Bourguignon Lilly Y W, Spevak Christina C, Wong Gabriel, Xia Weiliang, Gilad Eli
Endocrine Unit, Department of Medicine, University of California at San Francisco, and Veterans Affairs Medical Center, San Francisco, California 94121, USA.
J Biol Chem. 2009 Sep 25;284(39):26533-46. doi: 10.1074/jbc.M109.027466. Epub 2009 Jul 24.
Multidrug resistance and disease relapse is a challenging clinical problem in the treatment of breast cancer. In this study, we investigated the hyaluronan (HA)-induced interaction between CD44 (a primary HA receptor) and protein kinase Cepsilon (PKCepsilon), which regulates a number of human breast tumor cell functions. Our results indicate that HA binding to CD44 promotes PKCepsilon activation, which, in turn, increases the phosphorylation of the stem cell marker, Nanog, in the breast tumor cell line MCF-7. Phosphorylated Nanog is then translocated from the cytosol to the nucleus and becomes associated with RNase III DROSHA and the RNA helicase p68. This process leads to microRNA-21 (miR-21) production and a tumor suppressor protein (e.g. PDCD4 (program cell death 4)) reduction. All of these events contribute to up-regulation of inhibitors of apoptosis proteins (IAPs) and MDR1 (multidrug-resistant protein), resulting in anti-apoptosis and chemotherapy resistance. Transfection of MCF-7 cells with PKCepsilon or Nanog-specific small interfering RNAs effectively blocks HA-mediated PKCepsilon-Nanog signaling events, abrogates miR-21 production, and increases PDCD4 expression/eIF4A binding. Subsequently, this PKCepsilon-Nanog signaling inhibition causes IAP/MDR1 down-regulation, apoptosis, and chemosensitivity. To further evaluate the role of miR-21 in oncogenesis and chemoresistance, MCF-7 cells were also transfected with a specific anti-miR-21 inhibitor in order to silence miR-21 expression and inhibit its target functions. Our results indicate that anti-miR-21 inhibitor not only enhances PDCD4 expression/eIF4A binding but also blocks HA-CD44-mediated tumor cell behaviors. Thus, this newly discovered HA-CD44 signaling pathway should provide important drug targets for sensitizing tumor cell apoptosis and overcoming chemotherapy resistance in breast cancer cells.
多药耐药和疾病复发是乳腺癌治疗中一个具有挑战性的临床问题。在本研究中，我们研究了透明质酸（HA）诱导的CD44（主要的HA受体）与蛋白激酶Cε（PKCε）之间的相互作用，PKCε调节多种人类乳腺肿瘤细胞功能。我们的结果表明，HA与CD44的结合促进了PKCε的激活，进而增加了乳腺肿瘤细胞系MCF-7中干细胞标志物Nanog的磷酸化。磷酸化的Nanog随后从细胞质转移到细胞核，并与核糖核酸酶III Drosha和RNA解旋酶p68相关联。这个过程导致微小RNA-21（miR-21）的产生和肿瘤抑制蛋白（如程序性细胞死亡4（PDCD4））的减少。所有这些事件都有助于上调凋亡抑制蛋白（IAPs）和多药耐药蛋白1（MDR1），导致抗凋亡和化疗耐药。用PKCε或Nanog特异性小干扰RNA转染MCF-7细胞可有效阻断HA介导的PKCε-Nanog信号事件，消除miR-21的产生，并增加PDCD4表达/真核翻译起始因子4A（eIF4A）结合。随后，这种对PKCε-Nanog信号的抑制导致IAP/MDR1下调、细胞凋亡和化学敏感性。为了进一步评估miR-21在肿瘤发生和化疗耐药中的作用，MCF-7细胞也用特异性抗miR-21抑制剂进行转染，以沉默miR-21表达并抑制其靶功能。我们的结果表明，抗miR-21抑制剂不仅增强了PDCD4表达/eIF4A结合，还阻断了HA-CD44介导的肿瘤细胞行为。因此，这个新发现的HA-CD44信号通路应该为使肿瘤细胞凋亡敏感化和克服乳腺癌细胞的化疗耐药提供重要的药物靶点。
