Physical exercise-induced hypoglycemia caused by failed silencing of monocarboxylate transporter 1 in pancreatic beta cells.
Exercise-induced hyperinsulinism (EIHI) is a dominantly inherited hypoglycemic disorder characterized by inappropriate insulin secretion during anaerobic exercise or on pyruvate load. We aimed to identify the molecular basis of this novel disorder of beta -cell regulation. EIHI mapped to chromosome 1 (LOD score 3.6) in a genome scan performed for two families with 10 EIHI-affected patients. Mutational analysis of the promoter of the SLC16A1 gene, which encodes monocarboxylate transporter 1 (MCT1), located under the linkage peak, revealed changes in all 13 identified patients with EIHI. Patient fibroblasts displayed abnormally high SLC16A1 transcript levels, although monocarboxylate transport activities were not changed in these cells, reflecting additional posttranscriptional control of MCT1 levels in extrapancreatic tissues. By contrast, when examined in beta cells, either of two SLC16A1 mutations identified in separate pedigrees resulted in increased protein binding to the corresponding promoter elements and marked (3- or 10-fold) transcriptional stimulation of SLC16A1 promoter-reporter constructs. These studies show that promoter-activating mutations in EIHI induce SLC16A1 expression in beta cells, where this gene is not usually transcribed, permitting pyruvate uptake and pyruvate-stimulated insulin release despite ensuing hypoglycemia. These findings describe a novel disease mechanism based on the failure of cell-specific transcriptional silencing of a gene that is highly expressed in other tissues.
Otonkoski
Timo
T
Hospital for Children and Adolescents and Biomedicum Helsinki, University of Helsinki, Helsinki, Finland. timo.otonkoski@helsinki.fi
Jiao
Hong
H
Kaminen-Ahola
Nina
N
Tapia-Paez
Isabel
I
Ullah
Mohammed S
MS
Parton
Laura E
LE
Schuit
Frans
F
Quintens
Roel
R
Sipilä
Ilkka
I
Mayatepek
Ertan
E
Meissner
Thomas
T
Halestrap
Andrew P
AP
Rutter
Guy A
GA
Kere
Juha
J
D000818:Animals; D001483:Base Sequence; D024202:Electrophoretic Mobility Shift Assay; D015444:Exercise; D005260:Female; D020868:Gene Silencing; D006801:Humans; D007003:Hypoglycemia / Q000235:genetics*; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D027501:Monocarboxylic Acid Transporters / Q000235:genetics*; D009154:Mutation; D010375:Pedigree; D011401:Promoter Regions, Genetic; D027981:Symporters / Q000235:genetics*; D000099233:Monocarboxylate Transport Protein 1
D027501:Monocarboxylic Acid Transporters; D027981:Symporters; D000099233:Monocarboxylate Transport Protein 1
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