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Epstein-Barr virus (EBV) persistently infects over 95% of adults worldwide and is associated with a range of cancers, including lymphomas and epithelial malignancies. Despite advances in understanding EBV biology, targeted therapies for EBV-associated cancers remain limited. To identify novel dependencies in EBV-infected cancers, we performed genome-wide CRISPR-Cas9 loss-of-function screens in EBV+ lymphoblastoid versus Burkitt lymphoma cells, which differ by EBV latency programs. JunB emerged as a critical LCL-selective host dependency factor. LCL JunB knockout significantly decreased proliferation, with reduced G2/M progression, but without inducing apoptosis. JunB was more highly expressed in B cells with the EBV latency III than latency I program and correlated with LMPist1 levels in newly infected B cells. LMP1 stimulated JunB expression in a manner dependent on its cytoplasmic tail TES1/CTAR1 region and on canonical NF-κB. EBV-activated JunB played an obligatory role in repression of the G1/S phase inhibitor /p18 in LCLs but not Burkitt B cells. These findings establish an LMP1-JunB-p18 axis as essential for EBV- driven lymphoblastoid B cell proliferation, suggest JunB-mediated cross-talk between Epstein-Barr nuclear antigens and LMP1, and highlight JunB as a potential therapeutic target for EBV-associated lymphoproliferative disorders.