Inhibitory effect of green tea (-)-epigallocatechin gallate on resistin gene expression in 3T3-L1 adipocytes depends on the ERK pathway.

Resistin (Rstn) is known as an adipocyte-specific secretory hormone that can cause insulin resistance and decrease adipocyte differentiation. By contrast, green tea catechins, especially (-)-epigallocatechin gallate (EGCG), have been reported as body weight and diabetes chemopreventatives. Whether EGCG regulates production of Rstn is unknown. Using 3T3-L1 adipocytes, we found that EGCG at 20 and 100 microM suppressed Rstn mRNA levels by approximately 35 and 50%, respectively, after 3 h. The basal half-life of Rstn mRNA induced by actinomycin D was >12 h but shifted to 3 h in the presence of EGCG. This suggests that EGCG regulates the stability of Rstn mRNA. Treatment with cycloheximide did not prevent EGCG-suppressed Rstn mRNA levels, which suggests that the effect of EGCG does not require new protein synthesis. Intracellular Rstn protein significantly decreased in the presence of 100 microM EGCG 3 h after treatment, whereas the release of the Rstn protein did not significantly change. This suggests that EGCG may modulate the distribution of Rstn protein between the intracellular and extracellular compartments. EGCG did not affect the amounts of extracellular signal-related kinase-1/2 (ERK1/2), phospho-JNK, phospho-p38, and phospho-Akt proteins but reduced the amounts of phospho-ERK1/2 proteins. Overexpression with MEK1 blocked EGCG-inhibited Rstn mRNA expression. These data suggest that EGCG downregulates Rstn expression via a pathway that is dependent on the ERK pathway.