Insulin induces the expression of the SHARP-2/Stra13/DEC1 gene via a phosphoinositide 3-kinase pathway.
Transcription of the rat fatty acid synthase (FAS) gene in the rat liver can be regulated by feeding a high carbohydrate diet. A carbohydrate response element (ChoRE) located on the rat FAS gene promoter has been identified. Using multiple copies of the ChoRE as the bait in a yeast one-hybrid system, a rat liver cDNA library was screened, and the cDNA of ChoRE-binding proteins was cloned. A positive clone that encodes a basic helix-loop-helix protein, enhancer of split- and hairy-related protein-2 (SHARP-2), was obtained. Northern blot analysis revealed that the levels of SHARP-2 mRNA increase when a high carbohydrate diet is fed to normal rats or when insulin is administered to diabetic rats. In primary cultured rat hepatocytes, insulin rapidly induced an accumulation of SHARP-2 mRNA even in the absence of glucose. A time course for the increase in SHARP-2 mRNA levels indicated that it followed by those of FAS and L-type pyruvate kinase mRNAs and that the initial time course of SHARP-2 mRNA was similar to changes in the levels of glucokinase mRNA and phosphoenolpyruvate carboxykinase mRNA. Although wortmannin, LY294002, and actinomycin D blocked the increase in SHARP-2 mRNA levels by insulin, rapamycin, staurosporine, PD98059, okadaic acid, and 8-bromocyclic AMP had no effect. In addition, nuclear run-on assay revealed that transcription of the rat SHARP-2 gene was induced by insulin. Thus, we conclude that insulin induces the transcription of the rat SHARP-2 gene via a phosphoinositide 3-kinase pathway.
Yamada
Kazuya
K
Department of Biochemistry, Fukui Medical University, Japan. kazuya@fmsrsa.fukui-med.ac.jp
Kawata
Hiroko
H
Shou
Zhangfei
Z
Mizutani
Tetsuya
T
Noguchi
Tamio
T
Miyamoto
Kaoru
K
D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics; D003912:Dextrins / Q000494:pharmacology; D019422:Dietary Sucrose / Q000494:pharmacology; D015870:Gene Expression / Q000502:physiology; D005947:Glucose / Q000494:pharmacology; D018398:Homeodomain Proteins / Q000235:genetics*; D007004:Hypoglycemic Agents / Q000378:metabolism / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D008099:Liver / Q000502:physiology; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic / Q000502:physiology
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D003912:Dextrins; D019422:Dietary Sucrose; D005947:Glucose; D018398:Homeodomain Proteins; D007004:Hypoglycemic Agents; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D012333:RNA, Messenger; D014157:Transcription Factors; C491538:Bhlhe40 protein, rat; C442825:Mlxipl protein, rat