Importance of NFAT and NF-κB signaling in Diffuselarge B-cell lymphoma

Abstract

Diffuse large B-cell lymphomas (DLBCLs) represent the most frequent B-cell lymphoma and can be subdivided into two groups by their gene expression profile, the Activated B-cell-like (ABC) and the Germinal center B-cell-like (GCB) DLBCL subtype. Around 30% of all patients do not respond to standard immunotherapy or relapse, which highlights the need for further therapeutic options. Among the subtypes, ABC DLBCLs have a less favorable prognosis. ABC DLBCLs are characterized by chronic B-cell receptor signaling and concomitant NF-κB dependency. Since targeting NF-κB in patients is challenging due to severe side effects, we investigated other potential targets for ABC DLBCL treatment. We found elevated basal Ca2+ levels and NFAT activity in ABC and GCB DLBCLs. Surprisingly, chronic BCR signaling in ABC DLBCLs was not responsible for elevated Ca2+ levels and calcineurin activity, but for NFATc1 overexpression. By use of the clinically approved drugs Cyclosporin A and FK506 we could show that calcineurin inhibition impaired survival of ABC but not GCB DLBCLs. In ABC DLBCL, decreased NFAT activity after calcineurin inhibition correlated with reduced expression of relevant target genes, such as JUN, IL6 and IL10, which resulted in decreased c Jun levels and decreased cytokine mediated STAT3 activity. Furthermore, we identified dimethyl fumarate (DMF) as another therapeutic option for DLBCL treatment. In ABC DLBCLs, DMF induced cell death via inhibition of chronic NF-κB and STAT3 activity, which was mediated by succination of reactive cysteines of the respective upstream kinases IKKβ and JAK1. Intriguingly, not only ABC but also GCB DLBCLs exhibited cytotoxicity upon DMF treatment. We could show that the electrophilic drug DMF induced ferroptosis selectively in GCB DLBCLs by decreasing intracellular GSH levels. ABC DLBCL were more resistant to DMF induced ferroptosis, since chronic BCR signaling and the resulting NF-κB activity were responsible for increased antioxidant responses. Finally, we could demonstrate that DMF as well as calcineurin inhibitors synergized with Mcl-1 and Bcl-2 inhibitors in inducing cell death in ABC DLBCLs, whereas GCB DLBCLs showed increased sensitivity towards DMF and a inhibitor of ferroptosis suppressor protein 1. Collectively, we could show that the drugs DMF, Cylosporin A and FK506, all approved for treatment of autoimmune diseases, exhibited a broad anti-lymphoma effect, highlighting their potential for DLBCL treatment.