Technical Abstract: Tumor suppressor candidate 5 (Tusc5) is a cold-regulated gene expressed abundantly in human and rodent white adipose tissue (WAT), rodent brown adipose tissue (BAT), and peripheral afferent neurons. Strong adipocyte expression and our observation of increased expression following peroxisome proliferator activated receptor gamma (PPARg) agonist treatment of 3T3-L1 adipocytes suggested a role for Tusc5 in fat cell proliferation and/or metabolism. However, the regulation of Tusc5 in WAT and its potential association with obesity phenotypes remains unclear. In the current studies, we tested the hypothesis that the TUSC5 gene is a bona fide PPARg target, and evaluated whether its WAT expression or single-nucleotide polymorphisms (SNPs) in the TUSC5 coding region are associated with human obesity. Induction of Tusc5 mRNA levels in mature 3T3-L1 adipocytes by the PPARg agonists troglitazone and GW1929 followed a dose-response consistent with these agents’ known binding affinities for PPARg. Chromatin immunoprecipitation (ChIP) experiments confirmed that PPARg protein binds a ~-1.1 kb promotor sequence of murine TUSC5 transiently during maturation of 3T3-L1 adipocytes (around 4 days post-differentiation, when Tusc5 expression is typically induced), concurrent with increased histone H3 acetylation. Surprisingly, no change in Tusc5 mRNA or protein levels was evident in type 2 diabetic patients treated >11 wk with pioglitazone. Tusc5 expression could not be induced appreciably in liver despite maneuvers that increased hepatic PPAR expression, suggesting that tissue-specific factors regulate responsiveness of the TUSC5 gene to PPARg agonism. Finally, we observed no differences in Tusc5 WAT expression or the prevalence of coding region SNPs in lean versus obese human subjects. Therefore, the current studies firmly establish the murine TUSC5 gene locus as a PPARg target, but the significance of Tusc5 in obesity phenotypes or in the pharmacologic actions of PPARg agonists in humans remains equivocal.