Ha-ras oncogene mutation associated to progression of papillomavirus induced lesions of uterine cervix

An in vitro carcinogenesis model for cervical cancer harboring episomal form of HPV16

Deregulated expression of viral E6 and E7 genes often caused by viral genome integration of high-risk human papillomaviruses (HR-HPVs) into host DNA and additional host genetic alterations are thought to be required for the development of cervical cancer. However, approximately 15% of invasive cervical cancer specimens contain only episomal HPV genomes. In this study, we investigated the tumorigenic potential of human cervical keratinocytes harboring only the episomal form of HPV16 (HCK1T/16epi). We found that the HPV16 episomal form is sufficient for promoting cell proliferation and colony formation of parental HCK1T cells. Ectopic expression of host oncogenes, MYC and PIK3CAE545K, enhanced clonogenic growth of both early- and late-passage HCK1T/16epi cells, but conferred tumor-initiating ability only to late-passage HCK1T/16epi cells. Interestingly, the expression levels of E6 and E7 were rather lower in late-passage than in early-passage cells. Moreover, additional introduction of a constitutively active MEK1 (MEK1DD) and/or KRASG12V into HCK1T/16epi cells resulted in generation of highly potent tumor-initiating cells. Thus an in vitro model for progression of cervical neoplasia with episomal HPV16 was established. In the model, constitutively active mutation of PIK3CA, PIK3CAE545K, and overexpression of MYC, in the cells with episomal HPV16 genome were not sufficient, but an additional event such as activation of the RAS-MEK pathway was required for progression to tumorigenicity.

Autophagy buffers Ras-induced genotoxic stress enabling malignant transformation in keratinocytes primed by human papillomavirus

Malignant transformation involves an orchestrated rearrangement of cell cycle regulation mechanisms that must balance autonomic mitogenic impulses and deleterious oncogenic stress. Human papillomavirus (HPV) infection is highly prevalent in populations around the globe, whereas the incidence of cervical cancer is 0.15%. Since HPV infection primes cervical keratinocytes to undergo malignant transformation, we can assume that the balance between transforming mitogenic signals and oncogenic stress is rarely attained. We showed that highly transforming mitogenic signals triggered by HRasG12V activity in E6E7-HPV-keratinocytes generate strong replication and oxidative stresses. These stresses are counteracted by autophagy induction that buffers the rapid increase of ROS that is the main cause of genotoxic stress promoted by the oncoprotein. As a result, autophagy creates a narrow window of opportunity for malignant keratinocytes to emerge. This work shows that autophagy is crucial to allow the transition of E6E7 keratinocytes from an immortalized to a malignant state caused by HRasG12V.

TP53 and PIK3CA gene mutations in adenocarcinoma, squamous cell carcinoma and high-grade intraepithelial neoplasia of the cervix

BACKGROUND

Mutations in the tumor suppressor gene TP53 and proto-oncogene PIK3CA and alterations of p53 and PIK3CA AKT mTOR pathways are common events in several human cancers. We focused on the analysis of TP53 and PIK3CA gene variations in adenocarcinoma, squamous cell carcinoma as well as in intraepithelial neoplasia grade 3 of the cervix.

METHODS

DNA samples from 28 cervical adenocarcinoma, 55 squamous cell carcinoma and 31 intraepithelial neoplasia grade 3 (CIN3), previously characterized in terms of human papillomavirus (HPV) prevalence and genotype distribution, were analyzed for TP53 and PIK3CA mutations in the exons 4-9 and exon 9, respectively.

RESULTS

Single nucleotide substitutions in TP53 and PIK3CA genes were detected in 36% and 11% of adenocarcinoma, in 16% and in 5% of squamous cell carcinoma, and in 13% and none of CIN 3, respectively. Nucleotide changes in TP53 were significantly more frequent in adenocarcinoma cases than in squamous cell carcinoma and CIN3 (P = 0.035) and were independent from HPV infection status.

CONCLUSIONS

Mutations in the TP53 gene and to lesser extent in the PIK3CA gene seem more frequent in cervical adenocarcinoma than in squamous cell carcinoma and CIN3. Whether TP53 and PIK3CA gene mutations have an impact on prognosis and response to molecularly targeted therapies as well as in cytotoxic drugs in different cervical cancer histotypes needs to be analyzed in investigative clinical trials.

Mutations of the TP53 gene in adenocarcinoma and squamous cell carcinoma of the cervix: a systematic review

OBJECTIVE

Mutations of the tumor suppressor gene TP53 are the most significant events in several human cancers. Few studies have analyzed the frequency of TP53 alterations in squamous cell carcinoma and adenocarcinoma of the cervix with controversial results. This study provides a detailed analysis of TP53 mutation spectra in cervical squamous cell carcinoma and adenocarcinoma from different geographical regions.

METHODS

The analysis of TP53 mutational profiles was performed in 1353 cervical cancers retrieved from the IARC p53 mutation database (R15, 2010) and the COSMIC data along with the literature review of related studies identified by PubMed searching.

RESULTS

This analysis showed a significant higher mutation frequency of TP53 gene in cervical adenocarcinoma (32 of 241; 13.3%) compared to squamous cell carcinoma (39 of 657; 5.9%; P=0.0003, χ(2) test). The proportion of adenocarcinoma with mutated TP53 varied from 4% in North America to 19% in Asia. Among the six hot-spot codons of TP53 gene, three codons (175, 248 and 273) were the most commonly mutated in both types of cervical cancer, one codon (249) mainly in squamous cell carcinoma and one codon (282) only in adenocarcinoma. The G to A and C to T transitions were the prevalent type of mutations in both squamous cell carcinoma and adenocarcinoma (48.7% and 53.5% of all mutations, respectively). The frequency of C to A transversion was relatively high only in adenocarcinoma (25%), while the mirror mutation G to T was comparatively frequent in squamous cell carcinoma (14.6%).

CONCLUSIONS

Different patterns of TP53 mutations occur in squamous cell carcinoma and adenocarcinoma of the cervix in different regions of the world. The highest frequency of mutated TP53 has been observed in cervical adenocarcinoma from Asia. Further studies are needed to better define the role of TP53 alterations in cervical cancer and possibly to understand the impact of mutations on cancer prognosis and outcomes.

The B-Raf status of tumor cells may be a significant determinant of both antitumor and anti-angiogenic effects of pazopanib in xenograft tumor models

Pazopanib is an FDA approved Vascular Endothelial Growth Factor Receptor inhibitor. We previously reported that it also inhibits tumor cell B-Raf activity in an experimental brain metastatic setting. Here, we determine the effects of different B-Raf genotypes on pazopanib efficacy, in terms of primary tumor growth and anti-angiogenesis. A panel of seven human breast cancer and melanoma cell lines harboring different mutations in the Ras-Raf pathway was implanted orthotopically in mice, and tumor growth, ERK1/2, MEK1/2 and AKT activation, and blood vessel density and permeability were analyzed. Pazopanib was significantly inhibitory to xenografts expressing either exon 11 mutations of B-Raf, or HER2 activated wild type B-Raf; no significant inhibition of a xenograft expressing the common V600E B-Raf mutation was observed. Decreased pMEK staining in the responsive tumors confirmed that B-Raf was targeted by pazopanib. Interestingly, pazopanib inhibition of tumor cell B-Raf also correlated with its anti-angiogenic activity, as quantified by vessel density and area. In conclusion, using pazopanib, tumor B-Raf status was identified as a significant determinant of both tumor growth and angiogenesis.

Type-specific HPV prevalence in cervical cancer and high-grade lesions in Latin America and the Caribbean: systematic review and meta-analysis

Background

Cervical cancer is a major public health problem in Latin America and the Caribbean (LA&C), showing some of the highest incidence and mortality rates worldwide. Information on HPV type distribution in high-grade cervical lesions (HSIL) and invasive cervical cancer (ICC) is crucial to predict the future impact of HPV16/18 vaccines and screening programmes, and to establish an appropriate post-vaccinal virologic surveillance. The aim was to assess the prevalence of HPV types in HSIL and ICC in studies in LA&C.

Methods and Findings

We performed a systematic review, following the MOOSE guidelines for systematic reviews of observational studies, and the PRISMA statement for reporting systematic reviews and meta-analyses. Inclusion criteria were at least ten cases of HSIL/ICC, and HPV-type elicitation. The search, without language restrictions, was performed in MEDLINE, Cochrane Library, EMBASE, LILACS from inception date to December 2009, proceedings, reference lists and consulting experts. A meta-analysis was performed using arc-sine transformations to stabilize the variance of simple proportions. Seventy-nine studies from 18 countries were identified, including 2446 cases of HSIL and 5540 of ICC. Overall, 46.5% of HSIL cases harbored HPV 16 and 8.9% HPV18; in ICC, 53.2% of cases harbored HPV 16 and13.2% HPV 18. The next five most common types, in decreasing frequency, were HPV 31, 58, 33, 45, and 52.

Study's limitations comprise the cross-sectional design of most included studies and their inherent risk of bias, the lack of representativeness, and variations in the HPV type-specific sensitivity of different PCR protocols.

Conclusions

This study is the broadest summary of HPV type distribution in HSIL and ICC in LA&C to date. These data are essential for local decision makers regarding HPV screening and vaccination policies. Continued HPV surveillance would be useful, to assess the potential for changing type-specific HPV prevalence in the post-vaccination era in Latin America.

Molecular mechanisms of human papillomavirus-induced carcinogenesis

Approximately 20% of all cancers are associated with infectious agents. Among them, human papillomaviruses (HPVs) are very common and are now recognized as the etiological agent of cervical cancer, the second most common cancer in women worldwide, and they are increasingly linked with other forms of dysplasia. Carcinogenesis is a complex and multistep process requiring the acquisition of several genetic and/or epigenetic alterations. HPV-induced neoplasia, however, is in part mediated by the intrinsic functions of the viral proteins. In order to replicate its genome, HPV modulates the cell cycle, while deploying mechanisms to escape the host immune response, cellular senescence and apoptosis. As such, HPV infection leads directly and indirectly to genomic instability, further favouring transforming genetic events and progression to malignancy. This review aims to summarize our current understanding of the molecular mechanisms exploited by HPV to induce neoplasia, with an emphasis on the role of the 2 viral oncoproteins E6 and E7. Greater understanding of the role of HPV proteins in these processes will ultimately aid in the development of antiviral therapies, as well as unravel general mechanisms of oncogenesis.

[Molecular basis of cervical carcinogenesis by high-risk human papillomaviruses]

Over the last two decades since discovery of human papillomavirus (HPV) type 16 and 18 DNAs in cervical cancers by Dr. Harald zur Hausen, HPVs have been well characterized as causative agents for cervical cancer. Viral DNA from a specific group of HPVs can be detected in at least 90% of all cervical cancers and two viral genes, E6 and E7, are invariably expressed in HPV-positive cervical cancer cells. Their gene products are known to inactivate the major tumor suppressors, p53 and pRB, respectively. In addition, one function of E6 is to activate telomerase, and E6 and E7 cooperate to effectively immortalize human primary epithelial cells. Though expression of E6 and E7 is itself not sufficient for cancer development, it seems to be either directly or indirectly involved in every stage of multi-step carcinogenesis. Indeed, it has been shown that only one or two genetic alterations in addition to expression of E6 and E7 are experimentally sufficient to confer tumorigenicity to normal human cervical keratinocytes. Epidemiological and biological studies suggest the potential efficacy of prophylactic vaccines to prevent genital HPV infection as an anti-cancer strategy. However, given the widespread nature of HPV infection and unresolved issues about the duration and type specificity of the currently available HPV vaccines, it is crucial that molecular details of the natural history of HPV infection as well as the biological activities of the viral oncoproteins be elucidated in order to provide the basis for development of new therapeutic strategies against HPV-associated malignancies. This review highlights the novel functions of E6 and E7 as well as the molecular mechanisms of HPV-induced carcinogenesis.

Molecular mechanisms of cervical carcinogenesis by high-risk human papillomaviruses: novel functions of E6 and E7 oncoproteins

Over the last two decades, since the initial discovery of human papillomavirus (HPV) type 16 and 18 DNAs in cervical cancers by Dr. Harald zur Hausen (winner of the Nobel Prize in Physiology or Medicine, 2008), the HPVs have been well characterised as causative agents for cervical cancer. Viral DNA from a specific group of HPVs can be detected in at least 90% of all cervical cancers and two viral genes, E6 and E7, are invariably expressed in HPV-positive cervical cancer cells. Their gene products are known to inactivate the major tumour suppressors, p53 and retinoblastoma protein (pRB), respectively. In addition, one function of E6 is to activate telomerase, and E6 and E7 cooperate to effectively immortalise human primary epithelial cells. Though expression of E6 and E7 is itself not sufficient for cancer development, it seems to be either directly or indirectly involved in every stage of multi-step carcinogenesis. Epidemiological and biological studies suggest the potential efficacy of prophylactic vaccines to prevent genital HPV infection as an anti-cancer strategy. However, given the widespread nature of HPV infection and unresolved issues about the duration and type specificity of the currently available HPV vaccines, it is crucial that molecular details of the natural history of HPV infection as well as the biological activities of the viral oncoproteins be elucidated in order to provide the basis for development of new therapeutic strategies against HPV-associated malignancies. This review highlights novel functions of E6 and E7 as well as the molecular mechanisms of HPV-induced carcinogenesis.

Ras modifies proliferation and invasiveness of cells expressing human papillomavirus oncoproteins

Infection by human papillomavirus (HPV) is a major risk factor for human cervical carcinoma. However, the HPV infection alone is not sufficient for cancer formation. Cervical carcinogenesis is considered a multistep process accompanied by genetic alterations of the cell. Ras is activated in approximately 20% of human cancers, and it is related to the metastatic conversion of tumor cells. We investigated how Ras activation was involved in the malignant conversion of HPV-infected lesions. The active form of H-ras was introduced into human primary keratinocytes expressing the HPV type 18 (HPV18) oncoproteins E6 and/or E7. We analyzed the keratinocytes' growth potentials and found that the activation of the Ras pathway induced senescence-like growth arrest. Senescence could be eliminated by high-risk E7 expression, suggesting that the pRb pathway was important for Ras-induced senescence. Then we analyzed the effect of Ras activation on epidermis development by using an organotypic "raft" culture and found that the E7 and H-ras coexpressions conferred invasive potential on the epidermis. This invasiveness resulted from the upregulation of MT1-MMP and MMP9 by H-ras and E7, respectively, in which the activation of the MEK/extracellular signal-regulated kinase pathway was involved. These results indicated that the activation of Ras or the related signal pathways promoted the malignant conversion of HPV-infected cells.

Human papillomavirus and mutated H-ras oncogene in cervical carcinomas and pathological negative pelvic lymph nodes: a retrospective follow-up

The metastasis status of pelvic lymph nodes (PLNs) seems to be a predictive factor of survival. It was suggested that the presence of HPV DNA and other biological markers in PLN may indicate a sub clinical early metastasis. The aim was to describe the prevalence and distribution patterns of HPV DNA and H-ras mutations in intra operatively obtained cervical tumors and PLN. Thirty-seven cervical tumors and 61 lymph node biopsies from 37 patients with cervical cancer were selected. HPV typing and location were performed by PCR/dot blot and in situ hybridization (ISH) respectively. PCR/RFLP was used to scan for mutations in H-ras. Hundred percent of the cervical cancers and 85% of the PLN were HPV positive; co-infection with more than one type was 27%. HPV 16 was detected alone or co-infecting with other types in 84% of tumors and 46% of PLN; the second most frequent viral type was HPV 18 (tumor: 27%; PLN: 20%). In PLN, HPV was located in nuclei or/and cytoplasm of lymphocytes, macrophages, endothelial, and /or stromal cells. H-ras mutations were identified in 5/24 (21%) of patients with cervical tumors showing poor or moderated differentiation. HPV DNA in histological tumor-free PLN not necessary indicate metastasis, but it may be associated to an active immune reaction. Mutated H-ras is probably involved in cervical carcinogenesis and its detection in tumor and metastasis free PLN may be related to early metastasis or recurrence in at least a subset of poorly differentiated cervical tumors.

Glutathione-S-transferase M1 and T1 and cytochrome P1A1 genetic polymorphisms and susceptibility to cervical intraepithelial neoplasia in Greek women

The aim of the study was to determine the importance of genetic polymorphisms of glutathione-S-transferase T1 and M1 and cytochrome P1A1 genes in the development of cervical intraepithelial neoplasia in Greek women. This was a prospective, case-control study conducted by the Cervical Pathology and Colposcopy Unit of a University Ob/Gyn Department from 1999 to 2003. Cervical smears from 114 controls without any cytological and/or colposcopical evidence of cervical pathology and from 166 women with history of cervical intraepithelial neoplasia (56 CIN I, 54 CIN II and 56 CIN III) were examined with polymerase chain reaction for the above-mentioned genetic polymorphisms, taking also in mind their smoking attitudes. Statistical analysis was performed to detect any association between the null genotype of GSTM1 and GSTT1 genes and the CYP1A1 m1 polymorphism and the severity of cervical intraepithelial neoplasia. The distributions of the GSTT1 and GSTM1 wild-type genotypes were 57.48 and 39.75%, respectively. No woman with homozygous GSTT1 and GSTM1 null/null genotype was identified. CYP1A1 m1 polymorphism frequency was 24.49%. No woman with homozygous CYP1A1 m1/m1 genotype was detected as well. No significant difference in the frequencies of the GSTM1 and GSTT1 null alleles, and the CYP1A1 m1 polymorphism, was found between cases and controls. After application of Mantel-Haenszel chi procedure, there was no linear severity of the lesion and the frequency of these polymorphisms. According to our results, glutathione-S-transferase T1 and M1 and cytochrome P1A1 genetic polymporphisms do not appear to be a risk factor for cervical disease irrespective of smoking habits.

The PDZ binding motif of human papillomavirus type 16 E6 induces PTPN13 loss, which allows anchorage-independent growth and synergizes with ras for invasive growth

The human papillomavirus (HPV) oncogene E6 has been shown to perform multiple functions (p53 degradation, telomerase activation, etc.) that play a role in oncogenic transformation. Beyond known E6 functions, an undefined mechanism that allows cellular invasion requires the E6 PDZ binding motif (PDZBM). Here, we show that HPV type 16 (HPV16) E6 interacts with and induces loss of a protein tyrosine phosphatase (PTPN13) in a PDZBM-dependent manner. PTPN13 loss induced either by the presence of E6 or by a short hairpin RNA strategy allows for anchorage-independent growth (AIG) and synergy with a known oncogene, Ras(v12), resulting in invasive growth in vivo. Restoring PTPN13 expression reverses AIG in cells lacking PTPN13. A genomic analysis of colorectal carcinoma has identified an association between PTPN13 loss-of-function mutations and aberrant Ras signaling. Our findings support this correlation and provide methods for further evaluation of the mechanisms by which PTPN13 loss/Ras expression leads to invasive growth, the results of which will be important for treatment of HPV-related and non-HPV cancer.

Cervical keratinocytes containing stably replicating extrachromosomal HPV-16 are refractory to transformation by oncogenic H-Ras

Ras expression in human epithelial cells with integrated HPV genomes has been shown to cause tumorigenic transformation. The effects of Ras in cells representing early stage HPV-associated disease (i.e., when HPV is extrachromosomal and the oncogenes are under control of native promoters) have not been examined. Here, we used human cervical keratinocyte cell lines containing stably replicating extrachromosomal HPV-16 and present the novel finding that these cells resist transformation by oncogenic H-Ras. Ras expression consistently diminished anchorage-independent growth (AI), reduced E6 and E7 expression, and caused p53 induction in these cells. Conversely, AI was enhanced or maintained in Ras-transduced cervical cells that were immortalized with a 16E6/E7 retrovirus, and minimal effects on E6 and E7 expression were observed. Ras expression with either episomal HPV-16 or LXSN-E6/E7 was insufficient for tumorigenic growth suggesting that other events are needed for tumorigenic transformation. In conclusion, our results indicate that Ras-mediated transformation depends on the context of HPV oncogene expression and that this is an important point to address when developing HPV tumor models.

Augmentation of sodium butyrate-induced apoptosis by phosphatidylinositol 3-kinase inhibition in the human cervical cancer cell-line

PURPOSE

Sodium butyrate (NaBT) is principally a histone deacetylase (HDAC) inhibitor, and it has the potential to arrest HPV-positive carcinoma cells at the G1 to S phase transition of the cell cycle. The aim of study was to determine whether phosphatidylinositol 3-kinase (PI3K) inhibition can enhance the inhibitory effect of NaBT on a human cervical cancer cell line (HeLa).

MATERIALS AND METHODS

Cervical cancer cells (HeLa) were treated with NaBT alone or in combination with the PI3K inhibitors wortmannin or LY294002. Cell viability analysis and FACS analysis were carried out. The expressions of the cell cycle related proteins were evaluated by Western-blot analysis.

RESULTS

Inhibition of PI3K enhanced NaBT-mediated apoptosis and this decreased the HeLa cell viability. Either wortmannin or LY294002, combined with NaBT, enhanced the activation of caspase 3 and caspase 9, and this enhanced the subsequent cleavage of poly (ADP-ribose) polymerase (PARP). Cervical cancer cells were arrested in the subG1 and G2/M phase, as was detected by FACS analysis. NaBT treatment in combination with PI3K inhibitors showed the increased expression of the CDK inhibitors p21(Cip1/Waf1) and p27(Kip1), in a p53 dependent manner, and also the increased dephosphorylation of Rb whereas there was a reduction in the expression levels of cyclin A, cyclin D1 and cyclin B1.

CONCLUSION

The results demonstrate that inhibition of PI3K enhances NaBT-mediated cervical cancer cell apoptosis through the activation of the caspase pathway. Moreover, these findings will support future investigation using the PI3K inhibitors in combination with adjuvant treatment for treating carcinoma of the cervix.

Effects of HRAS oncogene on cell cycle progression in a cervical cancer-derived cell line

BACKGROUND

Human papillomavirus (HPV) infection is the most prevalent factor in anogenital cancers. However, epidemiological surveys and molecular data indicate that viral presence is not enough to induce cervical cancer, suggesting that cellular factors could play a key role. One of the most important genes involved in cancer development is the RAS oncogene, and activating mutations in this gene have been associated with HPV infection and cervical neoplasia. Thus, we determined the effect of HRAS oncogene expression on cell proliferation in a cell line immortalized by E6 and E7 oncogenes.

METHODS

HPV positive human cervical carcinoma-derived cell lines (HeLa), previously transfected with the HRAS oncogene or the empty vector, were used. We first determined the proliferation rate and cell cycle profile of these cells by using flow cytometry and BrdU incorporation assays. In order to determine the signaling pathway regulated by HRAS and implicated in the alteration of proliferation of these cells, we used specific chemical inhibitors to inactivate the Raf and PI3K pathways.

RESULTS

We observed that HeLa cells stably transfected with oncogenic HRAS progressed faster than control cells on the cell cycle by reducing their G1 phase. Additionally, HRAS overexpression accelerated the G1/S transition. Specific chemical inhibitors for PI3K and MEK activities indicated that both PI3K/AKT and RAF/MEK/ERK pathways are involved in the HRAS oncogene-induced reduction of the G1 phase.

CONCLUSIONS

Our results suggest that the HRAS oncogene could play an important role in the development of cervical cancer, in addition to the presence of HPV, by reducing the G1 phase and accelerating the G1/S transition of infected cells.

Strong synergy between mutant ras and HPV16 E6/E7 in the development of primary tumors

E6/E7 oncogenes of high-risk human papilloma virus (HPV) subtypes are essential for the development of certain types of cancers. However, these oncogenes are insufficient to transform normal cells into an immortalized or malignant state. Mutant Ha-ras cooperates with E6/E7 of HPV subtype 16 in transformation of cells in vitro and may contribute to some HPV-associated cancers in humans. This study investigates whether HPV16 E6/E7 and v-Ha-ras synergize in vivo. FVB/n mice transgenic for v-Ha-ras gene (R+) were crossed with transgenic C57BL/6 mice that harbor E6/E7 of HPV16 (E+). Beginning at about 3 months of age, the bitransgenic E(+)R(+)(C57BL/6 x FVB/n) F1 mice developed mouth, eye and ear tumors. By 6 months, the prevalence of these types of mouth, eye and ear tumors was 100, 71 and 79% respectively in the E(+)R+ mice. Most tumors grew progressively until the mice had to be killed. The median times for the appearance of the first mouth, eye and ear tumor were 3.6, 4.3 and 4.2 months, respectively. For the two singly transgenic groups of mice, the prevalence of mouth, eye and ear tumors was 0, 0 and 6% (E(-)R+) and 0, 0 and 0% (E(+)R-), respectively, and the median time to first tumor was greater than 12 months for singly transgenic mice (E(-)R+, E(+)R-). Thus, a remarkable synergy occurred between the v-Ha-ras and HPV16 E6/E7 oncogenes in the development of primary tumors in mice.