G-Protein-Coupled Receptor Kinase 2 Inhibition Induces Meiotic Arrest by Disturbing Ca2+ Release in Porcine Oocytes

G-protein-coupled receptor kinase 2 (GRK2) interacts with G beta gamma and G alpha q, subunits of G-protein alpha, to regulate cell signalling. The second messenger inositol trisphosphate, produced by activated G alpha q, promotes calcium release from the endoplasmic reticulum (ER) and regulates maturation-promoting factor (MPF) activity. This study aimed to investigate the role of GRK2 in MPF activity during the meiotic maturation of porcine oocytes. A specific inhibitor of GRK2 (beta i) was used in this study. The present study showed that GRK2 inhibition increased the percentage of oocyte arrest at the metaphase I (MI) stage (control: 13.84 +/- 0.95%; beta i: 31.30 +/- 4.18%), which resulted in the reduction of the maturation rate (control: 80.36 +/- 1.94%; beta i: 65.40 +/- 1.14%). The level of phospho-GRK2 decreased in the treated group, suggesting that GRK2 activity was reduced upon GRK2 inhibition. Furthermore, the addition of beta i decreased Ca2+ release from the ER. The protein levels of cyclin B and cyclin-dependent kinase 1 were higher in the treatment group than those in the control group, indicating that GRK2 inhibition prevented a decrease in MPF activity. Collectively, GRK2 inhibition induced meiotic arrest at the MI stage in porcine oocytes by preventing a decrease in MPF activity, suggesting that GRK2 is essential for oocyte meiotic maturation in pigs.