SUMMARY Aneuploidy is a hallmark of cancer, although its effects on tumorigenesis are unclear. Here, we investigated the relationship between aneuploidy and cancer development using cells engineered to harbor single extra chromosomes. We found that nearly all trisomic cell lines grew poorly in vitro and as xenografts, relative to genetically matched euploid cells. Moreover, the activation of several oncogenic pathways failed to alleviate the fitness defect induced by aneuploidy. However, following prolonged growth, trisomic cells acquired additional chromosomal alterations that were largely absent from their euploid counterparts and that correlated with improved fitness. Thus, while single-chromosome gains can suppress transformation, the genome-destabilizing effects of aneuploidy confer an evolutionary flexibility that may contribute to the aggressive growth of advanced malignancies with complex karyotypes.

Aneuploidy, defined as whole-chromosome gain or loss, causes cellular stress but, paradoxically, is a frequent occurrence in cancers. Here, we investigate why ∼50% of Ewing sarcomas, driven by the EWS-FLI1 fusion oncogene, harbor chromosome 8 gains. Expression of the EWS-FLI1 fusion in primary cells causes replication stress that can result in cellular senescence. Using an evolution approach, we show that trisomy 8 mitigates EWS-FLI1-induced replication stress through gain of a copy of RAD21. Low-level ectopic expression of RAD21 is sufficient to dampen replication stress and improve proliferation in EWS-FLI1-expressing cells. Conversely, deleting one copy in trisomy 8 cells largely neutralizes the fitness benefit of chromosome 8 gain and reduces tumorgenicity of a Ewing sarcoma cancer cell line in soft agar assays. We propose that RAD21 promotes tumorigenesis through single gene copy gain. Such genes may explain some recurrent aneuploidies in cancer.

Aneuploidy, defined as whole chromosome gains and losses, is associated with poor patient prognosis in many cancer types. However, the condition causes cellular stress and cell cycle delays, foremost in G1 and S phase. Here, we investigate how aneuploidy causes both slow proliferation and poor disease outcome. We test the hypothesis that aneuploidy brings about resistance to chemotherapies because of a general feature of the aneuploid condition—G1 delays. We show that single chromosome gains lead to increased resistance to the frontline chemotherapeutics cisplatin and paclitaxel. Furthermore, G1 cell cycle delays are sufficient to increase chemotherapeutic resistance in euploid cells. Mechanistically, G1 delays increase drug resistance to cisplatin and paclitaxel by reducing their ability to damage DNA and microtubules, respectively. Finally, we show that our findings are clinically relevant. Aneuploidy correlates with slowed proliferation and drug resistance in the Cancer Cell Line Encyclopedia (CCLE) dataset. We conclude that a general and seemingly detrimental effect of aneuploidy, slowed proliferation, provides a selective benefit to cancer cells during chemotherapy treatment.

As with all facultative pathogens, Vibrio cholerae must optimize its cellular processes to adapt to different environments with varying carbon sources and to environmental stresses. More specifically, in order to metabolize mannitol, V. cholerae must regulate the synthesis of MtlA, a mannitol transporter protein produced exclusively in the presence of mannitol. We previously showed that a cis-acting small RNA (sRNA) expressed by V. cholerae, MtlS, appears to post-transcriptionally downregulate the expression of mtlA and is produced in the absence of mannitol. We hypothesized that since it is complementary to the 5′ untranslated region (UTR) of mtlA mRNA, MtlS may affect synthesis of MtlA by forming an mtlA-MtlS complex that blocks translation of the mRNA through occlusion of its ribosome binding site. To test this hypothesis, we used in vitro translation assays in order to examine the role MtlS plays in mtlA regulation and found that MtlS is sufficient to suppress translation of transcripts harboring the 5′ UTR of mtlA. However, in a cellular context, the 5′ UTR of mtlA is not sufficient for targeted repression by endogenous MtlS; additional segments from the coding region of mtlA play a role in the ability of the sRNA to regulate translation of mtlA mRNA. Additionally, proximity of transcription sites between the sRNA and mRNA significantly affects the efficacy of MtlS.

Many tumor types harbor specific chromosome gains or losses. In Ewing sarcoma (ES) chromosome 8 gain is extremely common, indicating that this trisomy drives tumorigenesis. However, in primary cells, whole chromosome gains and losses are universally detrimental. We hypothesize that gain of chromosome 8 suppresses cellular stresses associated with oncogenic transformation in ES. In this study, we induced expression of EWS-FLI1 fusion oncogene, which drives ES, in various primary human mesenchymal progenitor and fibroblast cells. We showed that expression of EWS-FLI1 results in a strong cell cycle-dependent replication stress in euploid mesenchymal progenitor cells and fibroblast cells. As a consequence, proliferation is impaired when EWS-FLI1 is expressed in these cells. However, primary fibroblast cells carrying an extra copy of chromosome 8 (trisomy 8) exhibit much less replication stress, and the impairment of proliferation was also not seen in these cells. The levels of replication-associated DNA damage are lower in the trisomy 8 cells than in the euploid cells in the presence of EWS-FLI1. Then, we applied weighted co-expression network analysis (WGCNA) to RNA sequencing data obtained from ES patient tumor tissues in combination of mouse synteny analysis. We identified multiple potential genes and regions on chromosome 8, which are beneficial to ES oncogenesis when gain of extra copies. Above all, we demonstrate that gain of chromosome 8 in Ewing sarcoma facilitates the primary mesenchymal-lineage cells to overcome certain oncogenic stresses and reduces DNA damage associated with tumorigenic processes, which is achieved by cooperative upregulation of multiple gene expression on chromosome 8. Citation Format: Xiaofeng A. Su, Duanduan Ma, James V. Parsons, John M. Replogle, James F. Amatruda, Charles A. Whittaker, Kimberly Stegmaier, Angelika Amon. Ewing sarcoma: A case study of clonal aneuploidy and DNA damage repair in pediatric cancer [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B52.