Wang Jianrong, Lian Huiqin, Zhao Ying, Kauss Mara A, Spindel Samantha
Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853; Treman Research Institute, Ithaca, New York 14850.
Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853; Treman Research Institute, Ithaca, New York 14850.
J Biol Chem. 2008 Sep 12;283(37):25596-25605. doi: 10.1074/jbc.M801716200. Epub 2008 Jul 15.
Vitamin D3 causes potent suppression of various cancer cells; however, significant supraphysiological concentrations of this compound are required for antineoplastic effects. Current combinatorial therapies with vitamin D3 are restricted to differentiation effects. It remains uncertain if autophagy is involved in vitamin D3 inhibition on leukemia cells. Here we show that besides triggering differentiation and inhibiting apoptosis, which was previously known, vitamin D3 triggers autophagic death in human myeloid leukemia cells. Inhibiting differentiation does not efficiently diminish vitamin D3 suppression on leukemia cells. Vitamin D3 up-regulates Beclin1, which binds to class III phosphatidylinositol 3-kinase to trigger autophagy. Vitamin D3 phosphorylates Bad in its BH3 domain, resulting in disassociation of the apoptotic Bad-Bcl-xL complex and association of Bcl-xL with Beclin1 and ultimate suppression of apoptotic signaling. Knockdown of Beclin1 eliminates vitamin D3-induced autophagy and inhibits differentiation but activates apoptosis, suggesting that Beclin1 is required for both autophagy and differentiation, and autophagy cooperates with differentiation but excludes apoptosis, in which Beclin1 acts as an interface for these three different cascades. Moreover, additional up-regulation of autophagy, but not apoptosis, dramatically improves vitamin D3 inhibition on leukemia cells. These findings extend our understanding of the action of vitamin D3 in antineoplastic effects and the role of Beclin1 in regulating multiple cellular cascades and suggest a potentially promising strategy with a significantly better antileukemia effect.
维生素D3可有效抑制多种癌细胞；然而，该化合物发挥抗肿瘤作用需要显著高于生理浓度。目前维生素D3的联合疗法仅限于分化作用。维生素D3对白血病细胞的抑制作用是否涉及自噬仍不确定。在此我们表明，除了引发分化和抑制凋亡（这是之前已知的）外，维生素D3还可引发人髓系白血病细胞的自噬性死亡。抑制分化并不能有效减轻维生素D3对白血病细胞的抑制作用。维生素D3上调Beclin1，其与Ⅲ类磷脂酰肌醇3激酶结合以触发自噬。维生素D3使其BH3结构域中的Bad磷酸化，导致凋亡性Bad - Bcl - xL复合物解离以及Bcl - xL与Beclin1结合，最终抑制凋亡信号。敲低Beclin1可消除维生素D3诱导的自噬并抑制分化，但激活凋亡，这表明Beclin1对于自噬和分化均是必需的，并且自噬与分化协同作用但排除凋亡，其中Beclin1作为这三种不同级联反应的一个界面。此外，进一步上调自噬而非凋亡，可显著增强维生素D3对白血病细胞的抑制作用。这些发现扩展了我们对维生素D3抗肿瘤作用机制以及Beclin1在调节多种细胞级联反应中作用的理解，并提示了一种具有显著更好抗白血病效果的潜在有前景的策略。
