Recombinant human insulin-like growth factor binding proteins 4, 5, and 6: biological and physiochemical...

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Human insulin-like growth factor binding proteins (IGFBP) regulate IGF bioavailability.
• Understanding IGFBP-4, -5, and -6 functions is crucial for cellular processes.
• Previous studies focused on native IGFBPs, necessitating methods for recombinant expression.

Purpose of the Study:

• To express and characterize recombinant human IGFBP-4, -5, and -6 in yeast.
• To confirm the biological activity and IGF-binding properties of these recombinant proteins.
• To investigate their effects on IGF-stimulated cellular functions.

Main Methods:

• Cloning of cDNAs for human IGFBP-4, -5, and -6.
• Expression of ubiquitin-IGFBP fusion proteins in yeast.
• Western ligand blotting to assess IGF-II binding.
• HPLC purification and amino acid analysis.
• Antibody production and cross-reactivity testing.
• Affinity constant determination using IGF-I and IGF-II.
• Inhibition assays on IGF-stimulated DNA and glycogen synthesis in osteoblastic cells.

Main Results:

• Successful expression and processing of recombinant human IGFBP-4, -5, and -6 in yeast.
• Recombinant IGFBPs demonstrated specific binding to IGF-II and possessed similar amino acid composition and sequences to native proteins.
• Antisera against recombinant IGFBPs showed specific reactivity with native counterparts.
• High affinity constants for IGF-I and IGF-II were observed for IGFBP-4 and -5, with IGFBP-6 showing lower affinity for IGF-I.
• Recombinant IGFBP-4, -5, and -6 inhibited IGF-stimulated DNA and glycogen synthesis in human osteoblastic cells.

Conclusions:

• Recombinant yeast-expressed IGFBP-4, -5, and -6 are functional and biologically active.
• These recombinant proteins serve as valuable tools for studying IGFBP functions.
• The findings support the role of IGFBP-4, -5, and -6 in modulating IGF action on cellular metabolism.