Overlapping YY1- and aberrant SP1-binding sites proximal to the early promoter of human papillomavirus type 16

Three-dimensional chromatin analysis reveals Sp1 as a mediator to program and reprogram HPV-host epigenetic architecture in cervical cancer

Human papillomavirus (HPV) is predominantly associated with HPV-related cancers, however, the precise mechanisms underlying the HPV-host epigenetic architectures in HPV carcinogenesis remain elusive. Here, we employed high-throughput chromosome conformation capture (Hi-C) to comprehensively map HPV16/18-host chromatin interactions. Our study identified the transcription factor Sp1 as a pivotal mediator in programming HPV-host interactions. By targeting Sp1, the active histone modifications (H3K27ac, H3K4me1, and H3K4me3) and the HPV-host chromatin interactions are reprogrammed, which leads to the downregulation of oncogenes located near the integration sites in both HPV (E6/E7) and the host genome (KLF5/MYC). Additionally, Sp1 inhibition led to the upregulation of immune checkpoint genes by reprogramming histone modifications in host cells. Notably, humanized patient-derived xenograft (PDX-HuHSC-NSG) models demonstrated that Sp1 inhibition promoted anti-PD-1 immunotherapy via remodeling the tumor immune microenvironment in cervical cancer. Moreover, single-cell transcriptomic analysis validated the enrichment of transcription factor Sp1 in epithelial cells of cervical cancer. In summary, our findings elucidate Sp1 as a key mediator involved in the programming and reprogramming of HPV-host epigenetic architecture. Inhibiting Sp1 with plicamycin may represent a promising therapeutic option for HPV-related carcinoma.

Functional evaluation of human papillomavirus type 31 long control region variants

Persistent infections by high-risk human papillomavirus (HR-HPV) are a necessary condition, but not sufficient for cervical cancer development. Genetic variants of HR-HPV appear to be related to the risk of persistent infections. The study performed a functional evaluation of variants of the HPV-31 promoter region (LCR). For this, cloning and subcloning of variants HPV-31/UFPE-21 HPV-31/UFPE-89, HPV-31/UFPE-66, E2 gene and prototype HPV-31 were performed. Transfection with different concentrations of E2 was done and the concentration of 25 ng was determined to be ideal for LCR activation. HPV-31/UFPE-21 and HPV-31/UFPE-89 have a greater ability to alter Nluc reporter gene expression levels and HPV-31/UFPE-66 showed decreased levels of gene expression of Nluc reporter gene compared to control. Statistical analysis showed a significant difference between the polymorphic LCR regions and the control (p < 0.0001). A more refined profile of variants of HPV-31 and its importance for the prognosis of cervical lesions begins to be drawn.

Yin Yang 1 (YY1): Regulation of Survivin and Its Role In Invasion and Metastasis

Despite significant clinical and basic science advancements, cancer remains a devastating disease that affects people of all ages, races, and backgrounds. The pathogenesis of cancer has recently been described to result from eight biological capabilities or hallmarks and two enabling characteristics. These eight hallmarks are: deregulation of cellular energetics, avoiding immune destruction, enabling replicative immortality, inducing angiogenesis, sustaining proliferative signaling, evading growth suppressors, resisting cell death, and activating invasion and metastasis. The enabling characteristics are: genome instability and mutation and tumor-promoting inflammation. Survivin, the fourth most common transcript found in cancer cells, is a protein that is thought to be involved in the enhanced proliferation, survival, and metastasis and possibly other key hallmarks of cancer cells. Understanding how this gene is turned on and off is vitally important for attempt improving cancer management and therapy. Our work has identified a novel transcriptional regulator of survivin called Yin Yang 1 (YY1), which has been observed to activate some gene promoters and repress others and is gaining increasing interest as a target of cancer therapy. Our work shows for the first time that YY1 represses survivin transcription by physically interacting with the survivin promoter. Furthermore, YY1 appears to contribute to basal survivin transcriptional activity, indicating that disruption of its binding may in part contribute to survivin overexpression after cellular stress events including chemotherapy and radiotherapy.

Short half-life of HPV16 E6 and E7 mRNAs sensitizes HPV16-positive tonsillar cancer cell line HN26 to DNA-damaging drugs

Here we show that treatment of the HPV16-positive tonsillar cancer cell line HN26 with DNA alkylating cancer drug melphalan-induced p53 and activated apoptosis. Melphalan reduced the levels of RNA polymerase II and cellular transcription factor Sp1 that were associated with HPV16 DNA. The resulting inhibition of transcription caused a rapid loss of the HPV16 early mRNAs encoding E6 and E7 as a result of their inherent instability. As a consequence of HPV16 E6 and E7 down-regulation, the DNA damage inflicted on the cells by melphalan caused induction of p53 and activation of apoptosis in the HN26 cells. The BARD1-negative phenotype of the HN26 cells may have contributed to the failure to repair DNA damage caused by melphalan, as well as to the efficient apoptosis induction. Finally, nude mice carrying the HPV16 positive tonsillar cancer cells responded better to melphalan than to cisplatin, the chemotherapeutic drug of choice for tonsillar cancer. We concluded that the short half-life of the HPV16 E6 and E7 mRNAs renders HPV16-driven tonsillar cancer cells particularly sensitive to DNA damaging agents such as melphalan since melphalan both inhibits transcription and causes DNA damage.

The Yin and Yang of YY1 in tumor growth and suppression

Yin Yang-1 (YY1) is a zinc finger protein and member of the GLI-Kruppel family that can activate or inactivate gene expression depending on interacting partners, promoter context and chromatin structure, and may be involved in the transcriptional control of ∼10% of the total mammalian gene set. A growing body of literature indicates that YY1 is overexpressed in multiple cancer types and that increased YY1 levels correlate with poor clinical outcomes in many cancers. However, the role of YY1 in the promotion or suppression of tumor growth remains controversial and its regulatory effects may be tumor cell type dependent at least in experimental systems. The molecular mechanisms responsible for the apparently conflicting roles of YY1 are not yet fully elucidated. This review highlights recent advances in our understanding of regulatory insights involving YY1 function in a range of cancer types. For example, YY1's roles in tumor growth involve stabilization of hypoxia-inducible factor HIF-1α in a p53 independent manner, negative regulation of miR-9 transcription, control of MYCT1 transcription, a novel miR-193a-5p-YY1-APC axis, intracellular ROS and mitochondrial superoxide generation, p53 reduction and EGFR activation, control of genes associated with mitochondrial energy metabolism and miRNA regulatory networks involving miR-7, miR-9, miR-34a, miR-186, miR-381, miR-584-3p and miR-635. On the other hand, tumor suppressor roles of YY1 appear to involve YY1 stimulation of tumor suppressor BRCA1, increased Bax transcription and apoptosis involving cytochrome c release and caspase-3/-7 cleavage, induction of heme oxygenase-1, inhibition of pRb phosphorylation and p21 binding to cyclin D1 and cdk4, reduced expression of long noncoding RNA of SOX2 overlapping transcript, and MUC4/ErbB2/p38/MEF2C-dependent downregulation of MMP-10. YY1 expression is associated with that of cancer stem cell markers SOX2, BMI1 and OCT4 across many cancers suggesting multidynamic regulatory control and groups of cancers with distinct molecular signatures. Greater understanding of the mechanistic roles of YY1 will in turn lead to the development of more specific approaches to modulate YY1 expression and activity with therapeutic potential.

Role of WDHD1 in Human Papillomavirus-Mediated Oncogenesis Identified by Transcriptional Profiling of E7-Expressing Cells

The E7 oncoprotein of the high-risk human papillomavirus (HPV) plays a major role in HPV-induced carcinogenesis. E7 abrogates the G1 cell cycle checkpoint and induces genomic instability, but the mechanism is not fully understood. In this study, we performed RNA sequencing (RNA-seq) to characterize the transcriptional profile of keratinocytes expressing HPV 16 (HPV-16) E7. At the transcriptome level, 236 genes were differentially expressed between E7 and vector control cells. A subset of the differentially expressed genes, most of them novel to E7-expressing cells, was further confirmed by real-time PCR. Of interest, the activities of multiple transcription factors were altered in E7-expressing cells. Through bioinformatics analysis, pathways altered in E7-expressing cells were investigated. The upregulated genes were enriched in cell cycle and DNA replication, as well as in the DNA metabolic process, transcription, DNA damage, DNA repair, and nucleotide metabolism. Specifically, we focused our studies on the gene encoding WDHD1 (WD repeat and high mobility group [HMG]-box DNA-binding protein), one of the genes that was upregulated in E7-expressing cells. WDHD1 is a component of the replisome that regulates DNA replication. Recent studies suggest that WDHD1 may also function as a DNA replication initiation factor as well as a G1 checkpoint regulator. We found that in E7-expressing cells, the steady-state level of WDHD1 protein was increased along with the half-life. Moreover, downregulation of WDHD1 reduced E7-induced G1 checkpoint abrogation and rereplication, demonstrating a novel function for WDHD1. These studies shed light on mechanisms by which HPV induces genomic instability and have therapeutic implications.

IMPORTANCE

The high-risk HPV types induce cervical cancer and encode an E7 oncoprotein that plays a major role in HPV-induced carcinogenesis. However, the mechanism by which E7 induces carcinogenesis is not fully understood; specific anti-HPV agents are not available. In this study, we performed RNA-seq to characterize transcriptional profiling of keratinocytes expressing HPV-16 E7 and identified more than 200 genes that were differentially expressed between E7 and vector control cells. Through bioinformatics analysis, pathways altered in E7-expressing cells were identified. Significantly, the WDHD1 gene, one of the genes that is upregulated in E7-expressing cells, was found to play an important role in E7-induced G1 checkpoint abrogation and rereplication. These studies shed light on mechanisms by which HPV induces genomic instability and have therapeutic implications.

Negative regulation of DsbA-L gene expression by the transcription factor Sp1

Disulfide-bond A oxidoreductase-like protein (DsbA-L) possesses beneficial effects such as promoting adiponectin multimerization and stability, increasing insulin sensitivity, and enhancing energy metabolism. The expression level of DsbA-L is negatively correlated with obesity in mice and humans, but the underlying mechanisms remain unknown. To address this question, we generated reporter gene constructs containing the promoter sequence of the mouse DsbA-L gene. Deletion analysis showed that the proximal promoter of mouse DsbA-L is located between -186 and -34 bp relative to the transcription start site. In silico analysis identified a putative Sp1 transcription factor binding site in the first intron of the DsbA-L gene. Electrophoretic mobility shift assay and chromatin immunoprecipitation analysis indicated that Sp1 bound to this intron region in vitro and in intact cells. Overexpression of Sp1 or suppressing Sp1 expression by siRNA reduced or increased DsbA-L promoter activity, respectively. The binding activity of Sp1 was gradually decreased during 3T3-L1 cell differentiation and was significantly increased in adipose tissues of obese mice. Our results identify Sp1 as an inhibitor of DsbA-L gene transcription, and the Sp1-mediated inhibition of DsbA-L gene expression may provide a mechanism underlying obesity-induced adiponectin downregulation and insulin resistance.

Transcription of the vascular endothelial growth factor receptor-3 (VEGFR3) gene is regulated by the zinc finger proteins Sp1 and Sp3 and is under epigenetic control: transcription of vascular endothelial growth factor receptor 3

BACKGROUND

In the past, the vascular endothelial growth factor receptor-3 (VEGFR-3) has been linked to the regulation of lymphangiogenesis and the lymphatic spread of solid malignancies. The molecular mechanisms controlling VEGFR3 gene expression have, however, remained poorly understood. Here, we aimed at assessing these mechanisms through VEGFR3 gene promoter analysis and the identification of transcription factors binding to it. In addition, we focussed on epigenetic modifications underlying VEGFR3 transcription regulation.

METHODS

5' Deletion analyses for the identification of functional promoter elements, electrophoretic mobility shift assays, chromatin immunoprecipitations, methylation-specific PCRs, and Trichostatin A (TSA) and 5-Aza desoxycytidine (5-Aza dC) treatments were performed in this study.

RESULTS

Following the isolation of a 2 kb stretch of 5'-flanking DNA of VEGFR3, we identified a novel GC-rich element (GRE) spanning -101/-66 sufficient for VEGFR3 transcription and activated by Sp1 and Sp3, respectively. Histone de-acetylase inhibition by TSA led to the accumulation of acetylated histones H3/H4 at the VEGFR3 gene promoter, up-regulation of its mRNA levels, and transactivation of promoter reporter constructs in endothelial cell lines. Similarly, methylation inhibition by 5-Aza dC triggered up-regulation of VEGFR3 mRNA levels and increased promoter activity. TSA and 5-Aza-dC did not influence Sp1/Sp3 binding, but increased the transactivating capacity of both transcription factors, suggesting epigenetic modification as an underlying mechanism.

CONCLUSIONS

Here we describe the identification of regulatory elements controlling human VEGFR3 gene expression and show that histone acetylation and CpG methylation are important determinants of VEGFR3 transcription regulation. These findings may facilitate the development of intervention strategies aimed at targeting VEGFR3-based tumor lymphangiogenesis and/or lymphatic tumor spread.

Yin-Yang1 is required for epithelial-to-mesenchymal transition and regulation of Nodal signaling during mammalian gastrulation

The ubiquitously expressed Polycomb Group protein Yin-Yang1 (YY1) is believed to regulate gene expression through direct binding to DNA elements found in promoters or enhancers of target loci. Additionally, YY1 contains diverse domains that enable a plethora of protein-protein interactions, including association with the Oct4/Sox2 pluripotency complex and Polycomb Group silencing complexes. To elucidate the in vivo role of YY1 during gastrulation, we generated embryos with an epiblast specific deletion of Yy1. Yy1 conditional knockout (cKO) embryos initiate gastrulation, but both primitive streak formation and ingression through the streak is severely impaired. These streak descendants fail to repress E-Cadherin and are unable to undergo an appropriate epithelial to mesenchymal transition (EMT). Intriguingly, overexpression of Nodal and concomitant reduction of Lefty2 are observed in Yy1 cKO embryos, suggesting that YY1 is normally required for proper Nodal regulation during gastrulation. Furthermore, definitive endoderm is specified but fails to properly integrate into the outer layer. Although anterior neuroectoderm is specified, mesoderm production is severely restricted. We show that YY1 directly binds to the Lefty2 locus in E7.5 embryos and that pharmacological inhibition of Nodal signaling partially restores mesoderm production in Yy1 cKO mutant embryos. Our results reveal critical requirements for YY1 during several important developmental processes, including EMT and regulation of Nodal signaling. These results are the first to elucidate the diverse role of YY1 during gastrulation in vivo.

Susceptibility to cervical cancer: an overview

Cervical cancer is the second most common cancer in females worldwide. It is well-established that Human Papillomavirus (HPV) infections play a critical role in the development of cervical cancer. However, a large number of women infected with oncogenic HPV types will never develop cervical cancer. Thus, there are several external environment and genetic factors involved in the progression of a precancerous lesion to invasive cancer. In this review article, we addressed possible susceptible phenotypes to cervical cancer, focusing on host genome and HPV DNA variability, multiple HPV infections, co-infection with other agents, circulating HPV DNA and lifestyle.

YY1 is a novel potential therapeutic target for the treatment of HPV infection-induced cervical cancer by arsenic trioxide

OBJECTIVE

YY1 is a zinc finger transcription factor involved in the regulation of cell growth, development, and differentiation. Although YY1 can regulate human papillomavirus-type (HPV) viral oncogenes E6 and E7, it remains unknown if YY1 plays a key role in carcinoma progression of HPV-infected cells. Here we sought to determine whether YY1 is upregulated in the cervical cancer tissues and YY1 inhibition contributes to apoptosis of cervical cancer cells, which is at least partly p53 dependent. Therefore, YY1 can be a potential therapeutic target for cervical cancer treatment by arsenic trioxide (As2O3).

MATERIALS AND METHODS

The expression level of YY1 was examined and analyzed by Western blot in pathologically confirmed primary cervical cancer samples, in the adjacent normal samples, as well as in normal cervix samples. The effects of YY1 inhibition by specific small interfering RNA in HeLa cells were determined by Western blot analysis of p53 level, cell growth curve, colony formation assay, and apoptosis. The contribution of YY1 to As2O3-induced p53 activation and apoptosis was also examined by Western blot and cell cycle analysis.

RESULTS

Here we report that the expression level of YY1 is significantly elevated in the primary cancer tissues. In HPV-positive HeLa cells, small interfering RNA-mediated YY1 inhibition induced apoptosis and increased the expression of p53. Treatment of HeLa cells with As2O3, a known anti-cervical cancer agent, reduced both protein and mRNA levels of YY1 in HeLa cells. YY1 knockdown significantly further enhanced As2O3-induced apoptosis.

CONCLUSIONS

These results demonstrated that the expression of YY1 is upregulated in cervical carcinomas and that YY1 plays a critical role in the progression of HPV-positive cervical cancer. In addition, YY1 inhibition induces p53 activation and apoptosis in HPV-infected HeLa cells. Thus, YY1 is an As2O3 target and could serve as a potential drug sensitizer for anti-cervical cancer therapy.

Human papillomavirus 16 variants from Zambian women with normal pap smears

Human papillomavirus (HPV) type 16 is the most prevalent high-risk viral genotype associated with cervical cancer. Six distinct phylogenetic clusters of HPVs have been identified and are distributed differently across five continents. HPV16 DNA was extracted from cervicolavage samples from women with normal pap smears. The LCR regions were amplified in triplicate, cloned, sequenced, and analyzed from a total of 11 recovered HPV16 positive samples [Ng'andwe et al. (2007): BMC Infect Dis 7:77] were analyzed for sequence variation. The HPV16 LCR variants were assessed for promoter activity by use of a luciferase reporter gene. Six novel HPV16 variants with nucleotide exchanges in the LCR region were identified. Five clones were classified as European group HPV16 variants and one as an African group variant. Two of these variants had relatively lower promoter activity, 30% of that of the wild-type strain. The decreased promoter activity of some HPV16 variants may decrease expression of viral oncogenes and may be linked with the development, phenotype and severity of the cervical lesions in women infected with these across HPV16 variants.

Regulation of the human ascorbate transporter SVCT2 exon 1b gene by zinc-finger transcription factors

The sodium-dependent vitamin C transporter (SVCT) 2 is crucial for ascorbate uptake in metabolically active and specialized tissues. This study focused on the gene regulation of SVCT2 exon 1b, which is ubiquitously expressed in human and mouse tissues. Although the human SVCT2 exon 1b promoter does not contain a classical TATA box, we found that it does contain a functional initiator that binds Yin Yang-1 (YY1) and interacts with upstream Sp1/Sp3 elements in the proximal promoter region. These elements in turn play a critical role in regulating YY1-mediated transcription of exon 1b. Formation of YY1/Sp complexes on the promoter is required for its optional function. YY1 with Sp1 or Sp3 synergistically enhanced exon 1b promoter activity as well as the endogenous SVCT2 protein expression. Further, in addition to Sp1/Sp3, both EGR-1 and EGR-2 were detected in the protein complexes that bound the three GC boxes bearing overlapping binding sites for EGR/WT1 and Sp1/3. The EGR family factors WT1 and MAZ were found to differentially regulate exon 1b promoter activity. These results show that differential occupancy of transcription factors on the GC-rich consensus sequences in the SVCT2 exon 1b promoter contributes to the regulation of cell and tissue expression of SVCT2.

Upstream regulatory region alterations found in human papillomavirus type 16 (HPV-16) isolates from cervical carcinomas increase transcription, ori function, and HPV immortalization capacity in culture

Human papillomavirus (HPV) DNAs isolated from cervical and head and neck carcinomas frequently contain nucleotide sequence alterations in the viral upstream regulatory region (URR). Our study has addressed the role such sequence changes may play in the efficiency of establishing HPV persistence and altered keratinocyte growth. Genomic mapping of integrated HPV type 16 (HPV-16) genomes from 32 cervical cancers revealed that the viral E6 and E7 oncogenes, as well as the L1 region/URR, were intact in all of them. The URR sequences from integrated and unintegrated viral DNA were found to harbor distinct sets of nucleotide substitutions. A subset of the altered URRs increased the potential of HPV-16 to establish persistent, cell growth-altering viral-genome replication in the cell. This aggressive phenotype in culture was not solely due to increased viral early gene transcription, but also to augmented initial amplification of the viral genome. As revealed in a novel ori-dependent HPV-16 plasmid amplification assay, the altered motifs that led to increased viral transcription from the intact genome also greatly augmented HPV-16 ori function. The nucleotide sequence changes correlate with those previously described in the distinct geographical North American type 1 and Asian-American variants that are associated with more aggressive disease in epidemiologic studies and encompass, but are not limited to, alterations in previously characterized sites for the negative regulatory protein YY1. Our results thus provide evidence that nucleotide alterations in HPV regulatory sequences could serve as potential prognostic markers of HPV-associated carcinogenesis.

Control of the papillomavirus early-to-late switch by differentially expressed SRp20

The viral early-to-late switch of papillomavirus infection is tightly linked to keratinocyte differentiation and is mediated in part by alternative mRNA splicing. Here, we report that SRp20, a cellular splicing factor, controls the early-to-late switch via interactions with A/C-rich RNA elements. An A/C-rich SE4 element regulates the selection of a bovine papillomavirus type 1 (BPV-1) late-specific splice site, and binding of SRp20 to SE4 suppresses this selection. Expression of late BPV-1 L1 or human papillomavirus (HPV) L1, the major capsid protein, inversely correlates with SRp20 levels in the terminally differentiated keratinocytes. In HPV type 16, a similar SRp20-interacting element also controls the viral early-to-late switch. Keratinocytes in raft cultures, which support L1 expression, make considerably less SRp20 than keratinocytes in monolayer cultures, which do not support L1 expression. Conversely, abundant SRp20 in cancer cells or undifferentiated keratinocytes is important for the expression of the viral early E6 and E7 by promoting the expression of cellular transcription factor SP1 for transactivation of viral early promoters.

Human papillomavirus type 16 variant analysis of E6, E7, and L1 genes and long control region in biopsy samples from cervical cancer patients in north India

High-risk human papillomaviruses (HPVs), particularly HPV types 16 and 18 (HPV-16 and HPV-18, respectively), play a cardinal role in the etiology of cervical cancer. The most prevalent type, HPV-16, shows intratypic sequence variants that are known to differ in oncogenic potential and geographic distribution. This study was designed to analyze sequence variations in E6, E7, and L1 genes and the LCR (for long control region) of HPV-16 in cervical cancer patients to identify the most prevalent and novel HPV-16 variants and to correlate them with the severity of the disease. Cervical biopsies from 60 HPV-16-positive cancer cases were analyzed by PCR and DNA sequencing. The most frequently observed variations were T350G (100%) in E6, T789C (87.5%) in E7, A6695C (54.5%) in L1, and G7521A (91.1%) in the LCR. In addition, only one novel variant (T527A) in E6 and four new variants each in L1 (A6667C, A6691G, C6906T, and A6924C) and in the LCR (C13T, A7636C, C7678T, and G7799A) were identified. While E7 was found to be highly conserved, the variant 350G of E6 was the most prevalent in all of the histopathological grades. The majority of LCR variants were found at the YY1 transcription factor binding sites. Interestingly, a complete absence of the Asian lineage and a high prevalence of European lineages in E6, E7, L1, and the LCR (85, 86.7, 67.7, and 63.3%, respectively) indicate a possible epidemiological linkage between Europe and India with regard to the dissemination of HPV-16 infections in India.

Action of transcription factors in the control of transferrin receptor expression in human brain endothelium

Brain endothelium has a distinctive phenotype, including high expression of transferrin receptor, p-glycoprotein, claudin-5 and occludin. Dermal endothelium expresses lower levels of the transferrin receptor and it is absent from lung endothelium. All three endothelia were screened for transcription factors that bind the transferrin receptor promoter and show different patterns of binding between the endothelia. The transcription factor YY1 has distinct DNA-binding activities in brain endothelium and non-brain endothelium. The target-sites on the transferrin receptor promotor for YY1 lie in close proximity to those of the transcription initiation complex containing TFIID, so the two transcription factors potentially compete or interfere. Notably, the DNA-binding activity of TFIID was the converse of YY1, in different endothelia. YY1 knockdown reduced transferrin receptor expression in brain endothelium, but not in dermal endothelium, implying that YY1 is involved in tissue-specific regulation of the transferrin receptor. Moreover a distinct YY1 variant is present in brain endothelium and it associates with Sp3. A model is presented, in which expression from the transferrin receptor gene in endothelium requires the activity of both TFIID and Sp3, but whether the gene is transcribed in different endothelia, is related to the balance between activating and suppressive forms of YY1.

Essential role of the Box II cis element and cognate host factors in regulating the promoter of Rice tungro bacilliform virus

Rice tungro bacilliform virus (RTBV) is a double-stranded DNA virus with a single, tissue-specific promoter that is expressed primarily in phloem tissues. Rice transcription factors RF2a and RF2b bind to Box II, a cis element adjacent to the TATA box, and control gene expression from the promoter. Mutations were made in the promoter to delete or mutate Box II and the mutated promoters were fused to a reporter gene; the chimeric genes were expressed in transient BY-2 protoplast assays and in transgenic Arabidopsis plants. The results of these studies showed that Box II is essential to the activity of the RTBV promoter. A chimeric beta-glucuronidase (GUS) reporter gene containing the Box II sequence and a minimal promoter derived from the Cauliflower mosaic virus 35S promoter were co-transfected into protoplasts with gene constructs that encoded RF2a or RF2b. The reporter gene produced threefold higher GUS activity when co-transfected with RF2a, and 11-fold higher activity when co-transfected with RF2b, than in the absence of added transcription factors. Moreover, chimeric reporter genes were activated by approximately threefold following induction of expression of the RF2a gene in transgenic Arabidopsis plants. The work presented here and earlier findings show that Box II and its interactions with cognate rice transcription factors, including RF2a and RF2b, are essential to the activity of the RTBV promoter and are probably involved in expression of the RTBV genome during virus replication.

Variant upstream regulatory region sequences differentially regulate human papillomavirus type 16 DNA replication throughout the viral life cycle

While the central role of the viral upstream regulatory region (URR) in the human papillomavirus (HPV) life cycle has been well established, its effects on viral replication factor expression and plasmid replication of HPV type 16 (HPV16) remain unclear. Some nonprototypic variants of HPV16 contain altered URR sequences and are considered to increase the oncogenic risk of infections. To determine the relationship between viral replication and variant URRs, hybrid viral genomes were constructed with the replication-competent HPV16 prototype W12 and analyzed in assays which recapitulate the different phases of normal viral replication. The establishment efficiencies of hybrid HPV16 genomes differed about 20-fold among European prototypes and variants from Africa and America. Generally, European and African genomes exhibited the lowest replication efficiencies. The high replication levels observed with American variants were primarily attributable to their efficient expression of the replication factors E1 and E2. The maintenance levels of these viral genomes varied about fivefold, which correlated with their respective establishment phenotypes and published P(97) activities. Vegetative DNA amplification could also be observed with replicating HPV16 genomes. These results indicate that efficient E1/E2 expression and elevated plasmid replication levels during the persistent stage of infection may comprise a risk factor in HPV16-mediated oncogenesis.

Regulation of the Rat PhenylethanolamineN-Methyltransferase Gene by Transcription Factors Sp1 and MAZ

The rat phenylethanolamine N-methyltransferase (PNMT) gene promoter contains 1-base pair (bp) overlapping consensus sequences for Sp1 and MAZ transcription factors at -48 and -38 bp, respectively. Gel mobility assays using PC-12-derived RS1 cell nuclear extracts or in vitro translated proteins showed that Sp1 and MAZ specifically bind to these elements, that MAZ displaces/prevents Sp1 binding, and that Sp1 and MAZ binding is mutually exclusive, with occupancy dependent on each factor's concentration and affinity for its consensus element. In transfection assays, PNMT promoter activation by Sp1 and MAZ depends on promoter length, with -893 bp of sequence yielding greatest activation. Although MAZ has higher affinity for its binding element, it is a less effective activator. Changes in PNMT promoter activity for the constructs pGL3RP60 or pGL3RP893 using a fixed amount of MAZ expression construct and a variable amount of Sp1 expression construct or vice versa confirmed the latter. Mutation of the MAZ or Sp1 sites in pGL3RP60 attenuated but did not eliminate PNMT promoter activity, even though the proteins no longer bind to their consensus elements. Phosphatase treatment of RS1 cell nuclear extracts prevented MAZ- and Sp1-DNA binding complex formation. Although MAZ and Sp1 elevate endogenous PNMT mRNA in RS1 cells, MAZ preferentially increases intron-retaining whereas Sp1 preferentially increases intronless mRNA. Thus, expression of the PNMT gene seems to be modulated through competitive binding of phosphorylated Sp1 and MAZ to their consensus elements in the promoter. In addition, post-transcriptional regulation seems to be another important mechanism controlling PNMT expression.

Comparison of the basal and glucocorticoid-inducible activities of the upstream regulatory regions of HPV18 and HPV31 in multiple epithelial cell lines

Steroid hormone receptors have been shown to bind to response elements in the upstream regulatory region (URR) of human papillomavirus (HPV) in a ligand-dependent manner to affect viral promoter activity. To better understand how the enhancer activity of the URR differs between high risk HPV types, we chose to compare the basal and glucocorticoid-dependent activities of the URRs of HPV18 and HPV31. We found that the URR of HPV18 is a stronger enhancer than the URR of HPV31 in six different cell lines of epithelial origin. Furthermore, the activity of the URR of HPV31 was not inducible by the synthetic glucocorticoid dexamethasone (dex) in any cell line tested, while the URR of HPV18 was dex-inducible in the majority of these lines. These studies indicate significant differences between the URRs of high risk HPV types.

Intratype HPV16 sequence variation within LCR of isolates from asymptomatic carriers and cervical cancers

BACKGROUND

HPV16 is a predominant type of virus identified in genital lesions and strongly associated with the development of genital cancers. Infection with the virus is considered to be the main risk factor in the development of cervical cancer. Based on HPV16 DNA isolated from invasive cancers, a classification of intratype genetic variants was established and the strains were designated according to geographical regions. The HPV16 variants classification was based on isolates derived from cancers.

OBJECTIVES

Analysis of HPV16 LCR variants isolated from asymptomatic carriers for comparison with cervical cancer isolates to examine whether a correlation can be found between cervical epithelium state and variant of HPV16 it carries.

MATERIALS AND METHODS

The HPV16 LCR fragments were amplified by PCR using DNA isolated from cervical swabs and tissue sections then screened for nucleotide changes by SSCP. Polymorphic sites were analysed for regulatory protein binding properties by EMSA.

RESULTS

Comparison of the two groups revealed that isolates from cervical cancers predominantly carry changes in sequences of YY1 binding sites (especially at nucleotide 7519), while variants from asymptomatic carriers contained nucleotide changes within or close to transcription binding sites for AP-1, Oct-1, NF1, Tef-1, Tef-2, Sp1, YY1 and viral E2. EMSA study showed that sequence changes in the segment alter binding and formation of transcriptional complexes in quantitative and/or qualitative manner and so they may inflict viral activity.

CONCLUSION

The results of our study show that there might be HPV16 variants of decreased oncogenic potential therefore infection with such variants can recede.

Human homeobox HOXA7 regulates keratinocyte transglutaminase type 1 and inhibits differentiation

Keratinocyte proliferation and differentiation result from expression of specific groups of genes regulated by unique combinations of transcription factors. To better understand these regulatory processes, we studied HOXA7 expression and its regulation of differentiation-specific keratinocyte genes. We isolated the homeobox transcription factor HOXA7 from keratinocytes through binding to a differentiation-dependent viral enhancer and analyzed its effect on endogenous differentiation-dependent genes, primarily transglutaminase 1. HOXA7 overexpression repressed transglutaminase 1-reporter activity. HOXA7 message markedly decreased, and transglutaminase RNA increased, upon phorbol ester-induced differentiation, in a protein kinase C-dependent manner. Overexpression of HOXA7 attenuated the transglutaminase 1 induction by phorbol ester, demonstrating that HOXA7 expression is inversely related to keratinocyte differentiation, and to transglutaminase 1 expression. Antisense HOXA7 expression activated transglutaminase 1, involucrin, and keratin 10 message and protein levels, demonstrating that endogenous HOXA7 down-regulates multiple differentiation-specific keratinocyte genes. In keeping with these observations, epidermal growth factor receptor activation stimulated HOXA7 expression. HOX genes function in groups, and we found that HOXA5 and HOXB7 were also down-regulated by phorbol ester. These results provide the first example of protein kinase C-mediated homeobox gene regulation in keratinocytes, and new evidence that HOXA7, potentially in conjunction with HOXA5 and HOXAB7, silences differentiation-specific genes during keratinocyte proliferation, that are then released from inhibition in response to differentiation signals.

Human papillomavirus variants and squamous neoplasia of the cervix

Human papillomaviruses (HPVs) play a central role in the aetiology of cervical neoplasia. However, only a small proportion of cervical intraepithelial lesions infected with high-risk HPVs will progress to invasive cervical carcinoma, which indicates the involvement of additional factors. An important emerging viral factor is naturally occurring intratypic sequence variation. Such variation has been used to study the geographical spread of HPVs, but there is increasing evidence that it may be important in determining the risk of development of neoplastic disease. The collected data indicate that different HPV variants have altered biochemical and biological properties and represent an additional risk factor in the development of squamous intraepithelial lesions and invasive carcinoma of the cervix. This may be relevant not only to the biology of HPV infection and its association with squamous neoplasia, but also to the use of HPV typing in clinical practice.

Yin yang 1 negatively regulates the differentiation-specific E1 promoter of human papillomavirus type 6

Human papillomavirus type 6 (HPV-6) is a low-risk HPV whose replication cycle, like that of all HPVs, is differentiation dependent. We have previously shown that CCAAT displacement protein (CDP) binds the differentiation-induced HPV-6 E1 promoter and negatively regulates its activity in undifferentiated cells (W. Ai, E. Toussaint, and A. Roman, J. Virol. 73:4220-4229, 1999). Using electrophoretic mobility shift assays (EMSAs), we now report that Yin Yang 1 (YY1), a multifunctional protein that can act as a transcriptional activator or repressor and that can also inhibit HPV replication in vitro, binds the HPV-6 E1 promoter. EMSAs, using subfragments of the promoter as competitors, showed that the YY1 binding site is located at the 5' end of the E1 promoter. When a putative YY1 site was mutated, the ability of YY1 to bind was greatly decreased. The activity of the mutated E1 promoter, monitored with the reporter gene luciferase, was threefold greater than that of the wild-type promoter, suggesting that YY1 negatively regulates HPV-6 E1 promoter activity. Nuclear extracts from differentiated keratinocytes showed decreased binding of YY1 to the wild-type promoter. Consistent with this, in differentiated keratinocytes, the activity of the transfected luciferase gene transcribed from the mutated promoter was comparable to that of the wild-type promoter; both promoters were up-regulated in differentiated keratinocytes compared to undifferentiated cells. These data suggest that YY1 functions in undifferentiated keratinocytes but not in differentiated keratinocytes. Both the wild-type and mutated promoters could be negatively regulated by overexpression of a plasmid encoding CDP. Thus, both YY1 and CDP appear to be negative regulators of the differentiation-induced HPV-6 E1 promoter and thereby the HPV life cycle. In contrast, only binding of CDP was detected using the E1 promoter of the high-risk HPV-31.