Brunsing Ryan, Omori Sidne A, Weber Frank, Bicknell Alicia, Friend Leslie, Rickert Robert, Niwa Maho
Division of Biological Sciences, Section of Molecular Biology, University of California San Diego, La Jolla, CA 92093-0377, USA.
J Biol Chem. 2008 Jun 27;283(26):17954-61. doi: 10.1074/jbc.M801395200. Epub 2008 Mar 28.
The unfolded protein response (UPR) signaling pathway regulates the functional capacity of the endoplasmic reticulum for protein folding. Beyond a role for UPR signaling during terminal differentiation of mature B cells to antibody-secreting plasma cells, the status or importance of UPR signaling during hematopoiesis has not been explored, due in part to difficulties in isolating sufficient quantities of cells at developmentally intermediate stages required for biochemical analysis. Following reconstitution of irradiated mice with hematopoietic cells carrying a fluorescent UPR reporter construct, we found that IRE1 nuclease activity for XBP1 splicing is active at early stages of T- and B-lymphocyte differentiation: in bone marrow pro-B cells and in CD4(+)CD8(+) double positive thymic T cells. IRE1 was not active in B cells at later stages. In T cells, IRE activity was not detected in the more mature CD4(+) T-cell population but was active in the CD8(+) cytotoxic T-cell population. Multiple signals are likely to be involved in activating IRE1 during lymphocyte differentiation, including rearrangement of antigen receptor genes. Our results show that reporter-transduced hematopoietic stem cells provide a quick and easy means to identify UPR signaling component activation in physiological settings.
未折叠蛋白反应（UPR）信号通路调节内质网进行蛋白质折叠的功能能力。除了在成熟B细胞向分泌抗体的浆细胞终末分化过程中UPR信号发挥作用外，由于在生化分析所需的发育中间阶段难以分离出足够数量的细胞，UPR信号在造血过程中的状态或重要性尚未得到探索。在用携带荧光UPR报告构建体的造血细胞重建受辐照小鼠后，我们发现用于XBP1剪接的IRE1核酸酶活性在T和B淋巴细胞分化的早期阶段是活跃的：在骨髓前B细胞和CD4(+)CD8(+)双阳性胸腺T细胞中。IRE1在后期的B细胞中不活跃。在T细胞中，在更成熟的CD4(+) T细胞群体中未检测到IRE活性，但在CD8(+)细胞毒性T细胞群体中是活跃的。在淋巴细胞分化过程中，多种信号可能参与激活IRE1，包括抗原受体基因的重排。我们的结果表明，报告基因转导的造血干细胞提供了一种快速简便的方法来识别生理环境中UPR信号成分的激活。
