Cancer Letters

Cancer Letters

Volume 357, Issue 2, 28 February 2015, Pages 498-501
Cancer Letters

Original Articles
Activation of human telomerase reverse transcriptase through gene fusion in clear cell sarcoma of the kidney

https://doi.org/10.1016/j.canlet.2014.11.057Get rights and content

Highlights

  • The first report on RNA-sequencing data of clear cell sarcoma of the kidney (CCSK).

  • A novel fusion, IRX2-TERT, was identified that lead to increased TERT expression.

  • Telomerase reverse transcriptase can be activated via fusion transcripts.

  • A previously published YWHAE-NUTM2B/NUTM2E fusion was found in 2/22 CCSKs.

  • The majority of CCSKs appear to lack fusion transcripts.

Abstract

Clear cell sarcoma of the kidney (CCSK) is a rare tumor type affecting infants and young children. Most CCSKs display few genomic aberrations, and no general underlying mechanism for tumor initiation has yet been identified, although a YWHAE-NUTM2B/NUTM2E fusion gene has been observed in a minority of cases. We performed RNA-sequencing of 22 CCSKs to investigate the presence of additional fusion transcripts. The presence of the YWHAE-NUTM2B/NUTM2E fusion was confirmed in two cases. In addition, a novel IRX2-TERT fusion transcript was identified in one case. SNP-array analyses revealed the underlying event to be an interstitial deletion in the short arm of chromosome 5 (5p15.33). TERT was dramatically upregulated under the influence of the IRX2 promoter. In line with TERT expression being driven by active IRX2 regulatory elements, we found a high expression of IRX2 in CCSKs irrespective of fusion gene status. IRX2 was also expressed in human fetal kidney – the presumed tissue of origin for CCSK. We conclude that in addition to promoter mutations and epigenetic events, TERT can also be activated in tumors via formation of fusion transcripts.

Introduction

CCSK is a rare neoplasm, accounting for 2–5% of all pediatric renal tumors. The overall survival for patients with CCSK has historically been low, but has now improved by intensified chemotherapy treatment [1]. CCSK is often described as a puzzling tumor, since its histological appearance does not resemble that of the kidney and there is no specific positive biological diagnostic marker available [2]. Furthermore, most CCSKs lack large-scale chromosomal alterations, while a subset shows a translocation between chromosomes 10 and 17 [3], [4], [5], [6], [7], [8], resulting in a fusion transcript between YWHAE and NUTM2B/NUTM2E (also known as FAM22B/FAM22E) [9].

Maintenance of telomere length is essential for the immortalization of tumor cells, and reactivation of telomerase is found in approximately 90% of all cancers [10]. Telomerase reverse transcriptase (TERT), the gene coding for the catalytic subunit of telomerase, can be activated by promoter mutations in different neoplasms [11], [12], [13]. However, such mutations are not present in all investigated tumor types [13], indicating that TERT can be activated via other, unknown mechanisms. We here describe TERT overexpression resulting from gene fusion between TERT and the transcription factor IRX2 in a CCSK. The novel IRX2-TERT fusion was found during exploratory RNA sequencing of a CCSK cohort.

Section snippets

Tumor and kidney tissue

The study was reviewed and approved by the regional ethics committee (L119-03) and by the review boards of the participating institutes. Frozen CCSKs were obtained from the Children's Oncology Group (COG) of North America and from Skåne University Hospital, Lund, Sweden. CCSK diagnoses were corroborated by reference pathologists of COG for the American cases and the International Society of Pediatric Oncology for the two Swedish cases. Wilms tumors for comparative studies were obtained from

Results

A panel of 22 CCSK tumors was subjected to RNA sequencing to investigate the occurrence of fusion transcripts. A novel IRX2-TERT gene fusion was identified in a CCSK from a 4 year old boy (Fig. 1a). The finding was confirmed with RT-PCR followed by Sanger sequencing (Fig. 1c). The fusion occurred between amino acid 332 in exon 3 of IRX2 and amino acid 2 in exon 1 of TERT (IRX2 transcripts NM_001134222 and NM_033267; TERT transcripts NM_198253 and NM_001193376). As a result, this in-frame fusion

Discussion

The mechanism behind the reactivation of telomerase in tumor cells has for a long time been unknown, but the recent discovery of activating mutations in the TERT promoter has offered an explanation applicable to several tumor types [11], [12], [13]. In this study, we show that TERT also can be activated via gene fusion.

By RNA sequencing of 22 cases of the uncommon pediatric tumor CCSK, we found a novel in-frame fusion transcript between IRX2 and TERT in one of the tumors, resulting from a

Conflict of interest

None.

Acknowledgements

We are grateful to the COG Renal Tumor Study Group and the Tissue Bank for contributing with CCSK samples and Dr Martin Johansson at the Center for Molecular Pathology, Lund University, SUS Malmö, Sweden, for providing kidney tissue. We would also like to thank the Swegene Centre for Integrative Biology at Lund University (SCIBLU).

This work was supported by the Swedish Childhood Cancer Foundation (PROJ 2013-0011), the Swedish Cancer Society (CAN 2012/318), the Swedish Research Council (2013-2543

References (21)

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