Department of Biomedical and Clinical Sciences, Linköping University, S-58183 Linköping, Sweden.
Department of Immunology, Genetics and Pathology, Uppsala University, 751 85 Uppsala, Sweden.
Int J Mol Sci. 2020 Jul 4;21(13):4757. doi: 10.3390/ijms21134757.
The proteasome is a validated target of cancer therapeutics. Inhibition of proteasome activity results in the activation of the unfolded protein response (UPR) characterized by phosphorylation of eukaryotic initiation factor 2α (eIF2α), global translational arrest, and increased expression of the proapoptotic CHOP (C/EBP homologous protein) protein. Defects in the UPR response has been reported to result in altered sensitivity of tumor cells to proteasome inhibitors. Here, we characterized the effects of the deubiquitinase (DUB) inhibitor VLX1570 on protein homeostasis, both at the level of the UPR and on protein translation, in acute lymphoblastic leukemia (ALL). Similar to the 20S inhibitor bortezomib, VLX1570 induced accumulation of polyubiquitinated proteins and increased expression of the chaperone Grp78/Bip in ALL cells. Both compounds induced cleavage of PARP (Poly (ADP-ribose) polymerase) in ALL cells, consistent with induction of apoptosis. However, and in contrast to bortezomib, VLX1570 treatment resulted in limited induction of the proapoptotic CHOP protein. Translational inhibition was observed by both bortezomib and VLX1570. We report that in distinction to bortezomib, suppression of translation by VXL1570 occurred at the level of elongation. Increased levels of Hsc70/Hsp70 proteins were observed on polysomes following exposure to VLX1570, possibly suggesting defects in nascent protein folding. Our findings demonstrate apoptosis induction in ALL cells that appears to be uncoupled from CHOP induction, and show that VLX1570 suppresses protein translation by a mechanism distinct from that of bortezomib.
蛋白酶体是癌症治疗的一个已验证的靶点。抑制蛋白酶体活性会导致未折叠蛋白反应（UPR）的激活，其特征是真核起始因子 2α（eIF2α）的磷酸化、全局翻译停滞和促凋亡 CHOP（C/EBP 同源蛋白）蛋白的表达增加。据报道，UPR 反应的缺陷会导致肿瘤细胞对蛋白酶体抑制剂的敏感性改变。在这里，我们研究了去泛素化酶（DUB）抑制剂 VLX1570 对急性淋巴细胞白血病（ALL）中蛋白质平衡的影响，包括 UPR 水平和蛋白质翻译水平。与 20S 抑制剂硼替佐米相似，VLX1570 诱导 ALL 细胞中多泛素化蛋白的积累和伴侣蛋白 Grp78/Bip 的表达增加。这两种化合物均诱导 ALL 细胞中 PARP（多聚（ADP-核糖）聚合酶）的裂解，与诱导细胞凋亡一致。然而，与硼替佐米相反，VLX1570 处理导致促凋亡 CHOP 蛋白的诱导有限。硼替佐米和 VLX1570 均观察到翻译抑制。我们报告说，与硼替佐米不同，VXL1570 对翻译的抑制发生在延伸水平。暴露于 VLX1570 后，多核糖体上观察到 Hsc70/Hsp70 蛋白水平升高，这可能表明新生蛋白质折叠存在缺陷。我们的研究结果表明，在 ALL 细胞中诱导凋亡似乎与 CHOP 诱导脱耦联，并表明 VLX1570 通过与硼替佐米不同的机制抑制蛋白质翻译。
