Activation of phosphatidylinositol 3-kinase contributes to insulin-like growth factor I-mediated inhibition of pancreatic beta-cell death

Endocrinology. 2002 Oct;143(10):3802-12. doi: 10.1210/en.2002-220058.

Abstract

To begin to determine whether IGF-I treatment represents a potential means of enhancing the survival of islet cell grafts after transplantation, the present studies established a model of beta-cell death secondary to loss of trophic support and examined the ability of IGF-I to prevent cell death. The studies were performed using the rat pancreatic beta-cell line, INS-1. Incubating INS-1 cells in RPMI 1640 and 0.25% BSA for 48 h increased cell death, as determined by lactate dehydrogenase release, compared with that of cells maintained in RPMI and 10% fetal calf serum. Addition of 100 ng/ml IGF-I to the serum-free medium decreased lactate dehydrogenase release to a level comparable to that found in cells maintained in fetal calf serum. Similar results were seen using a mouse beta-cell line, MIN6, infected with an adenovirus expressing IGF-I. Examination of IGF-I-stimulated signaling demonstrated that IGF-I increased the phosphorylation of protein kinase B in both cell lines, whereas IGF-I-induced phosphorylation of the MAPKs, ERK1 and -2, was observed only in INS-1 cells. The effect of IGF-I on phosphorylation of substrates of phosphatidylinositol 3-kinase (PI 3-kinase) or protein kinase B was also examined in INS-1 cells. IGF-I increased the phosphorylation of glycogen synthase kinase 3beta, BAD, FKHR, and p70(S6) kinase. Another pathway that has been shown to mediate the protective of IGF-I in some cell types is activation of cAMP response element-binding protein (CREB). IGF-I increased CREB phosphorylation at a concentration as low as 10 ng/ml, and this effect was inhibited by H89, a PKA inhibitor, and PD98059, a MAPK kinase inhibitor. Consistent with the effect of IGF-I on CREB phosphorylation, IGF-I increased the transcriptional activity of CREB, although it had no effect on CREB binding to DNA. Use of inhibitors of the PI 3-kinase (LY 294002) or ERK (PD98059) pathways or CREB phosphorylation (H89) in the cell death assay demonstrated partial abrogation of the protective effect of IGF-I with LY 294002. These data demonstrate that IGF-I protects pancreatic beta-cells from cell death secondary to loss of trophic support and that, although IGF-I activates several signaling pathways that contribute to its protective effect in other cell types, only activation of PI 3-kinase contributes to this effect in beta-cells.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Cell Death / drug effects
  • Cell Death / physiology
  • Cell Line
  • Chromones / pharmacology
  • Culture Media, Serum-Free
  • Cyclic AMP Response Element-Binding Protein / drug effects
  • Cyclic AMP Response Element-Binding Protein / physiology
  • Enzyme Activation / physiology
  • Enzyme Inhibitors / pharmacology
  • Flavonoids / pharmacology
  • Insulin-Like Growth Factor I / pharmacology
  • Insulin-Like Growth Factor I / physiology*
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / physiology*
  • Mitogen-Activated Protein Kinases / metabolism
  • Morpholines / pharmacology
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphorylation / drug effects
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • Rats

Substances

  • Chromones
  • Culture Media, Serum-Free
  • Cyclic AMP Response Element-Binding Protein
  • Enzyme Inhibitors
  • Flavonoids
  • Morpholines
  • Proto-Oncogene Proteins
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Insulin-Like Growth Factor I
  • Phosphatidylinositol 3-Kinases
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinases
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one