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Sterol metabolism has recently been linked to innate and adaptive immune responses through liver X receptor (LXR) signaling. Whether products of sterol metabolism interfere with antitumor responses is currently unknown. Dendritic cells (DCs) initiate immune responses, including antitumor activity after their CC chemokine receptor-7 (CCR7)-dependent migration to lymphoid organs. Here we report that human and mouse tumors produce LXR ligands that inhibit CCR7 expression on maturing DCs and, therefore, their migration to lymphoid organs. In agreement with this observation, we detected CD83(+)CCR7(-) DCs within human tumors. Mice injected with tumors expressing the LXR ligand-inactivating enzyme sulfotransferase 2B1b (SULT2B1b) successfully controlled tumor growth by regaining DC migration to tumor-draining lymph nodes and by developing overt inflammation within tumors. The control of tumor growth was also observed in chimeric mice transplanted with bone marrow from mice lacking the gene encoding LXR-alpha (Nr1h3(-/-) mice) Thus, we show a new mechanism of tumor immunoescape involving products of cholesterol metabolism. The manipulation of this pathway could restore antitumor immunity in individuals with cancer.

The liver X receptors (LXRs) are nuclear receptors that form permissive heterodimers with retinoid X receptor (RXR) and are important regulators of lipid metabolism in the liver. We have recently shown that RXR agonist-induced hypertriglyceridemia and hepatic steatosis in mice are dependent on LXRs and correlate with an LXR-dependent hepatic induction of lipogenic genes. To further investigate the roles of RXR and LXR in the regulation of hepatic gene expression, we have mapped the ligandregulated genome-wide binding of these factors in mouse liver. We find that the RXR agonist bexarotene primarily increases the genomic binding of RXR, whereas the LXR agonist T0901317 greatly increases both LXR and RXR binding. T he liver plays a central role in the control of whole-body lipid homeostasis, and hepatic lipid metabolism is continuously adjusted to fit the needs of the organism. This adaptation requires major adjustments in the hepatic metabolic gene program, including a strong upregulation of lipogenic gene expression in the fed state, whereas in the fasting state, the expression of genes involved in fatty acid oxidation as well as ketogenesis and hepatic glucose production is highly induced. Class II nuclear receptors (NRs), i.e., NRs forming heterodimers with retinoid X receptor (RXR), play a key role in coordinating these changes. They include the liver X receptor (LXR) (29, 57) and peroxisome proliferatoractivated receptor (PPAR) (32, 34, 41) families as well as farnesoid X receptor (FXR) (44, 55, 88), pregnane X receptor (PXR) (5, 33), vitamin D receptor (VDR) (43), constitutive androstane receptor (CAR) (3, 9, 23), and retinoic acid receptors (RARs) (13).The LXR family consists of the two subtypes, LXR␣ (NR1H3) and LXR␤ (NR1H2), both of which form obligate heterodimers with RXR. LXR-RXR heterodimers are reported to bind to LXR response elements (LXREs) that consist of a direct repeat of the core sequence 5=-AGGTCA-3= spaced by 4 nucleotides (DR4) (2,72,76,79,92). LXRs are activated by oxidized cholesterol derivatives and play an important role in the regulation of cholesterol homeostasis in the liver. Thus, pharmacological activation of LXR leads to the induction of several genes implicated in reverse cholesterol transport and mobilization of cholesterol, such as the ATP binding cassette (ABC) transporter genes Abca1, Abcg1, Abcg5, and Abcg8 and the apolipoprotein E gene (ApoE) (12,31,37,60,63,84). Furthermore, a recent genomewide study of LXR in human hepatoma cells showed that LXR also downregulates expression of the cholesterologenic genes for lanosterol 14␣-demethylase (Cyp51A1) and squalene synthase (Fdst1) (89). Moreover, LXR activation induces triglyceride synthesis partly through induction of the lipogenic transcription factors sterol regulatory element-binding protein 1c (SREBP-1c) (42,61,95) and carbohydrate response element-binding protein (ChREBP) (8) but also by direct activation of genes encoding lipogenic enzymes such as fatty acid synthase (Fasn), stearoyl coenzyme A (CoA) desaturase (Scd1), ...

The oxysterol receptors [liver X receptors (LXRalpha and LXRbeta)] regulate cholesterol and lipid biosynthesis and several studies link dysregulation of these metabolic pathways to aberrant cell growth. Here, we show that activation of LXR significantly reduced proliferation in several human breast cancer cells lines. LXR suppressed messenger RNA and/or protein expression of Skp2, cyclin A2, cyclin D1 and estrogen receptor (ER) alpha, whereas it increased the expression of p53 at the protein level and maintained the retinoblastoma protein in a hypophosphorylated active form. These changes may constitute part of the molecular mechanisms behind the antiproliferative effect of LXR. Furthermore, activation of LXR induced expression of key lipogenic genes including sterol regulatory element-binding protein 1c (SREBP1c), fatty acid synthase and stearoyl-coenzyme A desaturase 1, leading to increased triglyceride production in MCF7 cells. Small interfering RNA knockdown of SREBP1c, a master regulator of the lipid biosynthesis, did not abolish the antiproliferative effect of LXR in these cells. Combined these studies identify LXRs as both antiproliferative and lipogenic factors in breast cancer cells and indicate that the antiproliferative effect of LXRs is independent of lipid biosynthesis.

Liver X receptors (LXRs) are nuclear hormone receptors that regulate cholesterol and fatty acid metabolism in liver tissue and in macrophages. Although LXR activation enhances lipogenesis, it is not well understood whether LXRs are involved in adipocyte differentiation. Here, we show that LXR activation stimulated the execution of adipogenesis, as determined by lipid droplet accumulation and adipocyte-specific gene expression in vivo and in vitro. In adipocytes, LXR activation with T0901317 primarily enhanced the expression of lipogenic genes such as the ADD1/SREBP1c and FAS genes and substantially increased the expression of the adipocyte-specific genes encoding PPAR␥ (peroxisome proliferator-activated receptor ␥) and aP2. Administration of the LXR agonist T0901317 to lean mice promoted the expression of most lipogenic and adipogenic genes in fat and liver tissues. It is of interest that the PPAR␥ gene is a novel target gene of LXR, since the PPAR␥ promoter contains the conserved binding site of LXR and was transactivated by the expression of LXR␣. Moreover, activated LXR␣ exhibited an increase of DNA binding to its target gene promoters, such as ADD1/SREBP1c and PPAR␥, which appeared to be closely associated with hyperacetylation of histone H3 in the promoter regions of those genes. Furthermore, the suppression of LXR␣ by small interfering RNA attenuated adipocyte differentiation. Taken together, these results suggest that LXR plays a role in the execution of adipocyte differentiation by regulation of lipogenesis and adipocyte-specific gene expression.Adipocyte differentiation, called adipogenesis, is a complex process accompanied by coordinated changes in morphology, hormone sensitivity, and gene expression. These changes are regulated by several transcription factors, including C/EBPs, peroxisome proliferator-activated receptor ␥ (PPAR␥), and ADD1/SREBP1c (44, 67). These transcription factors interact with each other to execute adipocyte differentiation, including lipogenesis and adipocyte-specific gene expression, which are pivotal for metabolism in adipocytes. Expression of C/EBP␤ and C/EBP␦ occurs at a very early stage of adipocyte differentiation, and overexpression of C/EBP␣ or C/EBP␤ promotes adipogenesis through cooperation with PPAR␥ (15, 32, 68, 69). PPAR␥, a member of the nuclear hormone receptor family, is predominantly expressed in brown and white adipose tissue (58, 59). PPAR␥ is activated by fatty acid-derived molecules such as prostaglandin J2 and synthetic thiazolidinediones (TZDs), novel drugs used in type II diabetes treatment (14,25,29). Recent studies involving PPAR␥ knockout mice indicated that the major roles of PPAR␥ are adipocyte differentiation and insulin sensitization (3,26,43). ADD1/SREBP1c, which also appears to be involved in adipocyte differentiation, is highly expressed in adipose tissue and liver and is also expressed early in adipocyte differentiation (22,60). ADD1/ SREBP1c stimulates the expression of several lipogenic genes, including FAS, LPL, ACC, SCD-1, and SCD-2 (22, 5...

The orphan receptor LRH-1 and the oxysterol receptors LXRa and LXRb are established transcriptional regulators of lipid metabolism that appear to control inflammatory processes. Here, we investigate the anti-inflammatory actions of these nuclear receptors in the hepatic acute phase response (APR). We report that selective synthetic agonists induce SUMOylation-dependent recruitment of either LRH-1 or LXR to hepatic APR promoters and prevent the clearance of the N-CoR corepressor complex upon cytokine stimulation. Investigations of the APR in vivo, using LXR knockout mice, indicate that the anti-inflammatory actions of LXR agonists are triggered selectively by the LXRb subtype. We further find that hepatic APR responses in small ubiquitin-like modifier-1 (SUMO-1) knockout mice are increased, which is due in part to diminished LRH-1 action at APR promoters. Finally, we provide evidence that the metabolically important coregulator GPS2 functions as a hitherto unrecognized transrepression mediator of interactions between SUMOylated nuclear receptors and the N-CoR corepressor complex. Our study extends the knowledge of anti-inflammatory mechanisms and pathways directed by metabolic nuclear receptor-corepressor networks to the control of the hepatic APR, and implies alternative pharmacological strategies for the treatment of human metabolic diseases associated with inflammation.[Keywords: LRH-1; LXR; GPS2; acute phase response; liver inflammation] Supplemental material is available at http://www.genesdev.org.

tion-mass spectrometry (LC-ESI-MS) analysis. We hereby report the exact identity of 16 oxysterols and downstream metabolites, including cholestenoic acids, found in human CSF (Supplemental Table 1; supplemental material available online with this article; doi:10.1172/JCI68506DS1). The most abundant of these metabolites (19.48-0.40 ng/ml; Supplemental Figure 1) were 7α-hydroxy-3-oxocholest-4-en-26-oic acid (7αH,3O-CA), 3β-hydroxycholest-5-en-26-oic acid (3β-HCA), and 2 newly identified metabolites in CSF, 3β,7α-diHCA and 3β,7β-dihydroxycholest-5-en-26-oic acid (3β,7β-diHCA). Precursors of these acids, including 26-HC and newly identified 7α,26-dihydroxycholesterol (7α,26-diHC; cholest-5-ene-3β,7α,26-triol) and 7α,26-dihydroxycholest-4-en-3-one (7α,26-diHCO), were also found, but at lower levels (0.15-0.03 ng/ml). Our results thus identified 4 novel oxysterol metabolites in human CSF that were downstream of 26-HC ( Figure 1A). 26-HC is metabolized via 7α,26-diHC and 7α,26-diHCO, or via 3β-HCA and 3β,7α-diHCA, to 7αH,3O-CA. While 26-HC can cross the blood-brain barrier (BBB) and enter the brain from the circulation (25), 7αH,3O-CA traverses the BBB and is exported from the brain (26). Very low levels of 24S-hydroxycholesterol (24S-HC; cholest-5-ene-3β,24S-diol), 25-hydroxycholesterol (25-HC; cholest-5-ene-3β,25-diol), and newly identified 7α,25-dihydroxycholesterol (7α,25-diHC; cholest-5-ene-3β,7α,25-triol) and 7α,25-dihydroxycholest-4-en-3-one (7α,25-diHCO) were also found in CSF (0.08-0.03 ng/ml).Reduced levels of 7α-hydroxylated cholestenoic acids in CSF and plasma/serum of human patients with SPG5. SPG5 presents with upper motor neuron signs and results from mutations in CYP7B1, encoding the oxysterol 7α-hydroxylase responsible for 7α-hydroxylation of side-chain oxidized sterols that is required for extrahepatic synthesis of 7αH,3O-CA and its precursor, 3β,7α-diHCA ( Figure 1A and ref. 18). In order to examine the pathogenic role of such mutations, we sought to identify alterations in oxysterol and cholestenoic acid profiles in CSF and plasma from these patients and then examine the biological activities of the altered metabolites. We first studied the CSF from 3 patients with SPG5

Tumor-derived oxysterols recruit protumor neutrophils in an LXR-independent, CXCR2-dependent manner, thus favoring tumor growth by promoting neoangiogenesis and immunosuppression.