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 3′ untranslated regionadenylate and uridylate–rich elements. It was previously demonstrated that HuR facilitates Th2 cytokine expression by mRNA stabilization. However, its effects upon IL-2 homeostasisand 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 homeostasisand 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 homeostasisand initiating CD4 + Th2 differentiation.