroderma pigmentosum (XP-F) cells. Several cell clones possessing transfected XPF cDNA were randomly isolated, and DNA repair characteristics of a clone, XP-FR2, were extensively analyzed. The XP-FR2 cells expressed high level of XPF protein as well as ERCC1 protein, although their parental XP-F cells expressed extremely low level of both proteins. The XP-FR2 cells showed UV resistance comparable to normal human cells, and had normal levels of UV-induced unscheduled DNA synthesis and normal capability to remove cyclobutane pyrimidine dimers and (6-4) photoproducts. Frequencies and types of UV-induced mutations examined by shuttle vector plasmids in XP-FR2 cells were similar to those in normal human cells. These results demonstrate that excision repair defect in XP-F cells is fully corrected by over-expression of XPF cDNA alone, although only partial correction of the cells by XPF cDNA has been reported before.

A spectrum of mutations induced by crotonaldehyde in shuttle vector plasmids propagated in human cells

A spectrum of crotonaldehyde-induced mutations in the supF gene of the shuttle vector plasmid pMY189 replicated in human fibroblast cells was examined. Base sequence analysis of 104 plasmids with mutations in the supF gene revealed that the majority of the mutations were base substitutions (85%) and the rest were frameshifts (15%). A single base substitution was most frequently found (47%), while 25% had multiple base substitutions and interestingly 13% had tandem (adjacent two) base substitutions. Of the base substitution mutations, 50% were G:C-->T:A transversions and 23% were G:C-->A:T transitions. The mutations were not distributed randomly but were located at several hotspots, most of which were G:C base pairs in 5'-AAGG-3' (or 5'-CCTT-3') sequences. Production of propanodeoxyguanosine adducts may be related to such specificity in the mutation spectrum.

Spectroscopic properties of Nd 3 + and Pr 3 + in gallate glasses with low phonon energies

Absorption and fluorescence spectra of Nd3 +were measured in potassium tantalum gallate, lead bismuth gallate (PBG), fluorozirconate (ZBLAN), and Ge-Ga-S glasses. A Judd -Ofelt analysis was performed to determine the spontaneous emission probability and stimulated emission cross section of the4 F3/2 ?4 I11/2 transition of Nd3 +. Raman spectra were studied to clarify the maximum phonon energies of the glasses. The fluorescence of the1 G4?3 H5 transition of Pr3 + in a dehydrated PBG glass was observed for the first time to our knowledge. The PBG glass has a higher quantum efficiency than that of ZBLAN glass based on the Judd -Ofelt analysis.

Enhanced radiosensitivity by inhibition of nuclear factor kappa B activation in human malignant glioma cells

To clarify the relationship between cellular radiosensitivity and nuclear factor kappa B (NF-kappa B) activation, an expression plasmid was constructed for I kappa B-alpha, a cellular inhibitory protein of NF-kappa B, and transfected it into two human malignant glioma cell lines. Cells overexpressing the I kappa B-alpha protein were more radiosensitive than the parental cells and one transfected clone with low expression. In the parental cell lines and one transfected clone with low expression, the sequence specific DNA-binding activity of NF-kappa B was considerably increased between 1 and 2 h after irradiation. In contrast, no increase in the DNA-binding activity was observed in the transfected clone overexpressing I kappa B-alpha protein. These results suggest that the activation of NF-kappa B may be one of the intrinsic responses determining cellular radiosensitivity.

Suppression of UV-induced mutations by wild-type p53 protein in human osteosarcoma cells

We have examined whether the tumour suppressor p53 protein suppressed UV-induced mutations in the hypoxathine-guanine phosphoribosyl transferase (HPRT) gene and in the supF gene of the shuttle vector plasmid pMY189. We used human osteosarcoma Saos-LP12 cells, in which wild type (wt) p53 protein was induced by treatment with isopopyl-beta-D-thiogalactopyranoside. The induction of wt p53 protein suppressed UV-induced mutations but not spontaneous mutations in the HPRT gene. The frequency of UV-induced mutations induced by UV-irradiation of the plasmid was also significantly lower in cells with induced wt p53 protein than in the uninduced cells. In addition, we found that frequency of G : C to A : T transition mutations which occurred at the 3' base pair of dipyrimidine sites were significantly lower in the cells with induced wt p53 protein than in the uninduced cells. These findings suggest that wt p53 protein may play roles in modulating DNA repair pathway, resulting in the suppression of UV-induced mutations.

Increase in radiation sensitivity of human malignant melanoma cells by expression of wild-type p16 gene

The influence of wild-type p16 expression on the radiation sensitivity of human melanoma cell lines was investigated. MeWo cells, which alone expressed intrinsic wild-type p16 among six melanoma cell lines examined, showed higher radiosensitivity in comparison with the other five melanoma cells. The introduction of human wild-type p16 cDNA into A875 cells, which homozygously lost p16 genes, and AKI cells, which retained p16 gene but did not express p16 mRNA, led to increased sensitivity of those cells to X-ray irradiation. The radiosensitizing effect by the p16 introduction to those cells was prominent after rather higher doses of X-rays (8 and 10 Gy). In both A875 and AKI, no significant difference in sensitivities to UVC and cisplatin was observed between the parental and p16-transfectant cells. These results suggest that the loss or dysfunction of p16 gives melanoma cells the radioresistant characteristics.

Decrease in the frequency of X-ray-induced mutation by wild-type p53 protein in human osteosarcoma cells

Tumor suppressor p53 protein acts as a checkpoint factor following DNA damage. Inactivation of checkpoint control may increase the frequency of mutation following DNA damage, resulting in tumor progression. Here we examine whether wild-type (wt) p53 protein suppresses X-ray-induced mutations using an isopropyl-beta-D-thiogalactopyranoside (IPTG)-regulated p53 expression system in human osteosarcoma Saos-2 cells. Frequency of X-ray-induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene was enhanced about 10 and 20 times by 1 and 2 Gy respectively in cells without expression of wt p53 protein, while enhancement of mutations by X-rays was slight in cells with expression of wt p53 protein. Furthermore, arrest at the G/S boundary was induced by X-ray irradiation when p53 protein was expressed by treatment with IPTG. These findings suggest that wt p53 protein has a function in maintaining genomic stability after X-ray irradiation through the G1 checkpoint and loss of p53 function(s) may lead to tumor progression in multi-step tumorigenesis.

Mutation induction by high-density, 50-Hz magnetic fields in human MeWo cells exposed in the DNA synthesis phase

Exposure of cultured human MeWo cells to high-density (400 mT at 50 Hz) extremely low frequency magnetic fields (ELF-MF) induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene. Mutation induced by the ELF-MF increased during the DNA-synthesis phase in synchronously growing cells. DNA replication errors and/or disturbance of the mismatch repair systems caused by exposure to ELF-MF may be involved in the mutagenic effect.

A low content of ERCC1 and a 120 kDa protein is a frequent feature of group F xeroderma pigmentosum fibroblast cells

The ERCC1 protein has been predicted to form part of a tight complex with a protein partner, the yet-unidentified XPF/ERCC4 protein, in normal human cells. We used an anti-ERCC1 antibody to detect the complex by immunoprecipitation and immunoblotting. The amount of ERCC1 protein expressed in five different XP-F cell strains was 1/ 5-1/34 of that of the protein in normal and XP cell strains representing other complementation groups. A 120 kDa protein was co-immunoprecipitated with ERCC1 by the anti-ERCC1 antibody, and the amount of the 120 kDa protein in XP-F cell strains was 1/5-1/8 of that of the protein in normal and XP cell strains representing other complementation groups. The XPA protein was not co-immunoprecipitated with ERCC1 in any cell strain. These results demonstrate that a low level of ERCC1 and the 120 kDa protein is a frequent feature of XP-F cell extracts and that a lower amount of a complex between these proteins occurs in XP-F cells than in normal cells.

Increased radiosensitivity of p16 gene-deleted human glioma cells after transfection with wild-type p16 gene

The A1235 and T98 cell lines derived from human gliomas have homozygous deletions in their p16 genes and are radiosensitive and radioresistant, respectively, with respect to other established glioma cell lines. These differences in radiosensitivity may be due to variations to some extent among cell lines, rather than genetically defined resistance or sensitivity. We examined the effect on radiation sensitivity of introducing a wild-type p16 gene into both p16-deficient glioma cell lines. The plasmid pOPMTS containing human wild-type p16 cDNA and a neomycin resistance gene, or the control plasmid pOPRSV1, were transfected into these cells. Clones from both cell lines, which expressed wild-type p16 mRNA constitutively after transfection with pOPMTS, were more radiosensitive than the parental cells and clones obtained after transfection with the negative control plasmid.

Sites and types of UV-induced mutations leading to inactivation of the growth-arresting activity in p21 (sdi1/cip1/waf1) cDNA

The p53-regulated gene product p21 (sdi1,cip1,waf1) negatively regulates cell growth and has been suggested to be a potential tumour-suppressor gene. To determine the sites and types of mutations which inactivate the growth-arresting activity in sdi1 cDNA, plasmids containing sdi1 cDNA and the neomycin-resistant gene were irradiated with UV light and transfected into CHO cells. The UV irradiation increased number of the geneticin-resistant colonies which should have the UV-mutated sdi1 cDNA. Sdi1 mRNA was expressed in 23 out of 36 colonies (64%). In 13 sdi1 cDNA sequences analysed, mutations were found at codon 46 in nine cDNAs, and one each at codons 34, 54, 66 and 73. All the mutation sites are in the CDK-binding region. Ten mutations (77%) (codons 46 and 66) are C to T transition mutation at the dipyrimidine sequences, which is the major type of the UV-induced mutation.

Exposure to magnetic field (5 mT at 60 Hz) does not affect cell growth and c-myc gene expression

We designed and manufactured equipment for long-term and low-density (0 to 9 mT) exposures of cultured cells to extremely low frequency magnetic fields (ELF-MF), and examined the effects of ELF-MF on cell growth and c-myc mRNA expression in Chinese hamster ovary (CHO) cells. The ELF-MF equipment consists of a CO2 incubator with a built-in magnet generator using Helmholtz coils being 250 mm in inner diameter, 160 mm in distance and 128 turns, a slide regulator and a thermocontroller. No significant difference in the growth rate and the c-myc expression of CHO cells was observed with 5 mT ELF-MF exposure, sham-exposure and incubation in a conventional incubator.

Effect of poling conditions on second-harmonic generation in fused silica

A systematic study of the effects of poling time and applied voltage on second-harmonic (SH) generation in thermally poled silica glass reveals that the SH signal is proportional to the square of the applied voltage and that the speed of the poling process increases with the applied voltage. Prior treatment of the samples is found to affect the poling process, and the optimum poling conditions are observed to depend on the poling atmosphere. The mechanism of thermal poling is discussed in the light of these new results.

Characterization of p53 gene mutations in basal-cell carcinomas: comparison between sun-exposed and less-exposed skin areas

Mutations in the p53 gene in 32 basal-cell carcinomas (BCC) developed in Japanese patients were identified by the polymerase chain reaction and single-strand-conformation polymorphism analysis, followed by sequencing the DNA. Among 16 BCC developed in continuously sun-exposed areas, 6 tumors showed 7 base substitutions, most of which were G:C to A:T transitions, mainly at the dipyrimidine sites. Seven out of 16 BCC developed in less-exposed areas showed 8 base substitutions, but the majority (75.0%) of them were transversions. These results suggest that the mutation in the p53 gene plays a significant role in the tumorigenesis of BCC developed in less-exposed areas as well as those in sun-exposed areas in Japanese patients. There must be therefore causative factors other than UV irradiation for BCC in less-exposed areas.

Aberrant splicing and truncated-protein expression due to a newly identified XPA gene mutation

A group A xeroderma pigmentosum (XPA) patient, XP2NI, is a compound heterozygote with a newly identified G to C transversion at the last nucleotide in exon 5 in one chromosome, and with the known splicing mutation in intron 3 in another chromosome in the XPA gene. XP2NI had mild skin symptoms and the cells were slightly less sensitive to UV radiation than the cells of typical severe XPA patients who have the splicing mutation in intron 3 homozygously. Reverse transcriptase (RT)-PCR and sequencing of the PCR products revealed that the mutation in exon 5 resulted in producing three types of aberrant mRNA, lacking 7 nucleotides at the end of exon 5, lacking entire exon 5, and lacking exons 3, 4 and 5. A significant amount of a truncated type of protein was produced in XP2NI cells, and the size of the protein indicated that it should have been translated from the mRNA, lacking the 7 nucleotides and retained one of the zinc-finger domains required for the DNA repair activity. The clinical mildness of XP2NI may be due to the residual DNA repair activity of the truncated XPA protein, while no XPA protein was detected in the XPA cells with the homozygous intron 3 splicing mutation.

Increase in hypoxanthine-guanine phosphoribosyl transferase gene mutations by exposure to high-density 50-Hz magnetic fields

Exposure to extremely low frequency magnetic field (ELFMF) of 50 Hz and 400 mT induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene of human melanoma MeWo cells. The mutant frequency was enhanced both by increasing the exposure period and the induced current intensity. Mutations induced by X-rays were enhanced by ELFMF exposure. No significant increase in mutant frequency occurred when DNA replication was inhibited during ELFMF exposure. DNA replication error is suspected of causing the mutations produced by ELFMF exposure.

Modification of the radiosensitivity of human cells to which simian virus 40 T-antigen was transfected

Effects of the introduction of the Simian virus 40 T-antigen (SV40 T-Ag) gene to cultured human cells were examined in relation to radiosensitivity. Two relatively radioresistant tumor cell lines (T98 and G361) became significantly radiosensitive after the introduction of SV40 T-Ag, whereas radiosensitive tumor cell lines did not show a change in radiosensitivity. In contrast, a human fibroblast cell line became radioresistant after SV40 T-Ag introduction. T98 cells which have a mutation at codon 237 in the p53 gene were unable to form a complex between p53 protein and SV40 T-Ag, whereas G361, which became radiosensitive by a SV40 T-Ag introduction, formed the complex. This indicates that the status of p53 is independent of the change in radiosensitivity in the cell lines studied.

[Mechanisms of hereditary tumorigenesis]

Hereditary cancers have been shown to develop through at least two mechanisms. Development of retinoblastoma and Wilms' tumor is usually not accompanied by other hereditary symptoms. Although they are inherited autosomal dominantly, gene mutations in recessive tumor suppressor genes were found to be responsible for these tumors. The other mechanism is the enhanced mutation in the cancer-prone hereditary diseases, such as xeroderma pigmentosum, Bloom's syndrome, etc. In xeroderma pigmentosum, for example, defects in DNA repair has been shown to enhance the frequency of mutation in the oncogenes and tumor suppressor genes. Recently, another repair-related mechanism, involving the mismatch repair, was found to be involved in the hereditary nonpolyposis colon cancer.

Molecular analysis of mutations induced by 2-chloroacetaldehyde, the ultimate carcinogenic form of vinyl chloride, in human cells using shuttle vectors

Vinyl chloride (VC) is a carcinogen associated with human and animal cancers. The ultimate carcinogenic form of VC, 2-chloroacetaldehyde (CAA), has been suspected to be mutagenic and we confirmed the mutagenicity of CAA using a modified shuttle vector plasmid. Base sequence analyses of 109 mutant plasmids with mutations in the supF gene, which were treated with CAA and propagated in the cultured human cells, revealed that more than half of the single base substitutions were G:C to A:T transitions with eight hotspots. The majority of the mutations involving G:C base pairs were in 5'-AAGG-3' or 5'-CCTT-3' sequences suggesting that these sequences are the main targets of mutagenesis caused by CAA.

High prevalence of mutations in the p53 gene in poorly differentiated squamous cell carcinomas in xeroderma pigmentosum patients

Mutations in the p53 gene were analyzed in 23 squamous cell carcinomas (SCCs) and five basal cell carcinomas from 10 xeroderma pigmentosum patients in Tunisia. Fourteen mutations were detected. Most occurred at the dipyrimidine sequences of DNA, suggesting that they were caused by ultraviolet light. A strong correlation was noted between the presence of the p53 mutations and clinical characteristics such as histology and growth of SCC. In well-differentiated grade 1 SCCs, three (27.3%) of 11 tumors had the p53 gene mutations, whereas in grade 2 and grade 3 SCCs, six (85.7%) of seven tumors had the p53 gene mutations (p < 0.05). Tumors less than 8.0 mm in diameter showed a relatively low frequency of mutation (two of 10 tumors, 20.0%), whereas most of the tumors larger than 8.1 mm (seven of eight tumors, 87.5%) had mutations of the p53 gene (p < 0.025). Multiple tumors in the same xeroderma pigmentosum patients also showed this relation. These results suggest that mutations in the p53 gene lead to the invasive and rapid-growing character of SCC.

Changes in radiation sensitivity of human osteosarcoma cells after p53 introduction

Human osteosarcoma SAOS-2 cells, which have a deletion in p53 gene, were transfected with plasmid pMSVneop53 containing human p53 cDNA and neomycin-resistance gene. Three clones (SAOS-MC10, SAOS-MC11 and SAOS-MC43) among 60 clones expressed p53 mRNA. No p53 protein was observed in SAOS-MC10, while SAOS-MC11 and SAOS-MC43 produced p53 protein. The molecular weight of p53 protein in SAOS-MC43 was lower than that in SAOS-MC11, SAOS-MC11 and SAOS-MC43 were more sensitive and more resistant, respectively, to ionizing radiation than the parental SAOS-2. We suggest that exogenous p53 protein might be one of the factors determining cellular radiosensitivity.

Enhancement of beta-galactosidase gene expression in rat pheochromocytoma cells by exposure to extremely low frequency magnetic fields

Exposure of PC12-VG cells to an extremely low frequency magnetic field (ELFMF) enhanced the beta-galactosidase gene expression stimulated by treatment of the cells with forskolin. The enhancing effect of the ELFMF was inhibited by treatment of the cells with a specific inhibitor of PKC, calphostin C, as well as with the Ca2+ entry blockers nifedipin and dantrolen. Enhancement appeared within the first hour of a 4h forskolin treatment when the ELFMF was given at different times during culture. We speculate that exposure of PC12-VG cells to an ELFMF during the early response to forskolin treatment affects cell signal transduction, resulting in enhanced gene expression.

Correlation of (6-4)photoproduct formation with transforming mutations in UV-irradiated Ha-ras

Sites and types of mutations in relation to the amount of cyclobutane pyrimidine dimers (CPDs) and (6-4)-photoproducts in UV-irradiated normal Ha-ras sequences were investigated. Mouse BALB/C 3T3 cells were transfected with UV-irradiated pYN-mHras plasmids containing mouse normal Ha-ras sequences, and transformed foci developed. Direct DNA sequencing of the Ha-ras retrieved from the foci revealed that most mutations (23/24, 96%) took place at dipyrimidine sequences, and the C-->T transition at the 3'-cytosine in 5'-TC or 5'-CC sequences was predominant (17/24, 71%) in codons 12, 13 and 60. In codon 61, where 5'-TC or 5'-CC is absent, two mutations were found at the 5'-TT sequence. More (6-4)photoproducts were produced than CPDs in codons 12, 13 and 60, and more CPDs were produced than (6-4)photoproducts in codon 61. These results suggest that (6-4)photoproducts are the major lesion leading to the mutations in the mouse Ha-ras sequence and subsequent transformation of BALB/C 3T3 cells.

Vasoactive intestinal peptide gene expression in the rat pheochromocytoma cell line PC12

Vasoactive intestinal peptide (VIP) gene expression was analyzed in PC12 cells. VIP mRNA was detected in PC12 cells treated with VIP or forskolin whereas no VIP mRNA was detected in the untreated cells. The induction of the VIP mRNA was enhanced by the simultaneous treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). PC12 cells stimulated with forskolin plus TPA released immunoreactive VIP. Sephadex G-50 column chromatography revealed that the immunoreactive VIP secreted from PC12 cells is comprised of multiple forms, one of which was indistinguishable from the authentic VIP. PC12 cells supported an efficient transcription from the human VIP gene promoter in a cell-specific as well as cAMP-dependent manner. These results definitely demonstrated the expression of the VIP gene in PC12 cells. VIP biosynthesis may be positively regulated by VIP in an autocrine fashion in PC12 cells.