Rationale: Inflammation impairs macrophage cholesterol clearance from vascular tissues and promotes atherosclerosis. Inflammatory macrophages suppress expression of the transcription cofactor interferon regulatory factor 2–binding protein 2 (IRF2BP2), and genetic variants near IRF2BP2 associate with ischemic heart disease progression in humans. Objectives: To test whether IRF2BP2 in macrophages affects atherosclerosis in mice and humans. Methods and Results: We generated mice that delete IRF2BP2 in macrophages. IRF2BP2-deficient macrophages worsened atherosclerosis in irradiated low-density lipoprotein receptor null-recipient mice and in apolipoprotein E null mice. IRF2BP2-deficient macrophages were inflammatory and had impaired cholesterol efflux because of their inability to activate the cholesterol transporter ABCA1 in response to cholesterol loading. Their expression of the anti-inflammatory transcription factor Krüppel-like factor 2 was markedly reduced. Promoter studies revealed that IRF2BP2 is required for MEF2-dependent activation of Krüppel-like factor 2. Importantly, restoring Krüppel-like factor 2 in IRF2BP2-deficient macrophages attenuated M1 inflammatory and rescued M2 anti-inflammatory gene activation and improved the cholesterol efflux deficit by restoring ABCA1 activation in response to cholesterol loading. In a cohort of 1066 angiographic cases and 1011 controls, homozygous carriers of a deletion polymorphism (rs3045215) in the 3′ untranslated region sequence of human IRF2BP2 mRNA had a higher risk of coronary artery disease (recessive model, odds ratio [95% confidence interval]=1.560 [1.179–2.065], P =1.73E-03) and had lower IRF2BP2 (and Krüppel-like factor 2) protein levels in peripheral blood mononuclear cells. The effect of this deletion polymorphism to suppress protein expression was confirmed in luciferase reporter studies. Conclusion: Ablation of IRF2BP2 in macrophages worsens atherosclerosis in mice, and a deletion variant that lowers IRF2BP2 expression predisposes to coronary artery disease in humans.

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Thyroid hormone nuclear receptors (TRs) are liganddependent transcription factors which regulate growth, differentiation, and development. The molecular mechanisms by which TRs mediate these diverse effects are unclear. One emerging hypothesis suggests that TRs could mediate these diverse effects via cooperation with different transcription factors/receptors. Indeed, we have recently shown that the human TR subtype ␤1 (h-TR␤1) interacts with the tumor suppressor p53. p53 is a transcription factor that plays a critical role in cell cycle regulation and tumor development. To assess the physiological relevance of the interaction of h-TR␤1 with p53, the present study addressed the question as to whether the functions of h-TR␤1 could be modulated by p53. We first compared the h-TR␤1-mediated transcriptional activity in two pairs of isogenic cell lines, RKO/ RKO E6 and MCF-7/MCF-7 E6. RKO and MCF-7 cells are colon and breast carcinoma cell lines, respectively, that contain p53 but lack TR␤1. The isogenic RKO E6 and MCF-7 E6 cells are stable clones expressing high levels of papillomavirus type 16 E6 protein. In these cells, the level of p53 protein was lower than the parental cells. The impairment of p53 functions in these E6-containing cells led to an activation of TR␤1-mediated transcriptional activity. Furthermore, in a growth hormone-producing cell line in which the expression of the growth hormone gene is positively regulated by TRs, overexpression of the wild-type p53 led to repression in the expression of the growth hormone gene. Thus, TRs could cross-talk with p53 in its signaling pathways to regulate gene regulatory functions. The present findings further strengthen the hypothesis that mediation of the pleiotropic effects of T 3 requires the cooperation of TRs with a large network of transcription factors. The thyroid hormone 3,3Ј-5-triiodo-L-thyronine (T 3 )1 promotes growth, induces differentiation, and regulates metabolic functions. These effects are mediated by the interaction of T 3 with the thyroid hormone nuclear receptors (TRs). Thyroid hormone receptors (TRs) belong to the steroid hormone/retinoic acid receptor superfamily and function as ligand-dependent transcription factors. Two TR genes, ␣ and ␤, encode two receptor variants through alternative splicing of each of the primary transcripts. The gene regulating activity of TRs depends not only on T 3 but also on the specific DNA sequences in the promoter regions of T 3 responsive genes, known as the thyroid hormone response elements (TREs) (1). Recent studies have indicated that the gene regulating activity of TR is further modulated via interaction with other cellular proteins including several members of the nuclear receptor superfamily (1-7). Despite recent progress, the molecular mechanisms by which TRs mediate the T 3 biological activities are still unclear. One of the central issues is how the diverse effects of T 3 are achieved. We hypothesized that the diverse effects of T 3 could be mediated by interaction of TRs with other transcription fac...

BackgroundLMO4 is a transcription cofactor expressed during retinal development and in amacrine neurons at birth. A previous study in zebrafish reported that morpholino RNA ablation of one of two related genes, LMO4b, increases the size of eyes in embryos. However, the significance of LMO4 in mammalian eye development and function remained unknown since LMO4 null mice die prior to birth.Methodology/Principal FindingsWe observed the presence of a smaller eye and/or coloboma in ∼40% LMO4 null mouse embryos. To investigate the postnatal role of LMO4 in retinal development and function, LMO4 was conditionally ablated in retinal progenitor cells using the Pax6 alpha-enhancer Cre/LMO4flox mice. We found that these mice have fewer Bhlhb5-positive GABAergic amacrine and OFF-cone bipolar cells. The deficit appears to affect the postnatal wave of Bhlhb5+ neurons, suggesting a temporal requirement for LMO4 in retinal neuron development. In contrast, cholinergic and dopaminergic amacrine, rod bipolar and photoreceptor cell numbers were not affected. The selective reduction in these interneurons was accompanied by a functional deficit revealed by electroretinography, with reduced amplitude of b-waves, indicating deficits in the inner nuclear layer of the retina.Conclusions/SignificanceInhibitory GABAergic interneurons play a critical function in controlling retinal image processing, and are important for neural networks in the central nervous system. Our finding of an essential postnatal function of LMO4 in the differentiation of Bhlhb5-expressing inhibitory interneurons in the retina may be a general mechanism whereby LMO4 controls the production of inhibitory interneurons in the nervous system.

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Introduction: Genetic variants near the gene encoding the transcription cofactor Interferon Regulatory Factor 2 Binding Protein 2 (IRF2BP2) have been tied to ischemic heart disease progression and elevated serum cholesterol. Expression of IRF2BP2 is suppressed in inflammatory macrophages, but the significance of this down-regulation was not known. Hypothesis: This study sought to determine the function of IRF2BP2 in macrophages and its effect on atherosclerosis in mice and humans. Methods and Results: We generated mice that delete IRF2BP2 in macrophages (LysMCre/IRF2BP2flox). IRF2BP2-deficient macrophages increased atherosclerosis in irradiated LDL-receptor null recipient mice and in ApoE null mice. Atherosclerosis was associated with a skewed inflammatory macrophage polarization and increased foam cell formation. Microarray analysis revealed and promoter studies confirmed that the anti-inflammatory transcription factor KLF2 is a target of IRF2BP2, indicating an important role for IRF2BP2 in macrophage polarization. A deletion polymorphism (rs3045215) in the 3’ untranslated sequence of human IRF2BP2 mRNA was examined for its effect on protein expression and on the susceptibility to coronary artery disease (CAD) risk in a cohort of 1,066 angiographic cases and 1,011 controls. Homozygous carriers of this deletion had lower IRF2BP2 (and its target KLF2) protein levels in peripheral blood mononuclear cells and a higher risk of CAD (recessive model, odds ratio (95%CI) = 1.560 (1.179-2.065), p=1.73E-03). The effect of this deletion to suppress protein expression was confirmed with luciferase reporter studies. Haplotype phasing identified two surrogate SNPs in modest LD (rs1887917, r2= 0.755 and rs632180, r2=0.614) that also associated with CAD in a recessive model. These SNPs are being tested for association with CAD in a large international consortium. Conclusion: Ablation of IRF2BP2 in macrophages worsens atherosclerosis in mice and a deletion variant that lowers IRF2BP2 expression predisposes to CAD in humans.