PMC:2586094 / 18752-24050 JSONTXT

{"project":"2_test","denotations":[{"id":"18793716-15907820-20139079","span":{"begin":157,"end":158},"obj":"15907820"},{"id":"18793716-15907820-20139080","span":{"begin":281,"end":283},"obj":"15907820"},{"id":"18793716-11929133-20139080","span":{"begin":281,"end":283},"obj":"11929133"},{"id":"18793716-11602641-20139080","span":{"begin":281,"end":283},"obj":"11602641"},{"id":"18793716-11796707-20139080","span":{"begin":281,"end":283},"obj":"11796707"},{"id":"18793716-12609974-20139080","span":{"begin":281,"end":283},"obj":"12609974"},{"id":"18793716-17255531-20139080","span":{"begin":281,"end":283},"obj":"17255531"},{"id":"18793716-11602641-20139081","span":{"begin":471,"end":472},"obj":"11602641"},{"id":"18793716-11796707-20139082","span":{"begin":643,"end":644},"obj":"11796707"},{"id":"18793716-18437331-20139083","span":{"begin":980,"end":982},"obj":"18437331"},{"id":"18793716-12609974-20139084","span":{"begin":1079,"end":1081},"obj":"12609974"},{"id":"18793716-18437331-20139084","span":{"begin":1079,"end":1081},"obj":"18437331"},{"id":"18793716-18437331-20139085","span":{"begin":1208,"end":1210},"obj":"18437331"},{"id":"18793716-15836981-20139086","span":{"begin":1349,"end":1351},"obj":"15836981"},{"id":"18793716-15897466-20139087","span":{"begin":1621,"end":1623},"obj":"15897466"},{"id":"18793716-18437331-20139088","span":{"begin":1795,"end":1797},"obj":"18437331"},{"id":"18793716-17009010-20139088","span":{"begin":1795,"end":1797},"obj":"17009010"},{"id":"18793716-12609974-20139089","span":{"begin":1894,"end":1896},"obj":"12609974"},{"id":"18793716-17255531-20139089","span":{"begin":1894,"end":1896},"obj":"17255531"},{"id":"18793716-12609974-20139090","span":{"begin":2232,"end":2234},"obj":"12609974"},{"id":"18793716-17255531-20139091","span":{"begin":2422,"end":2424},"obj":"17255531"},{"id":"18793716-17255531-20139092","span":{"begin":2500,"end":2502},"obj":"17255531"},{"id":"18793716-15345653-20139093","span":{"begin":2941,"end":2943},"obj":"15345653"},{"id":"18793716-9153193-20139094","span":{"begin":3074,"end":3076},"obj":"9153193"},{"id":"18793716-17255531-20139095","span":{"begin":3297,"end":3299},"obj":"17255531"},{"id":"18793716-17483449-20139096","span":{"begin":3448,"end":3450},"obj":"17483449"},{"id":"18793716-17255531-20139097","span":{"begin":3564,"end":3566},"obj":"17255531"},{"id":"18793716-17255531-20139098","span":{"begin":3713,"end":3715},"obj":"17255531"},{"id":"18793716-9591746-20139099","span":{"begin":4117,"end":4119},"obj":"9591746"},{"id":"18793716-18339807-20139100","span":{"begin":4421,"end":4423},"obj":"18339807"},{"id":"18793716-17275731-20139100","span":{"begin":4421,"end":4423},"obj":"17275731"},{"id":"18793716-17286201-20139101","span":{"begin":4784,"end":4786},"obj":"17286201"}],"text":"4 Discussion\nThe cytokine IFN-γ is a key regulator of the immune and inflammatory response and plays a crucial role in the pathogenesis of atherosclerosis [2]. The cellular actions of IFN-γ are associated with both the activation and the inhibition of gene transcription [2,5,6,9–11]. However, the mechanisms underlying the IFN-γ-mediated inhibition of gene transcription are poorly understood despite 25% of the macrophage transcriptome being regulated in this manner [6]. Our previous studies using LPL as a model gene identified a novel pathway involving the IFN-γ-mediated decrease in Sp1/Sp3 binding to regulatory sequences in the gene [9]. The studies presented here provide insights into the signalling pathways underlying such regulation and reveal potentially key roles for CK2 and the PI3K/PKB/mTOR pathways in the inhibition of gene transcription by IFN-γ.\nCK2 phosphorylates serine or threonine residues in acidic domains with (S/T)XX(D/E) being the canonical motif [22]. The constitutive activity of CK2 is stimulated further by several extracellular mediators [10,22]. A number of recent studies have suggested a potentially important role for CK2 in the control of the inflammatory response [22]. For example, inhibition of CK2 has been shown to reduce pain-related behaviors in murine models of acute and chronic inflammatory pain [31]. In addition, in a rat model of glomerulonephritis, which similar to atherosclerosis is an inflammatory disorder, the progression of the disease could be prevented by administration of either antisense oligodeoxynucleotides against CK2 or inhibitors such as apigenin [32]. CK2 is indeed a major regulator of nuclear factor-кB (NF-кB), a key transcription factor in signalling by pro-inflammatory cytokines such as interleukin-1 and TNF-α [22,33]. Our recent studies have revealed a potentially important role for CK2 in IFN-γ signalling [10,11]. Thus, the IFN-γ-induced expression of the inducible cAMP early repressor (ICER), a transcriptional inhibitor, was mediated via stimulation of CK2-α activity leading to the activation of transcription factors belonging to the cAMP response element binding protein family, which bind to regulatory sequences in the ICER gene promoter [10]. More recently, we have shown a key role for CK2 in the IFN-γ-induced expression of several genes implicated in atherosclerosis that are known targets of the classical JAK-STAT pathway [11]. CK2 regulates the phosphorylation of STAT1 at serine 727 in macrophages [11]. We have now extended these findings to indicate a role of CK2 in transcriptional suppression by IFN-γ mediated via phosphorylation of Sp1 (and possibly Sp3), which leads to decreased binding to regulatory sequences in the LPL gene. Transcriptional inhibition that is potentially mediated by a CK2-mediated phosphorylation of Sp1 has also been suggested for the flow-dependent suppression of endothelial Toll-like receptor 2 expression [34]. Indeed, CK2-mediated phosphorylation of the carboxyl terminus of Sp1 is associated with a decrease in its DNA binding activity [35].\nAn increasing body of evidence supports a role for the PI3K pathway in IFN-γ signalling and our previous studies have revealed a key function in the regulation of a large number of genes implicated in atherosclerosis [11]. Deletion of the PI3Kγ gene has been demonstrated to attenuate atherosclerosis in apolipoprotein E-deficient mice, a mouse model for this disease [36]. A large number of genes regulated by IFN-γ through PI3K signalling are known targets for the JAK/STAT pathway [11]. Indeed, the action of PI3K in these cases appears to be mediated, at least in part, through the regulation of STAT1 serine 727 phosphorylation [11]. The studies presented here extend the role of PI3K in IFN-γ signalling to transcriptional suppression by this cytokine through Sp1/Sp3. A potential role for mTOR was identified as pre-treatment of the cells with rapamycin attenuated the IFN-γ-mediated reduction in Sp1/Sp3 binding. The PI3K/mTOR pathway has previously been implicated in the insulin-mediated increase in LPL activity in adipocytes [37], and our studies extend this to transcriptional inhibition through Sp1/Sp3. The precise mechanisms underlying such regulation remain to be determined but could include direct phosphorylation-mediated reduction of Sp1 binding. In addition, as mTOR is also associated with translational regulation [24,27], it could potentially be involved in the reduction of Sp3 polypeptide levels observed when the cells are treated with IFN-γ. Interestingly, a recent study investigating the mechanisms underlying the PI3K-mediated suppression of PMA-induced expression of p21WAF1/Cip1 showed that blocking of the PI3K/mTOR pathway was associated with increased binding by Sp1 [38]. Such a mechanism might therefore be common in transcriptional inhibition through Sp1/Sp3.\nIn conclusion, our studies provide novel insights into the role and mechanism of action of CK2 and PI3K signalling in the IFN-γ-mediated suppression of LPL gene transcription. Although IFN-γ regulates gene transcription mainly through the JAK-STAT pathway, several studies have indicated the existence of alternative pathways. The CK2- and PI3K-mediated regulation of Sp1/Sp3 binding could represent one such mechanism."}