dc.description.abstract | Forkhead box class O (FoxO) transcription factors contained FoxO1, FoxO3, FoxO4, and FoxO6, and they have been respectively reported to regulate diverse cellular functions, including differentiation, energy metabolism, cell survival, and cell cycle. In this study using the preadipocyte-adipocyte differentiation system of 3T3-L1 cells induced by dexamethasone, insulin and 1-methyl-3-isobutylxanthine, we examined changes in the FoxO6 protein expression during the adipogenic process. We found that FoxO6 increased its protein levels by about 100% during the 14-day period of fat cell differentiation. Also, levels of cytosolic and nuclear FoxO6 were increased by 50% and 1100%, repectively. This suggests the differentiation-dependent protein expression of FoxO6. Because green tea catechins, especially (-)-epigallocatechin gallate(EGCG), were reported to reduce FoxO1 phosphorylation and increase its transcriptional activity, we studied herein whether EGCG altered protein levels of FoxO6 and other FoxO members during adipocyte differentiation. EGCG at 5 µM tended to increase FoxO6 protein levels at Day 2, 6, and 12 differentiating cells, while, at 25 µM, it tended to decrease FoxO6 protein expression at Day 8 and 10 differentiating cells. This suggests the dose- and differentiation stage-dependent effect of EGCG on FoxO6 protein expression. However, treatment with 5 µM EGCG decreased FoxO1 levels at Day 2 cells, unaltered FoxO1 levels at Day 6 cells, and increased FoxO1 at Day 12 cells, respectively. EGCG at 5 µM increased FoxO3 levels at Day 2 cells, decreased FoxO3 levels at Day 6 cells, and increased FoxO3 levels at Day 12 cells. Treatment with 25 µM EGCG decreased FoxO1 levels at Day 8 cells and unaltered FoxO1 levels at Day 10 cells, while it unaltered FoxO3 levels at Day 8 cells and decreased FoxO3 protein expression at Day 10 cells. These data suggest that EGCG selectively affects particular types of FoxO family members and the effect varies with the duration and dosage of EGCG treatment and with different differentiation stages of fat cells. | en_US |