The permissive effects of glucose on receptor-operated potentiation of insulin secretion from mouse islets: a role for ERK1/2 activation and cytoskeletal remodelling.
OBJECTIVE
Glucose plays two distinct roles in regulating insulin secretion from beta cells--an initiatory role, and a permissive role enabling receptor-operated secretagogues to potentiate glucose-induced insulin secretion. The molecular mechanisms underlying the permissive effects of glucose on receptor-operated insulin secretion remain uncertain. We have investigated the role of extracellular signal-regulated kinase 1/2 (ERK1/2) activation and consequent cytoskeletal remodelling in this process.


METHODS
Insulin release was measured from groups of isolated mouse islets using static incubation experiments and subsequent radioimmunoassay of samples. ERK1/2 activation was measured by western blotting of islet protein samples for both phosphorylated and total ERK1/2. Rhodamine-phalloidin staining was used to measure filamentous actin in dispersed primary beta cells.


RESULTS
Inhibition of ERK1/2 blocked potentiation of glucose-induced insulin release by the receptor-operated secretagogues kisspeptin, A568, exendin-4 and JWH015, although the agonists alone had minimal effects on ERK1/2 activation, suggesting a permissive rather than causal role for ERK1/2 activation in receptor-operated insulin release. Following pharmacological activation of ERK1/2 all agonists caused a significant increase in insulin release from islets incubated with sub-stimulatory levels of glucose. ERK1/2 inhibition significantly reduced the glucose-dependent decreases in filamentous actin observed in primary beta cells, while pharmacological dissociation of actin filaments enabled all receptor-operated secretagogues tested to significantly stimulate insulin release from islets at a sub-stimulatory glucose concentration.


CONCLUSIONS
Glucose-induced ERK1/2 activation in beta cells mediates the permissive effects of stimulatory glucose concentrations on receptor-operated insulin secretagogues, at least in part through effects on actin depolymerisation and cytoskeletal remodelling.
Diabetes Research Group, Division of Diabetes and Nutritional Sciences, Hodgkin Building, King's College London, London SE1 1UL, UK. james.bowe@kcl.ac.uk
J E
JE
Bowe
A
A
Chander
B
B
Liu
S J
SJ
Persaud
P M
PM
Jones
D000199:Actins / Q000378:metabolism; D000814:Aniline Compounds / Q000494:pharmacology; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000077270:Exenatide; D005419:Flavonoids / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000166:cytology* / Q000187:drug effects; D059648:Kisspeptins / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D010455:Peptides / Q000494:pharmacology; D010627:Phenethylamines; D010766:Phosphorylation; D011437:Propylamines; D011863:Radioimmunoassay; D014688:Venoms / Q000494:pharmacology
D000199:Actins; D000814:Aniline Compounds; D001786:Blood Glucose; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007211:Indoles; D007328:Insulin; C491407:Kiss1 protein, mouse; D059648:Kisspeptins; C107873:N-(2-chlorophenylpropyl)-1-(3-methoxyphenyl)ethylamine; D010455:Peptides; D010627:Phenethylamines; D011437:Propylamines; D014688:Venoms; D000077270:Exenatide; D005947:Glucose; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; C402944:JHW 015