Human GH receptor-IGF-1 receptor interaction: implications for GH signaling

Area of Science:

• Endocrinology
• Molecular Cell Biology
• Cancer Research

Background:

• Growth hormone (GH) exerts anabolic and metabolic effects through its receptor (GHR) and associated Janus kinase 2 (JAK2).
• GH signaling involves downstream effectors like STAT5 and insulin-like growth factor 1 (IGF-1) gene expression.
• Previous studies suggested that IGF-1 receptor (IGF-1R) presence augments GH signaling, even without IGF-1 binding.

Purpose of the Study:

• To investigate the role of IGF-1R in GH signaling using human LNCaP prostate cancer cells.
• To elucidate the mechanism by which IGF-1R influences GH receptor (GHR) and JAK2 activation.
• To explore the potential of soluble IGF-1R as an inhibitor of GH-mediated signaling.

Main Methods:

• Utilized human LNCaP prostate cancer cells and mouse primary osteoblast cells.
• Employed coimmunoprecipitation and a novel split luciferase complementation assay.
• Utilized short hairpin RNA (shRNA) for IGF-1R silencing and a soluble IGF-1R extracellular domain fragment (sol IGF-1R).

Main Results:

• GH promoted tyrosine phosphorylation of JAK2 and GHR, and STAT5 activation in LNCaP cells.
• GH enhanced GHR/IGF-1R complex formation, which was inhibited by an anti-GHR antibody fragment.
• IGF-1R silencing or treatment with sol IGF-1R reduced GH-induced phosphorylation of GHR, JAK2, and STAT5, and inhibited IGF-1 gene expression.

Conclusions:

• IGF-1R augments GH signaling, potentially by facilitating the interaction of a regulatory molecule with the activated GHR/JAK2 complex.
• Soluble IGF-1R acts as a dominant-negative inhibitor of IGF-1R-mediated augmentation of GH signaling.
• The findings propose a novel model for GH signaling and suggest therapeutic potential for sol IGF-1R.