Search

Many biological activities of green tea have been attributed to a major constituent, (minus;)-epigallocatechin gallate (EGCG). We previously reported that EGCG and an EGCG-free fraction derived from green tea modulated the gene expression of gluconeogenic enzymes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, in the mouse liver. EGCG is also known to affect the gene expression of enzymes related to lipid metabolism. However, it remains to be examined whether or not a constituent other than EGCG contributes to the change in gene expression of these enzymes. In this study, we prepared an EGCG-free water-soluble fraction (GT-W), and examined its effects on the hepatic gene expression of lipogenic enzymes in mice. The results of quantitative real-time PCR assays indicated that the dietary administration of GT-W for 4 weeks reduced the hepatic gene expression of lipogenic enzymes: fatty acid synthase, hydroxymethylglutaryl coenzyme A reductase, and acetyl-coenzyme A carboxylase alpha. Also, the gene expression of sterol regulatory element-binding transcription factor (Srebf)1 and/or Srebf2 was reduced, suggesting that the reduction of Srebfs contributed to the down-regulation of the lipogenic enzymes, since these transcription factors bind the promoter region to enhance their expression. The plasma levels of triglycerides and cholesterol were reduced with statistical significance in the group given a diet containing GT-W. These results suggest that in addition to EGCG, green tea contains some component(s) which may help to prevent arteriosclerosis and obesity.

Many biological activities of green tea have been attributed to a major constituent, (-)-epigallocatechin gallate (EGCG). We previously reported that EGCG and a catechin-rich green tea beverage modulated the gene expression of gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), in the mouse liver. However, it remains to be examined whether or not a constituent other than EGCG contributes to the change in gene expression of these enzymes. In this study, we separated the hot water infusion of green tea leaves (GT) into an ethanol-soluble fraction (GT-E) and an EGCG-free water-soluble fraction (GT-W), and examined their effects using rat hepatoma H4IIE cells. The inclusion of GT, GT-E, and GT-W in the culture medium reduced the gene expression of G6Pase and PEPCK. GT-W caused a decrease in expression of the transcription factor HNF4α. Reduced levels of PEPCK and HNF4α proteins were demonstrated in the cells treated with GT-W. GT-W showed an activity similar to insulin, but different from EGCG. Administration of GT-W to mice for 4 weeks reduced the hepatic expression of G6Pase, PEPCK, and HNF4α. These results suggest that green tea contains some component(s) with insulin-like activity distinguishable from EGCG and that drinking green tea may help to prevent diabetes.

Green tea and its constituent (-)-epigallocatechin-3-O-gallate (EGCG) are known to have apoptosis-inducing activity on tumor cells including human leukemia HL-60 cells, providing an explanation for their anti-cancer effects. In the present study, we compared the sensitivity of undifferentiated cells and differentiated HL-60 cells with normal-like phenotypic characters. HL-60 cells treated with three differentiating agents were found to be resistant to EGCG-mediated apoptosis as compared with undifferentiated cells. Gene and protein expression of 67 kDa laminin receptor was down-regulated in differentiated HL-60 cells, suggesting its contribution to the difference in sensitivity in view of the fact that the receptor is a target of EGCG's action to induce apoptosis. The finding supports the view that EGCG induces apoptosis preferentially in cancer cells as compared with normal counterparts.

Green tea has been shown to have many beneficial health effects. We have previously reported that dietary (-)-epigallocatechin-3-O-gallate (EGCG), the major polyphenol in green tea, reduced gene expressions of gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), in the normal mouse liver. In the present study, we examined the effects of intragastrical administration of EGCG on the expression of gluconeogenesis-related genes in the mouse intestine. The results of experiments with the semi-quantitative reverse transcription-polymerase chain reaction indicated that EGCG at 0.6 mg/head caused a reduced expression of G6Pase, PEPCK, hepatocyte nuclear factor 1α (HNF1α), and HNF4α. Experiments using the quantitative real-time polymerase chain reaction confirmed these effects. We then examined the effects of EGCG using human colon carcinoma Caco-2 cells stimulated with dexamethasone and dibutyryl cAMP. The results were generally consistent with those from the experiments in vivo. The present findings suggest EGCG to contribute to the beneficial effects of green tea on diabetes, obesity, and cancer by modulating gene expression in the intestine.

Tea has many beneficial effects. We have previously reported that green tea and a catechin-rich green tea beverage modulated the gene expression of the gluconeogenic enzymes glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) in the normal murine liver. In the present study, we examined the effects of oral administration of oolong tea on the hepatic expression of gluconeogenesis-related genes in the mouse. The intake of oolong tea for 4 weeks reduced the hepatic expression of G6Pase and PEPCK together with that of the transcription factor hepatocyte nuclear factor (HNF) 4α. When rat hepatoma H4IIE cells were incubated in the presence of oolong tea, the expression of these genes was repressed in accordance with the findings in vivo. The reduced protein expression of PEPCK and HNF4α was also demonstrated. We then fractionated oolong tea by sequential extraction with three organic solvents to give three fractions and the residual fraction (Fraction IV). In addition to organic fractions, Fraction IV, which was devoid of low-molecular-weight catechins such as (-)-epigallocatechin gallate (EGCG), had effects similar to those of oolong tea on H4IIE cells. Fraction IV repressed the gene expression of insulin-like growth factor binding protein 1, as insulin did. This activity was different from that of EGCG. The present findings suggest that drinking oolong tea may help to prevent diabetes and that oolong tea contains a component or components with insulin-like activity distinguishable from EGCG. Identification of such component(s) may open the way to developing a new drug for diabetes.

Rat hepatoma H4IIE cells were stimulated with dexamethasone and dibutyryl cAMP to increase gene expressions of gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Inclusion of catechin-rich green tea beverage (GTB) in the culture medium reduced the up-regulation of these genes as well as that of hepatocyte nuclear factor 4 alpha (HNF4alpha) gene. GTB was fractionated into chloroform-soluble (Fraction I), ethyl acetatesoluble (Fraction II), methanol-soluble (Fraction III) and residual (Fraction IV) fractions. Fractions II and III containing catechins caused an attenuation of the up-regulated expression of these genes as well as the down-regulation of HNF4alpha gene expression. Fraction IV had a synergistic effect on the up-regulation by dexamethasone/dibutyryl cAMP of the PEPCK gene expression and upregulated HNF4alpha gene expression. These results suggest that GTB down-regulated the expression of the HNF4alpha gene to cause the down-regulated gene expression of gluconeogenic enzymes. One reason why GTB did not down-regulate hepatic PEPCK gene expression in previous animal experiments may be that the component(s) acting to up-regulate PEPCK gene expression was more effective in vivo than in cultured cells.

The importin/exportin transport system provides the machinery involved in nucleocytoplasmic transport. Alterations of the levels of importins and exportins may play crucial roles in development, differentiation and transformation. Employing human leukaemia HL-60 cells, we and others have revealed the differentiation-associated changes in the protein and gene expression of these factors. The recent finding that a switch to the importin-alpha subtype triggers neural differentiation of embryonic stem cells underscores the importance of nucleocytoplasmic transport factors in cellular events. This review focuses on current research into the roles of importins and exportins in cell differentiation.

Employing the DNA microarray technique, we previously reported the alteration in gene expression of nucleocytoplasmic transport factors, importins and exportins, induced by 1,25-dihydroxyvitamin D3 (DVD) in human leukemia HL-60 cells. Here, we used the quantitative reverse transcription-polymerase chain reaction method to confirm such previous findings, and compared them with those from the cells treated with all-trans-retinoic acid (ATRA). The results indicated that the gene expression of the transport factors examined was mostly down-regulated following differentiation induced by DVD and ATRA, but importin alpha5 gene expression was up-regulated in either case. The differences were found in the gene expression of importin alpha3 and exportin 6 between the cells after treatments with DVD and ATRA. These variations may be related to the difference between HL-60 cell lineages differentiating into monocytes/macrophages and granulocytes. The present findings provide further evidence to support the important roles of importins and exportins in cell differentiation.