||Matsuzawa, Kenji; Ohga, Hayato; Shigetomi, Kenta; Shiiya, Tomohiro; Hirashima, Masanori; Ikenouchi, Junichi, MAGIs regulate aPKC to enable balanced distribution of intercellular tension for epithelial sheet homeostasis, COMMUNICATIONS BIOLOGY, 10.1038/s42003-021-01874-z, 4, 1, 2021.03, Constriction of the apical plasma membrane is a hallmark of epithelial cells that underlies cell shape changes in tissue morphogenesis and maintenance of tissue integrity in homeostasis. Contractile force is exerted by a cortical actomyosin network that is anchored to the plasma membrane by the apical junctional complexes (AJC). In this study, we present evidence that MAGI proteins, structural components of AJC whose function remained unclear, regulate apical constriction of epithelial cells through the Par polarity proteins. We reveal that MAGIs are required to uniformly distribute Partitioning defective-3 (Par-3) at AJC of cells throughout the epithelial monolayer. MAGIs recruit ankyrin-repeat-, SH3-domain- and proline-rich-region-containing protein 2 (ASPP2) to AJC, which modulates Par-3-aPKC to antagonize ROCK-driven contractility. By coupling the adhesion machinery to the polarity proteins to regulate cellular contractility, we propose that MAGIs play essential and central roles in maintaining steady state intercellular tension throughout the epithelial cell sheet..
||Aoki, Kana; Harada, Shota; Kawaji, Keita; Matsuzawa, Kenji; Uchida, Seiichi; Ikenouchi, Junichi, STIM-Orai1 signaling regulates fluidity of cytoplasm during membrane blebbing, NATURE COMMUNICATIONS, 10.1038/s41467-020-20826-5, 12, 1, 2021.01, The cytoplasm in mammalian cells is considered homogeneous. In this study, we report that the cytoplasmic fluidity is regulated in the blebbing cells; the cytoplasm of rapidly expanding membrane blebs is more disordered than the cytoplasm of retracting blebs. The increase of cytoplasmic fluidity in the expanding bleb is caused by a sharp rise in the calcium concentration. The STIM-Orai1 pathway regulates this rapid and restricted increase of calcium in the expanding blebs. Conversely, activated ERM protein binds to Orai1 to inhibit the store-operated calcium entry in retracting blebs, which results in decreased in cytoplasmic calcium, rapid reassembly of the actin cortex..
||Shiomi R, Shigetomi K, Inai T, Sakai M, Junichi Ikenouchi, CaMKII regulates the strength of the epithelial barrier, SCIENTIFIC REPORTS, 10.1038/srep13262, 5, 2015.08.
||池ノ内 順一, 平田 愛美, 米村 重信, 梅田 真郷, Sphingomyelin clustering is essential for the formation of microvilli., Journal of Cell Science, 10.1242/jcs.122325., 126, 16, 3585-3592, 2013.08, Cellular architectures require regulated mechanisms to correctly localize the appropriate plasma membrane lipids and proteins. Microvilli are dynamic filamentous-actin-based protrusions of the plasma membrane that are found in the apical membrane of epithelial cells. However, it remains poorly understood how their formation is regulated. In the present study, we found that sphingomyelin clustering underlies the formation of microvilli. Clustering of sphingomyelin is required for the co-clustering of the sialomucin membrane protein podocalyxin-1 at microvilli. Podocalyxin-1 recruits ezrin/radixin/moesin (ERM)-binding phosphoprotein-50 (EBP50; also known as NHERF1), which recruits ERM proteins and phosphatidylinositol 4-phosphate 5-kinase β (PIP5Kβ). Thus, clustering of PIP5Kβ leads to local accumulation of phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P2], which enhances the accumulation of ERM family proteins and induces the formation of microvilli. The present study revealed novel interactions between sphingomyelin and the cytoskeletal proteins from which microvilli are formed, and it clarified the physiological importance of the chemical properties of sphingomyelin that facilitate cluster formation. .