Limon Jose J, So Lomon, Jellbauer Stefan, Chiu Honyin, Corado Juana, Sykes Stephen M, Raffatellu Manuela, Fruman David A
Department of Molecular Biology & Biochemistry, Institute for Immunology, and.
Institute for Immunology, and Department of Microbiology & Molecular Genetics, University of California, Irvine, CA 92697; and.
Proc Natl Acad Sci U S A. 2014 Nov 25;111(47):E5076-85. doi: 10.1073/pnas.1407104111. Epub 2014 Nov 10.
The mammalian target of rapamycin (mTOR) is a kinase that functions in two distinct complexes, mTORC1 and mTORC2. In peripheral B cells, complete deletion of mTOR suppresses germinal center B-cell responses, including class switching and somatic hypermutation. The allosteric mTORC1 inhibitor rapamycin blocks proliferation and differentiation, but lower doses can promote protective IgM responses. To elucidate the complexity of mTOR signaling in B cells further, we used ATP-competitive mTOR kinase inhibitors (TOR-KIs), which inhibit both mTORC1 and mTORC2. Although TOR-KIs are in clinical development for cancer, their effects on mature lymphocytes are largely unknown. We show that high concentrations of TOR-KIs suppress B-cell proliferation and differentiation, yet lower concentrations that preserve proliferation increase the fraction of B cells undergoing class switching in vitro. Transient treatment of mice with the TOR-KI compound AZD8055 increased titers of class-switched high-affinity antibodies to a hapten-protein conjugate. Mechanistic investigation identified opposing roles for mTORC1 and mTORC2 in B-cell differentiation and showed that TOR-KIs enhance class switching in a manner dependent on forkhead box, subgroup O (FoxO) transcription factors. These observations emphasize the distinct actions of TOR-KIs compared with rapamycin and suggest that TOR-KIs might be useful to enhance production of class-switched antibodies following vaccination.
雷帕霉素的哺乳动物靶点（mTOR）是一种激酶，在两种不同的复合物mTORC1和mTORC2中发挥作用。在外周B细胞中，mTOR的完全缺失会抑制生发中心B细胞反应，包括类别转换和体细胞超突变。变构mTORC1抑制剂雷帕霉素会阻断增殖和分化，但较低剂量可促进保护性IgM反应。为了进一步阐明B细胞中mTOR信号传导的复杂性，我们使用了ATP竞争性mTOR激酶抑制剂（TOR-KIs），其可同时抑制mTORC1和mTORC2。尽管TOR-KIs正在进行癌症临床开发，但其对成熟淋巴细胞的影响在很大程度上尚不清楚。我们发现，高浓度的TOR-KIs会抑制B细胞增殖和分化，而较低浓度且能维持增殖的TOR-KIs会增加体外发生类别转换的B细胞比例。用TOR-KI化合物AZD8055对小鼠进行短暂治疗可提高对半抗原-蛋白质偶联物的类别转换高亲和力抗体的滴度。机制研究确定了mTORC1和mTORC2在B细胞分化中的相反作用，并表明TOR-KIs以依赖叉头框O亚组（FoxO）转录因子的方式增强类别转换。这些观察结果强调了TOR-KIs与雷帕霉素相比的独特作用，并表明TOR-KIs可能有助于在疫苗接种后提高类别转换抗体的产生。
