Adiponutrin, a transmembrane protein corresponding to a novel dietary- andobesity-linked mRNA specifically expressed in the adipose lineage

We have used a mRNA differential display technique to identify new genes in volved in the reprogramming of gene expression during the adipose conversio n of mouse 3T3 preadipocyte, cell lines. We report here on the identificati on and cloning of a novel adipose-specific cDNA encoding a predicted membra ne 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 fo und in inguinal and epididymal white adipose tissues and in interscapular b rown adipose tissue but not in any other tissues examined. Its expression i n adipose tissue is under tight nutritional regulation. The level of this n ovel 3.2-kilobase transcript becomes virtually nondetectable during fasting but is dramatically increased when fasted mice are refed a high carbohydra te diet. Based on its adipose specificity and dietary regulation, the novel gene product; has been designated adiponutrin. The expression of adiponutr in mRNA is also 50-fold elevated in genetically obese fa/fa rats, indicatin g a link between adiponutrin and obesity. Western blot and confocal imagery analyses with epitope-tagged protein transiently expressed in 3T3-L1 adipo cytes, 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 par alog, which has been recently described in vesicular transport mechanisms. This leads us to suggest that adiponutrin could be involved in vesicular ta rgeting and protein transport restricted to the adipocyte function.