Restoration of Glucose-Stimulated Cdc42-Pak1 Activation and Insulin Secretion by a Selective Epac Activator in Type 2 Diabetic Human Islets

Diabetes. 2018 Oct;67(10):1999-2011. doi: 10.2337/db17-1174. Epub 2018 Jul 9.

Abstract

Glucose metabolism stimulates cell division control protein 42 homolog (Cdc42)-p21-activated kinase (Pak1) activity and initiates filamentous actin (F-actin) cytoskeleton remodeling in pancreatic β-cells so that cytoplasmic secretory granules can translocate to the plasma membrane where insulin exocytosis occurs. Since glucose metabolism also generates cAMP in β-cells, the cross talk of cAMP signaling with Cdc42-Pak1 activation might be of fundamental importance to glucose-stimulated insulin secretion (GSIS). Previously, the type-2 isoform of cAMP-regulated guanine nucleotide exchange factor 2 (Epac2) was established to mediate a potentiation of GSIS by cAMP-elevating agents. Here we report that nondiabetic human islets and INS-1 832/13 β-cells treated with the selective Epac activator 8-pCPT-2'-O-Me-cAMP-AM exhibited Cdc42-Pak1 activation at 1 mmol/L glucose and that the magnitude of this effect was equivalent to that which was measured during stimulation with 20 mmol/L glucose in the absence of 8-pCPT-2'-O-Me-cAMP-AM. Conversely, the cAMP antagonist Rp-8-Br-cAMPS-pAB prevented glucose-stimulated Cdc42-Pak1 activation, thereby blocking GSIS while also increasing cellular F-actin content. Although islets from donors with type 2 diabetes had profound defects in glucose-stimulated Cdc42-Pak1 activation and insulin secretion, these defects were rescued by the Epac activator so that GSIS was restored. Collectively, these findings indicate an unexpected role for cAMP as a permissive or direct metabolic coupling factor in support of GSIS that is Epac2 and Cdc42-Pak1 regulated.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • 8-Bromo Cyclic Adenosine Monophosphate / analogs & derivatives
  • 8-Bromo Cyclic Adenosine Monophosphate / chemistry
  • 8-Bromo Cyclic Adenosine Monophosphate / pharmacology
  • Animals
  • Cell Line
  • Diabetes Mellitus, Type 2 / metabolism*
  • Glucose / pharmacology*
  • Guanine Nucleotide Exchange Factors / metabolism
  • Humans
  • Insulin / metabolism*
  • Insulin Secretion
  • Insulin-Secreting Cells / drug effects
  • Insulin-Secreting Cells / metabolism
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / metabolism*
  • Rats
  • Thionucleotides / chemistry
  • Thionucleotides / pharmacology
  • cdc42 GTP-Binding Protein / metabolism*
  • p21-Activated Kinases / metabolism*

Substances

  • 8-bromoadenosine-3',5'-cyclic monophosphorothioate
  • Guanine Nucleotide Exchange Factors
  • Insulin
  • Rapgef4 protein, rat
  • Thionucleotides
  • 8-Bromo Cyclic Adenosine Monophosphate
  • p21-Activated Kinases
  • cdc42 GTP-Binding Protein
  • Glucose