Cellular specificity of proexendin-4 processing in mammalian cells in vitro and in vivo

Endocrinology. 2002 Sep;143(9):3464-71. doi: 10.1210/en.2002-220251.


Glucagon-like peptide-1 (GLP-1) is a potent stimulator of glucose-dependent insulin secretion. Exendin-4(1-39) (Ex-4), isolated from Gila monster venom, is a highly specific GLP-1 receptor agonist that exhibits a prolonged duration of action in vivo. Although the processing mechanisms underlying liberation of GLP-1 from its prohormone have been elucidated, those for Ex-4 remain unknown. To examine the requirements for proEx-4 processing in mammalian cells, BHK fibroblasts, InR1-G9 islet A cells, and AtT-20 corticotropes, which express different prohormone convertases (furin, prohormone convertase 2, and prohormone convertase 1, respectively) were transfected with full-length lizard proEx-4, and the processing of proexendin was examined by HPLC and RIA (n = 3). All of the transfected cell lines exhibited Ex-4-like immunoreactivity in the media, and Ex-4-like immunoreactivity was detected in extracts of InR1-G9 and AtT-20 cells. However, only media and extracts from AtT-20 cells (not InR1-G9 and BHK cells) contained a single peak by HPLC corresponding to synthetic Ex-4. To establish whether proEx-4 can be processed to Ex-4 in nonimmortalized mammalian cells in vivo, the molecular forms of exendin-4 were examined in mice expressing a metallothionein-proEx-4 transgene (n = 3-6 for both males and females). ProEx4 mRNA transcripts were detected by RT-PCR in a broad range of both endocrine and nonendocrine tissues. Ex-4-like immunoreactivity was detected in pituitary, fat, adrenals, and testes; however HPLC analyses demonstrated that processed Ex-4 was found only in adrenals and testes. These results indicate that lizard proEx-4 is processed to mature bioactive Ex-4 in both rodent endocrine and nonendocrine mammalian cell types in vitro and in murine tissues in vivo. These findings may be useful for engineering cells that express a lizard pro-Ex4 transgene for the treatment of type 2 diabetes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenocorticotropic Hormone / metabolism
  • Animals
  • Antibody Specificity
  • Cell Line
  • Chromatography, High Pressure Liquid
  • Cricetinae
  • Exenatide
  • Female
  • Fibroblasts / metabolism
  • Glucagon / metabolism
  • Glucagon-Like Peptide 1
  • Immunohistochemistry
  • Islets of Langerhans / metabolism
  • Kidney / metabolism
  • Male
  • Mice
  • Mice, Transgenic
  • Organ Specificity
  • Peptide Fragments / metabolism
  • Peptides / genetics
  • Peptides / metabolism*
  • Pituitary Gland / metabolism
  • Protein Precursors / genetics
  • Protein Precursors / metabolism*
  • Radioimmunoassay
  • Reverse Transcriptase Polymerase Chain Reaction
  • Transfection
  • Venoms*


  • Peptide Fragments
  • Peptides
  • Protein Precursors
  • Venoms
  • Glucagon-Like Peptide 1
  • Adrenocorticotropic Hormone
  • Glucagon
  • Exenatide