Clofibric acid stimulates branched-chain amino acid catabolism by three mechanisms Rumi Kobayashi, a,b Taro Murakami, a,c Mariko Obayashi, a,c Naoya Nakai, c Jerzy Jaskiewicz, a Yoko Fujiwara, b Yoshiharu Shimomura, c and Robert A. Harris a, * a Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202-5122, USA b Department of Nutrition and Food Science, Ochanomizu University, Tokyo 112-8610, Japan c Department of Bioscience, Nagoya Institute of Technology, Nagoya 466-8555, Japan Received 10 July 2002, and in revised form 12 August 2002 Abstract Clofibrate promotes catabolism of branched-chain amino acids by increasing the activity of the branched-chain a-keto acid dehydrogenase [BCKDH] complex. Depending upon the sex of the rats, nutritional state, and tissue being studied, clofibrate can affect BCKDH complex activity by three different mechanisms. First, by directly inhibiting BCKDH kinase activity, clofibrate can increase the proportion of the BCKDH complex in the active, dephosphorylated state. This occurs in situations in which the BCKDHcomplexislargelyinactiveduetophosphorylation,e.g.,intheskeletalmuscleofchow-fedratsorintheliveroffemalerats late in the light cycle. Second, by increasing the levels at which the enzyme components of the BCKDH complex are expressed, clofibrate can increase the total enzymatic activity of the BCKDH complex. This is readily demonstrated in livers of rats fed a low- protein diet, a nutritional condition that induces a decrease in the level of expression of the BCKDH complex. Third, by decreasing the amount of BCKDH kinase expressed and therefore its activity, clofibrate induces an increase in the percentage of the BCKDH complex in the active, dephosphorylated state. This occurs in the livers of rats fed a low-protein diet, a nutritional condition that causes inactivation of the BCKDH complex due to upregulation of the amount of BCKDH kinase. WY-14,643, which, like clofibric acid, is a ligand for the peroxisome-proliferator-activated receptor a [PPARa], does not directly inhibit BCKDH kinase but pro- duces the same long-term effects as clofibrate on expression of the BCKDH complex and its kinase. Thus, clofibrate is unique in its capacitytostimulateBCAAoxidationthroughinhibitionofBCKDHkinaseactivity,whereasPPARa activatorsingeneralpromote BCAA oxidation by increasing expression of components of the BCKDH complex and decreasing expression of the BCKDH kinase. Ó 2002 Elsevier Science (USA). All rights reserved. Keywords: Clofibrate; Clofibric acid; Branched-chain amino acids; Branched-chain a-keto acid dehydrogenase complex; Branched-chain a-keto acid dehydrogenase kinase; Rat; Liver; WY-14,643; PPARa The branched-chain a-keto acid dehydrogenase [BCKDH] 1 complex is the most important regulatory enzyme in the catabolic pathways of the branched-chain amino acids, leucine, isoleucine, and valine (reviewed in [1]). The complex consists of three catalytic components: a branched-chain a-keto acid decarboxylase (E1; het- erotetramer of a and b subunits, EC 1.2.4.4), a di- hydrolipoyl transacylase (E2; no EC number), and a dihydrolipoyl dehydrogenase (E3; EC 1.8.1.4) (reviewed in [2]). Activity of the complex is controlled by covalent modification with phosphorylation of its E1a subunits by a specific kinase (BCKDH kinase, EC 2.7.1.115) causing inactivation [3,4] and dephosphorylation by a specific phosphatase (BCKDH phosphatase, EC 3.1.3.52) causing reactivation of the complex [5]. Known mechanisms for short-term control of the activity of BCKDH complex include direct inhibition of the activity of the complex by NADH and CoA esters Archives of Biochemistry and Biophysics 407 (2002) 231–240 www.academicpress.com ABB * Corresponding author. Fax: 1-317-274-4686. E-mail address: raharris@iupui.edu (R.A. Harris). 1 Abbreviations used: BCKDH, branched-chain a-keto acid dehy- drogenase; PPARa, peroxisome proliferator activated receptor a;WY- 14,643, 4-chloro-6-[2,3-xylidino]-2-pyrimidinylthiolacetic acid. 0003-9861/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII:S0003-9861(02)00472-1