1] Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, USA [2] Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
Oncogene. 2013 Oct;32(40):4836-44. doi: 10.1038/onc.2012.492. Epub 2012 Dec 3.
The ability of cells to invade into the dermis is a critical event in the development of cutaneous melanoma and ultimately an indicator of poor prognosis. However, the molecular events surrounding the acquisition of this invasive phenotype remain incompletely understood. Mutations in B-RAF are frequent in melanoma and are known to regulate the invasive phenotype. In this study, we sought to determine the molecular mechanisms controlling melanoma invasion. We found that mutant B-RAF signaling regulates a cadherin switch. In melanoma cells expressing mutant B-RAF we observed high levels of N-cadherin and low levels of E-cadherin. Depletion of mutant B-RAF, by small interfering RNA, caused a decrease in the levels of N-cadherin and an increase in the levels of E-cadherin. Mechanistically, we found that this cadherin switch required the activity of Rac1 and its GEF, Tiam1, both of which show suppressed activity in the presence of mutant B-RAF. Consistent with the work of others, we found that depletion of mutant B-RAF decreased the invasive capacity of the melanoma cells. However, simultaneous depletion of B-RAF and Rac or Tiam1 resulted in invasive capacity similar to that of control cells. Taken together, our results suggest that mutant B-RAF signaling downregulates Tiam1/Rac activity resulting in an increase in N-cadherin levels and a decrease in E-cadherin levels and ultimately enhanced invasion.
细胞侵入真皮的能力是皮肤黑色素瘤发展的关键事件，最终是预后不良的指标。然而，获得这种侵袭表型的分子事件仍不完全清楚。B-RAF 突变在黑色素瘤中很常见，已知可调节侵袭表型。在这项研究中，我们试图确定控制黑色素瘤侵袭的分子机制。我们发现突变型 B-RAF 信号调节钙粘蛋白开关。在表达突变型 B-RAF 的黑色素瘤细胞中，我们观察到高水平的 N-钙粘蛋白和低水平的 E-钙粘蛋白。通过小干扰 RNA 耗尽突变型 B-RAF 会导致 N-钙粘蛋白水平降低和 E-钙粘蛋白水平升高。从机制上讲，我们发现这种钙粘蛋白开关需要 Rac1 及其 GEF（Tiam1）的活性，在存在突变型 B-RAF 的情况下，两者的活性均受到抑制。与其他人的工作一致，我们发现耗尽突变型 B-RAF 会降低黑色素瘤细胞的侵袭能力。然而，同时耗尽 B-RAF 和 Rac 或 Tiam1 会导致侵袭能力与对照细胞相似。总之，我们的结果表明，突变型 B-RAF 信号下调 Tiam1/Rac 活性，导致 N-钙粘蛋白水平升高和 E-钙粘蛋白水平降低，最终增强侵袭。
