Cross-talk between peroxisome proliferator-activated receptor (PPAR) alpha and liver X receptor (LXR) in nutritional regulation of fatty acid metabolism. I. PPARs suppress sterol regulatory element binding protein-1c promoter through inhibition of LXR signaling.
Liver X receptors (LXRs) and peroxisome proliferator-activated receptors (PPARs) are members of nuclear receptors that form obligate heterodimers with retinoid X receptors (RXRs). These nuclear receptors play crucial roles in the regulation of fatty acid metabolism: LXRs activate expression of sterol regulatory element-binding protein 1c (SREBP-1c), a dominant lipogenic gene regulator, whereas PPARalpha promotes fatty acid beta-oxidation genes. In the current study, effects of PPARs on the LXR-SREBP-1c pathway were investigated. Luciferase assays in human embryonic kidney 293 cells showed that overexpression of PPARalpha and gamma dose-dependently inhibited SREBP-1c promoter activity induced by LXR. Deletion and mutation studies demonstrated that the two LXR response elements (LXREs) in the SREBP-1c promoter region are responsible for this inhibitory effect of PPARs. Gel shift assays indicated that PPARs reduce binding of LXR/RXR to LXRE. PPARalpha-selective agonist enhanced these inhibitory effects. Supplementation with RXR attenuated these inhibitions by PPARs in luciferase and gel shift assays, implicating receptor interaction among LXR, PPAR, and RXR as a plausible mechanism. Competition of PPARalpha ligand with LXR ligand was observed in LXR/RXR binding to LXRE in gel shift assay, in LXR/RXR formation in nuclear extracts by coimmunoprecipitation, and in gene expression of SREBP-1c by Northern blot analysis of rat primary hepatocytes and mouse liver RNA. These data suggest that PPARalpha activation can suppress LXR-SREBP-1c pathway through reduction of LXR/RXR formation, proposing a novel transcription factor cross-talk between LXR and PPARalpha in hepatic lipid homeostasis.
Yoshikawa
Tomohiro
T
Department of Metabolic Diseases, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Japan.
Ide
Tomohiro
T
Shimano
Hitoshi
H
Yahagi
Naoya
N
Amemiya-Kudo
Michiyo
M
Matsuzaka
Takashi
T
Yatoh
Shigeru
S
Kitamine
Tetsuya
T
Okazaki
Hiroaki
H
Tamura
Yoshiaki
Y
Sekiya
Motohiro
M
Takahashi
Akimitsu
A
Hasty
Alyssa H
AH
Sato
Ryuichiro
R
Sone
Hirohito
H
Osuga
Jun-Ichi
J
Ishibashi
Shun
S
Yamada
Nobuhiro
N
D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D022762:CCAAT-Enhancer-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006845:Hydrocarbons, Fluorinated; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D000071518:Liver X Receptors; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009747:Nutritional Physiological Phenomena; D057093:Orphan Nuclear Receptors; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000187:drug effects / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D047488:Retinoid X Receptors; D015398:Signal Transduction; D051780:Sterol Regulatory Element Binding Protein 1; D013449:Sulfonamides; D014157:Transcription Factors / Q000819:agonists / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
D000924:Anticholesteremic Agents; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D005227:Fatty Acids; D006845:Hydrocarbons, Fluorinated; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D011743:Pyrimidines; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D051780:Sterol Regulatory Element Binding Protein 1; D013449:Sulfonamides; D014157:Transcription Factors; C497387:SREBF1 protein, human; C497388:Srebf1 protein, mouse; C497389:Srebf1 protein, rat; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides; C006253:pirinixic acid