PAS kinase (PASK) is a
glucose-regulated
protein kinase involved in the control of pancreatic islet
hormone release and
insulin sensitivity. We aimed here to identify mutations in the PASK gene that may be associated with young-onset diabetes in humans. We screened 18 diabetic probands with unelucidated
maturity-onset diabetes of the young (
MODY). We identified two rare nonsynonymous mutations in the PASK gene (p.L1051V and p.G1117E), each of which was found in a single
MODY family. Wild type or mutant PASKs were expressed in HEK 293 cells.
Kinase activity of the affinity-purified
proteins was assayed as autophosphorylation at
amino acid Thr307 or against an Ugp1p-derived
peptide. Whereas the PASK p.G1117E mutant displayed a ∼25% increase with respect to wild type PASK in the extent of autophosphorylation, and a ∼2-fold increase in
kinase activity toward exogenous substrates, the activity of the p.L1051V mutant was unchanged.
Amino acid Gly1117 is located in an α helical region opposing the active site of PASK and may elicit either: (a) a conformational change that increases catalytic efficiency or (b) a diminished inhibitory interaction with the PAS domain. Mouse islets were therefore infected with adenoviruses expressing wild type or mutant PASK and the regulation of insulin secretion was examined. PASK p.G1117E-infected islets displayed a 4-fold decrease in
glucose-stimulated (16.7 versus 3 mM) insulin secretion, chiefly reflecting a 4.5-fold increase in
insulin release at low
glucose. In summary, we have characterized a rare mutation (p.G1117E) in the PASK gene from a young-onset diabetes family, which modulates
glucose-stimulated insulin secretion.