The export of major histocompatibility complex class I molecules from the endoplasmic reticulum of rat brown adipose cells is acutely stimulated by insulin.
Major histocompatibility complex class I (MHC-I) molecules have been implicated in several nonimmunological functions including the regulation and intracellular trafficking of the insulin-responsive glucose transporter GLUT4. We have used confocal microscopy to compare the effects of insulin on the intracellular trafficking of MHC-I and GLUT4 in freshly isolated rat brown adipose cells. We also used a recombinant vaccinia virus (rVV) to express influenza virus hemagglutinin (HA) as a generic integral membrane glycoprotein to distinguish global versus specific enhancement of protein export from the endoplasmic reticulum (ER) in response to insulin. In the absence of insulin, MHC-I molecules largely colocalize with the ER-resident protein calnexin and remain distinct from intracellular pools of GLUT4. Surprisingly, insulin induces the rapid export of MHC-I molecules from the ER with a concomitant approximately three-fold increase in their level on the cell surface. This ER export is blocked by brefeldin A and wortmannin but is unaffected by cytochalasin D, indicating that insulin stimulates the rapid transport of MHC-I molecules from the ER to the plasma membrane via the Golgi complex in a phosphatidyl-inositol 3-kinase-dependent and actin-independent manner. We further show that the effect of insulin on MHC-I molecules is selective, because insulin does not affect the intracellular distribution or cell-surface localization of rVV-expressed HA. These results demonstrate that in rat brown adipose cells MHC-I molecule export from the ER is stimulated by insulin and provide the first evidence that the trafficking of MHC-I molecules is acutely regulated by a hormone.
Malide
D
D
Experimental Diabetes, Metabolism, and Nutrition Section, Diabetes Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA. dmalide@nih.gov
Yewdell
J W
JW
Bennink
J R
JR
Cushman
S W
SW
D002001:Adipose Tissue, Brown / Q000187:drug effects* / Q000378:metabolism; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D003952:Diagnostic Imaging; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D051275:Glucose Transporter Type 4; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D023421:Models, Animal; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077191:Wortmannin
D000730:Androstadienes; D051275:Glucose Transporter Type 4; D015395:Histocompatibility Antigens Class I; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011500:Protein Synthesis Inhibitors; C495694:Slc2a4 protein, rat; D020126:Brefeldin A; D000077191:Wortmannin