Tricellulin secures the epithelial barrier at tricellular junctions by interacting with actomyosin.

The epithelial cell sheet functions as a barrier to prevent invasion of pathogens. It is necessary to eliminate intercellular gaps not only at bicellular junctions, but also at tricellular contacts, where three cells meet, to maintain epithelial barrier function. To that end, tight junctions between adjacent cells must associate as closely as possible, particularly at tricellular contacts. Tricellulin is an integral component of tricellular tight junctions (tTJs), but the molecular mechanism of its contribution to the epithelial barrier function remains unclear. In this study, we revealed that tricellulin contributes to barrier formation by regulating actomyosin organization at tricellular junctions. Furthermore, we identified α-catenin, which is thought to function only at adherens junctions, as a novel binding partner of tricellulin. α-catenin bridges tricellulin attachment to the bicellular actin cables that are anchored end-on at tricellular junctions. Thus, tricellulin mobilizes actomyosin contractility to close the lateral gap between the TJ strands of the three proximate cells that converge on tricellular junctions.

MAGIs regulate aPKC to enable balanced distribution of intercellular tension for epithelial sheet homeostasis.

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.

STIM-Orai1 signaling regulates fluidity of cytoplasm during membrane blebbing.

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.

α-Catenin Controls the Anisotropy of Force Distribution at Cell-Cell Junctions during Collective Cell Migration.

Adherens junctions (AJs) control epithelial cell behavior, such as collective movement and morphological changes, during development and in disease. However, the molecular mechanism of AJ remodeling remains incompletely understood. Here, we report that the conformational activation of α-catenin is the key event in the dynamic regulation of AJ remodeling. α-catenin activates RhoA to increase actomyosin contractility at cell-cell junctions. This leads to the stabilization of activated α-catenin, in part through the recruitment of the actin-binding proteins, vinculin and afadin. In this way, α-catenin regulates force sensing, as well as force transmission, through a Rho-mediated feedback mechanism. We further show that this is important for stable directional alignment of multiple cells during collective cell movement by both experimental observation and mathematical modeling. Taken together, our findings demonstrate that α-catenin controls the establishment of anisotropic force distribution at cell junctions to enable cooperative movement of the epithelial cell sheet.

PAR3-aPKC regulates Tiam1 by modulating suppressive internal interactions.

Tiam1 is one of the most extensively analyzed activators of the small GTPase Rac. However, fundamental aspects of its regulation are poorly understood. Here we demonstrate that Tiam1 is functionally suppressed by internal interactions and that the PAR complex participates in its full activation. The N-terminal region of Tiam1 binds to the protein-binding and catalytic domains to inhibit its localization and activation. Atypical PKCs phosphorylate Tiam1 to relieve its intramolecular interactions, and the subsequent stabilization of its interaction with PAR3 allows it to exert localized activity. By analyzing Tiam1 regulation by PAR3-aPKC within the context of PDGF signaling, we also show that PAR3 directly binds PDGF receptor ß. Thus we provide the first evidence for the negative regulation of Tiam1 by internal interactions, elucidate the nature of Tiam1 regulation by the PAR complex, and reveal a novel role for the PAR complex in PDGF signaling.

TTBK2 with EB1/3 regulates microtubule dynamics in migrating cells through KIF2A phosphorylation.

Microtubules (MTs) play critical roles in various cellular events, including cell migration. End-binding proteins (EBs) accumulate at the ends of growing MTs and regulate MT end dynamics by recruiting other plus end-tracking proteins (+TIPs). However, how EBs contribute to MT dynamics through +TIPs remains elusive. We focused on tau-tubulin kinase 2 (TTBK2) as an EB1/3-binding kinase and confirmed that TTBK2 acted as a +TIP. We identified MT-depolymerizing kinesin KIF2A as a novel substrate of TTBK2. TTBK2 phosphorylated KIF2A at S135 in intact cells in an EB1/3-dependent fashion and inactivated its MT-depolymerizing activity in vitro. TTBK2 depletion reduced MT lifetime (facilitated shrinkage and suppressed rescue) and impaired HeLa cell migration, and these phenotypes were partially restored by KIF2A co-depletion. Expression of nonphosphorylatable KIF2A, but not wild-type KIF2A, reduced MT lifetime and slowed down the cell migration. These findings indicate that TTBK2 with EB1/3 phosphorylates KIF2A and antagonizes KIF2A-induced depolymerization at MT plus ends for cell migration.

PAR3 and aPKC regulate Golgi organization through CLASP2 phosphorylation to generate cell polarity.

The organization of the Golgi apparatus is essential for cell polarization and its maintenance. The polarity regulator PAR complex (PAR3, PAR6, and aPKC) plays critical roles in several processes of cell polarization. However, how the PAR complex participates in regulating the organization of the Golgi remains largely unknown. Here we demonstrate the functional cross-talk of the PAR complex with CLASP2, which is a microtubule plus-end-tracking protein and is involved in organizing the Golgi ribbon. CLASP2 directly interacted with PAR3 and was phosphorylated by aPKC. In epithelial cells, knockdown of either PAR3 or aPKC induced the aberrant accumulation of CLASP2 at the trans-Golgi network (TGN) concomitantly with disruption of the Golgi ribbon organization. The expression of a CLASP2 mutant that inhibited the PAR3-CLASP2 interaction disrupted the organization of the Golgi ribbon. CLASP2 is known to localize to the TGN through its interaction with the TGN protein GCC185. This interaction was inhibited by the aPKC-mediated phosphorylation of CLASP2. Furthermore, the nonphosphorylatable mutant enhanced the colocalization of CLASP2 with GCC185, thereby perturbing the Golgi organization. On the basis of these observations, we propose that PAR3 and aPKC control the organization of the Golgi through CLASP2 phosphorylation.

Plk1 phosphorylates CLIP-170 and regulates its binding to microtubules for chromosome alignment.

The microtubule (MT) cytoskeleton is essential for cellular morphogenesis, cell migration, and cell division. MT organization is primarily mediated by a variety of MT-associated proteins. Among these proteins, plus-end-tracking proteins (+TIPs) are evolutionarily conserved factors that selectively accumulate at growing MT plus ends. Cytoplasmic linker protein (CLIP)-170 is a +TIP that associates with diverse proteins to determine the behavior of MT ends and their linkage to intracellular structures, including mitotic chromosomes. However, how CLIP-170 activity is spatially and temporally controlled is largely unknown. Here, we show that phosphorylation at Ser312 in the third serine-rich region of CLIP-170 is increased during mitosis. Polo-like kinase 1 (Plk1) is responsible for this phosphorylation during the mitotic phase of dividing cells. In vitro analysis using a purified CLIP-170 N-terminal fragment showed that phosphorylation by Plk1 diminishes CLIP-170 binding to the MT ends and lattice without affecting binding to EB3. Furthermore, we demonstrate that during mitosis, stable kinetochore/MT attachment and subsequent chromosome alignment require CLIP-170 and a proper phosphorylation/dephosphorylation cycle at Ser312. We propose that CLIP-170 phosphorylation by Plk1 regulates proper chromosome alignment by modulating the interaction between CLIP-170 and MTs in mitotic cells and that CLIP-170 activity is stringently controlled by its phosphorylation state, which depends on the cellular context.

Relation between bile acid reflux into the stomach and the risk of atrophic gastritis and intestinal metaplasia: a multicenter study of 2283 cases.

BACKGROUND: The relationship between bile acid reflux into the stomach and the risk of atrophic gastritis and intestinal metaplasia is still not well understood. Towards obtaining a better understanding, concentrations of bile acids were measured. PATIENTS AND METHODS: This study was carried out with the participation of 14 facilities in Japan, and 2283 samples were collected. The subjects with bile acid concentrations equal to or higher than the limit of detection were divided into four groups of equal size (group A: 0-25%, group B: 26-50%, group C: 51-75%, and group D: 76-100%). Thus, including the control group, there were five groups in total. The odds that the control group would develop atrophic gastritis and intestinal metaplasia was set as 1,and the odds ratios (OR) in groups A, B, C and D were calculated based on the odds in the control group. RESULTS: Regarding the development of atrophic gastritis, no increased risk was observed in either the Helicobacter pylori (H. pylori)-positive or -negative cases. The OR for the development of intestinal metaplasia were significantly higher, for both cases with and without H. pylori infection, in group D. CONCLUSION: High concentrations of bile acid seem to be associated with an elevated risk of intestinal metaplasia.

Tiam1 interaction with the PAR complex promotes talin-mediated Rac1 activation during polarized cell migration.

Migrating cells acquire front-rear polarity with a leading edge and a trailing tail for directional movement. The Rac exchange factor Tiam1 participates in polarized cell migration with the PAR complex of PAR3, PAR6, and atypical protein kinase C. However, it remains largely unknown how Tiam1 is regulated and contributes to the establishment of polarity in migrating cells. We show here that Tiam1 interacts directly with talin, which binds and activates integrins to mediate their signaling. Tiam1 accumulated at adhesions in a manner dependent on talin and the PAR complex. The interactions of talin with Tiam1 and the PAR complex were required for adhesion-induced Rac1 activation, cell spreading, and migration toward integrin substrates. Furthermore, Tiam1 acted with talin to regulate adhesion turnover. Thus, we propose that Tiam1, with the PAR complex, binds to integrins through talin and, together with the PAR complex, thereby regulates Rac1 activity and adhesion turnover for polarized migration.

Pathophysiological investigation of the gastric surface mucous gel layer of patients with Helicobacter pylori infection by using immunoassays for trefoil factor family 2 and gastric gland mucous cell-type mucin in gastric juice.

BACKGROUND: The trefoil factor family (TFF) 2 protein is produced by gastric gland mucous cells (GMCs), and the secreted TFF2 shares a mucosal barrier function with GMC-type mucin. Recently, we presented an enzyme-linked immunosorbent assay (ELISA) method for measurement of GMC-type mucin in the gastric juice. AIMS: We aimed to develop an ELISA for TFF2 and to assess pathophysiological changes in the gastric surface mucous gel layer (SMGL) of patients with Helicobacter pylori infection. METHODS: The distribution of TFF2 and GMC-type mucin in the SMGL was immunohistochemically determined. The ELISA for TFF2 was based on a polyclonal goat antibody. Recombinant TFF2 was employed to prepare the calibrators. TFF2 and GMC-type mucin in the gastric juice in healthy individuals (n = 33) and patients with gastritis (n = 37), gastric ulcer (n = 16), and duodenal ulcer (n = 10) were assayed using ELISA. RESULTS: TFF2 and GMC-type mucin were immunohistochemically co-localized in the gastric SMGL and GMCs. The TFF2 levels in the patients were significantly higher than those in the healthy individuals. Further, the TFF2 levels in the H. pylori-positive patients were significantly higher than those in the H. pylori-negative patients, and decreased after the eradication of the infection. GMC-type mucin levels showed a tendency similar to that of TFF2 levels. CONCLUSIONS: The upregulation of TFF2 and GMC-type mucin secretion may reflect the response of the gastric mucosa to H. pylori-induced injuries. TFF2 and GMC-type mucin secreted into the SMGL may protect the gastric mucosa against H. pylori.

Helicobacter heilmannii infection: clinical, endoscopic and histopathological features in Japanese patients.

Gastric biopsy materials of 4074 consecutive Japanese patients undergoing esophagogastroduodenoscopy were reviewed, along with those of 15 patients with Helicobacter heilmannii infection (11, chronic gastritis; four, mucosa-associated lymphoid tissue (MALT) lymphoma). In four patients with H. heilmannii infection, the materials were examined by transmission electronmicroscopy. Urea breath test (three patients) and antibody test (five patients) were performed in patients with H. heilmannii infection. In two patients with MALT lymphoma, H. heilmannii was eradicated. The prevalence of H. heilmannii was 0.1% in the consecutive series. In chronic gastritis, the gastric mucosa was endoscopically normal (13.3%), had erythema (33.3%), or had erosions (53.3%); histologically, it showed no epithelial change, mild mononuclear cell infiltration, and slight and focal neutrophil infiltration; Helicobacter heilmannii was positive with anti-H. pylori antibody, and was detected in the mucous gel layer and in foveolae. In MALT lymphoma, the gastric mucosa was coarsely granular with enlarged mucosal folds without ulcers (two cases), with small ulcers (one case), or with multiple erosions (one case). Urea breath test and antibody test were both negative. Eradication of H. heilmannii resulted in remission of MALT lymphoma. Helicobacter heilmannii infection is therefore uncommon in Japanese adults, but is associated with chronic gastritis and gastric MALT lymphoma.

Mesenteric malignant lymphoma detected with routine color Doppler ultrasonography.

This report concerns a case of primary mesenteric malignant lymphoma detected with routine color Doppler ultrasonography. When a 44-year-old man underwent a first-time medical checkup, ultrasonographic imaging and computed tomography showed the presence of a large tumor measuring about 8 cm in transverse diameter. Color Doppler ultrasonography identified the characteristic vessel structure of a nodal lesion, namely, a hilar vessel, a curved section of the central vessel together with peripheral branches, and focal absence of perfusion in a hypoechoic imaging of the left periumbilical area. These findings contributed to the diagnosis of a malignant lymphoma and the surgical treatment of the tumor was successful.