Karyotypic Flexibility of the Complex Cancer Genome and the Role of Polyploidization in Maintenance of Structural Integrity of Cancer Chromosomes.

Christina Raftopoulou,Stylianos E Antonarakis,Vasilis Gorgoulis,Eleni Dragona,Fani-Marlen Roumelioti,Frédérique Sloan-Béna,Stefanie Gimelli,Sarantis Gagos

doi:10.3390/cancers12030591

Abstract

Ongoing chromosomal instability in neoplasia (CIN) generates intratumor genomic heterogeneity and limits the efficiency of oncotherapeutics. Neoplastic human cells utilizing the alternative lengthening of telomeres (ALT)-pathway, display extensive structural and numerical CIN. To unravel patterns of genome evolution driven by oncogene-replication stress, telomere dysfunction, or genotoxic therapeutic interventions, we examined by comparative genomic hybridization five karyotypically-diverse outcomes of the ALT osteosarcoma cell line U2-OS. These results demonstrate a high tendency of the complex cancer genome to perpetuate specific genomic imbalances despite the karyotypic evolution, indicating an ongoing process of genome dosage maintenance. Molecular karyotyping in four ALT human cell lines showed that mitotic cells with low levels of random structural CIN display frequent evidence of whole genome doubling (WGD), suggesting that WGD may protect clonal chromosome aberrations from hypermutation. We tested this longstanding hypothesis in ALT cells exposed to gamma irradiation or to inducible DNA replication stress under overexpression of p21. Single-cell cytogenomic analyses revealed that although polyploidization promotes genomic heterogeneity, it also protects the complex cancer genome and hence confers genotoxic therapy resistance by generating identical extra copies of driver chromosomal aberrations, which can be spared in the process of tumor evolution if they undergo unstable or unfit rearrangements.

Highlights

From the pivotal work of Peter Nowell, tumor cell populations are known to undergo continuous genome evolution following Darwinian processes of selection and adaptation [1]
To address the flexibility of the complex alternative lengthening of telomeres (ALT) genome, and to unravel patterns of cancer genome evolution driven by oncogene induced replication stress, telomere dysfunction, or genotoxic damage, we examined five isogenic cell lines of the human ALT osteosarcoma cell line U2-OS, representing different karyotypic outcomes, using M-FISH/ (Multi-Color Fluorescent In Situ Hybridization) molecular karyotyping, combined with inverted DAPI banding and aCGH
At least four events of the U2-OS chromosomal evolution coincided with karyotypes bearing multiple duplicated copies of clonal recombinant chromosomes, suggesting that polyploidization and polyploidy reduction are frequent events during ALT tumor clonal evolution in culture

Summary

Introduction

From the pivotal work of Peter Nowell, tumor cell populations are known to undergo continuous genome evolution following Darwinian processes of selection and adaptation [1]. These biological processes are driven by genomic instability that accompanies neoplastic cell growth from the initial steps of carcinogenesis up to the last stages of metastases [2]. Continuous CIN generates widespread intratumor genomic heterogeneity, allowing selective processes that drive cancer cell populations into malignancy, limiting in parallel the efficiency of oncotherapeutic schemes [11,12]. A better understanding of CIN is critical for deciphering fundamental aspects of carcinogenesis and for achieving efficient therapies against advanced malignancies [3,8,13]

Results

Discussion

Conclusion