A Novel Two-Chain IGF-II-derived Peptide From Purified β-cell Granules

Growth Horm IGF Res. 2010 Oct;20(5):360-6. doi: 10.1016/j.ghir.2010.06.003. Epub 2010 Jul 24.

Abstract

Objective: Insulin-like growth factor II (IGF-II) is a potent mitogen that regulates prenatal growth and development in both humans and rodents. Its role in post-natal life is less clear although immunohistochemical studies have observed IGF-II-like immunoreactivity (IGF-II-LI) associated with insulin-producing pancreatic β-cells. Here we isolated secretory granules from a β-cell line, βTC6-F7, and characterized the nature of the IGF-II-LI located therein.

Design: Secretory granules were isolated from cultured mouse βTC6-F7 cells by ultracentrifugation. Granule protein content was separated by reversed-phase HPLC, and assayed for IGF-II (radioimmunoassay) prior to identification by gas-phase NH(2)-terminal sequencing and MALDI-TOF MS. Effects of glucose incorporation into muscle glycogen were determined by incubating with isolated rat soleus muscle strips.

Results: βTC6-F7 cells contained 60 ± 8 pmol of IGF-II-LI per 10⁶ cells compared to 340 ± 44 pmol insulin-LI per 10⁶ cells. IGF-II immunoreactive fractions were found to contain an IGF-II-like molecule with a molecular mass of 6847.6 Da. The protein was found to be a two-chain insulin-like product of Igf2 that corresponds to mouse des(37-40)IGF-II, which we termed 'vesiculin'. This molecule was also detectable in βTC6-F7 cells by intact-cell mass spectrometry. Mouse vesiculin evoked concentration-dependent stimulation of muscle glycogen synthesis ex vivo with an EC(50) value of 131 nM ± 1.35.

Conclusions: Vesiculin, des(37-40)IGF-II, is a novel two-chain insulin-like hormone and the major "IGF-II-like" peptide found in purified mouse βTC6-F7 secretory granules. It stimulated ex vivo muscle glycogen synthesis with an efficacy greater than or equal to the intrinsic potency of IGF-II when compared to insulin derived from the same species.

MeSH terms

  • Animals
  • Cell Line
  • Glycogen / biosynthesis
  • Humans
  • Insulin-Like Growth Factor II / analogs & derivatives*
  • Insulin-Like Growth Factor II / isolation & purification
  • Insulin-Like Growth Factor II / metabolism*
  • Insulin-Like Growth Factor II / pharmacology
  • Insulin-Secreting Cells / chemistry
  • Insulin-Secreting Cells / metabolism*
  • Male
  • Mice
  • Muscle, Skeletal / metabolism
  • Peptide Fragments / isolation & purification
  • Rats
  • Rats, Wistar
  • Secretory Vesicles / chemistry
  • Secretory Vesicles / metabolism*

Substances

  • Peptide Fragments
  • insulin-like growth factor II, des(37-40)
  • preptin
  • Insulin-Like Growth Factor II
  • Glycogen