Abstract 5276: Sumoylation Of Klf5 Is A Molecular Switch Regulating Ppar-δ-containing Transcriptional Programs Of Lipid Metabolism
Metabolic syndrome is increasingly recognized as a major risk factor for cardiovascular disease. We have previously shown that a zinc finger transcription factor, Krüppel-like factor 5 (KLF5), plays an important role in cardiovascular diseases, such as atherosclerosis and cardiac hypertrophy. Interestingly, KLF5 is also expressed in metabolic tissues, such as adipose tissue, skeletal muscle and pancreatic β-cells. Moreover, we found that KLF5 is crucial for adipocyte differentiation. Therefore, it is very likely that KLF5 plays multiple roles in development and progression of metabolic syndrome and its cardiovascular and metabolic consequences including atherosclerotic cardiovascular disease. Indeed, KLF5 heterozygous knockout (KLF5+/−) mice were resistant to high-fat-induced obesity and metabolic syndrome, despite consuming more food than wild-type mice. This appears to in part reflect their enhanced energy expenditure. Expression of the genes involved in lipid oxidation and energy uncoupling, including uncoupling protein (UCP) and carnitine-palmitoyl transferase 1b (CPT1b) was upregulated in the soleus muscles of KLF5+/− mice. KLF5 could be reversibly modified by small ubiquitin-like modifier 1 (SUMO1), after which SUMOylated KLF5 strongly inhibited CPT1b, UCP3 and UCP2 promoter activity. Results of chromatin immunoprecipitation, two-hybrid, and reporter assays showed that under basal conditions SUMOylated KLF5 associated with transcriptionally repressive regulatory complexes containing unliganded PPARδ and corepressors. However, upon agonist stimulation of PPARδ, the deSUMOylating enzyme was recruited and KLF5 was deSUMOylated. The unSUMOylated KLF5 now formed transactivating complexes with liganded PPARδ and CBP. Thus, SUMOylation appears to be a molecular switch affecting function of KLF5 and the transcriptional regulatory programs governing lipid metabolism. Moreover, KLF5 is essential for the PPARδ agonist-dependent transcriptional control. Results of the present study have established KLF5 as a novel key molecule in lipid metabolism and suggest that the posttranscriptional modification of KLF5 is an attractive novel therapeutic target for both metabolic and cardiovascular diseases.