YOPJ OF YERSINIA-PSEUDOTUBERCULOSIS IS REQUIRED FOR THE INHIBITION OFMACROPHAGE TNF-ALPHA PRODUCTION AND DOWN-REGULATION OF THE MAP KINASES P38 AND JNK

Exposure of macrophages to lipopolysaccharide (LPS) leads to productio n of the pro-inflammatory cytokine, tumour necrosis factor alpha (TNF- alpha). Previous studies have suggested that pathogenic Yersinia spp. inhibit LPS-mediated production of TNF-alpha in macrophages, and that one of the Yop proteins secreted by the plasmid-encoded type III pathw ay is required for this activity. We found that TNF-alpha production w as inhibited when J774A.1 murine macrophages were infected with wild-t ype Y. pseudotuberculosis but not with an isogenic ysc mutant defectiv e for Yop secretion. We inactivated multiple yop genes to identify whi ch of these factors are required for the inhibition of TNF-alpha produ ction. A mutant unable to express yopJ was defective for the inhibitio n of TNF-alpha production. Production of TNF-alpha is regulated at the transcriptional and translational levels by several mitogen-activated protein (MAP) kinases. The MAP kinases p38 and JNK underwent sustaine d activation in macrophages infected with the yopJ mutant. Conversely, p38 and JNK were downregulated in macrophages infected with the wild- type strain. The ability of the yopJ mutant to downregulate p38 and JN K and to inhibit production of TNF-alpha was restored by the expressio n of yopJ(+) in trans. Therefore, YopJ is required for Y. pseudotuberc ulosis to downregulate MAP kinases and inhibit the production of TNF-a lpha in macrophages.