IFN-gamma regulates the expression of key genes in macrophages implicated in the control of cholesterol homeostasis and the inflammaotry response, two critical events in the pathogenesis of atherosclerosis. We are investigating the molecular mechanisms underlying the IFN-gamma-regulated expression of such genes in detail, with emphasis on monocyte chemoattractant protein-1 (MCP-1), a key mediator of monocyte trafficking during atherogenesis. The IFN-gamma-mediated induction of MCP-1 expression was attenuated by inhibitors of Janus kinase (JAK)-2, casein kinase 2 (CK2) and phosphoinositide-3-kinase (PI3K). The action of PI3K was mediated through its downstream target AKT. A combination of chromatin immunoprecipitation assays and electrophoretic mobility shift assays showed that signal transducer and activator of transcription (STAT)-1 interacted with IFN-gamma response elements in the promoter region of the MCP-1 gene. Dominant negative forms of JAK-1 and -2, STAT1, AKT and CK2 attenuated the IFN-gamma-induced activity of the MCP-1 gene promoter and an artificial promoter containing three copies of STAT1 response elements. Gene expression profiling and reverse transcription polymerase chain reaction showed that CK2 and PI3K were also required for the IFN-gamma-mediated regulation of a large number of genes implicated in atherosclerosis. The action of CK2 and AKT was mediated, at least in part, through the control of STAT1 phosphorylation at serine 727, which is required for maximal transcriptional activation by this factor. More recently, we have found that extracellular signal regulated kinase (Erk) also plays a key role in the regulation of STAT1 serine 727 phosphorylation by IFN-gamma. The interactions between these different pathways and their roles in the regulation of macrophage gene expression and cholesterol homeostasis are currently being investigated. These studies provide novel insights into signalling pathways underlying the IFN-gamma-mediated changes in macrophage gene expression during atherosclerosis.