Troglitazone stimulates acetyl-CoA carboxylase activity through a post-translational mechanism

Troglitazone, a thiazolidinedione, is known to act as an insulin sensitizer . The various effects of the drug include stimulation of glucose utilizatio n and inhibition of gluconeogenesis and fatty acid oxidation. We studied th e effect of troglitazone treatment on rat liver acetyl-CoA carboxylase (ACC ), the key enzyme that catalyzes the formation of malonyl-CoA, the rate-lim iting step in the synthesis of long chain fatty acids. Treatment of rats wi th troglitazone for 18 days resulted in more than 200% increase in the acti vity of hepatic acetyl-CoA carboxylase (1.01 +/- 0.14 and 2.33 +/- 0.28 mU/ mg supernatant protein for control and troglitazone-treated rats, respectiv ely) (p<0.001). The expression of acetyl-CoA carboxylase mRNA, as studied b y RNAse protection assay, was not significantly different between the two g roups of animals. The ACC from control and troglitazone-treated groups was purified by avidin-affinity chromatography. The purified enzyme migrated as a major protein band (M-r 262,000) on SDS-polyacrylamide gels. Troglitazon e treatment was associated with increased citrate sensitivity of ACC. The s pecific activity of the purified preparation in troglitazone-treated rats w as increased by 67% (2.5 vs. 1.5 U/mg). Quantitation of alkali labile phosp hate content of the purified preparation revealed 5.66 +/- 0.17 and 6.29 +/ - 0.13 mol Pi/mol subunit of 262 Kda for control and troglitazone-treated r ats, respectively (P<0.01). The subtle increase in phosphate content does n ot explain the observed activation of the enzyme. It is possible that addit ional mechanisms such as troglitazone related rearrangement of the occupanc y of select phosphate binding sites or altered binding of the biotin cofact or may also contribute to the observed activation of ACC. (C) 2000 Elsevier Science Inc. All rights reserved.