Conventional protein kinase C and atypical protein kinase Cζ differentially regulate macrophage production of tumour necrosis factor-α and interleukin-10

Abstract

In chronic inflammatory diseases such as rheumatoid arthritis, joint macrophages/monocytes are the major source of pro- and anti-inflammatory cytokines. Little is understood regarding the signalling pathways which determine the production of the pro-inflammatory cytokine, tumour necrosis factor-α (TNF-α) and the anti-inflammatory cytokine, interleukin-10 (IL-10). Two pathways integral to macrophage function are the protein kinase C (PKC)- and the cAMP-dependent pathways. In this report, we have investigated the involvement of PKC and cAMP in the production of TNF-α and IL-10 by peripheral blood monocyte-derived macrophages. The utilization of the PKC inhibitors Go6983, Go6976 and RO-32-0432 demonstrated a role for conventional PKCs (α and β) in the production of TNF-α in response to stimulation by lipopolysaccharide and phorbol 12-myristate 13-acetate (PMA)/ionomycin, PKC stimulation resulted in the downstream activation of the p42/44 mitogen-activated protein kinase (MAPK) pathway which differentially regulates TNF-α and IL-10. The addition of cAMP however, suppressed activation of this MAPK and TNF-α production. Cyclic-AMP augmented IL-10 production and cAMP response element binding protein activation upon stimulation by PMA/ ionomycin. In addition, cAMP activated PKCζ; inhibition of which, by a dominant negative adenovirus construct, selectively suppressed IL-10 production. These observations suggest that pro-inflammatory and anti-inflammatory cytokines are differentially regulated by PKC isoforms; TNF-α being dependent on conventional PKCs (α and β) whereas IL-10 is regulated by the cAMP-regulated atypical PKCζ.