Telomerase, Cervical Cancer, and Human Papillomavirus

Human telomerase reverse transcriptase regulates vascular endothelial growth factor expression via human papillomavirus oncogene E7 in HPV-18-positive cervical cancer cells

Human papillomavirus (HPV) infection induces chronic and precancerous lesions and results in invasive cervical cancer. Human telomerase as well as inflammatory and angiogenic factors such as telomerase reverse transcriptase (hTERT) or vascular endothelial growth factor (VEGF) could play a role in regulating HPV-induced cervical cancer. This study investigated underlying molecular events in HPV-induced HPV-positive cervical cancer through hTERT and VEGF in vitro. Expressions of hTERT, a rate-limiting subunit of telomerase, and VEGF mRNA and proteins were, respectively, assessed by qRT-PCR, ELISA, and TRAP-ELISA in HPV-positive tissue samples and cervical cancer cell lines. To assess hTERT and VEGF secretion, hTERT overexpression and knockdown were conducted in HPV-18-positive Hela cells by hTERT cDNA and shRNA transfection, respectively. Then, the effect of HPV E6 and E7 on VEGF expressions was assessed in HPV-negative cervical cancer cells. Data have shown that VEGF expression levels are associated with hTERT expressions and telomerase activity in HPV-positive cervical cancer tissues and cells. Knockdown of hTERT expression down-regulated VEGF expressions, whereas overexpression of hTERT up-regulated VEGF expressions in HPV-18-positive Hela cells. Furthermore, HPV E7 oncoprotein was necessary for hTERT to up-regulate VEGF expressions in HPV-negative cervical cancer cells. Data from this current study indicate that HPV oncoproteins up-regulated hTERT and telomerase activity and in turn promoted VEGF expressions, which could be a key mechanism for HPV-induced cervical cancer development and progression.

Benzo[a]pyrene decreases global and gene specific DNA methylation during zebrafish development

DNA methylation is important for gene regulation and is vulnerable to early-life exposure to environmental contaminants. We found that direct waterborne benzo[a]pyrene (BaP) exposure at 24μg/L from 2.5 to 96hpf to zebrafish embryos significantly decreased global cytosine methylation by 44.8% and promoter methylation in vasa by 17%. Consequently, vasa expression was significantly increased by 33%. In contrast, BaP exposure at environmentally relevant concentrations did not change CpG island methylation or gene expression in cancer genes such as ras-association domain family member 1 (rassf1), telomerase reverse transcriptase (tert), c-jun, and c-myca. Similarly, BaP did not change gene expression of DNA methyltransferase 1 (dnmt1) and glycine N-methyltransferase (gnmt). While total DNMT activity was not affected, GNMT enzyme activity was moderately increased. In summary, BaP is an epigenetic modifier for global and gene specific DNA methylation status in zebrafish larvae.

Telomerase Activity as a Tumor Marker in Indian Women with Cervical Intraepithelial Neoplasia and Cervical Cancer

BACKGROUND AND OBJECTIVES

Cervical cancer is the most common cancer in Indian women and is a leading cause of death in women worldwide. Cervical cancer develops from pre-neoplastic cervical intraepithelial neoplasia (CIN). This study was conducted to evaluate telomerase activity as a tumor marker for the detection of cancer in patients with CIN and cervical cancer. The results were compared with human papillomavirus (HPV) status, clinical staging, and histopathologic studies.

METHODS

Telomerase activity was detected using the PCR-based telomeric repeat amplification protocol (TRAP) assay in cervical tissues collected by routine punch biopsy from the uterine cervix of patients with suspected cervical cancer. High-risk (HR) HPV-16 and -18 status was determined in all the study groups, including controls. A total of 125 patients (including 50 patients with CIN and 75 patients with cervical cancer [including nine patients with adeno-squamous disease]) and 22 control subjects were studied. The sensitivity and specificity for detecting CIN and cervical cancer were calculated.

RESULTS

Patients with grade I, II, and III CIN showed 17%, 33%, and 57% positivity for telomerase, respectively. In patients with cervical cancer, those at early clinical stages (Ia-IIb) showed 68% positivity and those at later clinical stages showed 92% positivity for telomerase activity. In the present study, telomerase positivity correlated significantly with the detection of HR HPV-16 and -18 (p < 0.001). As a diagnostic test, none of the described analyses combined a sensitivity of > or =90% with a specificity of > or =90%, except in patients with advanced cancer when telomerase activity was used as a diagnostic test.

CONCLUSION

Our findings suggest that telomerase activation is a relatively early event in cervical carcinogenesis and correlates with the grade of cervical lesion, HR-HPV status (16 and 18 subtypes), and clinical staging. Hence, these associations suggest it as a possible target for detection of cervical cancer.

Amplification of the human telomerase gene in liquid-based preparations is associated with cervical dysplasia and carcinoma

The aim of this study was to analyze the amplification of the human telomerase gene (TERC) in cervical specimens by fluorescence in situ hybridization (FISH), and FISH findings were compared with cytologic and histologic diagnoses. Slides prepared from 123 liquid-based preparations from cervical specimens with cytologic diagnoses of negative for squamous intraepithelial lesion or malignancy (n=20), atypical squamous cells of undetermined significance (n=22), low-grade squamous intraepithelial lesion (n=55), high-grade squamous intraepithelial lesion (n=21), or invasive cervical carcinomas (n=5) were analyzed for the amplification of TERC using a 2-color FISH probe. The results of the cytologic analysis and those of concurrent or subsequent biopsies were compared with the FISH findings. Results showed that amplification of TERC was significantly associated with both cytologic and histologic diagnoses (P<0.05). Patients with high-grade squamous intraepithelial lesion or squamous cell carcinoma cytology diagnoses had significantly higher percentages of cells with the amplification of TERC than did patients with low-grade squamous intraepithelial lesion, ASC-US, and negative for squamous intraepithelial lesion or malignancy (P<0.005). FISH can be performed on cervical liquid-based preparations to detect the amplification of TERC. This test may be an adjunct to cytology screening, early detection of cervix neoplasm, and may determine the progressive potential of individual lesions, especially in high-risk patients.

Genomic integration of oncogenic HPV and gain of the human telomerase geneTERC at 3q26 are strongly associated events in the progression of uterine cervical dysplasia to invasive cancer

Recently proposed events associated with the progression of cervical intraepithelial neoplasia (CIN) 2/3 to cervical carcinoma include integration of human papillomavirus (HPV) into the host genome, genomic instability, and an increase in chromosome 3q copy number. In particular, the gene coding for the RNA component of telomerase (TERC) at 3q26 has been implicated as a possible candidate gene. Since it is not known to date how these events are temporally related during cervical carcinogenesis, the aim of the present study was to assess the correlation between TERC gene copy number and the physical status of HPV during progression in cervical neoplasia. Solitary precursor lesions of the uterine cervix (CIN 2/3, n = 17), lesions associated with a micro-invasive carcinoma (CIN 3&mCA, n = 13), and advanced invasive carcinomas (invCA, n = 7) were analysed by fluorescence in situ hybridization (FISH) to determine the physical status of the virus and TERC gene copy number. The TERC gene was increasingly gained with progression of CIN 2/3 (3 of 17) through CIN 3&mCA (7 of 13) to invCA (5 of 7). In the lesions exhibiting gain of TERC, the virus was predominantly integrated. This was seen in eight of ten diploid lesions, indicating that these events can occur prior to aneuploidization and are strongly associated with the progression of CIN 3 to mCA and invCA (p < 0.001). With progression to carcinoma, a number of these lesions show polyploidization, resulting in aneuploidy and high TERC gene copy numbers. In conclusion, genomic integration of oncogenic HPV and gain of the human telomerase gene TERC appear to be important associated genetic events in the progression of uterine cervical dysplasia to invasive cancer.

Telomerase Activity as a Potential Diagnostic Marker for Triage of Abnormal Pap Smears

OBJECTIVES

To determine whether there is an association between high levels of telomerase and premalignant cervical disease and to provide a preliminary analysis of telomerase activity as a potential triage strategy.

MATERIALS AND METHODS

Premenopausal women were invited to participate in the study during routine gynecologic visits as well as visits where colposcopy was performed. Samples were taken from the cervix using a broom device and placed in cold phosphate-buffered saline. A total of 92 samples were evaluated. Cells were counted and lysed, and a semiquantitative measure of telomerase activity was determined using a commercially available telomerase enzyme-linked immunosorbent assay kit. The presence of human papillomavirus (HPV) types 16 and 18 was assessed by polymerase chain reaction analysis. One-way analysis of variance was used to test for the association of telomerase activity with cytology, HPV type 16 or 18 status, and colposcopy and/or biopsy findings.

RESULTS

When telomerase levels were analyzed according to Pap smear results, there were no differences among four groups of cytology findings (normal, atypical squamous cells of undetermined significance, low-grade squamous intraepithelial lesion, and high-grade squamous intraepithelial lesion). When colposcopy and/or biopsy results were considered, significantly higher levels of telomerase were detected in cervical intraepithelial neoplasia (CIN) 2,3 samples than in normal Pap smear samples and CIN 1 samples (p = .035). There was no significant difference in telomerase levels between samples that tested positive for HPV type 16 or 18 and those that did not (p = .111).

CONCLUSIONS

Telomerase levels were significantly higher in cytologic samples from women with biopsy-proven CIN 2,3 than in samples from women with normal cytology results or CIN 1. These results warrant larger studies to determine whether telomerase activity may be a useful triage tool for abnormal cytologic findings.

Expression of human telomerase reverse transcriptase in gastrointestinal stromal tumors occurs preferentially in malignant neoplasms

Telomerase is expressed in many human cancers and cell lines and is thought to contribute to their immortality. To date, little is known about the expression of telomerase in nonepithelial tumors. The objective of this study was to evaluate the expression of human telomerase reverse transcriptase (hTERT) in gastrointestinal stromal tumors (GISTs). Twenty-three GISTs (9 low malignant potential, 10 primary malignant, and 4 intra-abdominal recurrences) were evaluated for hTERT expression by using immunohistochemistry on tissue microarray. Tissue blocks were retrieved, and hematoxylin and eosin stains were performed to evaluate the histological tumor type. All cases were strongly positive for KIT (CD117). Immunohistochemistry for hTERT was performed. Eight of 9 cases of the low malignant potential group were negative for hTERT immunoexpression, whereas all malignant GISTs showed positive staining that varied from weak to strong immunoreactivity. Six of 10 cases of the primary malignant GISTs were strongly positive for hTERT. The remaining cases (4/10) showed weak staining. All recurrent GISTs (4/4) showed strong positive immunostaining for hTERT. One malignant case was weakly positive for hTERT, but its recurrence was strongly positive. These results suggest that hTERT expression occurs preferentially in malignant tumors and that telomerase activity may occur during the progression of GISTs. Immunohistochemical staining for hTERT may be a useful marker for the prognostication of GISTs.

Translational approaches to improving cervical screening

Screening programmes for cervical cancer using the current test--the Pap smear--have markedly reduced the incidence of the disease. However, an individual Pap test is of limited sensitivity and is difficult and expensive to perform. Increased understanding of the molecular pathogenesis of cervical cancer indicates that new approaches to screening might offer increased accuracy, affordability and the potential for automation. Such approaches exemplify how improved understanding of the biology of neoplasia might be translated into clinical benefit.

Progressive transformation of immortalized esophageal epithelial cells

AIM: To investigate the progressive transformation of immortal cells of human fetal esophageal epithelium induced by human papillomavirus, and to examine biological criteria of sequential passage of cells, including cellular phenotype, proliferative rate, telomerase, chromosome and tumorigenicity.

METHODS: The SHEE cell series consisted of immortalized embryonic esophageal epithelium which was in malignant transformation when cultivated over sixty passages without co-carcinogens. Cells of the 10th, 31st, 60th and 85th passages were present in progressive development after being transfected with HPV. Cells were cultivated in a culture flask and 24-hole cultural plates. Progressive changes of morphology, cell growth, contact-inhibition, and anchorage-dependent growth characteristics were examined by phase contrast microscopy. The cell proliferation rate was assayed by flow cytometry. The modal number of chromosomes was analyzed. HPV18E₆E₇ was detected by Western blot methods and activities of telomerase were analyzed by TRAP. Tumorigenicity of cells was detected with soft agar plates cultivated and with tumor formation in SCID mice.

RESULTS: In morphological examination the 10th passage cells were in good differentiation, the 60th and 85th passages cells were in relatively poor differentiation, and the 31st passage cells had two distinct differentiations. The characteristics of the 85th and 60th passage cells were weakened at contact-inhibition and anchorage-dependent growth. Karyotypes of four stages of cells belonged to hyperdiploid or hypotriploid, and bimodal distribution of chromosomes appeared in the 31st and 60th passage cells. All of these characteristics combined with a increasing trend. The activities of telomerase were expressed in the latter three passages. Four fourths of SCID mice in the 85th passage cells and one fourth of SCID mice in the 60th passage cells developed tumors, but the cells in the 10th and 31st passage displayed no tumor formation.

CONCLUSION: In continual cultivation of fetal esophageal epithelial cells with transduction of HPV18E₆E₇, cells from the 10th to the 85th passage were changed gradually from preimmortal, immortal, precancerous to malignantly transformed stages. All of these changes were in a dynamic progressive process. The establishment of a continuous line of esophageal epithelium may provide a in vitro model of carcinogenesis induced by HPV.

Telomerase activation in cervical keratinocytes containing stably replicating human papillomavirus type 16 episomes

Retroviral transduction and expression of the human papillomavirus type 16 (HPV-16) E6 gene has been shown to activate telomerase in human cervical and foreskin keratinocytes. There still remains some controversy, however, as to whether expression of E6 in the context of the whole HPV-16 genome can activate telomerase. In this study, we have generated human cervical keratinocyte clones that contain stably replicating HPV-16 episomes. Interestingly, the majority of the clones exhibited low or no telomerase activity at early passage and this was associated with low transcript levels of the reverse transcriptase component of telomerase, hTERT. The HPV-16-containing clones became immortal without a crisis and, at later passage, exhibited elevated levels of telomerase and higher levels of hTERT without any apparent increase in HPV-16 copy number, E6 transcript levels, or ability to degrade p53. These results indicate that HPV-16 by itself does not necessarily cause telomerase activation in cervical keratinocytes, but rather, supports a model in which HPV-16 facilitates telomerase activation in conjunction with other viral or cellular changes over time.

Telomere and telomerase in the initial stage of immortalization of esophageal epithelial cell

AIM: To search for the biomarker of cellular immortalization, the telomere length, telomerase activity and its subunits in cultured epithelial cells of human fetal esophagus in the process of immortalization.

METHODS: The transgenic cell line of human fetal esophageal epithelium (SHEE) was established with E₆E₇ genes of human papillomavirus (HPV) type 18 in our laboratory. Morphological phenotype of cultured SHEE cells from the 6th to 30th passages, was examined by phase contrast microscopy, the telomere length was assayed by Southern blot method, and the activity of telomerase was analyzed by telomeric repeat amplification protocol (TRAP). Expressions of subunits of telomerase, hTR and hTERT, were assessed by RT-PCR. DNA content in cell cycle was detected by flow cytometry. The cell apoptosis was examined by electron microscopy (EM) and TUNEL label.

RESULTS: SHEE cells from the 6th to 10th passages showed cellular proliferation with a good differentiation. From the 12th to the 16th passages, many senescent and apoptotic cells appeared, and the telomere length sharply shortened from 23 kb to 17 kb without expression of hTERT and telomerase activity. At the 20th passage, SHEE cells overcame the senescence and apoptosis and restored their proliferative activity with expression of telomerase and hTERT at low levels, but the telomere length shortened continuously to the lowest of 3 kb. After the 30th passage cells proliferation was restored by increment of cells at S and G₂M phase in the cell cycle and telomerase activity expressed at high levels and with maintenance of telomere length.

CONCLUSION: At the early stage of SHEE cells, telomeres are shortened without expression of telomerase and hTERT causing cellular senescence and cell death. From the 20th to the 30th passages, the activation of telomerase and maintenance of telomere length show a progressive process for immortalization of esophageal epithelial cells. The expression of telomerase may constitute a biomarker for detection of immortalization of cells.