Detection of alternative lengthening of telomeres mechanism on tumor sections

Cécile Boulanger,Etienne Marbaix,Maëlle De Ville De Goyet,Bénédicte Brichard,Eloïse Claude,An Van Damme,Guillaume De Lhoneux,Christophe E Pierreux,Anabelle Decottignies

doi:10.1186/s43556-021-00055-y

Cécile Boulanger, Etienne Marbaix + Show 7 more

Open Access

https://doi.org/10.1186/s43556-021-00055-y

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Abstract

The vast majority of adult cancer cells achieve cellular immortality by activating a telomere maintenance mechanism (TMM). While this is mostly achieved by the de-silencing of hTERT telomerase gene expression, an alternative homologous recombination-based and telomerase-independent mechanism, known as ALT (Alternative Lengthening of Telomeres), is frequently activated in a subset of tumors, including paediatric cancers. Being absent from normal cells, the ALT mechanism offers interesting perspectives for new targeted cancer therapies. To date, however, the development of better translationally applicable tools for ALT detection in tumor sections is still needed. Here, using a newly derived ALT-positive cancer cell mouse xenograft model, we extensively examined how the previously known ALT markers could be used as reliable tools for ALT diagnosis in tumor sections. We found that, together with the detection of ultra-bright telomeric signals (UBS), an ALT hallmark, native telomeric FISH, that detects single-stranded C-rich telomeric DNA, provides a very sensitive and robust tool for ALT diagnosis in tissues. We applied these assays to paediatric tumor samples and readily identified three ALT-positive tumors for which the TMM was confirmed by the gold-standard C-circle amplification assay. Although the latter offers a robust assay for ALT detection in the context of research laboratories, it is more difficult to set up in histopathological laboratories and could therefore be conveniently replaced by the combination of UBS detection and native telomeric FISH.

Highlights

The ability to maintain telomere length over successive cell divisions characterizes most cancer cells and confers the dangerous replicative immortality potential that underlies indefinite cancer cell proliferation and metastasis formation [1]
While tumor formation was not observed in nude mice injected with the SaOS-2/Alternative Lengthening of Telomeres (ALT)+ cell line [19], the same cells were able to form macroscopic tumors in NOD scid gamma (NSG) mice after a long incubation time of 3 months [20]
Cell lines as the study by Lauvrak et al [20] reported efficient tumor formation in NSG mice injected with other ALT+ osteosarcoma cell lines, including CAL-72, ZK-58, KPD or G-292, here too, conflicting results were observed as the ZK-58 and KPD cell lines failed to develop tumors in nude mice [19]

Summary

Introduction

The ability to maintain telomere length over successive cell divisions characterizes most cancer cells and confers the dangerous replicative immortality potential that underlies indefinite cancer cell proliferation and metastasis formation [1]. In this regard, the telomere maintenance mechanism (TMM) of cancer cells rapidly emerged as a promising therapeutic target for cancer treatment. No specific antiALT drug has been identified This results mainly from the fact that ALT relies on homologous recombination events between telomeric DNA sequences and seems to operate mostly through a bifurcated break-induced replication pathway [6] that, in its enzymatic requirements, does not differ from the DNA repair pathways that are used by the cells in response to DNA damage. If targeting homologous recombination does not offer specific therapeutic perspectives for A LT+ cancer treatment, the discovery that disrupting the interaction between TSPYL5 and USP7 seems to induce A LT+ cell death offers alternative perspectives [7, 8]

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