Telomerase activity and telomere length in human ovarian cancer and melanoma cell lines: correlation with sensitivity to DNA damaging agents

Potential impact of (rs 4645878) BAX promoter -248G>A and (rs 1042522) TP53 72Arg>pro polymorphisms on epithelial ovarian cancer patients

BACKGROUND

In India, Epithelial ovarian cancer has emerged as one of the most common malignancies affecting women. Tumor protein 53 (TP53) induces expression of the B cell lymphoma 2-associated X protein (BAX) gene by directly binding to the TP53-binding element in the BAX promoter. Therefore, we hypothesized that single-nucleotide polymorphism of BAX promoter -248G>A and TP53 72Arg>Pro gene may jointly contribute to ovarian cancer risk.

OBJECTIVES

This study aimed at exploring the association of BAX promoter -248G>A and TP53 72Arg>Pro gene polymorphism with risk of developing EOC and its clinicopathological features and to evaluate gene-gene interaction of these two polymorphisms with risk of developing EOC.

MATERIALS

The study was conducted on 70 Epithelial ovarian cancer patients and 70 healthy controls. Genotyping of p53 codon 72 and BAX promoter gene was examined by ASO-PCR and PICA-PCR, respectively. Odds ratios and 95 % confidence intervals were calculated.

RESULTS

We found an increased cancer risk associated with the BAX AA (ORs = 4.1, 95 %, CI = 1.23-13.97) genotype. An increased risk was also associated with the TP53 Pro/Pro (OR = 4.4, 95 % CI = 1.40-13.99) and Arg/Pro genotype (OR = 2.3, 95 % CI = 1.13-4.86). The gene-gene interaction of these polymorphisms increased EOC risk in a more than additive manner (ORs for the presence of both BAX AA and TP53 Arg/Pro genotypes = 8.7, 95 % CI = 1.66-45.48). BAX GG genotype was associated with adverse staging of cancer (P = 0.01).

CONCLUSIONS

The findings suggest that polymorphism of BAX and TP53 genes may be potential genetic modifiers for developing ovarian cancer.

Telomere maintenance mechanisms in malignant peripheral nerve sheath tumors: expression and prognostic relevance

This study investigated the prevalence and the prognostic relevance of the 2 known telomere maintenance mechanisms (TMMs), telomerase activity (TA) and alternative lengthening of telomeres (ALT), in malignant peripheral nerve sheath tumors (MPNST). In 57 specimens from 49 patients with MPNST (35 sporadic, 14 neurofibromatosis type 1-related), TA was determined using the telomeric repeat amplification protocol, and ALT was detected by assaying ALT-associated promyelocytic leukemia bodies (APB) and terminal restriction fragment (TRF) length distribution. TA or ALT (defined on the basis of APB) alone was found in 24.6% or 26.3% of the lesions, respectively, whereas 6 cases (10.5%) were TA+/ALT+. A concordance between APB and TRF results in defining the ALT status was observed in 44 of 57 cases (77.2%; P < .0001). TA was more frequently expressed in samples from patients with neurofibromatosis type 1 than in those with sporadic disease (60% vs 29.4%, P = 0.087). In the overall series, TA proved to be prognostic for 5-year disease-specific death (hazard ratio, 3.78; 95% confidence interval [CI], 1.60-8.95; P = .002), even when adjusted for the presence of neurofibromatosis type 1 (hazard ratio, 4.22; 95% CI, 1.804-9.874; P = .001) and margin status after surgery (hazard ratio, 5.78; 95% CI, 2.19-15.26; P < .001). Conversely, ALT did not significantly affect clinical outcome of MPNST using either APB expression (hazard ratio, 1.25; 95% CI 0.54-2.89; P = 0.605) or TRF distribution (hazard ratio, 0.57; 95% CI, 0.17-1.96; P = .375) as the detection approach. Our results indicate for the first time that both TMMs, TA and ALT, are present in MPNST and differentially affect patient prognosis.

Prognostic relevance of ALT-associated markers in liposarcoma: a comparative analysis

BACKGROUND

Most cancers maintain telomeres by activating telomerase but a significant minority, mainly of mesenchymal origin, utilize an alternative lengthening of telomeres (ALT) mechanism.

METHODS

In this study we comparatively analyzed the prognostic relevance of ALT in a monoinstitutional series of 85 liposarcoma patients as a function of the marker (ALT-associated promyelocytic leukemia bodies (APB) versus heterogeneous telomeres) used to classify the tumor.

RESULTS

Independently of the detection approach, ALT proved to be a prognostic discriminant of increased mortality, although the prognostic relevance of the two markers appeared at different follow-up intervals (at 10 years for APB and 15 years for telomeres).

CONCLUSIONS

Overall, we confirmed ALT as an indicator of poor clinical outcome in this disease and provide the first evidence that the sensitivity of the ALT predictive power depends, at least in part, on the method used.

Telomerase confers resistance to caspase-mediated apoptosis

There is growing evidence that accelerated telomeric attrition and/or aberrant telomerase activity contributes to pathogenesis in a number of diseases. Likewise, there is increasing interest to develop new therapies to restore or replace dysfunctional cells characterized by short telomeric length using telomerase-positive counterparts or stem cells. While telomerase adds telomeric repeats de novo contributing to enhanced proliferative capacity and lifespan, it may also increase cellular survival by conferring resistance to apoptosis. Consequently, we sought to determine the involvement of telomerase for reduced apoptosis using ovarian surface epithelial cells. We found that expression of hTERT, the catalytic component of telomerase, was sufficient and specific to reduce caspase-mediated cellular apoptosis. Further, hTERT expression reduced activation of caspases 3, 8, and 9, reduced expression of pro-apoptotic mitochondrial proteins t-BID, BAD, and BAX and increased expression of the anti-apoptotic mitochondrial protein, Bcl-2. The ability of telomerase to suppress caspase-mediated apoptosis was p-jnk dependent since abrogation of jnk expression with jip abolished resistance to apoptosis. Consequently, these findings indicate that telomerase may promote cellular survival in epithelial cells by suppressing jnk-dependent caspase-mediated apoptosis.

Photochemically enhanced delivery of a cell-penetrating peptide nucleic acid conjugate targeting human telomerase reverse transcriptase: effects on telomere status and proliferative potential of human prostate cancer cells

OBJECTIVES

Peptide nucleic acids (PNAs) are DNA mimics that have been demonstrated to be efficient antisense/antigene tools in cell-free systems. However, their potential as in vivo regulators of gene expression has been hampered by their poor uptake by living cells, and strategies need to be developed for their intracellular delivery. This study has aimed to demonstrate the possibility (i) of efficiently delivering a PNA, which targets mRNA of the catalytic component of human telomerase reverse transcriptase (hTERT), into DU145 prostate cancer cells through a combined approach based on conjugation of the PNA to Tat internalizing peptide (hTERT-PNA-Tat) and subsequent photochemical internalization, and (ii) to interfere with telomerase function.

MATERIALS AND METHODS

Treated cells were analysed for telomerase activity, hTERT expression, growth rate, ability to undergo apoptosis and telomere status.

RESULTS

After exposure to light, DU145 cells treated with hTERT-PNA-Tat and the photosensitiser TPPS2a showed dose-dependent inhibition of telomerase activity, which was accompanied by marked reduction of hTERT protein expression. A dose-dependent decline in DU145 cell population growth and induction of caspase-dependent apoptosis were also observed from 48 h after treatment. Such an antiproliferative effect was associated with the presence of telomeric dysfunction, as revealed by cytogenetic analysis, in the absence of telomere shrinkage, and with induction of DNA damage response as suggested by the increased expression of gamma-H2AX.

CONCLUSIONS

Our results (i) indicate photochemical internalization as an efficient approach for intracellular delivery of chimaeric PNAs, and (ii) corroborate earlier evidence suggesting pro-survival and anti-apoptotic roles of hTERT, which are independent of its ability to maintain telomere length.

Telomere maintenance mechanisms in liposarcomas: association with histologic subtypes and disease progression

Human cancer cells maintain telomeres by telomerase activity (TA) or by alternative lengthening of telomeres (ALT). We proposed to define the prevalence of the two telomere maintenance mechanisms (TMM), to assess their association with histology, and to compare their prognostic relevance in a series of 93 patients with liposarcoma. ALT was detected by assaying ALT-associated promyelocytic leukemia nuclear bodies and TA was assayed using the telomeric repeat amplification protocol. ALT or TA was found in 25.9% or 26.6% of 139 tested liposarcoma lesions, respectively. Three lesions were ALT+/TA+ whereas approximately 50% of lesions did not show any known TMM. TMM phenotype was consistent during disease progression. ALT was prevalent in dedifferentiated and in grade 3 liposarcomas whereas TA prevailed in most round-cell myxoid and in grade 2 liposarcomas. ALT and TA incidence was similar in primary and recurrent lesions whereas metastases were more frequently TA+ than ALT+ (59% versus 18%; P = 0.04). TMM presence negatively affected patient prognosis (P = 0.001): increased mortality was associated with positivity for TA (P = 0.038) or ALT (P < 0.0001) compared with TMM absence. ALT proved to be a stronger prognostic discriminant of increased mortality than TA even when adjusted for tumor location, grade, and histology (hazard ratio for cause-specific death, 3.58 versus 1.15). Our results indicate that ALT can support fully malignant liposarcomas and is associated with unfavorable disease outcome.

Human bone marrow derived mesenchymal stem cells do not undergo transformation after long-term in vitro culture and do not exhibit telomere maintenance mechanisms

Significant improvement in the understanding of mesenchymal stem cell (MSC) biology has opened the way to their clinical use. However, concerns regarding the possibility that MSCs undergo malignant transformation have been raised. We investigated the susceptibility to transformation of human bone marrow (BM)-derived MSCs at different in vitro culture time points. MSCs were isolated from BM of 10 healthy donors and propagated in vitro until reaching either senescence or passage (P) 25. MSCs in the senescence phase were closely monitored for 8 to 12 weeks before interrupting the cultures. The genetic characterization of MSCs was investigated through array-comparative genomic hybridization (array-CGH), conventional karyotyping, and subtelomeric fluorescent in situ hybridization analysis both before and after prolonged culture. MSCs were tested for the expression of telomerase activity, human telomerase reverse transcriptase (hTERT) transcripts, and alternative lengthening of telomere (ALT) mechanism at different passages. A huge variability in terms of proliferative capacity and MSCs life span was noted between donors. In eight of 10 donors, MSCs displayed a progressive decrease in proliferative capacity until reaching senescence. In the remaining two MSC samples, the cultures were interrupted at P25 to pursue data analysis. Array-CGH and cytogenetic analyses showed that MSCs expanded in vitro did not show chromosomal abnormalities. Telomerase activity and hTERT transcripts were not expressed in any of the examined cultures and telomeres shortened during the culture period. ALT was not evidenced in the MSCs tested. BM-derived MSCs can be safely expanded in vitro and are not susceptible to malignant transformation, thus rendering these cells suitable for cell therapy approaches.

Isolation and in vitro propagation of tumorigenic breast cancer cells with stem/progenitor cell properties

Breast cancer-initiating cells have been recently identified in breast carcinoma as CD44+/CD24(-/low) cells, which exclusively retain tumorigenic activity and display stem cell-like properties. However, at present, direct evidence that breast cancer-initiating cells can be propagated in vitro is still lacking. We report here the isolation and in vitro propagation of breast cancer-initiating cells from three breast cancer lesions and from an established breast carcinoma cell line. Our breast carcinoma-derived cultures encompassed undifferentiated cells capable of self-renewal, extensive proliferation as clonal nonadherent spherical clusters, and differentiation along different mammary epithelial lineages (ductal and myoepithelial). Interestingly, cultured cells were CD44+/CD24- and Cx43-, overexpressed neoangiogenic and cytoprotective factors, expressed the putative stem cell marker Oct-4, and gave rise to new tumors when as few as 10(3) cells were injected into the mammary fat pad of SCID mice. Long-term cultures of breast tumorigenic cells with stem/progenitor cell properties represent a suitable in vitro model to study breast cancer-initiating cells and to develop therapeutic strategies aimed at eradicating the tumorigenic subpopulation within breast cancer.

Lack of telomerase activity in lung carcinoids is dependent on human telomerase reverse transcriptase transcription and alternative splicing and is associated with long telomeres

PURPOSE

Preliminary evidence indicates that telomerase activity is significantly less expressed in typical carcinoids than in large cell neuroendocrine carcinomas or in small cell lung cancers. Knowledge of the mechanisms by which telomerase is differentially regulated in neuroendocrine lung tumors is important for a better understanding of the pathogenesis of these malignancies.

EXPERIMENTAL DESIGN

We investigated telomerase activity in 86 neuroendocrine lung tumors and correlated the enzyme activity with the expression of the enzyme subunits [human RNA component (hTR), human telomerase reverse transcriptase (hTERT), and alternatively spliced hTERT variants], with the telomere-associated protein human protection of telomere-1, and with the telomere length pattern.

RESULTS

A significantly (P = 0.0001) lower frequency of telomerase-positive cases was found in typical carcinoids (14%) than in large cell neuroendocrine carcinomas (87%) and small cell lung cancers (92%). hTR was constitutively expressed in all carcinoids. Telomerase-negative carcinoids were characterized by the absence of any hTERT transcript, only displayed the beta(-) alternatively spliced variant, or concomitantly expressed the alpha(+)beta(+) full-length message with different combinations of alternatively spliced variants. However, in these tumors, a more abundant level of alternatively spliced transcripts than that of the alpha(+)beta(+) full-length transcript was generally found. No significant difference was observed in human protection of telomere-1 expression between telomerase-negative and telomerase-positive carcinoids. Telomeres were significantly (P < 0.05) longer in telomerase-negative carcinoids than in telomerase-positive carcinoids (median value, 9.15 versus 4.47 kb). However, alternative lengthening of telomeres, as shown by associated promyelocytic leukemia bodies, was not observed in these tumors.

CONCLUSIONS

Our results indicate that telomerase is repressed in most lung carcinoids and that hTERT transcription and alternative splicing play a role in such a negative regulation. Moreover, the absence of any telomerase maintenance mechanism may contribute to the favorable prognosis of this malignancy.

Human telomerase reverse transcriptase mRNA expression assessed by real-time reverse transcription polymerase chain reaction predicts chemosensitivity in patients with ovarian carcinoma

PURPOSE

To evaluate in vivo whether the expression of the human telomerase reverse transcriptase (hTERT) gene, the catalytic subunit of the telomerase complex, is predictive of response to chemotherapy in ovarian cancer patients.

PATIENTS AND METHODS

Fifty-nine advanced-stage ovarian cancer patients who were treated with platinum-based chemotherapy were studied. hTERT levels were evaluated by real-time reverse transcriptase polymerase chain reaction (RT-PCR) on tumor specimens obtained before the treatment. Variables were analyzed by the chi(2) and Fisher's exact tests. Logistic regression analysis was also performed to account for the effects of all the covariates investigated (residual disease, stage, histotype, and grade).

RESULTS

Twenty-eight (47%) of the 59 tumors showed low hTERT levels, whereas 31 (53%) tumors displayed high hTERT levels. Seventy-five percent of complete responders showed high levels of hTERT expression, whereas 66% of partial responders or nonresponders exhibited low hTERT levels (P =.002). Only residual disease and hTERT expression were independent predictors of response (odds ratios, 13.455 and 7.586, respectively). The combination of these two parameters provides powerful predictive information: 18 of the 20 patients with residual disease more than 2 cm and low hTERT levels were partial responders or nonresponders, whereas 11 of the 12 patients with residual disease less than 2 cm and high hTERT levels showed a complete response (chi(2) = 21,416; P <.00001).

CONCLUSION

Our data indicate that hTERT expression, measured by real-time RT-PCR, is a possible independent marker of response to platinum-based therapy in advanced stage ovarian cancer patients. Prospective validation of this marker will be required to further define its predictive value.