Cd28 Regulates T Cell Metabolic Reprogramming Through Ars2-Dependent Effects On Alternative Splicing

Abstract An adaptive immune response requires activation of naïve T cells via T cell receptor (TCR) ligation and engagement of costimulatory molecules such as CD28, which enables cell growth, rapid proliferation, and effector differentiation. To accomplish such bioenergetically demanding processes, T cells must dynamically regulate their metabolism upon activation. After initial TCR triggering of aerobic glycolysis, CD28 co-stimulation maintains uptake and catabolism of glucose required for CD8+ T cells to attain full effector status. Despite evidence that CD28 signaling through the PI3-kinase pathway induces glucose uptake via increased GLUT1 surface expression, knockin T cells expressing PI3-kinase signaling-deficient CD28 are functional in vivo and displayed only transient defects in glycolysis. In contrast, knockin T cells expressing Grb2/Vav signaling-deficient CD28 lacked in vivo function and displayed sustained defects in glycolysis. Here we identify a novel link between CD28-Grb2/Vav signaling and T cell glycolytic reprogramming through the RNA binding protein ARS2, a protein central to co-transcriptional processing of nascent RNA polymerase II transcripts. Data show that ARS2 is a critical downstream mediator of CD28-Grb2/Vav signaling that supports alternative splicing (AS) of the rate-limiting glycolytic enzyme pyruvate kinase M from the M1 to M2 isoform. Mechanistically, ARS2 binds known Pkm splicing factors and promotes their interaction with Pkm mRNA. Consistent with this, ARS2 knockout T cells displayed reduced Pkm2 AS, defective glycolytic reprogramming and lacked the ability to control in vivo tumor growth, suggesting a novel mechanism by which co-stimulation drives T cell metabolic reprogramming.