Potentiation of nerve growth factor-induced neurite outgrowth by the ROCK inhibitor Y-27632: a possible role of IP₃ receptors.

ROCK, a serine/threonine protein kinase that has been identified as a Rho GTP-binding protein, is a promising target for neuropsychiatric disorders. The selective ROCK inhibitor Y-27632 has been shown to induce neurite outgrowth in PC12 cells. However, the precise cellular and molecular mechanisms underlying ROCK inhibition-induced neurite outgrowth are not fully understood. In this study, we examined the roles of cellular signaling pathways in the potentiation of nerve growth factor (NGF)-induced neurite outgrowth by Y-27632. Y-27632 significantly potentiated NGF (2.5 ng/ml)-induced neurite outgrowth in PC12 cells, in a concentration-dependent manner. Furthermore, another ROCK inhibitor, H-1152, and the Rho inhibitor botulinum exoenzyme C3 also potentiated NGF (2.5 ng/ml)-induced neurite outgrowth. The effects by Y-27632 were antagonized by co-administration of inositol 1,4,5-trisphosphate (IP(3)) receptor antagonists (xestospongin C or 2-aminoethoxydiphenylborate (2-APB)). Moreover, the potentiation by Y-27632 was blocked by co-administration of the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 or an Akt inhibitor. In contrast, the specific inhibitors of phospholipase C (PLC-γ), p38MAPK, c-Jun N-terminal kinase (JNK), and the Ras/Raf/mitogen-activated protein kinase (MAPK) signaling pathways did not affect the potentiation of NGF-induced neurite outgrowth by Y-27632. The results of double-staining immunocytochemistry suggested that both ROCK1 and type-1 IP₃ receptors may be co-localized in the cell body of PC12 cells. In conclusion, these findings suggest that IP₃ receptors and PI3K-Akt signaling pathways might be involved in the mechanisms of potentiation of NGF-induced neurite outgrowth by ROCK inhibitors.