Silencer activity of NFATc2 in the interleukin-12 receptor beta 2 proximalpromoter in human T helper cells

Interleukin 12 (IL-12) is a potent enhancer of interferon gamma production by activated T cells. The high-affinity IL-12 receptor (IL-12R) is a hetero dimer of a beta1 and a beta2 subunit. Expression of the signaling IL-12R be ta2 chain is usually low, as compared with the more abundant beta1 chain, a nd may be rate-limiting for IL-12 sensitivity. Little is known about the me chanisms controlling IL-12R beta2 gene expression. Reporter gene assays in IL-12R beta2-expressing Jurkat cells showed that truncation of the region f rom -151 to -61 abrogated promoter activity. The proximal promoter region d oes not contain a typical TATA box, suggesting a role for SP-1. Indeed, mut agenesis of the -63 SP-1 consensus site decreased transcription by 50%. Ele ctrophoretic mobility shift experiments confirmed the binding of SP-1 and S P-3 at this site. In contrast, truncation of -252 to -192 increased promote r activity. Likewise, mutagenesis of the consensus nuclear factor of activa ted T cells site at -206 increased promoter activity by 70%, suggesting sil encer activity of this element. Electrophoretic mobility shift experiments with primary Th (T helper) cells showed the formation of a specific, T-cell receptor-inducible complex at this site that is sensitive to cyclosporin A and supershifted with anti-NFATc2 in both Th1 and Th2 cells. Accordingly, cyclosporin A dose-dependently increased IL-12R beta2 mRNA expression. Thes e first data on IL-12R beta2 gene regulation indicate a TATA-less promoter, depending on SP-1/SP-3 transcription factors, and a negative regulatory NF AT element at -206. This element may contribute to the overall low level of IL-12R beta2 expression on Th cells.