Lipid extract of Mycoplasma penetrans proteinase K-digested lipid-associated membrane proteins rapidly activates NF-kappaB and activator protein 1.

Abstract

Lipid-associated membrane proteins (LAMPs) of Mycoplasma penetrans rapidly induced macrophages to produce proinflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha). Our analysis showed that the macrophage-stimulating activity of TNF-alpha production was mainly attributable to a lipid extractable component(s) in the LAMP preparation. Since induction of gene expression is normally preceded by activation of transcriptional factors that bind to their specific recognition elements located in the upstream promoter region, we examined the activity of transcriptional factors, namely, NF-kappaB and activator protein 1 (AP-1), in thioglycolate exudate peritoneal (TEP) macrophages treated with M. penetrans lipid extract of proteinase K (PK)-digested LAMPs. Initially, in the nuclei of unstimulated TEP cells, there was only a low basal level of active AP-1, and the active form of NF-kappaB could not be detected. M. penetrans lipid extract of PK-digested LAMPs activated both NF-kappaB and AP-1 in TEP macrophages within 15 min. The markedly increased activities of both factors gradually declined and dissipated after 2 h. Parallel to the rapid increase of NF-kappaB and AP-1, the TNF-alpha transcript also increased significantly 15 min after the stimulation. The high-level expression of TNF-alpha persisted over 2 h. Dexamethasone blocked the activation of both NF-kappaB and AP-1 and suppressed the production of TNF-alpha in TEP macrophages stimulated by M. penetrans lipid extract of PK-digested LAMPs. Our study demonstrates that the M. penetrans lipid extract of PK-digested LAMP is a potent activator for NF-kappaB and AP-1 in murine TEP macrophages. Our results also suggest that high-level expression of TNF-alpha in cells induced by M. penetrans lipid extract of PK-digested LAMPs is associated with rapid activation of transcriptional factors NF-kappaB and AP-1.