Karyopherin alpha2: a control step of glucose-sensitive gene expression in hepatic cells.
Glucose is required for an efficient expression of the glucose transporter GLUT2 and other genes. We have shown previously that the intracytoplasmic loop of GLUT2 can divert a signal, resulting in the stimulation of glucose-sensitive gene transcription. In the present study, by interaction with the GLUT2 loop, we have cloned the rat karyopherin alpha2, a receptor involved in nuclear import. The specificity of the binding was restricted to GLUT2, and not GLUT1 or GLUT4, and to karyopherin alpha2, not alpha1. When rendered irreversible by a cross-linking agent, this transitory interaction was detected in vivo in hepatocytes. A role for karyopherin alpha2 in the transcription of two glucose-sensitive genes was investigated by transfection of native and inactive green fluorescent protein-karyopherin alpha2 in GLUT2-expressing hepatoma cells. The amount of inactive karyopherin alpha2 receptor reduced, in a dose-dependent manner, the GLUT2 and liver pyruvate kinase mRNA levels by competition with endogenous active receptor. In contrast, the overexpression of karyopherin alpha2 did not significantly stimulate GLUT2 and liver pyruvate kinase mRNA accumulation in green fluorescent protein-sorted cells. The present study suggests that, in concert with glucose metabolism, karyopherin alpha2 transmits a signal to the nucleus to regulate glucose-sensitive gene expression. The transitory tethering of karyopherin alpha2 to GLUT2 at the plasma membrane might indicate that the receptor can load the cargo to be imported locally.
Guillemain
Ghislaine
G
INSERM U505, Université Pierre et Marie Curie 15, Rue de L'Ecole de Médecine, 75006 Paris, France.
Muñoz-Alonso
Maria J
MJ
Cassany
Aurélia
A
Loizeau
Martine
M
Faussat
Anne-Marie
AM
Burnol
Anne-Françoise
AF
Leturque
Armelle
A
D000818:Animals; D001692:Biological Transport; D015152:Blotting, Northern; D015153:Blotting, Western; D003001:Cloning, Molecular; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D051273:Glucose Transporter Type 2; D051275:Glucose Transporter Type 4; D049452:Green Fluorescent Proteins; D022781:Hepatocytes / Q000378:metabolism*; D008099:Liver / Q000166:cytology* / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D020798:Two-Hybrid System Techniques; D028901:alpha Karyopherins / Q000096:biosynthesis* / Q000235:genetics
D003432:Cross-Linking Reagents; D051272:Glucose Transporter Type 1; D051273:Glucose Transporter Type 2; D051275:Glucose Transporter Type 4; D008164:Luminescent Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; C495678:Slc2a1 protein, mouse; C495679:Slc2a1 protein, rat; C495693:Slc2a4 protein, mouse; C495694:Slc2a4 protein, rat; D028901:alpha Karyopherins; C087978:karyopherin alpha 2; D049452:Green Fluorescent Proteins; D005947:Glucose