Kulozik, A. E. | Search bioRxiv

bioRxiv2021

Haplotype-aware single-cell multiomics uncovers functional effects of somatic structural variation

Somatic structural variants (SVs) are widespread in cancer genomes, however, their impact on tumorigenesis and intra-tumour heterogeneity is incompletely understood, since methods to functionally characterize the broad spectrum of SVs arising in cancerous single-cells are lacking. We present a computational method, scNOVA, that couples SV discovery with nucleosome occupancy analysis by haplotype-resolved single-cell sequencing, to systematically uncover SV effects on cis-regulatory elements and gene activity. Application to leukemias and cell lines uncovered SV outcomes at several loci, including dysregulated cancer-related pathways and mono-allelic oncogene expression near SV breakpoints. At the intra-patient level, we identified different yet overlapping subclonal SVs that converge on aberrant Wnt signaling. We also deconvoluted the effects of catastrophic chromosomal rearrangements resulting in oncogenic transcription factor dysregulation. scNOVA directly links SVs to their functional consequences, opening the door for single-cell multiomics of SVs in heterogeneous cell populations.

genomics↗

bioRxiv2020

Pharmacological inhibition of nonsense-mediated RNA decay augments HLA class I-mediated presentation of neoepitopes in MSI CRC

Microsatellite-unstable (MSI) colorectal cancer is characterized by the accumulation of somatic insertion/deletion (InDel) mutations potentially generating tumor-specific, frameshifted protein sequences. Such mutations typically generate premature translation termination codons targeting the affected mRNAs to degradation by nonsense-mediated RNA decay (NMD), limiting the synthesis and HLA class I-mediated presentation of tumor-specific InDel neoepitopes. We reasoned that the NMD inhibitor 5-azacytidine (5AZA) could serve to increase the expression of NMD-sensitive neoepitopes and analyzed the immunopeptidome of MSI HCT-116 cells using a proteogenomic approach. After immunoprecipitation of HLA:peptide complexes, we identified more than 10,000 HLA class I-presented peptides by LC-MS/MS including five InDel neoepitopes. The InDel neoepitopes were verified on the genomic, transcriptomic, and peptidomic level. Treatment with 5AZA increased the expression of the corresponding frameshift- and premature termination codon-bearing mRNAs and enhanced the presentation of peptides originating from known NMD targets and one of the identified InDel neoepitopes. By analyzing an array of MSI colorectal cancer cell lines and patient samples, we found the underlying frameshift mutation to be highly recurrent and immunization with the corresponding neoepitope induced strong CD8+ T cell responses in an HLA-A*02:01 transgenic mouse model. Our data directly show that peptides originating from frameshifted open reading frames due to InDel mutations in mismatch repair-deficient cells are presented on the cell surface via HLA class I. Moreover, we demonstrate the utility of NMD inhibitor-enhanced HLA class I-mediated presentation of InDel neoepitopes as well as their immunogenicity, uncovering the clinical potential of NMD inhibition in anti-cancer immunotherapy strategies. One Sentence SummaryImmunopeptidomics identified increased HLA class I-mediated presentation of immunogenic, frameshift-derived neoepitopes following NMD inhibition.

cancer biology↗