Silencer Activity of NFATc2 in the Interleukin-12 Receptor β2 Proximal Promoter in Human T Helper Cells

Interleukin 12 (IL-12) is a potent enhancer of interferon γ production by activated T cells. The high-affinity IL-12 receptor (IL-12R) is a heterodimer of a β1 and a β2 subunit. Expression of the signaling IL-12Rβ2 chain is usually low, as compared with the more abundant β1 chain, and may be rate-limiting for IL-12 sensitivity. Little is known about the mechanisms controlling IL-12R β 2 gene expression. Reporter gene assays in IL-12Rβ2-expressing Jurkat cells showed that truncation of the region from −151 to −61 abrogated promoter activity. The proximal promoter region does not contain a typical TATA box, suggesting a role for SP-1. Indeed, mutagenesis of the −63 SP-1 consensus site decreased transcription by 50%. Electrophoretic mobility shift experiments confirmed the binding of SP-1 and SP-3 at this site. In contrast, truncation of −252 to −192 increased promoter activity. Likewise, mutagenesis of the consensus nuclear factor of activated T cells site at −206 increased promoter activity by 70%, suggesting silencer 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-12Rβ2 mRNA expression. These first data on IL-12R β 2 gene regulation indicate a TATA-less promoter, depending on SP-1/SP-3 transcription factors, and a negative regulatory NFAT element at −206. This element may contribute to the overall low level of IL-12Rβ2 expression on Th cells.