Pan-cancer characterization and clinical outcome of ecDNA-enhancer mediated transcriptional dysregulation
Extrachromosomal circular DNAs (ecDNAs) are extrachromosomal circular DNA elements harboring enhancers that can function as mobile transcriptional enhancers to promote oncogene amplification in diverse human cancers. However, little is known about the mechanism how ecDNA and relevant enhancers influence the transcription control in different cancers. Here, we performed a comprehensive pan-cancer analysis to explore the potential transcriptional regulatory network between ecDNA and enhancer, and the association with clinical outcomes in different human cancers. Firstly, we identified 18,385 enhancers on ecDNA in 1,921 samples of 20 TCGA tumors. By integrating corresponding RNA-seq data, we found that the expression levels of enhancer RNAs (eRNAs) were significantly different between ecDNA regions and corresponding linear chromosomes. This suggested that enhancers on ecDNA may employ eRNA to perform transcriptional regulation. Furthermore, we identified enhancer co-amplification with oncogenes and found that enhancers on ecDNA significantly affect the expression of co-amplified cancer genes and consequently influence the survival of cancer patients. In addition, we found that, compared to corresponding linear chromosomes, enhancers on ecDNA generally have lower levels of methylation, which may be mainly caused by the enhancer co-amplification with oncogenes. Genome-wide analysis of open chromatin regions revealed significantly higher levels of chromatin accessibility and certain chromosomal preferences in ecDNA regions comparing corresponding linear chromosomes. Moreover, we found that the downregulation of antigen presentation genes and the suppression of antigen presentation pathways may cause the tumor immune evasion mediated by ecDNA. Finally, we identified tumor-infiltrating activated mast cells in ecDNA-positive patients, which are associated with poorer prognosis. In summary, through pan-cancer analysis, we illustrate the characteristics and regulatory mechanisms of ecDNA and its enhancers in cancers, providing insights for future cancer treatment.