Role of the heat shock protein 90 in immune response stimulation by bacterial DNA and synthetic oligonucleotides

To elucidate the mechanisms of immunostimulation by bacterial DNA and synth etic oligonucleotides, the effects of heat shock protein 90 (Hsp90) inhibit ors on the activation of murine spleen cells and macrophages by these molec ules were investigated. Murine spleen cells and J774 and RAW264.7 macrophag es responded to a CpG-containing oligodeoxynucleotide (CpG ODN) and Escheri chia coli DNA by increased production of interleukin 6 (IL-6), IL-12, tumor necrosis factor alpha, and nitric oxide (NO). Pretreatment with any of the three Hsp90 inhibitors geldanamycin, radicicol, and herbimycin A resulted in a dose-dependent suppression of cytokine production from the spleen cell s and macrophages and of NO from macrophages stimulated with CpG ODN or E. coli DNA. These Hsp90 inhibitors, however, had no effect on Staphylococcus aureus Cowan strain 1-induced IL-12 production from either the murine splee n cells or macrophages. CpG ODN and E. coli DNA induced increased intracell ular levels of phosphorylated extracellular signal-regulated kinases (ERK1 and -2), which are members of the mitogen-activated protein (MAP) kinase fa mily, while geldanamycin and radicicol blocked the phosphorylation of ERK1 and -2 in J774 and RAW264.7 cells. These data indicate that DNA-induced act ivation of murine spleen cells and macrophages is mediated by Hsp90 and tha t Hsp90 inhibitor suppression of DNA-induced macrophage activation is assoc iated with disruption of the MAP kinase signaling pathway. Our findings sug gest that Hsp90 inhibitors may provide a useful means of elucidating the me chanisms of immunostimulation by bacterial DNA and CpG ODN as well as a str ategy for preventing adverse effects of bacterial DNA as well as lipopolysa ccharide.