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Serine-threonine kinase, ROCK2, regulates germinal center B cell positioning and cholesterol biosynthesis.

Germinal center (GC) responses require B cells to respond to a dynamic set of intercellular and microenvironmental signals that instruct B cell positioning, differentiation, and metabolic reprogramming. ROCK2, a serine-threonine kinase that can be therapeutically targeted by ROCK inhibitors or statins, is a key downstream effector of RHOA-GTPases. While RHOA-mediated pathways are emerging as critical regulators of GC responses, the role of ROCK2 in B cells is unknown. Here, we find that ROCK2 was activated in response to key T cell signals like CD40 and IL21 and that it regulated GC formation and maintenance. RNA-seq analyses revealed that ROCK2 controlled a unique transcriptional program in GC B cells that promoted optimal GC polarization and cholesterol biosynthesis. ROCK2 regulated this program by restraining AKT activation and subsequently enhancing FOXO1 activity. ATAC-seq and biochemical analyses revealed that the effects of ROCK2 on cholesterol biosynthesis were instead mediated via a novel mechanism. ROCK2 directly phosphorylated IRF8, a crucial mediator of GC responses, and promoted its interaction with SREBP2 at key regulatory regions controlling the expression of cholesterol biosynthetic enzymes, resulting in optimal recruitment of SREBP2 at these sites. These findings thus uncover ROCK2 as a multifaceted and therapeutically targetable regulator of GC responses.