Predominant expression of the mitochondrial dicarboxylate carrier in whiteadipose tissue

We report the identification of a novel mouse protein closely related to th e family of mitochondrial uncoupling proteins and the oxoglutarate carrier. The cDNA encodes a protein of 287 amino acids that shares all the hallmark features of the mitochondrial transporter superfamily, including six predi cted transmembrane domains. It is nearly identical to the sequence recently reported for the rat mitochondrial dicarboxylate carrier (DIC). We find th at murine DIC (mDIC) is expressed at very high levels in mitochondria of wh ite adipocytes and is strongly induced in the course of 3T3-L1 adipogenesis . To determine the consequences of the presence of mDIC on the mitochondria l membrane potential, we transiently expressed mDIC in 293-T cells. Over-ex pression of mDIC leads to significant mitochondrial hyperpolarization. In a ddition, exposure to cold down-regulates mDIC levels in vivo. In contrast, free fatty acids lead to an up-regulation of mDIC protein in 3T3-L1 adipocy tes. This is the first report demonstrating preferential expression in whit e adipose tissue of any mitochondrial transporter. However, it remains to b e determined which metabolic pathways most critically depend on high level expression of mDIC in the adipocyte.