👤 Won-A Joo

Current therapeutic approaches for Alzheimer's disease (AD) demonstrate limited efficacy and fail to address disease progression. In the present study, we present HSN-G1, a novel ginsenoside-enriched pharmaceutical formulation that employs a dual-target mechanism through the modulation of amyloid clearance pathways and cholinergic neurotransmission. HSN-G1 demonstrates a reproducible ginsenoside profile enriched with Re (33.27 mg/g), Rd (25.00 mg/g), and Rg3 stereoisomers (12.18 mg/g), ensuring pharmaceutical-grade reproducibility. HSN-G1 enhanced amyloid-beta (Aβ) clearance in microglial cells, with significantly greater effects observed in SRA-overexpressing cells, suggesting SRA-dependent clearance mechanisms. In APP/PS1 transgenic mice, six-week oral administration of HSN-G1 (100-400 mg/kg) elicited significant dose-dependent improvements in cognitive performance. Male mice exhibited more stable and consistent enhancements in both passive avoidance and spatial memory tests compared to vehicle controls (p < 0.001), while both sexes demonstrated comparable reductions in brain Aβ levels (approximately 45%) and differential increases in acetylcholine (73% in males; 55% in females, p < 0.01). HSN-G1 administration enhanced the expression of neurotrophic factors, with NGF upregulation predominantly observed in males, whereas BDNF, CNTF, and GDNF were consistently elevated across both sexes. These findings establish HSN-G1 as a promising disease-modifying agent with standardized composition and therapeutic efficacy, surpassing the limitations of conventional single-target approaches. The superior efficacy of HSN-G1 compared to existing treatments validates its potential for clinical development, highlighting the significance of sex-specific therapeutic responses in future AD therapeutics. Show less

BackgroundEpigenetic age acceleration (EAA) refers to the extent to which an individual's biological age, estimated from DNA methylation patterns, exceeds their chronological age, indicating accelerated cellular and tissue aging.ObjectiveWe investigated the association between EAA and Alzheimer's disease (AD), with a focus on sex-based differences.MethodsEAA was estimated from blood samples in 127 participants with Alzheimer's disease-related cognitive impairment (ADCI) and 143 cognitively unimpaired (CU) participants, recruited from a nationwide multicenter study under the Precision Medicine Platform for Mild Cognitive Impairment (PREMIER) consortium in Korea.ResultsEAA measures indicated higher acceleration in the ADCI group compared to the CU group, particularly for extrinsic epigenetic age acceleration (EEAA), AgeAccelResidualHannum, and AgeAccelPheno. Sex-specific analyses revealed that EEAA significantly differed between the ADCI and CU groups in both men and women, with a greater EEAA in men. Logistic regression analysis demonstrated that increased EEAA, the presence of Show less

Atherosclerosis, a chronic inflammatory disease, presents significant "residual risk" even with effective lipid-lowering therapies, primarily due to persistent vascular inflammation. Apolipoprotein B100 (ApoB100) acquires pro-inflammatory properties upon modification and binds to cell-surface enolase 1 (ENO1), an immune modulator upregulated in inflammatory conditions. This interaction induces inflammatory responses via NF-κB activation. Targeting the ApoB100-ENO1 interaction may offer a novel strategy to reduce vascular inflammation and atherosclerosis progression. We developed PP3m, a stabilized ApoB100-derived peptide, to selectively inhibit the ApoB100-ENO1 interaction. Single-cell RNA sequencing (scRNA-seq) data from human atherosclerotic plaques were reanalyzed to characterize ENO1 expression in myeloid cells. In vitro, PP3m's anti-inflammatory effects were evaluated across various macrophage models stimulated by diverse inflammatory stimuli. Outcomes included cytokine secretion, inflammatory gene expression, foam cell formation, oxidized low-density lipoprotein (oxLDL) uptake, and signaling pathways activation. In vivo, Ldlr scRNA-seq analysis revealed that human atherosclerotic plaques harbor significantly more ENO1 macrophages, with ENO1 expression enriched in CD68 The ApoB100-ENO1 axis is a critical driver of macrophage-mediated inflammation in atherosclerosis. The novel peptide PP3m effectively inhibits this interaction, reducing vascular inflammation and plaque progression without altering lipid levels. PP3m represents a promising therapeutic candidate for cardiovascular disease by targeting residual inflammatory risk through a lipid-independent mechanism. Show less

Dual specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is associated with the pathoprogression of neurodevelopmental and neurodegenerative disorders. However, the effects of direct genetic manipulation of DYRK1A in the brain on cognitive function, neuroinflammation and Alzheimer's disease (AD) pathology and underlying molecular mechanisms have not been fully investigated. To determine whether overexpressing or knocking down DYRK1A expression directly in the brain affects cognitive function, neuroinflammation and AD pathology, adeno-associated viruses (AAVs) were injected into the hippocampus of wild-type (WT), 5xFAD, and PS19 mice. Then, cognitive function was assessed via Y-maze and novel object recognition (NOR) tests, and neuroinflammatory responses and AD pathologies were analyzed by real-time PCR, Western blotting, immunofluorescence staining, AD-associated protein activity assays and ELISA. In WT mice, hippocampal DYRK1A overexpression significantly reduced short-term spatial/recognition memory and SynGAP expression while increasing p-P38 levels. Conversely, in amyloid-beta (Aβ)-overexpressing 5xFAD mice, hippocampal DYRK1A knockdown improved short-term spatial/recognition memory and significantly increased CaMKIIα and CREB phosphorylation. Moreover, hippocampal DYRK1A knockdown in 5xFAD mice significantly suppressed mRNA levels of proinflammatory cytokines and markers of AD-associated reactive astrocytes (RAs), disease-associated microglia (DAMs), and RA-DAM interactions. However, hippocampal DYRK1A overexpression in 5xFAD mice increased mRNA levels of the proinflammatory cytokine IL-1β, RA markers and the microglial marker Iba-1. Interestingly, hippocampal DYRK1A knockdown in 5xFAD mice significantly increased levels of the anti-oxidative/inflammatory molecule HO-1 without altering p-STAT3/p-NF-κB levels. By contrast, hippocampal DYRK1A overexpression in 5xFAD mice enhanced STAT3/NF-κB phosphorylation but did not affect ROS levels. Importantly, hippocampal DYRK1A knockdown in 5xFAD mice significantly reduced Aβ plaque number, soluble Aβ40 levels, and soluble/insoluble Aβ42 levels by suppressing β-secretase BACE1 activity but not tau hyperphosphorylation. Finally, hippocampal DYRK1A knockdown in PS19 mice [a model of AD that overexpresses human mutant tau (P301S)] selectively decreased insoluble tau hyperphosphorylation at Ser396 and Ser404 and alleviated proinflammatory responses/glial-associated neuroinflammatory dynamics. Taken together, our data indicate that DYRK1A modulates cognitive function, neuroinflammation, and AD pathology (Aβ and tauopathy) in mouse models of AD and/or WT mice and support DYRK1A as a potential therapeutic target for AD. Show less

Previous studies have reported that 40 Hz visual stimulation (acute white light exposure) reduced Aβ levels in Alzheimer's disease (AD) mouse model. However, whether different light colors distinctly regulate AD pathologies has not been well characterized. In the present study, an optimized organic light-emitting diode (OLED)-based visual stimulation platform was developed to provide uniform illumination without blind spots, and the color-dependent effects on cognitive function and amyloid-β (Aβ) pathology were investigated in 5xFAD mice, an Aβ-overexpressing AD model. Acute exposure to white or red OLED light (1 h/day for 2 days) significantly improved cognitive function, reduced hippocampal Aβ plaque accumulation via increasing ADAM17 activity, and downregulated proinflammatory cytokine IL-1β levels in 3-month-old 5xFAD mice, whereas green or blue OLED light did not produce these effects. In addition, chronic white and red OLED stimulation (1 h/day for 2 weeks) was shown to enhance recognition memory; however, only red light further diminished Aβ plaque deposition by upregulating ADAM17 activity and suppressing BACE-1 activity without altering neuroinflammation in 6-month-old 5xFAD mice. Moreover, acute white and red OLED exposure (1 h, single session) was observed to enhance c-fos expression, which is associated with neural activation along the visual pathway, thereby suggesting a mechanistic link between light stimulation and cognitive enhancement. Taken together, these findings demonstrate that color-dependent visual stimulation may serve as a promising electroceutical strategy for AD, with red light uniquely combining memory enhancement, Aβ reduction via ADAM17 upregulation and BACE1 suppression, and anti-inflammatory effects. Show less

Brain death induces systemic inflammation and hemodynamic changes that can lead to lung injury, impacting the quality of donor organs for transplantation. Extracellular vesicles (EVs) are cell-derived nanoparticles that carry functional biomolecules and reflect the physiological state of their cells of origin. We hypothesized that EVs from brain-dead donors may indicate lung injury and may be used to predict primary graft dysfunction (PGD) in lung transplant recipients. We performed transcriptomic profiling of plasma EVs from 44 brain-dead lung donors and 9 healthy controls using next-generation sequencing. Differential gene expression was assessed, followed by pathway enrichment analyses. The results were validated by quantitative polymerase chain reaction using the study cohort and an independent cohort. Variable importance of projection score analysis and regression models were used to identify EV transcripts associated with PGD in recipients. Transcriptomic analysis revealed that 13% of protein-coding genes were differentially expressed in lung donor EVs compared with controls, with 92% of these genes upregulated. Upregulated genes were enriched in pathways related to inflammation, coagulation, tissue remodeling, and metabolism. Seven key EV transcripts, RAD51D, ABL2, FGFR1, WDR82, PTBP3, OPRL1, and XG were identified as potential PGD indicator. These transcripts were associated with processes such as DNA damage repair, signal transduction, and inflammation, which may contribute to posttransplant lung injury. Donor plasma EVs carry distinct transcriptomic signatures associated with injury and inflammation. Specific EV transcripts, such as RAD51D and XG, hold promise as independent predictive biomarkers for PGD, possibly providing new tools for evaluating donor organ quality and improving lung transplant outcomes. Show less

We used next-generation sequencing (NGS) to investigate the genetic causes of suspected genetic short stature in 37 patients, and we describe their phenotypes and various genetic spectra. We reviewed the medical records of 50 patients who underwent genetic testing using NGS for suspected genetic short stature from June 2019 to December 2022. Patients with short stature caused by nongenetic factors or common chromosomal abnormalities were excluded. Thirty-seven patients from 35 families were enrolled in this study. We administered one of three genetic tests (2 targeted panel tests or whole exome sequencing) to patients according to their phenotypes. Clinical and molecular diagnoses were confirmed in 15 of the 37 patients, for an overall diagnostic yield of 40.5%. Fifteen pathogenic/likely pathogenic variants were identified in 13 genes (ACAN, ANKRD11, ARID1B, CEP152, COL10A1, COL1A2, EXT1, FGFR3, NIPBL, NRAS, PTPN11, SHOX, SLC16A2). The diagnostic rate was highest in patients who were small for their gestational age (7 of 11, 63.6%). Genetic evaluation using NGS can be helpful in patients with suspected genetic short stature who have clinical and genetic heterogeneity. Further studies are needed to develop patient selection algorithms and panels containing growth-related genes. Show less

Carbohydrate-responsive element-binding protein (ChREBP) is a transcription factor that regulates several metabolic genes, including the lipogenic enzymes necessary for the metabolic conversion of carbohydrates into lipids. Although the crucial role of ChREBP in the liver, the primary site of de novo lipogenesis, has been studied, its functional role in adipose tissues, particularly brown adipose tissue (BAT), remains unclear. In this study, we investigated the role of ChREBP in BAT under conditions of a high-carbohydrate diet (HCD) and ketogenic diet (KD), represented by extremely low carbohydrate intake. Using an adeno-associated virus and Cas9 knock-in mice, we rapidly generated Chrebp brown adipocyte-specific knock-out (B-KO) mice, bypassing the necessity for prolonged breeding by using the Cre-Lox system. We demonstrated that ChREBP is essential for glucose metabolism and lipogenic gene expression in BAT under HCD conditions in Chrebp B-KO mice. After nutrient intake, Chrebp B-KO attenuated the KD-induced expression of several inflammatory genes in BAT. Our results indicated that ChREBP, a nutrient-sensing regulator, is indispensable for expressing a diverse range of metabolic genes in BAT. Show less

Depressive mood is a major psychiatric symptom that causes serious disturbances in daily life. Unlike physical symptoms, psychiatric symptoms are more difficult to evaluate objectively. Therefore, we aimed to discover biomarkers that reflect changes in serum protein metabolism during a clinical depressive mood. Serum protein profiling was conducted in participants who were not experiencing a current depressive episode (healthy individuals and patients in remission). Serum proteins were identified and quantified using liquid chromatography-tandem mass spectrometry. Differentially expressed proteins with a Apolipoprotein A-IV levels were lower in the group with a current episode of depression than in the remission and healthy control groups. Further, fibronectin levels were also lower in the group with a current episode of depression than in the healthy control group but not in the remission group. We found that apolipoprotein A-IV-mediated inflammation is involved in clinical depressive moods, possibly by inducing neurological changes in the brain. Therefore, apolipoprotein A-IV and fibronectin levels may be explored as potentially novel biomarkers for detecting a current episode of depression. Show less

Fat accumulation results from increased fat absorption and/or defective fat metabolism. Currently, the lipid-sensing nuclear receptor that controls fat utilization in hepatocytes is elusive. Liver X receptor alpha (LXRα) promotes accumulation of lipids through the induction of several lipogenic genes. However, its effect on lipid degradation is open for study. Here, we investigated the inhibitory role of LXRα in autophagy/lipophagy in hepatocytes and the underlying basis. In LXRα knockout mice fed a high-fat diet, or cell models, LXRα activation suppressed the function of mitochondria by inhibiting autophagy/lipophagy and induced hepatic steatosis. Gene sets associated with "autophagy" were enriched in hepatic transcriptome data. Autophagy flux was markedly augmented in the LXRα knockout mouse liver and primary hepatocytes. Mechanistically, LXRα suppressed autophagy-related 4B cysteine peptidase (ATG4B) and Rab-8B, responsible for autophagosome and -lysosome formation, by inducing let-7a and microRNA (miR)-34a. Chromatin immunoprecipitation assay enabled us to find LXRα as a transcription factor of let-7a and miR-34a. Moreover, 3' untranslated region luciferase assay substantiated the direct inhibitory effects of let-7a and miR-34a on ATG4B and Rab-8B. Consistently, either LXRα activation or the let-7a/miR-34a transfection lowered mitochondrial oxygen consumption rate and mitochondrial transmembrane potential and increased fat levels. In obese animals or nonalcoholic fatty liver disease (NAFLD) patients, let-7a and miR-34a levels were elevated with simultaneous decreases in ATG4B and Rab-8B levels. LXRα inhibits autophagy in hepatocytes through down-regulating ATG4B and Rab-8B by transcriptionally activating microRNA let-7a-2 and microRNA 34a genes and suppresses mitochondrial biogenesis and fuel consumption. This highlights a function of LXRα that culminates in the progression of liver steatosis and steatohepatitis, and the identified targets may be applied for a therapeutic strategy in the treatment of NAFLD. Show less

Although epidemiological studies have shown that obesity is associated with increased incidence of hypertension during pregnancy, the mechanisms linking these two comorbidities are not as well studied. Previous investigations detected lower levels of the anti-hypertensive and pregnancy-related factor, placental growth factor (PlGF), in obese hypertensive pregnancies. Therefore, we examined whether obese hypertensive pregnant rats have reduced PlGF and whether increasing its levels by administering recombinant human (rh)PlGF reduces their blood pressure. We utilized a genetic model of obesity characterized to be heavier, hypertensive and fertile, namely rats having heterozygous deficiency of the melanocortin-4 receptor (MC4R-def). MC4R-def obese rats had lower circulating levels of PlGF than wild-type lean controls at gestational day 19. Also, assessment of the PlGF receptor, Flt-1, in the vasculature showed that its levels were reduced in aorta and kidney glomeruli but increased in small mesenteric arteries. Chronic intraperitoneal administration of rhPlGF from gestational day 13-19 significantly increased circulating PlGF levels in both obese and lean rats, but reduced blood pressure only in the obese pregnant group. The rhPlGF treatment did not alter maternal body and fat masses or circulating levels of the adipokines, leptin and adiponectin. In addition, this treatment did not impact average foetal weights but increased placental weights regardless of obese or lean pregnancy. PlGF is reduced in MC4R-def obese hypertensive pregnant rats, which is similar to findings in obese hypertensive pregnant women, while increasing its levels with exogenous rhPlGF reduces their blood pressure. Show less

Glucose-dependent insulinotropic polypeptide (GIP) is released during meals and promotes nutrient uptake and storage. GIP receptor knockout mice are protected from diet induced weight gain and thus GIP antagonists have been proposed as a treatment for obesity. In this study, we assessed the role of GIP in hyperphagia induced obesity and metabolic abnormalities in leptin deficient (Lep We crossbred GIP-GFP knock-in homozygous mice (GIP Postprandial GIP levels were markedly elevated in Lep Our results indicate that GIP knockout does not prevent excess weight gain and metabolic derangement in hyperphagic leptin deficient mice. Show less

Gastric inhibitory polypeptide receptor (GIPR) directly induces energy accumulation in adipose tissue in vitro. However, the importance of the direct effect of GIPR signaling on adipose tissue in vivo remains unclear. In the current study, we generated adipose tissue-specific GIPR knockout (GIPR Show less

Data regarding biomarkers to understand disease pathogenesis and to assess disease activity of intestinal Behçet's disease (BD) are limited. Therefore, we aimed to investigate the differentially expressed proteins in sera from patients with intestinal BD and to search for biomarkers using mass spectrometry-based proteomic analysis. Serum samples were pooled for the screening study, and two-dimensional electrophoresis (2-DE) was performed to characterize the proteins present in intestinal BD patients. Candidate protein spots were identified using matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF/TOF MS) and bioinformatic analysis. To validate the proteomic results, serum samples from an independent cohort were assessed by enzyme-linked immunosorbent assay. Pooled serum samples were used for 2-DE, and approximately 400 protein spots were detected in the sera of intestinal BD patients. Of the 22 differentially expressed proteins, 3 were successfully identified using MALDI-TOF/TOF MS. The three up-regulated proteins identified in the intestinal BD group included fibrin, apolipoprotein A-IV, and serum amyloid A (SAA). Serum SAA in intestinal BD patients (2.76 ± 2.50 ng/ml) was significantly higher than that in controls (1.68 ± 0.90 ng/ml, p = 0.007), which is consistent with the proteomic results. In addition, the level of IL-1β in patients with intestinal BD (8.96 ± 1.23 pg/ml) was higher than that in controls (5.40 ± 0.15 pg/ml, p = 0.009). SAA released by HT-29 cells was markedly increased by tumor necrosis factor-α (TNF-α) and lipopolysaccharides stimulation. Our proteomic analysis revealed that SAA was up-regulated in intestinal BD patients. Show less

Excess carbohydrate intake causes obesity in humans. On the other hand, acute administration of fructose, glucose or sucrose in experimental animals has been shown to increase the plasma concentration of anti-obesity hormones such as glucagon-like peptide 1 (GLP-1) and Fibroblast growth factor 21 (FGF21), which contribute to reducing body weight. However, the secretion and action of GLP-1 and FGF21 in mice chronically fed a high-sucrose diet has not been investigated. To address the role of anti-obesity hormones in response to increased sucrose intake, we analyzed mice fed a high-sucrose diet, a high-starch diet or a normal diet for 15 weeks. Mice fed a high-sucrose diet showed resistance to body weight gain, in comparison with mice fed a high-starch diet or control diet, due to increased energy expenditure. Plasma FGF21 levels were highest among the three groups in mice fed a high-sucrose diet, whereas no significant difference in GLP-1 levels was observed. Expression levels of uncoupling protein 1 (UCP-1), FGF receptor 1c (FGFR1c) and β-klotho (KLB) mRNA in brown adipose tissue were significantly increased in high sucrose-fed mice, suggesting increases in FGF21 sensitivity and energy expenditure. Expression of carbohydrate responsive element binding protein (ChREBP) mRNA in liver and brown adipose tissue was also increased in high sucrose-fed mice. These results indicate that FGF21 production in liver and brown adipose tissue is increased in high-sucrose diet and participates in resistance to weight gain. Show less

The dual-specificity phosphatase 6 (DUSP6) gene resides at chromosome location 12q22-23, which is one of the candidate loci for susceptibility to bipolar disorder and which encodes a phosphatase selective for extracellular signal-regulated kinase (ERK). Previously, we reported a positive association between the functional Leu114Val polymorphism (rs2279574) in DUSP6 and bipolar disorder. Given that the association between DUSP6 and the reported down-regulation of DUSP6 transcript in bipolar postmortem brains were sex-dimorphic, showing significance in women but not men, we performed two independent analyses in homogenous samples of male and female Korean patients with bipolar disorder or schizophrenia using samples enlarged from our previous report. Among the examined DUSP6 SNPs, five (rs769700, rs704076, rs770087, rs808820, and rs2279574) showed positive allelic associations, with the frequency of minor alleles (C, T, G, G, and G) in each SNP significantly increased in women with BD. Consequently, the "C-T-G-G-G" haplotype was significantly over-represented (P=0.016; OR=3.242), whereas the "T-G-T-A-T" haplotype was significantly under-represented (P=0.014; OR=0.697). We found no significant associations with DUSP6 SNPs in men with bipolar disorder or schizophrenia. We also investigated the functions of the functional SNPs' positive associations and found that Leu114Val (rs2279574; T/G) and Ser144Ala (rs770087; T/G) mutations in DUSP6 proteins reduced lithium-induced ERK1/2 phosphorylation in vitro, implicating the dominant active functions. Thus, DUSP6 may not only play important roles in the pathogenesis of bipolar disorder, particularly in women, but also affect the therapeutic response to lithium through modulating lithium's effects on intracellular signaling. Show less

Niemann Pick disease type C1 (NPC) is an autosomal recessive disease characterized by progressive neurological deterioration leading to premature death. In this study, we hypothesized that human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) have the multifunctional abilities to ameliorate NPC symptoms in the brain. To test this hypothesis, hUCB-MSCs were transplanted into the hippocampus of NPC mice in the early asymptomatic stage. This transplantation resulted in the recovery of motor function in the Rota Rod test and impaired cholesterol homeostasis leading to increased levels of cholesterol efflux-related genes such as LXRα, ABCA1, and ABCG5 while decreased levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase were observed in NPC mice. In the cerebrum, hUCB-MSCs enhanced neuronal cell survival and proliferation, where they directly differentiated into electrically active MAP2-positive neurons as demonstrated by whole-cell patch clamping. In addition, we observed that hUCB-MSCs reduced Purkinje neuronal loss by suppression of inflammatory and apoptotic signaling in the cerebellum as shown by immunohistochemistry. We further investigated how hUCB-MSCs enhance cellular survival and inhibit apoptosis in NPC mice. Neuronal cell survival was associated with increased PI3K/AKT and JAK2/STAT3 signaling; moreover, hUCB-MSCs modulated the levels of GABA/glutamate transporters such as GAT1, EAAT2, EAAT3, and GAD6 in NPC mice as assessed by Western blot analysis. Taken together, our findings suggest that hUCB-MSCs might play multifunctional roles in neuronal cell survival and ameliorating motor deficits of NPC mice. Show less

Dioxins are a class of polyhalogenated aromatic hydrocarbons that induce a wide spectrum of toxic responses in experimental animals. In this study, 2,3,7,8-tetrachlorobenzo-p-dioxin (TCDD) was exposed to two SD rat groups; one group for short-term exposure at a single dose of 1, 10, 20 and 50 mug/kg body weight (group 1) and the other for long-term exposure at daily and-low dose of 0.01, 0.1, 1 and 2.5 microg/kg body weight (group 2) for a month. Two-dimensional electrophoresis (2-DE) was utilized to resolve the protein profile of rat liver exposed to TCDD at different doses. In the analysis of 2-DE of the group 1, two new-expressed spots and seven volume-increased spots were detected and identified by ESI-Q-TOF MS/MS; especially, proteasome subunit beta type 3 was increased in all doses. In addition, in the group 2, six volume-increased spots were screened; particularly, histidine triad nucleotide binding protein was increased in both 0.1 microg/kg dose and 1 microg/kg dose. The identified proteins were confirmed using Western blot. Among the identified proteins, apolipoprotein A-IV may protect lipid peroxidation and atherosclerosis induced by TCDD exposure and the expression level of phosphoglycerate mutase increases due to hyperthyroidism induced by TCDD exposure. Show less

Adenomatous polyposis coli (APC) protein and Axin form a complex that mediates the down-regulation of beta-catenin, a key effector of Wnt signaling. Truncation mutations in APC are responsible for familial and sporadic colorectal tumors due to failure in the down-regulation of beta-catenin. While the regulation of beta-catenin by APC has been extensively studied, the regulation of APC itself has received little attention. Here we show that the level of APC is down-regulated by the ubiquitin-proteasome pathway and that Wnt signaling inhibits the process. The domain responsible for the down-regulation and direct ubiquitination was identified. We also show an unexpected role for Axin in facilitating the ubiquitination-proteasome-mediated down-regulation of APC through the oligomerization of Axin. Our results suggest a new mechanism for the regulation of APC by Axin and Wnt signaling. Show less