Mixed-Lineage Leukaemia Gene Regulates Glucose-Sensitive Gene Expression and Insulin Secretion in Pancreatic Beta Cells.

The escalating prevalence of diabetes mellitus underscores the need for a comprehensive understanding of pancreatic beta cell function. Interest in glucose effectiveness has prompted the exploration of novel regulatory factors. The myeloid/lymphoid or mixed-lineage leukaemia gene (MLL) is widely recognised for its role in leukemogenesis and nuclear regulatory mechanisms through its histone methyltransferase activity in active chromatin. However, its function within pancreatic endocrine tissues remains elusive. Herein, we unveil a novel role of MLL in glucose metabolism and insulin secretion. MLL knockdown in ßHC-9 pancreatic beta cells diminished insulin secretion in response to glucose loading, paralleled by the downregulation of the glucose-sensitive genes SLC2a1 and SLC2a2. Similar observations were made in MLL heterozygous knockout mice (MLL+/-), which exhibited impaired glucose tolerance and reduced insulin secretion without morphological anomalies in pancreatic endocrine cells. The reduction in insulin secretion was independent of changes in beta cell mass or insulin granule morphology, suggesting the regulatory role of MLL in glucose-sensitive gene expression. The current results suggest that MLL interacts with circadian-related complexes to modulate the expression of glucose transporter genes, thereby regulating glucose sensing and insulin secretion. Our findings shed light on insulin secretion control, providing potential avenues for therapeutics against diabetes.

A case of insulinoma-induced hypoglycemia managed by Dexcom G4 Platinum.

This report details the case of a 41-year-old woman who was diagnosed with insulinoma. As the patient developed severe life-threatening hypoglycemia, we introduced Dexcom G4 Platinum (DG4P), a modern continuous glucose-monitoring system (CGM). The algorithm of the sensor glucose (SG) values of CGM is based on patients with diabThis report details the case of a 41-year-old woman who was diagnosed with insulinoma. As the patient developed severe life-threatening hypoglycemia, we introduced Dexcom G4 Platinum (DG4P), a modern continuous glucose-monitoring system (CGM). The algorithm of the sensor glucose (SG) values of CGM is based on patients with diabetes; therefore, we evaluated the accuracy of DG4P in this patient. The mean absolute relative differences and absolute differences between SG of DG4P and self-monitoring of blood sugar values were 10.8%±8.3% and 6.8±5.7 mg/dL, respectively, in the hypoglycemic region, which verifies DG4P's accuracy. DG4P was found to be useful for monitoring hypoglycemia not only in patients with diabetes but also in those with insulinoma.etes; therefore, we evaluated the accuracy of DG4P in this patient. The mean absolute relative differences and absolute differences between SG of DG4P and self-monitoring of blood sugar values were 10.8%±8.3% and 6.8±5.7 mg/dL, respectively, in the hypoglycemic region, which verifies DG4P's accuracy. DG4P was found to be useful for monitoring hypoglycemia not only in patients with diabetes but also in those with insulinoma.

Superior Mesenteric Artery Syndrome Accompanied by Acute-onset Type 1 Diabetes Complicated with Graves' Disease.

A 35-year-old man experienced general fatigue and could not eat solid food because of nausea and vomiting. His weight abruptly decreased from 49 to 45 kg after 2 weeks. A detailed examination indicated superior mesenteric artery syndrome (SMAS) accompanied by acute-onset type 1 diabetes complicated by Graves' disease, referred to as autoimmune polyglandular syndrome type 3A (APS3A). Although SMAS has a good prognosis, some cases require emergency surgery, especially when complicated by gastric perforation. In our case, APS3A and SMAS developed rapidly and at approximately the same time, resulting in a cycle of mutual exacerbation.

SFPQ associated with a co-activator for PPARγ, HELZ2, regulates key nuclear factors for adipocyte differentiation.

We recently isolated a novel co-activator of peroxisome proliferator-activated receptor γ, helicase with zinc finger 2 (HELZ2). HELZ2 null mice were resistant to diet-induced obesity and NAFFL/NASH, and HELZ2 was phosphorylated at tyrosine residues. In order to find a factor related to HELZ2, we analyzed products co-immunoprecipitated with phosphorylated HELZ2 by mass spectrometry analyses. We identified proline- and glutamine-rich (SFPQ) as a protein associating with tyrosine-phosphorylated HELZ2. The knockdown of SFPQ in 3T3-L1 cells downregulated mRNA levels of transcription factors including Krox20, Cebpß, and Cebpδ: key factors for early-stage adipocyte differentiation. In addition, knockdown of SFPQ inhibited 3T3-L1 cell differentiation to mature adipocytes. These findings demonstrated that SFPQ associating with HELZ2 is an important novel transcriptional regulator of adipocyte differentiation.

Late-onset non-islet cell tumor hypoglycemia: A case report.

BACKGROUND: Hypoglycemia due to non-insulin-producing tumors is referred to as non-islet cell tumor hypoglycemia (NICTH). As NICTH is a rare lesion, the natural course of NICTH is not well understood. We report a case of NICTH that was observed 30 years before the onset of hypoglycemia. CASE SUMMARY: A 50-year-old man was diagnosed with an abnormal right chest shadow during a routine X-ray examination, but no further examination was undertaken because the lesion appeared benign. Thirty years after the tumor discovery, the patient was admitted to the hospital with symptoms of severe hypoglycemia, which was diagnosed as NICTH based on a complete examination. The tumor was resected and found to be a solitary fibrous mass (15.6 cm × 13.7 cm × 10.4 cm); thereafter, the patient's blood glucose levels normalized and he completely recovered. CONCLUSION: NICTH can have an acute onset, even if the tumor has been present and asymptomatic over a long time period.

Administration of small-molecule guanabenz acetate attenuates fatty liver and hyperglycemia associated with obesity.

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive accumulation of hepatic triglycerides (TG) and hyperglycemia arising due to persistent insulin resistance, and is profoundly linked to obesity. However, there is currently no established treatment for NAFLD in obese human subjects. We previously isolated Helz2, the expression of which was upregulated in human and mouse NAFLD, and its deletion activated the hepatic expression of functional leptin receptor long form (Leprb) and suppressed NAFLD development and body weight (BW) gain in obese mice. A high-throughput assay of small-molecule drugs revealed that guanabenz acetate (Ga), originally used to treat hypertension, possesses a high affinity constant against HELZ2, and its administration activates LEPRB expression in HepG2 cells in vitro. The chronic oral administration of Ga shows the selective leptin sensitization in the liver via upregulation of hepatic Leprb expression, which affects expression of genes involved in lipogenesis and fatty acid ß-oxidation and diminishes hepatocyte hypertrophy with droplets enriched in TG in high-fat diet-induced obese mice. This activity significantly improves insulin resistance to decrease hyperglycemia and hepatocyte and adipocyte weights, resulting in BW reduction without reducing food intake. Regarding drug repositioning, Ga has the potential to effectively treat NAFLD and hyperglycemia in obese patients.

Transcriptional Regulation of the Angptl8 Gene by Hepatocyte Nuclear Factor-1 in the Murine Liver.

Brief refeeding times (~60 min) enhanced hepatic Angptl8 expression in fasted mice. We cloned the mouse Angptl8 promoter region to characterise this rapid refeeding-induced increase in hepatic Angptl8 expression. Deletion of the -309/-60 promoter region significantly attenuated basal promoter activity in hepatocytes. A computational motif search revealed a potential binding motif for hepatocyte nuclear factor 1α/1ß (HNF-1α/ß) at -84/-68 bp of the promoter. Mutation of the HNF-1 binding site significantly decreased the promoter activity in hepatocytes, and the promoter carrying the mutated HNF-1 site was not transactivated by co-transfection of HNF-1 in a non-hepatic cell line. Silencing Hnf-1 in hepatoma cells and mouse primary hepatocytes reduced Angptl8 protein levels. Electrophoretic mobility-shift assays confirmed direct binding of Hnf-1 to its Angptl8 promoter binding motif. Hnf-1α expression levels increased after short-term refeeding, paralleling the enhanced in vivo expression of the Angptl8 protein. Chromatin immunoprecipitation (ChIP) confirmed the recruitment of endogenous Hnf-1 to the Angptl8 promoter region. Insulin-treated primary hepatocytes showed increased expression of Angptl8 protein, but knockdown of Hnf-1 completely abolished this enhancement. HNF-1 appears to play essential roles in the rapid refeeding-induced increases in Angptl8 expression. HNF-1α may therefore represent a primary medical target for ANGPTL8-related metabolic abnormalities. The study revealed the transcriptional regulation of the mouse hepatic Angptl8 gene by HNF-1.

Regulation of the KCNJ5 gene by SF-1 in the adrenal cortex: Complete genomic organization and promoter function.

Activating mutations in the KCNJ5 gene are responsible for the significant number of aldosterone-producing adenomas. To elucidate the molecular mechanisms underlying KCNJ5 expression, we characterized the entire human KCNJ5 gene. The gene spanned approximately 29.8 kb and contained three exons and two introns. The strongest expression of KCNJ5 mRNA was observed in the adrenal gland. The promoter region contained a putative binding site for SF-1 at -1782 bp. A construct containing -2444 bp of the promoter region exhibited the strongest promoter activity in adrenal H295R cells, and the introduction of a mutation in the SF-1 binding site almost completely abolished promoter activity. Furthermore, deletion mutation, EMSA, and knockdown analyses revealed that SF-1 bound to this element and was functional. Immunochemistry showed that KCNJ5 was predominantly expressed in the zona glomerulosa, while SF-1 was ubiquitously expressed in the adrenal cortex. These results demonstrated that SF-1 mediates the expression of human KCNJ5 in the adrenal cortex.

Central Hypothyroidism Related to Pituitary Adenomas: Low Incidence of Central Hypothyroidism in Patients With Acromegaly.

CONTEXT: The most frequent cause of central hypothyroidism (CeH) is pituitary adenomas, but the mechanisms remain unclear. OBJECTIVE: We investigated serum thyroid levels and GH/IGF-1 in central hypothyroidism in untreated patients with pituitary nonfunctioning and GH-secreting adenomas. DESIGN: This was a retrospective cross-sectional study of cases collected from Gunma University and Toranomon Hospitals between 2007 and 2016. PATIENTS: One-hundred thirty-nine cases of nonfunctioning pituitary adenoma (NFPA) and 150 cases of GH-secreting pituitary adenoma (GHPA) were analyzed. MAIN OUTCOME MEASURES: The correlations between thyroid levels, several clinicopathological parameters, and GH/IGF-1 were examined. RESULTS: Twenty-four percent of NFPA patients had CeH. The severity did not correlate with tumor size, age, or sex, and all cases had normal TSH levels. In contrast, only 8.7% of GHPA patients had CeH; approximately half had normal TSH levels and approximately half had low TSH levels. Serum TSH levels in GHPA patients were significantly lower and free T4 (FT4) and free T3 levels were higher than those in patients with NFPA. Furthermore, approximately one-fourth of GHPA patients had normal FT4 and low TSH levels. In addition, serum FT4 levels and serum TSH levels were positively and negatively correlated, respectively, with serum IGF-1 levels. Furthermore, IGF-1 levels in patients with GHPA decreased with age. CONCLUSIONS: (i) NFPA patients with CeH had TSH levels within a normal range. (ii) GHPA patients had a low incidence of CeH, which may be a result of stimulated thyroid function by GH/IGF-1. (iii) We found an age-dependent decrease in serum IGF-1 levels in patients with GHPA.

Transducin ß-like 1, X-linked and nuclear receptor co-repressor cooperatively augment the ligand-independent stimulation of TRH and TSHß gene promoters by thyroid hormone receptors.

Mutations in TBL1X, a component of the nuclear receptor co-repressor (N-CoR) and silencing mediator of retinoic acid and thyroid hormone receptor co-repressor complexes, have recently been implicated in isolated central hypothyroidism (CeH). However, the mechanisms by which TBL1X mutations affect negative feedback regulation in the hypothalamus-pituitary-thyroid axis remain unclear. N-CoR was previously reported to paradoxically enhance the ligand-independent stimulation of TRH and TSHß gene promoters by thyroid hormone receptors (TR) in cell culture systems. We herein investigated whether TBL1X affects the unliganded TR-mediated stimulation of the promoter activities of genes negatively regulated by T3 in cooperation with N-CoR. In a hypothalamic neuronal cell line, the unliganded TR-mediated stimulation of the TRH gene promoter was significantly enhanced by co-transfected TBL1X, and the co-transfection of TBL1X with N-CoR further enhanced promoter activity. In contrast, the knockdown of endogenous Tbl1x using short interfering RNA significantly attenuated the N-CoR-mediated enhancement of promoter activity in the presence of unliganded TR. The co-transfection of N365Y or Y458C, TBL1X mutants identified in CeH patients, showed impaired co-activation with N-CoR for the ligand-independent stimulation of the TRH promoter by TR. In the absence of T3, similar or impaired enhancement of the TSHß gene promoter by the wild type or TBL1X mutants, respectively, was observed in the presence of co-transfected TR and N-CoR in CV-1 cells. These results suggest that TBL1X is needed for the full activation of TRH and TSHß gene promoters by unliganded TR. Mutations in TBL1X may cause CeH due to the impaired up-regulation of TRH and/or TSHß gene transcription despite low T3 levels.

Characteristics of Japanese aldosterone-producing adenomas with KCNJ5 mutations.

Somatic mutations in KCNJ5 gene have been identified in patients with adrenal aldosterone-producing adenomas (APAs). We previously reported that Japanese patients with APAs had distinct characteristics from patients in Western countries; i.e. they had a high frequency of KCNJ5 mutations and exhibited a frequent association with cortisol co-secretion. Therefore, APAs among Japanese patients may have different features from those in Western countries. We added recent cases, examined 47 cases (43% male) of APAs, including clinicopathological features, KCNJ5 mutations, and the mRNA levels of several steroidogenic enzymes, and compared the results obtained to those reported in other countries. While the prevalence of KCNJ5 mutations is approximately 40% in Western countries, 37 APA cases (78.7%) showed mutations: 26 with p.G151R and 11 with p.L168R. Although a significant gender difference has been reported in the frequency of KCNJ5 mutations in Europe, we did not find any gender difference. However, the phenotypes of Japanese patients with mutations were similar to those of patients in Western countries; patients were younger and had higher plasma aldosterone levels, lower potassium levels, and higher diastolic blood pressure. Reflecting these phenotypes, APAs with mutations had higher CYP11B2 mRNA levels. However, in contrast to APAs in Western countries, Japanese APAs with mutations showed lower CYP11B1, CYP17A1, and CYP11A1 mRNA levels. These findings demonstrated that Japanese APA patients may have distinct features including a higher prevalence of KCNJ5 mutations, no gender difference in the frequency of these mutations, and characteristics similar to the zona glomerulosa.

Angiotensin-Converting Enzyme Inhibitor Prevents the Worsening of Renal Function in the Late Phase after Percutaneous Coronary Intervention.

AIM: The amount of contrast media and renal atheroemboli are risk factors for acute kidney injury after percutaneous coronary intervention (PCI). However, the chronic kidney injury after PCI has not been fully characterized. The purpose of this study was to investigate factors affecting renal function in the late phase after PCI by measuring serum Cystatin C (CysC). METHODS: In 143 consecutive patients who underwent elective PCI, CysC was evaluated at baseline and at 9 months after PCI, and the percent change in CysC (%CysC) was calculated. The association between %CysC and baseline characteristics, including medication use, was assessed. RESULTS: Of 143 patients, 86 had worsening renal function (WRF; %CysC ≥0), and 57 did not (non-WRF; %CysC <0). Only the use of angiotensin-converting enzyme inhibitor (ACEI) and baseline CysC were significantly different between WRF and non-WRF patients (15 vs. 40%, p=0.001 and 1.02±0.26 vs. 1.13±0.26 mg/L, p=0.015). In univariate analysis, the use of ACEI and CysC were negatively associated with WRF [Odds ratio (OR)=0.26, 95% confidence interval (CI)=0.12-0.57, p<0.001 and OR=0.20, 95% CI=0.05-0.73, p=0.015]. Furthermore, multivariate analysis revealed that the use of ACEI and CysC significantly correlated with WRF (OR=0.26, 95% CI=0.11-0.57, p<0.001 and OR=0.20, 95% CI=0.05-0.74, p=0.016). The %CysC in 36 patients with ACEI was significantly lower than that in 107 patients without ACEI [median: -3.8%; interquartile range (IQR), -11.0 to 4.2%; vs. median: 3.3%; IQR -2.9 to 11.0%, p=0.001]. CONCLUSION: The use of ACEI was associated with lower CysC after PCI, suggesting that ACEI prevents worsening of renal function in late phase after PCI.

Coordinated regulation of transcription and alternative splicing by the thyroid hormone receptor and its associating coregulators.

Emerging evidence has indicated that the transcription and processing of precursor mRNA (pre-mRNA) are functionally coupled to modulate gene expression. In collaboration with coregulators, several steroid hormone receptors have previously been shown to directly affect alternative pre-mRNA splicing coupled to hormone-induced gene transcription; however, the roles of the thyroid hormone receptor (TR) and its coregulators in alternative splicing coordinated with transcription remain unknown. In the present study, we constructed a luciferase reporter and CD44 alternative splicing (AS) minigene driven by a minimal promoter carrying 2 copies of the palindromic thyroid hormone-response element. We then examined whether TR could modulate pre-mRNA processing coupled to triiodothyronine (T3)-induced gene transcription using luciferase reporter and splicing minigene assays in HeLa cells. In the presence of cotransfected TRß1, T3 increased luciferase activities along with the inclusion of the CD44 variable exons 4 and 5 in a dose- and time-dependent manner. In contrast, cotransfected TRß1 did not affect the exon-inclusion of the CD44 minigene driven by the cytomegalovirus promoter. T3-induced two-exon inclusion was significantly increased by the cotransfection of the TR-associated protein, 150-kDa, a subunit of the TRAP/Mediator complex that has recently been shown to function as a splicing factor. In contrast, T3-induced two-exon inclusion was significantly decreased by cotransfection of the polypyrimidine tract-binding protein-associated splicing factor, which was previously shown to function as a corepressor of TR. These results demonstrated that liganded TR in cooperation with its associating cofactors could modulate alternative pre-mRNA splicing coupled to gene transcription.

Protection against high-fat diet-induced obesity in Helz2-deficient male mice due to enhanced expression of hepatic leptin receptor.

Obesity arises from impaired energy balance, which is centrally coordinated by leptin through activation of the long form of leptin receptor (Leprb). Obesity causes central leptin resistance. However, whether enhanced peripheral leptin sensitivity could overcome central leptin resistance remains obscure. A peripheral metabolic organ targeted by leptin is the liver, with low Leprb expression. We here show that mice fed a high-fat diet (HFD) and obese patients with hepatosteatosis exhibit increased expression of hepatic helicase with zinc finger 2, a transcriptional coactivator (Helz2), which functions as a transcriptional coregulator of several nuclear receptors, including peroxisome proliferator-activated receptor γ in vitro. To explore the physiological importance of Helz2, we generated Helz2-deficient mice and analyzed their metabolic phenotypes. Helz2-deficient mice showing hyperleptinemia associated with central leptin resistance were protected against HFD-induced obesity and had significantly up-regulated hepatic Leprb expression. Helz2 deficiency and adenovirus-mediated liver-specific exogenous Leprb overexpression in wild-type mice significantly stimulated hepatic AMP-activated protein kinase on HFD, whereas Helz2-deficient db/db mice lacking functional Leprb did not. Fatty acid-ß oxidation was increased in Helz2-deficeint hepatocytes, and Helz2-deficient mice revealed increased oxygen consumption and decreased respiratory quotient in calorimetry analyses. The enhanced hepatic AMP-activated protein kinase energy-sensing pathway in Helz2-deficient mice ameliorated hyperlipidemia, hepatosteatosis, and insulin resistance by reducing lipogenic gene expression and stimulating lipid-burning gene expression in the liver. These findings together demonstrate that Helz2 deficiency ameliorates HFD-induced metabolic abnormalities by stimulating endogenous hepatic Leprb expression, despite central leptin resistance. Hepatic HELZ2 might be a novel target molecule for the treatment of obesity with hepatosteatosis.

Single nucleotide polymorphisms associated with abnormal coronary microvascular function.

BACKGROUND: Single nucleotide polymorphisms (SNPs) are the most common source of genetic variation. Although microvascular pathology is associated with cardiovascular events, genetic phenotypes causing microvascular disease remain largely unknown. This study identifies sex-specific SNPs associated with coronary microvascular dysfunction. METHODS AND RESULTS: Six hundred and forty-three patients without significant obstructive coronary heart disease were enrolled, referred for cardiac catheterization, and underwent invasive coronary microcirculatory assessment. Patient data were collected from 1529 autosomal SNPs and seven X chromosome SNPs, which were selected to represent the variability from 76 candidate genes with published associations with coronary vasoreactivity, angiogenesis, inflammation, vascular calcification, atherosclerosis risk factors, female hormones, blood coagulation, or coronary heart disease. Coronary flow reserve (CFR) was assessed by an intracoronary injection of adenosine. Patients were categorized according to a CFR above or below 2.5 and were stratified by sex.After adjusting for age, sex, and BMI, this study shows that SNPs within VEGFA and CDKN2B-AS1 are associated with abnormal CFR (P<0.005). SNPs within MYH15, VEGFA, and NT5E are associated with abnormal CFR in men. No SNPs were associated with abnormal CFR in women. CONCLUSION: Genetic variations within defined regions of VEGFA and CDKN2B-AS1 genes are associated with coronary microvascular dysfunction. Furthermore, sex-specific allelic variants within MYH15, VEGFA, and NT5E are associated with an increased risk of coronary microvascular dysfunction in men.

Cardiac tamponade due to rupture of coronary artery fistula to the coronary sinus with giant aneurysm of coronary artery: usefulness of transthoracic echocardiography.

A 68-year-old woman was admitted to our hospital because of back pain and syncope. Transthoracic echocardiography revealed pericardial effusion, a collapsed right ventricle, a giant aneurysm connected to the coronary sinus, a dilated left main trunk coronary artery, and a dilated left circumflex artery (LCx). Furthermore, there was a coronary artery fistula arising from the LCx that drained into the coronary sinus. We diagnosed cardiac tamponade due to rupture of the coronary artery fistula or giant aneurysm, and successful emergency surgery was performed. Rupture of coronary artery aneurysm or coronary artery fistula is very rare. Transthoracic two-dimensional echocardiography was very useful in our case for the diagnosis of cardiac tamponade, giant coronary aneurysm, and coronary artery fistula.

KCNJ5 mutations in aldosterone- and cortisol-co-secreting adrenal adenomas.

Adrenal aldosterone-producing adenomas (APA) are rarely associated with the clear co-secretion of cortisol. Somatic mutations of the potassium channel KCNJ5 gene, with the hotspots G151R and L168R, have been recently identified in patients with APA. However, whether APAs that secrete cortisol have these mutations remains unclear. We examined three patients with APAs showing clear autonomous secretion of cortisol who possessed a 1 mg dexamethasone suppression test (DST) with a failure of the serum cortisol level to drop below 3.0 µg/dL, a morning plasma ACTH level of less than 10 pg/mL, and suppressed accumulation in the intact adrenal on (131)I- adosterol scintigraphy, or postoperative adrenal insufficiency. Laparoscopic adrenectomy revealed all tumors to be golden yellow, and histological examination confirmed them to be adrenocortical adenomas. All these patients required replacement therapy with hydrocortisone after surgery. Sequencing demonstrated that 2 of three cases showed a mutation of the KCNJ5 gene, one with c.451G>A, p.G151R and one with c.503T>G, p.L168R. Furthermore, the mRNA levels of steroidogenic enzymes including CYP11B1, CYP11B2, HSD3B2, CYP17A1, CYP11A1 and KCNJ5 in the 3 cases did not differ from those in 8 pure APAs not showing any of the above conditions for autonomous cortisol secretion. In addition, all 8 pure APAs harbored mutations of the KCNJ5 gene. These findings suggested that at least some aldosterone- and cortisol-co-secreting adrenal tumors have mutations of the KCNJ5 gene, suggesting the origin to be APA, and pure APAs may show a high incidence of KCNJ5 mutations.

Roles of proteasomal 19S regulatory particles in promoter loading of thyroid hormone receptor.

19S regulatory particles (19SRP) of 26S proteasome participate in multiple steps of gene transcription in yeast. We previously showed that Tat-binding protein-1 (TBP-1), an ATPase of 19SRP, interacts with thyroid hormone receptor (TR) and enhances TR-mediated transcription synergistically with steroid receptor coactivator-1 (SRC-1). To further elucidate the roles of ATPases and a non-ATPase component of 19SRP in gene regulation by TR, we investigated whether knockdown (KO) of TBP-1, TRIP1 or Rpn10 using small interfering RNA affects TR-mediated transactivation in HeLa cells. KO of individual subunits attenuated TR-mediated transactivation through the thyroid hormone response element (TRE) in the absence or presence of cotransfected SRC-1 without altering TR and SRC-1 protein levels. KO of TBP-1 disrupted ligand-induced loading of TR, SRC-1, and RNA polymerase II in chromatin immunoprecipitation assays. Collectively, both ATPase and non-ATPase components of 19SRP play critical roles in TR-mediated transactivation by coordinating the proper loading of liganded TR to TRE.

Tat-binding protein-1 (TBP-1), an ATPase of 19S regulatory particles of the 26S proteasome, enhances androgen receptor function in cooperation with TBP-1-interacting protein/Hop2.

The 26S proteasome, which degrades ubiquitinated proteins, appears to contribute to the cyclical loading of androgen receptor (AR) to androgen response elements of target gene promoters; however, the mechanism whereby the 26S proteasome modulates AR recruitment remains unknown. Using yeast two-hybrid screening, we previously identified Tat-binding protein-1 (TBP-1), an adenosine triphosphatase of 19S regulatory particles of the 26S proteasome, as a transcriptional coactivator of thyroid hormone receptor. Independently, TBP-1-interacting protein (TBPIP) was also identified as a coactivator of several nuclear receptors, including AR. Here, we investigated whether TBP-1 could interact with and modulate transcriptional activation by AR cooperatively with TBPIP. TBP-1 mRNA was ubiquitously expressed in human tissues, including the testis and prostate, as well as in LNCaP cells. TBP-1 directly bound TBPIP through the amino-terminal domain possessing the leucine zipper structure. AR is physically associated with TBP-1 and TBPIP in vitro and in LNCaP cells. TBP-1 similarly and additively augmented AR-mediated transcription upon coexpression with TBPIP, and the ATPase domain, as well as leucine zipper structure in TBP-1, was essential for transcriptional enhancement. Overexpression of TBP-1 did not alter AR protein and mRNA levels. In the chromatin immunoprecipitation assay, TBP-1 was transiently recruited to the proximal androgen response element of the prostate-specific antigen gene promoter in a ligand-dependent manner in LNCaP cells. These findings suggest that a component of 19S regulatory particles directly binds AR and might participate in AR-mediated transcriptional activation in cooperation with TBPIP.

Isolation and characterization of a transcriptional cofactor and its novel isoform that bind the deoxyribonucleic acid-binding domain of peroxisome proliferator-activated receptor-gamma.

Using the DNA-binding domain (DBD) and hinge region of human peroxisome proliferator-activated receptor (PPAR)-gamma as bait in yeast two-hybrid screen, we isolated partial cDNA identical with that of the C terminal of KIAA1769. KIAA1769 encodes a 2080-amino acid protein (molecular mass, 231 kDa) that was recently identified to interact with PPARalpha and termed PPARalpha-interacting cofactor 285 (here referred to as PPARgamma-DBD-interacting protein 1 (PDIP1)-alpha). PDIP1 mRNA was expressed in 3T3-L1 adipocytes and THP-1 macrophages. We also identified the expression of the N terminal extended form of PDIP1alpha (referred to as PDIP1beta) consisting of 2649 amino acids (295 kDa) in human cultured cell lines by RT-PCR, and 5' rapid amplification of cDNA ends. Ribonuclease protection assay revealed that PDIP1beta mRNA was expressed more abundantly than PDIP1alpha mRNA. The C-terminal region of PDIP1 directly binds DBD of PPARgamma, and multiple LXXLL motifs in PDIP1 were not required for the interaction. PDIP1alpha and -beta similarly enhanced PPARgamma-mediated transactivation in transfection assays and short interfering RNA targeting PDIP1 mRNA significantly reduced transactivation by PPARgamma. No potent intrinsic activation domain was identified in either PDIP1 isoforms in mammalian one-hybrid assays, and mutation of all LXXLL motifs did not affect enhancement of PPARgamma-mediated transactivation. PDIP1alpha and -beta similarly augmented transactivation by PPARalpha, PPARdelta, thyroid hormone receptor (TR)-alpha1, TRbeta1, and retinoid X receptor-alpha. PDIP1alpha also enhanced estrogen receptoralpha- and androgen receptor-mediated transactivation, whereas PDIP1beta did not. PDIP1alpha showed receptor-specific synergism with activation function-2-interacting coactivators in PPARgamma- and TRbeta1-mediated transactivation. Together, PDIP1 might function as a transcriptional cofactor for a broad range of nuclear receptors, possibly in collaboration with specific activation function-2 interacting coactivators.