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Junichi Ikenouchi Last modified date:2024.04.15

Professor / Cell biology
Department of Biology
Faculty of Sciences

Graduate School
Undergraduate School

 Reseacher Profiling Tool Kyushu University Pure
Ikenouchi Lab HP .
Academic Degree
Country of degree conferring institution (Overseas)
Field of Specialization
Cell Biology
Total Priod of education and research career in the foreign country
Research Interests
  • Elucidation of roles of lipids in the formation of epithelial polarity and cell adhesion
    Elucidation of the organizing principles of living cell membrane by combining synthetic biological approaches and cell biological approaches
    keyword : Epithelial cells, Tight junction, Microvilli, Cell polarity, Biological membrane, Cytoskeleton
Academic Activities
1. Shigetomi K, Ono Y, Matsuzawa K, Ikenouchi J., Cholesterol-rich domain formation mediated by ZO proteins is essential for tight junction formation, Proc Natl Acad Sci U S A, 10.1073/pnas.2217561120., 120, 8, e2217561120, 2023.02, [URL], Tight junctions (TJs) are cell-adhesion structures responsible for the epithelial barrier. We reported that accumulation of cholesterol at the apical junctions is required for TJ formation [K. Shigetomi, Y. Ono, T. Inai, J. Ikenouchi, J. Cell Biol. 217, 2373–2381 (2018)]. However, it is unclear how cholesterol accumulates and informs TJ formation—and whether cholesterol enrichment precedes or follows the assembly of claudins in the first place. Here, we established an epithelial cell line (claudin-null cells) that lacks TJs by knocking out claudins. Despite the lack of TJs, cholesterol normally accumulated in the vicinity of the apical junctions. Assembly of claudins at TJs is thought to require binding to zonula occludens (ZO) proteins; however, a claudin mutant that cannot bind to ZO proteins still formed TJ strands. ZO proteins were however necessary for cholesterol accumulation at the apical junctions through their effect on the junctional actomyosin cytoskeleton. We propose that ZO proteins not only function as scaffolds for claudins but also promote TJ formation of cholesterol-rich membrane domains at apical junctions..
2. 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..
3. 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..
4. 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.
5. 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. .
1. Junichi Ikenouchi, Roles of membrane lipids in tight junction formation, Tight Junctions: from Structure and Development to Therapeutics, 2023.06.
2. 池ノ内順一, Reciprocal Regulation of AJ and TJ During the Assembly of Apical Adhesion Complex, Gordon Research Conference "Cell Contact and Adhesion" 2019, 2019.06, There are many morphologically distinct membrane structures with different functions at the surface of epithelial cells. Among these, adherens junctions (AJ) and tight junctions (TJ) are responsible for the mechanical linkage of epithelial cells and epithelial barrier function, respectively. In the process of new cell–cell adhesion formation between two epithelial cells, such as after wounding, AJ form first and then TJ form on the apical side of AJ. This process is very complicated because AJ formation triggers drastic changes in the organization of actin cytoskeleton, the activity of Rho family of small GTPases, and the lipid composition of the plasma membrane, all of which are required for subsequent TJ formation. In this review, the authors focus on the relationship between AJ and TJ as a representative example of specialization of plasma membrane regions and introduce recent findings on how AJ formation promotes the subsequent formation of TJ..
3. 池ノ内 順一, 塩見 僚, 重富 健太, 上皮間葉転換における細胞膜脂質の質的変化の意義について, BMB2015(第38回日本分子生物学会年会、第88回日本生化学会大会 合同大会), 2015.12.
Membership in Academic Society
  • The Molecular Biology Society of Japan
  • Japan Society for Cell Biology