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United States Department of Agriculture

Agricultural Research Service

Research Project: Linking Foods, Behavior and Metabolism to Promote a Healthy Body Weight

Location: Obesity and Metabolism Research Unit

Title: Molecular Characterization of the Tumor Suppressor Candidate 5 Gene: Regulation by PPARg and Identification of TUSC5 Coding Variants in Lean and Obese Humans

Authors
item Knotts, Trina
item Lee, Hyum Woo -
item Kim, Jae Bum -
item Oort, Pieter
item Mcpherson, Ruth -
item Dent, Robert -
item Tachibana, Keisuke -
item Doi, Takefumi -
item Yu, Songtao -
item Reddy, Janardan -
item Uno, Kenji -
item Katagiri, Hideki -
item Pasarica, Magdalena -
item Smith, Steven -
item Sears, Dorothy -
item Grino, Michel -
item Adams, Sean

Submitted to: Trade Journal Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 13, 2009
Publication Date: November 1, 2009
Repository URL: http://downloads.hindawi.com/journals/ppar/2009/867678.pdf
Citation: Knotts, T.A., Lee, H., Kim, J., Oort, P.J., Mcpherson, R., Dent, R., Tachibana, K., Doi, T., Yu, S., Reddy, J.K., Uno, K., Katagiri, H., Pasarica, M., Smith, S.R., Sears, D.S., Grino, M., Adams, S.H. 2009. Molecular Characterization of the Tumor Suppressor Candidate 5 Gene: Regulation by PPARg and Identification of TUSC5 Coding Variants in Lean and Obese Humans. Trade Journal Publication. PPAR Research Vol. Article ID 867678. 1-13, 2009.

Interpretive Summary: Tumor suppressor candidate 5 (Tusc5) is a member of a new group of factors with unique robust expression in both fat cells and afferent peripheral neurons that carry information regarding tissue status to the brain. Since Tusc5 was initially found to be up-regulated by chemical activators of the adipose-abundant nuclear protein (PPARgamma, PPARg) known to influence metabolism-relevant genes, we reasoned that the gene is a bona fide PPARg target gene and is involved in important adipocyte functions. This study examined this question by testing if PPARg physically binds the Tusc5 gene sequence, and we tested if the increased Tusc5 expression in response to PPARg agonists seen in cultured fat cells is translatable to the human condition. We further determined if fat tissue expression of this gene or its sequence differs in obese persons. 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 PPAR' protein binds a ~-1.1 kb promotor sequence of murine TUSC5 transiently during maturation of 3T3-L1 fat cells (around 4 days post-differentiation, when Tusc5 expression is typically induced). Surprisingly, no change in Tusc5 mRNA or protein levels was evident in type 2 diabetic patients treated >11 wk with the PPARg agonist drug 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 PPAR-gamma agonism. Finally, we observed no differences in Tusc5 WAT expression or the prevalence of gene sequence differences in lean versus obese human subjects. Therefore, the current studies firmly establish the mouse 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.

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.

Last Modified: 9/2/2014
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