Departments of Medicine and Environmental Medicine, New York University Cancer Institute, New York University School of Medicine, New York, New York 10016.
Departments of Medicine and Environmental Medicine, New York University Cancer Institute, New York University School of Medicine, New York, New York 10016.
J Biol Chem. 2011 Oct 14;286(41):35708-35715. doi: 10.1074/jbc.M111.271585. Epub 2011 Aug 22.
Transferrin receptor 1 (TfR1) is a ubiquitous type II membrane receptor with 61 amino acids in the N-terminal cytoplasmic region. TfR1 is highly expressed in cancer cells, particularly under iron deficient conditions. Overexpression of TfR1 is thought to meet the increased requirement of iron uptake necessary for cell growth. In the present study, we used transferrin (Tf), a known ligand of TfR1, and gambogic acid (GA), an apoptosis-inducing agent and newly identified TfR1 ligand to investigate the signaling role of TfR1 in breast cancer cells. We found that GA but not Tf induced apoptosis in a TfR1-dependent manner in breast cancer MDA-MB-231 cells. Estrogen receptor-positive MCF-7 cells lack caspase-3 and were not responsive to GA treatment. GA activated the three major signaling pathways of the MAPK family, as well as caspase-3, -8, and Poly(ADP-ribose)polymerase apoptotic pathway. Interestingly, only Src inhibitor PP2 greatly sensitized the cells to GA-mediated apoptosis. Further investigations by confocal fluorescence microscopy and immunoprecipitation revealed that Src and TfR1 are constitutively bound. Using TfR1-deficient CHO TRVB cells, point mutation studies showed that Tyr(20) within the (20)YTRF(23) motif of the cytoplasmic region of TfR1 is the phosphorylation site by Src. TfR1 Tyr(20) phosphomutants were more sensitive to GA-mediated apoptosis. Our results indicate that, albeit its iron uptake function, TfR1 is a signaling molecule and tyrosine phosphorylation at position 20 by Src enhances anti-apoptosis and potentiates breast cancer cell survival.
转铁蛋白受体 1（TfR1）是一种普遍存在的 II 型膜受体，其 N 端胞质区有 61 个氨基酸。TfR1 在癌细胞中高度表达，特别是在缺铁条件下。TfR1 的过表达被认为满足了细胞生长所需的铁摄取增加的需求。在本研究中，我们使用转铁蛋白（Tf），一种已知的 TfR1 配体，和藤黄酸（GA），一种凋亡诱导剂和新鉴定的 TfR1 配体，来研究 TfR1 在乳腺癌细胞中的信号作用。我们发现，GA 但不是 Tf 以 TfR1 依赖性方式诱导乳腺癌 MDA-MB-231 细胞凋亡。雌激素受体阳性 MCF-7 细胞缺乏 caspase-3，对 GA 处理无反应。GA 激活了 MAPK 家族的三大信号通路，以及 caspase-3、-8 和聚（ADP-核糖）聚合酶凋亡途径。有趣的是，只有 Src 抑制剂 PP2 大大增强了细胞对 GA 介导的凋亡的敏感性。通过共聚焦荧光显微镜和免疫沉淀进一步研究表明，Src 和 TfR1 是持续结合的。使用 TfR1 缺陷型 CHO TRVB 细胞，点突变研究表明，TfR1 胞质区的（20）YTRF（23）基序内的 Tyr（20）是 Src 磷酸化的位点。TfR1 Tyr（20）磷酸突变体对 GA 介导的凋亡更为敏感。我们的结果表明，尽管 TfR1 具有铁摄取功能，但它是一种信号分子，Src 酪氨酸磷酸化位置 20 增强了抗凋亡作用，并增强了乳腺癌细胞的存活。
