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Roquin and Regnase-1 proteins bind and post-transcriptionally regulate proinflammatory target messenger RNAs to maintain immune homeostasis. Either the sanroque mutation in Roquin-1 or loss of Regnase-1 cause systemic lupus erythematosus-like phenotypes. Analyzing mice with T cells that lack expression of Roquin-1, its paralog Roquin-2 and Regnase-1 proteins, we detect overlapping or unique phenotypes by comparing individual and combined inactivation. These comprised spontaneous activation, metabolic reprogramming and persistence of T cells leading to autoimmunity. Here, we define an interaction surface in Roquin-1 for binding to Regnase-1 that included the sanroque residue. Mutations in Roquin-1 impairing this interaction and cooperative regulation of targets induced T follicular helper cells, germinal center B cells and autoantibody formation. These mutations also improved the functionality of tumor-specific T cells by promoting their accumulation in the tumor and reducing expression of exhaustion markers. Our data reveal the physical interaction of Roquin-1 with Regnase-1 as a hub to control self-reactivity and effector functions in immune cell therapies. Mutations in the RNA-binding proteins Roquin-1 or Regnase-1 cause systemic autoimmunity. Heissmeyer and colleagues show that Roquin-1 and Regnase-1 physically interact and thereby regulate CD4+ and CD8+ T cell metabolism and functionality.

Post-transcriptional gene regulation is complex, dynamic and ensures proper T cell function. The targeted transcripts can simultaneously respond to various factors as evident for Icos, an mRNA regulated by several RNA binding proteins (RBPs), including Roquin. However, fundamental information about the entire RBPome involved in post-transcriptional gene regulation in T cells is lacking. Here, we applied global RNA interactome capture (RNA-IC) and orthogonal organic phase separation (OOPS) to human and mouse primary T cells and identified the core T cell RBPome. This defined 798 mouse and 801 human proteins as RBPs, unexpectedly containing signaling proteins like Stat1, Stat4 and Vav1. Based on the vicinity to Roquin-1 in proximity labeling experiments, we selected ∼50 RBPs for testing coregulation of Roquin targets. Induced expression of these candidate RBPs in wildtype and Roquin-deficient T cells unraveled several Roquin-independent contributions, but also revealed Celf1 as a new Roquin-1-dependent and target-specific coregulator of Icos.One sentence statementWe provide an atlas of RNA-binding proteins in human and mouse T helper cells as a resource for studying higher order post-transcriptional gene regulation.