EBV and KSHV provide anti-apoptotic advantages to Primary Effusion Lymphoma (PEL)

This study investigated similarities between primary effusion lymphomas (PELs) and PEL-like cells (PEL-LCs). PEL-LCs represent an in vitro transformation of peripheral B cells by both KSHV and EBV, presenting an opportunity for a detailed mechanistic analysis of the viral and cellular genes that orchestrate the initial stages of the progression toward PEL. The study revealed a crucial dependency of both dually (EBV and KSHV) and KSHV-only infected PELs on the antiapoptotic MCL-1 protein for their survival, aligning with previously reported findings. Notably, inhibiting MCL-1 with a small molecule inhibitor led to cell death in PELs but not in PEL-LCs. Further scrutiny through mRNA and immunoblotting analyses uncovered that PEL- LCs transcribe MCL-1 mRNA without detectable translation into proteins, prompting an exploration into the identity of the antiapoptotic protein supporting the survival of PEL-LCs. The findings identified BCL2A1 as the antiapoptotic protein that is upregulated in PEL-LCs compared to PELs and underscore the potential significance of BCL2A1 in PEL pathogenesis, with PELs showing enhanced survival with BCL2A1 ectopic-expression following the inhibition of MCL-1. This study identifies BCL2A1 as a potential mediator of the resistance of PEL-LCs and implicates two EBV genes, EBNA3A and LMP1, in regulating BCL2A1 expression, providing a survival advantage to PEL-LCs. Experiments with CRISPRi-mediated knockdown of MCL-1 or BCL2A1, in PELs and PEL-LCs respectively, did not result in significant downregulation compared to the rhodopsin control, raising challenges in establishing a control for an unequivocal interpretation. The complex interplay between EBV genes and BCL2A1 regulation adds layers of complexity to the apoptotic regulatory network in PEL. This study sets the foundation for further investigations into the dual infection of KSHV and EBV in PEL, shedding light on the distinct contributions of each virus to tumor survival and proliferation.