casein-kinase-ii and Atherosclerosis

Dysregulation of liver X receptor alpha (LXRalpha) activity has been linked to cardiovascular and metabolic diseases. Here, we show that LXRalpha target gene selectivity is achieved by modulation of LXRalpha phosphorylation. Under basal conditions, LXRalpha is phosphorylated at S198; phosphorylation is enhanced by LXR ligands and reduced both by casein kinase 2 (CK2) inhibitors and by activation of its heterodimeric partner RXR with 9-cis-retinoic acid (9cRA). Expression of some (AIM and LPL), but not other (ABCA1 or SREBPc1) established LXR target genes is increased in RAW 264.7 cells expressing the LXRalpha S198A phosphorylation-deficient mutant compared to those with WT receptors. Surprisingly, a gene normally not expressed in macrophages, the chemokine CCL24, is activated specifically in cells expressing LXRalpha S198A. Furthermore, inhibition of S198 phosphorylation by 9cRA or by a CK2 inhibitor similarly promotes CCL24 expression, thereby phenocopying the S198A mutation. Thus, our findings reveal a previously unrecognized role for phosphorylation in restricting the repertoire of LXRalpha-responsive genes.

Topics: Amino Acid Sequence; Animals; Atherosclerosis; Casein Kinase II; Cell Line; Chemokine CCL24; Cholesterol; DNA-Binding Proteins; Gene Expression Regulation; Humans; Ligands; Liver X Receptors; Macrophages; Mice; Mice, Inbred C57BL; Models, Biological; Orphan Nuclear Receptors; Phosphorylation; Phosphoserine; Receptors, Cytoplasmic and Nuclear; Retinoid X Receptors; Transcription, Genetic

The interferon-gamma (IFN-gamma)-mediated regulation of macrophage gene expression is of crucial importance in the pathogenesis of atherosclerosis. The mechanisms underlying the actions of IFN-gamma signaling in macrophages were investigated using monocyte chemoattractant protein (MCP)-1 as a model gene.. The IFN-gamma-induced expression of MCP-1 in macrophages was attenuated by inhibitors of phosphoinositide-3-kinase (PI3K), casein kinase 2 (CK2), and Janus kinase (JAK)-2. AKT was the downstream target for PI3K action. Electrophoretic mobility shift assays and chromatin immunoprecipitation showed that signal transducer and activator of transcription (STAT)-1 interacted with IFN-gamma responsive elements in the MCP-1 gene promoter. The IFN-gamma-induced activity of the MCP-1 gene promoter and an artificial promoter containing STAT1 responsive elements was inhibited by expression of dominant negative forms of JAK-1 and -2, STAT1, CK2, and AKT. The action of CK2 and AKT on STAT1 activation was mediated, at least in part, through the regulation of serine 727 phosphorylation. Analysis of a number of other genes regulated by this cytokine and implicated in atherosclerosis revealed a gene-specific action for PI3K/AKT in IFN-gamma signaling.. These studies provide novel insights into the role of PI3K/AKT and CK2 in IFN-gamma signaling relevant to changes in macrophage gene expression during atherosclerosis.

Topics: Animals; Atherosclerosis; Casein Kinase II; Cell Line; Chemokine CCL2; Gene Expression Regulation; Humans; Interferon-gamma; Janus Kinases; Macrophages; Mice; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-akt; Signal Transduction; STAT1 Transcription Factor