Interaction of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2) with glucokinase activates glucose phosphorylation and glucose metabolism in insulin-producing cells.
The bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2) was recently identified as a new intracellular binding partner for glucokinase (GK). Therefore, we studied the importance of this interaction for the activity status of GK and glucose metabolism in insulin-producing cells by overexpression of the rat liver and pancreatic islet isoforms of PFK-2/FBPase-2. PFK-2/FBPase-2 overexpression in RINm5F-GK cells significantly increased the GK activity by 78% in cells expressing the islet isoform, by 130% in cells expressing the liver isoform, and by 116% in cells expressing a cAMP-insensitive liver S32A/H258A double mutant isoform. Only in cells overexpressing the wild-type liver PFK-2/FBPase-2 isoform was the increase of GK activity abolished by forskolin, apparently due to the regulatory site for phosphorylation by a cAMP-dependent protein kinase. In cells overexpressing any isoform of the PFK-2/FBPase-2, the increase of the GK enzyme activity was antagonized by treatment with anti-FBPase-2 antibody. Increasing the glucose concentration from 2 to 10 mmol/l had a significant stimulatory effect on the GK activity in RINm5F-GK cells overexpressing any isoform of PFK-2/FBPase-2. The interaction of GK with PFK-2/FBPase-2 takes place at glucose concentrations that are physiologically relevant for the activation of GK and the regulation of glucose-induced insulin secretion. This new mechanism of posttranslational GK regulation may also represent a new site for pharmacotherapeutic intervention in type 2 diabetes treatment.
Massa
Laura
L
Institute of Clinical Biochemistry, Hannover Medical School, Hannover, Germany.
Baltrusch
Simone
S
Okar
David A
DA
Lange
Alex J
AJ
Lenzen
Sigurd
S
Tiedge
Markus
M
D000256:Adenoviridae; D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D005576:Colforsin / Q000494:pharmacology; D005822:Genetic Vectors; D005941:Glucokinase / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007515:Islets of Langerhans / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D025481:Phosphofructokinase-2 / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D007527:Isoenzymes; D011994:Recombinant Proteins; D005576:Colforsin; D025481:Phosphofructokinase-2; D005941:Glucokinase; D005947:Glucose