Abstract 1743: Evaluating the effect of USP22 depletion on chromosome instability in colorectal cancer

Abstract

Abstract Chromosome instability (CIN) is an aberrant phenotype defined as an increase in the rate at which whole chromosomes or large chromosomal fragments are gained or lost, and is observed in virtually all cancer types. Although CIN is associated with aggressive tumors, multi-drug resistance and poor patient prognosis, the genetic defects underlying CIN remain poorly understood. Preliminary data from our laboratory suggest that diminished USP22 (Ubiquitin-Specific Peptidase 22) expression induces CIN. Importantly, USP22 deletions and reduced USP22 expression are frequently observed in multiple cancer types, including colorectal cancer, suggesting diminished USP22 expression/function may be a pathogenic event underlying oncogenesis. Therefore, the present study seeks to evaluate the impact diminished USP22 expression has on CIN by determining whether karyotypically stable colorectal cancer (HCT116) and immortalized fibroblast (hTERT) cell lines can be converted into karyotypically unstable lines following the reduction of USP22 expression. Diminished USP22 expression was achieved by siRNA-based silencing or CRISPR-Cas9-mediated gene knockout (KO) and quantitative image-based single-cell analyses were employed to monitor changes in surrogate markers for CIN, including nuclear areas and chromosome numbers. USP22 silencing induced significant changes in nuclear area as well as increased frequencies of chromosomes gains and losses, which suggest USP22 is a CIN gene. Next, to assess the long-term impact diminished USP22 expression has on CIN, two HCT116 USP22-KO clones were monitored for 10 weeks and revealed dynamic changes in nuclear areas and chromosome numbers over time relative to controls. Collectively, these data identify USP22 as a novel CIN gene and indicate that USP22 deletions in cancer may have long-term impact on CIN and may thereby promote oncogenesis. Further analysis is ongoing to investigate the mechanism through which USP22 depletion induces CIN, and in particular its effect on H2B monoubiquitination. Characterizing the effect diminished USP22 expression has on CIN is the first step towards the development of therapeutic strategies targeting USP22-deficient cancers. Citation Format: Lucile M. Jeusset, Kirk J. McManus. Evaluating the effect of USP22 depletion on chromosome instability in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1743.