Mitogen-Activated Protein Kinases and NF-κB Are Involved in TNF-α Responses to Group B Streptococci

Abstract

TNF-α is a mediator of lethality in experimental infections by group B streptococcus (GBS), an important human pathogen. Little is known of signal transduction pathways involved in GBS-induced TNF-α production. Here we investigate the role of mitogen-activated protein kinases (MAPKs) and NF-κB in TNF-α production by human monocytes stimulated with GBS or LPS, used as a positive control. Western blot analysis of cell lysates indicates that extracellular signal-regulated kinase 1/2 (ERK 1/2), p38, and c-Jun N-terminal kinase MAPKs, as well as IκBα, became phosphorylated, and hence activated, in both LPS- and GBS-stimulated monocytes. The kinetics of these phosphorylation events, as well as those of TNF-α production, were delayed by 30–60 min in GBS-stimulated, relative to LPS-stimulated, monocytes. Selective inhibitors of ERK 1/2 (PD98059 or U0126), p38 (SB203580), or NF-κB (caffeic acid phenetyl ester (CAPE)) could all significantly reduce TNF-α production, although none of the inhibitors used alone was able to completely prevent TNF-α release. However, this was completely blocked by combinations of the inhibitors, including PD98059-SB203580, PD98059-CAPE, or SB203580-CAPE combinations, in both LPS- and GBS-stimulated monocytes. In conclusion, our data indicate that the simultaneous activation of multiple pathways, including NF-κB, ERK 1/2, and p38 MAPKs, is required to induce maximal TNF-α production. Accordingly, in septic shock caused by either GBS or Gram-negative bacteria, complete inhibition of TNF-α release may require treatment with drugs or drug combinations capable of inhibiting multiple activation pathways.