Unacylated ghrelin binds heparan-sulfate proteoglycans which modulate its function

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• Acylated ghrelin (AG) and unacylated ghrelin (UAG) are gut peptides with distinct physiological roles.
• UAG's mechanism of action is unknown, as it does not antagonize AG at the GHS receptor-1a (GHSR) and affects cells lacking GHSR.

Purpose of the Study:

• To identify cell surface proteins that bind UAG.
• To understand how UAG binding modulates its biological effects, particularly ERK signaling in MCF7 cells.

Main Methods:

• Ligand-receptor capture assays combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS).
• Utilized MCF7 cell line, known to exhibit UAG-induced ERK signaling independent of GHSR.
• Investigated the role of heparin and heparan-sulfate proteoglycans (HSPGs) through binding assays, enzymatic treatments, and overexpression studies.

Main Results:

• Identified specific HSPGs as binding partners for UAG on cell surfaces.
• Demonstrated that both UAG and AG bind with high affinity to heparin.
• Heparin and heparinase treatment affected UAG binding and ERK response, while HSPG overexpression increased UAG binding.

Conclusions:

• UAG interacts with cell surface HSPGs, which modulates its biological activity.
• The interaction of UAG and AG with HSPGs may be crucial for their in vivo specificity and potency.