Oncogenic HPV infection interrupts the expression of tumor-suppressive miR-34a through viral oncoprotein E6

Differential effects of miR-34c-3p and miR-34c-5p on SiHa cells proliferation apoptosis, migration and invasion

MicroRNAs (miRNA) regulate expression of several genes associated with human cancer. Here, we analyzed the function of miR-34c, an effector of p53, in cervical carcinoma cells. Expression of either miR-34c-3p or miR-34c-5p mimics caused inhibition of cell proliferation in the HPV-containing SiHa cells but not in other cervical cells irrespective of tumorigenicity and HPV content. These results suggest that SiHa cells may lack of regulatory mechanisms for miR-34c. Monolayer proliferation results showed that miR-34c-3p produced a more pronounced inhibitory effect although both miRNAs caused inhibition of anchorage independent growth at similar extent. However, ectopic expression of pre-miR-34c-3p, but not pre-miR-34c-5p, caused S-phase arrest in SiHa cells triggering a strong dose-dependent apoptosis. A significant inhibition was observed only for miR-34c-3p on SiHa cells migration and invasion, therefore implying alternative regulatory pathways and targets. These results suggest differential tumor suppressor roles for miR-34c-3p and miR-34c-5p and provide new insights in the understanding of miRNA biology.

Suppression of latent transforming growth factor (TGF)-beta1 restores growth inhibitory TGF-beta signaling through microRNAs

Cancer cells secreting excess latent TGF-β are often resistant to TGF-β induced growth inhibition. We observed that RNAi against TGF-β1 led to apoptotic death in such cell lines with features that were, paradoxically, reminiscent of TGF-β signaling activity and that included transiently enhanced SMAD2 and AKT phosphorylation. A comprehensive search in Hela cells for potential microRNA drivers of this mechanism revealed that RNAi against TGF-β1 led to induction of pro-apoptotic miR-34a and to a globally decreased oncomir expression. The reduced levels of the oncomirs miR-18a and miR-24 accounted for the observed derepression of two TGF-β1 processing factors, thrombospondin-1, and furin, respectively. Our data suggest a novel mechanism in which latent TGF-β1, thrombospondin 1, and furin form a microRNA-mediated regulatory feedback loop. For cells with high levels of latent TGF-β, this provides a potentially widespread mechanism of escape from TGF-β-mediated growth arrest at the earliest point in the signaling pathway, TGF-β processing.

Progressive miRNA expression profiles in cervical carcinogenesis and identification of HPV-related target genes for miR-29

miRNAs have the potential to act on diverse downstream genes, and miRNA signatures of HPV-infected tissues may provide insight into HPV-related carcinogenesis. We set out to profile miRNA expression in HPV-infected samples and relate this to histological and grade-specific alterations in the spectrum of cervical carcinogenesis in vivo. A total of 31 miRNAs showed significant and continuous expression along with the progression from normal cervical tissue to cancer, and six of them were validated in 133 samples. By bioinformatics analyses, we established a putative HPV-associated miRNA-mRNA regulatory network, showing that miR-29 is the most highly enriched. We also found that YY1 and CDK6 were both positively correlated with E6/E7 RNA expression and targeted by tumour-suppressive miR-29. Evidence of miR-29 involvement in HPV infection was further verified in patient samples and by various experimental approaches. Taken together, our results suggest that HPVs have oncogenic properties at least in part by reshaping the milieu of cellular miRNAs. miR-29 restrains cell cycle progression and induces apoptosis via YY1 and CDK6 promoting malignant transformation induced by HPV, although the abnormality of miR-29 in HPV-infected cells might be regulated in an indirect way.

Upregulation of p18Ink4c expression by oncogenic HPV E6 via p53-miR-34a pathway

Binding of p53 to miR-34a promoter activates the expression of tumor-suppressive miR-34a. Oncogenic human papillomavirus (HPV) infection downregulates miR-34a expression through viral E6 degradation of p53. In our report, we found that miR-34a specifically targets p18Ink4c, a CDK4 and CDK6 inhibitor induced by E2F transactivation. HPV18(+) HeLa cells with ectopic miR-34a expression or by E6 siRNA knockdown-induced expression of endogenous miR-34a exhibited a substantial reduction of p18Ink4c in a dose-dependent manner, but had no effect on p16Ink4a, another member of CDK4/6 inhibitor family. In contrast, de novo infection by oncogenic HPVs of human keratinocyte-derived raft tissues increased p18Ink4c expression. Suppression of endogenous miR-34a in cell lines with a miR-34a inhibitor also increased p18Ink4c. We found that miR-34a suppresses the expression of p18Ink4c by binding to a specific seed match in the 5' UTR of p18Ink4c. Further investigation found remarkable increase of p18Ink4c in cervical precancer lesions and cervical cancer. Immunohistochemical staining of cervical tissue arrays showed increased expression of p18Ink4c in 68% of cervical cancer, 8.3% of chronic cervical inflammation and 4.8% of normal cervix. Although p18Ink4c inhibits cell proliferation in general and regulates E2F1 expression in HCT116 cells, it appears not to function as a tumor suppressor in cervical cancer cells lacking an intact G1 checkpoint because of viral E7 degradation of pRB. In summary, our study demonstrates an intimate connection among oncogenic HPV E6, p53, miR-34a and p18Ink4c and identifies p18Ink4c as a possible biomarker for cervical cancer.

Exploiting the therapeutic potential of microRNAs in viral diseases: expectations and limitations

New therapeutic approaches are urgently needed for serious diseases, including cancer, cardiovascular diseases, viral infections, and others. A recent direction in drug development is the utilization of nucleic acidbased therapeutic molecules, such as antisense oligonucleotides, ribozymes, short interfering RNA (siRNA), and microRNA (miRNA). miRNAs are endogenous, short, non-coding RNA molecules. Some viruses encode their own miRNAs, which play pivotal roles in viral replication and immune evasion strategies. Conversely, viruses that do not encode miRNAs may manipulate host cell miRNAs for the benefits of their replication. miRNAs have therefore become attractive tools for the study of viral pathogenesis. Lately, novel therapeutic strategies based on miRNA technology for the treatment of viral diseases have been progressing rapidly. Although this new generation of molecular therapy is promising, there are still several challenges to face, such as targeting delivery to specific tissues, avoiding off-target effects of miRNAs, reducing the toxicity of the drugs, and overcoming mutations and drug resistance. In this article, we review the current knowledge of the role and therapeutic potential of miRNAs in viral diseases, and discuss the limitations of these therapies, as well as strategies to overcome them to provide safe and effective clinical applications of these new therapeutics.

Human papillomavirus type 16 E6 induces cervical cancer cell migration through the p53/microRNA-23b/urokinase-type plasminogen activator pathway

Deregulation of microRNA (miRNA or miR) expression in human cervical cancer is associated frequently with human papillomavirus (HPV) integration. miR-23b is often downregulated in HPV-associated cervical cancer. Interestingly, urokinase-type plasminogen activator (uPA), the miR-23b target, is detected in cervical cancer, but not in normal cervical tissues. Thus, the importance of miR-23b and uPA in HPV-associated cervical cancer development is investigated. In this study, the high-risk subtype HPV-16 E6 oncoprotein was found to decrease the expression of miR-23b, increase the expression of uPA, and thus induce the migration of human cervical carcinoma SiHa and CaSki cells. uPA is the target gene for miR-23b as the miR repressed uPA expression and interacted with the 3'-untranslated region of uPA mRNA. The tumor suppressor p53 is known to be inactivated by HPV-16 E6. A consensus p53 binding site is detected in the promoter region of miR-23b, whereas p53 trans-activated and also interacted with the miR's promoter. Therefore, p53 is believed to mediate the HPV-16 E6 downregulation of miR-23b. From the above, miR-23b/uPA are confirmed to be involved in HPV-16 E6-associated cervical cancer development.

miR-34a confers chemosensitivity through modulation of MAGE-A and p53 in medulloblastoma

Recent studies have established miR-34a as a key effector of the p53 signaling pathway and have implicated its role in multiple cancer types. Here, we establish that miR-34a induces apoptosis, G2 arrest, and senescence in medulloblastoma and renders these cells more sensitive to chemotherapeutic agents. These effects are mediated in part by the direct post-transcriptional repression of the oncogenic MAGE-A gene family. We demonstrate that miR-34a directly targets the 3' untranslated regions of MAGE-A genes and decreases MAGE-A protein levels. This decrease in MAGE-A results in a concomitant increase in p53 and its associated transcriptional targets, p21/WAF1/CIP1 and, importantly, miR-34a. This establishes a positive feedback mechanism where miR-34a is not only induced by p53 but increases p53 mRNA and protein levels through the modulation of MAGE-A genes. Additionally, the forced expression of miR-34a or the knockdown of MAGE-A genes by small interfering RNA similarly sensitizes medulloblastoma cells to several classes of chemotherapeutic agents, including mitomycin C and cisplatin. Finally, the analysis of mRNA and micro-RNA transcriptional profiles of a series of primary medulloblastomas identifies a subset of tumors with low miR-34a expression and correspondingly high MAGE-A expression, suggesting the coordinate regulation of these genes. Our work establishes a role for miR-34a in modulating responsiveness to chemotherapy in medulloblastoma and presents a novel positive feedback mechanism involving miR-34a and p53, via direct targeting of MAGE-A.

Viruses, microRNAs, and host interactions

One of the most significant recent advances in biomedical research has been the discovery of the approximately 22-nt-long class of noncoding RNAs designated microRNAs (miRNAs). These regulatory RNAs provide a unique level of posttranscriptional gene regulation that modulates a range of fundamental cellular processes. Several viruses, especially herpesviruses, also encode miRNAs, and over 200 viral miRNAs have now been identified. Current evidence indicates that viruses use these miRNAs to manipulate both cellular and viral gene expression. Furthermore, viral infection can exert a profound impact on the cellular miRNA expression profile, and several RNA viruses have been reported to interact directly with cellular miRNAs and/or to use these miRNAs to augment their replication potential. Here we discuss our current knowledge of viral miRNAs and virally influenced cellular miRNAs and their relationship to viral infection.

Viruses, microRNAs, and host interactions

One of the most significant recent advances in biomedical research has been the discovery of the approximately 22-nt-long class of noncoding RNAs designated microRNAs (miRNAs). These regulatory RNAs provide a unique level of posttranscriptional gene regulation that modulates a range of fundamental cellular processes. Several viruses, especially herpesviruses, also encode miRNAs, and over 200 viral miRNAs have now been identified. Current evidence indicates that viruses use these miRNAs to manipulate both cellular and viral gene expression. Furthermore, viral infection can exert a profound impact on the cellular miRNA expression profile, and several RNA viruses have been reported to interact directly with cellular miRNAs and/or to use these miRNAs to augment their replication potential. Here we discuss our current knowledge of viral miRNAs and virally influenced cellular miRNAs and their relationship to viral infection.

MicroRNA regulation of core apoptosis pathways in cancer

Recent research has demonstrated that microRNAs (miRNAs) are key regulators of many cell processes often deregulated in cancer, including apoptosis. Indeed, it is becoming clear that many miRNAs are anti-apoptotic and mediate this effect by targeting pro-apoptotic mRNAs or positive regulators of pro-apoptotic mRNAs. Conversely, many pro-apoptotic miRNAs target anti-apoptotic mRNAs or their positive regulators. We have reviewed the current knowledge in this area including evidence of miRNA involvement in cancer drug resistance.

Strong inverse correlation between microRNA-125b and human papillomavirus DNA in productive infection

Infection by the human papillomavirus (HPV) is a cause of cervical intraepithelial neoplasia (CIN) and cancer. microRNA (miRNA) in situ analysis of the transformation zone epithelia, the site of initial cervical HPV infection, showed that miRNAs let-7c, -99a, 26a, and 125b were the most abundantly expressed. In situ testing of CIN 1 showed a dramatic reduction in miR-125b expression in the koilocytes, the cytologic marker of productive HPV infection. A marked reduction in miR-125b was likewise observed in the HPV-infected cells of the condyloma acuminatum, verruca vulgaris, and epidermodysplasia verruciformis. Reverse transcriptase in situ polymerase chain reaction (PCR) showed that the pre-miRNA 125b was present in the koilocyte, suggesting direct inactivation of the mature miRNA. HEK cells transfected with only the antimiR-125b showed perinuclear halos equivalent to HPV-infected koilocytes. NIH 3T3 cells transfected with the HPV 16 full-length genome and mimetic miR-125b showed a marked reduction in viral DNA and protein synthesis by quantitative PCR and in situ-based analyses, respectively (P=0.002). Alternatively, cotransfection with anti-miR-125b and HPV 16 markedly increased HPV DNA (P=0.002). Sequence analyses showed strong homology between L2 of different HPV genotypes and miR-125b. Transfection with HPV 16 L2 resulted in a marked reduction in miR-125b levels in the NIH 3T3 cells. HPV L2-induced inactivation of miR-125b is associated with the classic cytologic changes of the koilocyte, and the exogenous application of mimetic miR-125b markedly inhibits HPV DNA synthesis.

Viral oncogenes, noncoding RNAs, and RNA splicing in human tumor viruses

Viral oncogenes are responsible for oncogenesis resulting from persistent virus infection. Although different human tumor viruses express different viral oncogenes and induce different tumors, their oncoproteins often target similar sets of cellular tumor suppressors or signal pathways to immortalize and/or transform infected cells. Expression of the viral E6 and E7 oncogenes in papillomavirus, E1A and E1B oncogenes in adenovirus, large T and small t antigen in polyomavirus, and Tax oncogene in HTLV-1 are regulated by alternative RNA splicing. However, this regulation is only partially understood. DNA tumor viruses also encode noncoding RNAs, including viral microRNAs, that disturb normal cell functions. Among the determined viral microRNA precursors, EBV encodes 25 from two major clusters (BART and BHRF1), KSHV encodes 12 from a latent region, human polyomavirus MCV produce only one microRNA from the late region antisense to early transcripts, but HPVs appears to produce no viral microRNAs.

Reduced miR-34a expression in normal cervical tissues and cervical lesions with high-risk human papillomavirus infection

INTRODUCTION

Reduced miR-34a expression is associated with high-risk human papillomavirus (HR-HPV) infection and cervical cancer. Whether the reduction of miR-34a expression induced by HR-HPV E6 occurs in precancerous lesions, even before morphologic change, is still uncertain. Our study aimed to ascertain the possibility of pri-miR-34a involved in the development of cervical lesions and to explore the mechanism of altered pri-miR-34a expression induced by HPV-16 E6.

METHODS

The levels of pri-miR-34a expression were examined in different cervical tissues, including normal cervical epithelium with (n = 32) or without (n = 32) HR-HPV infection, cervical intraepithelial neoplasia (CIN) with (n = 32) or without (n = 12) HR-HPV infection, and cervical cancer (n = 32), by semiquantitative reverse transcription-polymerase chain reaction. The HPV-16 E6 expression vector and HPV-16 E6 small interfering RNAs were conducted and transfected into 293T cells and SiHa cells, respectively. The expression of pri-miR-34a and p53 protein was simultaneously analyzed by reverse transcription-polymerase chain reaction and Western blot in cells with gene transfection and without.

RESULTS

pri-miR-34a expression was significantly reduced in CIN and cervical cancer compared with normal cervical epithelium, as well as in CIN 2 and CIN 3 compared with CIN I. Moreover, the expression of pri-miR-34a was significantly lower in normal cervical epithelium and CIN with HR-HPV infection than in those without. Simultaneous down-regulation or up-regulation of pri-miR-34a and p53 expression was observed in E6-transfected 293T cells or E6 small interfering RNA-transferred SiHa cells compared with controls.

CONCLUSIONS

Reduced expression of pri-miR-34a occurs not only in cervical cancer but also in precancerous lesion even before morphologic change. The inhibition of miR-34a expression induced by HR-HPV E6 in the p53-dependent pathway is probably an early-onset event in the development of cervical cancer.

MicroRNA miR-886-5p inhibits apoptosis by down-regulating Bax expression in human cervical carcinoma cells

OBJECTIVE

MicroRNA (miRNA) plays an essential role in the progression of a variety of cancers, but its role in cervical cancer progression is not well defined. We aimed to test whether special miRNAs and their target mRNAs contribute to cervical cancer progression.

METHODS

The expression profiles of 1145 microRNAs in cervical squamous cell carcinomas (CSCC) and adjacent non-tumor tissues were investigated using an Illumina microRNA microarray platform. Differentially expressed miRNAs were validated by RT-PCR. Downstream target validation was performed for miR-886-5p.

RESULTS

We found that the expression levels of seven miRNAs differed significantly between CSCC tissues and adjacent non-tumor tissues. Forced expression of one miRNA, miR-886-5p, over-expressed in CSCC tissues lowered expression of the pro-apoptotic protein Bax, reduced apoptosis and promoted cell proliferation in H8, an HPV16-immortalized human cervical squamous epithelial cell line. Knockdown of miR-886-5p increased Bax protein and apoptotic cell death in cells of the cervical squamous carcinoma cell line, SiHa.

CONCLUSION

MicroRNA miR-886-5p inhibits apoptosis of cervical cancer cells by down-regulating the production of Bax.

miRNAs in the pathogenesis of oncogenic human viruses

Tumor viruses are a class of pathogens with well established roles in the development of malignant diseases. Numerous bodies of work have highlighted miRNAs (microRNAs) as critical regulators of tumor pathways and it is clear that the dysregulation of cellular miRNA expression can promote tumor formation. Tumor viruses encode their own miRNAs and/or manipulate the expression of cellular miRNAs to modulate their host cell environment, thereby facilitating their respective infection cycles. The modulation of these miRNA responsive pathways, however, often influences certain signal transduction cascades in ways that favor tumorigenesis. In this review, we discuss the roles of virally-encoded and virally-regulated cellular miRNAs in the respective viral life cycles and in virus associated pathogenesis.

hsa-miR-520h downregulates ABCG2 in pancreatic cancer cells to inhibit migration, invasion, and side populations

Background:

Expression of ABCG2 is normally absent or low in the pancreas, but high in human pancreatic cancer cells. The mechanism by which ABCG2 is altered in human cancers remains unknown.

Methods:

We investigated ABCG2 expression in four pancreatic cancer cell lines, and used three microRNA (miRNA) target prediction programmes, and information from the existing literature to predict and identify hsa-miR-520h as an miRNA that targets ABCG2. The function of this miRNA was investigated by transient transfection of the pancreatic cancer cell line PANC-1 with oligonucleotides that mimic hsa-miR-520h.

Results:

Results showed that both mRNA and protein levels of ABCG2 were reduced, indicating that it was a target of hsa-miR-520h. Introduction of hsa-miR-520h mimics into PANC-1 cells also resulted in inhibition of cell migration and invasion, and reduction of side population cells. Cell proliferation, cell cycle progression and apoptosis were not affected.

Conclusions:

We propose that the effects of hsa-miR-520h may be, at least in part, caused by its regulation of ABCG2. Thus, our findings provide a new insight into the function of miRNA in the regulation of ABCG2 expression in pancreatic cancer. Gene therapy using miRNA mimics may therefore be useful as a pancreatic cancer therapy.

Role of miR-34c microRNA in the late steps of spermatogenesis

Spermatogenesis is a cyclic process in which diploid spermatogonia differentiate into haploid spermatozoa. This process is highly regulated, notably at the post-transcriptional level. MicroRNAs (miRNAs), single-stranded noncoding RNA molecules of about 20-25 nucleotides, are implicated in the regulation of many important biological pathways such as proliferation, apoptosis, and differentiation. We wondered whether miRNAs could play a role during spermatogenesis. The miRNA expression repertoire was tested in germ cells, and we present data showing that miR-34c was highly expressed only in these cells. Furthermore, our findings indicate that in male gonads, miR-34c expression is largely p53 independent in contrast to previous results showing a direct link in somatic cells between the miR-34 family and this tumor suppressor protein. In order to identify target genes involved in germinal lineage differentiation, we overexpressed miR-34c in HeLa cells, analyzed the transcriptome of these modified cells, and noticed a shift of the expression profile toward the germinal lineage. Recently, it has been shown that exogenous expression of Ddx4/Vasa in embryonic chicken stem cells (cESC) induces cESC reprogramming toward a germ cell fate. When we simultaneously expressed miR-34c in such cells, we could detect an up-regulation of germ cell-specific genes whereas the expression of other lineage specific markers remained unchanged. These data suggest that miR-34c could play a role by enhancing the germinal phenotype of cells already committed to this lineage.

Are treatments for cervical precancerous lesions in less-developed countries safe enough to promote scaling-up of cervical screening programs? A systematic review

Background

Since the mid-1990s, there have been growing efforts to prevent cervical cancer in less-developed countries through the development of innovative screening approaches such as visual inspection of the cervix associated with same day management of cervical lesions with cryotherapy or loop electrosurgical excision procedure (LEEP). In the past, promising cancer screening interventions have been widely promoted despite incomplete evidence, only to become the subject of intense controversies about ensuing net health benefit. Because the efficacy and effectiveness of the new protocols for global cervical cancer screening have not been well characterized yet, and as a contribution to the evaluation of the balance between the benefits and risks of these protocols, we reviewed the literature on the safety of cryotherapy and LEEP for cervical intraepithelial neoplasia (CIN) in low- and middle-income countries.

Methods

We searched 12 databases (Medline, Google Scholar, Scopus, Cochrane Library, Web of Science, OCLC, PAIS International Database, WHO Global Health Library, CINAHL, Science.gov, NYAM Grey Literature Report, and POPLINE) for original research published between January 1995 and April 2009. Both peer-reviewed publications and items of "grey" literature were retrieved; no language restriction was applied. We calculated the median (minimum, maximum) reported rate for each harm considered. Because of limitations and heterogeneity in the data, no formal meta-analysis was performed.

Results

The search identified 32 articles that reported safety data from 24 cryotherapy and LEEP studies. The combined sample consisted of 6,902 women treated by cryotherapy and 4,524 women treated by LEEP. Most studies were conducted in reference or research settings in Asia and Africa. Short-term harms of cryotherapy and LEEP appeared to be similar to those described in the literature from high-income countries. Information was sparse on HIV-related harms and long-term reproductive outcomes of treatment.

Conclusions

When performed in resource-limited settings by qualified providers, cryotherapy and LEEP are not associated with excess harm. However, available data are insufficient to propose fully evidence-based protocols for routine screening of HIV-infected women and women of reproductive age.

MicroRNAs and their role in gynecological tumors

There have been only few events in the history of molecular biology that could be compared to the discovery of microRNAs and their role in cell physiology and pathology. MicroRNAs are small, single-stranded, noncoding RNAs composed of 19-25 nucleotides (∼22 nt), which have been proven to regulate gene expression at the posttranscriptional level. The regulatory function of microRNAs was demonstrated in normal and diseased conditions. In particular, it has been linked to cell cycle regulation, cell proliferation and differentiation, inflammatory response, and apoptosis. Altered expression profiles of microRNA have been observed in many pathologies, including diabetes, rheumatoid arthritis, and several cancers. To date, more than 700 human microRNAs have been identified and in silico-based analyses estimate at least 500 more to be identified. The purpose of this review is to present the current perspective on microRNAs structure and biogenesis as well as their contribution to the etiopathogenesis of gynecological tumors. We discuss results of the recent publications that indicate possibilities of microRNAs use as novel markers for tumors screening, early diagnosis, and treatment monitoring. The possible utilization of microRNAs as prognostic factors and specific therapy targets is also reviewed.

MicroRNA-34a suppresses invasion through downregulation of Notch1 and Jagged1 in cervical carcinoma and choriocarcinoma cells

MicroRNAs (miRNAs) are small non-coding RNAs that regulate the expression of other genes by transcriptional inhibition or translational repression. miR-34a is a known tumor suppressor gene and inhibits abnormal cell growth. However, its role in other tumorigenic processes is not fully known. This study aimed to investigate the action of miR-34a on cell invasion. We found that miR-34a is expressed at various levels in cervical cancer (HeLa, SiHa, C4I, C33a and CaSki) and trophoblast (BeWo and JAR) cell lines. Transient forced expression of miR-34a did not affect the proliferation of these cell lines. Computational miRNA target prediction suggested that Notch1 and Jagged1 were targets of miR-34a. By using functional assays, miR-34a was demonstrated to bind to the 3' untranslated regions of Notch1 and Jagged1. Forced expression of miR-34a altered the expression of Notch1 and Jagged1 protein as well as Notch signaling as shown by the response of Hairy Enhancer of Split-1 protein to these treatments using western blot analysis. Forced expression of miR-34a suppressed the invasiveness of HeLa and JAR cells. By using gamma-secretase inhibitor (N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester) that interfered Notch signaling and RNA interference that knockdown Notch1 expression, we confirmed that downregulation of Notch1 reduced the invasiveness of the cells. Transfection of intracellular domain of Notch nullifies the effect of miR-34a on the invasiveness of the cells. Besides, we identified that miR-34a affected cell invasion by regulating expression of urokinase plasminogen activator through Notch. Our results provide evidence that miR-34a inhibits invasiveness through regulation of the Notch pathway and its downstream matrix degrading enzyme.

Human papillomaviruses modulate expression of microRNA 203 upon epithelial differentiation to control levels of p63 proteins

Human papillomaviruses (HPV) link their life cycles to epithelial differentiation and induce productive replication of viral DNA in suprabasal cells. Viral-DNA amplification requires cells to remain active in the cell cycle upon differentiation. This is in contrast to normal cells, which lose proliferative capability upon differentiation. One factor that negatively regulates proliferative capability upon differentiation is microRNA 203 (miR-203), which is expressed primarily in suprabasal epithelial cells. Although HPVs do not encode their own microRNAs (miRNAs), they modulate expression of cellular miRNAs to regulate the activities of cellular proteins. We show that the HPV E7 protein downregulates miR-203 expression upon differentiation, which may occur through the mitogen-activated protein (MAP) kinase/protein kinase C (PKC) pathway. One target of miR-203 is the p63 family of transcription factors, and we demonstrate that HPV-positive cells maintain significantly higher levels of these factors upon differentiation than do normal keratinocytes. Several downstream targets of p63, CARM-1, p21, and Bax, were also increased in E7-expressing cells, and their levels were inversely correlated with amounts of miR-203. Introduction of expression vectors for miR-203 into keratinocytes that stably maintain HPV episomes resulted in short-term elevation of HPV genome copy numbers, but these were rapidly lost upon subsequent passage. When HPV-positive cells expressing high levels of miR-203 were induced to differentiate in methylcellulose, impaired genome amplification was observed. We conclude that high levels of miR-203 are inhibitory to HPV amplification and that HPV proteins act to suppress expression of this microRNA to allow productive replication in differentiating cells.

A microRNA expression signature for cervical cancer prognosis

Invasive cervical cancer is a leading cause of cancer death in women worldwide, resulting in about 300,000 deaths each year. The clinical outcomes of cervical cancer vary significantly and are difficult to predict. Thus, a method to reliably predict disease outcome would be important for individualized therapy by identifying patients with high risk of treatment failures before therapy. In this study, we have identified a microRNA (miRNA)-based signature for the prediction of cervical cancer survival. miRNAs are a newly identified family of small noncoding RNAs that are extensively involved in human cancers. Using an established PCR-based miRNA assay to analyze 102 cervical cancer samples, we identified miR-200a and miR-9 as two miRNAs that could predict patient survival. A logistic regression model was developed based on these two miRNAs and the prognostic value of the model was subsequently validated with independent cervical cancers. Furthermore, functional studies were done to characterize the effect of miRNAs in cervical cancer cells. Our results suggest that both miR-200a and miR-9 could play important regulatory roles in cervical cancer control. In particular, miR-200a is likely to affect the metastatic potential of cervical cancer cells by coordinate suppression of multiple genes controlling cell motility.

Viral epigenomes in human tumorigenesis

Viruses are associated with 15-20% of human cancers worldwide. In the last century, many studies were directed towards elucidating the molecular mechanisms and genetic alterations by which viruses cause cancer. The importance of epigenetics in the regulation of gene expression has prompted the investigation of virus and host interactions not only at the genetic level but also at the epigenetic level. In this study, we summarize the published epigenetic information relating to the genomes of viruses directly or indirectly associated with the establishment of tumorigenic processes. We also review aspects such as viral replication and latency associated with epigenetic changes and summarize what is known about epigenetic alterations in host genomes and the implications of these for the tumoral process. The advances made in characterizing epigenetic features in cancer-causing viruses have improved our understanding of their functional mechanisms. Knowledge of the epigenetic changes that occur in the genome of these viruses should provide us with markers for following cancer progression, as well as new tools for cancer therapy.

Viruses, microRNAs, and host interactions

One of the most significant recent advances in biomedical research has been the discovery of the approximately 22-nt-long class of noncoding RNAs designated microRNAs (miRNAs). These regulatory RNAs provide a unique level of posttranscriptional gene regulation that modulates a range of fundamental cellular processes. Several viruses, especially herpesviruses, also encode miRNAs, and over 200 viral miRNAs have now been identified. Current evidence indicates that viruses use these miRNAs to manipulate both cellular and viral gene expression. Furthermore, viral infection can exert a profound impact on the cellular miRNA expression profile, and several RNA viruses have been reported to interact directly with cellular miRNAs and/or to use these miRNAs to augment their replication potential. Here we discuss our current knowledge of viral miRNAs and virally influenced cellular miRNAs and their relationship to viral infection.