Essentiality of CREBBP in EP300 truncated B-cell lymphoma revealed by genome-wide CRISPR-Cas9 screen

Histone acetyltransferases (HATs), including CREBBP and EP300, are frequently mutated in B-cell malignancies and usually play a tumor-suppressive role. In this study, we performed whole genome and transcriptome sequencing and a genome-wide CRISPR-Cas9 knockout screen to study a germinal center B-cell like diffuse large B-cell lymphoma (DLBCL) cell line (RC-K8). Using a summarizing method that is optimized to address the complexity introduced by the time-course design, we identified a distinct pattern of genetic essentialities in RC-K8, including a dependency on CREBBP and MDM2, shown already at early time points and a gradually increased dependency on oxidative phosphorylation related genes. The dependency on CREBBP is associated with the corresponding genetic alterations identified in this cell line, i.e. a balanced translocation involves EP300, which resulted in a truncated form of protein that lacks the critical bromodomain and HAT domain. We further evaluated the previously published CRISPR-Cas9 screens and identified a genetic essentiality of CREBBP or EP300 gene in a small set of cancer cell lines, including several DLBCL cell lines that are highly sensitive for EP300 knockout and with CREBBP mutations or copy number loss. The dependency of the remaining HAT function in CREBBP and/or EP300-deficient genotype was validated by testing the HAT-domain inhibitor A-485. Our study suggests that integration of the unbiased, time-course-based functional screen results with the genomic and transcriptomic data can identify druggable vulnerability in individual or subgroups of cell lines/patients, which may help to develop more effective therapeutic strategies for cancers that are genetically highly heterogeneous, like DLBCL.