Marlene and Stewart Greenebaum National Cancer Institute Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland, USA.
Cancer Res. 2010 Oct 15;70(20):8127-37. doi: 10.1158/0008-5472.CAN-09-4613. Epub 2010 Oct 5.
Epithelial-to-mesenchymal transition (EMT) is associated with increased breast tumor metastasis; however, the specific mechanisms by which EMT promotes metastasis remain somewhat unclear. Despite the importance of cytoskeletal dynamics during both EMT and metastasis, very few current studies examine the cytoskeleton of detached and circulating tumor cells. Specific posttranslational α-tubulin modifications are critical for adherent cell motility and implicated in numerous pathologies, but also remain understudied in detached cells. We report here that EMT induced through ectopic expression of Twist or Snail promotes α-tubulin detyrosination and the formation of tubulin-based microtentacles in detached HMLEs. Mechanistically, EMT downregulates the tubulin tyrosine ligase enzyme, resulting in an accumulation of detyrosinated α-tubulin (Glu-tubulin), and increases microtentacles that penetrate endothelial layers to facilitate tumor cell reattachment. Confocal microscopy shows that microtentacles are capable of penetrating the junctions between endothelial cells. Suppression of endogenous Twist in metastatic human breast tumor cells is capable of reducing both tubulin detyrosination and microtentacles. Clinical breast tumor samples display high concordance between Glu-tubulin and Twist expression levels, emphasizing the coupling between EMT and tubulin detyrosination in vivo. Coordinated elevation of Twist and Glu-tubulin at invasive tumor fronts, particularly within ductal carcinoma in situ samples, establishes that EMT-induced tubulin detyrosination occurs at the earliest stages of tumor invasion. These data support a novel model where the EMT that occurs during tumor invasion downregulates tubulin tyrosine ligase, increasing α-tubulin detyrosination and promoting microtentacles that could enhance the reattachment of circulating tumor cells to the vascular endothelium during metastasis.
上皮间质转化（EMT）与增加的乳腺癌转移有关；然而，EMT 促进转移的确切机制仍有些不清楚。尽管细胞骨架动力学在 EMT 和转移过程中都很重要，但很少有当前的研究检查分离和循环肿瘤细胞的细胞骨架。翻译后α-微管蛋白的特定修饰对于附着细胞的迁移至关重要，并与许多病理学有关，但在分离细胞中仍研究不足。我们在这里报告，通过异位表达 Twist 或 Snail 诱导的 EMT 促进了分离的 HMLE 中α-微管蛋白脱酪氨酸化和基于微管的微绒毛的形成。在机制上，EMT 下调微管酪氨酸连接酶酶，导致脱酪氨酸化的α-微管蛋白（Glu-微管蛋白）积累，并增加穿透内皮层以促进肿瘤细胞再附着的微绒毛。共聚焦显微镜显示微绒毛能够穿透内皮细胞之间的连接。在转移性人类乳腺癌细胞中抑制内源性 Twist 能够减少微管蛋白脱酪氨酸化和微绒毛。临床乳腺癌样本显示 Glu-微管蛋白和 Twist 表达水平之间具有高度一致性，强调了 EMT 与体内微管蛋白脱酪氨酸化之间的耦合。侵袭性肿瘤前沿（特别是在原位导管癌样本中）协调升高的 Twist 和 Glu-微管蛋白，确立了 EMT 诱导的微管蛋白脱酪氨酸化发生在肿瘤侵袭的最早阶段。这些数据支持一种新模型，即肿瘤侵袭过程中发生的 EMT 下调微管酪氨酸连接酶，增加α-微管蛋白脱酪氨酸化，并促进微绒毛，从而增强循环肿瘤细胞在转移过程中与血管内皮的再附着。
