Cellular characterisation of the GCKR P446L variant associated with type 2 diabetes risk.
OBJECTIVE
Translation of genetic association signals into molecular mechanisms for diabetes has been slow. The glucokinase regulatory protein (GKRP; gene symbol GCKR) P446L variant, associated with inverse modulation of glucose- and lipid-related traits, has been shown to alter the kinetics of glucokinase (GCK) inhibition. As GCK inhibition is associated with nuclear sequestration, we aimed to determine whether this variant also alters the direct interaction between GKRP and GCK and their intracellular localisation.


METHODS
Fluorescently tagged rat and human wild-type (WT)- or P446L-GCKR and GCK were transiently transfected into HeLa cells and mouse primary hepatocytes. Whole-cell and nuclear fluorescence was quantified in individual cells exposed to low- or high-glucose conditions (5.5 or 25 mmol/l glucose, respectively). Interaction between GCK and GKRP was measured by sensitised emission-based fluorescence resonance energy transfer (FRET) efficiency.


RESULTS
P446L-GKRP had a decreased degree of nuclear localisation, ability to sequester GCK and direct interaction with GCK as measured by FRET compared with WT-GKRP. Decreased interaction was observed between WT-GKRP and GCK at high compared with low glucose, but not between P446L-GKRP and GCK. Rat WT-GKRP and P446L-GKRP behaved quite differently: both variants responded to high glucose by diminished sequestration of GCK but showed no effect of the P446L variant on nuclear localisation or GCK sequestration.


CONCLUSIONS
Our study suggests the common human P446L-GKRP variant protein results in elevated hepatic glucose uptake and disposal by increasing active cytosolic GCK. This would increase hepatic lipid biosynthesis but decrease fasting plasma glucose concentrations and provides a potential mechanism for the protective effect of this allele on type 2 diabetes risk.
Oxford Centre for Diabetes Endocrinology & Metabolism, University of Oxford, Churchill Hospital, Headington, Oxford, OX3 7LJ, UK.
M G
MG
Rees
S
S
Wincovitch
J
J
Schultz
R
R
Waterstradt
N L
NL
Beer
S
S
Baltrusch
F S
FS
Collins
A L
AL
Gloyn
D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D015723:Gene Library; D005941:Glucokinase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006367:HeLa Cells; D022781:Hepatocytes / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D021381:Protein Transport; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C485100:GCKR protein, human; C499484:Gckr protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D050505:Mutant Proteins; D011993:Recombinant Fusion Proteins; D005941:Glucokinase; D005947:Glucose