Insulin stimulates the expression of the SHARP-1 gene via multiple signaling pathways.
The rat enhancer of split- and hairy-related protein-1 (SHARP-1) is a basic helix-loop-helix transcription factor. An issue of whether SHARP-1 is an insulin-inducible transcription factor was examined. Insulin rapidly increased the level of SHARP-1 mRNA both in vivo and in vitro. Then, signaling pathways involved with the increase of SHARP-1 mRNA by insulin were determined in H4IIE rat hepatoma cells. Pretreatments with LY294002, wortmannin, and staurosporine completely blocked the induction effect, suggesting the involvement of both phosphoinositide 3-kinase (PI 3-K) and protein kinase C (PKC) pathways. In fact, overexpression of a dominant negative form of atypical protein kinase C lambda (aPKCλ) significantly decreased the induction of the SHARP-1 mRNA. In addition, inhibitors for the small GTPase Rac or Jun N-terminal kinase (JNK) also blocked the induction of SHARP-1 mRNA by insulin. Overexpression of a dominant negative form of Rac1 prevented the activation by insulin. Furthermore, actinomycin D and cycloheximide completely blocked the induction of SHARP-1 mRNA by insulin. Finally, when a SHARP-1 expression plasmid was transiently transfected with various reporter plasmids into H4IIE cells, the promoter activity of PEPCK reporter plasmid was specifically decreased. Thus, we conclude that insulin induces the SHARP-1 gene expression at the transcription level via a both PI 3-K/aPKCλ/JNK- and a PI 3-K/Rac/JNK-signaling pathway; protein synthesis is required for this induction; and that SHARP-1 is a potential repressor of the PEPCK gene expression.
Department of Health and Nutritional Science, Faculty of Human Health Science, Matsumoto University, Matsumoto, Nagano-, Japan.
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Takagi
Department of Health and Nutritional Science, Faculty of Human Health Science, Matsumoto University, Matsumoto, Nagano-, Japan.
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Asano
Department of Health and Nutritional Science, Faculty of Human Health Science, Matsumoto University, Matsumoto, Nagano-, Japan.
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Haneishi
Matsumoto University Graduate School of Health Science, Matsumoto, Nagano, Japan.
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Ono
Matsumoto University Graduate School of Health Science, Matsumoto, Nagano, Japan.
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Komatsu
Laboratory of Molecular Biology, Faculty of Pharmacy, Osaka Ohtani -University, Tondabayashi, Osaka, Japan.
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Yamamoto
Laboratory of Molecular Biology, Faculty of Pharmacy, Osaka Ohtani -University, Tondabayashi, Osaka, Japan.
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Tanaka
Department of Biochemistry and Molecular Pathophysiology, University of Occupational and Environmental Health, School of Medicine, -Yahata-nishi-ku, Kitakyushu, Fukuoka, Japan.
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Ueno
Department of Clinical Molecular Medicine, Division of Diabetes and -Digestive and Kidney Diseases, Kobe University Graduate School of -Medicine, Chuo-ku, Kobe, Japan.
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Ogawa
Laboratory of Molecular Biology, Faculty of Pharmacy, Osaka Ohtani -University, Tondabayashi, Osaka, Japan.
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Tomita
Laboratory of Molecular Biology, Faculty of Pharmacy, Osaka Ohtani -University, Tondabayashi, Osaka, Japan.
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Noguchi
Department of Health and Nutritional Science, Faculty of Human Health Science, Matsumoto University, Matsumoto, Nagano-, Japan.
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Yamada
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D014176:Protein Biosynthesis / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D000099293:Protein Kinase C-lambda
D051792:Basic Helix-Loop-Helix Proteins; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D010729:Phosphoenolpyruvate Carboxykinase (GTP); D011493:Protein Kinase C; D012333:RNA, Messenger; D020830:rac1 GTP-Binding Protein; D000099293:Protein Kinase C-lambda; C109509:Bhlhe41 protein, rat; C582554:Pck1 protein, rat