Expression of the RNA component of telomerase in Wilms tumor and nephrogenic rest recapitulates renal embryogenesis

Telomerase reverse transcriptase catalytic subunit expression and proliferation index in Wilms tumor

Telomerase activity provides telomere maintenance in chromosomes. It prevents cells from entering senescence. Telomerase activity is one of the crucial steps in various cancers. Wilms tumor (nephroblastoma) is one of the most common solid tumors of childhood. Hitherto, telomerase reverse transcriptase (TERT) catalytic subunit expression in Wilms tumor has not been investigated widely. The aim of this study was to explore the expression level of human TERT in Wilms tumor and to correlate with some clinical prognosis factors such as tumor weight, stage, histology, and Ki67 expression. This study included 41 nephroblastoma cases of childhood. The telomerase catalytic subunit expression and proliferation index was determined using an immunohistochemical method on archival paraffin-embedded tissue sections. Statistical analysis was done on SPSS 9.05 by Mann-Whitney U test and Spearman's correlation analysis. TERT expression was negative in 11 cases (26.8%), weakly positive in 14 cases (34.1%), and strongly positive in 16 cases (39%). The proliferation index was found to be 20 to 90 (mean 58.9 ± 26.8). Using Spearman correlation analysis, both the TERT expression (p=0.032) and Ki67 index (p=0.048) were found to be correlated with survival rate. Similarly, both the telomerase expression (p=0.011) and the Ki67 index (0.040) were correlated with the weight and dimension of the tumor. But there was no relationship between telomerase expression and Ki67 index (p=0.429). The mean survival time for telomerase negative cases was 56.6 ± 27.3 months, while it was 34.67 ± 28.36 months for positive cases. The Mann-Whitney U test revealed that levels of telomerase (p=0.040) significantly affected the survival rate. In the present study, we showed that the presence of TERT expression correlated with both tumor size and survival time. These findings suggest that senescence may play an important role in WT evolution, and determination of telomere maintenance will be useful to predict survival and follow-up of patients with Wilms tumor.

Telomere biology of pediatric cancer

One of the hallmarks of cancer is limitless proliferative capacity, which is tightly associated with the ability to maintain telomeres. Over the last decade, the telomere biology of pediatric cancers has begun to be elucidated. Most pediatric leukemias and embryonal solid tumors activate the enzyme telomerase, a specialized reverse transcriptase that adds nucleotide repeats to telomeres. In general, high levels of tumor telomerase expression are associated with unfavorable outcome, although results vary according to tumor type. Some pediatric tumors, including osteosarcoma and glioblastoma multiforme, lack telomerase activity and maintain telomeres via a recombination-based mechanism called ALT (alternative lengthening of telomeres). Telomerase is a highly attractive therapeutic target for pediatric cancer because the enzyme plays a key role in conferring cellular immortality, is present in most tumors, and is relatively specific for cancer cells. Telomerase inhibitors have been evaluated in preclinical models of adult cancers, but few studies have been conducted on pediatric cancers. Further research is required to define how telomere biology can be used to clinical advantage in malignancies of childhood.

High Telomerase RNA Expression Level Is an Adverse Prognostic Factor for Favorable-Histology Wilms' Tumor

Purpose

A primary objective of the fifth National Wilms Tumor Study (NWTS-5) was to identify prognostic indicators for patients with favorable-histology Wilms' tumor. The prognostic significance of telomerase expression level in primary tumor samples was assessed.

Patients and Methods

A case-cohort study was conducted involving 291 NWTS-5 registrants. Telomerase activity was measured using the telomeric repeat amplification protocol (TRAP). Expression levels of TERT mRNA (encoding the telomerase catalytic component) and TERC/hTR (the telomerase RNA template) were measured using quantitative real-time polymerase chain reaction.

Results

After excluding samples because of lack of viable tumor, RNA degradation, or insufficient clinical information, 244 patients remained for the final analysis (96 with relapse and 148 without relapse). Univariate analysis revealed a positive correlation between relative risk (RR) of relapse and levels of TERT mRNA and TERC expression. For each doubling in TERT mRNA and TERC level, the RR increased by a factor of 1.16 (95% CI, 1.04 to 1.29; P = .01) and 1.35 (95% CI, 1.11 to 1.64; P = .003), respectively. The one third of patients whose tumors had the highest TERC expression level had an RR of 2.06 (95% CI, 1.14 to 3.70; P = .02) compared with patients with the lowest level. TERC expression level remained a significant prognostic indicator in a multivariate analysis adjusting for TERT mRNA, tumor stage, and patient age. TRAP level did not correlate with RR of relapse. Telomerase expression levels were not predictive of overall survival.

Conclusion

Telomerase RNA expression level may provide a clinically useful adjunct to the current risk classification schema for favorable-histology Wilms' tumor.

Clinicopathologic features of nephrogenic rests and nephroblastomatosis

Nephrogenic rests are the consequence of residual metanephric tissue in a fully developed kidney. They usually occur along the perimeter of a mature renal lobe (i.e., perilobar), within the lobe itself (i.e., intralobar), or both (i.e., combined). Nephrogenic rests can be grossly obvious or microscopically discrete. Nephroblastomatosis designates nephrogenic rests that are multifocal or diffuse, and implies more extensive disease. Universal (panlobar) nephroblastomatosis denotes complete replacement of the renal lobe by nephrogenic tissue. The fate of nephrogenic rests and nephroblastomatosis varies and includes obsolescence, sclerosis, dormancy, hyperplasia, or neoplasia. Evidence strongly suggests that neoplastic transformation of nephrogenic rests results in Wilms' tumor (nephroblastoma). Nephrogenic rests almost always occur in the setting of Wilms' tumor; perilobar rests show a strong association with synchronous bilateral Wilms' tumors, whereas intralobar rests are more strongly associated with metachronous tumors. Genetic studies have shown that nephrogenic rests often share many of the same chromosomal defects as Wilms' tumor, which provides further evidence that they are precursors to nephroblastoma. Thus, nephrogenic rests are recognized as clinically significant entities requiring adequate detection and close surveillance. Heightened awareness regarding the clinical relevance of nephrogenic rests and nephroblastomatosis (1) has led to improved detection of these precancerous lesions, (2) fostered more intensive investigation into their biologic behavior, and (3) initiated in-depth discussions about potentially new treatment regimens. The pathologists' ability to identify and detect nephrogenic rests has benefited from the more efficient Beckwith classification. Radiologists have deployed high-resolution radiologic/imaging modalities to improve detection of nephrogenic rests in situ. Clinicians and surgeons are more aware of the impact that nephrogenic rests have upon patient management. Despite this progress, more data is needed to further define these lesions.

PCR and in situ hybridization studies of telomerase subunits in human non-neoplastic livers

Telomerase, a ribonucleoprotein enzyme associated with cellular immortality, consists of human telomerase RNA component (hTERC), human telomerase protein 1 (hTEP1), and human telomerase reverse transcriptase (hTERT). In this study, the expression of these subunits was examined in non-neoplastic livers [13 cases of chronic viral hepatitis (CVH), 16 of primary biliary cirrhosis (PBC), two of primary sclerosing cholangitis, and six normal livers], using the reverse transcription-polymerase chain reaction (RT-PCR), nested PCR, and in situ hybridization (ISH). Six hepatocellular carcinoma (HCC) cases and one colonic cancer were used as positive controls. Telomeric repeat amplification protocol (TRAP) assay disclosed distinct telomerase activity in all positive controls and weak telomerase activity in non-neoplastic livers in 4 of 13 CVH cases and 5 of 16 PBC cases. By RT- and nested PCR, both hTERC and hTEP1 mRNA were detectable in all non-neoplastic liver tissues; ISH revealed hTERC and hTEP1 mRNA in the periportal and periseptal hepatocytes and inflammatory mononuclear cells in those cases examined. ISH revealed hTERT mRNA only in a few infiltrating mononuclear cells in 3 of 13 CVH and 2 of 16 PBC livers and these five cases were also positive by TRAP assay. In four of these five cases, hTERT mRNA was also detectable by nested PCR, suggesting that hTERT mRNA in the non-neoplastic liver is expressed by infiltrating mononuclear cells. Biliary epithelial cells were totally negative for these human telomerase subunits. Three subunits were constantly detected in all positive controls by ISH as well as by RT- and nested PCR. The finding that hTERC and hTEP1 mRNA, but not hTERT mRNA, were detectable in the non-neoplastic hepatocytes suggests that telomerase is present but not activated and that additional factor(s) are necessary for the expression of hTERT mRNA in the hepatocytes, along with immortalization and neoplastic transformation.