Telomerase activity in the differentiation of benign and malignant adrenal tumors

Telomerase and the endocrine system

Telomeres are nucleoprotein complexes located at the ends of chromosomes that have a critical role in the maintenance of chromosomal integrity. This involvement is based on complex secondary and tertiary structures that rely on DNA-DNA, DNA-protein and protein-protein interactions. De novo synthesis and maintenance of telomere repeats is controlled by telomerase, a specialized complex that consists of a telomerase RNA component and a protein component--telomerase reverse transcriptase. When telomerase is silent (its default state in differentiated somatic cells), chromosomes shorten with every cell division, thus limiting the lifespan of the cells (the process of senescence) and preventing unlimited cell proliferation, which might eventually lead to the development of cancer. During this process, occasionally, a cell can activate telomerase, which stabilizes short telomeres and enables immortalization-a process essential for malignant transformation. Thus, although telomere erosion is a barrier to malignant progression, paradoxically, in certain circumstances it might also trigger tumorigenesis. A number of studies have demonstrated unequivocally that reactivation of telomerase in the presence of short telomeres is one of the most common features of human cancers, including those of the endocrine system.

Clinical utility of telomerase for the diagnosis of malignant well-differentiated endocrine tumours

OBJECTIVE

The distinction between benign and malignant well-differentiated endocrine tumours is hard to achieve. The aim of the present study was to determine whether detection of telomerase or quantification of human telomerase reverse transcriptase protein subunit (hTERT) differ between benign and malignant endocrine tumours.

PATIENTS AND METHODS

This retrospective study investigated 31 well-differentiated primary endocrine tumours. Based on clinical and histopathological criteria, tumours were categorized with the most recent WHO classification as 'benign' (n = 14), 'uncertain' (n = 5) or 'malignant' (n = 12) with (n = 7) or without (n = 5) metastasis after a mean follow-up of 40.4 +/- 25.8 months (4-122 months). All these tumours were assayed for telomerase activity and hTERT mRNA expression [real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR)].

RESULTS

Telomerase activity was detected in 7 malignant and metastatic tumours, in 1 malignant tumour without metastases, in 1 uncertain tumour and in 1 benign tumour. hTERT mRNA levels were significantly higher in malignant endocrine tumours with or without metastases (P = 0.001) when compared to benign tumours. The negative predictive value of hTERT mRNA quantification for the diagnosis of malignancy was 88.9%, whereas the positive predictive value was 68.7%.

CONCLUSION

The presence of telomerase activity within the primary endocrine tumour might indicate a malignant tumour and might suggest the need for an attentive search for concomitant metastases. Quantification of hTERT mRNA could be used in clinical practice to exclude malignancy in most endocrine tumours.

Bisphosphonates decrease telomerase activity and hTERT expression in MCF-7 breast cancer cells

Bisphosphonates are important in the management of tumours with secondary bone involvement. Recent findings have suggested that these drugs also have an effect on primary tumour burden. Telomerase is a cellular ribonucleoprotein reverse transcriptase responsible for elongation of the telomere. Telomerase expression is increased in many cancers. We studied the direct effects of clodronate, alendronate, and pamidronate (from 10(-6) to 10(-4) M) on MCF-7 human breast cancer cell line. In particular, we investigated their effect on viability, proliferation, apoptosis, human telomerase reverse transcriptase expression (h-TERT) by RT-PCR and telomerase activity. Alendronate and pamidronate showed an inhibition of viability (-63 and -35%, respectively; p < 0.0001) and proliferation of cancer cells, while no effect was observed with clodronate. Amino-bisphosphonates induced a significant increase of apoptosis in MCF-7. In addition, they showed a significant decrease in telomerase expression and activity with respect to control and to clodronate.

Telomerase is not required for experimental tumorigenesis of human and bovine adrenocortical cells

Telomerase has often been thought to be essential for tumorigenesis of human cells. Adrenocortical cancers, like other cancers, typically have telomerase activity. We reinvestigated the requirement for telomerase in the conversion of normal human and bovine adrenocortical cells to cancer cells. When primary adrenocortical cells were transduced with retroviruses encoding SV40 large T antigen and Ha-RasG12V and immediately transplanted into immunodeficient mice they produced invasive and metastatic tumors. Cells had negligible telomerase activity before transplantation and after recovery from tumors. However, these tumors were not immortal and cells entered crisis, limiting further growth of the tumor as well as invasion and metastasis. Infection of these tumor cells with a retrovirus encoding hTERT restored growth in culture and restored the malignant properties of the cells in immunodeficient animals. These experiments differ from previous studies in which telomerase was found to be essential for tumorigenicity: 1) we used tissue reconstruction techniques for introduction of cells into host animals and 2) we infected primary cells with retroviruses and immediately transplanted them without drug selection.

Apoptosis regulating genes, bcl-2 and bax, and human telomerase reverse transcriptase messenger RNA expression in adrenal tumors: possible diagnostic and prognostic importance

BACKGROUND

Apoptosis-suppressing gene, bcl-2, and apoptosis-inducing gene, bax, are expressed in various tumors. Human telomerase reverse transcriptase (hTERT) expression is increased in many cancers. The purpose of this investigation was to determine whether bcl-2 or bax gene expression differs between benign and malignant adrenal tumors, and whether hTERT gene expression correlates with the prognosis of patients with adrenal cancer.

METHODS

Expression of bcl-2 and bax from 52 adrenal surgical specimens was analyzed by reverse transcription-polymerase chain reaction. Expression of hTERT was analyzed by real-time quantitative reverse transcription-polymerase chain reaction, and expressed using the delta-delta threshold cycle method.

RESULTS

All normal adrenal tissues (n = 7) and benign adrenal tumors (n = 41) expressed bcl-2 and bax, whereas all adrenocortical cancers (n = 4) expressed bcl-2 but not bax. Expression of hTERT was increased in adrenocortical cancers compared with that in normal tissues (P <.05), cortical adenomas (n = 17) (P <.05), cortical hyperplasias (n = 4) (P <.05), and pheochromocytomas (n = 20) (P <.05). The one patient with an adrenocortical cancer without increased hTERT expression is alive with distant metastasis 5 years after adrenalectomy. The other 3 patients with adrenocortical cancer died 5 to 24 months after adrenalectomy.

CONCLUSIONS

Expression of bax gene appears to distinguish adrenal cancer from benign adrenal tumors. Gene expression of hTERT should be investigated as a prognostic marker in adrenal cortical cancers.

Histologically benign but telomerase positive adrenal pheochromocytoma

Adrenalectomy was performed on a 37-year-old woman with right adrenal pheochromocytoma. Although the histological diagnosis was benign, telomerase repeat amplification protocol (TRAP) demonstrated positive telomerase activity. Thirty-five months after adrenalectomy, a recurrent tumor was found. Forty-seven months after adrenalectomy, bone metastases also appeared. Malignant pheochromocytoma was clinically diagnosed. Our experience suggests that telomerase-positive tumor cells are highly likely to repeat cell proliferation when they are left in the patient's body, and lead to recurrence. Therefore, telomerase-positive tumors should be clinically treated as malignant even if they have been histologically diagnosed as benign.

The molecular pathogenesis of hereditary and sporadic adrenocortical and adrenomedullary tumors

Modern imaging modalities lead to frequent detection of adrenal masses, most of them incidental findings. Although the majority of adrenocortical and adrenomedullary tumors are benign, there are no reliable clinical and laboratory markers to distinguish most of them from malignant neoplasms. The molecular mechanisms underlying the pathogenesis of these tumors have recently begun to be unraveled. A fruitful avenue for the elucidation of tumorigenesis has been the study of adrenal tumors that are manifestations of hereditary or postzygotic genetic syndromes, because one knows the "first hit", i.e. the primary gene defect. In contrast, in sporadic adrenal tumors the first hit, possibly a somatic mutation of a tumor-related gene, is unknown, and therefore the sequence of genetic alterations is difficult to establish. In this article we review in addition to our own work the literature on molecular aspects of adrenocortical and adrenomedullary tumorigenesis.

Telomerase in endocrine and endocrine-dependent tumors

Telomerase, the ribonucleoprotein enzyme that elongates chromosomal ends, or telomeres, is repressed in most normal somatic cells but reactivated in transformed cells to compensate for the progressive erosion of the telomeres during cell divisions. In accordance with this hypothesis, the presence of telomerase activity has been reported in more than 90% of human cancers, whereas most normal tissues or benign tumors contain low or undetectable telomerase activity. Reactivation of telomerase has also been widely reported in endocrine neoplasms and in hormone-related cancers. In the present study, we review the most recent publications on telomerase in these types of tumors. The hormonal regulation of telomerase activity and the possible strategies for cancer therapy based on the inhibition of telomerase has also been discussed.

Adrenal cancer

Adrenal cancer is a rare neoplasm. Up to 1 in 1500 adrenal incidentalomas, however, may hide a carcinoma, which, if diagnosed late or left untreated, is associated with significant morbidity and mortality. Despite extensive investigation of the molecular mechanisms involved in adrenal carcinogenesis and significant improvements in diagnostic imaging, efforts to cure advanced adrenal cancer remain largely unsuccessful. This article reviews the recent advances in molecular understanding, clinical diagnosis, and treatment of adrenal cancer.