Division of Molecular Medicine, Bose Institute, P-1/12, CIT, Scheme VIIM, Kolkata, India.
Carcinogenesis. 2010 Feb;31(2):259-68. doi: 10.1093/carcin/bgp240. Epub 2009 Dec 7.
The most common alterations found in breast cancer are inactivation or mutation of tumor suppressor gene p53. The present study revealed that theaflavins induced p53-mutated human breast cancer cell apoptosis. Pharmacological inhibition of caspase-8 or expression of dominant-negative (Dn)-caspase-8/Fas-associated death domain (FADD) partially inhibited apoptosis, whereas caspase-9 inhibitor completely blocked the killing indicating involvement of parallel pathways that converged to mitochondria. Further studies demonstrated theaflavin-induced Fas upregulation through the activation of c-jun N-terminal kinase, Fas-FADD interaction in a Fas ligand-independent manner, caspase-8 activation and t-Bid formation. A search for the parallel pathway revealed theaflavin-induced inhibition of survival pathway, mediated by Akt deactivation and Bcl-xL/Bcl-2-associated death promoter dephosphorylation. These well-defined routes of growth control converged to a common process of mitochondrial transmembrane potential loss, cytochrome c release and activation of the executioner caspase-9 and -3. Overexpression of either constitutively active myristylated-Akt (Myr-Akt) or Dn-caspase-8 partially blocked theaflavin-induced mitochondrial permeability transition and apoptosis of p53-mutated cells, whereas cotransfection of Myr-Akt and Dn-caspase-8 completely abolished theaflavin effect thereby negating the possibility of existence of third pathways. These results and other biochemical correlates established the concept that two distinct signaling pathways were regulated by theaflavins to induce mitochondrial death cascade, eventually culminating to apoptosis of p53-mutated human breast cancer cells that are strongly resistant to conventional therapies.
在乳腺癌中最常见的改变是肿瘤抑制基因 p53 的失活或突变。本研究表明，茶黄素诱导 p53 突变的人乳腺癌细胞凋亡。半胱天冬酶-8 的药理学抑制或显性负性（Dn）-半胱天冬酶-8/Fas 相关死亡结构域（FADD）的表达部分抑制凋亡，而半胱天冬酶-9 抑制剂完全阻断杀伤，表明涉及平行途径，这些途径汇聚到线粒体。进一步的研究表明，茶黄素通过激活 c-jun N 末端激酶诱导 Fas 上调，以 Fas 配体非依赖性方式与 Fas-FADD 相互作用，激活半胱天冬酶-8 和 t-Bid 形成。对平行途径的搜索表明，茶黄素诱导的生存途径抑制，由 Akt 失活和 Bcl-xL/Bcl-2 相关死亡促进子去磷酸化介导。这些明确的生长控制途径汇聚到一个共同的过程，即线粒体跨膜电位丧失、细胞色素 c 释放和执行器半胱天冬酶-9 和 -3 的激活。组成型激活的豆蔻酰化-Akt（Myr-Akt）或 Dn-caspase-8 的过表达部分阻断茶黄素诱导的线粒体通透性转换和 p53 突变细胞的凋亡，而 Myr-Akt 和 Dn-caspase-8 的共转染完全消除了茶黄素的作用，从而否定了存在第三种途径的可能性。这些结果和其他生化相关性确立了这样一种概念，即两种不同的信号通路被茶黄素调节以诱导线粒体死亡级联，最终导致对传统疗法具有强烈抗性的 p53 突变人乳腺癌细胞的凋亡。
