Osmotic shock induces G1 arrest through p53 phosphorylation at Ser33 by activated p38MAPK without phosphorylation at Ser15 and Ser20

Osmotic shock induced transient stabilization of p53, possibly due to increased degradation of Mdm2. Stabilized p53 was activated by p38(MAPK), resulting in G(1) arrest through induction of p21(WAF1). Among the postulated phosphorylation sites involved in p53 stabilization or activation (Ser(15), Ser(20), Ser(33), and Ser(46)), only Ser(33) was phosphorylated. Furthermore, interaction of p53 with the transcriptional coactivator p300 was induced, and Lys(382) of p53 was acetylated. Although inhibition of p38(MAPK) did not prevent nuclear accumulation of p53, phosphorylation of Ser(33) was markedly suppressed by SB203580, a specific inhibitor of p38(MAPK). Under these conditions, acetylation of Lys(382) and induction of p21(WAF1) were also inhibited, and cells with elevated levels of p53 showed normal cell cycle progression. Activated p38(MAPK) phosphorylated endogenous p53 at Ser(33) in living cells. In stable transformants expressing dominant negative MKK6, an upstream protein kinase of p38(MAPK), p53 stabilization was induced normally following osmotic shock, but phosphorylation of Ser(33), acetylation of Lys(382), and induction of p21(WAF1) were almost completely inhibited. These results suggest that phosphorylation at Ser(33) by p38(MAPK) is critical for activation of p53 following osmotic shock. Phosphorylation of neither Ser(15) nor Ser(20) was needed in this activation.

Characterization and tumorigenicity of human ovarian surface epithelial cells immortalized by SV40 large T antigen

OBJECTIVES

Epithelial ovarian cancers are considered to arise from neoplastic transformation of the ovarian surface epithelium (OSE). However, the earliest events in ovarian carcinogenesis have not been clearly defined because patients are often diagnosed in the advanced stages and useful in vivo and in vitro experimental systems using human OSE cells are lacking. We aimed to improve the availability of experimental models for the study of human ovarian carcinogenesis.

METHODS

Subcultured human OSE cells were transfected with SV40 large T antigen. Resulting OSE cell lines were characterized using immunocytochemistry and tested tumorigenicity.

RESULTS

Six immortalized OSE cell lines were obtained. All cell lines essentially retained the original morphological features of normal OSE cells and showed higher proliferation rates and saturation density. Although they were all nontumorigenic in athymic mice, OSE2b-2 sv cells, which were selected in soft agar from colonies of an SV40 large T antigen-expressing transfectant, OSE2b sv, produced tumors on the peritoneal surface, mesothelium, and diaphragm and induced ascites after being injected intraperitoneally. Solid tumors also grew when mice were inoculated subcutaneously. The tumor cells were formed in a solid sheet arrangement and no evidence of glandular or squamous differentiation was present. They were weakly immunostained with an antibody against cytokeratin, and intercellular junctions resembling attachment devices were ultrastructurally present between cells. The tumors were histologically diagnosed as undifferentiated carcinomas.

CONCLUSIONS

The established cell lines may provide a model system to investigate the mechanisms of cytogenic and molecular changes from normal OSE cells through the various steps of transformation.

Xeroderma pigmentosum variant heterozygotes show reduced levels of recovery of replicative DNA synthesis in the presence of caffeine after ultraviolet irradiation

Patients with xeroderma pigmentosum variant show clinical photosensitivity, skin neoplasias induced by ultraviolet light, and defective postreplication repair, but normal nucleotide excision repair. We recently reported an alternative, simple method for the diagnosis of xeroderma pigmentosum variant that measures by autoradiography three cellular markers for DNA repair after ultraviolet irradiation: unscheduled DNA synthesis, recovery of RNA synthesis, and recovery of replicative DNA synthesis. Among hereditary photosensitive disorders, including other xeroderma pigmentosum groups, Cockayne syndrome, and a newly established ultraviolet-sensitive syndrome, only xeroderma pigmentosum variant cells exhibited normal unscheduled DNA synthesis, normal recovery of RNA synthesis, but reduced recovery of replicative DNA synthesis (51 +/- 6% the rate relative to normal controls). This reduction of recovery of replicative DNA synthesis was enhanced in the presence of a nontoxic level of caffeine to 36 +/- 5%. In this study we assess the cellular markers in two independent families that included two photosensitive patients that were identified as xeroderma pigmentosum variant. Cells from heterozygotic parents showed normal levels of unscheduled DNA synthesis, recovery of RNA synthesis, and recovery of replicative DNA synthesis, but reduced rates of recovery of replicative DNA synthesis in the presence of 1 mM caffeine (53 +/- 8% relative to the normal control). Furthermore, with a colony-forming assay, the cells showed normal survival by ultraviolet without caffeine, but slightly reduced survival by ultraviolet with 1 mM caffeine present. In one family, we confirmed inheritance of two heterozygous mis-sense mutations. One mutation is an A-->G transition at nucleotide 1840 that generates a K535E mis-sense mutation. Another mutation is an A-->C transversion at nucleotide 2003 that generates a K589 mis-sense mutation. Each of these mutations were absent in 52 unrelated Japanese individuals. These results suggest that xeroderma pigmentosum variant heterozygotes can be identified by their sensitivity to ultraviolet irradiation in the presence of nontoxic levels of caffeine.

Human damage-specific DNA-binding protein p48. Characterization of XPE mutations and regulation following UV irradiation

Damage-specific DNA binding (DDB) activity purifies from HeLa cells as a heterodimer (p127 and p48) and is absent from cells of a subset (Ddb(-)) of xeroderma pigmentosum Group E (XPE) patients. Each subunit was overexpressed in insect cells and purified. Both must be present for the damaged DNA band shift characteristic of the HeLa heterodimer. However, overexpressed p48 peptides containing the mutations found in three Ddb(-) XPE strains are inactive, and wild type p48 restores DDB activity to extracts from a fourth XPE Ddb(-) strain, GM01389, in which compound heterozygous mutations in DDB2 (p48) lead to a L350P change from one allele and a Asn-349 deletion from the other. Although these results indicate that these mutations are each responsible for the loss of DDB activity, they do not affect nuclear localization of p48. In normal fibroblasts, a 4-fold increase in p48 mRNA amount was observed 38 h after UV irradiation, preceding a similar elevation in p48 protein and DDB activity at 48 h, implying that p48 limits DDB activity in vivo. Because DNA repair is virtually complete before 48 h, a role for DDB other than DNA repair is suggested.

Dysfunction of human Rad18 results in defective postreplication repair and hypersensitivity to multiple mutagens

Postreplication repair functions in gap-filling of a daughter strand on replication of damaged DNA. The yeast Saccharomyces cerevisiae Rad18 protein plays a pivotal role in the process together with the Rad6 protein. Here, we have cloned a human homologue of RAD18, hRAD18. It maps on chromosome 3p24-25, where deletions are often found in lung, breast, ovary, and testis cancers. In vivo, hRad18 protein binds to hHR6 protein through a conserved ring-finger motif. Stable transformants with hRad18 mutated in this motif become sensitive to UV, methyl methanesulfonate, and mitomycin C, and are defective in the replication of UV-damaged DNA. Thus, hRAD18 is a functional homologue of RAD18.

Reinvestigation of the classification of five cell strains of xeroderma pigmentosum group E with reclassification of three of them

Xeroderma pigmentosum is a photosensitive syndrome caused by a defect in nucleotide excision repair or postreplication repair. Individuals of xeroderma pigmentosum group E (xeroderma pigmentosum E) have a mild clinical form of the disease and their cells exhibit a high level of nucleotide excision repair as measured by unscheduled DNA synthesis, as well as biochemical heterogeneity. Cell strains from one group of xeroderma pigmentosum E patients have normal damage-specific DNA binding activity (Ddb+), whereas others do not (Ddb-). Using a refinement of a previously reported cell fusion complementation assay, the previously assigned Ddb+ xeroderma pigmentosum E strains, XP89TO, XP43TO, and XP24KO, with various phenotypes in DNA repair markers, were reassigned to xeroderma pigmentosum group F, xeroderma pigmentosum variant, and ultraviolet-sensitive syndrome, respectively. The Ddb- xeroderma pigmentosum E strains, XP82TO, and GM02415B, which showed almost normal cellular phenotypes in DNA repair markers, however, remained assigned to xeroderma pigmentosum group E. With the exception of the Ddb+ strain XP89TO, which demonstrated defective nucleotide excision repair, both Ddb- and Ddb+ xeroderma pigmentosum E cells exhibited the same levels of variation in unscheduled DNA synthesis that were seen in normal control cells. By genome DNA sequencing, the two Ddb- xeroderma pigmentosum E strains were shown to have mutations in the DDB2 gene, confirming previous reports for XP82TO and GM02415B, and validating the classification of both cells. As only the Ddb- strains investigated remain classified in the xeroderma pigmentosum E complementation group, it is feasible that only Ddb- cells are xeroderma pigmentosum E and that mutations in the DDB2 gene are solely responsible for the xeroderma pigmentosum E group.

UVs syndrome: establishment and characterization of fibroblastic cell lines transformed with simian virus 40 DNA

Ultraviolet-sensitive syndrome (UVsS) is a newly established photosensitive disorder. Patients with UVsS showed mild clinical manifestations similar to classical types of xeroderma pigmentosum, and had biochemical phenotypes of Cockayne syndrome but not those of xeroderma pigmentosum. Fibroblasts from a UVsS patient were treated with simian virus 40 DNA containing the large T antigen with a defective origin of DNA replication to establish a transformed cell line. We obtained two independent transformed cell lines (Kps3SVY and Kps3SVI3) and report their initial characterization. These cells showed the same pattern in variable number of tandem repeat analyses as a primary fibroblast cell strain, Kps3, and retain the UVsS phenotype as demonstrated by increased UV sensitivity (three to four times more sensitive to UV than normal cells) and by reduced recovery of RNA synthesis after UV irradiation (20% - 30% of that of normal cells). These cells, however, showed different phenotypes as regards plating efficiency, doubling time, and transfection efficiency in spite of the fact that the same method was used to transform the cells. Kps3SVY cells were closer in phenotype to Kps3 cells than Kps3SVI3 cells. As a variable number of tandem repeat analyses also showed that Kps3SVI3 cells have lost one of the two alleles in some chromosomes, this may explain the different phenotypes between Kps3SVY and Kps3SVI3 cells. Moreover, these cells were distinct from cells with Cockayne syndrome group A or B. Thus, these cell lines provide the opportunity to conduct transfection studies on cells with the UVsS defect in DNA repair and transcription.

A newly identified patient with clinical xeroderma pigmentosum phenotype has a non-sense mutation in the DDB2 gene and incomplete repair in (6-4) photoproducts

We report here a patient (Ops1) with clinical photosensitivity, including pigmented or depigmented macules and patches, and multiple skin neoplasias (malignant melanomas, basal cell carcinomas, and squamous cell carcinomas in situ) in sun-exposed areas. These clinical features are reminiscent of xeroderma pigmentosum. As cells from Ops1 showed normal levels in DNA repair synthesis in vivo (unscheduled DNA synthesis and recovery of RNA synthesis after ultraviolet irradiation), we performed a postreplication repair assay and recovery of replicative DNA synthesis after ultraviolet irradiation to investigate if Ops1 cells belonged to a xeroderma pigmentosum variant pattern. Ops1 cells were normal, but there was an incomplete pattern repair in (6-4) photoproducts in contrast to a normal pattern repair in cis-syn cyclobutane pyrimidine dimers by repair kinetics using the enzyme-linked immunosorbent assay. Moreover, Ops1 cells were defective in a damage-specific DNA binding protein and carried a non-sense mutation in the DDB2 gene. These results suggest that (i) the DDB2 gene is somewhat related to skin carcinogenesis, photoaging skin, and the removal of (6-4) photoproducts; (ii) although it is believed that cyclobutane pyrimidine dimers are the principal mutagenic lesion and (6-4) photoproducts are less likely to contribute to ultraviolet-induced mutations in mammals, Ops1 is one of the ultraviolet-induced mutagenic models induced by (6-4) photoproducts.

Topostatin, a novel inhibitor of topoisomerases I and II produced by Thermomonospora alba strain No. 1520. III. Inhibitory properties

A novel inhibitor of topoisomerases designated as topostatin was isolated from the culture filtrate of Thermomonospora alba strain No. 1520. The inhibitory activity of topostatin was shown to be pH- and temperature-dependent with a maximum around at pH 6 and 28 degrees C. The stability of topostatin decreased with decreasing pH and rising temperature. Topostatin inhibited topoisomerases I and II in a competitive manner with respect to DNA. The inhibitor also inhibited some restriction endonucleases such as Sca I, Hind III and Pst I, but not Alu I, Bam HI, Eco RI, RNase A, DNase I, DNase II and DNA ligase. Topostatin did not induce the nuclear accumulation of p53 protein by DNA damage in the normal human cells.

Requirement of ATM in phosphorylation of the human p53 protein at serine 15 following DNA double-strand breaks

Microinjection of the restriction endonuclease HaeIII, which causes DNA double-strand breaks with blunt ends, induces nuclear accumulation of p53 protein in normal and xeroderma pigmentosum (XP) primary fibroblasts. In contrast, this induction of p53 accumulation is not observed in ataxia telangiectasia (AT) fibroblasts. HaeIII-induced p53 protein in normal fibroblasts is phosphorylated at serine 15, as determined by immunostaining with an antibody specific for phosphorylated serine 15 of p53. This phosphorylation correlates well with p53 accumulation. Treatment with lactacystin (an inhibitor of the proteasome) or heat shock leads to similar levels of p53 accumulation in normal and AT fibroblasts, but the p53 protein lacks a phosphorylated serine 15. Following microinjection of HaeIII into lactacystin-treated normal fibroblasts, lactacystin-induced p53 protein is phosphorylated at serine 15 and stabilized even in the presence of cycloheximide. However, neither stabilization nor phosphorylation at serine 15 is observed in AT fibroblasts under the same conditions. These results indicate the significance of serine 15 phosphorylation for p53 stabilization after DNA double-strand breaks and an absolute requirement for ATM in this phosphorylation process.

High sensitivity of the ultraviolet-induced p53 response in ultraviolet-sensitive syndrome, a photosensitive disorder with a putative defect in deoxyribonucleic acid repair of actively transcribed genes

Previously, we reported a new category of photosensitive disorder named ultraviolet-sensitive syndrome (UVs S) [T. Itoh, T. Fujiwara, T. Ono, M. Yamaizumi, UVs syndrome, a new general category of photosensitive disorder with defective DNA repair, is distinct from xeroderma pigmentosum variant and rodent complementation group 1, Am. J. Hum. Genet. 56 (1995) 1267-1276.]. Cells derived from these patients show impaired recovery of RNA synthesis (RRS) after UV-irradiation irrespective of having a normal level of unscheduled DNA synthesis (UDS). These characteristics are reminiscent of Cockayne syndrome (CS) cells. By comparing sensitivity of the UV-induced p53 response in cells with different types of defects in nucleotide excision repair, we hypothesized that the UV-induced p53 response is triggered by inhibition of RNA synthesis [M. Yamaizumi, T. Sugano, UV-induced nuclear accumulation of p53 is evoked through DNA damage of actively transcribed genes independent of the cell cycle, Oncogene 9 (1994) 2775-2784.]. To test this hypothesis, we determined sensitivity of the p53 response in UVs S cells by immunostaining, Western blotting, and FACScan analysis. Maximal nuclear accumulation of p53 in the UVs S cells was observed with a one-third UV dose required for that in normal cells, while almost identical p53 responses were observed in UVs S and normal cells following treatment with heat or alpha-amanitin. Recovery of RNA synthesis after a low dose of UV-irradiation was impaired in UVs S cells to the same extent as seen in CS cells. These results provide further evidence to support our previous hypothesis regarding the mechanism of the p53 response induced by DNA damage.

Cell cycle control is aberrant in Chinese hamster ovary cell mutants exhibiting apoptosis after serum deprivation

We isolated mutants of Chinese hamster ovary cells that exhibit excessive apoptosis after serum deprivation. In the medium containing 10% serum, the growth rates of the mutants were 1.4 to 1.5-fold faster than those of wild-type cells. Whereas the cell cycle of wild-type cells was arrested at the G1 phase after serum deprivation, the cell cycle of the mutant cells was not fully arrested at this phase, suggesting that cell cycle regulation was disorganized in the mutants. The mutants were highly sensitive to a nucleotide-analogue 5-fluorouracil in the absence of serum, whereas wild-type cells were resistant to the drug. Based on the sensitivity to the drug after serum deprivation, we could classify the mutants into dominant groups and at least two recessive complementation groups. Thus, these mutants presumably contain different lesions in gene(s) required for cell cycle regulation and apoptosis.

Heat shock induces transient p53-dependent cell cycle arrest at G1/S

Heat shock (43 degrees C, 45 min) induced transient nuclear accumulation of p53 in primary human fibroblasts without any clonogenically toxic effects. The accumulation of p53 reached a maximal level 3 approximately 5 h after heat shock, and returned to the basal level within 12 h. Following the increase in p53 level, cell cycle arrest at G1/S was observed in normal fibroblasts, whereas neither nuclear accumulation of p53 nor cell cycle arrest were observed in HeLa cells. By comparing cell cycle patterns of heat-treated mouse cells with different genotypes at the p53 locus (+/+, +/-, -/-), the observed cell cycle arrest at G1/S was demonstrated to be p53-dependent. Cell cycle arrest in normal human fibroblasts continued for nearly 24 h, resulting in a one day delay of cell growth compared with non-treated cells. Following enhancement of the p53 level, the amount of p21/WAF1/ CIP1 increased, and the high level of p21 was sustained for almost one day in a cell cycle-independent manner, suggesting the involvement of p21 in the inhibition of cell cycle progression by heat shock.

Visualization of mitochondrial protein import in cultured mammalian cells with green fluorescent protein and effects of overexpression of the human import receptor Tom20

The presequence of the ornithine transcarbamylase precursor (pOTC) was fused to green fluorescent protein (GFP), yielding pOTC-GFP and pOTCN-GFP containing the presequence plus 4 and 58 residues of mature ornithine transcarbamylase, respectively. When GFP cDNA was transfected into COS-7 cells, the cytosol and nucleus were fluorescent. On the other hand, pOTC-GFP cDNA gave strong fluorescence of a unique mitochondrial pattern. After fractionation of cells expressing pOTC-GFP with digitonin, fluorescence was recovered mostly in the particulate fraction. Immunoblot analysis showed that processed GFP was present in the particulate fraction, whereas pOTC-GFP was recovered in both the soluble and particulate fractions. pOTC-GFP and pOTCN-GFP synthesized in vitro were imported efficiently into the isolated mitochondria. Single and triple amino acid mutations in the presequence resulted in impaired mitochondrial import and in a loss of mitochondrial fluorescence. Perinuclear aggregation of fluorescent mitochondria was observed when the human mitochondrial import receptor Tom20 (hTom20) was coexpressed with pOTC-GFP. Overexpression of hTom20 (not DeltahTom20, which lacks the anchor sequence) resulted in stimulated mitochondrial import of pOTC-GFP in COS-7 cells. When pOTC-GFP cDNA was microinjected into nuclei of human fibroblast cells, mitochondrial fluorescence was detected as early as 2-3 h after injection. These results show that GFP fusion protein can be used to visualize mitochondrial structures and to monitor mitochondrial protein import in a single cell in real time.

A simple method for diagnosing xeroderma pigmentosum variant

Patients with xeroderma pigmentosum variant have been diagnosed based on a post-replication repair assay using their cells together with their clinical manifestations. We present here an alternative simple method for the diagnosis of xeroderma pigmentosum variant that measures three cellular markers for DNA repair by autoradiography, unscheduled DNA synthesis, recovery of RNA synthesis, and recovery of replicative DNA synthesis after ultraviolet irradiation. Fibroblasts from a patient are plated on three coverslips parallel with normal cells (control). Unscheduled DNA synthesis, recovery of RNA synthesis, and recovery of replicative DNA synthesis after ultraviolet irradiation in the patient's cells are compared with those of adjacent normal cells by counting numbers of grains on nuclei for each coverslip. Of the hereditary photosensitive disorders including xeroderma pigmentosum, Cockayne syndrome, and newly established ultraviolet-sensitive syndrome, only xeroderma pigmentosum variant cells exhibit normal unscheduled DNA synthesis, normal recovery of RNA synthesis, but reduced recovery of replicative DNA synthesis (approximately 50% of that of control cells). This reduction of DNA synthesis is enhanced in the presence of caffeine. Because each disorder yields a different combination of these three markers, this method also provides a systematic basis for the diagnosis of these diseases.

Roles of XPG and XPF/ERCC1 endonucleases in UV-induced immunostaining of PCNA in fibroblasts

To investigate the relationship between proliferating cell nuclear antigen (PCNA) complex formation and dual incisions in the nucleotide excision repair (NER) process, xeroderma pigmentosum group G (XP-G), XP-F, and XP-G equivalent mouse UV-sensitive mutant ERCC group 5 cells were utilized as a model in this study. These cells are deficient in endonucleases related to 3' (XP-G and ERCC group 5) or 5' (XP-F) incision of the DNA lesions in the NER process. PCNA complex formation was detected by an indirect immunofluorescence method after the cells were fixed in methanol. When Sps1 (XP-G) and XL216-7 (ERCC group 5) cells were UV irradiated, neither of them showed PCNA staining. In contrast, SFN4 (a human normal strain) and heterokaryons of Sps1 and XP96TO (XP-A) cells fused by polyethylene glycol treatment showed PCNA staining following UV irradiation. Furthermore, XLgfPAneo1 cells, derived from XL216-7 cells transfected with a plasmid containing mouse ERCC5 (xpg) cDNA, also restored staining and UV sensitivity. On the other hand, we observed a very faint PCNA staining in XP2YO (XP-F) cells, expressing no detectable ERCC1 or XPF protein, after UV irradiation. X rays induced PCNA staining in all cell lines with a similar staining pattern, and radiosensitivity was exactly the same between XL216-7 and XLgfPAneo1 cells. These results may have implications for the NER process in vivo in that coordinately occurring dual incisions by XPG and XPF/ERCC1 proteins play an important role in inducing PCNA complex formation, but the step may not be required for PCNA-dependent repair of X-ray-induced DNA damage.

Clinical characteristics of three patients with UVs syndrome, a photosensitive disorder with defective DNA repair

Recently, we established a new category of photosensitive disorder termed UVs syndrome. Cells from patients with UVs syndrome have a similar UV sensitivity as xeroderma pigmentosum (XP) cells, but have a normal level of unscheduled DNA synthesis (UDS) unlike XP. UVs syndrome is distinct from Cockayne syndrome (CS) or XP including XP variant (XP-V), as determined by studies of genetic factors using cell fusion, microinjection, and postreplication repair assays. In this study, we identified three Japanese patients with UVs syndrome: an 11-year-old girl, a 17-year-old male, and an 8-year-old boy. The first two patients were siblings, while the third was a case from a different family. All of these patients exhibited acute recurrent sunburn. Common clinical manifestations of these patients were slight erythema and dryness, a number of freckles on sun-exposed areas, and slight telangiectasia only seen on the cheek and nose. Patient 3 showed a lowered minimal erythema dose between 280 and 300 nm. The patients' fibroblasts showed similar characteristics to those in CS, such as UV sensitivity, and a failure of RNA synthesis (RRS) after UV irradiation, despite a normal level of UDS. Thus, UVs syndrome is a new hereditary photosensitive disorder with clinical manifestations similar to a mild form of XP but showing the cellular characteristics of CS.

Rodent complementation group 8 (ERCC8) corresponds to Cockayne syndrome complementation group A

US31 is a UV-sensitive mutant cell line (rodent complementation group 8) derived from a mouse T cell line L5178Y. We analyzed removal kinetics for UV-induced cyclobutane pyrimidine dimers and (6-4) photoproducts in US31 cells using monoclonal antibodies against these photoproducts. While nearly all (6-4) photoproducts were repaired within 6 h after UV-irradiation, more than 70% of cyclobutane pyrimidine dimers remained unrepaired even 24 h after UV-irradiation. These kinetics resembled those of Cockayne syndrome (CS) cells. Since US31 cells had a low efficiency of cell fusion and transfection, which hampered both complementation tests and gene cloning, we constructed fibroblastic complementation group 8 cell line 6L1030 by fusion of US31 cells with X-irradiated normal mouse fibroblastic LTA cells. Complementation tests by cell fusion and transfection using 6L1030 cells revealed that rodent complementation group 8 corresponded to CS complementation group A.

Cockayne syndrome complementation group B associated with xeroderma pigmentosum phenotype

Two siblings have been reported whose clinical manifestations (cutaneous photosensitivity and central nervous system dysfunction) are strongly reminiscent of the DeSanctis-Cacchione syndrome (DCS) variant of xeroderma pigmentosum (XP), a severe form of XP. Fibroblasts from the siblings showed UV sensitivity, a failure of recovery of RNA synthesis (RRS) after UV-irradiation, and a normal level of unscheduled DNA synthesis (UDS), which were, unexpectedly, the biochemical characteristics usually associated with Cockayne syndrome (CS). However, no complementation group assignment in these cells has yet been performed. We here report that these patients can be assigned to CS complementation group B (CSB) by cell fusion complementation analysis. To our knowledge, these are the first patients with defects in the CSB gene to be associated with an XP phenotype. The results imply that the gene product from the CSB gene must interact with the gene products involved in excision repair and associated with XP.

Separation of protein factors that correct the defects in the seven complementation groups of xeroderma pigmentosum cells

We fractionated HeLa cell extracts by gel filtration and then micro-injected them into cells derived from the seven complementation groups (A-G) of xeroderma pigmentosum (XP). Distinct fractions that corrected the unscheduled DNA synthesis (UDS) of the complementation group XP cells were identified. The apparent molecular weights corresponding to complementation groups A, B, C, D, E, F, and G were estimated to be 80, 600, 600, 240, 100, 240, and 280 kDa, respectively. These factors were stable in the respective cell lines, the shortest half life being 16 h for the XP-A and XP-G complementing factors. The fraction (80 kDa) that corrected the UDS in XP-A cells also complemented the defect of the XP-A cell extract in the incision of DNA containing a pyrimidine dimer in a cell-free system. The separated fractions will be useful for understanding the molecular nature of these factors and for assigning complementation groups of cells derived from suspected XP patients.

UVs syndrome, a new general category of photosensitive disorder with defective DNA repair, is distinct from xeroderma pigmentosum variant and rodent complementation group I

Previously, we reported two DNA repair-defective siblings who did not belong to any complementation group of xeroderma pigmentosum (XP) or Cockayne syndrome (CS). By surveying other photosensitive patients whose fibroblasts showed similar biochemical phenotypes, we found another nonconsanguineous Japanese patient belonging to the same complementation group as our previous cases. Postreplication repair of the cells derived from these patients was normal, indicating that they cannot be classified as XP variant. Neither transfection nor microinjection of the cells with the human DNA repair gene ERCC1, which is known not to correct any complementation groups of XP or CS, failed to correct the defect of these cells, indicating that they do not belong to the rodent complementation group 1. However, the defect in recovery of RNA synthesis (RRS) after UV irradiation was restored by microinjection of HeLa cell extract. Although clinical manifestations of these patients--such as acute sunburn, dryness, freckling, pigmentation anomalies on sun-exposed skin, and teleangiectasia without neurological abnormalities or tumors--are similar to a mild XP phenotype, cellular characteristics such as UV sensitivity and defective RRS after UV irradiation with normal unscheduled DNA synthesis (UDS) are reminiscent of CS. On the basis of these results, we propose that these patients be included under a general category designated "UV-sensitive" (UVs) syndrome.

Group D xeroderma pigmentosum: a case with a number of nevocellular nevi

A 12-year-old boy was diagnosed as having group D xeroderma pigmentosum based on the results of unscheduled DNA synthesis (UDS) tests and complementation tests. More than 200 moles were distributed all over his body, including the unexposed areas of his torso and scalp. All of eight removed specimens were compatible histologically with nevocellular nevi.

Nuclear accumulation of p53 in normal human fibroblasts is induced by various cellular stresses which evoke the heat shock response, independently of the cell cycle

Nuclear accumulation of p53 is induced by various DNA damaging agents (the p53 response). Induction of nuclear accumulation of p53 after various cellular stresses, mostly other than DNA damage, including heat shock, was examined in normal human fibroblasts by immunostaining and flow cytometry using a mouse anti-p53 monoclonal antibody. Immunostaining revealed nuclear accumulation of p53 within 6 h after various stresses [heat shock, osmotic shock, heavy metal (Cd), blockers of the cellular respiratory system (NaN3), amino acid analogues (azetidine and canavanine), an inhibitor of protein synthesis (puromycin), and oxygen free radicals (H2O2)]. Heat shock proved to be one of the most effective inducers among these stresses. FACScan analysis revealed that this induction of p53 occurred regardless of the stage in the cell cycle and that accumulation of cells in G2/M occurred. As all of these stresses are known to induce the heat shock response, the mechanism of p53 induction after stresses and that of heat shock response may share, at least partly, some common signaling pathway(s).

A young woman with xeroderma pigmentosum complementation group F and a morphoeic basal cell carcinoma

We report an 18-year-old Japanese woman who had mild photosensitivity and a facial tumour, which was shown to be a morphoeic basal cell carcinoma. Although a line of fibroblasts derived from the patient, Kps6 cells, were slightly more sensitive to UV irradiation than normal cells, their level of unscheduled DNA synthesis was about 20% that of normal cells, and recovery of RNA synthesis after UV irradiation was moderately depressed. Complementation tests, carried out by cell fusion or by microinjection of plasmids harbouring xeroderma pigmentosum (XP) genes, indicated that the patient had XP group F. To our knowledge, this is the youngest XP group F patient with a malignant tumour reported to date.

U.v.-induced nuclear accumulation of p53 is evoked through DNA damage of actively transcribed genes independent of the cell cycle

Induction of p53 in u.v.-irradiated primary human fibroblasts was monitored by immunostaining and Western blotting. Minimum u.v. doses required for induction of nuclear accumulation of p53 (minimum response dose: MRD) were estimated in various cells with different DNA repair capacities. The MRD in repair deficient xeroderma pigmentosum (XP) group A cells is eightfold lower than in normal cells, indicating that nuclear accumulation of p53 is related to DNA repair capacity. Cells from patients with another u.v.-sensitive disorder, Cockayne syndrome (CS), which have normal repair capacity for the overall genome but have a specific defect in preferential repair of lesions in active genes, have the same low MRD as of XP-A cells. Furthermore, the MRD in XP-C cells, which have normal preferential repair but have defects in overall genome repair, is as high as that of normal cells. DNA damage induced by X-ray is repaired at similar rates in normal, XP and CS cells. In contrast to u.v.-irradiation, the minimum dose of X-rays that induces nuclear accumulation of p53 is the same in these cells. Inhibition of transcription with alpha-amanitin evokes nuclear accumulation of p53 both in normal cells and in XP cells. These results strongly suggest that u.v.-induced nuclear accumulation of p53 is evoked through DNA damage of actively transcribed genes. Nuclear accumulation of p53 is observed in any phase of the cell cycle at both low and high u.v. doses.

A new UV-sensitive syndrome not belonging to any complementation groups of xeroderma pigmentosum or Cockayne syndrome: siblings showing biochemical characteristics of Cockayne syndrome without typical clinical manifestations

We report here on two siblings who show no clinical manifestations except for slight cutaneous photosensitivity and cutaneous pigmentation but have biochemical characteristics of Cockayne syndrome (CS). Fibroblasts derived from the patients (Kps2 and Kps3) were 3-4 times more sensitive to UV than normal cells. Although unscheduled DNA synthesis (UDS) in these cells was at a normal level, recovery of RNA synthesis (RRS) after UV irradiation was severely depressed. Microinjection of bacteriophage T4 endonuclease V into the cells corrected RRS after UV irradiation to a level near normal. These results indicate that DNA repair of cyclobutane-type pyrimidine dimers is impaired in the cells and the biochemical characteristics are similar to those of CS cells. However, cell fusion complementation tests with CS group A and B cells resulted in correction of RRS after UV irradiation. Cell fusion with XP group A, B, D, F and G cells also corrected RRS after UV irradiation, and microinjection of cell extracts prepared from Kps3 cells corrected UDS in XP group C and E cells, indicating that the patients do not belong to any complementation group of XP or CS. These results suggest that the patients have a new UV-sensitive syndrome with a biochemical phenotype of CS.

An ERCC5 gene with homology to yeast RAD2 is involved in group G xeroderma pigmentosum

We have isolated a human excision repair gene ERCC5 which complements the defect of the mouse UV-sensitive mutant XL216 (rodent complementation group 5). Here we report cDNA cloning of human and mouse ERCC5 genes using an exon containing an ERCC5 fragment as a probe. The ERCC5 cDNA encodes a predicted 133-kDa nuclear protein that shares some homology with the product of the yeast DNA repair gene RAD2. Transfection with mouse ERCC5 cDNA restored normal levels of UV resistance to XL216 cells. Microinjection of ERCC5 cDNA specifically restored the defect of xeroderma pigmentosum group G cells (XP-G) as measured by unscheduled DNA synthesis, and XP-G cells stably transformed with ERCC5 cDNA showed nearly normal UV resistance.

Complementation of xeroderma pigmentosum cells by microinjection of mRNA fractionated under denaturing conditions: an estimation of sizes of XP-E and XP-G mRNA

Excision repair deficiencies in groups A and G xeroderma pigmentosum (XP) cells are transiently complemented after microinjection of HeLa poly(A)+RNA, but those in groups D and F are not complemented (Legerski et al., 1984). We tested XP cells belonging to the seven complementation groups, A-G, and Cockayne's syndrome (CS) cells belonging to the two complementation groups, A and B, for transient correction by microinjection of total poly(A)+RNA from HeLa cells. Among the XP cells, unscheduled DNA synthesis (UDS) was increased only in XP-A cells by microinjection of total poly(A)+RNA. However, UDS was increased in XP-E and XP-G cells as well as in XP-A cells by microinjection of concentrated poly(A)+RNA fractionated on a 5-25% sucrose density gradient containing methylmercuric hydroxide. The sizes of XP-E and XP-G mRNA were estimated to be 1.5-2.7 kb and 2.0-3.8 kb, respectively, by comparison to internal marker RNAs including 18S rRNA, 28S rRNA, HPRT mRNA and XPAC mRNA. RNA synthesis recovery after UV exposure in CS cells was not increased by microinjection of either total poly(A)+RNA or fractionated RNA. These results provide estimates of the sizes of XP-E and XP-G proteins and will facilitate molecular cloning of DNA repair genes, especially of XP-E and XP-G genes.

Human nucleotide excision nuclease incises synthetic double-stranded DNA containing a pyrimidine dimer at the fourth phosphodiester linkage 3' to the pyrimidine dimer

Linear 75mer double-stranded DNA containing a single pyrimidine dimer at a unique site was used to investigate pyrimidine dimer-dependent endonuclease activities from human cells. HeLaS3 cell extract incised the target DNA at the fourth phosphodiester linkage 3' to the pyrimidine dimer. However, incision of the DNA at 5' side of the pyrimidine dimer was not detected. The incision was also detected in cell extracts prepared from other excision repair-proficient cell lines. Incision was detected only on the DNA strand containing a pyrimidine dimer in the presence of poly(dI-dC)-poly(dI- dC) double strand. The reaction required Mg2+ but not ATP. The extract prepared from excision repair-deficient xeroderma pigmentosum (XP) cells belonging to the complementation group A was unable to incise the DNA. Extracts from the complementation groups C, D, and G incised the DNA very weakly at the third phosphodiester linkage 3' to the pyrimidine dimer, a site different from that incised by normal human cell extract. These results suggest that the observed incision reaction is associated with excision repair in human cells.

Identification of a specific protein factor defective in group A xeroderma pigmentosum cells

A protein factor which corrects the defect in xeroderma pigmentosum cells belonging to complementation group A (XP-A cells) was detected in a cell extract prepared from calf thymus. The activity of this factor was measured as the amount of unscheduled DNA synthesis (UDS) reappearing in UV-irradiated XP-A cells after microinjection of the extract. The native molecular mass of this factor was estimated to be 80 kDa by gel-filtration and 25 kDa by glycerol gradient centrifugation. The activity was, however, recovered at a position corresponding to 43 kDa after renaturation on an SDS-PAGE gel. The isoelectric point was determined to be approximately 7.5 by measuring the activity after renaturation on an IEF gel. These values were obtained with a partially purified sample. A spot corresponding to these values was detected on two-dimensional gel electrophoresis with a highly purified sample recovered from an SDS-PAGE gel. The purified protein stimulated UDS specifically in the XP-A cells and endowed the cells with a normal level of UV-resistance. The XP-A cells injected with the factor also showed a normal level of UDS after treatment with either 4HAQO or psoralen plus UV-A. This factor (XP-A complementing factor; XP-ACF) may be involved in the repair of DNA damage induced by various agents.

Microinjection of T4 endonuclease V produced by a synthetic denV gene stimulates unscheduled DNA synthesis in both xeroderma pigmentosum and normal cells

A structural gene for T4 endonuclease V was constructed by ligating synthetic oligonucleotides. The endonuclease V was overproduced in E. coli under control of the E. coli tryptophan promoter and purified to apparent homogeneity. The product had comparable DNA glycosylase and apurinic/apyrimidinic (AP) endonuclease activities to the natural enzyme in vitro. When this endonuclease V was microinjected into the cytoplasm of xeroderma pigmentosum (XP) cells of complementation group A, B, C, D, F, G or H, unscheduled DNA synthesis (UDS) above the residual level was detected in all the cells at a dose of about 10(3) molecules following UV irradiation. The gain numbers of UDS in these XP cells increased with increase in the dose of enzyme and reached a plateau at the normal cell level on introduction of about 10(4) molecules. Introduction of more enzyme into either XP cells or normal human cells did not increase the grain number under regular labelling conditions (2.5 h, 37 degrees C). In normal mouse cells, introduction of the enzyme increased the grain number more than 4-fold under the same conditions during at least 8.5 h following UV irradiation. Furthermore, with a labelling time of 30 min, the enzyme more than doubled the grain number even in normal human cells.

Reversible inhibition of protein import into the nucleus by wheat germ agglutinin injected into cultured cells

The importance of glycoproteins located in the nuclear envelope in nuclear transport was tested by microinjection of karyophilic proteins into the cytoplasm of cultured human cells together with various lectins. Wheat germ agglutinin (WGA) blocked the nuclear transport of nucleoplasmin, a nuclear protein of Xenopus laevis oocytes, and of nonnuclear proteins conjugated with a synthetic peptide containing the nuclear localization signal sequence for simian virus 40 (SV40) large T antigen. Its inhibitory activity persisted for about 1 h after its injection into the cells and then gradually decreased. Export of at least some kinds of RNA from the nucleus seemed not to be affected by WGA even when import of the proteins into the nucleus was completely blocked (within 1 h after WGA injection). Moreover, WGA did not inhibit the passive diffusion of fluorescein isothiocyanate (FITC)-dextran (average Mr 17,900) into the nucleus. Wistaria floribunda agglutinin (WFA), concanavalin A (Con A), and lentil lectin did not block nuclear transport. These results indicate that WGA specifically blocks active protein import, but not passive diffusion of materials into the nucleus.

Microinjection of partially purified protein factor restores DNA damage specifically in group A of xeroderma pigmentosum cells

Microinjection of cell extracts prepared from both human placenta and HeLa cells into xeroderma pigmentosum (XP) cells of complementation group A restores unscheduled DNA synthesis (UDS) in these cells after UV irradiation [de Jonge, A., Vermeulen, W., Klein, B. & Hoeijmakers, J. (1983) EMBO J. 2, 637-641]. These cells also showed normal resistance to UV irradiation. The half-life of the factors in the cell extracts corresponding to the UDS activity (factor A) was 14 hr in XP cells of group A, and the maximal level of UDS was exerted 2 hr after microinjection. The factors were sensitive to protease treatment but not to RNase treatment and were found to be approximately equal to 160 and approximately equal to 90 kDa by gel filtration. These two fractions of the factor(s) acted specifically in XP cells of complementation group A among complementation groups A, B, C, D, F, G, and probably E and H.

Expression and stabilization of microinjected plasmids containing the herpes simplex virus thymidine kinase gene and polyoma virus DNA in mouse cells

To observe the effects of polyoma virus DNA on the expression of the herpes simplex virus (HSV) thymidine kinase (TK) gene early after transfer into TK-deficient mouse cells and the subsequent development of stable TK-positive transformants, we constructed a series of recombinant plasmids containing the herpes simplex virus TK gene joined with various segments of the polyoma virus genome and microinjected them into the nuclei or cytoplasm of LTK-A cells (TK(-), APRT(-)). The frequency of nucleus-injected cells expressing TK after 1 day, measured by autoradiography of cells incubated with [(3)H]thymidine, increased approximately 30-fold when the plasmids contained the polyoma virus origin of replication. The origin includes sequences with homology to the simian virus 40 origin of replication and adjoining sequences, including a recently defined transcription-enhancing sequence. After microinjection of a single origin-containing plasmid molecule per cell, TK expression was detected in approximately 50% of the injected cells. When a larger number of origin-containing plasmid molecules were injected per cell, all cells showed early TK activity. When the entire polyoma virus early region was present, neighboring uninjected cells became TK positive. When plasmids were injected into the cell cytoplasm, approximately 400 times as many molecules per cell were needed to cause early TK activity. The frequency of stable transformation observed 2 weeks after nuclear injection of 10 to 20 polyoma virus origin-containing plasmid molecules per cell was at least 2 orders of magnitude greater than with plasmids containing the TK gene alone. The greatest enhancement of stable TK transformation was obtained with plasmids containing the origin alone, when the maximum frequency of stable transformation was 5%. The addition of the coding regions for the small and medium T antigens or the entire early region significantly decreased TK transformation frequency in a copy-dependent fashion. The timing of stabilization of TK-positive transformation was analyzed by releasing hypoxanthine-aminopterin-thymidine selection pressure at various times after microinjection, culturing the cells in nonselective medium, and assaying for TK activity. Stabilization was found to occur between 3 and 6 days after nuclear injection. Cells injected with a plasmid containing the origin and the early region were examined for expression of the large T antigen with polyoma virus antitumor serum and immunofluorescent staining. The expression of the large T antigen was clearly associated with a cytopathic effect. TK-positive clones observed 2 weeks after injection of the plasmid were uniformly T antigen negative. Cytotoxicity may be the result of plasmid replication and toxic levels of T antigen or TK. In addition, expression of the large T antigen may block stabilization by preventing the integration of origin-containing plasmid molecules.

Partial purification and characterization of the mRNA for human thymidine kinase and hypoxanthine/guanine phosphoribosyltransferase

We used direct microinjection of poly(A)+RNA into individual hypoxanthine/guanine phosphoribosyltransferase-deficient or thymidine kinase-deficient cells and detected the specific in vivo translation products as an assay for human hypoxanthine/guanine phosphoribosyltransferase or thymidine kinase mRNAs. The incorporation of [3H]hypoxanthine or [3H]thymidine into cells in response to injected mRNA was assayed in situ by autoradiography. Methylmercuric hydroxide/agarose gel analysis showed that human hypoxanthine/guanine phosphoribosyltransferase mRNA contains approximately 1,530 nucleotides, which is twice the number required for its protein coding capacity. The mRNA for human cytoplasmic thymidine kinase is estimated to be approximately the same length; thus, the size of the cytosol thymidine kinase subunit can be predicted to be approximately 47,000 daltons, if the full coding capacity of its mRNA is utilized.