Silencing of human papillomavirus (HPV) E6/E7 oncogene expression affects both the contents and the amounts of extracellular microvesicles released from HPV‐positive cancer cells

The human papillomavirus (HPV) E6/E7 oncogenes play a crucial role in the HPV‐induced carcinogenesis. In this study, the authors investigated whether silencing of endogenous HPV E6/E7 expression may influence the contents or amounts of extracellular microvesicles (eMVs) released from HPV‐positive cancer cells. It was found that eMVs secreted from HeLa cells are enriched for Survivin protein. RNA interference studies revealed that maintenance of both intracellular and microvesicular Survivin amounts was strongly dependent on continuous E6/E7 expression. This indicates that intracellular HPV activities are translated into visible alterations of protein contents in eMVs. Besides Survivin, eMVs from HeLa cells contain additional members of the inhibitor of apoptosis protein (IAP) family (XIAP, c‐IAP1 and Livin). In contrast, no evidence for the presence of the HPV E6 and E7 oncoproteins in eMVs was obtained. Moreover, it was found that silencing of HPV E6/E7 expression led to a significant increase of exosomes—representing eMVs of endocytic origin—released from HeLa cells. This effect was associated with the reinduction of p53, stimulation of the p53 target genes TSAP6 and CHMP4C that can enhance exosome production and induction of senescence. Taken together, these results show that silencing of HPV E6/E7 oncogene expression profoundly affects both the composition and amounts of eMVs secreted by HPV‐positive cancer cells. This indicates that HPVs can induce molecular signatures in eMVs that may affect intercellular communication and could be explored for diagnostic purposes.     

p16INK4a overexpression predicts translational active human papillomavirus infection in tonsillar cancer

The causal role of human papillomaviruses (HPV) in squamous cell carcinogenesis of tonsillar cancers (TSCC) depends on the activity of the viral oncoproteins E6 and E7, leading to inactivation of the cellular tumor suppressor p53 and the retinoblastoma gene product pRb. Because of the negative feedback mechanisms, the pRb inactivation causes an increase of the inhibitor of the cyclin‐dependent kinases p16^INK4a. In 39 TSCC specimens, genotyping based on the amplification of HPV DNA was carried out using PCR by applying HPV type‐specific oligonucleotides. Subsequently, amplicons were hybridised with fluorescence‐labeled complementary probes using the Southern blot technology. For HPV E6/E7 mRNA expression, Northern hybridization and RT‐PCR were performed, and for p16^INK4a detection, immunohistochemistry was performed. With 21/39 (53%) HPV‐positives, the detection rate is within the range that can be expected in TSCC. The E6/E7 oncogene mRNA was detectable in 11 cases, 10 of which showed positive signals after p16^INK4a staining. Albeit the small study group was investigated, the correlation of the HPV DNA status with the p16^INK4a expression was of statistical significance (p = 0.02). Kaplan‐Meier estimations revealed better survival outcome for patients with HPV‐positive tumors with detectable E6/E7 mRNA and p16^INK4a overexpression (p = 0.02, median observation time 29 months). As mRNA expression tests are not routinely available in many clinical diagnostic laboratories, and based on the high correlation of p16^INK4a staining with HPV E6/E7 mRNA expression, in conclusion we suggest for a deeper exploration for the use of p16^INK4a as a surrogate marker with the potential to impact the standard of care of HPV DNA‐positive head and neck carcinomas.     

Estradiol downregulation of the tumor suppressor gene BTG2 requires estrogen receptor‐α and the REA corepressor

B‐cell Translocation Gene 2 (BTG2/TIS21/PC3) is an anti‐proliferative tumor suppressor gene whose expression is significantly reduced in breast carcinomas, and in MCF‐7 and T‐47D breast cancer cell lines treated with estradiol (E2). In this study the mechanisms involved in E2 down regulation of BTG2 gene expression were examined. Depletion of ERα by siRNA indicated that the receptor is required for E2 down regulation of BTG2 mRNA levels, and cycloheximide experiments indicated that the effect of E2 on BTG2 expression was independent of intermediary protein synthesis. Chromatin immunoprecipitation analyses revealed that ERα interacts with the BTG2 promoter in a ligand‐independent fashion whereas transfection experiments indicated that ERα's DNA and ligand binding domains are required for E2 repression of BTG promoter activity. Surprisingly, histone deacetylase (HDACs) activity is essential for basal expression as evidenced by trichostatin A inhibition of BTG2 mRNA levels. Estradiol treatment did not alter histone H3 acetylation although it did induce displacement of RNA polymerase II from the BTG2 gene. Depletion of the ER specific corepressor REA (Repressor of Estrogen Receptor Activity) significantly abrogated E2‐mediated BTG2 repression. Taken together, our results reveal a requirement of HDAC activity for basal BTG2 expression and the ERα‐REA interaction for estrogen repression of the BTG2 gene. The ability of E2‐bound ERα and REA to suppress BTG2 expression indicates a positive role for this corepressor in regulation of breast cancer cell proliferation. © 2008 Wiley‐Liss, Inc.     

Inhibitors of differentiation‐1 promotes nitrosopyrrolidine‐induced transformation of HPV 16‐immortalized cervical epithelial cell

Our previous study implied a correlation between inhibitors of differentiation‐1 (Id‐1) and cervical cancer development. However, how Id‐1 contributes to cervical carcinogenesis is unknown. In the present study, we used an in vitro transformation model to investigate the role of Id‐1 in the transformation of cervical cells. Human papillomavirus (HPV)‐immortalized cervical epithelial cells (H8) were successfully transformed by exposure to the carcinogen N‐nitrosopyrrolidine (NPYR). The expression of both Id‐1 RNA and protein was significantly increased in transformed H8 cells, suggesting a possible role of Id‐1 in cervical cell transformation. Ectopic expression of Id‐1 in H8 cells potentiated NPYR‐induced cell transformation. In contrast, silencing of Id‐1 suppressed NPYR‐induced H8 cell transformation. In addition, the expression of HPV E6 and E7 oncoproteins was upregulated while that of the tumor suppressors p53 and pRb was suppressed after H8 cell transformation. Our results suggest that Id‐1 plays an oncogenic role in HPV‐related cervical carcinogenesis, which sheds light on cervical cancer development mechanisms and implies that Id‐1 is a potential target for cervical cancer prevention and therapy.     

Functional interaction of p53 with HPV18 E6, c-myc and H-ras in 3T3 cells.

Wild-type (wt) p53 has been suggested to be the product of a tumor-suppressor gene. Recently, it has been shown that the E6 oncoproteins of human papillomavirus (HPV) types 16 and 18, like the SV40 large T antigen, are physically associated with wt p53. We have investigated the functional interaction of wt p53 with the viral oncogene products of HPV16 and 18 and with cellular oncogenes by transfection of NIH3T3 cells with p53 wt alone or with several oncogene(s). We found that over-expression of HPV18 E6, c-myc or activated H-ras, like SV40 large T, can partially overcome the growth-inhibitory effect of wt p53 in NIH3T3 cells, while HPV16 E6 and E7, HPV18 E7, k-fgf, c-fos and mutant (mt) p53 do not. Further studies indicate that HPV18 E6 and c-myc can overcome the antiproliferative effect, but not the antitransforming effect, of wt p53, while activated H-ras can overcome both the antiproliferative and antitransforming effects of wt p53. These data show evidence of a functional interaction between HPV18 E6 and wt p53, and suggest that the cooperation of HPV E6 and cellular oncogenes c-myc and H-ras, which are activated in several cases of human cervical cancers, may be necessary to overcome completely the anti-oncogenic function of p53 in the development of these tumors.     

Loss of B‐cell translocation gene 2 expression in estrogen receptor‐positive breast cancer predicts tamoxifen resistance

B‐cell translocation gene 2 (BTG2), a gene suppressed in a subset of aggressive breast cancer, is repressed by estrogen. BTG2 inhibits the expression of HER ligands and promotes AKT activation, which plays an essential role in the tamoxifen resistance of estrogen receptor (ER)‐positive breast cancer. To determine if BTG2 expression modifies tamoxifen efficacy, a cohort of 60 patients treated with adjuvant tamoxifen monotherapy was analyzed. We found that increased BTG2 expression showed better clinical survival and was the only independent prognostic factor for disease‐free survival (hazard ratio, 0.691; 95% confidence interval, 0.495–0.963; P = 0.029). Tamoxifen suppressed the human epidermal growth factor receptor 2 (HER2)‐Akt signaling in BTG2 expressing ER‐positive breast cancer cells with a correlated increase in sensitivity, whereas BTG2 knockdown abrogated this sensitivity. Consistent with this observation, tamoxifen significantly suppressed the growth ratio, tumor weight and Ki‐67 expression in BTG2 expressing breast cancer xenografts in mice. These studies demonstrate that BTG2 is a significant factor in tamoxifen response, acting through modification of AKT activation in ER‐positive/HER2‐negative breast cancer.     

p53 Loss synergizes with estrogen and papillomaviral oncogenes to induce cervical and breast cancers

Whereas the tumor suppressor p53 gene is frequently mutated in most human cancers, this is not the case in human papillomavirus (HPV)-associated cancers, presumably because the viral E6 oncoprotein inactivates the p53 protein. The ability of E6 to transform cells in tissue culture and induce cancers in mice correlates in part with its ability to inactivate p53. In this study, we compared the expression of the HPV16 E6 oncogene to the conditional genetic disruption of p53 in the context of a mouse model for cervical cancer in which estrogen is a critical cofactor. Nearly all of the K14Crep53(f/f) mice treated with estrogen developed cervical cancer, a stark contrast to its complete absence in like-treated K14E6(WT)p53(f/f) mice, indicating that HPV16 E6 must only partially inactivate p53. p53-independent activities of E6 also contributed to carcinogenesis, but in the female reproductive tract, these activities were manifested only in the presence of the HPV16 E7 oncogene. Interestingly, treatment of K14Crep53(f/f) mice with estrogen also resulted in mammary tumors after only a short latency, many of which were positive for estrogen receptor alpha. The majority of these mammary tumors were of mixed cell types, suggestive of their originating from a multipotent progenitor. Furthermore, a subset of mammary tumors arising in the estrogen-treated, p53-deficient mammary glands exhibited evidence of an epithelial to mesenchymal transition. These data show the importance of the synergy between estrogen and p53 insufficiency in determining basic properties of carcinogenesis in hormone-responsive tissues, such as the breast and the reproductive tract.     

Effectiveness of novel,lower cost molecular human papillomavirus‐based tests for cervical cancer screening in rural china

This study examined the efficacy of the OncoE6? Cervical Test, careHPV? and visual inspection with acetic acid (VIA) in identifying women at risk for cervical cancer and their capability to detect incident cervical precancer and cancer at 1‐year follow‐up. In a population of 7,543 women living in rural China, women provided a self‐collected and two clinician‐collected specimens and underwent VIA. All screen positive women for any of the tests, a ～10% random sample of test‐negative women that underwent colposcopy at baseline, and an additional ～10% random sample of test‐negative women who did not undergo colposcopy at baseline (n = 3,290) were recruited. 2,904 women were rescreened 1 year later using the same tests, colposcopic referral criteria, and procedures. Sensitivities of baseline tests to detect 1‐year cumulative cervical intraepithelial neoplasia Grade 3 or cancer (CIN3+) were 96.5% and 81.6% for careHPV? on clinician‐collected and self‐collected specimens, respectively, and 54.4% for OncoE6? test. The OncoE6? test was very specific (99.1%) and had the greatest positive predictive value (PPV; 47.7%) for CIN3+. Baseline and 1‐year follow‐up cervical specimens testing HPV DNA positive was sensitive (88.0%) but poorly predictive (5.5–6.0%) of incident CIN2+, whereas testing repeat HPV16, 18 and 45 E6 positive identified only 24.0% of incident CIN2+ but had a predictive value of 33.3%. This study highlights the different utility of HPV DNA and E6 tests, the former as a screening and the latter as a diagnostic test, for detection of cervical precancer and cancer.     

Induction of the p53-target gene GADD45 in HPV-positive cancer cells.

The E6 oncoprotein of human papillomaviruses (HPVs) has the potential to functionally antagonize p53. In several experimental model systems, ectopic expression of E6 can block the genotoxic induction of the growth inhibitory p53 target gene gadd45, suggesting that the inactivation of this pathway may play a major role for HPV-associated cell transformation. Here, we investigated whether this reflects the regulation of gadd45 expression in carcinoma-derived HPV-positive cells. We found that the gadd45 gene is efficiently induced by mitomycin C, cisplatin, and UV irradiation in a series of HPV-positive cervical cancer cell lines. Moreover, clear induction of gadd45 gene expression was also observed following treatment with gamma-irradiation, a pathway that is strictly dependent on functional p53. This contrasted with findings in human foreskin keratinocytes experimentally immortalized by expressing the HPV16 E6, E7, or E6/E7 oncogenes from the heterologous CMV promoter, where expression of the E6 gene was linked to a lack of gadd45 induction following gamma-irradiation. These results indicate (1) that the tumorigenic phenotype of HPV-positive cancer cells is not linked to an inability to induce the gadd45 gene following DNA damage, (2) that experimental model systems in which the E6 gene is expressed ectopically and/or in a different cellular context do not necessarily reflect the regulation of p53-associated pathways in HPV-positive cancer cells and (3) that a pathway strictly depending on functional p53 is inducible in HPV-positive cancer cells, providing direct evidence that the endogenous p53 protein in these cells is competent to activate a cellular target gene, despite coexpression of the viral E6 oncogene.     

Lower cost strategies for triage of human papillomavirus DNA‐positive women

Using human papillomavirus (HPV) testing for cervical cancer screening in lower‐resource settings (LRS) will result in a significant number of screen‐positive women. This analysis compares different triage strategies for detecting cervical precancer and cancer among HPV‐positive women in LRS. This was a population‐based study of women aged 25–65 years living in China (n = 7,541). Each woman provided a self‐collected and two clinician‐collected specimens. The self‐collected and one clinician‐collected specimen were tested by two HPV DNA tests—careHPV? and Hybrid Capture 2; the other clinician‐collected specimen was tested for HPV16/18/45 E6 protein. CareHPV?‐positive specimens were tested for HPV16/18/45 DNA. HPV DNA‐positive women underwent visual inspection with acetic acid (VIA) and then colposcopic evaluation with biopsies. The performance for detection of cervical intraepithelial neoplasia grade 3 or cancer (CIN3+) among HPV DNA‐positive women was assessed for different triage strategies: HPV16/18/45 E6 or DNA detection, VIA, colposcopic impression, or higher signal strength (≥10 relative light units/positive control [rlu/pc]). The percent triage positive ranges were 14.8–17.4% for VIA, 17.8–20.9% for an abnormal colposcopic impression; 7.9–10.5% for HPV16/18/45 E6; 23.4–28.4% for HPV16/18/45 DNA; and 48.0–62.6% for higher signal strength (≥10 rlu/pc), depending on the HPV test/specimen combination. The positivity for all triage tests increased with severity of diagnosis. HPV16/18/45 DNA detection was approximately 70% sensitive and had positive predictive values (PPV) of approximately 25% for CIN3+. HPV16/18/45 E6 detection was approximately 50% sensitive with a PPV of nearly 50% for CIN3+. Different triage strategies for HPV DNA‐positive women provide important tradeoffs in colposcopy or treatment referral percentages and sensitivity for prevalent CIN3+.