Glucose-induced stimulation of human insulin-receptor mRNA and tyrosine kinase activity in cultured cells.
The effects of high glucose on insulin-receptor tyrosine kinase activity and gene expression were investigated in 3T3-HIR cells. Cells incubated for 48 h in the presence of 25 mM glucose showed a 5-fold increase in the amount of insulin receptors per cell, receptor autophosphorylation and phosphorylation of the exogenous substrate poly(Glu/Tyr) compared with cells grown in the absence of glucose but in the presence of 25 mM fructose. These effects were associated with a 4-fold stimulation in steady-state levels of insulin-receptor mRNA. Significant cellular glucose utilization and lactate production were observed in the presence of high glucose in the culture medium, indicating a functional glycolytic pathway in glucose-treated cells, but not in cells treated with fructose. Such a differential response to hexoses favours the hypothesis of a carbohydrate regulation via a glycolytic intermediate. This was further supported by a similar glucose-induced increase in mRNA levels of the enzyme glyceraldehyde-3-phosphate dehydrogenase. To test the hypothesis that the stimulatory effect of glucose on amount of insulin receptors and phosphorylation state could result from post-transcriptional modifications, cells exposed to glucose were incubated with actinomycin D, a potent inhibitor of gene transcription. In cells challenged with high glucose plus inhibitor, insulin-receptor mRNA half-life was increased from 1 to 3 h, indicating that posttranscriptional mechanisms are involved in these processes of glucose regulation. Inhibition of protein synthesis by cycloheximide induced an overexpression of insulin-receptor mRNA levels in the presence of glucose, suggesting that labile repressor protein(s) could be implicated in the effects of glucose. We conclude that (1) long-term culture with high glucose increases the amount of insulin receptors and their tyrosine kinase activity and (2) the glucose-induced increase in insulin-receptor mRNA levels can be accounted for, at least in part, by posttranscriptional events.
Hauguel-de-Mouzon
S
S
CNRS-CEREMOD, Meudon-bellevue, France.
Mrejen
C
C
Alengrin
F
F
Van Obberghen
E
E
D016475:3T3 Cells / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D000818:Animals; D002478:Cells, Cultured; D005632:Fructose / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D011505:Protein-Tyrosine Kinases / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D011972:Receptor, Insulin / Q000187:drug effects* / Q000235:genetics*; D013268:Stimulation, Chemical
D007328:Insulin; D012333:RNA, Messenger; D005632:Fructose; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D005947:Glucose