Jiang Hua, Zou Jianfeng, Zhang Hui, Fu Weijun, Zeng Tianmei, Huang Hejing, Zhou Fan, Hou Jian
Department of Hematology, The Myeloma and Lymphoma Center, Changzheng Hospital, The Second Military Medical University, 415 Fengyang Rd, Shanghai, 200003, China.
Clin Exp Med. 2015 Feb;15(1):85-96. doi: 10.1007/s10238-013-0269-y. Epub 2013 Dec 20.
The unfolded protein response (UPR) is an essential pathway for both normal and malignant plasma cells to maintain endoplasmic reticulum (ER) homeostasis in response to the large amount of immunoglobulin (Ig) output. The inositol-requiring enzyme 1-X-box binding protein-1 (IRE1-XBP-1) arm of the UPR pathway has been shown to play crucial roles not only in relieving the ER stress by up-regulating a series of genes favoring ER-associated protein degradation and protein folding, but in mediating terminal plasmacytic differentiation and maturation. Myeloma cells comprise various subsets arrested in diverse differentiated phases, and the immaturity of myeloma cells has been taken as a marker for poor prognosis, suggesting that differentiation induction would be a promising therapeutic strategy for myeloma. Herein, we used low-dose pharmacological UPR inducers such as tunicamycin (TM) and dithiothreitol (DTT) to efficiently activate the IRE1-XBP-1 pathway in myeloma cells characterized by transcriptional expression increase in spliced XBP-1 and molecular chaperons, accompanied by significant differentiation and maturation of these myeloma cells, without concomitant cytotoxicity. These differentiated myeloma cells exhibited a more mature appearance with well-developed cytoplasm and a reduced nucleocytoplasmic ratio, and a further differentiated phenotype with markedly increased expression of CD49e together with significantly elevated cellular secretion of Ig light chain as shown by flow cytometry and ELISA, in contrast to the control myeloma cells without exposed to TM or DTT. Moreover, siRNA knockdown of XBP-1 disrupted TM- or DTT-induced myeloma cell differentiation and maturation. Our study, for the first time, validated that the modest activation of the UPR pathway enables myeloma cells to further differentiate, and identified that XBP-1 plays an indispensable role in UPR-mediated myeloma cell differentiation and maturation. Thus, we provided the rationale and feasibility for the exploration of the novel therapeutic strategy of differentiation induction for plasmacytic malignancies.
未折叠蛋白反应（UPR）是正常和恶性浆细胞维持内质网（ER）稳态以应对大量免疫球蛋白（Ig）输出的重要途径。UPR途径中的肌醇需求酶1-X盒结合蛋白1（IRE1-XBP-1）分支不仅在通过上调一系列有利于ER相关蛋白降解和蛋白折叠的基因来缓解ER应激方面发挥关键作用，还在介导终末浆细胞分化和成熟中起作用。骨髓瘤细胞包含停滞在不同分化阶段的各种亚群，骨髓瘤细胞的不成熟已被视为预后不良的标志物，这表明诱导分化将是骨髓瘤一种有前景的治疗策略。在此，我们使用低剂量的药理学UPR诱导剂，如衣霉素（TM）和二硫苏糖醇（DTT），以有效激活骨髓瘤细胞中的IRE1-XBP-1途径，其特征是剪接XBP-1和分子伴侣的转录表达增加，同时这些骨髓瘤细胞显著分化和成熟，且无伴随的细胞毒性。与未暴露于TM或DTT的对照骨髓瘤细胞相比，这些分化的骨髓瘤细胞表现出更成熟的外观，细胞质发达，核质比降低，并且通过流式细胞术和ELISA显示出进一步分化的表型，CD49e表达明显增加，同时细胞分泌的Ig轻链显著升高。此外，XBP-1的siRNA敲低破坏了TM或DTT诱导的骨髓瘤细胞分化和成熟。我们的研究首次证实适度激活UPR途径可使骨髓瘤细胞进一步分化，并确定XBP-1在UPR介导的骨髓瘤细胞分化和成熟中起不可或缺的作用。因此，我们为探索浆细胞恶性肿瘤分化诱导的新型治疗策略提供了理论依据和可行性。
