1. Large-scale copy number alterations are enriched for synthetic viability in BRCA1/BRCA2 tumors
- Author
-
Yingjie Zhu, Xin Pei, Ardijana Novaj, Jeremy Setton, Daniel Bronder, Fatemeh Derakhshan, Pier Selenica, Niamh McDermott, Mehmet Orman, Sarina Plum, Shyamal Subramanyan, Sara H. Braverman, Biko McMillan, Sonali Sinha, Jennifer Ma, Andrea Gazzo, Atif Khan, Samuel Bakhoum, Simon N. Powell, Jorge S. Reis-Filho, and Nadeem Riaz
- Subjects
BRCA1 ,BRCA2 ,Copy number alterations ,Gene expression ,Synthetic viability ,CRISPR-Cas9 knockout ,Medicine ,Genetics ,QH426-470 - Abstract
Abstract Background Pathogenic BRCA1 or BRCA2 germline mutations contribute to hereditary breast, ovarian, prostate, and pancreatic cancer. Paradoxically, bi-allelic inactivation of BRCA1 or BRCA2 (bBRCA1/2) is embryonically lethal and decreases cellular proliferation. The compensatory mechanisms that facilitate oncogenesis in bBRCA1/2 tumors remain unclear. Methods We identified recurrent genetic alterations enriched in human bBRCA1/2 tumors and experimentally validated if these improved proliferation in cellular models. We analyzed mutations and copy number alterations (CNAs) in bBRCA1/2 breast and ovarian cancer from the TCGA and ICGC. We used Fisher’s exact test to identify CNAs enriched in bBRCA1/2 tumors compared to control tumors that lacked evidence of homologous recombination deficiency. Genes located in CNA regions enriched in bBRCA1/2 tumors were further screened by gene expression and their effects on proliferation in genome-wide CRISPR/Cas9 screens. A set of candidate genes was functionally validated with in vitro clonogenic survival and functional assays to validate their influence on proliferation in the setting of bBRCA1/2 mutations. Results We found that bBRCA1/2 tumors harbor recurrent large-scale genomic deletions significantly more frequently than histologically matched controls (n = 238 cytobands in breast and ovarian cancers). Within the deleted regions, we identified 277 BRCA1-related genes and 218 BRCA2-related genes that had reduced expression and increased proliferation in bBRCA1/2 but not in wild-type cells in genome-wide CRISPR screens. In vitro validation of 20 candidate genes with clonogenic proliferation assays validated 9 genes, including RIC8A and ATMIN (ATM-Interacting protein). We identified loss of RIC8A, which occurs frequently in both bBRCA1/2 tumors and is synthetically viable with loss of both BRCA1 and BRCA2. Furthermore, we found that metastatic homologous recombination deficient cancers acquire loss-of-function mutations in RIC8A. Lastly, we identified that RIC8A does not rescue homologous recombination deficiency but may influence mitosis in bBRCA1/2 tumors, potentially leading to increased micronuclei formation. Conclusions This study provides a means to solve the tumor suppressor paradox by identifying synthetic viability interactions and causal driver genes affected by large-scale CNAs in human cancers.
- Published
- 2024
- Full Text
- View/download PDF