Activity of hepatocyte nuclear factor 1alpha and hepatocyte nuclear factor 1beta isoforms is differently affected by the inhibition of protein phosphatases 1/2A.
Phosphorylation/dephosphorylation processes are known to control the activity of several transcription factors. The nutrition-dependent expression of sucrase-isomaltase and Na+/glucose co-transporter 1, two proteins implicated in the intestinal absorption of glucose, has been shown to be closely related to modifications of hepatocyte nuclear factor 1 (HNF1) activity. This study was conducted to determine whether phosphorylation/dephosphorylation processes could control HNF1 activity. We show that expression of the gene encoding sucrase-isomaltase is inhibited in the enterocytic Caco-2 clone TC7 by okadaic acid at a concentration that is known to inhibit protein phosphatases 1/2A and that does not affect cell viability. At the same concentration, phosphorylation of the HNF1alpha and HNF1beta isoforms is greatly enhanced and their DNA-binding capacity is decreased. The phosphorylation state of HNF1beta isoforms directly affects their DNA-binding capacity. In contrast, the decreased DNA-binding activity of the HNF1alpha isoforms, which was observed after the inhibition of protein phosphatases 1/2A, is due to a net decrease in their total cellular and nuclear amounts. Such an effect results from a decrease in both the HNF1alpha mRNA levels and the half-life of the protein. This is the first evidence for the implication of protein phosphatases 1/2A in the control of the activity of HNF1 isoforms. Moreover, these results emphasize a physiological role for the balance between phosphatases and kinases in the nutrition-dependent regulation of HNF1-controlled genes.
Carrière
V
V
INSERM U505, Université Pierre et Marie Curie, 15 rue de l'école de Médecine, 75006 Paris, France. veronique.carriere-u505@bhdc.jussieu.fr
Lacasa
M
M
Rousset
M
M
D018938:Caco-2 Cells; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D006801:Humans; D008112:Liver Glycogen / Q000378:metabolism; D009687:Nuclear Proteins; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010844:Picibanil / Q000494:pharmacology; D011487:Protein Conformation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C496487:HNF1A protein, human; C496495:HNF1B protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; D008112:Liver Glycogen; D009687:Nuclear Proteins; D014157:Transcription Factors; D051537:Hepatocyte Nuclear Factor 1; D051539:Hepatocyte Nuclear Factor 1-beta; D010844:Picibanil; D004247:DNA; D010749:Phosphoprotein Phosphatases; D005947:Glucose