OTUB1 controls marginal zone B-cell development by stabilizing RelA in a CD40-dependent manner

Ubiquitin-dependent regulation of NF-κB signaling is essential for B-cell homeostasis and fate decisions, yet the contribution of specific deubiquitinating enzymes remains incompletely defined. OTUB1, a lysine-48–specific deubiquitinase, has been broadly implicated in immune regulation, including control of NF-κB signaling and prevention of immune hyperactivation. Previous studies have demonstrated that B cell-specific deletion of OTUB1 leads to B cell hyperplasia, increased antibody production, and lupus-like autoimmunity, highlighting its importance in maintaining B cell tolerance and immune homeostasis. Using B cell-specific OTUB1-deficient mice, we show that loss of OTUB1 leads to a marked expansion of marginal zone (MZ) B cells and their precursor populations in the spleen, accompanied by an activated phenotype and enhanced proliferative responses, particularly upon CD40 stimulation. OTUB1 deficiency results in altered CD40-induced NF-κB signaling, characterized by enhanced IκB degradation and increased nuclear accumulation of p50-containing NF-κB complexes, despite reduced RelA stability. Mechanistically, we show that OTUB1 interacts with RelA, restricting its lysine-48–linked ubiquitination and proteasomal degradation, thereby stabilizing this key transcription factor. Collectively, these findings identify RelA as a novel OTUB1 target and uncover an additional layer of ubiquitin-dependent control of NF-κB signaling that governs splenic B-cell homeostasis and marginal zone B-cell development.