HuR controls apoptosis and activation response without effects on cytokine 3' UTRs.

RNA binding proteins regulate gene expression through several post-transcriptional mechanisms. The broadly expressed HuR/ELAVL1 is important for proper function of multiple immune cell types, and has been proposed to regulate cytokine and other mRNA 3' UTRs upon activation. However, this mechanism has not been previously dissected in stable cellular settings. In this study, HuR demonstrated strong anti-apoptotic and activation roles in Jurkat T cells. Detailed transcriptomic analysis of HuR knockout cells revealed a substantial negative impact on the activation program, coordinately preventing the expression of immune response gene categories, including all cytokines. Knockout cells showed a significant defect in IL-2 production, which was rescued upon reintroduction of HuR. Interestingly, the mechanism of HuR regulation did not involve control of the cytokine 3' UTRs: HuR knockout did not affect the activity of 3' UTR reporters in 293 cells, and had no effect on IL-2 and TNF 3' UTRs in resting or activated Jurkats. Instead, impaired cytokine production corresponded with defective induction of the IL-2 promoter upon activation. Accordingly, upregulation of NFATC1 was also impaired, without 3' UTR effects. Together, these results indicate that HuR controls cytokine production through coordinated upstream pathways, and that additional mechanisms must be considered in investigating its function.