The effects of troglitazone on AMPK in HepG2 cells

AMP-activated protein kinase (AMPK) is an enzyme crucial in cellular metabolism found to be inhibited in many metabolic diseases including type 2 diabetes. Thiazolidinediones (TZDs) are a class of anti-diabetic drug known to activate AMPK through increased phosphorylation at Thr¹⁷², however there has been no research to date on whether they have any effect on inhibition of AMPK's lesser known site of inhibition, Ser^485/491. HepG2 cells were treated with troglitazone and phosphorylation of AMPK was found to increase at both Thr¹⁷² and Ser⁴⁸⁵ in a dose- and time-dependent manner. Treatment of HepG2 cells with insulin and PMA led to increases in p-AMPK Ser⁴⁸⁵ via Akt and PKD1 respectively; however these kinases were not found to be implicated in increases seen from troglitazone. Incubation with the other TZDs, rosiglitazone and pioglitazone, let to a minor increase in p-AMPK Ser⁴⁸⁵ phosphorylation as well as AMPK activity; however these findings were significantly less than those of troglitazone under equal conditions. These data suggest that the effects of troglitazone on AMPK are more complex than previously thought. Phosphorylation at sites of both activation and inhibition can occur in tandem, although the mechanism by which this occurs has not yet been elucidated.