Saito Akira C, Endo Chisato, Fukazawa Yugo, Higashi Tomohito, Chiba Hideki
Department of Basic Pathology, Fukushima Medical University, Fukushima, Japan.
Division of Brain Structure and Function, Faculty of Medical Science, Life Science Innovation Center, University of Fukui, Fukui, Japan.
Ann N Y Acad Sci. 2022 Nov;1517(1):234-250. doi: 10.1111/nyas.14889. Epub 2022 Sep 7.
Occludin, tricellulin, and marvelD3 belong to the tight junction (TJ)-associated MARVEL protein family. Occludin and tricellulin jointly contribute to TJ strand branching point formation and epithelial barrier maintenance. However, whether marvelD3 has the same function remains unclear. Furthermore, the roles of the carboxy-terminal cytoplasmic tail, which is conserved in occludin and tricellulin, on the regulation of TJ strand morphology have not yet been explored in epithelial cells. We established tricellulin/occludin/marveld3 triple-gene knockout (tKO) MDCK II cells and evaluated the roles of marvelD3 in the TJ strand structure and barrier function using MDCK II cells and a mathematical model. The complexity of TJ strand networks and paracellular barrier did not change in tKO cells compared to that in tricellulin/occludin double-gene knockout (dKO) cells. Exogenous marvelD3 expression in dKO cells did not increase the complexity of TJ strand networks and epithelial barrier tightness. The expression of the carboxy-terminal truncation mutant of tricellulin restored the barrier function in the dKO cells, whereas occludin lacking the carboxy-terminal cytoplasmic tail was not expressed on the plasma membrane. These data suggest that marvelD3 does not affect the morphology of TJ strands and barrier function in MDCK II cells and that the carboxy-terminal cytoplasmic tail of tricellulin is dispensable for barrier improvement.
闭合蛋白、三细胞紧密连接蛋白和marvelD3属于紧密连接（TJ）相关的MARVEL蛋白家族。闭合蛋白和三细胞紧密连接蛋白共同促进TJ链分支点的形成和上皮屏障的维持。然而，marvelD3是否具有相同功能仍不清楚。此外，在闭合蛋白和三细胞紧密连接蛋白中保守的羧基末端细胞质尾巴在上皮细胞中对TJ链形态调节的作用尚未得到探索。我们建立了三细胞紧密连接蛋白/闭合蛋白/marveld3三基因敲除（tKO）的MDCK II细胞，并使用MDCK II细胞和一个数学模型评估了marvelD3在TJ链结构和屏障功能中的作用。与三细胞紧密连接蛋白/闭合蛋白双基因敲除（dKO）细胞相比，tKO细胞中TJ链网络和细胞旁屏障的复杂性没有变化。在dKO细胞中外源表达marvelD3并没有增加TJ链网络的复杂性和上皮屏障的紧密性。三细胞紧密连接蛋白羧基末端截短突变体的表达恢复了dKO细胞中的屏障功能，而缺乏羧基末端细胞质尾巴的闭合蛋白未在质膜上表达。这些数据表明，marvelD3不影响MDCK II细胞中TJ链的形态和屏障功能，并且三细胞紧密连接蛋白的羧基末端细胞质尾巴对于改善屏障功能是可有可无的。
