Structural and Functional Evidence for Testosterone Activation of GPRC6A in Peripheral Tissues

Area of Science:

• Endocrinology
• Molecular Biology
• Structural Biology

Background:

• G protein-coupled receptor family C group 6 member A (GPRC6A) is a multiligand receptor implicated in testosterone (T) production and energy metabolism.
• Rapid, non-genomic effects of T are proposed to be mediated by a GPRC6A, but direct T binding remains controversial.

Purpose of the Study:

• To demonstrate direct binding of T to GPRC6A.
• To elucidate the structural basis of T-GPRC6A interaction.
• To confirm the role of GPRC6A in T rapid signaling and identify associated biological functions.

Main Methods:

• In vitro binding assays to demonstrate direct T-GPRC6A interaction.
• Computational modeling to predict T binding poses within GPRC6A.
• Site-directed mutagenesis to validate predicted binding sites.
• Phenotypic analysis of Gpr6ca(-/-) mice to assess T signaling.
• Pharmacological characterization of a selective androgen receptor modulator isomer.

Main Results:

• Direct binding of T to GPRC6A was demonstrated, with computational models identifying potential binding sites.
• Mutagenesis studies confirmed the functional importance of the predicted binding residues.
• Gpr6ca(-/-) mice exhibited impaired rapid T signaling, including reduced insulin secretion and altered Leydig cell enzyme expression.
• An R-isomer of a selective androgen receptor modulator specifically activated GPRC6A, independent of the androgen receptor.

Conclusions:

• GPRC6A directly mediates the rapid signaling response to testosterone.
• GPRC6A plays a critical role in regulating insulin secretion and testosterone biosynthesis.
• This study uncovers novel endocrine networks regulated by GPRC6A-dependent testosterone signaling.