INSL5 is a high affinity specific agonist for GPCR142 (GPR100)

Area of Science:

• Endocrinology
• Molecular Biology
• G protein-coupled receptors

Background:

• Insulin-like peptide 5 (INSL5) is a member of the relaxin/insulin family.
• The specific receptor for INSL5 has remained unidentified.
• GPCR142 is a G protein-coupled receptor with known expression in peripheral tissues.

Purpose of the Study:

• To identify the specific receptor for Insulin-like peptide 5 (INSL5).
• To characterize the interaction between INSL5 and potential receptors.
• To determine if INSL5 acts as an endogenous ligand for GPCR142.

Main Methods:

• Radioligand binding assays using (125)I-relaxin-3 and (125)I-INSL5 to assess binding affinity to GPCR142.
• Functional assays including guanosine (gamma-thio)-triphosphate binding and cAMP accumulation to measure receptor activation.
• Calcium (Ca2+) mobilization assays in HEK293 cells to confirm functional activity.
• Testing INSL5 activity against other related receptors like GPCR135 and LGR7/8.

Main Results:

• Human INSL5 demonstrated high-affinity binding to GPCR142 (K(i) = 1.5 nM) and potent activation (EC(50) values of 1.3 nM and 1.2 nM for GTP binding and cAMP accumulation, respectively).
• INSL5 stimulated Ca2+ mobilization in cells expressing GPCR142.
• INSL5 showed no significant activity at GPCR135 or LGR7/8, differentiating it from relaxin-3.
• INSL5 mRNA expression patterns partially overlap with GPCR142 mRNA expression in peripheral tissues.

Conclusions:

• INSL5 is a specific and potent agonist for GPCR142.
• The high-affinity interaction, co-evolution, and overlapping tissue expression strongly suggest INSL5 is the endogenous ligand for GPCR142.
• This finding elucidates a novel ligand-receptor relationship within the relaxin/insulin peptide family and GPCR signaling.