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 NH2-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±8pmol of IGF-II-LI per 106 cells compared to 340±44pmol insulin-LI per 106 cells. IGF-II immunoreactive fractions were found to contain an IGF-II-like molecule with a molecular mass of 6847.6Da. 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 EC50 value of 131nM±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. © 2010 Growth Hormone Research Society.
Original language | English |
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Pages (from-to) | 360-366 |
Number of pages | 6 |
Journal | Growth Hormone and IGF Research |
Volume | 20 |
Issue number | 5 |
DOIs | |
Publication status | Published - Oct 2010 |
Keywords
- Beta cell
- Cell line
- Cultured cells
- Insulin-like growth factor II
- Isoform
- Metabolism
- Secretory granule