High mobility group box-1 protein acts as a coactivator of nuclear factor of activated T cells-2 in promoting interleukin-2 transcription

High mobility group box-1 protein, an abundant and conserved constituent of vertebrate nuclei, has recently been reported to be an endogenous immune signal [Rovere-Querini P, Capobianco A, Scaffidi P, Valentinis B, Catalanotti F, Giazzon M, et al. HMGB1 is an endogenous immune adjuvant released by necrotic cells. EMBO Reports 2004;5:825–30]. High mobility group box-1 protein can trigger the release of interleukin-2 and interleukin-12 from lymphocytes. However, at present the underlying mechanism remains unknown. It has been clarified that nuclear factor of activated T cells-2 transduces most immunological signals in T cells and modulates the production of interleukin-2. So it is natural that we asked whether high mobility group box-1 protein could promote production of interleukin-2 in a nuclear factor of activated T cells-2-dependent way. Our experiments firstly showed that high mobility group box-1 protein could bind to nuclear factor of activated T cells-2 in vivo and in vitro. High mobility group box-1 protein cotransfection markedly upregulated the transcription activity of nuclear factor of activated T cells-2 in promoting interleukin-2 reporter gene transcription, which was demonstrated to be dose-dependent. Cotransfection of high mobility group box-1 protein and nuclear factor of activated T cells-2 induced an 18.4-time increase of interleukin-2 activity in 293T cells and a 117.7-time increase in Hela cells. Moreover, inhibition of either high mobility group box-1 protein or nuclear factor of activated T cells -2 expression by sRNAi led to significant decrease of transcription activity of interleukin-2 reporter gene, suggesting that high mobility group box-1 protein and nuclear factor of activated T cells-2 both take important roles in facilitating interleukin-2 transcription, and high mobility group box-1 protein could act as a coactivator for nuclear factor of activated T cells-2 in enhancing transcription of interleukin-2. This discovery has not been reported elsewhere, and helps to understand the newly highlighted immunological role of high mobility group box-1 protein.