The GH receptor and signal transduction

Area of Science:

• Endocrinology
• Molecular Biology
• Structural Biology

Background:

• Growth hormone (GH) initiates cellular responses via its receptor.
• A GH-binding protein (GHbp) exists in serum, with different transcripts in various species.
• The homodimeric structure of GH and its receptor is crucial for biological activity.

Purpose of the Study:

• To elucidate the structural and functional characteristics of the GH receptor.
• To identify critical regions within the GH receptor essential for its activity.
• To investigate the downstream signaling events initiated by GH receptor activation.

Main Methods:

• Complementary DNA cloning to determine receptor primary structure.
• Analysis of receptor transcripts and alternative splicing.
• X-ray crystallography to resolve GH-receptor complex structure.
• Site-directed mutagenesis (alanine scanning) to probe functional domains.
• Reporter gene assays (CAT) to assess transcriptional activity.
• Analysis of protein tyrosine phosphorylation, including JAK2 and MAP kinase identification.

Main Results:

• The GH receptor is a single membrane-spanning protein of ~620 amino acids.
• A 25-amino acid region near the transmembrane domain, particularly a proline-rich 'Box 1' region, is vital for function.
• Mutations in the proline-rich region abolish receptor activity.
• GH induces rapid tyrosine phosphorylation of JAK2 and MAP kinase in cells expressing the receptor.

Conclusions:

• GH receptor dimerization is a prerequisite for GH signaling.
• Specific proline residues within the GH receptor are essential for its functional activity.
• GH receptor activation triggers downstream signaling cascades involving JAK2 and MAP kinase.