Our immune system is an efficient protector against the daily onslaught of foreign pathogens, but the strength, targeting, and extent of immune responses must be tightly regulated. When these control mechanisms are breached, autoimmune diseases can occur. B cells of the adaptive immune system produce antibodies, which form a barrier against bacteria and viruses, and are key mediators of protective vaccinations. During their terminal differentiation, B cells are licensed for their tasks, beginning with germinal center reactions followed by the production of antibody-secreting plasma cells. B cell-derived autoantibodies and proinflammatory cytokines cause or significantly contribute to autoimmune diseases. The rising incidence of these diseases in recent years highlights the need to better understand disease pathomechanisms in order to tailor novel therapies.
Cellular fates and responses are largely controlled by transcription factors, which control the production of mRNAs that encode specific proteins. Major transcription factor networks regulating protective germinal center B cell responses were identified and characterized in the past. However, growing evidence suggests that global protein abundance is determined to a great degree at the translational level, emphasizing the importance of post-transcriptional gene regulation. There are over 1500 human RNA-binding proteins, with 690 of them binding mRNA through various RNA recognition motifs. Little is known about the role of post-transcriptional regulation by these proteins in terminal (protective or autoimmune) B cell differentiation. We hypothesized that RNA-binding proteins play critical roles in germinal center B cell and plasmacytic cell physiology. To identify and characterize these regulatory mechanisms, we combined the analysis of sophisticated genetic mouse models with experiments using novel cell culture systems, as well as genetic, molecular biological, and biochemical approaches. A better understanding of the roles of RNA-binding proteins in both protective and autoimmune B cell responses could open up novel possibilities for therapeutic targets.
We described in detail how B cell-specific expression changes of TNFAIP3/A20 and c-Rel, whose proteins levels are regulated by post-transcriptional gene regulation, impact terminal B cell differentiation and autoimmunity. We employed interaction proteomics to identify novel proteins binding to the untranslated regions of mRNAs encoding for critical mediators of germinal center B cell and plasmacytic cell fates, including Bcl6 and c-Rel. The regulatory functions of these RNA-binding proteins were validated by CRISPR-mediated knockout in germinal center B cell-like cell lines. In addition, we conducted genetic screens to uncover RNA-binding proteins whose loss enhanced or decreased germinal center B cell generation in vivo. We then used cellular immunology and RNA biochemistry techniques to elucidate how individual RNA-binding proteins or protein families exert their post-transcriptional control. Through the integrated power of our multi-disciplinary approach ,we thus pinpointed functions of key RNA-binding proteins regulating the biology of germinal center B cell and plasmacytic cells. Through GCB-PRID we thus uncovered new insights into post-transcriptional regulation of adaptive immunity.
