Abstract
Nucleotide sequencing of cDNAs encoding human insulin-like growth factor I (IGF-I) predicts the existence of two different prohormone forms of IGF-I. The E peptide regions extend the carboxy-terminus of the 70 amino acid core IGF-I molecule (BCAD domains) by either an additional 35 (IGF-Ia) or 77 (IGF-Ib) amino acids. Employing antiserum directed against a peptide sequence unique to the E peptide region of IGF-Ia prohormone, we have identified EIa immunoreactive material (IR-EIa) in the conditioned medium of a human hepatoma cell line, HepG2. Human growth hormone (GH) had dose-dependent stimulatory effects on IR-EIa secretion; incubation of HepG2 cells with GH at maximal concentrations (1-5 μg/ml) increased specific IR-EIa in 24 h conditioned medium 3-fold. The addition of human placental lactogen, insulin, IGF-I, dexamethasone, β-estradiol, or progesterone had no significant effect. Acid chromatography of HepG2 cell conditioned medium revealed a single elution peak of IR-EIa corresponding to Mr = 12,000-20,000. There was no immunologically detectable 7500 Mr IGF-I peptide in acid-chromatographed conditioned medium under either basal or stimulated conditions. Biosynthetic labelling of HepG2 cell products with [35S]Trans label and immunoprecipitation with antisera specific to the E or to the AD regions of the IGF-Ia molecule indicated a single species of approx. 14,000 Mr. These data indicate that the E peptide region of IGF-Ia is translated and released as part of the larger molecule in cultured HepG2 cells, and that the levels of this prohormone are regulated by GH.
Original language | English (US) |
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Pages (from-to) | 1-8 |
Number of pages | 8 |
Journal | Regulatory Peptides |
Volume | 48 |
Issue number | 1-2 |
DOIs | |
State | Published - Oct 20 1993 |
Keywords
- Growth hormone
- HepG2
- IGF-Ia
ASJC Scopus subject areas
- Biochemistry
- Physiology
- Endocrinology
- Clinical Biochemistry
- Cellular and Molecular Neuroscience