Comparative studies of host-cell reactivation, cellular capacity and enhanced reactivation of herpes simplex virus in normal, xeroderma pigmentosum and Cockayne syndrome fibroblasts

Host-cell reactivation (HCR) of UV-irradiated herpes simplex virus type 2 (HSV-2), capacity of UV-irradiated cells to support HSV-2 plaque formation and UV-enhanced reactivation (UVER) of UV-irradiated HSV-2 were examined in fibroblasts from 4 patients with Cockayne syndrome (CS), 5 with xeroderma pigmentosum and 5 normals. All UV-survival curves for HSV-2 plaque formation showed 2 components. HCR was similar to normal for the XP variant strain and the 2 CS strains tested, but substantially reduced in the 4 excision-deficient XP strains. The capacity of UV-irradiated fibroblasts to support HSV-2 plaque formation was determined by UV-irradiating fibroblast monolayers with various doses of UV and 48 h later, infecting the monolayers with unirradiated HSV-2. The D37 values for the delayed-capacity curves so obtained were in the range 8.6-12.4 J/m2 for the normal strains, 2.8-3.2 J/m2 for the CS strains, 6.7 J/m2 for an XP variant strain and between 0.3 and 1.5 for the XP excision-deficient strains tested. These results indicate that delayed capacity for HSV-2 plaque formation is a more sensitive assay than HCR in the detection of cellular DNA-repair deficiency for XP and CS. For the examination of UVER, fibroblasts were irradiated with various UV doses and subsequently infected with either unirradiated or UV-irradiated HSV and scored for plaque formation 2 days later. UVER expression was maximum when the delay between UV-irradiation of the cells and HSV infection was 48 h. The magnitude of UVER expression was also found to be dependent on the UV dose to the cells and increased with increasing UV dose to the virus. Using a UV dose to the virus resulting in a plaque survival of about 10(-2) on unirradiated cells, the the maximum UVER factor had a mean value of 1.3 for the normal strains following a dose of 15 J/m2 to the cells. Somewhat higher UVER values were found for all the patient strains tested and resulted from lower UV doses to the cells than for normal strains. Maximum UVER factors for the CS strains ranged from 2.2 to 3.3 at a dose of 5 J/m2 to the cells, for the XP excision-deficient strains; 2.1 to 2.6 at doses of 0.5 to 2.5 J/m2 to the cells and for the XP variant strain tested; 2.5 at UV dose of 10 J/m2 to the cells.     

Host cell reactivation by excision repair is error-free in human cells

Do host cell repair processes affect the mutagenesis of UV-irradiated virus in human cells? The answer was obtained by investigating the mutagenesis of UV-irradiated herpes simplex virus after the irradiated virus was grown in human cells that possess normal repair capacity (normal) or lack excision repair (XPA) or post-replication repair (XP var). Evidence is presented which indicate that XPA cells express no host cell reactivation, while XP var cells express the normal level. Viral mutagenesis was measured as the fraction of the progeny of the surviving virus capable of plaque formation in the presence of iododeoxycytidine. In the normal and XPA cells mutagenesis of the irradiated virus increased linearly with UV exposure. The UV exposure needed to yield a given mutagenesis level for virus grown in XPA cells was much lower than that for virus grown in normal cells. However, when the mutation frequencies were compared at similar virus survival levels, the data from virus grown in normal cells and in XPA cells were indistinguishable. Mutagenesis in XP var cells increased as dose squared and was similar in magnitude to that in normal cells. Thus the excision repair of normal cells which provided host cell reactivation by removing lethal UV damage also removed mutagenic lesions from the virus with the same efficiency, while the repair deficiency of XP var cells had a minor role in host cell reactivation and in mutagenesis. This demonstrates that in human cells host cell reactivation by excision repair is primarily an error-free process.     

Host-cell reactivation of UV-irradiated and chemically-treated herpes simplex virus-1 by xeroderma pigmentosum, XP heterozygotes and normal skin fibroblasts

The host-cell reactivation of UV-irradiated and N-acetoxy-2-acetylamino-fluorene-treated herpes simplex virus type 1 strain MP was studied in normal and xeroderma pigmentosum human skin fibroblasts. Virus treated with either agent demonstrated lower survival in XP cells from complementation groups A, B, C and D than in normal fibroblasts. The relative reactivation ability of XP cells from the different genetic complementation groups was found to be the same for both irradiated and chemically treated virus. In addition, the inactivation kinetics for virus treated with either agent in the XP variant were comparable to that seen in normal skin fibroblasts. The addition of 2 or 4 mmoles caffeine to the post-infection assay medium had no effect on the inactivation kinetics of virus treated by either agent in the XP variant or in XP cells from the different genetic complementation groups. Treatment of the virus with nitrogen mustard resulted in equivalent survival in normal and XP genetic complementation group D cells. No apparent defect was observed in the ability of XP heterozygous skin fibroblasts to repair virus damaged with up to 100 μg N-acetoxy-2-acetylaminofluorene per ml. These findings indicate that the repair of UV-irradiated and N-acetoxy-2-acetylaminofluorene-treated virus is accomplished by the same pathway or different pathways sharing a common intermediate step and that the excision defect of XP cells plays little if any role in the reactivation of nitrogen mustard treated virus.     

Ultraviolet enhanced reactivation of a human virus: effect of delayed infection

The ability of UV-irradiated herpes simplex virus to form plaques was examined in monolayers of CV-1 monkey kidney cells preexposed to UV radiation at different intervals before virus assay. From analysis of UV reactivation (Weigle reactivation) curves it was found that as the interval between cell UV irradiation (0-20 J/m2) and initiation of the virus assay was increased over a period of five days, (1) the capacity of the cells to support unirradiated virus plaque formation, which was decreased immediately following UV exposure to the monolayers, increased and returned to approximately normal levels within five days, and (2) at five days an exponential increase was observed in the relative plaque formation of irradiated virus as a function of UV fluence to the monolayers. For high UV fluence (20 J/m2) to the cells, the relative plaque formation by the UV-irradiated virus at five days was about 10-fold higher than that obtained from assay on unirradiated cells. This enhancement in plaque formation is interpreted as a delayed expression of Weigle reactivation. The amount of enhancement resulting from this delayed reactivation was several fold greater than that produced by the Weigle reactivation which occurred when irradiated herpes virus was assayed immediately following cell irradiation.     

Enhanced induction of SV40 replication from transformed rat cells by fusion with UV-irradiated normal and repair-deficient human fibroblasts

Fusion of SV40-transformed rat (BRKSV) cells which do not spontaneously produce infectious virus, with permissive monkey cells resulted in a low level of production of infectious virus in the heterokaryons. UV-Irradiation of the BRKSV cells prior to fusion did not result in increased virus production, but irradiation of the monkey cells prior to fusion did result in enhanced induction (EI) of SV40, as compared to control experiments in which neither cell type was irradiated. This indicated that rat cells lack the ability to initiate replication of integrated SV40 upon UV-irradiation and do not contain "permissiveness" factors that are required to support SV40 replication. In contrast, monkey cells do contain such permissiveness factors which seem to be temporally enhanced by UV-irradiation, and thus may be responsible for the EI phenomenon. Expression of EI was dose-dependent and reached maximum values approximately 24 h after UV-irradiation. The kinetics of EI resembled that of EI previously established for SV40 induction in semi-permissive cells, and of enhanced reactivation (ER) and enhanced mutagenesis (EM) of SV40 in monkey cells. Similar kinetics of EI were obtained when human diploid fibroblasts were used for fusion with BRKSV cells. Similar levels of EI were found with normal human cells and repair-deficient xeroderma pigmentosum (XP) cells of complementation groups A and C, and XP variant cells. This suggests that expression of EI is not related to excision repair. Since EI is also normally expressed in XP cells which display an abnormal ER of HSV and in XP variant cells which show a delayed EM of HSV, we conclude that EI may occur independently of ER and EM. Finally it was shown that treatment of human cells with N-ethyl-N-nitrosourea results in similar induction of EI as irradiation with UV-light, and that addition of TPA in fusion experiments has no effect on EI.     

Infection of UV-irradiated xeroderma pigmentosum fibroblasts by herpes simplex virus: study of capacity and Weigle reactivation.

The capacity of monolayers of both normal human and xeroderma pigmentosum (XP) filbroblasts to support plaque formation by herpes simplex virus was decreased when the monolayers were ultraviolet (UV) irradiated and infected with virus. Fibroblasts of XP complementation groups A, B, and D were sensitive to UV, being 4-6 fold more sensitive than either fibroblasts of XP complementation group C or fibroblasts from a normal individual. When the monolayers were irradiated 4 days prior to infection, the capacity of normal fibroblasts to support herpes virus growth recovered, whereas the capacity of the XP strains decreased further compared to that measured when infection immediately followed irradiation. Concurrent experiments with UV-irradiated herpes virus showed that the survival of this virus did not increase when infection by irradiated virus immediately followed irradiation of the monolayers. However, if the monolayers were irradiated 4 days prior to infection, the survival of this virus increased by a factor of nearly 2. Such Weigle reactivation (WR) occurred at lower fluences to the XP fibroblasts than to normal fibroblasts, suggesting that WR results from residual cellular DNA damage left after excision repair.     

Reactivation of UV and γ-inactivated herpes virus in BHK cells

The DNA-repair capabilities of baby hamster kidney (BHK) cells were investigated by comparing the reactivation of irradiated herpes simplex virus type I (HSV1) in BHK cells with its reactivation in mouse fibroblasts and in normal and repairdeficient human diploid fibroblasts. BHK cells were found to have an intermediate ability to reactive UV-irradiated HSV1 (the viral D_o was 14 J/m²) relative to normal human fibroblasts (viral D_o = 19 J/m²) and xeroderma pigmentosum (XP) group A cells (viral D_o = 4.5 J/m²). With mouse L929 cells as the host, the response of the UV-irradiated virus was biphasic with D_os of 4.6 and 30 J/m² for the low- and high-dose components respectively. In contrast to the response following UV radiation, γ-irradiated HSV1 was similarly reactivated by BHK and normal human cells (the D_os for the irradiated virus in BHK and CRl 1106 were 55 and 51 krad, respectively, whereas xeroderma pigmentosum cells were slightly less efficient in the repair of γ-irradiated virus (D_o = 45 krad). UV irradiation of BHK host cells 0–48 h prior to infection enhanced the reactivation of UV-irradiated HSV.     

Genetic recombination of herpes simplex virus, the role of the host cell and UV-irradiation of the virus

Summary Recombination frequencies for two sets of genetic markers of herpes simplex virus were determined in various host cells with and without ultraviolet irradiation of the virus. UV irradiation increased the recombination frequency in all the cell types studied in direct proportion to the unrepaired lethal damage. In human skin fibroblasts derived from a patient with xeroderma pigmentosum (XP) of complementation group A, a given dose of UV stimulated recombination more than that in fibroblasts from normal individuals. On the other hand, UV stimulation of HSV recombination was slightly less than normal in fibroblasts derived from a patient with a variant form XP and from an ataxia telangiectasia patient. Caffeine, an agent known to inhibit repair of UV damage, reduced recombination in most of the cell types studied but did not suppress the UV-induced increase in recombination. These findings suggest that for virus DNA with the same number of unrepaired UV-lesions, each of the tested cell types promoted HSV-recombination to an equivalent extent.     

Effects of Nerve Growth Factor and Phorbol Derivative on Reactivation of Herpes Simplex Virus Type 1 in Cultured Cells of Latently Infected Adult Mouse Trigeminal Ganglia

Reactivation of herpes simplex virus type 1 (HSV-1) occurred rapidly in cells of latently infected adult mouse trigeminal ganglia which were cultured in serum-free medium in the presence of sufficient nerve growth factor (NGF). However, HSV-1 reactivation was delayed significantly in ganglionic cultures in the absence of exogenous NGF or in cultures treated with 2-aminopurine in the presence of NGF. The delayed viral reactivation in ganglionic cultures without NGF was accelerated by treatment with phorbol myristate acetate or dibutyryl cyclic AMP. Culture conditions which affected HSV-1 reactivation did not affect replication of HSV-1 in normal ganglionic cultures.     

Enhanced induction of SV40 replication from transformed mammalian cells by fusion with UV-irradiated untransformed cells

DNA-damaging agents such as ultraviolet (UV) light are known to cause stimulation of virus replication in SV40-transformed hamster and human cells. The dose-response curves of UV-induced SV40 replication in transformed hamster cells resemble that obtained for UV-enhanced reactivation (ER) and UV-enhanced mutagenesis (EM) of SV40 or herpes viruses in mammalian cells. We have investigated whether UV-enhanced production of SV40 from transformed hamster (THK) and human (NB-E) cells belongs to the same category of conditional responses as ER and EM. To answer this question we have made use of the phenomenon that fusion of the SV40-transformed cells with monkey cells that are permissive to SV40 results in a considerable increase in the production of SV40 virus. When THK or NB-E cells were fused with UV-irradiated CV-1 cells at various times after irradiation, induction of SV40 was further increased and reached a maximum value of 2--3-fold when fusion was delayed for 24-48 h after irradiation. The kinetics of enhanced SV40 induction resembled that of ER and EM, suggesting that the UV-stimulated part of the induction represents one of the pleiotropic responses that are transiently induced in mammalian cells by DNA-damaging agents. Evidence is presented, showing that this transient effect can be induced only in cells that are permissive to SV40 replication. This suggests that the enhanced induction observed after fusion with irradiated monkey cells may be attributed to a transient increase in the activity of "permissiveness' factors. No enhanced induction was found when the THK or NB-E cells were fused with irradiated rodent cells, that are not or only slightly permissive to SV40 replication.     

Ultraviolet mutagenesis of normal and xeroderma pigmentosum variant human fibroblasts

The mutabilities of normal and xeroderma pigmentosum variant (XP4BE) human fibroblasts by ultraviolet light (UV) were compared under conditions of maximum expression of the 6-thioguanine resistance (TGr) phenotype. Selection was with 20 micrograms TG/ml on populations reseeded at various times after irradiation. Approx. 6--12 days (4--8 population doublings), depending on the UV dose, were necessary for complete expression. The induced mutation frequencies were linear functions of the UV dose but the slope of the line for normal cells extrapolated to zero induced mutants at 3 J/m2. The postreplication repair-defective XP4BE cells showed a higher frequency of TGr colonies than normal fibroblasts when compared at equal UV doses or at equitoxic treatments. The induced frequency of TGr colonies was not a linear function of the logarithm of survival for either cell type. Instead, the initial slope decreased to a constant slope for survivals less than about 50%. The UV doses and induced mutation frequencies corresponding to 37% survival of cloning abilities were 6.7 J/m2 and 6.2 X 10(-5), respectively, for normal cells and 3.75 J/m2 and 17.3 X 10(-5) for the XP4BE cells. The lack of an observable increase in the mutant frequency for normal fibroblasts exposed to slightly lethal UV doses suggests that normal postreplication repair of UV-induced lesions is error-free (or nearly so) until a threshold dose is exceeded.     

X-Ray-Enhanced Reactivation of Ultraviolet-Irradiated Human Virus

When CV-1 mammalian cells were X-irradiated before infection with ultraviolet (UV)-irradiated herpes simplex virus, an increase in survival of this virus was observed. X-ray reactivation is proposed as the name of this phenomenon by analogy with UV reactivation. The amount of survival enhancement was about the same as that found for UV reactivation in the same virus-host system. The enhancement reached a plateau at approximately 1000 rads and appeared to be radiation-insensitive at high doses.     

Excision repair of UV- or benzo[a]pyrene diol epoxide-induced lesions in xeroderma pigmentosum variant cells is 'error free'

It is known that cells from one class of xeroderma pigmentosum (XP) patients, called XP variants, carry out excision repair of UV-induced DNA damage at a normal rate and are only slightly more sensitive than normal cells to the cytotoxic effect of UV radiation, but are much more sensitive to the mutagenic effect of UV. To see if this hypermutability were the result of an 'error-prone', excision repair process, we irradiated fibroblasts derived from an XP variant patient, XP4BE, under conditions that allowed the cells various lengths of time for excision repair before the onset of DNA synthesis (S phase) and assayed the frequency of 6-thioguanine (TG)-resistant mutants. Cells synchronized by release from confluence (G0 state) and irradiated just prior to S phase showed a dose-dependent increase in mutants at very high frequencies; cells irradiated in early G1, approximately 12 h before the onset of S phase, showed frequencies 4 times lower. Cells irradiated in the G0 state and allowed 24 h or 48 h for excision repair before the onset of S phase showed still lower frequencies. A comparison of the relative rates of decrease in mutant frequency with time for excision repair before the onset of S phase in XP variant cells and normal human fibroblasts after a dose of 4 or 6 J/m2 showed that these were equal. However, for every time point, the frequency of mutants induced per dose of UV was significantly higher in the XP variant population than in the normal, suggesting that the XP variant cells have an abnormally error-prone process of replicating DNA on a template containing unexcised lesions or normal cells are by-passing many of such lesions using an error-free process. A similar comparative study in synchronized populations of XP4BE cells and normal cells, using the anti 7,8-diol-9,10-epoxide of benzo[a]pyrene, showed that excision repair prior to the onset of S phase also decreased the frequency of mutants induced in XP variant cells by this agent. But for every dose and time point, the frequencies induced in XP4BE cells and normal cells were identical. Thus, the hypermutability of the XP4BE cells was specific to UV radiation-induced DNA lesions.     

A seventh complementation group in excision-deficient xeroderma pigmentosum.

Cells from a xeroderma pigmentosum patient XP2BI who has reached 17 years of age with no keratoses or skin tumours constitute a new, 7th complementation group G. These cells exhibit a low residual level of excision repair, 2% of normal after a UV dose of 5 J/m2 and an impairment of post-replication repair characteristic of excision-defective XPs. They are also sensitive to the lethal effects of UV and defective in host-cell reactivation of UV-irradiated SV40 DNA.     

Persistent cyclic herpes simplex virus infection in vitro. IV. Changes in the severity of the infections in the presence of antibody

Hampar, Berge (National Institute of Dental Research, Bethesda, Md.). Persistent cyclic herpes simplex virus infection in vitro. IV. Changes in the severity of the infections in the presence of antibody. J. Bacteriol. 92:1741-1747. 1966.-The severity of persistent herpes simplex virus (HSV) infections maintained in the presence of viral antibody (AB) changed with time. These changes could be divided into three distinct phases during which the severity of the infections were maintained at low (phase 1), high (phase 2), and intermediate (phase 3) levels. Paralleling these changes was the appearance in the cultures of a new HSV variant which induced the formation of giant cells. The changes in the severity of the infections were attributable to three factors. The first was the presence in the cultures of virus-resistant cells. The second was the suppressive effects due to virus neutralization by the AB. The third was the inherent properties of each HSV variant which determined the amount of virus remaining in an infectious form in the presence of AB. Finally, the period of "exacerbation" in vitro (phase 2) was compared with recurrent episodes in human herpes infection.     

Reactivation of herpes simplex virus in a cell line inducible for simian virus 40 synthesis

The reactivation of UV-irradiated herpes simplex virus (HSV) was investigated in irradiated and unirradiated transformed hamster cells in which infectious simian virus 40 (SV40) can be induced. Reactivation was enhanced when the cells were treated with UV light or mitomycin C prior to infection with HSV. The IV dose-response curve of this enhanced reactivation was strikingly similar to that found for induction of SV40 virus synthesis in cells treated under identical condictions. This is the first time that two SOS functions described in bacteria have been demonstrated in a single mammalian cell line.     

Host-cell reactivation of ultraviolet-irradiated SV40 DNA in five complementation groups of xeroderma pigmentosum.

Host-cell reactivation of UV-irradiated double-stranded SV40 DNA was studied in BSC-1 monkey cells, normal human cells, heterozygous Xeroderma pigmentosum (XP) cells, representative cell strains of the five complemention groups of XP and in XP "variant" cells. The following percentages of survival of the plaque-forming ability of double-stranded SV40 DNA were found in XP cells compared with the value found in normal monkey and human cells: group A, 13%; group B, 30%; group C, 18%; group D, 14%; group E, 59%; and in the heterozygous XP cells almost 100%. The survival in XP "variant" cells was 66%. The survival of single-stranded SV40 DNA in BSC-1 cells was much lower than that of double-stranded SV40 DNA in XP cells of complementation group A, which possibly indicates that some repair of UV damage occurs even in XP cells of group A.     

Correlation of increased nuclease activity with enhanced virus reactivation

An increase in nuctease activity, which degraded both unirradiated and ultraviolet (UV)-irradiated DNA, was observed in the extract of monkey Vero cells after irradiation with an appropriate amount of UV. In contrast, no increase was observed with mouse L cells. Neither DNA polymerases nor uracil-DNA glycosylase was enhanced but rather suppressed by UV irradiation in both cell lines. Cytological studies showed that, in Vero cells, the reactivation of UV-irradiated herpes simplex virus was markedly enhanced by irradiating cells with UV before infection. However, no enhancement was observed with L cells. These results suggest that an increase in nuclease activity may be one of underlying mechanisms for the enhanced reactivation of DNA viruses.     

Inhibition of human excision DNA repair by inorganic arsenic and the co-mutagenic effect in V79 Chinese hamster cells

We investigated the lethal, UV killing-potentiating and repair-inhibiting effects of trivalent arsenic trioxide (As2O3) and pentavalent sodium arsenate (Na2HAsO4) in normal human and xeroderma pigmentosum (XP) fibroblasts. The presence of As2O3 for 24 h after UV irradiation inhibited the thymine dimer excision from the DNA of normal and XP variant cells and thus the subsequent unscheduled DNA synthesis (UDS): excision inhibitions were partial, 30-40%, at a physiological dose of 1 microgram/ml and 100% at a supralethal dose of 5 micrograms/ml. Correspondingly, As2O3 also potentiated the lethal effect of UV on excision-proficient normal and XP variant cells in a concentration-dependent manner, but not on excision-defective XP group A cells. Na2HAsO4 (As5+) was approximately an order of magnitude less effective in preventing all the above repair events than As2O3 (As3+) which is highly affinic to SH-containing proteins. The above results provide the first evidence that arsenic inhibits the excision of pyrimidine dimers. Partially repair-suppressing small doses of As2O3 (0.5 microgram/ml) and Na2HAsO4 (5 micrograms/ml) enhanced co-mutagenically the UV induction of 6-thioguanine-resistant mutations of V79 Chinese hamster cells. Thus, such a repair inhibition may be one of the basic mechanisms for the co-mutagenicity and presumably co-carcinogenicity of arsenic. XP group A and variant strains showed a unique higher sensitivity to As2O3 and Na2HAsO4 killing by a yet unidentified mechanism.