In the developing forebrain, the migration and positioning of neural progenitor cells (NPCs) are regulated coordinately by various molecules. Mutation of these molecules, therefore, causes cortical malformation. GPR56 has been reported as a cortical malformation-related gene that is mutated in patients with bilateral frontoparietal polymicrogyria. GPR56 encodes an orphan G protein-coupled receptor, and its mutations reduce the cell surface expression. It has also been reported that the expression level of GPR56 is involved in cancer cell adhesion and metastasis. However, it remains to be clarified how GPR56 functions in brain development and which signaling pathways are activated by GPR56. In this study, we showed that GPR56 is highly expressed in NPCs and has the ability to inhibit NPC migration. We found that GPR56 coupled with G␣ 12/13 and induced Rho-dependent activation of the transcription mediated through a serum-responsive element and NF-B-responsive element and actin fiber reorganization. The transcriptional activation and actin reorganization were inhibited by an RGS domain of the p115 Rho-specific guanine nucleotide exchange factor (p115 RhoGEF RGS) and dominant negative form of Rho. Moreover, we have demonstrated that a functional anti-GPR56 antibody, which has an agonistic activity, inhibited NPC migration. This inhibition was attenuated by p115 RhoGEF RGS, C3 exoenzyme, and GPR56 knockdown. These results indicate that GPR56 participates in the regulation of NPC movement through the G␣ 12/13 and Rho signaling pathway, suggesting its important role in the development of the central nervous system.

Abstract. Phosphoinositide-3 kinase (PI3K) and phospholipase C (PLC) utilize the same phosphoinositides as substrates to produce different signaling molecules. These enzymes are activated by a similar set of cell signaling mechanisms, i.e., tyrosine kinases and G proteins, and affect common cell functions, including proliferation, motility, and intracellular trafficking. Despite these similarities, the interplay between these enzymes is not well understood. To address this issue, the effects of the PI3K inhibitor LY294002 on carbachol-induced calcium increase in PC12h cells were examined. As carbachol stimulates both Gq-and Gi-coupled muscarinic acetylcholine receptors (mAChRs), PI3K and PLC are activated simultaneously in this protocol. LY294002 was found to reduce the carbachol-induced calcium increase, and the reduction was attributed to suppression of calcium entry. As LY294002 did not affect either carbachol-induced calcium release or calcium entry induced by calcium store depletion, this agent was found to suppress calcium entry directly activated by mAChRs. Although PI3K was supposed to compete for substrates with PLC, the PI3K inhibitor did not enhance PLC-dependent cellular responses. As LY294002 was still effective by treating cells after carbachol stimulation, it is likely that this agent blocks the calcium entry channels directly.