CPG-DNA-SPECIFIC ACTIVATION OF ANTIGEN-PRESENTING CELLS REQUIRES STRESS KINASE-ACTIVITY AND IS PRECEDED BY NONSPECIFIC ENDOCYTOSIS AND ENDOSOMAL MATURATION

Unmethylated CpG moths in bacterial DNA, plasmid DNA and synthetic oli godeoxynucleotides (CpG ODN) activate dendritic cells (DC) and macroph ages in a CD40-CD40 ligand-independent fashion. To understand the mole cular mechanisms involved we focused on the cellular uptake of CpG ODN , the need for endosomal maturation and the role of the stress kinase pathway. Here we demonstrate that CpG-DNA induces phosphorylation of J un N-terminal kinase kinase 1 (JNKK1/SEK/MKK4) and subsequent activati on of the stress kinases JNK1/2 and p38 in murine macrophages and dend ritic cells. This Leads to activation of the transcription factor acti vating protein-1 (AP-I) via phosphorylation of its constituents c-Jun and ATF2, Moreover, stress kinase activation is essential for CpG-DNA- induced cytokine release of tumor necrosis factor alpha (TNF alpha) an d interleukin-12 (IL-12), as inhibition of p38 results in severe impai rment of this biological response. We further demonstrate that cellula r uptake via endocytosis and subsequent endosomal maturation is essent ial for sig-nailing, since competition by non-CpG-DNA or compounds blo cking endosomal maturation such as chloroquine or bafilomycin A preven t all aspects of cellular activation, The data suggest that endosomal maturation is required for translation of intraendosomal CpG ODN seque nces into signalling via the stress kinase pathway, where p38 kinase a ctivation represents an essential step in CpG-ODN-triggered activation of antigen-presenting cells.