Characterization of rare human papillomavirus type 11 mRNAs coding for regulatory and structural proteins, using the polymerase chain reaction

Human papillomavirus type 18 E6*, E6, and E7 protein synthesis in cell-free translation systems and comparison of E6 and E7 in vitro translation products to proteins immunoprecipitated from human epithelial cells

Expression of the E6 and E7 transforming genes of human papillomavirus type 18 (HPV18) occurs via structurally bicistronic mRNAs in which the downstream open reading frame (ORF) E7 is preceded either by the full-length ORF E6 or by a spliced ORF, E6*. We have used in vitro transcription and translation of HPV18 cDNAs in order to analyze the synthesis of E6*, E6, and E7 proteins and to compare the E6 and E7 in vitro translation products with the authentic proteins immunoprecipitated from cervical cancer cells. In wheat germ extract, in vitro translation resulted in the production of all three proteins, E6*, E6, and E7. In rabbit reticulocyte lysate, however, only the E6 and E7 proteins were produced. The lack of E6* protein was due neither to template RNA degradation nor to an inhibitory influence of the RNA 5' leader sequences, thus indicating the possibility of either inhibition of synthesis or degradation of E6* protein in reticulocyte lysate. The E7 protein was synthesized from both E6*-E7 and E6-E7 RNAs. In vitro-synthesized and authentic HPV18 E7 proteins revealed identical electrophoretic mobilities in two-dimensional gel electrophoresis, thus indicating similar modifications. By using a monoclonal antibody against the N terminus of HPV18 E6* and E6, an 18-kDa protein was detected not only in HPV18-positive but also in HPV18-negative epithelial cells. The 18-kDa proteins and the in vitro-synthesized HPV18 E6 protein exhibited comparable electrophoretic characteristics in two-dimensional gels. These results suggest the possible existence of a cellular protein related to HPV18 E6.

Human papillomavirus type 16 immortalized cervical keratinocytes contain transcripts encoding E6, E7, and E2 initiated at the P97 promoter and express high levels of E7

Human cervical keratinocytes represent the specific host for the genital human papillomaviruses (HPV). Transfection of these cells with the DNA of a number of the oncogenic HPVs including type 16 was recently shown to result in their immortalization but not in malignant transformation. In this report we show that viral transcripts for E6 and E7 in these cells were as abundant as in cancer derived cell lines. However, in contrast to cancer derived cell lines, immortalized cervical keratinocytes contained RNA with the potential to encode a full-length E2 protein. In addition, the levels of the E7 oncoprotein were at least as high as in cancer derived cell lines, suggesting that E2 interruption, observed in cancer derived cell lines, is not causally related to the high level of E7 expression and, therefore, deregulation of the P97 promoter may not be a prerequisite for HPV-16 associated cancer development. Furthermore, we show that E6, E7, and E2 encoding transcripts all originate from the viral promoter, P97. Unlike in cancer derived cell lines, all transcripts terminated at the early poly(A) site.

Use of the polymerase chain reaction to study the relationship between human papillomavirus infections and cervical cancer

Although it is now evident that human papillomaviruses (HPV) are strongly associated with cervical cancer, their etiological role in the oncogenesis of this disease is still unknown. However, HPV screening may identify women at risk of acquiring this disease. With the recent development of the polymerase chain reaction (PCR), it has become possible to detect small numbers of human papillomavirus genomes in clinical samples. The sensitivity and specificity of this technique, together with the possibility of performing the test on crude cervical scrapes, makes PCR the method of choice for screening. In this paper, data on the detection of human papillomavirus by PCR are presented and the applicability of this technique for the screening of human papillomavirus genotypes is evaluated. The question arises whether screening for diagnostic purposes must include all the human papillomavirus types associated with infections of the genital tract or only those which are strongly associated with cervical cancer (HPV 16 and HPV 18). It is proposed that an international council must be created that is responsible for standardised epidemiological screening strategies and follow-up programmes.

Biologic properties and nucleotide sequence analysis of human papillomavirus type 51

Human papillomaviruses (HPVs) may be grouped according to the site from which they are isolated and the disease with which they are associated. We recently identified and cloned HPV type 51 (HPV-51) from a low-grade precancerous lesion (G. Nuovo, E. DeVilliers, R. Levine, S. Silverstein, and C. Crum. J. Virol. 62:1452-1455, 1988). Molecular epidemiologic analysis of cervical lesions, including condylomata and low- and high-grade precancers, revealed that HPV-51 was present in about 5% of the samples we examined. We have now determined the complete nucleotide sequence of this virus and compared it with other sequenced HPVs. Our analysis reveals that the 7,808-bp genome is composed of eight open reading frames which are encoded on the same strand and that this virus is most closely related to HPV-31. Sequence comparisons place this virus in the group of high-risk viruses (those with an increased risk of progressing to malignancy) along with HPV-16, -18, -31, and -33. Morphologic transformation experiments demonstrated that HPV-51 had transformation potential and that transformed cells contained RNAs homologous to E6 and E7.

Viral transcription in human keratinocyte cell lines immortalized by human papillomavirus type-16

Human papillomavirus type-16 (HPV-16) transcription in two human keratinocyte cell lines (HPK) immortalized by transfection of viral DNA in vitro was analyzed by nucleotide sequencing of cDNA clones, and in addition by primer extension analysis and S1 nuclease and exonuclease VII digestion of poly(A)+ RNA. A novel mRNA species which probably initiates in the E7 ORF and in which the 5'-part of the E1 ORF (splice donor at position (pos.) 880) is joined to an exon comprising the entire E2 ORF (splice acceptor at pos. 2708) was found in both cell lines. This mRNA has the potential to encode a full-length E2 protein, which is known to function as a repressor of transcription initiated at P97. cDNAs derived from the late region of the viral genome and the use of a late polyadenylation signal at pos. 7320-7325 are described. In agreement with RNA data published by others the major promoter for HPV-16 transcription is located at pos. 97. mRNA species encoding full-length or truncated forms of the E6 protein, and species characterized by an E1i [symbol see text] E4 splice junction (which provided the E4 open reading frame (ORF) with an ATG triplet) were identified.

Rapid induction of heme oxygenase 1 mRNA and protein by hyperthermia in rat brain: heme oxygenase 2 is not a heat shock protein

Catalytic activity of heme oxygenase (heme, hydrogen-donor:oxygen oxidoreductase, EC 1.14.99.3) isozymes, HO-1 and HO-2, permits production of physiologic isomers of bile pigments. In turn, bile pigments biliverdin and bilirubin are effective antioxidants in biological systems. In the rat brain we have identified only the HO-1 isozyme of heme oxygenase as a heat shock protein and defined hyperthermia as a stimulus that causes an increase in brain HO-1 protein. Exposure of male rats to 42 degrees C for 20 min caused a rapid and marked increase in brain 1.8-kilobase HO-1 mRNA. Specifically, a 33-fold increase in brain HO-1 mRNA was observed within 1 h and sustained for at least 6 h posttreatment. In contrast, the two HO-2 homologous transcripts (1.3 and 1.9 kilobases) did not respond to heat shock; neither the ratio nor the level of the two messages differed from that of the control when measured either at 1, 6, or 24 h after hyperthermia. The induction of a 1.8-kilobase HO-1 mRNA resulted in a pronounced increase in HO-1 protein 6 h after hyperthermia, as detected by both Western immunoblot and RIA. Immunocytochemistry of rat brain showed discrete localization of HO-1-like protein only in neurons of select brain regions. Six hours after heat shock, an intense increase in HO-1-like protein was observed in both Purkinje cells of the cerebellum and epithelial cells lining the cerebral aqueduct of the brain. We suggest that the increase in HO-1 protein, hence increased capacity to form bile pigments, represents a neuronal defense mechanism against heat shock stress.

An E1M--E2C fusion protein encoded by human papillomavirus type 11 is asequence-specific transcription repressor

We have isolated a putative, spliced E5 cDNA of human papillomavirus type 11 (HPV-11) by polymerase chain reaction amplification of cDNAs from an experimental condyloma. Using retrovirus-mediated gene transfer, we isolated two novel HPV-11 cDNAs, one of which had a splice linking nucleotides 1272 and 3377. This transcript also existed in experimental condylomata and in cervical carcinoma cells transfected with cloned genomic HPV-11 DNAs. The 5' end of the transcript in transfected cells originated upstream of the initiation codon of the E1 open reading frame (ORF). It could conceptually encode a fusion protein consisting of the amino-terminal 23% of the E1 ORF and the carboxy-terminal 40% of the E2 ORF. This E1M--E2C fusion protein contained both the DNA replication modulator domain E1M, as defined in the bovine papillomavirus system, and the DNA binding domain of the E2 protein, which regulates viral transcriptional activities. Indirect immunofluorescence with polyclonal antibodies raised against the bacterially expressed TrpE-HPV-11 E2 protein demonstrated nuclear localization of the E1M--E2C protein in cells transiently transfected with an expression plasmid. Immunoprecipitation revealed a specific protein with an apparent molecular weight of 42,000 in transfected cells. The chloramphenicol acetyltransferase assay established that the putative E1M--E2C protein was a potent transcriptional repressor of both E2-dependent and E2-independent HPV-11 enhancer/promoter activities. Northern (RNA) blot hybridization indicated the repression was on the transcriptional level. Mutational analysis suggested that the E1M--E2C protein is an E2-binding site-specific repressor. The fusion protein also repressed bovine papillomavirus type 1 (BPV-1) E2 protein-dependent BPV-1 enhancer activity. When constitutively expressed in mouse C127 cells, the E1M--E2C protein inhibited BPV-1 transformation and episomal DNA replication, consistent with a role in the modulation of replication.

Mapping of linear epitopes of human papillomavirus type 16: the E1, E2, E4, E5, E6 and E7 open reading frames

Certain types of human papillomavirus (HPV), especially HPV type 16, are associated with proliferative lesions of the cervix uteri that can progress to malignancy. In order to map the linear epitopes of the HPV-encoded proteins, we have synthesized the predicted amino acid sequences of the open reading frames (ORFs) in the early region of HPV 16, as a set of 94 synthetic 20-residue peptides overlapping each other with 5 amino acids. The peptides were tested for reactivity with IgA, IgG and IgM antibodies in the sera of 30 patients with HPV 16-carrying cervical neoplasia. The EI ORF had only low immunoreactivity, but several relatively minor epitopes were identified in the carboxyterminal part. The E2 ORF was found to contain several epitopes that were highly immunoreactive with a majority (up to 87%) of the cervical cancer patients' sera. The E4 ORF had one major, regularly IgA- and IgG-reactive epitope, whereas the E5 and E6 ORFs had only a few minor epitopes. The E7 ORF had several epitopes that were highly immunoreactive, but only with a minority of patients' sera. The 10 most immunoreactive peptides were also analyzed for immunoreactivity with 60 control sera, of which 22 were derived from patients with parotid gland tumors and 38 were derived from healthy volunteers. Most of the peptides were also immunoreactive with the control sera. However, the IgA antibodies, and to some extent the IgG antibodies, were found at much lower levels among the controls.

Detection of novel splicing patterns in a HPV16-containing keratinocyte cell line

The W12 cell line was derived from a low grade cervical lesion, and is unique among HPV16-containing cell lines in carrying its HPV16 genome as a multicopy episome. As such it is thought to be more representative of a premalignant HPV16-induced tumor than the cervical cancers from which other cell lines have been derived. Using the polymerase chain reaction (PCR), we report here the identification and cloning of a number of novel cDNA species, which appear to be characteristic of the W12 cell line. Two species were identified with E6* coding capacity (E6*I and E6*III). The smaller of these (1009 bp) was predicted to encode a novel E6*III polypeptide containing C-terminal amino acids derived from an out of frame region of the E2/E4 ORFs. The larger species (1480 bp) contained, in addition to the E6*I ORF, an intact E7 ORF and probably represents the transcript for E7 expression, as the E7 protein was readily detectable in the W12 cell line. Both species appeared to be transcribed from the p97 promoter which has been shown to be active in other cell lines. A putative E2 repressor cDNA (891 bp), an E1/E4 message (883 bp), and two novel late cDNA species (1757 and 2031 bp) were also detected, allowing the identification of a splice acceptor immediately in front of the L1 open reading frame (nt 5637) and a splice donor at nt 3631. Although the 1757-base species has the capacity to encode a full-length L1 protein, both messages use a splice donor at nt 1301, and are thus not analogous to late species previously identified in HPV11. Of the six cDNAs cloned, only the 1480-bp E7 message has been observed in other HPV16-containing cell lines. The presence of L1 transcripts, and an E2 repressor mRNA, although unexpected, may reflect the different origins of the W12 cell line.

Infectious cycle of human papillomavirus type 11 in human foreskin xenografts in nude mice

We have performed the first molecular analysis of a time course of infection by a papillomavirus. The Hershey isolate of the human papillomavirus type 11 was used to infect human foreskin tissues, which were then implanted under the renal capsules of nude mice. The xenografts were recovered every 2 weeks for 14 weeks, fixed in formalin, and embedded in paraffin. Four-micrometer serial sections were examined by light microscopy for morphological changes, by immunocytochemistry for virion antigen production, and by in situ hybridization with 3H-labeled RNA probes for viral DNA replication and expression of the major mRNA species. After a lag period, probes spanning the E4 and E5 open reading frames, which are present in all E region viral mRNAs, generated the first detectable signals at week 4. Signals of other E region probes were minimally detected at week 6. Between weeks 6 and 8, there was an abrupt change in the implant such that cellular proliferation, viral DNA replication, and E and L region mRNA transcription were robust and reached a plateau. By weeks 10 to 12, the experimental condylomata were morphologically and histologically indistinguishable from naturally occurring condylomata acuminata. These findings suggest that cellular hyperproliferation and the morphologic features of condylomata are direct results of viral genetic activities. Unlike other DNA viruses, the E region transcripts increased with cell age and cellular differentiation and persisted throughout the entire experiment. In particular, the mRNA encoding the E1iE4 and perhaps E5 proteins remained overwhelmingly abundant. In contrast, viral DNA replication, L region mRNA synthesis, and virion antigen production were restricted to the most differentiated, superficial cells.

Human papillomavirus type 1 produces redundant as well as polycistronic mRNAs in plantar warts

Human papillomavirus type 1 (HPV-1) causes plantar warts. On the basis of previously mapped mRNAs and sequence homologies of HPV-1 to other papillomaviruses, we designed oligonucleotide primers and employed the polymerase chain reaction to recover HPV-1 cDNAs from plantar warts. Seven spliced RNA species were characterized, including three not previously detected, and the coding potentials of each were deduced. The most abundant viral mRNA encodes an E1i--E4 protein. One new species is predicted to encode the full-length E2 protein, and another can, theoretically, encode the E2-C or E1-M proteins, three products that regulate mRNA transcription and DNA replication. One RNA species originating from a novel HPV promoter in the upstream regulatory region has the potential to encode the minor capsid protein L2. A newly recognized E5a open reading frame (ORF) is contained in all mRNAs that are polyadenylated at the E-region poly(A) site and also in a putative L2 mRNA. Three distinct species, two of which are derived from the upstream regulatory region promoter, have the potential to encode the L1 protein; the third species also contains the entire coding region of the E1i--E4 protein 5' to the L1 ORF. Both the E1i--E4 mRNA and the potentially bicistronic L1 mRNA are derived from a promoter located in the E7 ORF. We uncovered no evidence of alternatively spliced mRNAs that could account for the multiple, abundant E4 proteins in plantar warts, suggesting that posttranslational modification is mainly responsible for the observed protein heterogeneity.

Characterization of cDNAs of spliced HPV-11 E2 mRNA and other HPV mRNAs recovered via retrovirus-mediated gene transfer

Human papillomaviruses (HPVs) are associated with hyperproliferations of cutaneous or mucosal epithelium. These viruses cannot be propagated in any cell culture system. Because cloning cDNA copies of HPV mRNAs recovered from human lesions has met with only very limited success, the characterization of HPV mRNAs has been problematic. Using the Moloney murine leukemia virus vector system (C.L. Cepko, B.E. Roberts, and R.C. Mulligan, 1984, Cell 37, 1053-1062), we have recovered cDNAs of spliced E2 mRNAs of human papillomavirus type 11 and additional mRNAs of type 11 and type 18 and determined the utilization of open reading frames (ORFs) in the DNA sequences. The recovery of cDNA copies of messages with splice sites identical to those previously described strongly suggests that the newly characterized splice donors and acceptors are also authentic. The HPV-11 E2 cDNA contains the intact E6 and E7 ORFs and the beginning of the E1 ORF in the first exon, which is then spliced from nt 847 to the second exon at nt 2622, 100 nucleotides upstream from the initiation codon for the E2 ORF. The initiation codon in the E1 ORF is followed by four additional in-frame AUG triplets and an in-frame termination codon positioned 30 nucleotides upstream from the initiation codon for the E2 protein. The authenticity of this putative E2 cDNA was shown by its ability to provide enhancer transactivating activity in chloramphenicol acetyltransferase (CAT) assays in several cell lines. A mutation in the genomic DNA at this splice acceptor site eliminates its activity, demonstrating that the splice is essential for the expression of the E2 protein. We conclude that the translation of the HPV-11 E2 protein requires internal initiation.

Differentiation-linked human papillomavirus types 6 and 11 transcription in genital condylomata revealed by in situ hybridization with message-specific RNA probes

Human papillomaviruses (HPVs) infect specific human epithelial tissues. Because viral propagation in cultured cells has not been achieved, studies of HPV genetic activities have been difficult and rely largely on analyses of patient specimens by conventional biochemical methods. HPV type 6 and type 11 infections often result in genital warts (condylomata acuminata). Structural mapping of RNAs from such warts reveals that they use alternative promoters, splice sites, and polyadenylation sites to produce complex families of overlapping mRNAs that span multiple open reading frames. Based on the mRNA structures, we have developed message-specific subgenomic clones of HPV-6 and HPV-11 in pGEM vectors. Tritium-labeled, single-stranded RNA probes were synthesized in vitro and applied to serial thin sections of patient specimens for in situ hybridization. Our results reveal the qualitative and quantitative transcription patterns of different viral messages in relationship to one another, to viral DNA replication, and to cellular differentiation. The viral "E region" is transcribed before the onset of vegetative DNA replication and continues to be expressed in increasing amounts in the maturing epithelium. Even in mature epithelia, E region messengers are far more abundant than "L region" mRNAs. The L region messages encoding capsid proteins are truly late in that they appear concomitant with or after the onset of vegetative viral DNA replication and are only present in the superficial strata of the epithelium, which contain the oldest and most differentiated keratinocytes. Abundant intron material derived from processing E region transcripts accumulates in the nuclei. Strictly nuclear signals from the L region transcripts in the midepithelium suggest that regulation of their expression is at the level of transcription elongation.