Search

Methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) plays an important role in one-carbon metabolism. The MTHFD2 gene is upregulated in various cancers but very low or undetectable in normal proliferating cells, and therefore a potential target for cancer treatment. In this study, we present the structure of MTHFD2 in complex with xanthine derivative 15, which allosterically binds to MTHFD2 and coexists with the substrate analogue. A kinetic study demonstrated the uncompetitive inhibition of MTHFD2 by 15. Allosteric inhibitors often provide good selectivity and, indeed, xanthine derivatives are highly selective for MTHFD2. Moreover, several conformational changes were observed upon the binding of 15, which impeded the binding of the cofactor and phosphate to MTHFD2. To the best of our knowledge, this is the first study to identify allosteric inhibitors targeting the MTHFD family and our results would provide insights on the inhibition mechanism of MTHFD proteins and the development of novel inhibitors.

A rare case of a heart transplantation recipient with Guillain-Barre syndrome occurred, which was associated with peripheral nervous system damage. Based on a review of epidemiological research, the symptom development process, and diagnostic tools, the authors highlight the extreme rarity of this postinfectious immune disease. After diagnosis, plasma exchange and immunoregulatory therapy should be performed because they result in rapid recovery. If there is delayed diagnosis and treatment, there is a high risk of disability or death. When patients experience acute limb paralysis as the main symptom, nurse practitioners (NPs) should focus on the patient's history, particularly with regard to infectious agents. Closely monitoring the patient to detect respiratory failure and the need for early respiratory intervention can help the patient to avoid the severe complication of permanent brain injury. For NPs, performance of early differential diagnosis is important, especially among patients who have immunosuppressive dependence after transplantation.

Indoleamine 2,3-dioxygenase-1 (IDO1) is a potential target for the next generation of cancer immunotherapies. We describe the development of two series of IDO1 inhibitors incorporating a N-hydroxy-thiophene-carboximidamide core generated by knowledge-based drug design. Structural modifications to improve the cellular activity and pharmacokinetic (PK) properties of the compounds synthesized, including extension of the side chain of the N-hydroxythiophene-2-carboximidamide core, resulted in compound 27a, a potent IDO1 inhibitor which demonstrated significant (51%) in vivo target inhibition on IDO1 in a human SK-OV-3 ovarian xenograft tumor mouse model. This strategy is expected to be applicable to the discovery of additional IDO1 inhibitors for the treatment of other diseases susceptible to modulation of IDO1.

NRF2/ARE signaling pathway is a principal regulator of cellular redox homoeostasis. The stress-induced transcription factor, NRF2, can shield cells from the oxidative damages via binding to the consensus antioxidant-responsive element (ARE) and driving several cyto-protective genes expression. Increasing evidence indicated that aberrant activation of NRF2 in malignant cells may support their survival through various pathways to detoxify chemotherapy drugs, attenuate drug-induced oxidative stress, or induce drug efflux, all of which are crucial in developing drug resistance. Accordingly, NRF2 is a potential drug target for improving the effectiveness of chemotherapy and to reverse drug resistance in cancer cells. A stable ARE-driven reporter human head and neck squamous cell carcinoma (HNSCC) cell line, HSC3-ARE9, was established and utilized to screen novel NRF2 inhibitors from a compound library. The cotton plant derived phenolic aldehyde-gossypol was selected for further analyses. The effects of gossypol in cancer cells were determined by western blotting, RT-qPCR, clonogenic assay, and cell viability assays. The gossypol-responsive gene expression levels were assessed in the Oncomine database. The effects of gossypol on conferring chemo-sensitization were evaluated in etoposide-resistant and cisplatin-resistant cancer cells. Our study is the first to identify that gossypol is effective to reduce both basal and NRF2 activator tert-butylhydroquinone (t-BHQ)-induced ARE-luciferase activity. Gossypol diminishes NRF2 protein stability and thereby leads to the suppression of NRF2/ARE pathway, which resulted in decreasing the expression levels of NRF2 downstream genes in both time- and dose-dependent manners. Inhibition of NRF2 by gossypol significantly decreases cell viabilities in human cancer cells. In addition, we find that gossypol re-sensitizes topoisomerase II poison treatment in etoposide-resistant cancer cells via suppression of NRF2/ABCC1 axis. Moreover, gossypol suppresses NRF2-mediated G6PD expression thereby leads to induce synthetic lethality with cisplatin not only in parental cancer cells but also in cisplatin-resistant cancer cells. These findings suggest that gossypol is a novel NRF2/ARE inhibitor, and can be a potential adjuvant chemotherapeutic agent for treatment of chemo-refractory tumor.

Nuclear factor erythroid-2-related factor 2 (NRF2) mainly regulates transcriptional activation through antioxidant-responsive elements (AREs) present in the promoters of NRF2 target genes. Recently, we found that NRF2 was overexpressed in a KB-derived drug-resistant cancer cell panel. In this panel, KB-7D cells, which show acquired resistance to topoisomerase II (Top II) poisons, exhibited the highest NRF2 activation. To investigate whether NRF2 directly contributed to acquired resistance against Top II poisons, we manipulated NRF2 by genetic and pharmacological approaches. The result demonstrated that silencing of NRF2 by RNA interference increased the sensitivity and treatment with NRF2 activator decreased the sensitivity of KB and KB-7D cells toward Top II poisons. Further, increased B-Raf-mediated NRF2 gene transcription and HATs-mediated NRF2 protein acetylation activated NRF2 signaling in KB-7D cells. Moreover, increased binding of NRF2 to an ARE in the promoter of ATP-binding cassette subfamily C member 1 (ABCC1) directly contributed to Top II poison resistance. In addition, activation of NRF2 increased glutathione level and antioxidant capacity in KB-7D cells compared with that in KB cells; moreover, high glutathione level provided survival advantage to KB-7D cells. Our study is the first to show that aberrant NRF2 activation is via increased B-Raf-mediated NRF2 gene transcription and HATs-mediated NRF2 protein acetylation, which increases the acquired resistance and promote the survival of Top II poison-resistant cancer cells. Importantly, NRF2 downstream effectors ABCC1 and glutathione directly contribute to acquired resistance and survival, respectively. These results suggest that blockade of NRF2 signaling may enhance therapeutic efficacy and reduce the survival of Top II poison-refractory tumors in clinical.

A rare case of a heart transplantation recipient with Guillain-Barré syndrome occurred, which was associated with peripheral nervous system damage. Based on a review of epidemiological research, the symptom development process, and diagnostic tools, the authors highlight the extreme rarity of this postinfectious immune disease. After diagnosis, plasma exchange and immunoregulatory therapy should be performed because they result in rapid recovery. If there is delayed diagnosis and treatment, there is a high risk of disability or death. When patients experience acute limb paralysis as the main symptom, nurse practitioners (NPs) should focus on the patient's history, particularly with regard to infectious agents. Closely monitoring the patient to detect respiratory failure and the need for early respiratory intervention can help the patient to avoid the severe complication of permanent brain injury. For NPs, performance of early differential diagnosis is important, especially among patients who have immunosuppressive dependence after transplantation.

Chronic myeloid leukemia (CML) is caused by chromosomal rearrangement resulting in the expression of Bcr-Abl fusion protein with deregulated Abl tyrosine kinase activity. Approved drugs - imatinib, dasatinib, nilotinib, and ponatinib - target the ATP-binding site of Abl kinase. Even though these drugs are initially effective, long-term usefulness is limited by the development of resistance. To overcome this problem, targeting the allosteric site of Abl kinase, which is remote from the ATP-binding site is found to be a useful strategy. In this study, structure-based and ligand-based virtual screening methods were applied to narrow down possible drugs (from DrugBank database) that could target the allosteric site of Abl kinase. Detailed investigations of the selected drugs in the allosteric site of Abl kinase, using molecular dynamics and steered molecular dynamics simulation shows that gefitinib, an EGFR inhibitor approved for the treatment of lung cancer, could bind effectively to the allosteric site of Bcr-Abl. More interestingly, gefitinib was found to enhance the ability of imatinib to bind at the ATP-binding site of Bcr-Abl kinase. Based on the in silico findings, gefitinib was tested in combination with imatinib in K562 CML cell line using MTT cell proliferation assay and found to have a synergistic antiproliferative activity. Further detailed mechanistic study could help to unravel the full potential of imatinib - gefitinib combination for the treatment of CML.

We have designed and synthesized certain novel oxime- and amide-bearing coumarin derivatives as nuclear factor erythroid 2 p45-related factor 2 (Nrf2) activators. The potency of these compounds was measured by antioxidant responsive element (ARE)-driven luciferase activity, level of Nrf2-related cytoprotective genes and proteins, and antioxidant activity. Among them, (Z)-3-(2-(hydroxyimino)-2-phenylethoxy)-2H-chromen-2-one (17a) was the most active, and more potent than the positive t-BHQ in the induction of ARE-driven luciferase activity. Exposure of HSC-3 cells to various concentrations of 17a strongly increased Nrf2 nuclear translocation and the expression level of Nrf2-mediated cytoprotective proteins in a concentration-dependent manner. HSC-3 cells pretreated with 17a significantly reduced t-BOOH-induced oxidative stress. In the animal experiment, Nrf2-mediated cytoprotective proteins, such as aldo-keto reductase 1 subunit C-1 (AKR1C1), glutathione reductase (GR), and heme oxygenase (HO-1), were obviously elevated in the liver of 17a-treated mice than that of control. These results suggested that novel oxime-bearing coumarin 17a is able to activate Nrf2/ARE pathway in vivo and are therefore seen as a promising candidate for further investigation.

Indoleamine 2,3-dioxygenase is a heme-containing enzyme implicated in the down regulation of the anti-tumor immune response, and considered a promising anti-cancer drug target. Several pharmaceutical companies, including Pfizer, Merck, and Bristol-Myers Squibb, are known to be in pursuit of IDO inhibitors, and Incyte recently reported good results in the phase II clinical trial of the IDO inhibitor Epacadostat. In previous work, we developed a series of IDO inhibitors based on a sulfonylhydrazide core structure, and explored how they could serve as potent IDO inhibitors with good drug profiles. Herein, we disclose the development of the 4-bromophenylhydrazinyl benzenesulfonylphenylurea 5k, a potent IDO inhibitor which demonstrated 25% tumor growth inhibition in a murine CT26 syngeneic model on day 18 with 100 mg/kg oral administration twice daily, and a 30% reduction in tumor weight. Pharmacodynamic testing of 5k found it to cause a 25% and 21% reduction in kyn/trp ratio at the plasma and tumor, respectively. In the CT26 tumor model, 5k was found to slightly increase the percentage of CD3+ T cells and lymphocyte responsiveness, indicating that 5k may have potential in modulating anti-tumor immunity. These data suggest 5k to be worthy of further investigation in the development of anti-tumor drugs.

This study investigated the pathways involved in EGCG modulation of insulin-like growth factor (IGF)-stimulated glucose uptake in 3T3-L1 adipocytes. EGCG inhibited IGF-I and IGF-II stimulation of adipocyte glucose uptake with dose and time dependencies. EGCG at 20μM for 2h decreased IGF-I- and IGF-II-stimulated glucose uptake by 59% and 64%, respectively. Pretreatment of adipocytes with antibody against the EGCG receptor (also known as the 67-kDa laminin receptor; 67LR), prevented the effects of EGCG on IGF-increased glucose uptake, but pretreatment with normal rabbit immunoglobulin did not. This suggests that the 67LR mediates the anti-IGF effect of EGCG on adipocyte glucose uptake. Further analysis indicated EGCG, IGF-I, and IGF-II did not alter total levels of GLUT1 or GLUT4 protein. However, EGCG prevented the IGF-increased GLUT4 levels in the plasma membrane and blocked the IGF-decreased GLUT4 levels in low-density microsomes. Neither EGCG nor its combination with IGF altered GLUT1 protein levels in the plasma membrane and low-density microsomes. EGCG also suppressed the IGF-stimulated phosphorylation of IGF signaling molecules, PKCζ/λ, but not AKT and ERK1/2, proteins. This study suggests that EGCG suppresses IGF stimulation of 3T3-L1 adipocyte glucose uptake through inhibition of the GLUT4 translocation, but not through alterations of the GLUT1 pathway.

Resistin and endothelin (ET)-1 have been reported to inhibit adipogenesis and regulate adipocyte insulin resistance, respectively. Although both hormones interact with each other, the exact signaling pathway of ET-1 to act on resistin gene expression is still unknown. Using 3T3-L1 adipocytes, we investigated the signaling pathways involved in ET-1-stimulated resistin gene expression. The up-regulation of resistin mRNA expression by ET-1 depends on concentration and timing. The concentration of ET-1 that increased resistin mRNA levels by 100%-250% was approximately 100 nM for a range of 0.25-12 hours of treatment. Treatment with actinomycin D blocked ET-1-increased resistin mRNA levels, suggesting that the effect of ET-1 requires new mRNA synthesis. Treatment with an inhibitor of the ET type-A receptor, such as N-[1-Formyl-N-[N-[(hexahydro-1H-azepin-1-yl)carbonyl]-L-leucyl]-D-tryptophyl]-D-tryptophan (BQ610), but not with the ET type-B receptor antagonist N-[(cis-2,6-Dimethyl-1-piperidinyl)carbonyl]-4-methyl-L-leucyl-1-(methoxycarbonyl)-D-tryptophyl-D-norleucine (BQ788), blocked ET-1, increased the levels of resistin mRNA, and phosphorylated levels of downstream signaling molecules, such as ERK1/2, c-Jun N-terminal kinases (JNKs), protein kinase B (AKT), and signal transducer and activator of transcription 3 (STAT3). Moreover, pretreatment of specific inhibitors of either ERK1/2 (1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene [U0126] and 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one [PD98059], two inhibitors of MEK1), JNKs (SP600125), phosphatidylinositol 3-kinase/AKT (LY294002 and Wortmannin), or Janus kinase 2 (JAK2)/STAT3 ((E)-2-Cyano-3-(3,4-dihydrophenyl)-N-(phenylmethyl)-2-propenamide, AG490) prevented ET-1-increased levels of resistin mRNA and reduced the ET-1-stimulated phosphorylation of ERK1/2, JNKs, AKT, and STAT3, respectively. However, the p38 kinase antagonist 4-[5-(4-Fluorophenyl)-2-[4-(methylsulfonyl)phenyl]-1H-imidazol-4-yl]pyridine (SB203580) did not alter the effect of ET-1. These results imply that ET type-A receptor, ERK1/2, JNKs, AKT, and JAK2, but not ET type-B receptor or p38, are necessary for the ET-1 stimulation of resistin gene expression. In vivo observations that ET-1 increased resistin mRNA and protein levels in sc and epididymal adipose tissues support the in vitro findings.

Suppressor of cytokine signaling (SOCS)-3 can act as a regulator of energy metabolism and cytokine signaling in fat cells. It is regulated by hormones and toxicological factors. However, the action of cycloheximide on expression of adipocyte SOCS-3 gene is unknown. Using 3T3-L1 adipocytes, we found that cycloheximide up-regulated SOCS-3 mRNA expression in dose- and time-dependent manners. Treatment with actinomycin D prevented cycloheximide-stimulated SOCS-3 mRNA expression, suggesting that the effect of cycloheximide requires new mRNA synthesis. While cycloheximide was shown to increase activities of MEK1 and JNK, signaling was demonstrated to be inhibited by pretreatment with either MEK1 inhibitors U0126 and PD98059, or with the JNK inhibitor SP600125. U0126 and PD98059, respectively, reduced cycloheximide-stimulated SOCS-3 mRNA expression, but SP600125 did not antagonize cycloheximide effect. Moreover, cycloheximide was observed to up-regulate expression of other SOCS family members, such as SOCS-1, -2, -4, -5, -6, -7, and cytokine-inducible SH2-containing protein (CIS)-1 mRNAs. Such effects varied with the dosage and duration of cycloheximide treatment. These results imply the functional MEK1/ERK-mediated pathway is necessary for the cycloheximide stimulation of SOCS-3 gene expression.

Endothelin (ET)-1 and suppressor of cytokine signaling (SOCS)-3 were respectively found to regulate energy metabolism and hormone signaling in fat cells. Although ET-1 can also regulate the expression of SOCS-3-stimulating hormones, it is still unknown whether ET-1 regulates SOCS-3 gene expression. This study investigated the pathways involved in ET-1's modulation of SOCS-3 gene expression in 3T3-L1 adipocytes. ET-1 upregulated SOCS-3 mRNA and protein expression in dose- and time-dependent manners. The concentration of ET-1 that increased SOCS-3 mRNA levels by 250-400% was ∼100nM with 2-4h of treatment. Treatment with actinomycin D prevented ET-1-stimulated SOCS-3 mRNA expression, suggesting that the effect of ET-1 requires new mRNA synthesis. Pretreatment with the ET type A receptor (ET(A)R) antagonist, BQ-610, but not the ET type B receptor (ET(B)R) antagonist, BQ-788, prevented the stimulatory effect of ET-1 on SOCS-3 gene expression. The specific inhibitors of either MEK1 (U-0126 and PD-98059), JAK (AG-490), JNK (SP-600125), or PI3K (LY-294002 and wortmannin) reduced ET-1-increased levels of SOCS-3 mRNA and respectively inhibited ET-1-stimulated activities of MEK1, JAK, JNK, and PI3K. These results imply that the ET(A)R, ERK, JAK, JNK, and PI3K are functionally necessary for ET-1's stimulation of SOCS-3 gene expression. Moreover, ET-1 was observed to upregulate expressions of SOCS-1, -2, -3, -4, -5, and -6 mRNAs, but not SOCS-7 or cytokine-inducible SH2-containing protein-1 mRNAs. This suggests that ET-1 selectively affects particular types of SOCS family members. Changes in SOCS gene expressions induced by ET-1 may help explain the mechanism by which ET-1 modulates hormone signaling of adipocytes.

Insulin and (−)-epigallocatechin gallate (EGCG) are reported to regulate obesity and fat accumulation, respectively. This study investigated the pathways involved in EGCG modulation of insulin-stimulated glucose uptake in 3T3-L1 and C3H10T1/2 adipocytes. EGCG inhibited insulin stimulation of adipocyte glucose uptake in a dose- and time-dependent manner. The concentration of EGCG that decreased insulin-stimulated glucose uptake by 50-60 % was approximately 5-10 μM for a period of 2 h. At 10 μM, EGCG and gallic acid were more effective than (−)-epicatechin, (−)-epigallocatechin, and (−)-epicatechin 3-gallate. We identified the EGCG receptor [also known as the 67-kDa laminin receptor (67LR)] in fat cells and extended the findings for this study to clarify whether EGCG-induced changes in insulin-stimulated glucose uptake in adipocytes could be mediated through the 67LR. Pretreatment of adipocytes with a 67LR antibody, but not normal rabbit immunoglobulin, prevented the effects of EGCG on insulin-increased glucose uptake. This suggests that the 67LR mediates the effect of EGCG on insulin-stimulated glucose uptake in adipocytes. Moreover, pretreatment with an AMP-activated protein kinase (AMPK) inhibitor, such as compound C, but not with a glutathione (GSH) activator, such as N-acetyl- L-cysteine (NAC), blocked the antiinsulin effect of EGCG on adipocyte glucose uptake. These data suggest that EGCG exerts its anti-insulin action on adipocyte glucose uptake via the AMPK, but not the GSH, pathway. The results of this study possibly support that EGCG mediates fat content.

The induction of detoxifying enzymes and antioxidant proteins by chemopreventive agents protects cells from oxidizing substances capable of damaging DNA integrity and initiating carcinogenesis. Coniferyl aldehyde, a naturally occurring substance, has been found in many foods and edible plants. We and others previously demonstrated that trans-coniferylaldehyde (t-CA) has potential antimutagenic and antioxidant properties. However, the mechanism underlying its Nrf2-mediated antioxidant effect remains largely unknown. In the present study, we demonstrated that t-CA significantly stimulated antioxidant-responsive element (ARE)-driven luciferase activity in a cell model and increased the expression of ARE-dependent detoxifying/antioxidant genes and their protein products in vitro and in vivo. The detoxifying/antioxidant genes activated by t-CA, especially heme oxygenase-1 (HO-1), were found to be involved in its cytoprotective effects against oxidative stress and cell injuries elicited by carcinogens tert-butylhydroperoxide and arecoline. Furthermore, the t-CA-induced phosphorylation and nuclear translocation of nuclear factor erythroid-2-related factor 2 (Nrf2) played a crucial role in this ARE-mediated cellular defense. Moreover, we found that p38 MAPK and protein kinase C (PKC) signaling pathways participated in the t-CA-induced, Nrf2-mediated cytoprotective effect. Among them, p38α/MAPKAPK-2 and an atypical PKC, PK-N3, were critical for the activation of the Nrf2/HO-1 axis by t-CA. In conclusion, we demonstrated for the first time that t-CA attenuates carcinogen-induced oxidative stress by activating Nrf2 via p38α/MAPKAPK-2- and PK-N3-dependent signaling pathways. In addition, t-CA increased the level of Nrf2-mediated detoxifying/antioxidant proteins in vivo, suggesting that t-CA may have potential for use in the management of carcinogenesis and meriting further investigation.

Tea has been found to possess widespread biological functions based on a variety of laboratory data. The effects of tea on obesity and diabetes have received increasing attention. This paper reviews the evidence for the connections among tea catechins, and obesity and diabetes. Tea catechins, especially (-)-epigallocatechin gallate (EGCG), appear to have antiobesity and antidiabetic effects. While few epidemiological and clinical studies show the health benefits of EGCG on obesity and diabetes, the mechanisms of its actions are emerging based on the various laboratory data. These mechanisms may be related to certain pathways, such as through the modulations of energy balance, endocrine systems, food intake, lipid and carbohydrate metabolism, the redox status, and activities of different types of cells (i. e., fat, liver, muscle, and beta-pancreatic cells). Because the EGCG receptor, the so-called 67-kDa laminin receptor (LR), has been discovered with colocalization of other types of LR and cytoskeleton in both cancer cells and normal cells, this may explain that EGCG possesses numerous actions. The mechanistic results of this review may possibly be utilized in the treatment of obesity, diabetes, and other related diseases using tea- and EGCG-based folk medicines.

Resistin is known as an adipocyte-specific hormone that can cause insulin resistance and decrease adipocyte differentiation. It can be regulated by transcriptional factors, but the possible role of forkhead transcription factor FOXO1 in regulating resistin gene expression is still unknown. Using 3T3 fibroblast and C3H10T1/2 and 3T3-L1 adipocytes, we found that transient overexpression of a non-phosphorylatable, constitutively active FOXO1, but not the wild type of FOXO1 or a DNA binding-deficient FOXO1, activated resistin promoter-directed luciferase expression. However, transient overexpression of a dominant-negative FOXO1 inactivated resistin promoter activity and reduced resistin mRNA expression. These observations indicate that the action of FOXO1 on resistin gene expression requires the activation of FOXO1 and that the effect of FOXO1 depends on the phosphorylation and dephosphorylation of FOXO1. The FOXO1 protein target sites on the resistin promoter were localized to the proximal -3545 to -787bp of 5'-flanking region of the resistin promoter. A chromatin immunoprecipitation assay also showed that FOXO1 bound the resistin promoter at nucleotide regions of -1539 to -1366bp and -1016 to -835bp, but not at the regions of -795 to -632bp. Results of this study suggest that FOXO1 transcription factor likely activates the expression of adipocyte resistin gene via direct association with the upstream resistin promoter.

Green tea catechins, especially (−)-epigallocatechin-3-gallate (EGCG), regulate fat cell functions. This chapter reviews the evidence for understanding EGCG signaling in modulating multiple processes of fat cells, such as growth, apoptosis, differentiation, metabolism, and endocrine activity. Based on a variety of laboratory data, EGCG signaling in regulating these processes may be related to certain pathways and molecules, including (1) the EGCG receptor in association with receptor tyrosine kinase (RTK) signaling molecules, (2) phosphorylation of RTK signaling elements, (3) production of reactive oxygen species, (4) activities and expression of cell cycle-controlling and differentiation-controlling factors, (5) activity and expression of apoptotic and metabolic enzymes, (6) activity of energy substrate transporters, and (7) expression and secretion of adipokines. These EGCG signaling pathways associated with fat cells may explain the in vivo actions of EGCG on adipose tissues and indicate its possible use in the prevention of obesity.

Scope This study investigated the pathways involved in epigallocatechin gallate (EGCG) modulation of insulin-like growth factor (IGF)-I-stimulated and IGF-II-stimulated mitogenesis in 3T3-L1 preadipocytes. Methods and results We found that this process was dose and time dependent, and caused by suppression of IGF-I-stimulated and IGF-II-stimulated phosphorylation of p66Shc and mitogen-activated protein kinase (MAPK) pathway proteins, including MEK1 kinase (RAF1), extracellular signal-regulated protein kinase (ERK) kinase (MEK1), and ERK 1 and ERK 2 (ERK1/2), but not phospho-Jun-N-terminal kinase, protein kinase B, p52Shc, or p46Shc. Furthermore, EGCGinhibited the IGF-I-stimulated phosphorylation of the IGF-I receptor-beta (IGF-IR β), the association of IGF-IRwith the p66Shc protein, and the IGF-II-stimulated associations of the IGF-IIreceptor with Gαi-2 and p66Shc proteins, suggesting that EGCGselectively affects particular types of Shc and MAPKfamily members. Pretreatment with antiserum against the EGCGreceptor (also known as the 67-kDa laminin receptor; 67LR), but not with an adenosine monophosphate (AMP)-activated protein kinase (AMPK) inhibitor, prevented the inhibitory actions of EGCGon IGF-I- and IGF-II-stimulated ERK1/2 phosphorylation and subsequent preadipocyte proliferation. Conclusion The results of this study suggest that EGCGmediates anti-IGF-I and anti-IGF-IIsignals in preadipocyte mitogenesis via the 67LR but not the AMPKpathway.

Insulin and (−)-epigallocatechin gallate (EGCG) have been reported to regulate fat cell mitogenesis and adipogenesis, respectively. This study investigated the pathways involved in EGCG modulation of insulin-stimulated mitogenesis in 3T3-L1 preadipocytes. EGCG inhibited insulin stimulation of preadipocyte proliferation in a dose- and time-dependent manner. EGCG also suppressed insulin-stimulated phosphorylation of the insulin receptor-β, insulin receptor (IR) substrates 1 and 2 (IRS1 and IRS2), and mitogen-activated protein kinase pathway proteins, RAF1, MEK1/2, and ERK1/2, but not JNK. Furthermore, EGCG inhibited the association of IR with the IRS1 and IRS2 proteins, but not with the IRS4 protein. These data suggest that EGCG selectively affects particular types of IRS and MAPK family members. Generally, EGCG was more effective than epicatechin, epicatechin gallate, and epigallocatechin in modulating insulin-stimulated mitogenic signaling. We identified the EGCG receptor [also known as the 67-kDa laminin receptor (67LR)] in fat cells and found that its expression was sensitive to growth phase, tissue type, and differentiation state. Pretreatment of preadipocytes with 67LR antiserum prevented the effects of EGCG on insulin-stimulated phosphorylation of IRS2, RAF1, and ERK1/2 and insulin-stimulated preadipocyte proliferation (cell number and bromodeoxyuridine incorporation). Moreover, EGCG tended to increase insulin-stimulated associations between the 67LR and IR, IRS1, IRS2, and IRS4 proteins. These data suggest that EGCG mediates anti-insulin signaling in preadipocyte mitogenesis via the 67LR pathway.

Green tea (-)-epigallocatechin-3-gallate (EGCG) is known as to regulate obesity and fat cell activity. However, little information is known about the effects of EGCG on oxidative reactive oxygen species (ROS) of fat cells. Using 3T3-L1 preadipocytes and adipocytes, we found that EGCG increased ROS production in dose- and time-dependent manners. The concentration of EGCG that increased ROS levels by 180-500% was approximately 50 muM for a range of 8-16 h of treatment. In contrast, EGCG dose- and time-dependently decreased the amount of intracellular glutathione (GSH) levels. EGCG was more effective than (-)-epicatechin, (-)-epicatechin-3-gallate, and (-)-epigallocatechin in changing ROS and GSH levels. This suggests a catechin-specific effect. To further examine the relation of GSH to ROS as altered by EGCG, we observed that exposure of preadipocytes and adipocytes to N-acetyl-L-cysteine (a GSH precursor) blocked the EGCG-induced increases in ROS levels and decreases in GSH levels. These observations suggest a GSH-dependent effect of EGCG on ROS production. While EGCG was demonstrated to alter levels of ROS and GSH, its signaling was altered by an EGCG receptor (the so-called 67 kDa laminin receptor(67LR)) antiserum, but not by normal rabbit serum. These data suggest that EGCG mediates GSH and ROS levels via the 67LR pathway.

Resistin is known as an adipocyte-specific secretory hormone that can cause insulin resistance and decrease adipocyte differentiation. It can be regulated by sexual hormones. Whether environmental estrogens regulate the production of resistin is still not clear. Using 3T3-L1 adipocytes, we found that octylphenol upregulated resistin mRNA expression in dose- and time-dependent manners. The concentration of octylphenol that increased resistin mRNA levels by 50% was approximately 100 nM within 6 h of treatment. The basal half-life of resistin mRNA induced by actinomycin D was lengthened by octylphenol treatment, suggesting that octylphenol decreases the rate of resistin mRNA degradation. In addition, octylphenol stimulated resistin protein expression and release. The basal half-life of resistin protein induced by cycloheximide was lengthened by octylphenol treatment, suggesting that octylphenol decreases the rate of resistin protein degradation. While octylphenol was shown to increase activities of the estrogen receptor (ER) and MEK1, signaling was demonstrated to be blocked by pretreatment with either ICI-182780 (an ERalpha antagonist) or U-0126 (a MEK1 inhibitor), in which both inhibitors prevented octylphenol-stimulated phosphorylation of ERK. These results imply that ERalpha and ERK are necessary for the octylphenol stimulation of resistin mRNA expression. Moreover, U-0126 antagonized the octylphenol-increased resistin protein expression and release. These data suggest that the way octylphenol signaling increases resistin protein levels is similar to that by which it increases resistin mRNA levels; it is likely mediated through an ERK-dependent pathway. In vivo, octylphenol increased adipose resistin mRNA expression and serum resistin and glucose levels, supporting its in vitro effect.

Resistin is known as an adipocyte-specific secretory hormone that can cause insulin resistance and decrease adipocyte differentiation. It can be regulated by sexual hormones, but the mechanism of estrogen's actions is still not clear. Using 3T3-L1 adipocytes, we found that 17 beta-estradiol (E2) up-regulated resistin mRNA expression in a dose- and time-dependent manner. The concentration of E2 that increased resistin mRNA levels by 100-250% was approximately 1 nM for a range of 1-24 h of treatment. Treatment with either actinomycin D or cycloheximide prevented E2-stimulated resistin mRNA expression, suggesting that the effect of E2 requires new mRNA and protein synthesis. Although E2 was shown to increase activities of the estrogen receptor (ER) and MAPK kinase 1 and the association of nuclear ER alpha and CCAAT/enhancer binding protein-alpha with the resistin gene promoter, signaling was demonstrated to be blocked by pretreatment with either ICI182780 or PD98059. Neither SB203580 nor LY294002 changed the E2-increased levels of resistin mRNA, but they respectively inhibited E2-stimulated phosphorylation of p38 MAPK and Akt. These results imply the ER alpha, ERK, and CCAAT/enhancer binding protein- are necessary for the E2 stimulation of transcription from the resistin promoter. Moreover, PD98059, but not SB203580 or LY294002, antagonized E2-increased resistin protein release. These data suggest that E2 likely modifies the distribution of the resistin protein between the intracellular and extracellular compartments via an ERK-dependent pathway.

This study was designed to investigate the effect of green tea catechins, especially (-)-epigallocatechin gallate (EGCG), on the apoptosis of 3T3-L1 preadipocytes. Preadipocyte apoptosis as indicated by formation of DNA fragments was induced by EGCG in dose-dependent manners. While EGCG was demonstrated to decrease Cdk2 expression and activity and increase caspase-3 activity, overexpression of Cdk2 and treatment with the caspase-3 inhibitor respectively prevented preadipocytes from induction of DNA fragmentation and caspase-3 activity by doses of 100-400 muM of EGCG. This suggests the Cdk2- and caspase-3-dependent apoptotic effects of EGCG. Moreover, EGCG was more effective than EC, ECG, and EGC in changing the apoptotic signals. Results of this study may relate to the mechanism by which EGCG modulates body weight.