RU486 inhibits glucocorticoid hormone-dependent oncogenesis by human papillomavirus type 16 DNA

The oncogenic potential of human papillomaviruses: a review on the role of host genetics and environmental cofactors

Human papillomaviruses (HPVs), with over 100 genotypes, are a very complex group of human pathogenic viruses. In most cases, HPV infection results in benign epithelial proliferations (verrucae). However, oncogenic types of HPV may induce malignant transformation in the presence of cofactors. For example, over 99% of all cervical cancers and a majority of vulval, vaginal, anal and penile cancers are the result of oncogenic HPV types. Such HPV types have been increasingly linked to other epithelial cancers involving the skin, larynx and oesophagus. Although viral infection is necessary for neoplastic transformation, evidence suggests that host and environmental cofactors are also required. Research investigating HPV oncogenesis is complex and quite extensive. The inability to produce mature HPV virions in animal models has been a major limitation in fully elucidating the oncogenic potential and role of associated cofactors in promoting malignant transformation in HPV-infected cells. We have reviewed the literature and provide a brief account of the current understanding of HPV oncogenesis, emphasizing the role of genetic susceptibility, immune response, and environmental and infectious cofactors.

The influence of bio-behavioural factors on tumour biology: pathways and mechanisms

Epidemiological studies indicate that stress, chronic depression and lack of social support might serve as risk factors for cancer development and progression. Recent cellular and molecular studies have identified biological processes that could potentially mediate such effects. This review integrates clinical, cellular and molecular studies to provide a mechanistic understanding of the interface between biological and behavioural influences in cancer, and identifies novel behavioural or pharmacological interventions that might help improve cancer outcomes.

Evaluation of tamoxifen in persistent or recurrent nonsquamous cell carcinoma of the cervix: a Gynecologic Oncology Group study

This study was undertaken to estimate the antitumor activity of tamoxifen in patients with persistent or recurrent nonsquamous cell carcinoma of the cervix. Furthermore, the nature and degree of adverse effects from tamoxifen in this cohort of individuals was examined. Tamoxifen citrate was to be administered at a dose of 10 mg per orally twice a day until disease progression or unacceptable side effects prevented further therapy. A total of 34 patients (median age: 49 years) were registered to this trial; two were declared ineligible. Thirty-two patients were evaluable for adverse effects and 27 were evaluable for response. There were only six grades 3 and 4 adverse effects reported: leukopenia (in one patient), anemia (in two), emesis (in one), gastrointestinal distress (in one), and neuropathy (in one). The objective response rate was 11.1%, with one complete and two partial responses. In conclusion, tamoxifen appears to have minimal activity in nonsquamous cell carcinoma of the cervix.

Relationship between steroid hormone contraceptives and HPV, cervical intraepithelial neoplasia and cervical carcinoma

Available data demonstrate an increase in the transcription of high-risk papillomaviruses by the 16alpha-hydroxylation of estrogens, which is in line with the epidemiologic data showing an increased cervical carcinogenesis risk for long-term contraceptive-using, HPV-infected women. No evidence exists for an increase in HPV-negative contraceptive users.

The role of steroid contraceptive hormones in the pathogenesis of invasive cervical cancer: a review

Invasive cervical cancer remains a leading cause of morbidity and mortality, especially among women in the developing world where screening is either deficient or absent. Of all agents linked to the causation of this disease, high-risk human papillomavirus (HPV) appears to be the strongest factor. However, not all women with HPV develop cervical cancer. Steroid contraception has been postulated to be one mechanism whereby HPV exerts its tumorigenic effect on cervical tissue. Steroids are thought to bind to specific DNA sequences within transcriptional regulatory regions on the HPV DNA to either increase or suppress transcription of various genes. Although some earlier studies were reassuring as no increased incidence of cervical cancer was observed, subsequent research has shown a causative association, especially among long-term users. The role of steroids was further enhanced by the discovery of hormone receptors in cervical tissue. Some earlier studies of oral contraceptive steroids found no increased risk, even after controlling for other risk factors, including smoking and number of partners. However, prospective studies have shown a greater progression of dysplasia to carcinoma-in-situ with more than 6 years of oral steroid contraceptive use. Similar findings were also evident from other work, including the Royal College of General Practitioners Oral Contraception Study. The WHO Collaborative Study of Neoplasia and Steroid Contraceptives showed a relative risk of 1.2 for invasive cancer in users of the long-acting progestational contraceptive, depo-medroxyprogesterone acetate. However, in users of more than 5 years duration, an estimate of 2.4 was reported. The upstream regulatory region (URR) of the HPV type 16 viral genome, mediates transcriptional control of the HPV genome and is thought to contain enhancer elements that are activated by steroid hormones. It has been shown that steroid hormones bind to specific glucorticoid-response elements within HPV-DNA. Experimental evidence has revealed that high-risk type HPV 16 are able to stimulate the development of vaginal and cervical squamous cell carcinomas in transgenic mice exposed to slow-release pellets of 17 beta-estradiol in the presence of human keratin-14 promoter. Squamous cell carcinomas developed in a multi-stage pathway only in transgenic mice and not in nontransgenic mice. The E6 oncoprotein of HPV 16 has been shown to bind to the p53 tumor suppressor gene and stimulate its degradation by a ubiquitin-dependent protease system. Steroid hormones are thought to increase the expression of the E6 and E7 HPV 16 oncogenes, which in turn bind to and degrade the p53 gene product, leading to apoptotic failure and carcinogenesis. However, the molecular basis of this remains to be proven.

RU486 increases radiosensitivity and restores apoptosis through modulation of HPV E6/E7 in dexamethasone-treated cervical carcinoma cells

OBJECTIVE

Cervical carcinoma tumors containing radioresistant cells are associated with decreased local control and survival. Therefore, strategies to increase cell kill during radiotherapy have a clear rationale. It was previously determined that treatment with the corticosteroid dexamethasone increased radioresistance and decreased apoptosis in C4-1 cervical carcinoma cells. The goal of this study was to determine whether hormone antagonists, specifically Mifepristone (RU486), could reverse the effects of dexamethasone on clonogenic survival and apoptosis following gamma-irradiation.

METHODS

Cervical carcinoma cell line C4-1 cells were exposed to 1 microM dexamethasone in the presence or absence of 1 microM Mifepristone (RU486), a hormone antagonist, and irradiation. Cells were analyzed for steroid-dependent HPV E6/E7 mRNA expression (by Northern blot analysis), clonogenic survival, and apoptosis (by Annexin V staining and the DNA fragmentation assay). In addition, p53 protein levels were determined by Western blot analysis.

RESULTS

The hormone antagonist RU486 reversed dexamethasone-dependent upregulation of E6/E7 mRNA and restored radiation-induced p53 expression, apoptosis, and clonogenic survival to levels similar to those observed following irradiation alone.

CONCLUSION

RU486 reverses glucocorticoid-dependent upregulation of HPV E6/E7, which corresponds to restoration of p53 expression, and restores radiosensitivity and apoptosis following gamma-irradiation. Therefore, it appears that along with radiation, RU486 may be a beneficial agent in the treatment of hormone-reactive cervical tumors.

Glucocorticoids stimulate growth of human papillomavirus type 16 (HPV16)-immortalized human keratinocytes and support HPV16-mediated immortalization without affecting the levels of HPV16 E6/E7 mRNA

We investigated the effects of the glucocorticoids hydrocortisone and dexamethasone on human papillomavirus type 16 (HPV16)-mediated human cell carcinogenesis using normal human keratinocytes (HKc) and HKc immortalized by transfection with HPV16 DNA (HKc/HPV16). Normal HKc did not require glucocorticoids for proliferation. In contrast, growth of early passage HKc/HPV16 strictly required these hormones, although glucocorticoid dependence became less stringent during in vitro progression. Glucocorticoid dependence was acquired by HKc early after immortalization with HPV16 DNA, and glucocorticoids were required for efficient HKc immortalization. However, treatment of HKc/HPV16 with hydrocortisone or dexamethasone did not increase the steady-state levels of HPV16 E6/E7 mRNA or protein. Firefly luciferase activity expressed under the control of the HPV16 upstream regulatory region and P97 promoter increased by about fourfold following dexamethasone treatment of HeLa, but only twofold in HKc/HPV16, and less than twofold in SiHa. However, all of these cell lines expressed sufficient endogenous glucocorticoid receptors to allow for a dexamethasone response of the mouse mammary tumor virus promoter. These results indicate that mechanisms other than a direct influence by glucocorticoids on HPV16 early gene expression may contribute to the striking biological effects of these steroids on HPV16-mediated human cell carcinogenesis.

Effect of glucocorticoid hormones on viral gene expression, growth, and dysplastic differentiation in HPV16-immortalized ectocervical cells

Steroid hormones are proposed to act as cofactors with human papillomaviruses (HPVs) in the etiology of cervical cancer. We and others reported that progesterone and glucocorticoid hormones induce the expression of HPV16 via three glucocorticoid response elements (GREs) in the viral regulatory region. Consensus GREs (GREcs) are useful in other systems for examining the effect of hormones after enhancing the response with mutated GREc constructs. Therefore, this study used human ectocervical cells (HEC) and HPV type 16 containing three GREcs to establish immortalized cells (HEC-16GREc). Northern blot assays showed that the level of viral E6-E7 oncogene RNA was increased by hormones substantially more in HEC-16GREc than in wild-type HPV16-immortalized human ectocervical cells (HEC-16). The saturation density and the hormone response of the growth rate were significantly higher for HEC-16GREc and the doubling was faster in the presence of hormone than for HEC-16. Although both were nontumorigenic, only HEC-16GREc showed anchorage-independent growth, which was dependent on hormone. Also, HEC-16GREc were more abnormal in their epithelium differentiation pattern in organotypic (raft) cultures. Furthermore, hormone-treated HEC-16GREc rafts showed more dysplastic features than hormone-treated HEC-16 rafts. These results suggest new features of the role of hormones: that enhanced expression of viral oncogenes in response to hormones apparently confers a greater risk for cervical cells containing HPV16. Further, HEC-16GREc could be ideal for studying hormone-dependent and -independent malignant transformation.

Human papillomaviruses and cervical cancer

Molecular and epidemiological studies conducted over the last 20 years led to the recognition of certain types of human papillomavirus (HPV) as the etiological agents of cervical cancer, a very common neoplasia, particularly in developing countries. More than 70 HPVs have been described, including both cutaneous and mucosal types. About half of the known HPVs, and an even higher number of variants, have been isolated from genital mucosas. The association of certain types primarily with normal tissues and benign lesions, as opposed to cancer-associated types, has led to the concept of low and high oncogenic risk HPVs, respectively. The latter express oncogenic proteins that interfere with cell growth control functions. As a consequence of the continuous expression of these viral genomes, chromosome instability may occur, leading to fully transformed cells. Studies indicate that persistence of high-risk HPVs may determine progression to more severe stages of cervical disease, while the majority of HPV infections are transient and do not seem to be important in cervical carcinogenesis. The risk for disease progression seems also to be associated with viral burden. Prospective epidemiological studies will contribute to the knowledge of the natural history of HPV infections and provide information on the determinants of viral persistence. Data derived from these studies may define the clinical utility of HPV testing and its use in cervical cancer prevention programs.

Papillomavirus infections--a major cause of human cancers

The papillomavirus family represents a remarkably heterogeneous group of viruses. At present, 77 distinct genotypes have been identified in humans and partial sequences have been obtained from more than 30 putative novel genotypes. Geographic differences in base composition of individual genotypes are generally small and suggest a low mutation rate and thus an ancient origin of today's prototypes. The relatively small size of the genome permitted an analysis of individual gene functions and of interactions of viral proteins with host cell components. Proliferating cells contain the viral genome in a latent form, large scale viral DNA replication, as well as translation and functional activity of late viral proteins, and viral particle assembly are restricted to differentiating layers of skin and mucosa. In humans papillomavirus infections cause a variety of benign proliferations: warts, epithelial cysts, intraepithelial neoplasias, anogenital, oro-laryngeal and -pharyngeal papillomas, keratoacanthomas and other types of hyperkeratoses. Their involvement in the etiology of some major human cancers is of particular interest: specific types (HPV 16, 18 and several others) have been identified as causative agents of at least 90% of cancers of the cervix and are also linked to more than 50% of other anogenital cancers. These HPV types are considered as 'high risk' infections. Their E6/E7 oncoproteins stimulate cell proliferation by activating cyclins E and A, and interfere with the functions of the cellular proteins RB and p53. The latter interaction appears to be responsible for their mutagenic and aneuploidizing activity as an underlying principle for the progression of these HPV-containing lesions and the role of high risk HPV types as solitary carcinogens. In non-transformed human keratinocytes transcription and function of viral oncoproteins is controlled by intercellular and intracellular signalling cascades, their interruption emerges as a precondition for immortalization and malignant growth. Recently, novel and known HPV types have also been identified in a high percentage of non-melanoma skin cancers (basal and squamous cell carcinomas). Similar to observations in patients with a rare hereditary condition, epidermodysplasia verruciformis, characterized by an extensive verrucosis and development of skin cancer, basal and squamous cell carcinomas develop preferentially in light-exposed sites. This could suggest an interaction between a physical carcinogen (UV-part of the sunlight) and a 'low risk' (non-mutagenic) papillomavirus infection. Reports on the presence of HPV infections in cancers of the oral cavity, the larynx, and the esophagus further emphasize the importance of this virus group as proven and suspected human carcinogens.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.

Simultaneous polymerase chain reaction detection and restriction typing for the diagnosis of human genital papillomavirus infection

A polymerase chain reaction method has been developed which allows the simultaneous detection of the majority of clinically relevant HPV types. Degenerate HPV-specific primers direct the one-step amplification of a DNA region spanning E1 and E7 genes. This enables an immediate distinction between the two groups of papillomaviruses, characterized by high or low oncogenic potential, simply from the size of amplified DNA. The PCR product can be subjected to a second round of amplification with internal primers, which are specific for 7 high-risk HPV types, HPV-16, -18, -31, -33, -35, -45 and -58. Precise identification of one-step or two-step amplified DNA is done by endonuclease digestion with one or two enzymes. The detection sensitivity, which has been assessed using cloned HPV genomes and HeLa and CaSki cell lines, varies from a few tens to a few hundreds of viral genome equivalents. The accuracy of the method has been confirmed by examining cervical scrapings of 44 patients.

Cellular control of human papillomavirus oncogene transcription

Specific types of human papillomaviruses (HPVs) are closely associated with the development of cervical cancer. The transforming ability of these high-risk HPV types depends on the expression of the viral E6 and E7 oncogenes. It is therefore of particular interest to elucidate the molecular mechanisms that result in the activation of E6/E7 expression during HPV-associated tumorigenesis. Recently, much progress has been made in characterizing the proteins involved in the regulation of HPV oncogene transcription. This review describes the functional significance of cellular factors involved in the transcriptional control of the E6/E7 promoter for the two most common HPV types associated with cervical cancer, HPV16 and HPV18. In addition, we discuss regulatory pathways that may contribute to the epithelial cells specificity of E6/E7 transcription. The definition of the factors that regulate HPV oncogene transcription could provide new insights into the molecular mechanisms activating viral oncogene expression during cervical carcinogenesis and forms an experimental basis for investigating the specific biochemical pathways that contribute to HPV-associated malignant cell transformation.

Multiple human papillomavirus type 16 glucocorticoid response elements functional for transformation, transient expression, and DNA-protein interactions

We have previously shown that human papillomavirus type 16 (HPV-16) can efficiently transform primary baby rat kidney cells in the presence of the steroid hormones progesterone and the glucocorticoid dexamethasone. To study this effect of hormone, different combinations of the previously identified glucocorticoid response element (GRE) at nucleotide 7640 of HPV-16 and the other two GREs that we have recently identified, at nucleotides 7385 and 7474, were mutated. The previously described GRE and the other two GREs were shown to be functional for the induction of transformation by dexamethasone. In addition, transient assays in cervical HeLa cells demonstrated the functional importance of the three individual GREs. Assays for in vitro interaction demonstrated the specific binding of a 97-kDa protein, the glucocorticoid receptor, to both recently identified HPV-16 GREs.