Danforth David N, Zhu Yuelin
Surgery Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Breast Cancer Res Treat. 2005 Nov;94(1):81-91. doi: 10.1007/s10549-005-7491-6.
The membrane receptor Fas (Apo-1/CD95) is an important initiator of programmed cell death induced by anti-Fas antibody or Fas ligand. MCF-7 human breast cancer cells have low levels of Fas receptor (FasR) and are resistant to anti-FasR antibody mediated apoptosis, however two naturally occurring substances, interferon and all-trans retinoic acid (AT), act synergistically to enhance antiproliferative processes in these cells, suggesting this combination may also be an effective means for enhancing FasR expression. When this was studied, it was found that IFN-gamma and AT in combination acted synergistically to induce expression of FasR mRNA and FasR protein in a time-dependent and dose-dependent manner. This induction required continuous protein synthesis, and STAT1 protein, but not PKR or TR1 protein, was induced in a manner quantitatively and temporally related to FasR protein induction, and consistent with STAT1 mediation of the synergistic effect of IFN-gamma and AT on FasR expression. FasR-induced cells were resistant to stimulation of apoptosis by anti-FasR antibody, however treatment with cycloheximide rendered these cells sensitive to antibody-induced apoptosis, suggesting endogenous blockade to signaling. These cells did not express caspase 3, or FLIP(L), but strongly expressed the endogenous inhibitor of apoptosis Bcl-2, indicating a type II Fas signaling pathway. Expression of these proteins was not modulated by IFN/AT, however treatment of Fas-induced cells with Bcl-2 specific small interfering RNA (SiRNA) downregulated Bcl-2 protein expression and rendered these cells sensitive to the cytotoxic effects of anti-Fas antibody. These findings indicate that IFN-gamma+AT in combination modulate Fas signaling and provide a novel mechanism for the promotion of cell death in breast cancer cells.
膜受体Fas（Apo-1/CD95）是抗Fas抗体或Fas配体诱导程序性细胞死亡的重要启动因子。MCF-7人乳腺癌细胞的Fas受体（FasR）水平较低，对抗FasR抗体介导的凋亡具有抗性，然而，两种天然物质干扰素和全反式维甲酸（AT）协同作用可增强这些细胞的抗增殖过程，提示这种联合可能也是增强FasR表达的有效手段。当对此进行研究时，发现IFN-γ和AT联合以时间和剂量依赖性方式协同诱导FasR mRNA和FasR蛋白的表达。这种诱导需要持续的蛋白质合成，并且STAT1蛋白而非PKR或TR1蛋白的诱导方式在数量和时间上与FasR蛋白的诱导相关，且与STAT1介导IFN-γ和AT对FasR表达的协同作用一致。FasR诱导的细胞对抗FasR抗体刺激的凋亡具有抗性，然而用放线菌酮处理使这些细胞对抗体诱导的凋亡敏感，提示存在内源性信号传导阻断。这些细胞不表达半胱天冬酶3或FLIP(L)，但强烈表达内源性凋亡抑制剂Bcl-2，表明存在II型Fas信号通路。这些蛋白质的表达不受IFN/AT调节，然而用Bcl-2特异性小干扰RNA（SiRNA）处理Fas诱导的细胞可下调Bcl-2蛋白表达并使这些细胞对抗Fas抗体的细胞毒性作用敏感。这些发现表明IFN-γ+AT联合调节Fas信号传导，并为促进乳腺癌细胞死亡提供了一种新机制。
