Protein I/II, a modulin from oral streptococci, is a potent inducer of IL-6 and IL-8 synthesis and release from fibroblast-like synoviocytes. FAK (focal adhesion molecule) is proposed to play a role in the MAPKs pathway converting extracellular stimuli of integrins to intracellular signals central to many cellular functions. However, the role of FAK in MAPKs-dependent synthesis of IL-6 and IL-8 in response to protein I/II was still elusive. The authors nucleofected fibroblasts with FRNK, a dominant negative form of FAK and determined the release of inflammatory mediators IL-6 and IL-8 upon activation with protein I/II. Overexpression of FRNK inhibited IL-6 and IL-8 release. To further demonstrate that Shc is not involved in cytokine synthesis, cell were nucleofected with a dominant negative version of Shc. Overexpression of the dominant negative version of Shc had no effect on IL-6 and IL-8 release.
Protein I/II, a pathogen-associated molecular pattern from oral streptococci, is a potent inducer of interleukin-6 (IL-6) and IL-8 synthesis and release from fibroblast-like synoviocytes (FLSs), cells that are critically involved in joint inflammation. This synthesis implicates ERK 1/2 and JNKs as well as AP-1-binding activity and nuclear translocation of NF-kappaB. The mechanisms by which protein I/II activates MAPKs remain, however, elusive. Because focal adhesion kinase (FAK) was proposed to play a role in signaling to MAPKs, we examined its ability to contribute to the MAPKs-dependent synthesis of IL-6 and IL-8 in response to protein I/II. We used FAK-/- fibroblasts as well as FAK+/+ fibroblasts and FLSs transfected with FRNK, a dominant negative form of FAK. The results demonstrate that IL-6 and IL-8 release in response to protein I/II was strongly inhibited in both protein I/II-stimulated FAK-/- and FRNK-transfected cells. Cytochalasin D, which inhibits protein I/II-induced phosphorylation of FAK (Tyr-397), had no effect either on activation of ERK 1/2 and JNKs or on IL-6 and IL-8 release. Taken together, these results indicate that IL-6 and IL-8 release by protein I/II-activated FLSs is regulated by FAK independently of Tyr-397 phosphorylation.