Acetylation-mediated proteasomal degradation of core histones during DNA repair and spermatogenesis.

Histone acetylation plays critical roles in chromatin remodeling, DNA repair, and epigenetic regulation of gene expression, but the underlying mechanisms are unclear. Proteasomes usually catalyze ATP- and polyubiquitin-dependent proteolysis. Here, we show that the proteasomes containing the activator PA200 catalyze the polyubiquitin-independent degradation of histones. Most proteasomes in mammalian testes ("spermatoproteasomes") contain a spermatid/sperm-specific α subunit α4 s/PSMA8 and/or the catalytic ß subunits of immunoproteasomes in addition to PA200. Deletion of PA200 in mice abolishes acetylation-dependent degradation of somatic core histones during DNA double-strand breaks and delays core histone disappearance in elongated spermatids. Purified PA200 greatly promotes ATP-independent proteasomal degradation of the acetylated core histones, but not polyubiquitinated proteins. Furthermore, acetylation on histones is required for their binding to the bromodomain-like regions in PA200 and its yeast ortholog, Blm10. Thus, PA200/Blm10 specifically targets the core histones for acetylation-mediated degradation by proteasomes, providing mechanisms by which acetylation regulates histone degradation, DNA repair, and spermatogenesis.

Environmental chemical TCPOBOP exposure alters milk liposomes and offspring growth trajectories in mice.

Exposure to environmental endocrine disruptors (EEDs) has become a global health concern, and EEDs are known to be potent inducers of constitutive androstane receptor (CAR). 1,4-bis [2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP, hereafter abbreviated as TC), a specific ligand for CAR, has been considered as a potential EED. Here, we analyzed the effect of TC exposure to female mice on the histological morphology of their alveoli in the basic unit of lactation. We quantified differences in the milk metabolome of the control and TC-exposed group while assessing the correlations between metabolites and neonatal growth. Mammary histological results showed that TC exposure inhibited alveolar development. Based on the milk metabolomic data, we identified a total of 1505 differential metabolites in both the positive and negative ion mode, which indicated that TC exposure affected milk composition. As expected, the differential metabolites were significantly enriched in the drug metabolism pathway. Further analyses revealed that differential metabolites were significantly enriched in multiple lipid metabolic pathways, such as fatty acid biosynthesis, suggesting that most differential metabolites were concentrated in lipids. Simultaneously, a quantitative analysis showed that TC exposure led to a decrease in the relative abundance of total milk lipids, affecting the proportion of some lipid subclasses. Notably, a portion of lipid metabolites were associated with neonatal growth. Taken together, these findings suggest that TC exposure may affect milk lipidomes, resulting in the inability of mothers to provide adequate nutrients, ultimately affecting the growth and health of their offspring.

Environmental chemical TCPOBOP disrupts milk lipid homeostasis during pregnancy and lactation.

Humans are exposed to different kinds of environmental contaminants or drugs throughout their lifetimes. The widespread presence of these compounds has raised concerns about the consequent adverse effects on lactating women. The constitutive androstane receptor (CAR, Nr1i3) is known as a xenobiotic sensor for environmental pollution or drugs. In this study, the model environmental chemical 1, 4-bis [2-(3, 5-dichloropyridyloxy)] benzene, TCPOBOP (TC), which is a highly specific agonist of CAR, was used to investigate the effects of exogenous exposure on lactation function and offspring health in mice. The results revealed that TC exposure decreased the proliferation of mammary epithelial cells during pregnancy. This deficiency further compromised lobular-alveolar structures, resulting in alveolar cell apoptosis, as well as premature stoppage of the lactation cycle and aberrant lactation. Furthermore, TC exposure significantly altered the size and number of milk lipid droplets, suggesting that TC exposure inhibits milk lipid synthesis. Additionally, TC exposure interfered with the milk lipid metabolism network, resulting in the inability of TC-exposed mice to efficiently secrete nutrients and feed their offspring. These findings demonstrated that restricted synthesis and secretion of milk lipids would indirectly block mammary gland form and function, which explained the possible reasons for lactation failure and retarded offspring growth.

Constitutive Androstane Receptor Agonist, TCPOBOP: Maternal Exposure Impairs the Growth and Development of Female Offspring in Mice.

Environmental chemicals, which are known to impact offspring health, have become a public concern. Constitutive activated receptor (CAR) is activated by various environmental chemicals and participates in xenobiotic metabolism. Here, we described the effects of maternal exposure to the CAR-specific ligand 1,4-bis[2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP, TC) on offspring health outcomes. Maternal TC exposure exhibited a stronger inhibition of body weight in 3-week-old and 8-week-old first-generation (F1) offspring female mice compared to controls. Further, maternal TC exposure obtained a strong increase in hepatic drug-metabolizing enzyme expression in 3-week-old female mice that persisted into 8-week-old adulthood. Interestingly, we observed distorted intestinal morphological features in 8-week-old F1 female mice in the TC-exposed group. Moreover, maternal TC exposure triggered a loss of intestinal barrier integrity by reducing the expression of intestinal tight junction proteins. Accordingly, maternal exposure to TC down-regulated serum triglyceride levels as well as decreased the expression of intestinal lipid uptake and transport marker genes. Mechanistically, maternal TC exposure activated the intestinal inflammatory response and disrupted the antioxidant system in the offspring female mice, thereby impeding the intestinal absorption of nutrients and seriously threatening offspring health. Altogether, these findings highlight that the effects of maternal TC exposure on offspring toxicity could not be ignored.

GdX/UBL4A specifically stabilizes the TC45/STAT3 association and promotes dephosphorylation of STAT3 to repress tumorigenesis.

Impaired phosphatase activity contributes to the persistent activation of STAT3 in tumors. Given that STAT family members with various or even opposite functions are often phosphorylated or dephosphorylated by the same enzymes, the mechanism for STAT3-specific dephosphorylation in cells remains largely unknown. Here, we report that GdX (UBL4A) promotes STAT3 dephosphorylation via mediating the interaction between TC45 (the nuclear isoform of TC-PTP) and STAT3 specifically. GdX stabilizes the TC45-STAT3 complex to bestow upon STAT3 an efficient dephosphorylation by TC45. Inasmuch, GdX suppresses tumorigenesis and tumor development by reducing the level of phospho-STAT3 (p-STAT3), whereas deletion of GdX results in a high level of p-STAT3 and accelerated colorectal tumorigenesis induced by AOM/DSS. Thus, GdX converts TC45, a nonspecific phosphatase, into a STAT3-specific phosphatase by bridging an association between TC45 and STAT3.

High-Protein Diet Induces Hyperuricemia in a New Animal Model for Studying Human Gout.

Hyperuricemia is a central risk factor for gout and increases the risk for other chronic diseases, including cardiometabolic disease, kidney disease, and hypertension. Overproduction of urate is one of the main reasons for hyperuricemia, and dietary factors including seafoods, meats, and drinking are contributed to the development of it. However, the lack of a suitable animal model for urate metabolism is one of the main reasons for the delay and limitations of hyperuricemia research. Combining evolutionary biological studies and clinical studies, we conclude that chicken is a preferred animal model for hyperuricemia. Thus, we provided chickens a high-protein diet (HPD) to evaluate the changes in the serum urate levels in chickens. In our study, the HPD increased the serum urate level and maintained it at a long-term high level in chickens. Long-term high serum urate levels induced an abnormal chicken claw morphology and the precipitation of monosodium urate (MSU) in joint synovial fluid. In addition, a long-term HPD also decreased the glomerular filtration rate and induced mild renal injury. Most importantly, allopurinol and probenecid displayed the positive effects in decreasing serum urate and then attenuated hyperuricemia in chicken model. These findings provide a novel model for hyperuricemia and a new opportunity to further investigate the effects of long-term hyperuricemia on other metabolic diseases.

PPARs as Nuclear Receptors for Nutrient and Energy Metabolism.

It has been more than 36 years since peroxisome proliferator-activated receptors (PPARs) were first recognized as enhancers of peroxisome proliferation. Consequently, many studies in different fields have illustrated that PPARs are nuclear receptors that participate in nutrient and energy metabolism and regulate cellular and whole-body energy homeostasis during lipid and carbohydrate metabolism, cell growth, cancer development, and so on. With increasing challenges to human health, PPARs have attracted much attention for their ability to ameliorate metabolic syndromes. In our previous studies, we found that the complex functions of PPARs may be used as future targets in obesity and atherosclerosis treatments. Here, we review three types of PPARs that play overlapping but distinct roles in nutrient and energy metabolism during different metabolic states and in different organs. Furthermore, research has emerged showing that PPARs also play many other roles in inflammation, central nervous system-related diseases, and cancer. Increasingly, drug development has been based on the use of several selective PPARs as modulators to diminish the adverse effects of the PPAR agonists previously used in clinical practice. In conclusion, the complex roles of PPARs in metabolic networks keep these factors in the forefront of research because it is hoped that they will have potential therapeutic effects in future applications.

Combination exposure of melamine and cyanuric acid is associated with polyuria and activation of NLRP3 inflammasome in rats.

The molecular mechanisms of melamine-induced renal toxicity have not been fully understood. The purpose of the study aimed to investigate whether melamine and cyanuric acid induced NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation in the kidney, which may contribute to abnormal water and sodium handling in a rat model. Wistar rats received melamine (Mel; 200 mg·kg body wt-1·day-1), cyanuric acid (CA; 200 mg·kg body wt-1·day-1), or Mel plus CA (Mel + CA; 100 mg·kg body wt-1·day-1, each) for 2 wk. Mel + CA caused damaged tubular epithelial structure and organelles, dilated tubular lumen, and inflammatory responses. Crystals were observed in urine and serum specimen, also in the lumen of dilated distal renal tubules. The combined ingestion of Mel and CA in rats caused a markedly impaired urinary concentration, which was associated with reduced protein expression of aquaporin (AQP)1, 2, and 3 in inner medulla and α-Na-K-ATPase and Na-K-2Cl transporters in cortex and outer medulla. Mel + CA treatment was associated with increased protein expression of CD3 and mRNA levels of CD68 and F4/80 as well as phosphorylation of NF-κB in the kidney. Mel + CA treatment increased protein and mRNA expression of NLRP3 inflammasome components apoptosis-associated speck-like protein containing a caspase recruitment domain, caspase-1, and IL-1ß in the inner medulla of rats. NF-κB inhibitor Bay 11-7082 reduced IL-1ß expression induced by Mel + CA and prevented downregulation of AQP2 in inner medullary collecting duct cell suspensions. In conclusion, Mel + CA treatment caused urinary-concentrating defects and reduced expression of renal AQPs and key sodium transporters, which is likely due to the inflammatory responses and activation of NLRP3 inflammasome induced by crystals formed in the kidney.

The Opportunities and Challenges of Peroxisome Proliferator-Activated Receptors Ligands in Clinical Drug Discovery and Development.

Peroxisome proliferator-activated receptors (PPARs) are a well-known pharmacological target for the treatment of multiple diseases, including diabetes mellitus, dyslipidemia, cardiovascular diseases and even primary biliary cholangitis, gout, cancer, Alzheimer's disease and ulcerative colitis. The three PPAR isoforms (α, ß/δ and γ) have emerged as integrators of glucose and lipid metabolic signaling networks. Typically, PPARα is activated by fibrates, which are commonly used therapeutic agents in the treatment of dyslipidemia. The pharmacological activators of PPARγ include thiazolidinediones (TZDs), which are insulin sensitizers used in the treatment of type 2 diabetes mellitus (T2DM), despite some drawbacks. In this review, we summarize 84 types of PPAR synthetic ligands introduced to date for the treatment of metabolic and other diseases and provide a comprehensive analysis of the current applications and problems of these ligands in clinical drug discovery and development.

The Role of PPAR and Its Cross-Talk with CAR and LXR in Obesity and Atherosclerosis.

The prevalence of obesity and atherosclerosis has substantially increased worldwide over the past several decades. Peroxisome proliferator-activated receptors (PPARs), as fatty acids sensors, have been therapeutic targets in several human lipid metabolic diseases, such as obesity, atherosclerosis, diabetes, hyperlipidaemia, and non-alcoholic fatty liver disease. Constitutive androstane receptor (CAR) and liver X receptors (LXRs) were also reported as potential therapeutic targets for the treatment of obesity and atherosclerosis, respectively. Further clarification of the internal relationships between these three lipid metabolic nuclear receptors is necessary to enable drug discovery. In this review, we mainly summarized the cross-talk of PPARs-CAR in obesity and PPARs-LXRs in atherosclerosis.

DBZ is a putative PPARγ agonist that prevents high fat diet-induced obesity, insulin resistance and gut dysbiosis.

BACKGROUND: The nuclear receptor PPARγ is an effective pharmacological target for some types of metabolic syndrome, including obesity, diabetes, nonalcoholic fatty liver disease, and cardiovascular disease. However, the current PPARγ-targeting thiazolidinedione drugs have undesirable side effects. Danshensu Bingpian Zhi (DBZ), also known as tanshinol borneol ester derived from Salvia miltiorrhiza, is a synthetic derivative of natural compounds used in traditional Chinese medicine for its anti-inflammatory activity. METHODS: In vitro, investigations of DBZ using a luciferase reporter assay and molecular docking identified this compound as a novel promising PPARγ agonist. Ten-week-old C57BL/6J mice were fed either a normal chow diet (NCD) or a high-fat diet (HFD). The HFD-fed mice were gavaged daily with either vehicle or DBZ (50mg/kg or 100mg/kg) for 10weeks. The gut microbiota composition was assessed by analyzing the 16S rRNA gene V3+V4 regions via pyrosequencing. RESULTS: DBZ is an efficient natural PPARγ agonist that shows lower PPARγ-responsive luciferase reporter activity than thiazolidinediones, has excellent effects on the metabolic phenotype and exhibits no unwanted adverse effects in a HFD-induced obese mouse model. DBZ protects against HFD-induced body weight gain, insulin resistance, hepatic steatosis and inflammation in mice. DBZ not only stimulates brown adipose tissue (BAT) browning and maintains intestinal barrier integrity but also reverses HFD-induced intestinal microbiota dysbiosis. CONCLUSIONS: DBZ is a putative PPARγ agonist that prevents HFD-induced obesity-related metabolic syndrome and reverse gut dysbiosis. GENERAL SIGNIFICANCE: DBZ may be used as a beneficial probiotic agent to improve HFD-induced obesity-related metabolic syndrome in obese individuals.

Melatonin prevents obesity through modulation of gut microbiota in mice.

Excess weight and obesity are severe public health threats worldwide. Recent evidence demonstrates that gut microbiota dysbiosis contributes to obesity and its comorbidities. The body weight-reducing and energy balancing effects of melatonin have been reported in several studies, but to date, no investigations toward examining whether the beneficial effects of melatonin are associated with gut microbiota have been carried out. In this study, we show that melatonin reduces body weight, liver steatosis, and low-grade inflammation as well as improving insulin resistance in high fat diet (HFD)-fed mice. High-throughput pyrosequencing of the 16S rRNA demonstrated that melatonin treatment significantly changed the composition of the gut microbiota in mice fed an HFD. The richness and diversity of gut microbiota were notably decreased by melatonin. HFD feeding altered 69 operational taxonomic units (OTUs) compare with a normal chow diet (NCD) group, and melatonin supplementation reversed 14 OTUs to the same configuration than those present in the NCD group, thereby impacting various functions, in particular through its ability to decrease the Firmicutes-to-Bacteroidetes ratio and increase the abundance of mucin-degrading bacteria Akkermansia, which is associated with healthy mucosa. Taken together, our results suggest that melatonin may be used as a probiotic agent to reverse HFD-induced gut microbiota dysbiosis and help us to gain a better understanding of the mechanisms governing the various melatonin beneficial effects.

RORα inhibits adipocyte-conditioned medium-induced colorectal cancer cell proliferation and migration and chick embryo chorioallantoic membrane angiopoiesis.

Lipid metabolic disturbances are related to many diseases, such as obesity, diabetes, and certain cancers. Notably, lipid metabolic disturbances have been reported to be a risk factor for colorectal cancer. Nuclear receptors act as ligand-dependent transcription regulators and play key roles in the regulation of body lipid metabolism and the development of many cancers. Retinoic acid receptor-related orphan receptor α (RORα) is a nuclear receptor and can regulate several lipid metabolism genes in certain cancers. Herein, we demonstrate that the conditioned medium from adipocytes has a proproliferative and promigratory effect on colorectal cancer cells and enhances angiogenesis in chicken embryonic chorioallantoic membranes. In addition, the conditioned medium leads to a decrease in the expression of RORα and its target genes. Meanwhile, RORα and its target gene expressions are lower in human colorectal tumor tissue compared with control colorectal tissue. Activation of RORα inhibits the effect of conditioned medium on the proliferation and migration of colorectal cancer cells as well as the angiogenesis in chicken embryonic allantoic membranes. In colorectal cancer cells, the putative ligand of RORα, cholesterol sulfate (CS), prevents cell cycle progression at the G1/S boundary and concurrently modulates the expression of cell cycle-regulatory genes in colorectal cancer cell. CS inhibits angiogenesis in chicken embryonic chorioallantoic membranes and concurrently decreases the mRNA expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α as well as the secretion of VEGF. In addition, lipogenic gene expression is higher in human colorectal tumor tissue compared with control colorectal tissue. CS inhibits the expression of lipogenic genes in colorectal cancer cells. These results suggest that RORα could represent a direct link between local lipid metabolism of colorectal tissue and colorectal cancer. Therefore, the reduction of the expression of RORα could represent a potential warning sign of colorectal cancer.

Comparative gene identification-58 (CGI-58) promotes autophagy as a putative lysophosphatidylglycerol acyltransferase.

CGI-58 is a lipid droplet-associated protein that, when mutated, causes Chanarin-Dorfman syndrome in humans, which is characterized by excessive storage of triglyceride in various tissues. However, the molecular mechanisms underlying the defect remain elusive. CGI-58 was previously reported to catalyze the resynthesis of phosphatidic acid as a lysophosphatidic acid acyltransferase. In addition to triglyceride, phosphatidic acid is also used a substrate for the synthesis of various mitochondrial phospholipids. In this report, we investigated the propensity of CGI-58 in the remodeling of various phospholipids. We found that the recombinant CGI-58 overexpressed in mammalian cells or purified from Sf9 insect cells catalyzed efficiently the reacylation of lysophosphatidylglycerol to phosphatidylglycerol (PG), which requires acyl-CoA as the acyl donor. In contrast, the recombinant CGI-58 was devoid of acyltransferase activity toward other lysophospholipids. Accordingly, overexpression and knockdown of CGI-58 adversely affected the endogenous PG level in C2C12 cells. PG is a substrate for the synthesis of cardiolipin, which is required for mitochondrial oxidative phosphorylation and mitophagy. Consequently, overexpression and knockdown of CGI-58 adversely affected autophagy and mitophagy in C2C12 cells. In support for a key role of CGI-58 in mitophagy, overexpression of CGI-58 significantly stimulated mitochondrial fission and translocation of PINK1 to mitochondria, key steps involved in mitophagy. Furthermore, overexpression of CGI-58 promoted mitophagic initiation through activation of 5'-AMP-activated protein kinase and inhibition of mTORC1 mammalian target of rapamycin complex 1 signaling, the positive and negative regulators of autophagy, respectively. Together, these findings identified novel molecular mechanisms by which CGI-58 regulates lipid homeostasis, because defective autophagy is implicated in dyslipidemia and fatty liver diseases.

Monoacylglycerol acyltransferase-2 is a tetrameric enzyme that selectively heterodimerizes with diacylglycerol acyltransferase-1.

Acyl-CoA:monoacylglycerol acyltransferases (MGATs) and diacylglycerol acyltransferases (DGATs) catalyze the two consecutive steps in the synthesis of triacylglycerol, a key process required for dietary fat absorption into the enterocytes of the small intestine. In this report, we investigated the tendency of MGAT2 to form an enzyme complex with DGAT1 and DGAT2 in intact cells. We demonstrated that in addition to the 38-kDa monomer of the MGAT2 enzyme predicted by its peptide sequence, a 76-kDa moiety was detected in SDS-PAGE without reducing agent and heat inactivation. The 76-kDa MGAT2 moiety was greatly enhanced by treatment with a cross-linking reagent in intact cells. Additionally, the cross-linking reagent dose-dependently yielded a band corresponding to the tetramer (152 kDa) in SDS-PAGE, suggesting that the MGAT2 enzyme primarily functions as a homotetrameric protein and as a tetrameric protein. Likewise, DGAT1 also forms a homodimer under nondenaturing conditions. When co-expressed in COS-7 cells, MGAT2 heterodimerized with DGAT1 without treatment with a cross-linking reagent. MGAT2 also co-eluted with DGAT1 on a gel filtration column, suggesting that the two enzymes form a complex in intact cells. In contrast, MGAT2 did not heterodimerize with DGAT2 when co-expressed in COS-7 cells, despite high sequence homology between the two enzymes. Furthermore, systematic deletion analysis demonstrates that N-terminal amino acids 35-80 of DGAT1, but not a signal peptide at the N terminus of MGAT2, is required for the heterodimerization. Finally, co-expression of MGAT2 with DGAT1 significantly increased lipogenesis in COS-7 cells, indicating the functional importance of the dimerization.

Synthesis of bifunctional molecules containing [12]aneN3 and coumarin moieties as effective DNA condensation agents and new non-viral gene vectors.

A series of bifunctional molecules with different combinations of macrocyclic polyamine [12]aneN3 and coumarin moieties, 4a/b and 5a/b, were synthesized by a two-step copper(I)-mediated alkyne­azide click reactions between 1,3,5-tris(azidomethyl)benzene and Boc-protected N-propynyl-[12]aneN3/7-propynyloxycoumarins. Agarose gel electrophoresis experiments indicated that bifunctional molecules 4b and 5b effectively induced complete plasmid DNA condensation at concentrations up to 40 µM. It was found that the structural variation had a major impact on the condensation behavior of these compounds. The electrostatic interaction involving the [12]aneN3 moiety can be compensated by the binding contribution of the coumarin units during the DNA condensation process. These two types of interaction showed different effects on the reversibility of DNA condensation. Results from studies using dynamic laser scattering, atomic force microscopy, and EB replacement assay further supported the above conclusion. Cytotoxicity assays on bifunctional compounds 4a/b and 5a/b indicated their low cytotoxicity. Results from cellular uptake and cell transfection experiments proved that bifunctional compounds 4b and 5b successfully served as non-viral gene vectors. Furthermore, methyl substituents attached to the coumarin unit (4b and 5b) greatly enhanced their DNA condensation capability and gene transfection. These bifunctional molecules, with the advantages of lower cytotoxicity, good water solubility, and potential structural modification, will have great potential for the development of new non-viral gene delivery agents.

Celastrol inhibits store operated calcium entry and suppresses psoriasis.

Introduction: Psoriasis is an inflammatory autoimmune skin disease that is hard to cure and prone to relapse. Currently available global immunosuppressive agents for psoriasis may cause severe side effects, thus it is crucial to identify new therapeutic reagents and druggable signaling pathways for psoriasis. Methods: To check the effects of SOCE inhibitors on psoriasis, we used animal models, biochemical approaches, together with various imaging techniques, including calcium, confocal and FRET imaging. Results and discussion: Store operated calcium (Ca2+) entry (SOCE), mediated by STIM1 and Orai1, is crucial for the function of keratinocytes and immune cells, the two major players in psoriasis. Here we showed that a natural compound celastrol is a novel SOCE inhibitor, and it ameliorated the skin lesion and reduced PASI scores in imiquimod-induced psoriasis-like mice. Celastrol dose- and time-dependently inhibited SOCE in HEK cells and HaCaT cells, a keratinocyte cell line. Mechanistically, celastrol inhibited SOCE via its actions both on STIM1 and Orai1. It inhibited Ca2+ entry through constitutively-active Orai1 mutants independent of STIM1. Rather than blocking the conformational switch and oligomerization of STIM1 during SOCE activation, celastrol diminished the transition from oligomerized STIM1 into aggregates, thus locking STIM1 in a partially active state. As a result, it abolished the functional coupling between STIM1 and Orai1, diminishing SOCE signals. Overall, our findings identified a new SOCE inhibitor celastrol that suppresses psoriasis, suggesting that SOCE pathway may serve as a new druggable target for treating psoriasis.

Activation of liver X receptor increases acetaminophen clearance and prevents its toxicity in mice.

UNLABELLED: Overdose of acetaminophen (APAP), the active ingredient of Tylenol, is the leading cause of drug-induced acute liver failure in the United States. As such, it is necessary to develop novel strategies to prevent or manage APAP toxicity. In this report, we reveal a novel function of the liver X receptor (LXR) in preventing APAP-induced hepatotoxicity. Activation of LXR in transgenic (Tg) mice or by an LXR agonist conferred resistance to the hepatotoxicity of APAP, whereas the effect of LXR agonist on APAP toxicity was abolished in LXR-deficient mice. The increased APAP resistance in LXR Tg mice was associated with increased APAP clearance, increased APAP sulfation, and decreased formation of toxic APAP metabolites. The hepatoprotective effect of LXR may have resulted from the induction of antitoxic phase II conjugating enzymes, such as Gst and Sult2a1, as well as the suppression of protoxic phase I P450 enzymes, such as Cyp3a11 and Cyp2e1. Promoter analysis suggested the mouse Gst isoforms as novel transcriptional targets of LXR. The suppression of Cyp3a11 may be accounted for by the inhibitory effect of LXR on the PXR-responsive transactivation of Cyp3a11. The protective effect of LXR in preventing APAP toxicity is opposite to the sensitizing effect of pregnane X receptor, constitutive androstane receptor, and retinoid X receptor alpha. CONCLUSION: We conclude that LXR represents a potential therapeutic target for the prevention and treatment of Tylenol toxicity.

Therapeutic potential of melatonin in colorectal cancer: Focus on lipid metabolism and gut microbiota.

Colorectal cancer (CRC) is one of the most common gastrointestinal malignancies. The occurrence and development of CRC are complicated processes. Obesity and dysbacteriosis have been increasingly regarded as the main risk factors for CRC. Understanding the etiology of CRC from multiple perspectives is conducive to screening for some potential drugs or new treatment strategies to limit the serious side effects of conventional treatment and prolong the survival of CRC patients. Melatonin, a natural indoleamine, is mainly produced by the pineal gland, but it is also abundant in other tissues, including the gastrointestinal tract, retina, testes, lymphocytes, and Harder's glands. Melatonin could participate in lipid metabolism by regulating adipogenesis and lipolysis. Additionally, many studies have focused on the potential beneficial effects of melatonin in CRC, such as promotion of apoptosis; inhibition of cell proliferation, migration, and invasion; antioxidant activity; and immune regulation. Meaningfully, gut microbiota is the main determinant of all aspects of health and disease (including obesity and tumorigenesis). The gut microbiota is of great significance for understanding the relationship between obesity and increased risk of CRC. Although the current understanding of how the melatonin-mediated gut microbiota coordinates a variety of physiological and pathological activities is fairly comprehensive, there are still many unknown topics to be explored in the face of a complex nutritional status and a changeable microbiota. This review summarizes the potential links among melatonin, lipid metabolism, gut microbiota, and CRC to promote the development of melatonin as a preventive and therapeutic agent for CRC.

p15RS attenuates Wnt/{beta}-catenin signaling by disrupting {beta}-catenin·TCF4 Interaction.

The formation of a ß-catenin·TCF4 complex in the nucleus of cells is well known as a prerequisite for the transcription of Wnt target genes. Although many co-factors have been identified to regulate the activity of the ß-catenin·TCF4 complex, it remains unclear how the complex association is negatively regulated. In this study, we report that p15RS, a negative regulator of the cell cycle, blocks ß-catenin·TCF4 complex formation and inhibits Wnt signaling. We observed that p15RS interacts with ß-catenin and TCF4. Interestingly, whereas the interaction of p15RS with ß-catenin is increased, its interaction with TCF4 is decreased upon Wnt1 stimulation. Moreover, overexpression of p15RS reduces the interaction of ß-catenin with TCF4, whereas the depletion of p15RS enhances their interaction. We further demonstrate that overexpression of p15RS suppresses canonical Wnt signaling and results in retarded cell growth, whereas depletion of p15RS shows an enhanced effect on Wnt signaling. We analyzed that inhibition of Wnt signaling by p15RS leads to decreased expression of CYCLIN D1 and c-MYC, two Wnt targeted genes critical for cell growth. Our data suggest that p15RS inhibits Wnt signaling by interrupting ß-catenin·TCF4 complex formation and that Wnt signaling initiates downstream gene expression by removing p15RS from promoters.