Palmitate inhibits insulin gene expression by altering PDX-1 nuclear localization and reducing MafA expression in isolated rat islets of Langerhans.
Abnormalities in lipid metabolism have been proposed as contributing factors to both defective insulin secretion from the pancreatic beta cell and peripheral insulin resistance in type 2 diabetes. Previously, we have shown that prolonged exposure of isolated rat islets of Langerhans to excessive fatty acid levels impairs insulin gene transcription. This study was designed to assess whether palmitate alters the expression and binding activity of the key regulatory factors pancreas-duodenum homeobox-1 (PDX-1), MafA, and Beta2, which respectively bind to the A3, C1, and E1 elements in the proximal region of the insulin promoter. Nuclear extracts of isolated rat islets cultured with 0.5 mm palmitate exhibited reduced binding activity to the A3 and C1 elements but not the E1 element. Palmitate did not affect the overall expression of PDX-1 but reduced its nuclear localization. In contrast, palmitate blocked the stimulation of MafA mRNA and protein expression by glucose. Combined adenovirus-mediated overexpression of PDX-1 and MafA in islets completely prevented the inhibition of insulin gene expression by palmitate. These results demonstrate that prolonged exposure of islets to palmitate inhibits insulin gene transcription by impairing nuclear localization of PDX-1 and cellular expression of MafA.
Hagman
Derek K
DK
Pacific Northwest Research Institute, Seattle, Washington 98122, USA.
Hays
Lori B
LB
Parazzoli
Susan D
SD
Poitout
Vincent
V
D000256:Adenoviridae / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism; D015151:Immunoblotting; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism*; D037181:Lectins, C-Type / Q000096:biosynthesis* / Q000378:metabolism; D050356:Lipid Metabolism; D008156:Luciferases / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000378:metabolism; D018613:Microscopy, Confocal; D019308:Palmitic Acid / Q000494:pharmacology*; D011499:Protein Processing, Post-Translational; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014158:Transcription, Genetic
D007328:Insulin; C094696:Klrg1 protein, rat; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D019308:Palmitic Acid; D012313:RNA; D008156:Luciferases; D005947:Glucose