We have used a mRNA differential display technique to identify new genes involved in the reprogramming of gene expression during the adipose conversion of mouse 3T3 preadipocyte cell lines. We report here on the identification and cloning of a novel adipose-specific cDNA encoding a predicted membrane protein of 413 amino acids. The level of the corresponding 3.2-kilobase mRNA is tremendously increased during 3T3-L1 and 3T3-F442A differentiation into adipocytes. A single, very abundant 3.2-kilobase transcript is also found in inguinal and epididymal white adipose tissues and in interscapular brown adipose tissue but not in any other tissues examined. Its expression in adipose tissue is under tight nutritional regulation. The level of this novel 3.2-kilobase transcript becomes virtually nondetectable during fasting but is dramatically increased when fasted mice are refed a high carbohydrate diet. Based on its adipose specificity and dietary regulation, the novel gene product has been designated adiponutrin. The expression of adiponutrin mRNA is also 50-fold elevated in genetically obese fa/fa rats, indicating a link between adiponutrin and obesity. Western blot and confocal imagery analyses with epitope-tagged protein transiently expressed in 3T3-L1 adipocytes, and COS cells show that adiponutrin strictly localizes to membranes and is absent from the cytosol. Sequence analysis reveals homologies with several other members of related eukaryotic proteins, including a human paralog, which has been recently described in vesicular transport mechanisms. This leads us to suggest that adiponutrin could be involved in vesicular targeting and protein transport restricted to the adipocyte function.

Tumor necrosis factor-␣ (TNF␣) is involved in the physiological and biological abnormalities found in two opposite metabolic situations: cachexia and obesity. In an attempt to identify novel genes and proteins that could mediate the effects of TNF␣ on adipocyte metabolism and development, we have used a differential display technique comparing 3T3-L1 cells exposed or not to the cytokine. We have isolated a novel adipose cDNA encoding a TNF␣-inducible 470-amino acid protein termed TIARP, with six putative transmembrane regions flanked by a large amino-terminal and a short carboxyl-terminal domain, a structure reminiscent of channel and transporter proteins. Commitment into the differentiation process is required for cytokine responsiveness. The differentiation process per se is accompanied by a sharp emergence of TIARP mRNA transcripts, in parallel with the expression of the protein at the plasma membrane. Transcripts are present at high levels in white and brown adipose tissues, and are also detectable in liver, kidney, heart, and skeletal muscle. Whereas the biological function of TIARP is presently unknown, its pattern of expression during adipose conversion and in response to TNF␣ exposure as a transmembrane protein mainly located at the cell surface suggest that TIARP might participate in adipocyte development and metabolism and mediate some TNF␣ effects on the fat cell as a channel or a transporter. Tumor necrosis factor-alpha (TNF␣)1 exerts a wide range of effects on cells and tissues. In addition to its immunological functions, TNF␣ also markedly alters adipose tissue development and metabolism. Surprisingly, TNF␣ seems to be involved in the pathophysiology of two opposite metabolic disorders (1). High plasma levels of TNF␣ likely play an important role in the onset of cachectic states observed during cancer or severe infectious diseases (2). By contrast, more recent studies have indicated that the cytokine is overexpressed in adipose tissue of obese rodents or humans, and that this locally produced TNF␣ may be involved in the obesity-linked insulin resistance (3). Thus, since abnormalities in its production or action are associated with alterations in body fat mass, TNF␣ is likely an important effector of adipose tissue development and metabolism in vivo.Many in vitro studies also support the view that TNF␣ has profound effects on lipid metabolism and adipocyte differentiation. TNF␣ was reported to inhibit lipid storage by reducing synthesis and activity of several proteins essential for lipogenesis, such as lipoprotein lipase (4) and acetyl-coenzyme A carboxylase (5), or by inhibition in the expression and/or function of the insulin-sensitive glucose transporter GLUT4 pathway (6). Otherwise TNF␣ is able to stimulate lipolysis in adipocytes by different mechanisms (7,8). In addition to the above effects on lipid storage or mobilization, TNF␣ potently inhibits adipose conversion and even causes a dramatic de-differentiation of adipocytes in culture (9). Prevention of adipose conversion by TNF␣ has been es...