Narvaez C J, Welsh J
Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana 46556, USA.
J Biol Chem. 2001 Mar 23;276(12):9101-7. doi: 10.1074/jbc.M006876200. Epub 2000 Oct 26.
Vitamin D(3) compounds are currently in clinical trials for human breast cancer and offer an alternative approach to anti-hormonal therapies for this disease. 1alpha,25-Dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)), the active form of vitamin D(3), induces apoptosis in breast cancer cells and tumors, but the underlying mechanisms are poorly characterized. In these studies, we focused on the role of caspase activation and mitochondrial disruption in 1alpha,25(OH)(2)D(3)-mediated apoptosis in breast cancer cells (MCF-7) in vitro. The effect of 1alpha,25(OH)(2)D(3) on MCF-7 cells was compared with that of tumor necrosis factor alpha, which induces apoptosis via a caspase-dependent pathway. Our major findings are that 1alpha,25(OH)(2)D(3) induces apoptosis in MCF-7 cells by disruption of mitochondrial function, which is associated with Bax translocation to mitochondria, cytochrome c release, and production of reactive oxygen species. Moreover, we show that Bax translocation and mitochondrial disruption do not occur after 1alpha,25(OH)(2)D(3) treatment of a MCF-7 cell clone selected for resistance to 1alpha,25(OH)(2)D(3)-mediated apoptosis. These mitochondrial effects of 1alpha,25(OH)(2)D(3) do not require caspase activation, since they are not blocked by the cell-permeable caspase inhibitor z-Val-Ala-Asp-fluoromethylketone. Although caspase inhibition blocks 1alpha,25(OH)(2)D(3)-mediated events downstream of mitochondria such as poly(ADP-ribose) polymerase cleavage, external display of phosphatidylserine, and DNA fragmentation, MCF-7 cells still execute apoptosis in the presence of z-Val-Ala-Asp-fluoromethylketone, indicating that the commitment to 1alpha,25(OH)(2)D(3)-mediated cell death is caspase-independent.
维生素D(3)化合物目前正处于针对人类乳腺癌的临床试验阶段，为该疾病的抗激素疗法提供了一种替代方法。1α,25 - 二羟基维生素D(3)（1α,25(OH)₂D₃）是维生素D(3)的活性形式，可诱导乳腺癌细胞和肿瘤发生凋亡，但其潜在机制尚不明确。在这些研究中，我们聚焦于半胱天冬酶激活和线粒体破坏在1α,25(OH)₂D₃介导的体外乳腺癌细胞（MCF - 7）凋亡中的作用。将1α,25(OH)₂D₃对MCF - 7细胞的作用与肿瘤坏死因子α进行比较，后者通过半胱天冬酶依赖性途径诱导凋亡。我们的主要发现是，1α,25(OH)₂D₃通过破坏线粒体功能诱导MCF - 7细胞凋亡，这与Bax转位至线粒体、细胞色素c释放及活性氧生成有关。此外，我们发现对1α,25(OH)₂D₃介导的凋亡具有抗性的MCF - 7细胞克隆经1α,25(OH)₂D₃处理后，未发生Bax转位和线粒体破坏。1α,25(OH)₂D₃的这些线粒体效应不需要半胱天冬酶激活，因为它们不受细胞可渗透的半胱天冬酶抑制剂z - Val - Ala - Asp - 氟甲基酮的阻断。虽然半胱天冬酶抑制可阻断1α,25(OH)₂D₃介导的线粒体下游事件，如聚（ADP - 核糖）聚合酶裂解、磷脂酰丝氨酸外翻及DNA片段化，但MCF - 7细胞在存在z - Val - Ala - Asp - 氟甲基酮的情况下仍会发生凋亡，这表明1α,25(OH)₂D₃介导的细胞死亡过程不依赖半胱天冬酶。
