Foreign body-type multinucleated giant cell formation requires protein kinase C β, δ, and ζ

Multinucleated giant cells are a classic cellular feature of chronic inflammation, although the mechanism of macrophage fusion leading to their formation is not well understood. Here, we investigate the participation of protein kinase C (PKC) in the interleukin (IL)-4-induced fusion of human monocyte-derived macrophages and foreign body giant cell (FBGC) formation in vitro. The PKC inhibitors H-7 and calphostin C attenuated macrophage fusion, whereas H-8, which is more selective for PKA and PKG, did not. Macrophage fusion was also prevented by the phospholipase C inhibitor, Et-18-OCH3, the PKC isoform inhibitors GO6983 or rottlerin and by peptide inhibitors for PKC (20–28), PKCβ, or PKCζ but not by HBDDE or peptide inhibitors for PKCɛ or PKA. In cultures of fusing macrophages/FBGC, we detected only PKCα, β, δ, and ζ by immunoprecipitation and immunoblotting, and we also observed strong expression of these isoforms by immunocytochemistry. Our collective results suggest that the γ, ɛ, η, μ, θ, or ι PKC isoforms are not required in the mechanism of IL-4-induced macrophage fusion; whether PKCα is required is unclear. However, new evidence is provided that FBGC formation is supported by PKCβ, PKCδ, and PKCζ in combined diacylglycerol-dependent (PKCβ and PKCδ) and -independent (PKCζ) signaling pathways.