The early HPV16 proteins can regulate mRNA levels of cell cycle genes in human cervical carcinoma cells by p53-independent mechanisms

Human papillomavirus type 16 E6 promotes cervical cancer proliferation by upregulating transketolase enzymatic activity through the activation of protein kinase B

Over 99% of precancerous cervical lesions are associated with human papillomavirus (HPV) infection, with HPV types 16 and 18 (especially type 16) found in over 70% of cervical cancer cases globally. E6, a critical HPV gene, triggers malignant proliferation by degrading p53; however, this mechanism alone cannot fully explain the oncogenic effects of HPV16 E6. Therefore, we aimed to investigate new targets of HPV oncogenic mechanisms. Our results revealed significant changes in nonoxidative pentose phosphate pathway (PPP) metabolites in HPV16-positive cells. However, the role of nonoxidative PPP in HPV-associated cell transformation and tumor development remained unexplored. In this study, we investigated the impact and mechanisms of HPV16 E6 on cervical cancer proliferation using the HPV-negative cervical cancer cell line (C33A). HPV16 E6 was found to promote cervical cancer cell proliferation both in vitro and in vivo, activating the nonoxidative PPP. Transketolase (TKT), a key enzyme in the nonoxidative PPP, is highly expressed in cervical cancer tissues and associated with poor prognosis. HPV16 E6 promotes cervical cancer cell proliferation by upregulating TKT activity through the activation of AKT. In addition, oxythiamine (OT), a TKT inhibitor, hindered tumor growth, with enhanced effects when combined with cisplatin (DDP). In conclusion, HPV16 E6 promotes cervical cancer proliferation by upregulating TKT activity through the activation of AKT. OT demonstrates the potential to inhibit HPV16-positive cervical cancer growth, and when combined with DDP, could further enhance the tumor-suppressive effect of DDP.

Human papillomavirus maybe is a critical player in the regulation of chemoresistance related factors (P53, Rb, TWIST, Bcl-2, Bcl-XL, c-IAP2, cytochrome C, and caspase 3) in breast cancer

As one of the frequent malignancies, breast cancer (BCa) is the foremost reason for cancer-related deaths among women. The role of Human papillomavirus (HPV) in chemoresistance has rarely been investigated in previous studies. The current study sets out to the possible role of HPV in BCa chemoresistance. In this research, 90 BCa tissue and 33 normal breast tissue were collected. We evaluated the presence of the HPV genome along with the viral (E2, E6, E7) and cellular gene expression associated with cell resistance to death. Statically significant differences in the prevalence of HPV between the BCa group (25.2% or 23/90) and the control group (21.8% or 7/32) were not found. HPV-16 and HPV-18 genotypes were the abundant HPV genotypes. Resistance to the Adriamycin-Cyclophosphamide (AC), paclitaxel regimen was elevated in the HPV- group (56/70) in comparison to the HPV+ group (14/70). Nevertheless, there was no significant difference in the prevalence of resistance to AC + paclitaxel + triple-negative breast cancer combination therapy between the HPV+ group (9/20) and in the HPV- group (11/20). In the BCa group in contrast to the control group, the expression level of Bcl-2, BCL-XL, and c-IAP2 demonstrated a significant decrease, while, the expression level of cytochrome C and caspase 3 was significantly increased. This study suggests that HPV infection might contribute to BCa chemoresistance through disrupt cellular genes involved in cell death.

Oncogenic viruses and chemoresistance: What do we know?

Chemoresistance is often referred to as a major leading reason for cancer therapy failure, causing cancer relapse and further metastasis. As a result, an urgent need has been raised to reach a full comprehension of chemoresistance-associated molecular pathways, thereby designing new therapy methods. Many of metastatic tumor masses are found to be related with a viral cause. Although combined therapy is perceived as the model role therapy in such cases, chemoresistant features, which is more common in viral carcinogenesis, often get into way of this kind of therapy, minimizing the chance of survival. Some investigations indicate that the infecting virus dominates other leading factors, i.e., genetic alternations and tumor microenvironment, in development of cancer cell chemoresistance. Herein, we have gathered the available evidence on the mechanisms under which oncogenic viruses cause drug-resistance in chemotherapy.

Malignant Transformation of Fanconi Anemia Complementation Group D2-deficient (Fancd2 -/-) Hematopoietic Progenitor Cells by a Single HPV16 Oncogene

AIM

To demonstrate that Fanconi anemia complementation group D2-deficient (Fancd2^-/-) hematopoietic progenitor cell lines can be transformed by transfection with a plasmid containing either the E6 or E7 oncogene of human papillomavirus (HPV) to generate malignant plasmacytoma-inducing cell lines.

MATERIALS AND METHODS

In order to determine whether a single HPV type 16 (HPV16) oncogene induced malignant transformation, Fancd2^-/- and Fancd2^+/+ interleukin 3 (IL3)-dependent hematopoietic progenitor cell lines were transfected with plasmids containing E6 or E7 oncogene, or control empty plasmid.

RESULTS

Fancd2^-/- but not Fancd2^+/+ cells were transformed into malignant IL3-independent cells by both E6, and E7 oncogenes, but not by empty plasmid. Hematopoietic cell lines and tumors induced by Fancd2^-/- E6 and Fancd2^-/- E7 cell lines were positive for each respective HPV RNA and protein.

CONCLUSION

A single HPV16 oncogene is adequate to produce malignant transformation of Fancd2^-/- hematopoietic cells.

Evolution of malignant plasmacytoma cell lines from K14E7 Fancd2-/- mouse long-term bone marrow cultures

We tested the effect of expression of the Human Papilloma Virus (HPV E7) oncogene on hematopoiesis in long-term bone marrow cultures (LTBMCs) derived from K14E7 (FVB) Fancd2-/- (129/Sv), K14E7 Fancd2+/+, Fancd2-/-, and control (FVB X 129/Sv) Fl mice. K14E7 Fancd2-/- and Fancd2-/- LTBMCs showed decreased duration of production of total nonadherent hematopoietic cells and progenitors forming day 7 and day 14 multilineage CFU-GEMM colonies in secondary cultures (7 wks and 8 wks respectively) compared to cultures from K14E7 Fancd2+/+ (17 wks) or control mice (18 wks) p < 0.0001. Marrow stromal cell lines derived from both K14E7 Fancd2-/- and Fancd2-/- cultures were radiosensitive, as were IL-3 dependent hematopoietic progenitor cell lines derived from K14E7 Fancd2-/- cultures. In contrast, Fancd2-/- mouse hematopoietic progenitor cell lines and fresh marrow were radioresistant. K14E7 Fancd2-/- mouse freshly explanted bone marrow expressed no detectable K14 or E7; however, LTBMCs produced K14 positive factor-independent (FI) clonal malignant plasmacytoma forming cell lines in which E7 was detected in the nucleus with p53 and Rb. Transfection of an E6/E7 plasmid into Fancd2-/-, but not control Fancd2+/+ IL-3 dependent hematopoietic progenitor cell lines, increased cloning efficiency, cell growth, and induced malignant cell lines. Therefore, the altered radiobiology of hematopoietic progenitor cells and malignant transformation in vitro by K14E7 expression in cells of the Fancd2-/- genotype suggests a potential role of HPV in hematopoietic malignancies in FA patients.

Oncogenic Ras-transformed human fibroblasts exhibit differential changes in contraction and migration in 3D collagen matrices

Tractional force exerted by tissue cells in 3D collagen matrices can be utilized for matrix remodeling or cell migration. The interrelationship between these motile processes is not well understood. The current studies were carried out to test the consequences of oncogenic Ras (H-Ras(V12)) transformation on human fibroblast contraction and migration in 3D collagen matrices. Beginning with hTERT-immortalized cells, we prepared fibroblasts stably transformed with E6/E7 and with the combination HPV16 E6/E7 and H-Ras(V12). Oncogenic Ras-transformed cells lost contact inhibition of cell growth, formed colonies in soft agar and were unable to make adherens junctions. We observed no changes in the extent or growth factor dependence of collagen matrix contraction (floating or stress-relaxation) by oncogenic Ras-transformed cells. On the other hand, transformed cells in nested collagen matrices lost not only growth factor selectivity, but also cell-matrix density-dependent inhibition of migration. These findings demonstrate differential regulation of collagen matrix contraction and cell migration in 3D collagen matrices.

Sensitization of cervical cancer cell lines to low-dose radiation by retinoic acid does not require functional p53

OBJECTIVE

Current therapy for cervical cancer includes radiation therapy. Retinoic acid (RA) can increase the sensitivity of cervical cancer cell lines to radiation. The mechanism of this sensitization may not involve the p53 protein because the human papillomavirus (HPV) E6 protein, which is present in the majority of cervical cancers, promotes p53 degradation. The objective of this study was to determine if p53 is involved in the mechanism of RA radiosensitization.

METHOD

The effects of radiation on cervical (SiHa, CC-1, and C33a) and vulvar (SW962) cancer cell lines under various experimental conditions were evaluated using clonogenic, Coulter Counter, electrophoretic mobility shift (EMSA) and a multi-probe RNase protection assay of p53-inducible genes.

RESULTS

RA (5 microM 9-cis-RA) radiosensitized the SiHa and CC-1 cell lines that contain HPV-degraded p53, but did not radiosensitize the SW962 cell line, which is HPV negative and contains wild-type p53, nor the C33a cell line, which contains mutant p53 (R273C). Expression of mutant p53 (R273H) in SiHa cells increased the growth rate, but did not prevent RA-induced differentiation or radiosensitization at clinically relevant doses. Inhibition of p53 transactivation with pifithirin alpha did not prevent RA radiosensitization of SiHa at 5 Gy. RA repressed c-fos mRNA expression in control and irradiated SiHa cultures, but did not repress bcl-x(L), p53, GADD45, p21, bax, bcl-2, or mcl-1 mRNA expression.

CONCLUSIONS

The mechanism of RA radiosensitization does not require functional p53 and may involve c-fos in cervical cancer cell lines.

The human papillomavirus 16 E6 protein binds to Fas-associated death domain and protects cells from Fas-triggered apoptosis

High risk strains of human papillomavirus (HPV), such as HPV 16, cause human cervical carcinoma. The E6 protein of HPV 16 mediates the rapid degradation of the tumor suppressor p53, although this is not the only function of E6 and cannot completely explain its transforming potential. Previous work in our laboratory has demonstrated that E6 can protect cells from tumor necrosis factor-induced apoptosis by binding to the C-terminal end of tumor necrosis factor R1, thus blocking apoptotic signal transduction. In this study, E6 was shown to also protect cells from apoptosis induced via the Fas pathway. Furthermore, use of an inducible E6 expression system demonstrated that this protection is dose-dependent, with higher levels of E6 leading to greater protection. Although E6 suppresses activation of both caspase 3 and caspase 8, it does not affect apoptotic signaling through the mitochondrial pathway. Mammalian two-hybrid and in vitro pull-down assays were then used to demonstrate that E6 binds directly to the death effector domain of Fas-associated death domain (FADD), with deletion and site-directed mutants enabling the localization of the E6-binding site to the N-terminal end of the FADD death effector domain. E6 is produced in two forms as follows: a full-length version of approximately 16 kDa and a smaller version of about half that size corresponding to the N-terminal half of the full-length protein. Pull-down and functional assays demonstrated that the full-length version, but not the small version of E6, was able to bind to FADD and to protect cells from Fas-induced apoptosis. In addition, binding to E6 leads to degradation of FADD, with the loss of cellular FADD proportional to the amount of E6 expressed. These results support a model in which E6-mediated degradation of FADD prevents transmission of apoptotic signals via the Fas pathway.

Destruxin E, a Cyclodepsipeptide Antibiotic, Reduces Cyclin D1 Levels and Inhibits Anchorage-Independent Growth of v-Ki-ras-Expressed pMAM-ras-REF Cells

Destruxin E (DE), a cyclodepsipeptide isolated from fermentation broths of Metarhizium sp. MA324, inhibited the growth of v-Ki-ras-expressed pMAM-ras-REF (rasREF) cells in the suspension (anchorage-independent) culture (a) more strongly than that in the substratum-attached (anchorage-dependent) culture (b) or that of v-Ki-ras-unexpressed pMAM-ras-REF (REF) cells in the substratum-attached culture (c); the IC(50) values of DE were 0.07 microM (a), 0.4 microM (b), and 1.2 microM (c). DE arrested G1 phase cell cycle progression of rasREF cells in the substratum-attached culture (b). In rasREF cells treated with DE for 72 h in suspension culture (a), the levels of cyclin D1, cyclin A, p27(Kip1), and hyperphosphorylated Rb were decreased, but the levels of cdk4, cdk6, cdk2, p16(INK4a), and p21(Cip1) were not affected. Among these effects, the decrease in cyclin D1 was prominent. DE decreased the level of cyclin D1 in rasREF cells in the suspension culture (a) at 0.1 microM and in the substratum-attached culture (b) at 1 microM, while the level of cyclin D1 in REF cells in the substratum-attached culture (c) was not decreased at 1 microM. The extent of growth inhibition correlated with the decrease in cyclin D1. The level of cyclin D1 mRNA of rasREF cells in the suspension culture (a) was also decreased by DE. DE decreased cyclin D1 mRNA, resulting in inhibition of anchorage-independent growth of rasREF cells.

The adeno-associated virus major regulatory protein Rep78-c-Jun-DNA motif complex modulates AP-1 activity

Multiple epidemiologic studies show that adeno-associated virus (AAV) is negatively associated with cervical cancer (CX CA), a cancer which is positively associated with human papillomavirus (HPV) infection. Mechanisms for this correlation may be by Rep78's (AAV's major regulatory protein) ability to bind the HPV-16 p97 promoter DNA and inhibit transcription, to bind and interfere with the functions of the E7 oncoprotein of HPV-16, and to bind a variety of HPV-important cellular transcription factors such as Sp1 and TBP. c-Jun is another important cellular factor intimately linked to the HPV life cycle, as well as keratinocyte differentiation and skin development. Skin is the natural host tissue for both HPV and AAV. In this article it is demonstrated that Rep78 directly interacts with c-Jun, both in vitro and in vivo, as analyzed by Western blot, yeast two-hybrid cDNA, and electrophoretic mobility shift-supershift assay (EMSA supershift). Addition of anti-Rep78 antibodies inhibited the EMSA supershift. Investigating the biological implications of this interaction, Rep78 inhibited the c-Jun-dependent c-jun promoter in transient and stable chloramphenicol acetyl-transferase (CAT) assays. Rep78 also inhibited c-Jun-augmented c-jun promoter as well as the HPV-16 p97 promoter activity (also c-Jun regulated) in in vitro transcription assays in T47D nuclear extracts. Finally, the Rep78-c-Jun interaction mapped to the amino-half of Rep78. The ability of Rep78 to interact with c-Jun and down-regulate AP-1-dependent transcription suggests one more mechanism by which AAV may modulate the HPV life cycle and the carcinogenesis process.

The human papillomavirus 16 E6 protein binds to tumor necrosis factor (TNF) R1 and protects cells from TNF-induced apoptosis

High risk strains of human papillomavirus (HPV), such as HPV 16, cause human cervical carcinoma. The E6 protein of HPV 16 mediates the rapid degradation of p53, although this is not the only function of E6 and cannot completely explain its transforming potential. Previous work in our laboratory has demonstrated that transfection of HPV 16 E6 into the tumor necrosis factor (TNF)-sensitive LM cell line protects expressing cells from TNF-induced apoptosis in a p53-independent manner, and the purpose of this study was to determine the molecular mechanism underlying this protection. Caspase 3 and caspase 8 activation were significantly reduced in E6-expressing cells, indicating that E6 acts early in the TNF apoptotic pathway. In fact, E6 binds directly to TNF R1, as shown both by co-immunoprecipitation and mammalian two-hybrid approaches. E6 requires the same C-terminal portion of TNF R1 for binding as does TNF R1-associated death domain, and TNF R1/TNF R1-associated death domain interactions are decreased in the presence of E6. HA-E6 also blocked cell death triggered by transfection of the death domain of TNF R1. Together, these results provide strong support for a model in which HPV E6 binding to TNF R1 interferes with formation of the death-inducing signaling complex and thus with transduction of proapoptotic signals. They also demonstrate that HPV, like several other viruses, has developed a method for evading the TNF-mediated host immune response.

High risk HPV and p53 protein expression in cervical intraepithelial neoplasia

INTRODUCTION

Cervical intraepithelial lesions due to HPV infection are common in Brazil. An understanding of the mechanisms of the interaction between HPV and host factors is still incomplete. In spite of the high incidence of cervical cancer in Brazil, such studies with Brazilian patients are scarce. The purpose of this study was to correlate the presence of high-risk types of HPV and expression of p53 protein, grade of cervical lesion, age, high-risk sexual behaviors and smoking. It was also intended to establish whether p53 expression might be useful as a marker for CIN progression.

METHODS

HPV detection was performed on paraffin sections using biotin-labeled probes by in situ hybridization. p53 protein expression was evaluated by immunohistochemistry.

RESULTS

Seventy-eight patients with cervical dysplasia were included in the study. CIN 1 was diagnosed in 38 cases, and CIN 2+3 in 40 cases. High-risk HPV was detected in 42 patients. No correlation was found between the grade of cervical lesion or the presence of HPV and smoking, and high-risk sexual behavior. Expression of p53 was significantly higher in CIN 1, as compared with CIN 2+3, but did not correlate with HPV status.

CONCLUSION

Higher expression of p53 protein in early lesions supports the hypothesis of a partially protective role of the wild-type p53 in early stages of cervical lesions.

HPV 16 E6 blocks TNF-mediated apoptosis in mouse fibroblast LM cells

The interaction between hosts and the viruses that infect them is a dynamic one, and a growing literature documents the fact that many viruses have developed mechanisms designed to avoid elimination by the host immune system. One of the immune strategies used by the host and targeted by virus proteins is apoptosis triggered by the cytokine tumor necrosis factor (TNF). Mouse fibroblast LM cells are spontaneously sensitive to TNF. When the wild-type E6 protein from the human papillomavirus type 16 (HPV 16) was expressed in LM cells, the cells became resistant to TNF. This resistance was examined by several means, including cell morphology, the dose- and time-independent response to TNF in a cell death ELISA, trypan blue exclusion, and cell proliferation. The level of p53 did not rise in TNF-treated cells prior to apoptosis, suggesting a p53-independent mechanism. Significant, though not complete, resistance to TNF was also observed following transfection of a plasmid expressing a mutant E6 protein, which is unable to mediate rapid degradation of the p53 tumor suppressor. These results indicate that the HPV 16 E6 protein can protect LM cells from TNF-triggered apoptosis and likely does so by a mechanism other than mediation of p53 degradation.