School of Medicine and Institute for Immunology, Tsinghua University, Beijing Key Lab for Immunological Research on Chronic Diseases, Tsinghua University, Beijing, China.
Zhuhai Precision Medical Center, Zhuhai People's Hospital (Zhuhai Hospital Affiliated with Jinan University), Jinan University, Zhuhai, Guangdong, China.
Front Immunol. 2021 Feb 9;11:617404. doi: 10.3389/fimmu.2020.617404. eCollection 2020.
The role of PI3K-mTOR pathway in regulating NK cell development has been widely reported. However, it remains unclear whether NK cell development depends on the protein kinase B (PKB), which links PI3K and mTOR, perhaps due to the potential redundancy of PKB. PKB has two phosphorylation sites, threonine 308 (T308) and serine 473 (S473), which can be phosphorylated by phosphoinositide-dependent protein kinase-1 (PDK1) and mTORC2, respectively. In this study, we established a mouse model in which PKB was inactivated through the deletion of PDK1 and Rictor, a key component of mTORC2, respectively. We found that the single deletion of PDK1 or Rictor could lead to a significant defect in NK cell development, while combined deletion of PDK1 and Rictor severely hindered NK cell development at the early stage. Notably, ectopic expression of myristoylated PKB significantly rescued this defect. In terms of mechanism, in PDK1/Rictor-deficient NK cells, E4BP4, a transcription factor for NK cell development, was less expressed, and the exogenous supply of E4BP4 could alleviate the developmental defect of NK cell in these mice. Besides, overexpression of Bcl-2 also helped the survival of PDK1/Rictor-deficient NK cells, suggesting an anti-apoptotic role of PKB in NK cells. In summary, complete phosphorylation of PKB at T308 and S473 by PDK1 and mTORC2 is necessary for optimal NK cell development, and PKB regulates NK cell development by promoting E4BP4 expression and preventing cell apoptosis.
PI3K-mTOR 通路在调节 NK 细胞发育中的作用已被广泛报道。然而，NK 细胞的发育是否依赖于将 PI3K 和 mTOR 联系起来的蛋白激酶 B（PKB）尚不清楚，这可能是由于 PKB 的潜在冗余性。PKB 有两个磷酸化位点，丝氨酸 308（T308）和丝氨酸 473（S473），分别可以被磷酸肌醇依赖性蛋白激酶-1（PDK1）和 mTORC2 磷酸化。在这项研究中，我们建立了一个通过分别敲除 PDK1 和 mTORC2 的关键成分 Rictor 使 PKB 失活的小鼠模型。我们发现，单独敲除 PDK1 或 Rictor 会导致 NK 细胞发育严重缺陷，而 PDK1 和 Rictor 的联合缺失则严重阻碍了 NK 细胞的早期发育。值得注意的是，myristoylated PKB 的异位表达显著挽救了这一缺陷。在 PDK1/Rictor 缺陷型 NK 细胞中，E4BP4（NK 细胞发育的转录因子）的表达减少，外源性提供 E4BP4 可以减轻这些小鼠中 NK 细胞发育缺陷。此外，Bcl-2 的过表达也有助于 PDK1/Rictor 缺陷型 NK 细胞的存活，提示 PKB 在 NK 细胞中具有抗凋亡作用。综上所述，PDK1 和 mTORC2 完全磷酸化 PKB 的 T308 和 S473 对于 NK 细胞的最佳发育是必要的，PKB 通过促进 E4BP4 的表达和防止细胞凋亡来调节 NK 细胞的发育。
