Institute of Biomedical Sciences, National Sun Yat-Sen University, Kaohsiung 804, Taiwan.
Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, Kaohsiung 807, Taiwan.
Int J Biol Macromol. 2021 Sep 30;187:513-527. doi: 10.1016/j.ijbiomac.2021.07.133. Epub 2021 Jul 24.
To clarify the mechanism of semicarbazide-modified α-lactalbumin (SEM-LA)-mediated cytotoxicity, we investigated its effect on human U937 leukemia cells and MCF-7 breast cancer cells in the current study. SEM-LA induced apoptosis in U937 cells, which showed increased NOX4 expression, procaspase-8 degradation, and t-Bid production. FADD depletion inhibited SEM-LA-elicited caspase-8 activation, t-Bid production, and cell death, indicating that SEM-LA activated death receptor-mediated apoptosis in U937 cells. SEM-LA stimulated Ca-mediated Akt activation, which in turn increased Sp1- and p300-mediated NOX4 transcription. The upregulation of NOX4 expression promoted ROS-mediated p38 MAPK phosphorylation, leading to protein phosphatase 2A (PP2A)-regulated tristetraprolin (TTP) degradation. Remarkably, TTP downregulation increased the stability of TNF-α mRNA, resulting in the upregulation of TNF-α protein expression. Abolishment of Ca-NOX4-ROS axis-mediated p38 MAPK activation attenuated SEM-LA-induced TNF-α upregulation and protected U937 cells from SEM-LA-mediated cytotoxicity. The restoration of TTP expression alleviated the effect of TNF-α upregulation and cell death induced by SEM-LA. Altogether, the data in this study demonstrate that SEM-LA activates TNF-α-mediated apoptosis in U937 cells through the NOX4/p38 MAPK/PP2A axis. We think that a similar pathway can also explain the death of MCF-7 human breast cancer cells after SEM-LA treatment.
为阐明三聚氰胺修饰的α-乳白蛋白（SEM-LA）介导细胞毒性的机制，本研究探讨了其对人 U937 白血病细胞和 MCF-7 乳腺癌细胞的影响。SEM-LA 诱导 U937 细胞凋亡，表现为 NOX4 表达增加、procaspase-8 降解和 t-Bid 产生。FADD 耗竭抑制 SEM-LA 诱导的 caspase-8 激活、t-Bid 产生和细胞死亡，表明 SEM-LA 激活了 U937 细胞死亡受体介导的细胞凋亡。SEM-LA 刺激 Ca2+介导的 Akt 激活，进而增加 Sp1 和 p300 介导的 NOX4 转录。NOX4 表达上调促进 ROS 介导的 p38 MAPK 磷酸化，导致蛋白磷酸酶 2A（PP2A）调节的 tristetraprolin（TTP）降解。值得注意的是，TTP 下调增加了 TNF-α mRNA 的稳定性，导致 TNF-α蛋白表达上调。Ca-NOX4-ROS 轴介导的 p38 MAPK 激活的消除减弱了 SEM-LA 诱导的 TNF-α上调和对 U937 细胞的 SEM-LA 介导的细胞毒性。TTP 表达的恢复减轻了 SEM-LA 诱导的 TNF-α上调和细胞死亡的作用。总之，本研究的数据表明，SEM-LA 通过 NOX4/p38 MAPK/PP2A 轴激活 TNF-α 介导的 U937 细胞凋亡。我们认为，类似的途径也可以解释 SEM-LA 处理后 MCF-7 人乳腺癌细胞的死亡。
