A promoter in the novel exon of hPPARgamma directs the circadian expression of PPARgamma.
OBJECTIVE
PPARgamma (peroxisome proliferator-activated receptor gamma) is a member of the nuclear receptor superfamily of ligand-activated transcription factors that regulate the expression of genes associated with lipid metabolism. Herein, we show that expression levels of the novel PPARgamma transcript exhibit circadian oscillation. To study the mechanisms controlling PPARgamma expression, a novel PPARgamma gene promoter was cloned and characterized.


METHODS
We analyzed the novel PPARgamma promoter by luciferase reporter assays and gel shift analysis.


RESULTS
Surprisingly, it was not an intron but rather the novel first exon of PPARgamma that was found to have functional minimal promoter activity. Luciferase reporter assays and gel shift assays revealed that the novel first exon is essential for novel PPARgamma promoter activation and that DBP (albumin gene D-site binding protein) and E4BP4 (E4 promoter A binding protein 4) bind directly to D-sites in the novel first exon.


CONCLUSIONS
Our results demonstrate that the PAR-bZIP (bZIP, basic leucine zipper) family and E4BP4 are the main regulatory factors involved in oscillation of novel PPARgamma expression. This regulatory mechanism clearly differs from that of the circadian expression of PPARalpha.
Takahashi
Seiichiro
S
Department of Diabetes and Endocrinology, Saitama Medical University, Saitama 350-0495, Japan. se_takah@saitama-med.ac.jp
Inoue
Ikuo
I
Nakajima
Yoshihiro
Y
Seo
Makoto
M
Nakano
Takanari
T
Yang
Fang
F
Kumagai
Megumi
M
Komoda
Tsugikazu
T
Awata
Takuya
T
Ikeda
Masaaki
M
Katayama
Shigehiro
S
D024506:5' Flanking Region / Q000235:genetics; D056930:ARNTL Transcription Factors / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism; D056926:CLOCK Proteins / Q000235:genetics; D018938:Caco-2 Cells; D006528:Carcinoma, Hepatocellular; D002940:Circadian Rhythm / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005091:Exons / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D050356:Lipid Metabolism / Q000235:genetics*; D008113:Liver Neoplasms; D008156:Luciferases / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D047495:PPAR gamma / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation / Q000502:physiology
D056930:ARNTL Transcription Factors; C538960:BMAL1 protein, human; D050976:Basic-Leucine Zipper Transcription Factors; C063898:DBP protein, human; D004268:DNA-Binding Proteins; C497440:NFIL3 protein, human; D047495:PPAR gamma; D012333:RNA, Messenger; D014157:Transcription Factors; D008156:Luciferases; D056926:CLOCK Proteins; C538943:CLOCK protein, human