Endocytosis plays an important role in the immune defence systems of invertebrates through the interaction between the mechanical target of rapamycin complex 2 (mTORC2) and the AGC kinase family. Rictor is the most important unique subunit protein of mTORC2 and is thought to regulate almost all functions of mTORC2, including endocytosis. In the present study, a novel invertebrate Rictor homologue was identified from Apostichopus japonicus (designated as AjRictor) via the rapid amplification of cDNA ends (RACE). Spatial expression analysis indicated that AjRictor is ubiquitously expressed in all the examined tissues and has the highest transcript level in coelomocytes. Vibrio splendidus challenge in vivo and lipopolysaccharide (LPS) exposure in vitro could remarkably up-regulate the messenger RNA (mRNA) expression of AjRictor compared with the control group. AjRictor knockdown by 0.49- and 0.69-fold resulted in the significant decrease in endocytosis rate by 0.53- (P < 0.01) and 0.59-fold (P < 0.01) in vivo and in vitro compared with the control group, respectively. Similarly, the treatment of coelomocytes with rapamycin for 24 h and the destruction of the assembly of mTORC2 markedly decreased the endocytosis rate of the coelomocytes by 35.92% (P < 0.05). We detected the expression levels of endocytosis-related molecular markers after AjRictor knockdown and rapamycin treatment to further study the molecular mechanism between mTORC2 and endocytosis. Our results showed that AGC kinase family members (PKCα and Pan1) and the phosphorylation level of Akt^S473 were remarkably decreased after reducing mTORC2 activity; thus, mTORC2/Rictor plays a key role in the immune regulation of endocytosis in coelomocytes. Our current study indicates that mTORC2/Rictor is involved in the coelomocyte endocytosis of sea cucumber and plays an essential regulation role in defending pathogen invasion.

内吞作用通过雷帕霉素复合物 2 (mTORC2) 的机械靶标与 AGC 激酶家族之间的相互作用在无脊椎动物的免疫防御系统中发挥重要作用。Rictor 是 mTORC2 最重要的独特亚基蛋白，被认为可以调节 mTORC2 的几乎所有功能，包括内吞作用。在本研究中，通过 cDNA 末端的快速扩增 (RACE) 从刺参（称为 AjRictor）中鉴定出一种新的无脊椎动物 Rictor 同源物。空间表达分析表明，AjRictor在所有检查的组织中普遍表达，并且在体腔细胞中具有最高的转录水平。体内灿烂弧菌挑战与对照组相比，体外暴露脂多糖 (LPS)可以显着上调AjRictor的信使 RNA (mRNA) 表达。与对照组相比，在体内和体外， AjRictor敲低 0.49 倍和 0.69 倍导致内吞率分别显着降低 0.53 倍（P  < 0.01）和 0.59 倍（P  < 0.01） 。同样，用雷帕霉素处理体腔细胞 24 h 并破坏 mTORC2 的组装，显着降低了体腔细胞的内吞率 35.92% ( P < 0.05)。我们检测了AjRictor敲低和雷帕霉素处理后内吞相关分子标志物的表达水平，以进一步研究 mTORC2 与内吞之间的分子机制。我们的研究结果表明，降低 mTORC2 活性后，AGC 激酶家族成员（PKCα 和 Pan1）和 Akt ^{S473的磷酸化水平显着降低；}因此，mTORC2/Rictor 在体腔细胞内吞作用的免疫调节中起关键作用。我们目前的研究表明，mTORC2/Rictor 参与了海参的体腔细胞内吞作用，并在防御病原体入侵中起重要的调节作用。