Xue Liang-yan, Chiu Song-mao, Oleinick Nancy L
Department of Radiation Oncology and the Case Comprehensive Cancer Center, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4942, USA.
Oncogene. 2005 Oct 20;24(46):6987-92. doi: 10.1038/sj.onc.1208837.
The antiapoptotic Bcl-2-family proteins, Bcl-2 and Bcl-xL, are recognized phototargets of photodynamic therapy (PDT) with the mitochondrion-targeting phthalocyanine photosensitizer Pc 4. In the present study, we found that myeloid cell leukemia 1 (Mcl-1), another antiapoptotic member of the Bcl-2 family, was not photodamaged in Pc 4-PDT-treated human carcinoma cells MCF-7c3, MDA-MB468, DU145, and A431, although Mcl-1 turnover was observed after exposure of HeLa or MCF-7c3 cells to a supralethal dose of UVC. In contrast, when human lymphoma U937 and Jurkat cells were treated with Pc 4-PDT, staurosporine (STS) or UVC, Mcl-1 was cleaved to generate a 28-kDa fragment over a 2-4 h period. The cleavage of Mcl-1 was accompanied by the activation of caspases-3, -9, and -8. The broad-specificity caspase inhibitor z-VAD-fmk completely blocked Mcl-1 cleavage induced by PDT, STS or UVC, providing evidence for Mcl-1 as a substrate for caspases. Western blot analysis localized Mcl-1 to mitochondria, ER, and cytosol of both MCF-7c3 and U937 cells, suggesting that Mcl-1 protein, unlike Bcl-2 and Bcl-xL, is not a target for Pc 4-PDT, probably due to its localization to sites removed from those of Pc 4 binding. The 28-kDa cleaved fragment of Mcl-1, which has proapoptotic activity, was produced in PDT-treated lymphoid-derived cells, but not in cells of epithelial origin, suggesting that PDT-induced rapid and extensive apoptosis in lymphoma cells may result in part from the sensitivity of their Mcl-1 to caspase cleavage, removing an important negative control on apoptosis.
抗凋亡的Bcl-2家族蛋白Bcl-2和Bcl-xL，是线粒体靶向酞菁光敏剂Pc 4光动力疗法（PDT）的公认光靶点。在本研究中，我们发现，Bcl-2家族的另一个抗凋亡成员髓样细胞白血病1（Mcl-1），在经Pc 4-PDT处理的人癌细胞MCF-7c3、MDA-MB468、DU145和A431中未受到光损伤，尽管在HeLa或MCF-7c3细胞暴露于超致死剂量的紫外线C（UVC）后观察到了Mcl-1的周转。相反，当用人淋巴瘤U937和Jurkat细胞进行Pc 4-PDT、星形孢菌素（STS）或UVC处理时，Mcl-1在2至4小时内被切割产生一个28 kDa的片段。Mcl-1的切割伴随着半胱天冬酶-3、-9和-8的激活。广谱特异性半胱天冬酶抑制剂z-VAD-fmk完全阻断了由PDT、STS或UVC诱导的Mcl-1切割，为Mcl-1作为半胱天冬酶的底物提供了证据。蛋白质印迹分析将Mcl-1定位于MCF-7c3和U937细胞的线粒体、内质网和细胞质中，这表明Mcl-1蛋白与Bcl-2和Bcl-xL不同，不是Pc 4-PDT的靶点，可能是由于其定位于远离Pc 4结合位点的位置。具有促凋亡活性的Mcl-1的28 kDa切割片段在经PDT处理的淋巴来源细胞中产生，但在上皮来源细胞中未产生，这表明PDT诱导淋巴瘤细胞快速广泛凋亡可能部分是由于其Mcl-1对半胱天冬酶切割敏感，从而消除了对凋亡的重要负调控。
