The Division of Hematology/Oncology, Department of Medicine, The Tisch Cancer Institute, Mount Sinai School of Medicine, New York, NY, USA.
Cancer Biol Ther. 2012 Nov;13(13):1276-83. doi: 10.4161/cbt.21784. Epub 2012 Aug 16.
CD44 is a cell surface antigen expressed on acute myeloid leukemia cells and is used as a marker to isolate leukemia stem cells. CD44 ligation with the antibody A3D8 has been found to induce apoptosis in human acute promyelocytic leukemia (APL) cells via activation of caspase-8. The mechanism of A3D8-induced caspase-8 activation was studied in APL NB4 cells. A3D8 induces lipid raft clustering which causes Fas aggregation as determined with a confocal microscope. A3D8-induced apoptosis is abrogated by the lipid raft disrupting agent methyl-β-cyclodextrin and the caspase-8 inhibitor Z-IETD-fmk. Western blot analysis reveals that A3D8 binds to the standard form of CD44 (CD44s). HL-60 cells without detectable CD44s protein are not responsive to A3D8-induced apoptosis. SKNO-1 cells containing higher level of CD44s protein are more sensitive to A3D8-induced apoptosis than NB4 cells. These results indicate that A3D8 induces apoptosis in leukemia cells through caspase-8 activation by binding to CD44s protein and inducing lipid raft clustering.
CD44 是一种在急性髓系白血病细胞表面表达的抗原，被用作分离白血病干细胞的标志物。已经发现，CD44 与抗体 A3D8 的结合通过激活半胱天冬酶-8 诱导人急性早幼粒细胞白血病 (APL) 细胞凋亡。本研究在 APL NB4 细胞中研究了 A3D8 诱导的 caspase-8 激活的机制。A3D8 诱导脂筏聚集，这导致 Fas 聚集，这可以通过共聚焦显微镜来确定。脂筏破坏剂甲基-β-环糊精和半胱天冬酶-8 抑制剂 Z-IETD-fmk 可阻断 A3D8 诱导的细胞凋亡。Western blot 分析表明，A3D8 与标准形式的 CD44（CD44s）结合。没有检测到 CD44s 蛋白的 HL-60 细胞对 A3D8 诱导的凋亡无反应。含有更高水平 CD44s 蛋白的 SKNO-1 细胞比 NB4 细胞对 A3D8 诱导的凋亡更敏感。这些结果表明，A3D8 通过与 CD44s 蛋白结合并诱导脂筏聚集，通过激活半胱天冬酶-8 诱导白血病细胞凋亡。
