Effect of X-ray tube on image quality and pancreatic ductal adenocarcinoma conspicuity in pancreatic protocol dual-energy CT.

AIM: To compare the radiation dose, image quality, and conspicuity of pancreatic ductal adenocarcinoma (PDAC) in pancreatic protocol dual-energy computed tomography (CT) between two X-ray tubes mounted in the same CT machine. MATERIAL AND METHODS: This retrospective study comprised 80 patients (median age, 73 years; 45 men) who underwent pancreatic protocol dual-energy CT from January 2019 to March 2022 using either old (Group A, n=41) or new (Group B, n=39) X-ray tubes mounted in the same CT machine. The imaging parameters were completely matched between the two groups, and CT data were reconstructed at 70 and 40 keV. The CT dose-index volume (CTDIvol); CT attenuation of the abdominal aorta, pancreas, and PDAC; background noise; and qualitative scores for the image noise, overall image quality, and PDAC conspicuity were compared between the two groups. RESULTS: The CTDIvol was lower in Group B than Group A (7.9 versus 9.2 mGy; p<0.001). The CT attenuation of all anatomical structures at 70 and 40 keV was comparable between the two groups (p=0.06-0.78). The background noise was lower in Group B than Group A (12 versus 14 HU at 70 keV, p=0.046; and 26 versus 30 HU at 40 keV, p<0.001). Qualitative scores for image noise and overall image quality at 70 and 40 keV and PDAC conspicuity at 40 keV were higher in Group B than Group A (p<0.001-0.045). CONCLUSION: The latest X-ray tube could reduce the radiation dose and improve image quality in pancreatic protocol dual-energy CT.

Not Only Hypoxia- but Radiation-Induced Epithelial-Mesenchymal Transition Is Modulated by Hypoxia-Inducible Factor 1 in A549 Lung Cancer Cells.

Hypoxia leads to post-treatment metastasis and recurrences of cancer via the epithelial-mesenchymal transition (EMT). Radiotherapy itself may also contribute to the acquisition of EMT phenotypes. Despite extensive studies on the EMT driven by either hypoxia or radiation stimuli, the molecular mechanisms characterizing these EMT events remain unclear. Thus, we aimed to evaluate the differences in the molecular pathways between hypoxia-induced EMT (Hypo-EMT) and radiation-induced EMT (R-EMT). Further, we investigated the therapeutic effects of HIF-1α inhibitor (LW6) on Hypo-EMT and R-EMT cells. A549 cells, lung adenocarcinoma cell line, acquired enhanced wound-healing activity under both hypoxia and irradiation. Localization of E-cadherin was altered from the cell membrane to the cytoplasm in both hypoxia and irradiated conditions. Of note, the expression levels of vimentin, one of the major EMT markers, was enhanced in irradiated cells, while it decreased under hypoxia condition. Importantly, LW6 significantly blocked EMT-related malignant phenotypes in both Hypo-EMT cells and R-EMT cells with concomitant re-location of E-cadherin onto the cell membrane. Moreover, LW6 deflected stress responsive signalling, JNK, activated sustainably under hypoxic condition, and the blockage of JNK impaired EMT phenotypes. Together, this work demonstrated the molecular events underlying Hypo-EMT and R-EMT, and highlighted HIF-1α as a therapeutic target not only in Hypo- EMT, but also in R-EMT.

Clinical results of accelerated hypofractionated radiotherapy for central-type small lung tumours.

PURPOSE: We evaluated the efficacy and toxicity of accelerated hypofractionated radiotherapy (ahypof-rt) for central-type small lung tumours. METHODS: Between November 2006 and January 2015, 40 patients with central-type small lung tumours underwent ahypof-rt delivered using 10 MV X-rays and a coplanar 3-field technique. The number of fractions ranged from 24 to 28, with a fraction size of 2.5-3 Gy. A total dose of 69-75 Gy to the isocentre of the planning target volume was administered to each patient. Cumulative survival and local control rates were calculated using the Kaplan-Meier method. RESULTS: The 27 men and 13 women enrolled in the study had a median age of 79 years (range: 60-87 years). The tumour stage was T1a in 9 patients, T1b in 17 patients, and T2a in 14 patients, with a median size of 26.5 cm (range: 11-49 cm). The median follow-up period was 23 months. A complete response was achieved in 3 patients (7.5%), and a partial response, in 17 patients (42.5%). The overall 2-year and 3-year local control rates were 87.3% and 81.8% respectively; the 2-year and 3-year overall survival rates were 78.9% and 66.7% respectively. Grade 3 pneumonitis occurred in 3 patients; no other severe adverse events (≥grade 3) were observed in any patient. CONCLUSIONS: Accelerated hypofractionated radiotherapy using a fraction size of 2.5-3 Gy was highly safe and can be a more effective treatment option than conventional radiotherapy for patients with central-type small lung tumours.

Intra-abdominal Pressure and Trunk Muscular Activities during Abdominal Bracing and Hollowing.

This study examined the difference in intra-abdominal pressure (IAP) between abdominal bracing and hollowing in relation to trunk muscular activities. IAP with a pressure transducer placed in the rectum and surface electromyograms for rectus abdominis, external oblique, internal oblique, and erector spinae during the 2 tasks were obtained in 7 young adult men. The difference between IAP at rest and its peak value (ΔIAPmax) showed high intra- and inter-day repeatability, and was significantly greater in abdominal bracing (116.4±15.0 mmHg) than in abdominal hollowing (9.9±4.5 mmHg). The trunk muscular activities at ΔIAPmax were significantly higher in abdominal bracing than in abdominal hollowing, and in the internal oblique than in the other 3 muscles. In both abdominal bracing and hollowing, the changes in IAP during the tasks were linearly correlated with those in trunk muscular activities, but the slope of the regression line for the relationship differed between the 2 tasks. The current results indicate that 1) abdominal bracing is an effective maneuver to elevate IAP compared with abdominal hollowing, and 2) in the 2 tasks, the changes in IAP are linked with those in trunk muscular activities, but the association is task-specific.

Preliminary results of proton-beam therapy for stage III non-small-cell lung cancer.

BACKGROUND: We conducted a preliminary retrospective evaluation of the efficacy and toxicity of proton-beam therapy (pbt) for stage iii non-small-cell lung cancer. METHODS: Between January 2009 and August 2013, 27 patients (26 men, 1 woman) with stage iii non-small-cell lung cancer underwent pbt. The relative biologic effectiveness value of the proton beam was defined as 1.1. The beam energy and spread-out Bragg peak were fine-tuned such that the 90% isodose volume of the prescribed dose encompassed the planning target volume. Of the 27 patients, 11 underwent neoadjuvant chemotherapy. Cumulative survival curves were calculated using the Kaplan-Meier method. Treatment toxicities were evaluated using version 4 of the Common Terminology Criteria for Adverse Events. RESULTS: Median age of the patients was 72 years (range: 57-91 years), and median follow-up was 15.4 months (range: 7.8-36.9 months). Clinical stage was iiia in 14 patients (52%) and iiib in 13 (48%). The median dose of pbt was 77 GyE (range: 66-86.4 GyE). The overall survival rate in the cohort was 92.3% at 1 year and 51.1% at 2 years. Locoregional failure occurred in 7 patients, and distant metastasis, in 10. In 2 patients, initial failure was both locoregional and distant. The 1-year and 2-year rates of local control were 68.1% and 36.4% respectively. The 1-year and 2-year rates of progression-free survival were 39.9% and 21.4% respectively. Two patients experienced grade 3 pneumonitis. CONCLUSIONS: For patients with stage iii non-small-cell lung cancer, pbt can be an effective and safe treatment option.

Brainstem manifestations in neuromyelitis optica: a multicenter study of 258 patients.

BACKGROUND: Neuromyelitis optica (NMO) is a severe autoimmune disease of the central nervous system characterized by spinal cord and optic nerve involvement. Brainstem manifestations have recently been described. OBJECTIVE: To evaluate the time of occurrence, the frequency and the characteristics of brainstem symptoms in a cohort of patients with NMO according to the ethnic background and the serologic status for anti-aquaporin-4 antibodies (AQP4-abs). METHODS: We performed a multicenter study of 258 patients with NMO according to the 2006 Wingerchuk criteria and we evaluated prospectively the frequency, the date of onset and the duration of various brainstem signs in this population. RESULTS: Brainstem signs were observed in 81 patients (31.4%). The most frequently observed signs were vomiting (33.1%), hiccups (22.3%), oculomotor dysfunction (19.8%), pruritus (12.4%), followed by hearing loss (2.5%), facial palsy (2.5%), vertigo or vestibular ataxia (1.7%), trigeminal neuralgia (2.5%) and other cranial nerve signs (3.3%). They were inaugural in 44 patients (54.3%). The prevalence was higher in the non-Caucasian population (36.6%) than in the Caucasian population (26%) (p<0.05) and was higher in AQP4-ab-seropositive patients (32.7%) than in seronegative patients (26%) (not significant). CONCLUSIONS: This study confirms the high frequency of brainstem symptoms in NMO with a majority of vomiting and hiccups. The prevalence of these manifestations was higher in the non Caucasian population.

Effect of short-term maximal voluntary co-contraction training on neuromuscular function.

The present study aimed to examine the effect of short-term training utilizing voluntary co-contraction with maximal efforts. 23 healthy young men (training group: TG, n = 13; control group: CG, n = 10) participated in this study. TG conducted a 4-week training program (3 days/week), which consisted of 4 s simultaneous maximal voluntary contractions of elbow flexors and extensors at 90° of the elbow joint, followed by 4 s muscle relaxation (10 repetitions/set, 5 sets/day). Before and after the intervention, maximal voluntary isometric and isokinetic torques and the muscle thicknesses of the elbow flexors and extensors were determined. The electromyograms (EMGs) of the 2 muscle groups during isometric maximal voluntary contraction (MVC) were also recorded. After the intervention, CG did not show any significant changes in all measured variables. In TG, significant increases were found in the agonist EMG activities during MVC, and maximal isometric and isokinetic torques of the elbow flexors and extensors, without significant changes in the muscle thicknesses and involuntary coactivation levels during MVC. The current results indicate that the training mode with maximal voluntary co-contraction is effective for improving the force-generating capabilities of the exercising muscles, without any increases in the level of involuntary coactivation during MVC.

Control of reorganization of the actin cytoskeleton by Rho family small GTP-binding proteins in yeast.

Accumulating evidence indicates that Rho family small GTP-binding proteins regulate reorganization of the actin cytoskeleton. There are members of the Rho family in the budding yeast Saccharomyces cerevisiae, in which powerful molecular genetical approaches are applicable. Recent identification of regulators and targets of the Rho family members has enhanced our understanding of the regulation and modes of action of Rho family members in reorganization of the actin cytoskeleton.

cAMP-GEFII is a direct target of cAMP in regulated exocytosis.

Although cAMP is well known to regulate exocytosis in many secretory cells, its direct target in the exocytotic machinery is not known. Here we show that cAMP-GEFII, a cAMP sensor, binds to Rim (Rab3-interacting molecule, Rab3 being a small G protein) and to a new isoform, Rim2, both of which are putative regulators of fusion of vesicles to the plasma membrane. We also show that cAMP-GEFII, through its interaction with Rim2, mediates cAMP-induced, Ca2+-dependent secretion that is not blocked by an inhibitor of cAMP-dependent protein kinase (PKA). Accordingly, cAMP-GEFII is a direct target of cAMP in regulated exocytosis and is responsible for cAMP-dependent, PKA-independent exocytosis.

Thoracic mass in a cynomolgus macaque (Macaca fascicularis).

A male cynomolgus macaque at the age of 3 years and 11 months suffered sudden cardiac arrest during a surgical operation. This animal had been clinically asymptomatic for 6 months from the acclimatization period to death. At necropsy, a white mass approximately 5 cm in diameter was found at the base of the heart. Histopathologically, the mass consisted of a granuloma with a number of multinucleated giant cells and multiple necrotic foci. Fungal hyphae characterized by parallel cell walls, distinct septa, and branching were observed in the lesion. The granuloma extended into the thoracic lymph nodes and the subepicardium of the left atrium, compressed the bronchioli, and was separated from the pulmonary parenchyma by a thick fibrous layer. The hyphal morphology and results of polymerase chain reaction assays demonstrated that the pathogen was Aspergillus sp.

Body mass-based exercise in middle-aged and older women.

The present study examined whether the degree to which muscle strength is improved by a body mass-based home exercise program in middle-aged and older women depends on the force-generating capabilities of the muscles prior to the intervention. 75 women (53-76 years) voluntarily participated in a circuit training program consisting of 5 exercises (16 repetitions/exercise, 2 or 3 circuits/day) using only body mass as resistance for 3 months. The subjects performed the training program 6 days a week in their own home and once a week in a local gym. Before and after intervention, isometric torques during maximal voluntary knee extension (KET) and plantar flexion (PFT) were determined and expressed relative to body mass (KET/BM and PFT/BM, respectively). KET/BM and PFT/BM increased significantly after intervention, and their relative changes were negatively correlated to the absolute values before intervention. Most of the subjects whose KET/BM and PFT/BM values before intervention were greater than 2.8 Nm/kg and 1.7 Nm/kg, respectively, did not show increases in strength after intervention. Thus, although body mass-based exercise at home is effective in improving lower limb strength in middle-aged and older women, the magnitude of the improvement is influenced by the force-generating capability before intervention.

Rho family GTPase Cdc42 is essential for the actin-based motility of Shigella in mammalian cells.

Shigella, the causative agent of bacillary dysentery, is capable of directing its movement within host cells by exploiting actin dynamics. The VirG protein expressed at one pole of the bacterium can recruit neural Wiskott-Aldrich syndrome protein (N-WASP), a downstream effector of Cdc42. Here, we show that Cdc42 is required for the actin-based motility of Shigella. Microinjection of a dominant active mutant Cdc42, but not Rac1 or RhoA, into Swiss 3T3 cells accelerated Shigella motility. In add-back experiments in Xenopus egg extracts, addition of a guanine nucleotide dissociation inhibitor for the Rho family, RhoGDI, greatly diminished the bacterial motility or actin assembly, which was restored by adding activated Cdc42. In N-WASP-depleted extracts, the bacterial movement almost arrested was restored by adding exogenous N-WASP but not H208D, an N-WASP mutant defective in binding to Cdc42. In pyrene actin assay, Cdc42 enhanced VirG-stimulating actin polymerization by N-WASP-actin-related protein (Arp)2/3 complex. Actually, Cdc42 stimulated actin cloud formation on the surface of bacteria expressing VirG in a solution containing N-WASP, Arp2/3 complex, and G-actin. Immunohistological study of Shigella-infected cells expressing green fluorescent protein-tagged Cdc42 revealed that Cdc42 accumulated by being colocalized with actin cloud at one pole of intracellular bacterium. Furthermore, overexpression of H208D mutant in cells interfered with the actin assembly of infected Shigella and diminished the intra- and intercellular spreading. These results suggest that Cdc42 activity is involved in initiating actin nucleation mediated by VirG-N-WASP-Arp2/3 complex formed on intracellular Shigella.

Role of Necl-5 in the pathophysiology of colorectal lesions induced by dimethylhydrazine and/or dextran sodium sulphate.

Necl-5 is an immunoglobulin-like molecule that was originally identified as a poliovirus receptor. Although Necl-5 expression is often up-regulated in cancer cells, its pathophysiological significance in the development of cancer remains unclear. We investigated the roles of Necl-5 in the development of colitis-associated neoplasia. Necl-5-deficient mice were generated and treated with dimethylhydrazine (DMH) and/or dextran sodium sulphate (DSS) to induce colitis and its associated neoplasias. Colon tissues were examined for histology, Ki-67 expression by immunohistochemistry and K-ras gene mutation. Colon tumours occurred significantly less frequently in heterozygous (Necl-5(+/-)) or homozygous Necl-5-deficient (Necl-5(-/-)) mice than in wild-type (WT) mice with DMH/DSS treatment. Total ulcer index and inflammatory cell infiltration were significantly lower in Necl-5(-/-) mice than in WT mice with DSS alone or DMH/DSS treatment. Colon tumours in both WT and Necl-5(-/-) mice showed high cell proliferation ability but lacked K-ras mutation. The total Ki-67 labelling index in non-neoplastic colon epithelium was significantly higher in WT (45.9 +/- 0.94) than in Necl-5(+/-) (34.3 +/- 1.40) or Necl-5(-/-) (27.7 +/- 1.15) mice with DMH/DSS treatment (p < 0.001). Necl-5 plays a role in the development of colitis-associated cancer by up-regulating colonic mucosal cell proliferation.

Cofilin phosphorylation and actin cytoskeletal dynamics regulated by rho- and Cdc42-activated LIM-kinase 2.

The rapid turnover of actin filaments and the tertiary meshwork formation are regulated by a variety of actin-binding proteins. Protein phosphorylation of cofilin, an actin-binding protein that depolymerizes actin filaments, suppresses its function. Thus, cofilin is a terminal effector of signaling cascades that evokes actin cytoskeletal rearrangement. When wild-type LIMK2 and kinase-dead LIMK2 (LIMK2/KD) were respectively expressed in cells, LIMK2, but not LIMK2/KD, phosphorylated cofilin and induced formation of stress fibers and focal complexes. LIMK2 activity toward cofilin phosphorylation was stimulated by coexpression of activated Rho and Cdc42, but not Rac. Importantly, expression of activated Rho and Cdc42, respectively, induced stress fibers and filopodia, whereas both Rho- induced stress fibers and Cdc42-induced filopodia were abrogated by the coexpression of LIMK2/KD. In contrast, the coexpression of LIMK2/KD with the activated Rac did not affect Rac-induced lamellipodia formation. These results indicate that LIMK2 plays a crucial role both in Rho- and Cdc42-induced actin cytoskeletal reorganization, at least in part by inhibiting the functions of cofilin. Together with recent findings that LIMK1 participates in Rac-induced lamellipodia formation, LIMK1 and LIMK2 function under control of distinct Rho subfamily GTPases and are essential regulators in the Rho subfamilies-induced actin cytoskeletal reorganization.

Regulation of cytoplasmic division of Xenopus embryo by rho p21 and its inhibitory GDP/GTP exchange protein (rho GDI).

Evidence is accumulating that the rho family, a member of the ras p21-related small GTP-binding protein superfamily, regulates cell morphology, cell motility, and smooth muscle contraction through the actomyosin system. The actomyosin system is also known to be essential for cytoplasmic division of cells (cytokinesis). In this study, we examined the action of rho p21, its inhibitory GDP/GTP exchange protein, named rho GDI, its stimulatory GDP/GTP exchange protein, named smg GDS, and botulinum ADP-ribosyltransferase C3, known to selectively ADP-ribosylate rho p21 and to impair its function, in the cytoplasmic division using Xenopus embryos. The sperm-induced cytoplasmic division of Xenopus embryos was not affected by microinjection into the embryos of either smg GDS or the guanosine-5'-(3-O-thio)triphosphate (GTP gamma S)-bound form of rhoA p21, one member of the rho family, but completely inhibited by microinjection of rho GDI or C3. Under these conditions, nuclear division occurred normally but the furrow formation, which was induced by the contractile ring consisting of actomyosin just beneath the plasma membrane, was impaired. Comicroinjection of rho GDI with the GTP gamma S-bound form of rhoA p21 prevented the rho GDI action. Moreover, the sperm-induced cytoplasmic division of Xenopus embryos was inhibited by microinjection into the embryos of the rhoA p21 pre-ADP-ribosylated by C3 which might serve as a dominant negative inhibitor of endogenous rho p21. These results indicate that rho p21 together with its regulatory proteins regulates the cytoplasmic division through the actomyosin system.

Regulation of cell-cell adhesion by rac and rho small G proteins in MDCK cells.

The Rho small G protein family, consisting of the Rho, Rac, and Cdc42 subfamilies, regulates various cell functions, such as cell shape change, cell motility, and cytokinesis, through reorganization of the actin cytoskeleton. We show here that the Rac and Rho subfamilies furthermore regulate cell-cell adhesion. We prepared MDCK cell lines stably expressing each of dominant active mutants of RhoA (sMDCK-RhoDA), Rac1 (sMDCK-RacDA), and Cdc42 (sMDCK-Cdc42DA) and dominant negative mutants of Rac1 (sMDCK-RacDN) and Cdc42 (sMDCK-Cdc42DN) and analyzed cell adhesion in these cell lines. The actin filaments at the cell-cell adhesion sites markedly increased in sMDCK-RacDA cells, whereas they apparently decreased in sMDCK-RacDN cells, compared with those in wild-type MDCK cells. Both E-cadherin and beta-catenin, adherens junctional proteins, at the cell-cell adhesion sites also increased in sMDCK-RacDA cells, whereas both of them decreased in sMDCK-RacDN cells. The detergent solubility assay indicated that the amount of detergent-insoluble E-cadherin increased in sMDCK-RacDA cells, whereas it slightly decreased in sMDCK-RacDN cells, compared with that in wild-type MDCK cells. In sMDCK-RhoDA, -Cdc42DA, and -Cdc42DN cells, neither of these proteins at the cell-cell adhesion sites was apparently affected. ZO-1, a tight junctional protein, was not apparently affected in any of the transformant cell lines. Electron microscopic analysis revealed that sMDCK-RacDA cells tightly made contact with each other throughout the lateral membranes, whereas wild-type MDCK and sMDCK-RacDN cells tightly and linearly made contact at the apical area of the lateral membranes. These results suggest that the Rac subfamily regulates the formation of the cadherin-based cell- cell adhesion. Microinjection of C3 into wild-type MDCK cells inhibited the formation of both the cadherin-based cell-cell adhesion and the tight junction, but microinjection of C3 into sMDCK-RacDA cells showed little effect on the localization of the actin filaments and E-cadherin at the cell-cell adhesion sites. These results suggest that the Rho subfamily is necessary for the formation of both the cadherin-based cell- cell adhesion and the tight junction, but not essential for the Rac subfamily-regulated, cadherin-based cell- cell adhesion.

Nexilin: a novel actin filament-binding protein localized at cell-matrix adherens junction.

We isolated two novel actin filament (F-actin)-binding proteins from rat brain and rat 3Y1 fibroblast. They were splicing variants, and we named brain big one b-nexilin and fibroblast small one s-nexilin. b-Nexilin purified from rat brain was a protein of 656 amino acids (aa) with a calculated molecular weight of 78,392, whereas s-nexilin, encoded by the cDNA isolated from rat 3Y1 cells by the reverse transcriptase-PCR method, was a protein of 606 aa with a calculated molecular weight of 71,942. b-Nexilin had two F-actin- binding domains (ABDs) at the NH2-terminal and middle regions, whereas s-nexilin had one ABD at the middle region because 64 aa residues were deleted and 14 aa residues were inserted in the first NH2-terminal ABD of b-nexilin, and thereby the first ABD lost its activity. b- and s-nexilins bound along the sides of F-actin, but only b-nexilin showed F-actin cross-linking activity. b-Nexilin was mainly expressed in brain and testis, whereas s-nexilin was mainly expressed in testis, spleen, and fibroblasts, such as rat 3Y1 and mouse Swiss 3T3 cells, but neither b- nor s-nexilin was detected in liver, kidney, or cultured epithelial cells. An immunofluorescence microscopic study revealed that s-nexilin was colocalized with vinculin, talin, and paxillin at cell- matrix adherens junction (AJ) and focal contacts, but not at cell-cell AJ, in 3Y1 cells. Overexpressed b- and s-nexilins were localized at focal contacts but not at cell-cell AJ. These results indicate that nexilin is a novel F-actin-binding protein localized at cell-matrix AJ.

Growth site localization of Rho1 small GTP-binding protein and its involvement in bud formation in Saccharomyces cerevisiae.

The Rho small GTP-binding protein family regulates various actomyosin-dependent cell functions, such as cell morphology, locomotion, cytokinesis, membrane ruffling, and smooth muscle contraction. In the yeast Saccharomyces cerevisiae, there is a homologue of mammalian RhoA, RHO1, which is essential for vegetative growth of yeast cells. To explore the function of the RHO1 gene, we isolated a recessive temperature-sensitive mutation of RHO1, rho1-104. The rho1-104 mutation caused amino acid substitutions of Asp 72 to Asn and Cys 164 to Tyr of Rho1p. Strains bearing the rho1-104 mutation accumulated tiny- or small-budded cells in which cortical actin patches were clustered to buds at the restrictive temperature. Cell lysis and cell death were also seen with the rho1-104 mutant. Indirect immunofluorescence microscopic study demonstrated that Rho1p was concentrated to the periphery of the cells where cortical actin patches were clustered, including the site of bud emergence, the tip of the growing buds, and the mother-bud neck region of cells prior to cytokinesis. Indirect immunofluorescence study with cells overexpressing RHO1 suggested that the Rho1p-binding site was saturable. A mutant Rho1p with an amino acid substitution at the lipid modification site remained in the cytoplasm. These results suggest that Rho1 small GTP-binding protein binds to a specific site at the growth region of cells, where Rho1p exerts its function in controlling cell growth.

Two cell adhesion molecules, nectin and cadherin, interact through their cytoplasmic domain-associated proteins.

We have found a new cell-cell adhesion system at cadherin-based cell-cell adherens junctions (AJs) consisting of at least nectin and l-afadin. Nectin is a Ca(2+)-independent homophilic immunoglobulin-like adhesion molecule, and l-afadin is an actin filament-binding protein that connects the cytoplasmic region of nectin to the actin cytoskeleton. Both the trans-interaction of nectin and the interaction of nectin with l-afadin are necessary for their colocalization with E-cadherin and catenins at AJs. Here, we examined the mechanism of interaction between these two cell-cell adhesion systems at AJs by the use of alpha-catenin-deficient F9 cell lines and cadherin-deficient L cell lines stably expressing their various components. We showed here that nectin and E-cadherin were colocalized through l-afadin and the COOH-terminal half of alpha-catenin at AJs. Nectin trans-interacted independently of E-cadherin, and the complex of E-cadherin and alpha- and beta-catenins was recruited to nectin-based cell-cell adhesion sites through l-afadin without the trans-interaction of E-cadherin. Our results indicate that nectin and cadherin interact through their cytoplasmic domain-associated proteins and suggest that these two cell-cell adhesion systems cooperatively organize cell-cell AJs.

Regulation mechanism of ERM (ezrin/radixin/moesin) protein/plasma membrane association: possible involvement of phosphatidylinositol turnover and Rho-dependent signaling pathway.

The ERM proteins, ezrin, radixin, and moesin, are involved in the actin filament/plasma membrane interaction as cross-linkers. CD44 has been identified as one of the major membrane binding partners for ERM proteins. To examine the CD44/ERM protein interaction in vitro, we produced mouse ezrin, radixin, moesin, and the glutathione-S-transferase (GST)/CD44 cytoplasmic domain fusion protein (GST-CD44cyt) by means of recombinant baculovirus infection, and constructed an in vitro assay for the binding between ERM proteins and the cytoplasmic domain of CD44. In this system, ERM proteins bound to GST-CD44cyt with high affinity (Kd of moesin was 9.3 +/- 1.6nM) at a low ionic strength, but with low affinity at a physiological ionic strength. However, in the presence of phosphoinositides (phosphatidylinositol [PI], phosphatidylinositol 4-monophosphate [4-PIP], and phosphatidylinositol 4.5-bisphosphate [4,5-PIP2]), ERM proteins bound with a relatively high affinity to GST-CD44cyt even at a physiological ionic strength: 4,5-PIP2 showed a marked effect (Kd of moesin in the presence of 4,5-PIP2 was 9.3 +/- 4.8 nM). Next, to examine the regulation mechanism of CD44/ERM interaction in vivo, we reexamined the immunoprecipitated CD44/ERM complex from BHK cells and found that it contains Rho-GDP dissociation inhibitor (GDI), a regulator of Rho GTPase. We then evaluated the involvement of Rho in the regulation of the CD44/ERM complex formation. When recombinant ERM proteins were added and incubated with lysates of cultured BHK cells followed by centrifugation, a portion of the recombinant ERM proteins was recovered in the insoluble fraction. This binding was enhanced by GTP gamma S and markedly suppressed by C3 toxin, a specific inhibitor of Rho, indicating that the GTP form of Rho in the lysate is required for this binding. A mAb specific for the cytoplasmic domain of CD44 also markedly suppressed this binding, identifying most of the binding partners for exogenous ERM proteins in the insoluble fraction as CD44. Consistent with this binding analysis, in living BHK cells treated with C3 toxin, most insoluble ERM proteins moved to soluble compartments in the cytoplasm, leaving CD44 free from ERM. These findings indicate that Rho regulates the CD44/ERM complex formation in vivo and that the phosphatidylinositol turnover may be involved in this regulation mechanism.