Expression of herpesvirus thymidine kinase gene under control of early promoter of SV40

Mitochondrial nucleic acids as internal standards for blot hybridization analyses

A plasmid, designated p72, constructed from human lung carcinoma DNA inserted into the promoterless herpes simplex virus thymidine kinase gene pML-TK-Bgl II vector, hybridizes strongly to human nucleic acids on Southern and Northern blots. The portion of the DNA insert responsible for the strong signal following hybridization to human DNA or RNA is a 167-bp 3' terminal portion of the mitochondrial 16S ribosomal RNA gene. The expression of this gene is constitutive in the several human cell lines that were tested and is unaffected by exposure to cytotoxic chemicals that alter the expression of nuclear genes. This plasmid offers an excellent tool for studies of perturbations of gene expression and for controlling for the variations in sample preparation, loading, and transfer in Southern or Northern analysis of nucleic acids.

Glucocorticoid-dependent oncogenic transformation by type 16 but not type 11 human papilloma virus DNA

Squamous cell carcinoma of the uterine cervix is one of the most common cancers among women. Correlation between human papilloma virus (HPV) infection of the uterine cervix and the development of cervical neoplasia has been established. More recent studies have shown the presence and expression of integrated HPV types 16 and 18 DNA sequences in 70-80% of cervical tumours and tumour cell lines. It has been suggested that, in addition to HPVs, other agents such as hormones and tobacco products act as cofactors in cervical neoplasia (for review see ref. 15). The presence and expression of a glucocorticoid-responsive element in HPV-16 has been reported. Here we provide evidence for the oncogenic transformation of primary cells with a combination of HPV-16 DNA, but not HPV-11 DNA, and the activated form of the human Ha-ras oncogene only in the presence of the glucocorticoid hormone dexamethasone.

Expression of human papillomavirus types 16 and 18 DNA sequences in cervical carcinoma cell lines

A total of six cervical carcinoma cell lines, of which two contained human papillomavirus (HPV) type 16 and four contained HPV type 18 DNA, were examined for viral RNA expression by spot-blot hybridization. All six cell lines contained HPV-specific cytoplasmic poly(A)-containing RNA. The same RNA species were detected in both cytoplasmic and polysomal fractions, indicating nonselective translation of these messages into protein products. Primer extension analysis of RNA from the cell lines revealed the presence of three major start sites at the 5' end of the E6 gene for RNA from HPV 16-containing cell lines and four major start sites at the 5' end of the E6 gene for RNA from HPV 18-containing cell lines. One cell line, ME 180, had a distinct pattern with only one minor HPV 18 start site. Northern-blot hybridization using the E6-E7 region of HPV 16 and 18 DNAs as probes revealed the presence of E6-E7 transcripts in all the cell lines except ME 180. Southern-blot analysis revealed that while sequences hybridizing to the E6-E7 coding region were present, the 5' end region containing the enhancer-promoter region of viral DNA is deleted in ME 180. Subsequent Northern-blot hybridization using the E1 region of HPV 18 DNA as probe revealed that the viral RNA in ME 180 is transcribed from this region.

Isolation and characterization of a variant of human papillomavirus type 11 from a nasal inverting (Schneiderian) papilloma

We have previously reported the presence of a variant of human papillomavirus (HPV) type 11 in a nasal inverting papilloma [Respler et al., 1987]. In the present study, we have cloned molecularly the DNA of this variant at its unique restriction enzyme Bam HI site into lambda BF101 phage. Restriction enzyme mapping and DNA sequencing revealed that the genome of this virus contained an extra 531 base pair (bp) which was the repeat of most of the noncoding region (ncr) of HPV 11. Insertion of transcriptional control elements, including the repeated sequence, in front of the chloramphenicol acetyltransferase (CAT) gene resulted in a 5- to 30-fold increase in expression in transfected cells, as compared to the constructs containing a single ncr of HPV 11. This increased expression was due to enhanced levels of CAT RNA the synthesis of which is initiated by the viral promoter element.

Transformation of primary human embryonic kidney cells to anchorage independence by a combination of BK virus DNA and the Harvey-ras oncogene

Primary human embryonic kidney (HEK) cells were transformed by a focus assay with BK virus (BKV) DNA molecularly cloned at its unique EcoRI site. Both viral DNA sequences and viral tumor antigens were present and expressed in all the foci that we examined. However, cells isolated from foci were incapable of growth in soft agar. We then examined the transformation of HEK cells after their transfection with a combination of BKV DNA and either the normal or the activated form of the human Ha-ras oncogene (EJ c-Ha-ras-1). Only the cells transfected with a combination of BKV DNA and the activated form of Ha-ras were capable of growth in soft agar. Both BKV and Ha-ras DNAs were present in the transformed colonies. BKV tumor antigens and the Ha-ras p21 protein were also expressed.

A plasmid vehicle suitable for the molecular cloning and characterization of mammalian promoters

We have constructed a plasmid, pPSG4, that carries only the coding sequences for polyomavirus (Py) small, middle and truncated large T-antigens. A unique HindIII site allows the introduction of foreign promoters directly in front of viral coding sequences. The simian virus 40 (SV40) early and late, adenovirus-2 (Ad-2) major late and herpes simplex virus-1 (HSV-1) thymidine kinase (TK) promoters all confer on pPSG4 the ability to transform rat embryonic fibroblasts with high efficiency. Sequential deletion of the 72 bp repeats, the 21 bp repeats and the TATA box from the SV40 early region in pPSG4 produced a 50, then 30 and then a further 5 to 10-fold decrease in transformation efficiency, respectively. Thus pPSG4 is a convenient vector for the cloning and characterization of mammalian promoters.

Transactivation of a late herpes simplex virus promoter

We have asked whether the promoter for the gene encoding the major capsid protein (VP5) of herpes simplex virus functions in uninfected mouse cells. Our experimental strategy was to first fuse the VP5 promoter to the herpes simplex virus thymidine kinase (TK) structural sequence and then to use the resulting hybrid gene to transform TK- cells to TK+. The recombinant gene transferred TK at an extremely low frequency by comparison with the wild-type TK gene, and the TK transcripts present within the resulting rare transformants initiated within the TK structural gene, rather than in the vicinity of the VP5 promoter. However, after infection with herpes simplex virus, large amounts of RNA driven from the VP5 promoter accumulated. We conclude that the VP5 promoter does not function in uninfected cells but is efficiently activated by virally coded factors, most likely one or more immediate-early proteins.

Transactivation of a late herpes simplex virus promoter

We have asked whether the promoter for the gene encoding the major capsid protein (VP5) of herpes simplex virus functions in uninfected mouse cells. Our experimental strategy was to first fuse the VP5 promoter to the herpes simplex virus thymidine kinase (TK) structural sequence and then to use the resulting hybrid gene to transform TK- cells to TK+. The recombinant gene transferred TK at an extremely low frequency by comparison with the wild-type TK gene, and the TK transcripts present within the resulting rare transformants initiated within the TK structural gene, rather than in the vicinity of the VP5 promoter. However, after infection with herpes simplex virus, large amounts of RNA driven from the VP5 promoter accumulated. We conclude that the VP5 promoter does not function in uninfected cells but is efficiently activated by virally coded factors, most likely one or more immediate-early proteins.

Incorporation of 5-substituted analogs of deoxycytidine into DNA of herpes simplex virus-infected or - transformed cells without deamination to the thymidine analog

The incorporation into DNA of 5-bromocytosine and 5-iodocytosine, derived from their respective administered deoxyribonucleoside analogs, has been demonstrated in studies with cells infected with herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) and in cells transformed with the thymidine kinase gene of HSV-1. No significant incorporation of iodocytosine or iodouracil occurred in the DNA of uninfected or nontransformed cells when the deaminating enzymes were inhibited, in accord with past studies in our laboratory with 5-bromodeoxycytidine and tetrahydrouridine. When 2'-deoxytetrahydrouridine, a potent inhibitor of cytidine deaminase and dCMP deaminase, was utilized, all the counts in DNA that were derived from [(125)I]iododeoxycytidine appeared as iodocytosine in HSV-infected cells. In the absence of a deaminase inhibitor, 32 to 45% of the counts associated with DNA pyrimidines appeared as iodocytosine, and 55 to 68% appeared as iodouracil in HSV-infected cells. Substantial incorporation of iodocytosine (16%) occurred in cells transformed with the HSV thymidine kinase gene, suggesting the importance of the specificity of cellular nucleoside kinases and the activity of the deaminases in presenting unmodified bases to an undiscriminating polymerase. Incorporation into DNA of bromocytosine derived from [(3)H]bromodeoxycytidine was demonstrated in HSV-2 infected cells; very little incorporation of bromocytosine compared with bromouracil could be demonstrated in these cells in the absence of inhibition of the deaminases (19% of the total counts associated with pyrimidines with deaminase inhibition and 1.5% without). Limited studies with 5-methyl[5-(3)H]deoxycytidine indicated essentially no (or very little) incorporation of this analog as such in the DNA of HSV-1- and HSV-2-infected and -transformed cells. This suggests an exclusion or repair mechanism preventing inappropriate methylcytosine incorporation in DNA. The addition of nucleoside and deoxyribonucleoside deaminase inhibitors, which leads to the incorporation of 5-halogenated analogs of deoxycytidine into DNA as such, does not impair their antiviral activity. We infer from studies with 4-N-alkyl (ethyl and isopropyl)-substituted analogs of iododeoxycytidine that they are incorporated as such into DNA without deamination and effectively inhibit the virus at concentrations that are marginally toxic. Among the several reasons presented for the heightened potential efficacy of analogs of deoxycytidine compared with those of deoxyuridine is that the former, as analogs of 5-methyldeoxycytidine, may impair viral replication by perturbing processes involving methylation and changes in the methylation of deoxycytidine in DNA which appear to be important for the process of HSV maturation. In addition, this capacity to perturb methylation may, in turn, be the key to their potential as agents affecting entry into or emergence from latency, a process in which dramatic changes in the postpolymer 5-methylation of deoxycytidine occur in the DNA of herpesviruses.