YY-1 and c-Jun transcription factors participate in the repression of the human involucrin promoter.

The human involucrin gene, which encodes a precursor of the keratinocyte cornified layer, is strongly expressed in response to differentiation stimuli. Earlier studies suggested that YY1 and components of the AP-1 family might participate in the silencing of involucrin in proliferating keratinocytes. This study shows that overexpression of either YY1 or c-Jun represses transcription of the human involucrin gene in multiplying keratinocytes. Transient overexpression and site-directed mutagenesis experiments of the involucrin 5'-non-coding region (5'-NCR) confirmed that YY1 and c-Jun repress involucrin transcription. This repression involves the distal zinc fingers of YY1 protein and the DNA binding and leucine zipper domains of c-Jun. The results with protein pull-down experiments are consistent with the hypothesis that interaction of YY1 with c-Jun is an important mechanism for involucrin repression. Cotransfection of YY1 modified the stimulatory function of mutant c-Jun proteins independently of their DNA binding capacity suggesting that interactions may be more complex in vivo. Additionally, c-Jun protein levels are affected by differentiation stimuli indicating the importance of c-Jun in the YY1 repression pathway. Thus YY1 and c-Jun have an important role in epidermal differentiation by negatively regulating the human involucrin gene.

Antisense activity detection by inhibition of fluorescence resonance energy transfer.

Use of antisense nucleic acids to modulate expression of particular genes is a promising approach to the therapy of human papillomavirus type 16 (HPV-16)-associated cervical cancer. Understandably, evaluation of the in vivo performance of synthetic antisense oligodeoxynucleotides (AS-ODNs) or ribozymes is of ultimate importance to development of effective antisense tools. Here we report the use of a bacterial reporter system based on the inhibition of fluorescence resonance energy transfer (FRET) to measure the interaction of AS-ODNs with HPV-16 target nt 410-445, using variants of the green fluorescent protein (GFP). An optimal FRET-producing pair was selected with GFP as the donor and yellow fluorescent protein (YFP) as the acceptor molecule. Hybridization of AS-ODNs with a chimaeric mRNA containing the antisense target site flanked by GFP variants resulted in the inhibition of the FRET effect. Use of different linkers suggested that the amino acid content of the linker has no significant effect on FRET effect. Antisense accessibility, tested by RNaseH assays with phosphorothioated target-specific and mutant AS-ODNs, suggested a specific effect on the chimaeric mRNA. FRET inhibition measurements correlated with the presence of truncated proteins confirming true antisense activity over the target. Therefore, FRET inhibition may be used for the direct measurement of AS-ODNs activity in vivo.

Growth inhibition of cervical tumor cells by antisense oligodeoxynucleotides directed to the human papillomavirus type 16 E6 gene.

Human papillomavirus type 16 (HPV-16) is the HPV type most frequently associated with cervical carcinomas. Based on our previous research with anti-HPV ribozymes, we developed a 16-nucleotide antisense oligodeoxynucleotide (AntiE6) able to direct RNase H activity on full-length HPV-16 E6/E7 mRNA. Although the precise mechanism is not completely understood, addition of 50 microM AntiE6 oligodeoxynucleotide in sterile water caused a significant decrease in the growth rate of CaSki and QGU cervical tumor cell lines. In contrast, addition of a mismatched mutant oligodeoxynucleotide (M7) did not affect cell growth after 72 hours. Treatment with AntiE6 resulted in down-regulation of E6/E7 mRNA and an increase in p53 levels in QGU cells. AntiE6 was also able to (>70%) inhibit significantly growth of transplanted cervical tumors in nude mice after 2 weeks treatment using constant delivery by osmotic pumps. These results indicate that the AntiE6 antisense oligodeoxynucleotides can act as a therapeutic agent against cervical carcinomas.

Molecular aspects of neoplasia of Syrian hamster cells transformed in vitro by chemical carcinogens.

The addition of environmental agents (carcinogens) induces transformation that can be quantitated. Its frequency follows a linear relationship with dose and is consistent with a 'one hit' phenomenon. Transformed colonies produce transformed lines with attributes of neoplastic cells including production of tumors. The results parallel in vivo activity. Although, molecular analysis of most animal assay indicate the presence of activated oncogenes belonging to the ras family, ras activation is a low frequency event in the neoplastic conversion of Syrian hamster cells just as is found with human malignancies. In our analysis of 22 independently derived lines N-ras activation was found only with sodium bisulfite transformed lines. A novel oncogene named carcinogenesis promotion hamster (cph) because its association with the carcinogenic process has been identified. This resulted from focusing on Syrian hamster cells transformed with a single dose of 3-methylcholanthrene (MCA) and cosmid-rescue-techniques from a third-cycle NIH3T3 transformant obtained by sequential transfections of genomic DNA from MCA-initiated hamster fetal cells. cph transforms NIH3T3 cells and acts synergistically with Ha-ras to transform murine fibroblasts. Gene expression analysis using cph genomic fragments from normal and neoplastic cells identifies a number of transcripts including a major mRNA of 2.5 kb as well as several larger transcripts. cph is actively transcribed in different tissues and different species. In the hamster it is a single copy gene localized by FISH to the euchromatic short arm of the X chromosome, at region Xpa7. cph does not have any significant global homology to sequences deposited in date banks, confirming that it is a novel gene. The transforming gene codes for a truncated 246 amino acids whereas the normal cph has a residue of 469 amino acids. In conclusion cph oncogene is activated by a single point-mutation; its activation appears an important mechanism for the conversion of carcinogen treated hamster cells to malignancy and because homologous sequences occur in human DNA it may also be important to the neoplastic conversion of human cells.

Relationship of stable integration of herpes simplex virus-2 Bg/II N subfragment Xho2 to malignant transformation of human papillomavirus-immortalized cervical keratinocytes.

Transfection of the right end Xho2 subfragment of Bg/II N of herpes simplex virus-2 (HSV-2) into human genital keratinocytes immortalized by human papillomavirus (HPV) type 16 or 18 resulted in invasive and noninvasive indolent cystic squamous carcinomas when cells were injected into immunocompromised mice. Retention and expression of the right end portion of the Bg/II N fragment correlated with malignancy, as the corresponding HSV-2 sequences were integrated and transcribed in the tumorigenic cell lines. HPV-immortalized cells alone were not tumorigenic. In contrast, previous results have shown that using the entire Bg/II N region can malignantly transform HPV-immortalized cells, although HSV2 DNA was not retained. Together, these observations localize the transforming activity of Bg/II N to Xho2 and suggest that the remaining sequences have an inhibitory effect on stable integration. The Xho2 sequence is 2480 bp long and contains an open reading frame (ORF) extending from nucleotides 559 to 1797. The ORF encodes a putative protein of 412-aa with a m.w. of 42-43 kDa and is highly homologous to UL43 of HSV-I. The correlation of tumorigenicity with stable integration and expression of Xho2 DNA in HPV-immortalized cells indicates that HSV-2 should be investigated further for a possible role in cervical cancer.

Sites of recombinant adeno-associated virus integration.

Adeno-associated virus (AAV), a defective parvovirus, is considered a promising vector for the delivery of therapeutic genes to cells. Both wild-type and recombinant AAV display a wide tropism and integrate into the host genome, in the absence of helper virus, establishing a latent infection. A unique characteristic of wild-type AAV and a potential advantage for use as a delivery system for gene therapy is the site-specific integration of wild-type virus within a small region of chromosome 19, 19q13.3-qter (AAVS1), in up to 85% of cell lines infected with the virus. Although recombinant AAVs, containing only the inverted terminal repeats of wild-type virus, can integrate efficiently into the host genome, specificity for the AAVS1 site appears to be lost. To address this question, the integration characteristics of two recombinant AAVs lacking the rep and cap genes in HeLa cells were examined. Analysis of Southern blots indicated that none of twenty-six cell clones generated after infection with either one of the recombinant AAVs demonstrated integration within the AAVS1 locus on chromo-some 19. Analysis of five of the cell lines by fluorescent chromosome in situ hybridization confirmed the loss of chromosome 19 specificity. Each integration site mapped near a known fragile site and/or location of a proto-oncogene or growth regulatory gene. Retention of site-specific integration of wild-type AAV will require the inclusion of additional AAV-specific sequences within the recombinant vectors.

Inhibition of HPV-16 E6/E7 immortalization of normal keratinocytes by hairpin ribozymes.

HPV-16 E6 and E7 genes are required to efficiently immortalize a broad spectrum of cell types including cervical keratinocytes. Therefore, the E6/E7 genes can be considered relevant targets for anti-cancer therapy. We produced several engineered hairpin (HP) ribozymes to specifically disrupt HPV-16 E6/E7 mRNA. After extensive biochemical characterization, one anti-E6 HP ribozyme (R434) was selected for in vivo testing because of its superior catalytic capabilities. When expressed in cis, R434 efficiently inhibited E6 in vitro translation. Cis-expression of the HP ribozyme with HPV-16 E6/E7 genes in normal human keratinocytes reduced the growth rate and prevented immortalization. RNA analysis by reverse transcription-PCR showed that E6/E7 transcripts were cleaved in post-transfected cells and virtually were eliminated after long term expression. Of interest, an inactive version of the HP also was able to significantly affect the immortalizing ability of E6/E7, probably through passive hybridization. The combination of passive and cleaving antisense RNA therefore is established as an effective inhibitor of HPV-16 E6/E7 immortalization.

Selection of human cervical epithelial cells that possess reduced apoptotic potential to low-oxygen conditions.

Since human papillomavirus (HPV) infection is strongly associated with cervical neoplasia and tumor hypoxia has prognostic significance in human cervical carcinomas, we examined the relationship between hypoxia and apoptosis in human cervical epithelial cells expressing high-risk HPV type 16 oncoproteins. In vitro, hypoxia stimulated both p53 induction and apoptosis in primary cervical epithelial cells infected with the HPV E6 and E7 genes but not in cervical fibroblasts infected with E6 and E7. Furthermore, cell lines derived from HPV-associated human cervical squamous cell carcinomas were substantially less sensitive to apoptosis induced by hypoxia, indicating that these cell lines have acquired additional genetic alterations that reduced their apoptotic sensitivity. Although the process of long-term cell culturing resulted in selection for subpopulations of HPV oncoprotein-expressing cervical epithelial cells with diminished apoptotic potential, the exposure of cells to hypoxia greatly accelerated the selection process. These results provide evidence for the role of hypoxia-mediated selection of cells with diminished apoptotic potential in the progression of human tumors and can in part explain why cervical tumors that possess low pO2 values are more aggressive.

Altered expression of Erg and Ets-2 transcription factors is associated with genetic changes at 21q22.2-22.3 in immortal and cervical carcinoma cell lines.

Human Papillomavirus (HPV) type 16 is the most frequently detected HPV in cervical cancer. Although epidemiologic and experimental evidence indicates a prominent role for HPV infection in the development of this disease, other factors are also involved. Altered expression of the ets family transcription factors erg and ets-2 was found associated with the development of cervical carcinoma. Overexpression also occurred in a HPV-16-immortalized cervical cell line, CX16-2, which has HPV integrated at a translocation breakpoint t(19;21) involving 21q22.2-22.3, where these genes have been mapped. Six of 10 cervical carcinoma cell lines overexpressed ets-2 RNA suggesting an association of overexpression with cervical cell neoplasia. A clonally related pair of cervical carcinoma cell lines, C-4I and C-4II, showed differential expression of erg and ets-2. C-4I overexpressed ets-2 RNA compared to normal cervical cells and C-4II. C-4II expressed a 5.3 kb erg transcript not seen in C-4I, ectocervical cells or other cervical carcinoma cell lines examined. Pulsed field gel electrophoresis was used to analyse changes in DNA fragments related to structural changes and to construct a physical map encompassing erg and ets-2. Alterations in erg and ets-2 RNA expression in each of three different cell lines examined were associated with translocations. Association between altered expression of erg and ets-2 and altered regional structural suggests that these genes are important targets in cervical carcinogenesis.

Papillomaviruses and potential copathogens.

An in vitro multistage genital epithelial cell model for cervical cancer that parallels the in vivo neoplastic process has been developed using recombinant human papillomavirus (HPV) DNA and genital cells. HPV-16-immortalized genital cells are responsive to the genotoxic action of known chemical carcinogens (polycyclic hydrocarbons, alkylating agents or cigarette smoke condensate), but are not converted to malignancy. Ras oncogene and human herpes virus-2 did convert HPV immortalized cells to malignancy, whereas human herpes virus-6 infection only increased HPV expression. Human immunodeficiency virus did not infect genital cells.

Enhancement of TAT-induced transactivation of the HIV-1 LTR by two genomic fragments of HHV-6.

Clinical and experimental observations suggest that human herpesvirus-6 (HHV-6), a T-lymphotropic herpesvirus, may act as a cofactor in the acquired immunodeficiency syndrome (AIDS). Moreover, a possible role of HHV-6 in the increased incidence and severity of cervical carcinoma in human immunodeficiency virus (HIV)-infected women was suggested by the recent observation that HHV-6 can infect cervical carcinoma cells, accelerating their tumorigenicity in vivo. Therefore, the ability of four HHV-6 genomic clones derived from HHV-6 to transactivate the long terminal repeat (LTR) of HIV-1 in two cervical carcinoma cell lines and in a T-lymphoid cell line was tested. Two HHV-6 clones, pZVH-14 and pZVB-70, which were previously shown to increase the expression of human papillomavirus (HPV)-transforming genes, were, per se, weak transactivators of the HIV-1 LTR. However, an increased effect occurred when these clones were combined with the HIV-1 transactivator TAT-1. No such effect was seen with two other HHV-6 clones used as controls. Analysis with HIV-1 LTR deletion mutants indicated that this enhancing effect requires the presence of elements contained in both the enhancer region and the TAT activation region (TAR) of HIV-1. This data may have implications for the potential role of HHV-6 in AIDS and AIDS-related cervical carcinoma.

Tissue-specific expression, evolutionary conservation and localization of the cph proto-oncogene on Syrian hamster chromosome X.

Treatment of Syrian hamster embryo fibroblasts with a single dose of 3-methylcholanthrene caused the activation of the transforming potential of cellular sequences (Notario et al, Oncogene 5: 1425-1430, 1990), which were subsequently isolated by cosmid rescue techniques, and further identified as a novel oncogene, termed cph because of its involvement in the carcinogenic progression of hamster embryo cells (Velasco et al, Oncogene 9: 2065-2069, 1994). We have analysed the expression of the cph proto-oncogene in adult Syrian hamster tissues by northern hybridization using cph-specific genomic probes. The three cph transcripts expressed in normal and neoplastic Syrian hamster embryo cells in culture (5.0, 3.5 and 2.0 kb) were also present in most adult tissues, although different mRNA species, most likely resulting from alternative splicing events, were expressed in testes. The highest steady-state level of cph mRNA was found in kidney, whereas cph expression was nearly undetectable in skin and skeletal muscle. Southern blot analyses of DNAs from other eucaryotic organisms were performed under moderate stringency conditions with a Syrian hamster-specific cph probe. Discrete cph-hybridizing sequences were present in genomes from yeast to mammalian species, including humans, thus demonstrating that cph is a highly conserved gene in eucaryotic evolution. Using fluorescence in situ hybridization (FISH), we have determined also the chromosomal localization of the cph proto-oncogene in the hamster genome. FISH experiments demonstrated that cph is a single copy gene, localized on the euchromatic short arm of the X chromosome, at region Xpa7. Because chromosome X is frequently involved in structural alterations in neoplastic Syrian hamster cells transformed by chemical carcinogens and oncogenic viruses, the localization of the cph locus on this chromosome supports the notion that the cph oncogene plays a role in the malignant conversion of chemically transformed hamster fibroblasts. The wide range of tissue-specific expression and species-specific distribution of cph strongly suggest that the normal function of the cph protein product(s) may be essential for metabolic processes involved in the regulation of cell proliferation and survival.

Immortalization of human adult prostatic adenocarcinoma cells by human papilloma virus HPV16 and -18 DNA.

Primary prostate epithelial and prostate adenocarcinoma cells cultured in serum-free medium grew for up to 10 passages before senescence. Cells from prostate adenocarcinoma of a 55-year-old patient without lymph node involvement were transfected with plasmids containing recombinant human papilloma virus HPV16 or HPV18 DNA and the selectable neomycin-resistance gene. After G-418 selection, cells underwent crisis, and surviving cells infected with retroviruses encoding the HPV18 E6/E7 genes (HPV-PAC1), transfected with a head-to-tail dimer of the complete HPV16 genome (HPV-PAC2), or transfected with HPV18 E6/E7 early genes (HPV-PAC3) were established. HPV-PAC1 and HPV-PAC2 cultures appeared morphologically similar to primary cultures even after 40 passages. However, HPV-PAC2 cultures had a clonal morphology. All lines were positive for cytokeratin 18, had acquired vimentin expression, and contained either HPV16 or HPV18 sequences integrated into host DNA. None was tumorigenic in nude mice or formed colonies in soft agar. These cells did not secrete prostate specific antigen nor respond to androgen although tamoxifen inhibited the growth of the cells. Immunohistochemistry showed no evidence of p53 overexpression. Further characterization of these cell lines and examination of their response to chemotherapeutic agents may provide relevant information for the study of hormone-independent PC.

CDKN2 in HPV-positive and HPV-negative cervical-carcinoma cell lines.

Human cervical cancers frequently contain retinoblastoma protein (Rb) that is inactivated by binding with human papilloma virus (HPV) E7 protein or through mutation. The CDKN2 gene encodes p16INK4 which inhibits cdk4-cyclin D phosphorylation of Rb, preventing the G1-S transition. To determine whether abnormalities of CDKN2 occur in cervical-cancer cells, II cervical cell lines, including 8 HPV-positive cell lines, 2 HPV-negative cell lines containing mutant Rb, and one tumorigenic cell line derived from normal cervical cells following transfection with HPV-16 and v-H-ras (CX16-2HR), were analyzed. No cell line had a homozygous deletion of exon 1 or 2 of CDKN2, and only one cell line, CX16-2HR, had an altered DNA sequence, which represents a common polymorphism at codon 148. To exclude the possibility of other subtle inactivating mutations, immunoblot analysis of protein lysates was performed using a polyclonal anti-p16INK4 rabbit anti-serum. Abundant levels of normal-sized p16INK4 were observed in all cell samples. Thus, no alterations of CDKN2 were detected in these cervical cell lines. These results confirm that mutational inactivation of p16INK4 is a rare event in tumor samples with compromised Rb activity.

Human herpesvirus 6 as a potential copathogen.

The molecular, biological and immunological studies of the recently identified human herpesvirus 6 (HHV-6) suggest that the virus is involved in the etiology of at least three lymphoproliferative diseases. Furthermore, HHV-6 may be an important cofactor in the pathogenesis of several other diseases, including HIV-associated disease and some cancers, but further investigation is needed to establish a causal relationship.

Molecular cytogenetics of human papillomavirus-negative cervical carcinoma cell lines.

Cervical cancer is a malignancy closely associated with human papillomavirus (HPV). However, some cervical carcinomas occur in the absence of the virus. Two HPV-negative cervical carcinoma cell lines, C-33A and HT-3, were examined by G-banding and fluorescence in situ hybridization (FISH) using several whole chromosome and satellite probes. Combined conventional banding and FISH analysis significantly enhanced identification of complex and cryptic chromosome rearrangements. Common to both cell lines were translocations of chromosome 1, involving a specific site on the short arm and partial or complete loss of the short arm of chromosome 9, as well as loss of chromosome 13. The C-33A line had a relatively simple chromosomal constitution, with chromosome 1 being involved in translocations with chromosomes 9, 18, and 21. Karyotype reconstruction of G-banded and painted chromosomes indicate a net loss of DNA as a result of unbalanced translocations, which occurred only at site 9p24 and loss of one copy of chromosomes 13 and 14. In contrast, HT-3 cells had complex rearrangements and deletions of chromosomes 1p, 3p, 9p, 10q/p, 11p/q, and 17p, all regions with known tumor suppressor genes. The deletions observed in these HPV-negative cervical carcinomas will be important in delineating regions of tumor suppressor genes.

Transcriptional repression in normal human keratinocytes by wild-type and mutant p53.

Wild-type p53 is a nuclear phosphoprotein that inhibits cell proliferation and represses transcriptionally most TATA box-containing promoters in transformed or tumor-derived cell lines. This study demonstrates that p53 alters transcription of the long control region (LCR) of human papillomavirus type 18 (HPV-18). Wild-type and mutant p53 143Val to Ala repressed the HPV-18 LCR promoter in normal human keratinocytes, the natural host cell for HPV infections. Repression by wild-type p53 was also observed in C-33A cells and in an HPV-16-immortalized cell line with an inducible wild-type p53. However, when C-33A cells were cotransfected with the HPV-18 LCR and mutant 143Val to Ala, repression did not occur. Mutant p53 135Cys to Ser did not induce repression in either normal human keratinocytes or in the C-33A line; although like 143Val to Ala, it is thought to affect the DNA binding activity of the wild-type protein. The ability of mutant p53 143Val to Ala to inactivate the HPV early promoter in normal cells (by approximately 60% reduction) suggests that this mutant may be able to associate with wild-type p53 and interact with TATA box-binding proteins. Therefore, these results demonstrate that the transcriptional activities of p53 mutants may be dependent upon the cell type assayed and the form of its endogenous p53. Furthermore, normal human keratinocytes represent an alternative model for determining the activities of p53 mutants.

Refined localization of the erbB-3 proto-oncogene by direct visualization of FISH signals on LUT-inverted and contrast-enhanced digital images of DAPI-banded chromosomes.

Contrast-enhanced, look-up-table (LUT)-inverted digital images of DAPI-banded chromosomes after fluorescence in situ hybridization (FISH) permit direct regional chromosomal localization of the fluorescent signals of single-copy gene probes. Improved quality and resolution of chromosome banding allowed a refined localization of the erbB-3 protooncogene from chromosome band 12q13 to sub-bands 12q13.2-13.3. This procedure can be used for direct and precise mapping of single-copy genes on both normal and cancer-cell-rearranged chromosomes.

Detection of human herpesvirus 6 and human papillomavirus 16 in cervical carcinoma.

A subset of human papillomaviruses (HPVs) is associated with the majority of cervical cancers; however, cofactors appear to be required for carcinogenic progression of HPV-induced neoplasia. As human herpesvirus-6 (HHV-6) was recently shown to infect cervical epithelial cells in vitro and activate transcription of HPV-transforming genes, human cervical dysplasia and cancers were analyzed for the presence of HHV-6 by multiple methods, including polymerase chain reaction, slot blot, Southern blot, and in situ hybridization. HHV-6 DNA sequences were detected in 6 of 72 cases of squamous cervical carcinoma and cervical intraepithelial neoplasia. HPV-16 was found in four of the HHV-6-positive cases (two squamous cervical carcinomas and two cervical intraepithelial neoplasias). None of the 30 normal cervices and biopsies of patients with cervicitis was positive for HHV-6 DNA. These results are the first suggestion of an in vivo association between HHV-6 and some cervical neoplasia.

cph, a novel oncogene which cooperates with H-ras in the transformation of NIH3T3 fibroblasts.

We have performed the molecular cloning of the non-ras transforming sequences previously detected in neoplastic Syrian hamster embryo fibroblasts initiated in vitro with 3-methylcholanthrene (MCA) (Notario et al., 1990). These sequences were isolated using cosmid-rescue techniques from a third-cycle NIH3T3 transformant obtained by sequential transfections of genomic DNA from MCA-initiated hamster fetal cells. Rescued (C-5) clones encompassed about 42.5 kbp of Syrian hamster genomic DNA containing hamster-specific repetitive elements (HRS). An internal 19 kbp BamHI fragment (B-1) was the only C-5 fragment which recognized specific transcripts in poly(A)+ RNA from hamster embryo cells. The same mRNA species were present in both normal and MCA-initiated neoplastic cells: a major transcript of about 2.5 kb, and other less abundant ones, ranging from approximately 2.0 kb to 5.0 kb. These mRNA species were detected consistently by each of several B-1 DNA subfragments located at positions spanning almost the entire B-1 length. The nucleotide sequence of some transcript-positive (S5P2 and S6) genomic B-1 fragments was determined. No significant homology exists between the nucleotide sequences of these B-1 subfragments and established DNA databases. Therefore, the C-5 cosmid clone contains novel genomic sequences. Transfection of C-5 DNA into mouse NIH3T3 cells resulted in the appearance of transformed foci (about five foci per microgram of DNA) within 25 days post-transfection, thus demonstrating the transforming activity of the C-5 clone, which was consequently renamed as the cph oncogene. Co-transfection of the cph oncogene with the human H-ras oncogene (T24), demonstrated a synergistic action between the two oncogenes in the transformation of murine fibroblasts.