Expression of a novel insulin-activated amino acid transporter gene during differentiation of 3T3-L1 preadipocytes into adipocytes.

A cDNA encoding a novel insulin-activated adipocyte amino acid transporter (designated AAAT) was cloned from a mouse 3T3-L1 adipocyte library. The deduced amino acid sequence of the cDNA corresponds to a protein of 553 amino acids that possesses 56% amino acid sequence identity to the human neutral amino acid transporter and 42% identity to the rat brain glutamate transporter. Transient transfection of 3T3-L1 preadipocytes with an AAAT expression vector led to insulin-dependent uptake of L-serine and to a lesser extent, uptake of L-alanine and L-glutamate. Expression of the AAAT message is tissue-specific, with the highest level occurring in mouse adipose tissue and a lower level in lung. Unlike other sodium-dependent amino acid transporter mRNAs, the AAAT message is not expressed in brain, kidney, liver or heart and only traces are detected in spleen, thymus and skeletal muscle. Consistent with its high level in adipose tissue, expression of the AAAT message is markedly increased when 3T3-L1 preadipocytes are induced to differentiate into adipocytes.