Division of Molecular Oncology, Institute for Genetic Medicine, Hokkaido University; Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Hokkaido 060-0815, Japan.
Faculty of Advanced Life Science, Hokkaido University, Sapporo, Hokkaido 001-0021, Japan.
Microscopy (Oxf). 2022 Aug 1;71(4):195-205. doi: 10.1093/jmicro/dfac017.
A small number of oncogenic mutated cells sporadically arise within the epithelial monolayer. Newly emerging Ras- or Src-transformed epithelial cells are often apically eliminated during competitive interactions between normal and transformed cells. Our recent electron microscopy (EM) analyses revealed that characteristic finger-like membrane protrusions are formed at the interface between normal and RasV12-transformed cells via the cdc42-formin-binding protein 17 (FBP17) pathway, potentially playing a positive role in intercellular recognition during apical extrusion. However, the spatial distribution and ultrastructural characteristics of finger-like protrusions remain unknown. In this study, we performed both X-Y and X-Z EM analyses of finger-like protrusions during the apical extrusion of RasV12-transformed cells. Quantification of the distribution and widths of the protrusions showed comparable results between the X-Y and X-Z sections. Finger-like protrusions were observed throughout the cell boundary between normal and RasV12 cells, except for apicalmost tight junctions. In addition, a non-cell-autonomous reduction in protrusion widths was observed between RasV12 cells and surrounding normal cells under the mix culture condition. In the finger-like protrusions, intercellular adhesions via thin electron-dense plaques were observed, implying that immature and transient forms of desmosomes, adherens junctions or unknown weak adhesions were distributed. Interestingly, unlike RasV12-transformed cells, Src-transformed cells form fewer evident protrusions, and FBP17 in Src cells is dispensable for apical extrusion. Collectively, these results suggest that the dynamic reorganization of intercellular adhesions via finger-like protrusions may positively control cell competition between normal and RasV12-transformed cells. Furthermore, our data indicate a cell context-dependent diversity in the modes of apical extrusion.
上皮细胞单层中偶尔会出现少量致癌突变细胞。在正常细胞和转化细胞之间的竞争相互作用中，新出现的 Ras 或 Src 转化上皮细胞通常会在顶端被消除。我们最近的电子显微镜 (EM) 分析表明，通过 cdc42-形成蛋白结合蛋白 17 (FBP17) 途径，在正常和 RasV12 转化细胞之间的界面处形成特征性的指状膜突起，这可能在顶端挤出过程中发挥正向作用细胞间识别。然而，指状突起的空间分布和超微结构特征尚不清楚。在这项研究中，我们对 RasV12 转化细胞的顶端挤出过程中的指状突起进行了 X-Y 和 X-Z EM 分析。突起分布和宽度的定量分析显示 X-Y 和 X-Z 切片之间的结果相似。指状突起在上皮细胞的 RasV12 转化细胞的顶端挤出过程中观察到整个正常和 RasV12 细胞之间的细胞边界，除了最顶端的紧密连接。此外，在混合培养条件下，观察到 RasV12 细胞与周围正常细胞之间的突起宽度呈非细胞自主性减小。在指状突起中，通过薄电子致密斑观察到细胞间黏附，表明分布有不成熟和短暂形式的桥粒、黏附连接或未知的弱黏附。有趣的是，与 RasV12 转化细胞不同，Src 转化细胞形成的突起不那么明显，并且 Src 细胞中的 FBP17 对于顶端挤出是可有可无的。总之，这些结果表明，通过指状突起的细胞间黏附的动态重排可能正向控制正常和 RasV12 转化细胞之间的细胞竞争。此外，我们的数据表明，顶端挤出的模式存在细胞上下文依赖性的多样性。
