Differential Regulation of TCR-Induced ZFP36 and ZFP36L1 Expression by Cyclosporin A in CD8⁺ T Cells

CD8⁺ T cells target infected or malignant cells via the production of pro-inflammatory cytokines and direct target cell killing. Members of the ZFP36-family of RNA-binding proteins, ZFP36 and ZFP36L1, regulate these functions in T cells via the regulation of mRNA stability and protein translation. We investigate the regulation of ZFP36 and ZFP36L1 expression using in vitro differentiated OT1 TCR transgenic memory-like T cells. We characterise the differential kinetics and sensitivity of ZFP36 and ZFP36L1 to antigen affinity and PMA versus ionomycin stimulation. By selectively inhibiting TCR-induced signalling pathways, we find that p38 MAPK, MEK1/2, and PKC contribute to inducing both ZFP36 and ZFP36L1 expression. By contrast, inhibition of calcineurin using cyclosporin A potently inhibits ZFP36L1 expression while increasing and prolonging ZFP36 expression. The Zfp36 promoter contains many binding sites for the transcription factors ELK-1/4 and few binding sites for NFAT, while the Zfp36l1 promoter contains many NFAT binding sites and few ELK1/4 binding sites. Our findings suggest that the regulation of divergent transcription factors enables calcineurin to act as a signalling node that mediates the differential regulation of ZFP36 and ZFP36L1 during T cell activation.