The RNA-Binding Protein HuR Posttranscriptionally Regulates IL-2 Homeostasis and CD4⁺ Th2 Differentiation

Posttranscriptional gene regulation by RNA-binding proteins, such as HuR (elavl1), fine-tune gene expression in T cells, leading to powerful effects on immune responses. HuR can stabilize target mRNAs and/or promote translation by interacting with their 39 untranslated region adenylate and uridylate–rich elements. It was previously demonstrated that HuR facilitates Th2 cytokine expression by mRNA stabilization. However, its effects upon IL-2 homeostasis and CD4⁺ Th2 differentiation are not as well understood. We found that optimal translation of Il2ra (CD25) required interaction of its mRNA with HuR. Conditional HuR knockout in CD4⁺ T cells resulted in loss of IL-2 homeostasis and defects in JAK–STAT signaling, Th2 differentiation, and cytokine production. HuR-knockout CD4⁺ T cells from OVA-immunized mice also failed to proliferate in response to Ag. These results demonstrate that HuR plays a pivotal role in maintaining normal IL-2 homeostasis and initiating CD4⁺ Th2 differentiation.