Improved metabolic stimulus for glucose-induced insulin secretion through GK and PFK-2/FBPase-2 coexpression in insulin-producing RINm5F cells.
The glucose sensor enzyme glucokinase plays a pivotal role in the regulation of glucose-induced insulin secretion in pancreatic beta-cells. Activation of glucokinase represents a promising concept for the treatment of type 2 diabetes. Therefore, we analyzed the glucokinase activation through its physiological interaction partner, the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2) and the resulting effect on glucose metabolism in insulin-producing cells. In RINm5F-GK-PFK-2/FBPase-2 cells stably overexpressing glucokinase plus islet PFK-2/FBPase-2, colocalization between both enzymes as well as elevation of glucokinase activity were significantly increased at a stimulatory glucose concentration of 10 mmol/liter. RINm5F-GK-PFK-2/FBPase-2 cells showed under this culture condition a significant increase in glucose utilization and in the ATP/ADP ratio compared with RINm5F-GK cells, which only overexpress glucokinase. Also glucose-induced insulin secretion was elevated in RINm5F-GK-PFK-2/FBPase-2 cells in comparison to RINm5F-GK cells. Furthermore, pyruvate accumulation and lactate production in RINm5F-GK-PFK-2/FBPase-2 cells were significantly lower at both 10 and 30 mmol/liter glucose than in RINm5F-GK and RINm5F cells. The significant improvement of glucose metabolism after PFK-2/FBPase-2 overexpression is apparently not exclusively the result of high glucokinase enzyme activity. Stabilization of the closed glucokinase conformation by PFK-2/FBPase-2 may not only activate the enzyme but also improve metabolic channeling in beta-cells.
Baltrusch
Simone
S
Institute of Clinical Biochemistry, Hannover Medical School, 30623 Hannover, Germany. baltrusch.simone@mh-hannover.de
Langer
Sara
S
Massa
Laura
L
Tiedge
Markus
M
Lenzen
Sigurd
S
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002470:Cell Survival; D005941:Glucokinase / Q000378:metabolism / Q000502:physiology*; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism; D019344:Lactic Acid / Q000096:biosynthesis; D053858:Metabolic Networks and Pathways; D025481:Phosphofructokinase-2 / Q000378:metabolism*; D011485:Protein Binding; D019289:Pyruvic Acid / Q000378:metabolism; D051381:Rats; D014162:Transfection
D007328:Insulin; D019344:Lactic Acid; D000244:Adenosine Diphosphate; D019289:Pyruvic Acid; D000255:Adenosine Triphosphate; D025481:Phosphofructokinase-2; D005941:Glucokinase; D005947:Glucose