Overexpression of PAX5 in mouse B cell lymphoma cell lines increased tumor growth when these cells were transplanted into mice. Conversely, knocking down expression of PAX5 in these cell lines decreased tumor growth when the cells were transplanted into mice. Further analysis revealed that PAX5 promoted B cell lymphomagenesis by increasing the level of expression of molecules involved in B cell receptor signaling and decreasing the level of expression of molecules that inhibit B cell receptor signaling. Inhibitors of the BCR signaling pathway blocked tumor growth further highlighting the importance of BCR signaling in PAX5-driven growth of B cell lymphomas.-Journal of Clinical Investigation