Beta-catenin inhibits TR4-mediated lipid accumulation in 3T3-L1 adipocytes via induction of Slug.

Background: TR4, an orphan nuclear receptor plays a key role in glucose and lipid metabolism by regulating the expression of genes involved in energy metabolism. We previously reported that overexpression of TR4 in 3T3-L1 adipocytes promotes lipid accumulation in part by facilitating fatty acid uptake and synthesis, indicating that TR4 tightly regulates lipid homeostasis during adipogenesis. Here, we report that β-catenin suppresses TR4 transcriptional activity and that this inhibition is achieved through induction of Slug gene, a well-known transcription repressor in a variety of cells.

Methods: To generate the stable cell line, 3T3-L1 cells were transfected with plasmids then cultured in presence of geneticin and/or blasticidin for 2 weeks. The lipid accumulation was measured by Oil Red O. The TR4-Slug and TR4-β-catenin interactions were checked by GST pull-down and mammalian two-hybrid assay. The TR4 transcriptional activities on various promoters were measured by luciferase activity. To check the binding affinity of TR4, we performed the gel shift and chromatin immunoprecipitation (ChIP) assay. Gene expression was detected by RT-qPCR at the mRNA level and western blotting at the protein level.

Results: Stable overexpression of Slug gene in 3T3-L1 preadipocytes strongly inhibited differentiation of 3T3-L1 preadipocytes. Using GST pull-down, gel shift and ChIP assays, we found that Slug abolished the formation of TR4 homodimers through direct interaction with TR4 and reduced the binding affinity of TR4 for its response elements located in TR4 target gene promoters such as fatty acid transport protein 1 and pyruvate carboxylase. Consistently, Slug inhibited TR4 target gene expression and was accompanied by repression of TR4-induced lipid accumulation in 3T3-L1 adipocytes.

Conclusions: Our results demonstrated that Slug inhibits 3T3-L1 adipogenesis through suppression of TR4 transcriptional activity.