Defective erythropoiesis caused by mutations of the thyroid hormone receptor α gene.

Patients with mutations of the THRA gene exhibit classical features of hypothyroidism, including erythroid disorders. We previously created a mutant mouse expressing a mutated TRα1 (denoted as PV; Thra1PV/+ mouse) that faithfully reproduces the classical hypothyroidism seen in patients. Using Thra1PV/+ mice, we explored how the TRα1PV mutant acted to cause abnormalities in erythropoiesis. Thra1PV/+ mice exhibited abnormal red blood cell indices similarly as reported for patients. The total bone marrow cells and erythrocytic progenitors were markedly reduced in the bone marrow of Thra1PV/+ mice. In vitro terminal differentiation assays showed a significant reduction of mature erythrocytes in Thra1PV/+ mice. In wild-type mice, the clonogenic potential of progenitors in the erythrocytic lineage was stimulated by thyroid hormone (T3), suggesting that T3 could directly accelerate the differentiation of progenitors to mature erythrocytes. Analysis of gene expression profiles showed that the key regulator of erythropoiesis, the Gata-1 gene, and its regulated genes, such as the Klf1, ß-globin, dematin genes, CAII, band3 and eALAS genes, involved in the maturation of erythrocytes, was decreased in the bone marrow cells of Thra1PV/+ mice. We further elucidated that the Gata-1 gene was a T3-directly regulated gene and that TRα1PV could impair erythropoiesis via repression of the Gata-1 gene and its regulated genes. These results provide new insights into how TRα1 mutants acted to cause erythroid abnormalities in patients with mutations of the THRA gene. Importantly, the Thra1PV/+ mouse could serve as a preclinical mouse model to identify novel molecular targets for treatment of erythroid disorders.

Prometaphase arrest-dependent phosphorylation of Bcl-2 family proteins and activation of mitochondrial apoptotic pathway are associated with 17α-estradiol-induced apoptosis in human Jurkat T cells.

In Jurkat T cell clone (JT/Neo), G2/M arrest, apoptotic sub-G1 peak, mitochondrial membrane potential (Δψm) loss, and TUNEL-positive DNA fragmentation were induced following exposure to 17α-estradiol (17α-E2), whereas none of these events (except for G2/M arrest) were induced in Jurkat cells overexpressing Bcl-2 (JT/Bcl-2). Under these conditions, phosphorylation at Thr161 and dephosphorylation at Tyr15 of Cdk1, upregulation of cyclin B1 level, histone H1 phosphorylation, Cdc25C phosphorylation at Thr-48, Bcl-2 phosphorylation at Thr-56 and Ser-70, Mcl-1 phosphorylation, and Bim phosphorylation were detected in the presence of Bcl-2 overexpression. However, the 17α-E2-induced upregulation of Bak levels, activation of Bak, activation of caspase-3, and PARP degradation were abrogated by Bcl-2 overexpression. In the presence of the G1/S blocking agent hydroxyurea, 17α-E2 failed to induce G2/M arrest and all apoptotic events including Cdk1 activation and phosphorylation of Bcl-2, Mcl-1 and Bim. The 17α-E2-induced phosphorylation of Bcl-2 family proteins and mitochondrial apoptotic events were suppressed by a Cdk1 inhibitor but not by aurora A and aurora B kinase inhibitors. Immunofluorescence microscopic analysis showed that an aberrant bipolar microtubule array, incomplete chromosome congression at the metaphase plate, and prometaphase arrest, which was reversible, were the underlying factors for 17α-E2-induced mitotic arrest. The in vitro microtubule polymerization assay showed that 17α-E2 could directly inhibit microtubule formation. These results show that the apoptogenic activity of 17α-E2 was due to the impaired mitotic spindle assembly causing prometaphase arrest and prolonged Cdk1 activation, the phosphorylation of Bcl-2, Mcl-1 and Bim, and the activation of Bak and mitochondria-dependent caspase cascade.

Prometaphase arrest-dependent phosphorylation of Bcl-2 and Bim reduces the association of Bcl-2 with Bak or Bim, provoking Bak activation and mitochondrial apoptosis in nocodazole-treated Jurkat T cells.

Treatment of Jurkat T cells with the microtubule-depolymerizing agent nocodazole (NOC) caused prometaphase arrest and apoptosis. NOC-induced mitochondrial apoptotic events including Bak activation, Δψm loss, cytochrome c release, and caspase cascade activation were blocked by Bcl-2 overexpression. However, mitotic arrest, Cdc25C activation, upregulation of cyclin B1 levels, Cdk1 activation, Bcl-2 phosphorylation at Thr-56 and Ser-70, and Bim phosphorylation were retained. The treatment of Jurkat T cells concomitantly with NOC and the G1/S-blocking agent hydroxyurea resulted in G1/S arrest and complete abrogation of all apoptotic events. The association of Bcl-2 with Bim or Bak declined after the prometaphase arrest-dependent phosphorylation of Bcl-2 and Bim, whereas the association of Bcl-2 with Bax remained relatively constant. Although Bax was redistributed from the cytosol to the mitochondria, resulting in an increase in the mitochondrial level of Bax following NOC treatment, the subcellular localization of Bcl-2, Bim, Bak and apoptosis-inducing factor was confined to the mitochondrial fraction irrespective of NOC treatment. Experiments using selective caspase inhibitors showed that mitochondria-dependent activation of caspase-9 and -3 was crucial for NOC-induced apoptosis. NOC-induced phosphorylation of Bcl-2 and Bim, Δψm loss, and mitochondria-dependent apoptotic events were significantly suppressed by a Cdk1 inhibitor roscovitine, but not by the JNK inhibitor SP600125 or the p38 MAPK inhibitor SB203580. These results show that the prometaphase arrest-dependent phosphorylation of Bcl-2 and Bim, which was mediated by Cdk1, could reduce the association of Bcl-2 with Bak or Bim to allow Bak activation and mitochondrial apoptotic events in Jurkat T cells exposed to NOC.

Disruption of Thyroid Hormone Receptor Thrab Leads to Female Infertility in Zebrafish.

Thyroid hormones (THs) T4 and T3 are vital for development, growth, and metabolism. Thyroid dysfunction can also cause problems in fertility, suggesting involvement of THs in reproduction. In zebrafish, there exist 2 forms of TH receptor alpha gene (thraa and thrab). Disruption of these genes by CRISPR/Cas9 showed no reproductive irregularities in the thraa mutant; however, inactivation of the thrab gene resulted in female infertility. Although young female mutants (thrabm/m) showed normal ovarian development and folliculogenesis before sexual maturation, they failed to release eggs during oviposition after sexual maturation. This spawning failure was due to oviductal blockage at the genital papilla. The obstruction of the oviduct subsequently caused an accumulation of the eggs in the ovary, resulting in severe ovarian hypertrophy, abdominal distention, and disruption of folliculogenesis. Gene expression analysis showed expression of both TH receptors and estrogen receptors in the genital papilla, suggesting a direct TH action and potential interactions between thyroid and estrogen signaling pathways in controlling genital papilla development and function. In addition to their actions in the reproductive tracts, THs may also have direct effects in the ovary, as suggested by follicle atresia and cessation of folliculogenesis in the heterozygous mutant (thrab+/m), which was normal in all aspects of female reproduction in young and sexually mature fish but exhibited premature ovarian failure in aged females. In summary, this study provides substantial evidence for roles of THs in controlling the development and functions of both reproductive tract and ovary.

Induction of microtubule-damage, mitotic arrest, Bcl-2 phosphorylation, Bak activation, and mitochondria-dependent caspase cascade is involved in human Jurkat T-cell apoptosis by aruncin B from Aruncus dioicus var. kamtschaticus.

Exposure of human Jurkat T cells to aruncin B, purified from Aruncus dioicus, caused apoptosis along with microtubule damage, G(2)/M-arrest, Bcl-2 phosphorylation, Bak activation, mitochondrial membrane potential (Δψm) loss, cytochrome c release, activation of multiple caspases, and PARP degradation. Analyses by employing Bcl-2 overexpression and selective caspase inhibitors revealed that G(2)/M-arrest and Bcl-2 phosphorylation occurred prior to mitochondria-dependent activation of caspase-9, -3, and -8. The IC(50) values for human resting T cells, activated T cells, and Jurkat T cells were >60µg/ml, 49µg/ml, and 22µg/ml, respectively. These results demonstrate the apoptogenic activity of a novel microtubule-damaging agent aruncin B.

Effect of mollugin on apoptosis and adipogenesis of 3T3-L1 preadipocytes.

The effect of mollugin, isolated from the roots of Rubia cordifolia L., on cell viability, apoptosis and adipogenesis in 3T3-L1 preadipocytes was investigated. The inhibitory effect of mollugin (40-60 µM) on cell viability was more significant in differentiated adipocytes than in 3T3-L1 preadipocytes. In 3T3-L1 cells, the cytotoxicity of mollugin was accompanied by apoptotic events including mitochondrial membrane potential (Δψm) loss and activation of caspase-9, -3 and -7, leading to PARP degradation. Although the presence of 20 µM mollugin during induced adipocytic differentiation of 3T3-L1 cells for 6 days failed to affect the cell viability, it could almost completely abrogate the differentiation-associated morphology change and intracellular lipid accumulation. A similar level of inhibition was observed, when 20 µM mollugin was present during the early stage (D0-D2) of the differentiation period. In addition, the expression of C/EBPα, PPARγ1 and PPARγ2 was significantly down-regulated. The presence of 20 µM mollugin during either middle stage (D2-D4) or late stage (D4-D6) of the differentiation period, however, caused the inhibition to a lesser extent. These results indicated that mollugin at high concentrations (40-60 µM) exerted cytotoxicity via inducing apoptosis, whereas mollugin at a low concentration (20 µM) suppressed adipocytic differentiation without exerting cytotoxicity in 3T3-L1 preadipocytes.

Thyroid Hormone Receptor α Mutations Cause Heart Defects in Zebrafish.

Background: Mutations of thyroid hormone receptor α1 (TRα1) cause resistance to thyroid hormone (RTHα). Patients exhibit growth retardation, delayed bone development, anemia, and bradycardia. By using mouse models of RTHα, much has been learned about the molecular actions of TRα1 mutants that underlie these abnormalities in adults. Using zebrafish models of RTHα that we have recently created, we aimed to understand how TRα1 mutants affect the heart function during this period. Methods: In contrast to human and mice, the thra gene is duplicated, thraa and thrab, in zebrafish. Using CRISPR/Cas9-mediated targeted mutagenesis, we created C-terminal mutations in each of two duplicated thra genes in zebrafish (thraa 8-bp insertion or thrab 1-bp insertion mutations). We recently showed that these mutant fish faithfully recapitulated growth retardation as found in patients and thra mutant mice. In the present study, we used histological analysis, gene expression profiles, confocal fluorescence, and transmission electron microscopy (TEM) to comprehensively analyze the phenotypic characteristics of mutant fish heart during development. Results: We found both a dilated atrium and an abnormally shaped ventricle in adult mutant fish. The retention of red blood cells in the two abnormal heart chambers, and the decreased circulating blood speed and reduced expression of contractile genes indicated weakened contractility in the heart of mutant fish. These abnormalities were detected in mutant fish as early as 35 days postfertilization (juveniles). Furthermore, the expression of genes associated with the sarcomere assembly was suppressed in the heart of mutant fish, resulting in abnormalities of sarcomere organization as revealed by TEM, suggesting that the abnormal sarcomere organization could underlie the bradycardia exhibited in mutant fish. Conclusions: Using a zebrafish model of RTHα, the present study demonstrated for the first time that TRα1 mutants could act to cause abnormal heart structure, weaken contractility, and disrupt sarcomere organization that affect heart functions. These findings provide new insights into the bradycardia found in RTHα patients.

Thyroid Hormone Receptor α Regulates Autophagy, Mitochondrial Biogenesis, and Fatty Acid Use in Skeletal Muscle.

Skeletal muscle (SM) weakness occurs in hypothyroidism and resistance to thyroid hormone α (RTHα) syndrome. However, the cell signaling and molecular mechanism(s) underlying muscle weakness under these conditions is not well understood. We thus examined the role of thyroid hormone receptor α (TRα), the predominant TR isoform in SM, on autophagy, mitochondrial biogenesis, and metabolism to demonstrate the molecular mechanism(s) underlying muscle weakness in these two conditions. Two genetic mouse models were used in this study: TRα1PV/+ mice, which express the mutant Thra1PV gene ubiquitously, and SM-TRα1L400R/+ mice, which express TRα1L400R in a muscle-specific manner. Gastrocnemius muscle from TRα1PV/+, SM-TRα1L400R/+, and their control mice was harvested for analyses. We demonstrated that loss of TRα1 signaling in gastrocnemius muscle from both the genetic mouse models led to decreased autophagy as evidenced by accumulation of p62 and decreased expression of lysosomal markers (lysosomal-associated membrane protein [LAMP]-1 and LAMP-2) and lysosomal proteases (cathepsin B and cathepsin D). The expression of peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α), mitochondrial transcription factor A (TFAM), and estrogen-related receptor α (ERRα), key factors contributing to mitochondrial biogenesis as well as mitochondrial proteins, were decreased, suggesting that there was reduced mitochondrial biogenesis due to the expression of mutant TRα1. Transcriptomic and metabolomic analyses of SM suggested that lipid catabolism was impaired and was associated with decreased acylcarnitines and tricarboxylic acid cycle intermediates in the SM from the mouse line expressing SM-specific mutant TRα1. Our results provide new insight into TRα1-mediated cell signaling, molecular, and metabolic changes that occur in SM when TR action is impaired.

Isolation of a novel freshwater agarolytic Cellvibrio sp. KY-YJ-3 and characterization of its extracellular beta-agarase.

A novel agarolytic bacterium KY-YJ-3, producing extracellular agarase, was isolated from the freshwater sediment of the Sincheon River in Daegu, Korea. On the basis of gram-staining data, morphology, and phylogenetic analysis of the 16S rDNA sequence, the isolate was identified as Cellvibrio sp. By ammonium sulfate precipitation followed by Toyopearl QAE-550C, Toyopearl HW-55F, and Mono-Q column chromatography, the extracellular agarase in the culture fluid could be purified 120.2-fold with yield of 8.1%. The specific activity of the purified agarase was 84.2 U/mg. The molecular mass of the purified agarase was 70 kDa as determined by dodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimal temperature and pH of the purified agarase were 35 degrees C and pH 7.0, respectively. The purified agarase failed to hydrolyze the other polysaccharide substrates, including carboxymethyl (CM)-cellulose, dextran, soluble starch, pectin, and polygalacturonic acid. Kinetic analysis of the agarose-hydrolysis catalyzed by the purified agarase using thin layer chromatography (TLC) exhibited that the main products were neoagarobiose, neoagarotetraose, and neoagarohexaose. These results demonstrated that the newly isolated freshwater agarolytic bacterium KY-YJ-3 was a Cellvibrio sp., and could produce an extracellular beta-agarase, which hydrolyzed agarose to yield neoagarobiose, neoagarotetraose, and neoagarohexaose as the main products.

Generation of Novel Genetic Models to Dissect Resistance to Thyroid Hormone Receptor α in Zebrafish.

Background: Patients with mutations of the thyroid hormone receptor alpha (THRA) gene show resistance to thyroid hormone alpha (RTHα). No amendable mouse models are currently available to elucidate deleterious effects of TRα1 mutants during early development. Zebrafish with transient suppressed expression by morpholino knockdown and ectopic expression of TRα1 mutants in the embryos have been reported. However, zebrafish with germline transmittable mutations have not been reported. The stable expression of thra mutants from embryos to adulthood facilitated the study of molecular actions of TRα1 mutants during development. Methods: In contrast to human and mice, the thra gene is duplicated in zebrafish, thraa, and thrab. Using CRISPR/Cas9-mediated targeted mutagenesis, we created dominant negative mutations in the two duplicated thra genes. We comprehensively analyzed the molecular and phenotypic characteristics of mutant fish during development. Results: Adult and juvenile homozygous thrab 1-bp ins (m/m) mutants exhibited severe growth retardation, but adult homozygous thraa 8-bp ins (m/m) mutants had very mild growth impairment. Expression of the growth hormone (gh1) and insulin-like growth factor 1 was markedly suppressed in homozygous thrab 1-bp ins (m/m) mutants. Decreased messenger RNA and protein levels of triiodothyronine-regulated keratin genes and inhibited keratinocyte proliferation resulted in hypoplasia of the epidermis in adult and juvenile homozygous thrab 1-bp ins (m/m) mutants, but not homozygous thraa 8-bp ins (m/m) mutants. RNA-seq analysis showed that homozygous thrab 1-bp ins (m/m) mutation had global impact on the functions of the adult pituitary. However, no morphological defects nor any changes in the expression of gh1 and keratin genes were observed in the embryos and early larvae. Thus, mutations of either the thraa or thrab gene did not affect initiation of embryogenesis. But the mutation of the thrab gene, but not the thraa gene, is detrimental in postlarval growth and skin development. Conclusions: The thra duplicated genes are essential to control temporal coordination in postlarval growth and development in a tissue-specific manner. We uncovered novel functions of the duplicated thra genes in zebrafish in development. These mutant zebrafish could be used as a model for further analysis of TRα1 mutant actions and for rapid screening of therapeutics for RTHα.

Genetic and Pharmacological Targeting of Transcriptional Repression in Resistance to Thyroid Hormone Alpha.

Background: Thyroid hormones act in bone and cartilage via thyroid hormone receptor alpha (TRα). In the absence of triiodothyronine (T3), TRα interacts with co-repressors, including nuclear receptor co-repressor-1 (NCoR1), which recruit histone deacetylases (HDACs) and mediate transcriptional repression. Dominant-negative mutations of TRα cause resistance to thyroid hormone alpha (RTHα; OMIM 614450), characterized by excessive repression of T3 target genes leading to delayed skeletal development, growth retardation, and bone dysplasia. Treatment with thyroxine has been of limited benefit, even in mildly affected individuals, and there is a need for new therapeutic strategies. It was hypothesized that (i) the skeletal manifestations of RTHα are mediated by the persistent TRα/NCoR1/HDAC repressor complex containing mutant TRα, and (ii) treatment with the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) would ameliorate these manifestations. Methods: The skeletal phenotypes of (i) Thra1PV/+ mice, a well characterized model of RTHα; (ii) Ncor1ΔID/ΔID mice, which express an NCoR1 mutant that fails to interact with TRα; and (iii) Thra1PV/+Ncor1ΔID/ΔID double-mutant adult mice were determined. Wild-type, Thra1PV/+, Ncor1ΔID/ΔID, and Thra1PV/+Ncor1ΔID/ΔID double-mutant mice were also treated with SAHA to determine whether HDAC inhibition results in amelioration of skeletal abnormalities. Results:Thra1PV/+ mice had a severe skeletal dysplasia, characterized by short stature, abnormal bone morphology, and increased bone mineral content. Despite normal bone length, Ncor1ΔID/ΔID mice displayed increased cortical bone mass, mineralization, and strength. Thra1PV/+Ncor1ΔID/ΔID double-mutant mice displayed only a small improvement of skeletal abnormalities compared to Thra1PV/+ mice. Treatment with SAHA to inhibit histone deacetylation had no beneficial or detrimental effects on bone structure, mineralization, or strength in wild-type or mutant mice. Conclusions: These studies indicate treatment with SAHA is unlikely to improve the skeletal manifestations of RTHα. Nevertheless, the findings (i) confirm that TRα1 has a critical role in the regulation of skeletal development and adult bone mass, (ii) suggest a physiological role for alternative co-repressors that interact with TR in skeletal cells, and (iii) demonstrate a novel role for NCoR1 in the regulation of adult bone mass and strength.

Protein tyrosine kinase p56lck-deficiency confers hypersusceptibility to rho-fluorophenylalanine (pFPhe)-induced apoptosis by augmenting mitochondrial apoptotic pathway in human Jurkat T cells.

Phenylalanine analog, rho-fluorophenylalanine (pFPhe)-mediated cytotoxicity and several apoptotic events including mitochondrial cytochrome c release, activation of caspase-9, -3, and -8, Bid cleavage, degradation of PARP and PLCgamma-1, and DNA fragmentation were more significant in p56(lck)-deficient Jurkat T cells (JCaM1.6) than in wild-type Jurkat T cells (E6.1). The susceptibility of JCaM1.6 toward apoptogenic activity of pFPhe decreased after acquisition of p56(lck) by transfection. The p56(lck) kinase activity increased 1.6-fold at 15-30 min after pFPhe treatment. The pan-caspase inhibitor (z-VAD-fmk) completely blocked the pFPhe-mediated apoptotic changes except caspase-9 activation. The caspase-8 inhibitor (z-IETD-fmk), which failed to influence pFPhe-induced caspase-9 activation, completely blocked caspase-8 activation and PLCgamma-1 degradation with a marked reduction in caspase-3 activation and PARP degradation, indicating pFPhe-induced caspase-8 activation as a downstream event of mitochondria-dependent activation of caspase-9. These results indicate that the deficiency of p56(lck) augments pFPhe-induced mitochondrial cytochrome c release and resultant apoptotic cell death in Jurkat T cells.

NCOR1 modulates erythroid disorders caused by mutations of thyroid hormone receptor α1.

Thyroid hormone receptor α (THRA) gene mutations, via dominant negative mode, cause erythroid abnormalities in patients. Using mice expressing a dominant negative TRα1 mutant (TRα1PV; Thra1 PV/+ mice), we showed that TRα1PV acted directly to suppress the expression of key erythroid genes, causing erythroid defects. The nuclear receptor corepressor 1 (NCOR1) was reported to mediate the dominant negative effects of mutated TRα1. However, how NCOR1 could regulate TRα1 mutants in erythroid defects in vivo is not known. In the present study, we crossed Thra1 PV/+ mice with mice expressing a mutant Ncor1 allele (NCOR1ΔID; Ncor1 ΔID mice). TRα1PV mutant cannot bind to NCOR1ΔID. The expression of NCOR1ΔID ameliorated abnormalities in the peripheral blood indices, and corrected the defective differentiation potential of progenitors in the erythroid lineage. The defective terminal erythropoiesis of lineage-negative bone marrow cells of Thra1 PV/+ mice was rescued by the expression of NCOR1ΔID. De-repression of key erythroid genes in Thra1 PV/+ Ncor1 ΔID/ΔID mice led to partial rescue of terminal erythroid differentiation. These results indicate that the inability of TRα1PV to recruit NCOR1ΔID to form a repressor complex relieved the deleterious actions of TRα1 mutants in vivo. NCOR1 is a critical novel regulator underpining the pathogenesis of erythroid abnormalities caused by TRα1 mutants.

Inhibition of STAT3 activity delays obesity-induced thyroid carcinogenesis in a mouse model.

Compelling epidemiologic studies indicate that obesity is a risk factor for many human cancers, including thyroid cancer. In recent decades, the incidence of thyroid cancer has dramatically increased along with a marked rise in obesity prevalence. We previously demonstrated that a high fat diet (HFD) effectively induced the obese phenotype in a mouse model of thyroid cancer (Thrb(PV/PV)Pten(+/-) mice). Moreover, HFD activates the STAT3 signal pathway to promote more aggressive tumor phenotypes. The aim of the present study was to evaluate the effect of S3I-201, a specific inhibitor of STAT3 activity, on HFD-induced aggressive cancer progression in the mouse model of thyroid cancer. WT and Thrb(PV/PV)Pten(+/-) mice were treated with HFD together with S3I-201 or vehicle-only as controls. We assessed the effects of S3I-201 on HFD-induced thyroid cancer progression, the leptin-JAK2-STAT3 signaling pathway, and key regulators of epithelial-mesenchymal transition (EMT). S3I-201 effectively inhibited HFD-induced aberrant activation of STAT3 and its downstream targets to markedly inhibit thyroid tumor growth and to prolong survival. Decreased protein levels of cyclins D1 and B1, cyclin dependent kinase 4 (CDK4), CDK6, and phosphorylated retinoblastoma protein led to the inhibition of tumor cell proliferation in S3I-201-treated Thrb(PV/PV)Pten(+/-) mice. Reduced occurrence of vascular invasion and blocking of anaplasia and lung metastasis in thyroid tumors of S3I-201-treated Thrb(PV/PV)Pten(+/-) mice were mediated via decreased expression of vimentin and matrix metalloproteinases, two key effectors of EMT. The present findings suggest that inhibition of the STAT3 activity would be a novel treatment strategy for obesity-induced thyroid cancer.

Dependency of 2-methoxyestradiol-induced mitochondrial apoptosis on mitotic spindle network impairment and prometaphase arrest in human Jurkat T cells.

The present study sought to determine the correlation between 2-methoxyestradiol (2-MeO-E2)-induced cell cycle arrest and 2-MeO-E2-induced apoptosis. Exposure of Jurkat T cell clone (JT/Neo) to 2-MeO-E2 (0.5-1.0 µM) caused G2/M arrest, Bak activation, Δψm loss, caspase-9 and -3 activation, PARP cleavage, intracellular ROS accumulation, and apoptotic DNA fragmentation, whereas none of these events except for G2/M arrest were induced in Jurkat T cells overexpressing Bcl-2 (JT/Bcl-2). Under these conditions, Cdk1 phosphorylation at Thr-161 and dephosphorylation at Tyr-15, up-regulation of cyclin B1 expression, histone H1 phosphorylation, Cdc25C phosphorylation at Thr-48, Bcl-2 phosphorylation at Thr-56 and Ser-70, Mcl-1 phosphorylation at Ser-159/Thr-163, and Bim phosphorylation were detected irrespective of Bcl-2 overexpression. Concomitant treatment of JT/Neo cells with 2-MeO-E2 and the G1/S blocking agent aphidicolin resulted in G1/S arrest and abrogation of all apoptotic events, including Cdk1 activation, phosphorylation of Bcl-2, Mcl-1 and Bim, and ROS accumulation. The 2-MeO-E2-induced phosphorylation of Bcl-2 family proteins and mitochondrial apoptotic events were suppressed by a Cdk1 inhibitor, but not by an Aurora A kinase (AURKA), Aurora B kinase (AURKB), JNK, or p38 MAPK inhibitor. Immunofluorescence microscopic analysis revealed that 2-MeO-E2-induced mitotic arrest was caused by mitotic spindle network impairment and prometaphase arrest. Whereas 10-20 µM 2-MeO-E2 reduced the proportion of intracellular polymeric tubulin to monomeric tubulin, 0.5-5.0 µM 2-MeO-E2 increased it. These results demonstrate that the apoptogenic effect of 2-MeO-E2 (0.5-1.0 µM) was attributable to mitotic spindle defect-mediated prometaphase arrest, Cdk1 activation, phosphorylation of Bcl-2, Mcl-1, and Bim, and activation of Bak and mitochondria-dependent caspase cascade.

Anti-adipogenic activity of 2-carbomethoxy-2,3-epoxy-3-prenyl-1,4-naphthoquinone from Rubia cordifolia L.

To examine anti-adipogenic activity of 2-carbomethoxy-2,3-epoxy-3-prenyl-1,4-naphthoquinone (CMEP-NQ) isolated from the roots of Rubia cordifolia L., its effects on cell viability, apoptosis, and adipogenesis in 3T3-L1 preadipocytes were investigated. The inhibitory effect of CMEP-NQ on cell viability was more significant in differentiated mature adipocytes than in 3T3-L1 preadipocytes. In 3T3-L1 cells, the cytotoxicity of CMEP-NQ (20-40 µM) was accompanied by apoptotic events such as mitochondrial membrane potential loss, caspase-3 activation, poly(ADP-ribose) polymerase degradation, and terminal deoxynucleotidyl transferase-meidated dUTP nick-end labeling-positive apoptotic DNA fragmentation. Although the presence of 10 µM CMEP-NQ during induced adipocytic differentiation of 3T3-L1 cells for 6 days failed to influence the cell viability, it did reduce the differentiation-associated accumulation of intracellular lipid by approximately 48.5%. A similar level of inhibition was observed when 10 µM CMEP-NQ was present during the early stage (Days 0-2) of the differentiation period. At the same time, the expressions of CCAAT/enhancer binding protein-α, peroxisome proliferator-activated receptor γ1, peroxisome proliferator-activated receptor γ2, and adiponectin were down-regulated. However, the presence of 10 µM CMEP-NQ during either the middle (Days 2-4) or late (Days 4-6) stage of the differentiation period caused the inhibition to a lesser extent. These results indicated that CMEP-NQ at high concentrations (20-40 µM) exerted cytotoxicity via inducing apoptosis, whereas CMEP-NQ at a low concentration (10 µM) suppressed adipocytic differentiation without exerting cytotoxicity in 3T3-L1 preadipocytes.

Proteasome inhibitor MG132-induced apoptosis via ER stress-mediated apoptotic pathway and its potentiation by protein tyrosine kinase p56lck in human Jurkat T cells.

Exposure of human Jurkat T cells to MG132 caused apoptosis along with upregulation of Grp78/BiP and CHOP/GADD153, activation of JNK and p38MAPK, activation of Bak, mitochondrial membrane potential (Δψm) loss, cytochrome c release, activation of caspase-12, -9, -3, -7, and -8, cleavage of Bid and PARP, and DNA fragmentation. However, these MG132-induced apoptotic events, with the exceptions of upregulation of Grp78/BiP and CHOP/GADD153 and activation of JNK and p38MAPK, were abrogated by overexpression of Bcl-xL. Pretreatment with the pan-caspase inhibitor z-VAD-fmk prevented MG132-induced apoptotic caspase cascade, but allowed upregulation of Grp78/BiP and CHOP/GADD153 levels, activation of JNK and p38MAPK, Δψm loss, and cleavage of procaspase-9 (47kDa) to active form (35kDa). Further analysis using selective caspase inhibitors revealed that caspase-12 activation was required for activation of caspase-9 and -3 to the sufficient level for subsequent activation of caspase-7 and -8. MG132-induced cytotoxicity, apoptotic sub-G(1) peak, Bak activation, and Δψm loss were markedly reduced by p38MAPK inhibitor, but not by JNK inhibitor. MG132-induced apoptotic changes, including upregulation of Grp78/BiP and CHOP/GADD153 levels, activation of caspase-12, p38MAPK and Bak, and mitochondria-dependent activation of caspase cascade were more significant in p56(lck)-stable transfectant JCaM1.6/lck than in p56(lck)-deficient JCaM1.6/vector. The cytotoxicity of MG132 toward p56(lck)-positive Jurkat T cell clone was not affected by the Src-like kinase inhibitor PP2. These results demonstrated that MG132-induced apoptosis was caused by ER stress and subsequent activation of mitochondria-dependent caspase cascade, and that the presence of p56(lck) enhances MG132-induced apoptosis by augmenting ER stress-mediated apoptotic events in Jurkat T cells.