Structure and Biomechanics of the Endothelial Transcellular Circumferential Invasion Array in Tumor Invasion

Cancer cells breach the endothelium not only through cell-cell junctions but also via individual endothelial cells (ECs), or transcellular invasion. The underlying EC forms a circular structure around the transcellular invasion pore that is dependent on myosin light chain kinase (MLCK) and myosin II regulatory light chain (RLC) phosphorylation. Here we offer mechanistic insights into transcellular invasive array formation amid persistent tensile force from activated EC myosin. Fluorescence recovery after photobleaching (FRAP) experiments, sarcomeric distance measurements using super-resolution microscopy and electron microscopy provide details about the nature of the myosin II invasion array. To probe the relationship between biomechanical forces and the tension required to maintain the curvature of contractile filaments, we targeted individual actin-myosin fibers at the invasion site for photoablation. We showed that adjacent filaments rapidly replace the ablat11ed structures. We propose that the transcellular circumferential invasion array (TCIA) provides the necessary constraint within the EC to blunt the radial compression from the invading cancer cell.癌细胞突破内皮屏障的途径不仅涵盖细胞间连接，还可通过单个内皮细胞（endothelial cells, ECs）实现，即跨细胞侵袭。依赖肌球蛋白轻链激酶（myosin light chain kinase, MLCK）与肌球蛋白II调节轻链（myosin II regulatory light chain, RLC）磷酸化的内皮细胞，会在跨细胞侵袭孔周围形成环状结构。本研究在激活的内皮细胞肌球蛋白所产生的持续拉力环境下，针对跨细胞侵袭阵列的形成机制提供了机理性见解。我们通过荧光漂白恢复实验（Fluorescence recovery after photobleaching, FRAP）、超分辨率显微镜与电子显微镜开展肌节距离测量，对肌球蛋白II侵袭阵列的特性进行了细致表征。为探究生物力学力与维持收缩丝曲率所需张力之间的关联，我们针对侵袭位点的单个肌动蛋白-肌球蛋白纤维实施光消融操作，结果显示相邻纤维会快速替代被消融的结构。我们提出，跨细胞环形侵袭阵列（transcellular circumferential invasion array, TCIA）可在内皮细胞内部提供必要的约束条件，以抵消入侵癌细胞产生的径向压缩力。