We report the cloning and expressional analysis of rat brain endothelial cell derived gene-1 (BEC-1), detected as a gene dominantly expressed in rat brain endothelial cells by the use of suppression subtractive hybridization technique. The complementary deoxyribonucleic acid sequence of BEC-1 messenger ribonucleic acid was completely determined with a full length of 3410 bp. The open reading frame within the sequence consisted of 522 bp, and the predicted protein sequence was 173 amino acid residues. BEC-1 gene was thought to be rat tumor suppressor candidate 5 (TUSC5), since BEC-1 had considerable homology with both mouse TUSC5 and human located at 17-p-13 point three 1 (LOST1) categorized as human TUSC5 (identities of 97% and 85%, respectively), which were recently identified as a novel tumor suppressor gene candidate. Expressional analyses for BEC-1 mRNA with real-time PCR and of BEC-1 protein by Western blotting demonstrated that both were dominantly expressed in the adipose tissues of Sprague-Dawley (SD) rats. We analyzed and compared the differential expressions of BEC-1 (TUSC5) mRNA and protein in fat tissues between obese homozygous (fa/fa) and lean wild-type (+/+) Zucker rats. Both expressions in the epididymal white adipose tissue (WAT) were highest, followed by those in the interscapular brown adipose tissue (BAT), subcutaneous, and mesenteric WATs, respectively. Interestingly, both expressions in epididymal WAT of obese Zucker rats were significantly lower than those in lean rats. Although cold exposure at 4 degrees C for 6 h significantly stimulated uncoupling protein-1 (UCP-1) mRNA expression, it significantly inhibited BEC-1 (TUSC5) mRNA expression in the interscapular BAT. These data indicated that rat BEC-1 (TUSC5) was abundantly expressed in adipose tissues, and that it might be involved in their regulation independently of UCP-1.