Cytokine signalling in macrophages and the expression of key genes implicated in atherosclerosis [Abstract]

Background and aims: Although the control of macrophage gene expression by cytokines is of crucial importance in the pathogenesis of atherosclerosis, the regulatory mechanisms are poorly understood. The objective of this study was to investigate the mechanisms underlying cytokine-regulated expression of key genes implicated in atherosclerosis [e.g. lipoprotein lipase (LPL), monocyte chemoattractant protein-1 (MCP- 1), apolipoprotein E (apoE), ATP-binding cassette transporter-1 (ABCA1)] with emphasis on the actions of interferon-gamma (IFN-gamma) and transforming growth factor-beta (TGF-beta). Methods: Gene expression was investigated by a combination of RTPCR, western blot analysis, transient transfection assays using promoterluciferase DNA constructs and expression profiling. Signaling pathways were studied using pharmacological agents, small interfering RNAs and biochemical analysis. Results: Investigation of mechanisms underlying IFN-gamma-inhibited expression of the LPL gene identified a potentially novel pathway involving activation of casein kinase 2 (CK2) and phosphoinositide-3-kinase (PI3K) leading to decreased binding of transcription factors Sp1 and Sp3 to regulatory sequences in the LPL gene. Further studies on MCP-1 along with RT-PCR and gene expression profiling of many atherosclerosis markers revealed key roles for CK2 and PI3K in the IFN-gamma-regulated expression of large number of genes implicated in atherosclerosis. TGF-beta also inhibited LPL gene transcription through Sp1 and Sp3 but required the actions of the c-Jun N-terminal kinase (JNK) signaling pathway. The JNK pathway was also involved in the TGF-beta-mediated induction of apoE and ABCA1 expression. Conclusions: These studies provide novel insights into the molecular mechanisms underlying cytokine-regulated expression of key genes in macrophages implicated in atherosclerosis