ERM (ezrin/radixin/moesin)-based molecular mechanism of microvillar breakdown at an early stage of apoptosis

Redistribution of the glycocalyx exposes phagocytic determinants on apoptotic cells

Phagocytes remove dead and dying cells by engaging "eat-me" ligands such as phosphatidylserine (PtdSer) on the surface of apoptotic targets. However, PtdSer is obscured by the bulky exofacial glycocalyx, which also exposes ligands that activate "don't-eat-me" receptors such as Siglecs. Clearly, unshielding the juxtamembrane "eat-me" ligands is required for the successful engulfment of apoptotic cells, but the mechanisms underlying this process have not been described. Using human and murine cells, we find that apoptosis-induced retraction and weakening of the cytoskeleton that anchors transmembrane proteins cause an inhomogeneous redistribution of the glycocalyx: actin-depleted blebs emerge, lacking the glycocalyx, while the rest of the apoptotic cell body retains sufficient actin to tether the glycocalyx in place. Thus, apoptotic blebs can be engaged by phagocytes and are targeted for engulfment. Therefore, in cells with an elaborate glycocalyx, such as mucinous cancer cells, this "don't-come-close-to-me" barrier must be removed to enable clearance by phagocytosis.

A Murine Model of X-Linked Moesin-Associated Immunodeficiency (X-MAID) Reveals Defects in T Cell Homeostasis and Migration

X-linked moesin associated immunodeficiency (X-MAID) is a primary immunodeficiency disease in which patients suffer from profound lymphopenia leading to recurrent infections. The disease is caused by a single point mutation leading to a R171W amino acid change in the protein moesin (moesinR171W). Moesin is a member of the ERM family of proteins, which reversibly link the cortical actin cytoskeleton to the plasma membrane. Here, we describe a novel mouse model with global expression of moesinR171W that recapitulates multiple facets of patient disease, including severe lymphopenia. Further analysis reveals that these mice have diminished numbers of thymocytes and bone marrow precursors. X-MAID mice also exhibit systemic inflammation that is ameliorated by elimination of mature lymphocytes through breeding to a Rag1-deficient background. The few T cells in the periphery of X-MAID mice are highly activated and have mostly lost moesinR171W expression. In contrast, single-positive (SP) thymocytes do not appear activated and retain high expression levels of moesinR171W. Analysis of ex vivo CD4 SP thymocytes reveals defects in chemotactic responses and reduced migration on integrin ligands. While chemokine signaling appears intact, CD4 SP thymocytes from X-MAID mice are unable to polarize and rearrange cytoskeletal elements. This mouse model will be a valuable tool for teasing apart the complexity of the immunodeficiency caused by moesinR171W, and will provide new insights into how the actin cortex regulates lymphocyte function.

Advances in the study of CDC42 in the female reproductive system

CDC42 is a member of the Rho‐GTPase family and is involved in a variety of cellular functions including regulation of cell cycle progression, constitution of the actin backbone and membrane transport. In particular, CDC42 plays a key role in the establishment of polarity in female vertebrate oocytes, and essential to this major regulatory role is its local occupation of specific regions of the cell to ensure that the contractile ring is assembled at the right time and place to ensure proper gametogenesis. The multifactor controlled ‘inactivation‐activation’ process of CDC42 also allows it to play an important role in the multilevel signalling network, and the synergistic regulation of multiple genes ensures maximum precision during gametogenesis. The purpose of this paper is to review the role of CDC42 in the control of gametogenesis and to explore its related mechanisms, with the aim of further understanding the great research potential of CDC42 in female vertebrate germ cells and its future clinical translation.

Development of conformational BRET biosensors that monitor ezrin, radixin and moesin activation in real time

Ezrin, radixin and moesin compose the family of ERM proteins. They link actin filaments and microtubules to the plasma membrane to control signaling and cell morphogenesis. Importantly, their activity promotes invasive properties of metastatic cells from different cancer origins. Therefore, a precise understanding of how these proteins are regulated is important for the understanding of the mechanism controlling cell shape, as well as providing new opportunities for the development of innovative cancer therapies. Here, we developed and characterized novel bioluminescence resonance energy transfer (BRET)-based conformational biosensors, compatible with high-throughput screening, that monitor individual ezrin, radixin or moesin activation in living cells. We showed that these biosensors faithfully monitor ERM activation and can be used to quantify the impact of small molecules, mutation of regulatory amino acids or depletion of upstream regulators on their activity. The use of these biosensors allowed us to characterize the activation process of ERMs that involves a pool of closed-inactive ERMs stably associated with the plasma membrane. Upon stimulation, we discovered that this pool serves as a cortical reserve that is rapidly activated before the recruitment of cytoplasmic ERMs.

C-terminal phosphorylation modulates ERM-1 localization and dynamics to control cortical actin organization and support lumen formation during Caenorhabditiselegans development

ERM proteins are conserved regulators of cortical membrane specialization that function as membrane-actin linkers and molecular hubs. The activity of ERM proteins requires a conformational switch from an inactive cytoplasmic form into an active membrane- and actin-bound form, which is thought to be mediated by sequential PIP2 binding and phosphorylation of a conserved C-terminal threonine residue. Here, we use the single Caenorhabditiselegans ERM ortholog, ERM-1, to study the contribution of these regulatory events to ERM activity and tissue formation in vivo Using CRISPR/Cas9-generated erm-1 mutant alleles, we demonstrate that a PIP2-binding site is crucially required for ERM-1 function. By contrast, dynamic regulation of C-terminal T544 phosphorylation is not essential but modulates ERM-1 apical localization and dynamics in a tissue-specific manner, to control cortical actin organization and support lumen formation in epithelial tubes. Our work highlights the dynamic nature of ERM protein regulation during tissue morphogenesis and the importance of C-terminal phosphorylation in fine-tuning ERM activity in a tissue-specific context.

Mechanical phenotyping of K562 cells by the Micropipette Aspiration Technique allows identifying mechanical changes induced by drugs

Mechanical properties of living cells can be used as reliable markers of their state, such as the presence of a pathological state or their differentiation phase. The mechanical behavior of cells depends on the organization of their cytoskeletal network and the main contribution typically comes from the actomyosin contractile system, in both suspended and adherent cells. In the present study, we investigated the effect of a pharmaceutical formulation (OTC – Ossitetraciclina liquida 20%) used as antibiotic, on the mechanical properties of K562 cells by using the Micropipette Aspiration Technique (MAT). This formulation has been shown to increase in a time dependent way the inflammation and toxicity in terms of apoptosis in in vitro experiments on K562 and other types of cells. Here we show that by measuring the mechanical properties of cells exposed to OTC for different incubation times, it is possible to infer modifications induced by the formulation to the actomyosin contractile system. We emphasize that this system is involved in the first stages of the apoptotic process where an increase of the cortical tension leads to the formation of blebs. We discuss the possible relation between the observed mechanical behavior of cells aspirated inside a micropipette and apoptosis.

Expression of ezrin and moesin in primary breast carcinoma and matched lymph node metastases

Ezrin, radixin, moesin (ERM) are important membrane-cytoskeletal crosslinkers and are suggested to play important role in cancer progression and metastasis. Even though ERM proteins were generally considered to be functionally redundant and the most studied was ezrin, recent studies highlight their distinct roles in metastatic process. Little information is available regarding the role of individual ERM proteins and their phosphorylated forms in human breast cancer. Our study is the first to examine expression of ezrin, moesin and their phosphorylated forms in primary breast tumors and matched lymph node metastases (LNMs) and their correlation with clinicopathological variables. A total of 88 primary breast cancer, 91 LNMs, 54 intraductal carcinoma and 26 normal adjacent breast tissue samples from tissue microarrays were studied. Expression was determined by immunohistochemistry, the intensity and number of positive cells was scored. Statistical analysis of protein expression and patients' age, tumor grade and hormonal status was performed. No statistical significant difference was found in ezrin, moesin, p-ezrinTyr353 and pan-p-ezrinThr567/radixinThr564/moesinThr558 expression between primary tumors and LNMs. Even though it was not significant, moesin expression varied between primary tumors, intraductal carcinoma, normal breast adjacent tissue and LNMs. A significant positive correlation between moesin and tumor grade has been proven. Even though primary tumors and matched LNMs did not show different expression patterns, moesin correlated significantly with higher tumor grade. Its positivity in intraductal carcinoma and normal breast tissue adjacent to cancer might indicate its role in tumor intiation/progression.

Ion transporters in brain tumors

Ion transporters are important in regulation of ionic homeostasis, cell volume, and cellular signal transduction under physiological conditions. They have recently emerged as important players in cancer progression. In this review, we discussed two important ion transporter proteins, sodium-potassium-chloride cotransporter isoform 1 (NKCC-1) and sodium-hydrogen exchanger isoform 1 (NHE-1) in Glioblastoma multiforme (GBM) and other malignant tumors. NKCC-1 is a Na(+)- dependent Cl(-) transporter that mediates the movement of Na(+), K(+), and Cl(-) ions across the plasma membrane and maintains cell volume and intracellular K(+) and Cl(-) homeostasis. NHE-1 is a ubiquitously expressed cell membrane protein which regulates intracellular pH (pH(i)) and extracellular pH (pH(e)) homeostasis and cell volume. Here, we summarized recent pre-clinical experimental studies on NKCC-1 and NHE-1 in GBM and other malignant tumors, such as breast cancer, hepatocellular carcinoma, and lung cancer cells. These studies illustrated that pharmacological inhibition or down-regulation of these ion transporter proteins reduces proliferation, increases apoptosis, and suppresses migration and invasion of cancer cells. These new findings reveal the potentials of these ion transporters as new targets for cancer diagnosis and/or treatment.

The chloride intracellular channel 5A stimulates podocyte Rac1, protecting against hypertension-induced glomerular injury

Glomerular capillary hypertension elicits podocyte remodeling and is a risk factor for the progression of glomerular disease. Ezrin, which links podocalyxin to actin in podocytes, is activated through the chloride intracellular channel 5A (CLIC5A)-dependent phosphatidylinositol 4,5 bisphosphate (PI[4,5]P2) accumulation. Because Rac1 is involved in podocyte actin remodeling and can promote PI[4,5]P2 production we determined whether CLIC5A-dependent PI[4,5]P2 generation and ezrin activation are mediated by Rac1. In COS7 cells, CLIC5A expression stimulated Rac1 but not Cdc42 or Rho activity. CLIC5A also stimulated phosphorylation of the Rac1 effector Pak1 in COS7 cells and in cultured mouse podocytes. CLIC5A-induced PI[4,5]P2 accumulation and Pak1 and ezrin phosphorylation were all Rac1 dependent. In DOCA/Salt hypertension, phosphorylated Pak increased in podocytes of wild-type, but not CLIC5-deficient mice. In DOCA/salt hypertensive mice lacking CLIC5, glomerular capillary microaneurysms were more frequent and albuminuria was greater than in wild-type mice. Thus, augmented hypertension-induced glomerular capillary injury in mice lacking CLIC5 results from abrogation of Rac1-dependent Pak and ezrin activation, perhaps reducing the tensile strength of the podocyte actin cytoskeleton.

Hypothermic Machine Perfusion Decreases Renal Cell Apoptosis During Ischemia/Reperfusion Injury via the Ezrin/AKT Pathway

This study aimed to explore the potential mechanisms of hypothermic machine perfusion (HMP)-a more efficient way to preserve kidneys from donors after cardiac death than static cold storage (CS), then to provide the basis for further improving donor quality. Twelve healthy male New Zealand rabbits (12 weeks old, weighing 3.0 ± 0.3 kg) were randomly divided into two groups: the HMP group and CS group (n = 6). Rabbits' left kidney was subjected to 35 min of warm ischemic time by clamping the left renal pedicle and 1 h of reperfusion. The kidneys were then hypothermically (4-8°C) preserved in vivo for 4 h with HCA-II solution using HMP or CS methods. Then rabbits underwent a right nephrectomy and the kidney tissues were collected after 24 h of reperfusion. TUNEL staining was performed on paraffin sections to detect apoptosis, and the expressions of cleaved caspase-3, ezrin, AKT, and p-AKT in frozen kidney tissues were detected by Western blotting. The ezrin expression was further confirmed by immunohistochemistry analysis. The apoptosis rate and expression of cleaved caspase-3 in the HMP group were significantly lower than the CS group (P < 0.001 and P = 0.002), meanwhile the expression of cleaved caspase-3 in the HMP and CS groups was significantly increased compared with the normal group (P = 0.035 and P < 0.001), and the expression of ezrin and p-AKT in the HMP group was significantly higher than the CS group (P = 0.005, 0.014). HMP decreased the renal cell apoptosis rate during ischemia/reperfusion injury via the ezrin/AKT pathway.

Role of ezrin in osteosarcoma metastasis

The cause of death for the vast majority of cancer patients is the development of metastases at sites distant from that of the primary tumor. For most pediatric sarcoma patients such as those with osteosarcoma (OS), despite successful management of the primary tumor through multimodality approaches, the development of metastases, commonly to the lungs, is the cause of death. Significant improvements in long-term outcome for these patients have not been seen in more than 30 years. Furthermore, the long-term outcome for patients who present with metastatic disease is grave [1-5]. New treatment options are needed.Opportunities to improve outcomes for patients who present with metastases and those at-risk for progression and metastasis require an improved understanding of cancer progression and metastasis. With this goal in mind we and others have identified ezrin as a metastasis-associated protein that associated with OS and other cancers. Ezrin is the prototypical ERM (Ezrin/Radixin/Moesin) protein family member. ERMs function as linker proteins connecting the actin cytoskeleton and the plasma membrane. Since our initial identification of ezrin in pediatric sarcoma, an increasing understanding the role of ezrin in metastasis has emerged. Briefly, ezrin appears to allow metastatic cells to overcome a number of stresses experienced during the metastatic cascade, most notably the stress experienced as cells interact with the microenvironment of the secondary site. Cells must rapidly adapt to this environment in order to survive. Evidence now suggests a connection between ezrin expression and a variety of mechanisms linked to this important cellular adaptation including the ability of metastatic cells to initiate the translation of new proteins and to allow the efficient generation of ATP through a variety of sources. This understanding of the role of ezrin in the biology of metastasis is now sufficient to consider ezrin as an important therapeutic target in osteosarcoma patients. This chapter reviews our understanding of ezrin and the related ERM proteins in normal tissues and physiology, summarizes the expression of ezrin in human cancers and associations with clinical parameters of disease progression, reviews reports that detail a biological understanding of ezrin's role in metastatic progression, and concludes with a rationale that may be considered to target ezrin and ezrin biology in osteosarcoma.

Ran GTPase promotes oocyte polarization by regulating ERM (Ezrin/Radixin/Moesin) inactivation

Asymmetric meiotic divisions in mammalian oocytes are driven by the eccentric positioning of the spindle, along with a dramatic reorganization of the overlying cortex, including a loss of microvilli and formation of a thick actin cap. Actin polarization relies on a Ran-GTP gradient centered on metaphase chromosomes; however, the downstream signaling cascade is not completely understood. In a recent study, we have shown that Ran promotes actin cap formation via the polarized activation of Cdc42. The related GTPase Rac is also activated in a polarized fashion in the oocyte cortex and co-localizes with active Cdc42. In other cells, microvilli collapse can be triggered by inactivation of the ERM (Ezrin/Radixin/Moesin) family of actin-membrane crosslinkers under the control of Rac. Accordingly, we show here that Ran-GTP promotes a substantial loss of phosphorylated ERMs in the cortex overlying the spindle in mouse oocytes. However, this polarized phospho-ERM exclusion zone was unaffected by Rac or Cdc42 inhibition. Therefore, we suggest that Ran activates two distinct pathways to regulate actin cap formation and microvilli disassembly in the polarized cortex of mouse oocytes. The possibility of a crosstalk between Rho GTPase and ERM signaling and a role for ERM inactivation in promoting cortical actin dynamics are also discussed.

Macrophage recognition of cells with elevated calcium is mediated by carbohydrate chains of CD43

Macrophages remove deteriorating cells (those undergoing apoptosis and oxidation) via poly-N-acetyllactosaminyl chains on CD43 caps, a major cell-surface glycoprotein. Unusually high intracellular calcium levels are also deteriorating for cells and tissue. Here we artificially elevated calcium levels in cells and examined the mechanism by which this elevation was resolved by macrophages. Results showed that treatment with the calcium ionophore A23187 and ionomycin induces capping of CD43 on Jurkat cells, which are subsequently recognized and phagocytosed by macrophages, indicating that macrophages regard cells with elevated calcium as targets for removal. Further tests showed that A23187- and ionomycin-treated Jurkat cells did not induce apoptotic changes such as DNA fragmentation or phosphatidylserine expression, indicating that these cells were removed despite still being viable. Jurkat cells pretreated with anti-CD43 antibody or those with poly-N-acetyllactosaminyl chains containing oligosaccharides inhibited macrophage binding, indicating that macrophages recognize the poly-N-acetyllactosaminyl chains on CD43. Binding was also inhibited by treating macrophages with anti-nucleolin antibody, indicating that recognition occurs through nucleolin, a cell-surface receptor. Further, nucleolin-transfected HEK293 cells bound A23187-treated cells, and this binding was inhibited by in the presence of oligosaccharides. Taken together, these results show that elevated calcium levels induce CD43 capping, and macrophages remove the cells if their nucleolin receptors can bind to the poly-N-acetyllactosaminyl chains of capped CD43.

Depletion of PtdIns(4,5)P₂ underlies retinal degeneration in Drosophila trp mutants

The prototypical transient receptor potential (TRP) channel is the major light-sensitive, and Ca(2+)-permeable channel in the microvillar photoreceptors of Drosophila. TRP channels are activated following hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] by the key effector enzyme phospholipase C (PLC). Mutants lacking TRP channels undergo light-dependent retinal degeneration, as a consequence of the reduced Ca(2+) influx. It has been proposed that degeneration is caused by defects in the Ca(2+)-dependent visual pigment cycle, which result in accumulation of toxic phosphorylated metarhodopsin-arrestin complexes (MPP-Arr2). Here we show that two interventions, which prevent accumulation of MPP-Arr2, namely rearing under red light or eliminating the C-terminal rhodopsin phosphorylation sites, failed to rescue degeneration in trp mutants. Instead, degeneration in trp mutants reared under red light was rescued by mutation of PLC. Degeneration correlated closely with the light-induced depletion of PtdIns(4,5)P₂ that occurs in trp mutants due to failure of Ca(2+)-dependent inhibition of PLC. Severe retinal degeneration was also induced in the dark in otherwise wild-type flies by overexpression of a bacterial PtdInsPn phosphatase (SigD) to deplete PtdIns(4,5)P₂. In degenerating trp photoreceptors, phosphorylated Moesin, a PtdIns(4,5)P₂-regulated membrane-cytoskeleton linker essential for normal microvillar morphology, was found to delocalize from the rhabdomere and there was extensive microvillar actin depolymerisation. The results suggest that compromised light-induced Ca(2+) influx, due to loss of TRP channels, leads to PtdIns(4,5)P₂ depletion, resulting in dephosphorylation of Moesin, actin depolymerisation and disintegration of photoreceptor structure.

Model membranes to shed light on the biochemical and physical properties of ezrin/radixin/moesin

Ezrin, radixin and moesin (ERM) proteins are now more and more recognized to play a key role in a large number of important physiological processes such as morphogenesis, cancer metastasis and virus infection. Several recent reviews extensively discuss their biological functions [1 -4 ]. In this review, we will first remind the main features of this family of proteins, which are now known as linkers and regulators of the plasma membrane/cytoskeleton linkage. We will then briefly review their implication in pathological processes such as cancer and viral infection. In a second part, we will focus on biochemical and biophysical approaches to study ERM interaction with lipid membranes and conformational change in well-defined environments. In vitro studies using biomimetic lipid membranes, especially large unilamellar vesicles (LUVs), giant unilamellar vesicles (GUVs) and supported lipid bilayers (SLBs) and recombinant proteins help to understand the molecular mechanism of conformational activation of ERM proteins. These tools are aimed to decorticate the different steps of the interaction, to simplify the experiments performed in vivo in much more complex biological environments.

Macrophage recognition of thiol-group oxidized cells: recognition of carbohydrate chains by macrophage surface nucleolin as apoptotic cells

The mechanism was investigated for macrophage recognition of cells oxidized by diamide, a thiol group-specific oxidizing reagent. Jurkat cells exposed to various concentrations of diamide were recognized by macrophages, the cells exposed to 25 µM diamide being best recognized. CD43, a major glycoprotein on the Jurkat cell surface, tended to form clusters upon diamide oxidization, and pretreating Jurkat cells with the anti-CD43 antibody inhibited macrophage binding. This indicates that macrophages appeared to recognize CD43. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and a Western blot analysis of CD43 of the diamide-oxidized cells showed no increase in the amount of cross-linked CD43 compared with control cells, indicating that cross-linking of CD43 by a disulphide bond was not involved in the clustering. Both CD43 clustering and binding of the oxidized cells to macrophages was prevented by the caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethyl ketone (Z-VAD-fmk), suggesting that the oxidized and macrophage-bound cells were undergoing apoptosis. A closer examination revealed that the caspase-3 activity, chromatin condensation, and DNA fragmentation in Jurkat cells were all increased by oxidation. The macrophage receptor involved in the binding appeared to be the cell-surface protein, nucleolin; an anti-nucleolin antibody treatment inhibited the binding. These results suggest that thiol group-oxidized cells underwent early apoptosis and were recognized by nucleolin on macrophages as early apoptotic cells.

FLT3-driven redox-modulation of Ezrin regulates leukaemic cell migration

The concept of reactive oxygen species (ROS) being produced via the activation of specific oncogenes provides a basis for generating genomic instability and pro-survival signalling in tumour cells. The purpose of this study was to identify downstream targets of NADPH oxidase (Nox)-derived ROS signalling in acute myeloid leukaemia cells, by performing a proteomic analysis utilizing two-dimensional phosphotyrosine immunoblotting. The majority of the targets identified were cytoskeletal-associated proteins including Ezrin, a known regulator of the cytoskeleton, which was examined further. The study demonstrated that inhibition of Nox enzymes, using diphenyleneiodonium chloride in the acute myeloid leukaemia cell line MOLM-13, resulted in a decrease in Ezrin tyrosine phosphorylation and also triggered a shift in Ezrin sub-cellular localization as detected by immunofluorescence. The change in Ezrin localization coincided with altered cell morphology, observed using scanning electron microscopy and a decreased ability to migrate through a polycarbonate transwell membrane. Similar effects were observed upon inhibition of the oncogenic receptor tyrosine kinase FLT3 using the staurosporine derivate PKC412, implicating a role for FLT3 as an upstream regulator of Ezrin. Our results indicate that FLT3 drives production of ROS by Nox, which stimulates changes in Ezrin tyrosine phosphorylation and localization via redox regulation of Src. Furthermore, inhibition of FLT3 signalling leads to alterations in MOLM-13 cell morphology and has a significant influence on cell motility.

Ezrin, a membrane cytoskeletal cross-linker, is essential for the regulation of phosphate and calcium homeostasis

Ezrin cross-links plasma membrane proteins with the actin cytoskeleton. In the kidney, ezrin mainly localizes at the brush border membrane of proximal tubules with the scaffolding protein, Na(+)/H(+) exchanger regulatory factor (NHERF) 1. NHERF1 interacts with the sodium/phosphate cotransporter, Npt2a. Defects in NHERF1 or Npt2a in mice cause hypophosphatemia. Here we studied the physiological role of ezrin in renal phosphate reabsorption using ezrin knockdown mice (Vil2). These mice exhibit hypophosphatemia, hypocalcemia, and osteomalacia. The reduced plasma phosphate concentrations were ascribed to defects in urinary phosphate reabsorption. Immunofluorescence and immunoblotting indicated a marked reduction in renal Npt2a and NHERF1 expression at the apical membrane of proximal tubules in the knockdown mice. On the other hand, urinary loss of calcium was not found in Vil2 mice. Plasma concentrations of 1,25-dihydroxyvitamin D were elevated following reduced plasma phosphate levels, and mRNA of the vitamin D-dependent TRPV6 calcium channel were significantly increased in the duodenum of knockdown mice. Expression of TRPV6 at the apical membrane, however, was significantly decreased. Furthermore, tibial bone mineral density was significantly lower in both the adult and young Vil2 mice. These results suggest that ezrin is required for the regulation of systemic phosphate and calcium homeostasis in vivo.

Ezrin functionality and hypothermic preservation injury in LLC-PK1 cells

Renal epithelial cells from donor kidneys are susceptible to hypothermic preservation injury, which is attenuated when they over express the cytoskeletal linker protein ezrin. This study was designed to characterize the mechanisms of this protection. Renal epithelial cell lines were created from LLC-PK1 cells, which expressed mutant forms of ezrin with site directed alterations in membrane binding functionality. The study used cells expressing wild type ezrin, T567A, and T567D ezrin point mutants. The A and D mutants have constitutively inactive and active membrane binding conformations, respectively. Cells were cold stored (4 °C) for 6-24 h and reperfused for 1h to simulate transplant preservation injury. Preservation injury was assessed by mitochondrial activity (WST-1) and LDH release. Cells expressing the active ezrin mutant (T567D) showed significantly less preservation injury compared to wild type or the inactive mutant (T567A), while ezrin-specific siRNA knockdown and the inactive mutant potentiated preservation injury. Ezrin was extracted and identified from purified mitochondria. Furthermore, isolated mitochondria specifically bound anti-ezrin antibodies, which were reversed with the addition of exogenous recombinant ezrin. Recombinant wild type ezrin significantly reduced the sensitivity of the mitochondrial permeability transition pore (mPTP) to calcium, suggesting ezrin may modify mitochondrial function. In conclusion, the cytoskeletal linker protein ezrin plays a significant role in hypothermic preservation injury in renal epithelia. The mechanisms appear dependent on the molecule's open configuration (traditional linker functionality) and possibly a novel mitochondrial specific role, which may include modulation of mPTP function or calcium sensitivity.

Clearance of CD43-capped cells by macrophages: capping alone leads to phagocytosis

Apoptotic cells must be recognized early for phagocytosis to ensure that their toxic contents do not damage neighboring cells. In some cases this is achieved via CD43-capped membrane glycoproteins, the sialylpolylactosaminyl chains of which serve as ligands for phagocytosis by macrophages. However, because many additional changes occur during apoptosis, determining exactly which events are responsible for signaling macrophages to initiate phagocytosis remains a challenge. Here, we examined one clearance mechanism in detail and determined that capping of CD43 alone is sufficient to initiate phagocytosis. We induced macrophage-mediated phagocytosis by using cytochalasin B to artificially cap CD43 on healthy (non-apoptotic) Jurkat cells. Additional experiments confirmed that sialylpolylactosaminyl chains formed through this capping method are a prerequisite for removal, and that nucleolin is the macrophage receptor responsible for their detection. These findings strongly suggest that capping of CD43 presents a sufficient signal for phagocytosis without any additional membrane changes.

Effects of serum-free storage on morphology, phenotype, and viability of ex vivo cultured human conjunctival epithelium

The use of amniotic membrane (AM) represents one of the major developments in ocular surface reconstruction. However, in a study on patients with primary pterygium, transplantation of AM with ex vivo expanded human conjunctival epithelial cells (HCjE) promoted earlier epithelialization than AM alone. We previously showed that cultured human limbal epithelial cells maintain their morphology, phenotype, and viability for one week when stored at 23°C. The current study investigates the feasibility of storing HCjE in HEPES-MEM and Optisol-GS at 23°C for 4 and 7 days, respectively. The five experimental groups were analyzed by light microscopy, immunohistochemistry, transmission electron microscopy, and a viability assay. The ultrastructural integrity of cultured HCjE was well preserved following 4 days of storage, however, 7 days of storage resulted in some loss of cell-cell contacts and epithelial detachment from the amniotic membrane. The number of microvilli in cultured HCjE not subjected to storage was 2.03±0.38 microvilli/μm. In comparison, after 4 and 7 days of HEPES-MEM storage this number was 1.69±0.54 microvilli/μm; P=0.98 and 0.89±1.0 microvilli/μm; P=0.28, respectively. After Optisol-GS storage for 4 and 7 days, the mean number of microvilli was 1.07±1.0 microvilli/μm; P=0.47 and 0.07±0.07 microvilli/μm; P=0.03, respectively. The number of cell layers in cultured HCjE not subjected to storage was 4.4±0.3 cell layers, as opposed to 4.0±0.9 cell layers; P=0.89 after 4 days of HEPES-MEM storage and 2.8±0.6 cell layers; P=0.01 after 7 days of storage in HEPES-MEM. The number of cell layers after 4 and 7 days of storage in Optisol-GS was 3.7±0.2 cell layers; P=0.46 and 3.4±0.4 cell layers; P=0.18, respectively. The expression of markers for undifferentiated cells (ΔNp63α, ABCG2 and p63), proliferating cells (Ki67 and PCNA), goblet cells (Ck7 and MUC5AC), stratified squamous epithelial cells (Ck4), and apoptotic cells (caspase-3) in cultured HCjE appeared to be unchanged after 4 and 7 days of HEPES-MEM and Optisol-GS storage. The percentage of viable cells in cultured HCjE not subjected to storage (91.4%±3.2%) was sustained after 4 and 7 days of storage in HEPES-MEM (94.1%±4.5%; P=0.99 and 85.1%±13.7%; P=0.87, respectively) as well as after 4 and 7 days of storage in Optisol-GS (87.7%±15.2%; P=0.97 and 79.8%±15.7%; P=0.48, respectively). We conclude that cultured HCjE may be stored for at least 4 days in serum-free conditions at 23°C while maintaining the phenotype and viability. HEPES-MEM appears to be comparable to Optisol-GS for serum-free storage with preservation of the ultrastructure for at least 4 days.

EphrinA1-EphA2 signal induces compaction and polarization of Madin-Darby canine kidney cells by inactivating Ezrin through negative regulation of RhoA

The epithelial cells exhibit either a columnar or a flat shape dependent on extracellular stimuli or the cell-cell adhesion. Membrane-anchored ephrinA stimulates EphA receptor tyrosine kinases as a ligand in a cell-cell contact-dependent manner. The mechanism through which ephrinA1/EphA2 signal regulates the cell morphology remains elusive. We demonstrate here that ephrinA1/EphA2 signal induces compaction and enhanced polarization (columnar change) of Madin-Darby canine kidney epithelial cells by regulating Ezrin, a linker that connects plasma membrane and actin cytoskeleton. Activation of EphA2 resulted in RhoA inactivation through p190RhoGAP-A and subsequent dephosphorylation of Ezrin on Thr-567 phosphorylated by Rho kinase. Consistently, the cells expressing an active mutant of Ezrin in which Thr-567 was replaced with Asp did not change their shape in response to ephrinA1. Furthermore, depletion of Ezrin led to compaction and enhanced polarization without ephrinA1 stimulation, suggesting the role for active Ezrin in keeping the flat cell shape. Ezrin localized to apical domain irrespective of ephrinA1 stimulation, whereas phosphorylated Ezrin on the apical domain was reduced by ephrinA1 stimulation. Collectively, ephrinA1/EphA2 signal negatively regulates Ezrin and promotes the alteration of cell shape, from flat to columnar shape.

Increased phosphorylation of ezrin/radixin/moesin proteins contributes to proliferation of rheumatoid fibroblast-like synoviocytes

OBJECTIVES

Increasing evidence indicates that ezrin/radixin/moesin (ERM) proteins may play a critical role in cell proliferation. This study examined the role of ERM proteins in proliferation of fibroblast-like synoviocytes (FLS) from patients with RA.

METHODS

Synovial tissues (STs) were obtained from 18 RA and 6 OA patients. The expression of ERM and its phosphorylated proteins in cultured FLS and ST was assessed by western blots or IF staining. Small interference RNA (siRNA)-mediated ERM knockdown was used to inhibit phosphorylation of ERM. Proliferation of FLS was measured by bromodeoxyuridine (BrdU) incorporation into cell DNA and by PCNA immunoblotting.

RESULTS

Our study showed that increased phosphorylation of ERM proteins was found in ST and FLS from patients with RA as compared with OA patients and non-arthritis controls. Treatment with TNF-α, IL-1β or PDGF-induced phosphorylation of ERM proteins in dose- and time-dependent manner by RA FLS, but did not affect the expression of total ERM protein. Rho kinase and p38MAPK signal pathways were involved in TNF-α-induced ERM phosphorylation. We further showed that inhibition of ERM phosphorylation by siRNA-mediated ERM knockdown suppressed TNF-α- or IL-1β-induced BrdU incorporation and PCNA expression in RA FLS.

CONCLUSIONS

This study provides the novel evidence that increased phosphorylation of ERM proteins may contribute to proliferation of RA FLS, suggesting that specific inhibition of ERM phosphorylation may be a new therapeutic approach for RA.

Attenuation of pulmonary hypertension secondary to left ventricular dysfunction in the rat by Rho-kinase inhibitor fasudil

Pulmonary hypertension (PH) in left ventricular dysfunction is attributable not only to backward failure of the left ventricle, but also to increased pulmonary vascular resistance (PVR) in some patients. Recently, Rho-kinase has been known as a potent growth stimulator and mediator of vasoconstriction, and Rho-kinase inhibitors could ameliorate PVR, little is known about the role of Rho-kinase in left ventricular dysfunction-induced PH. We utilized the ascending aortic-banded rat and assessed the effect of Rho-kinase inhibitor fasudil on the development of PH secondary to left ventricular dysfunction. Subsequently, in rats subjected to aortic banding for 6 weeks, there were increases in mean pulmonary arterial pressure, pulmonary arteriolar medial thickness, active RhoA, Rho-kinase II, Rho-kinase activity, endothelial nitric oxide synthase (eNOS) and endothelin-1(ET-1) concomitant with decreased levels in NO and cGMP in the lung. Treatment with fasudil at a dose of 30 mg/kg/day from days 1 to 28 or from days 29 to 42 decreased the mean pulmonary arterial pressure by 57% and 56%, right ventricular hypertrophy by 31% and 30%, pulmonary arteriolar medial thickness by 50% and 50%, and pulmonary expression of Rho-kinase II by 41% and 28%, respectively, as well as augmented pulmonary expression of eNOS by 16% and 31% and NO by 50% and 76%, respectively, when compared with the vehicle controls. In conclusion, these results suggest that inhibition of Rho-kinase may provide therapeutic potential for preventing and attenuating the development of PH in left ventricular dysfunction. Further translational study in human is needed to substantiate the findings.

Quantitative proteome profiling of respiratory virus-infected lung epithelial cells

Respiratory virus infections are among the primary causes of morbidity and mortality in humans. Influenza virus, respiratory syncytial virus (RSV), parainfluenza (PIV) and human metapneumovirus (hMPV) are major causes of respiratory illness in humans. Especially young children and the elderly are susceptible to infections with these viruses. In this study we aim to gain detailed insight into the molecular pathogenesis of respiratory virus infections by studying the protein expression profiles of infected lung epithelial cells. A549 cells were exposed to a set of respiratory viruses [RSV, hMPV, PIV and Measles virus (MV)] using both live and UV-inactivated virus preparations. Cells were harvested at different time points after infection and processed for proteomics analysis by 2-dimensional difference gel electrophoresis. Samples derived from infected cells were compared to mock-infected cells to identify proteins that are differentially expressed due to infection. We show that RSV, hMPV, PIV3, and MV induced similar core host responses and that mainly proteins involved in defense against ER stress and apoptosis were affected which points towards an induction of apoptosis upon infection. By 2-D DIGE analyses we have gathered information on the induction of apoptosis by respiratory viruses in A549 cells.

Ezrin is a negative regulator of death receptor-induced apoptosis

Ezrin links cortical actin filaments with the cell membrane, and has a critical role in many membrane-initiated events. Fas is directly associated with ezrin, but conflicting results have been reported for the involvement of ezrin in Fas-induced cell death. In this study we show that ezrin was associated with Fas in T cells before stimulation and was released shortly after Fas ligand (FasL) engagement. The knockdown of ezrin moderately increased Fas-triggered or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-triggered cell death in normal T lymphocytes and in H9 cells, but had no effect on death receptor-induced apoptosis in type II cells, such as Jurkat and CEM. Expression of a dominant-negative form of ezrin also led to an increased Fas-induced apoptosis in H9 cells. Ezrin deficiency did not affect the internalization of Fas after Fas ligation. Instead, an enhanced formation of death-inducing signaling complex (DISC) was observed in H9 cells with ezrin knockdown, leading to accelerated caspase-8 activation. Together, our results suggest that ezrin has a negative role in the recruitment of Fas into signaling complexes in type I T cells. Loss of ezrin likely removes the constraint imposed by ezrin and facilitates the assembly of death receptor complex in T cells.

Upregulation of soluble resistance-related calcium-binding protein (sorcin) in gastric cancer

The aim of this paper was to identify novel proteins involved in the development of gastric cancer (GC). Isobaric tags for relative and absolute quantification (iTRAQ) analysis was adopted to separate the differentially expressed proteins between normal gastric epithelial cell line GES-1 and GC cell line SGC7901. Western blotting was utilized to validate the increased expression of sorcin in SGC7901; immunohistochemistry was performed to investigate its relationship with clinicopathological features of GC. Twelve differential proteins were identified. Seven proteins were found to be significantly upregulated (≥two-fold), while five proteins were markedly downregulated (≤0.5-fold), in SGC7901 cells. Sorcin was detected by this proteomic approach with a 5.4-fold upregulation in SGC7901. Western blotting and immunohistochemistry confirmed the overexpression of sorcin in GC. Immunohistochemistry showed us that sorcin was overexpressed in 55 samples of GC tissue (55/85, 64.71%) and was related closely to the depth of invasion, TNM stage, and lymph node metastasis of GC (P<0.05). The development of GC is regulated by multiple genes. Sorcin will be a novel molecular biomarker for the diagnosis, treatment, and prognosis of GC.

Protective effects of ezrin on cold storage preservation injury in the pig kidney proximal tubular epithelial cell line (LLC-PK1)

BACKGROUND

Renal damage caused by cold preservation and warm reperfusion has been well documented and involves tissue edema, cell swelling, ATP depletion, calcium toxicity, and oxidative stress. However, more common proximal mechanisms have not been identified, which may limit the development of effective clinical treatment strategies. Previous work indicates that many cytoskeletal structures are affected by cold preservation and reperfusion, including membrane-rich ezrin-associated complexes. The aim of this study was to investigate whether the sublamellar cytoskeletal protein ezrin is causally involved in cold preservation injury in renal tubule epithelial cells.

METHODS

We created a stably transfected cell line (LLC-EZ) using the pig kidney proximal tubular epithelial cell line (LLC-PK1), which constitutively overexpresses wild-type ezrin. These cells were cold stored in University of Wisconsin Solution and reperfused in vitro to model renal tubule preservation injury, which was assessed by biochemical, metabolic, functional, and structural endpoints.

RESULTS

Overexpression of ezrin increased cell viability (lactate dehydrogenase release), mitochondrial activity (ATP synthesis, dehydrogenase activity, and inner mitochondrial membrane potential), and protected the structure of cell membrane microvilli and mitochondria after cold storage preservation injury. Reperfusion-induced apoptosis was also significantly reduced in LLC-EZ cells overexpressing ezrin.

CONCLUSIONS

Enhanced ezrin expression protects tubule epithelial cells from cold storage preservation injury, possibly by membrane or mitochondrial mechanisms.

Posttranslational regulation of Abcc2 expression by SUMOylation system

The ATP-binding cassette transporter family C 2 (Abcc2) is a member of efflux transporters involved in the biliary excretion of organic anions from hepatocytes. Posttranslational regulation of Abcc2 has been implicated, although the molecular mechanism is not fully understood. In the present study, we performed yeast two-hybrid screening to identify novel protein(s) that particularly interacts with the linker region of Abcc2 located between the NH(2)-terminal nucleotide binding domain and the last membrane-spanning domain. The screening resulted in the identification of a series of small ubiquitin-like modifier (SUMO)-related enzymes and their substrates. In yeast experiments, all of these interactions were abolished by substituting the putative SUMO consensus site in the linker region (IKKE) in Abcc2 to IRKE. In vitro SUMOylation experiments confirmed that the Abcc2 linker was a substrate of Ubc9-mediated SUMOylation. It was also found that the IKKE sequence is the target of SUMOylation, since a mutant with IKKE is substituted by IRKE was not SUMOylated. Furthermore, we demonstrated for the first time that Abcc2, endogenously expressed in rat hepatoma-derived McARH7777 cells, is SUMOylated. Suppression of endogenous Ubc9 by small interfering RNA resulted in a selective 30% reduction in Abcc2 protein expression in the postnuclear supernatant, whereas subcellular localization of Abcc2 confirmed by semiquantitative immunofluorescence analysis was minimally affected. This is the first demonstration showing the regulation of ABC transporter expression by SUMOylation.

Comparative proteomics analysis of caspase-9-protein complexes in untreated and cytochrome c/dATP stimulated lysates of NSCLC cells

Apoptosis is a process of cellular suicide executed by caspases. Impaired activation of caspase-9 may contribute to chemoresistance in cancer. Activation of caspase-9 occurs after binding to Apaf-1 and formation of the apoptosome in the presence of cytochrome c/(d)ATP. We used a proteomics approach to identify proteins in caspase-9-protein complexes in extracts derived from NSCLC cells with(out) cytochrome c/dATP. Using co-immunoprecipitation, one-dimensional gel electrophoresis and tandem mass spectrometry, 38 proteins were identified of which 24 differential interactors. The differential interactors can be functionally assigned to cytoskeletal (re)organization and cell motility, catalytic activity, and transcriptional processes and apoptosis. The interaction of caspase-9 with Apaf-1 was confirmed and acetylserotonin-O-methyltransferase-like protein was identified as a candidate substrate of caspase-9. Novel interactors were found including galectin-3, swiprosin-1 and the membrane-cytoskeleton linkers Ezrin/Radixin/Moesin. Co-immunoprecipitation and Western blot experiments confirmed the interaction of caspase-9 with several identified binding partners. A large number of cytoskeletal proteins associated with unprocessed caspase-9 may indicate a scaffold function of this structure and/or may act as caspase substrates during apoptosis. Together, our results indicate that proteomic analysis of the caspase-9-associated protein complexes is a powerful exploratory approach to identify novel caspase substrates and/or regulators of caspase-9-dependent apoptosis.

Regulation of expression of microvillus membrane proteins by estrogen in baboon fetal ovarian oocytes

We previously demonstrated that the number and height of oocyte microvilli were reduced in baboon fetuses deprived of estrogen in utero and restored to normal in animals supplemented with estradiol. Phosphorylated ezrin and Na+/H+ exchange regulatory factor 1 (NHERF, now termed SLC9A3R1) link f-actin bundles to the membrane, whereas alpha-actinin cross-links f-actin to form microvilli. Therefore, we determined whether these proteins were expressed in oocytes of the fetal baboon ovary and whether expression and/or localization were altered between mid and late gestation in association with an increase in estrogen and in late gestation in animals in which estrogen was suppressed (>95%) or restored by treatment with an aromatase inhibitor with or without estradiol. Expression of alpha-actinin was low at mid gestation, increased on the surface of oocytes of primordial follicles in late gestation, and was negligible in the ovaries of estrogen-suppressed fetuses and normal in animals treated with estrogen. Ezrin (total and phosphorylated) and SLC9A3R1 expression was localized to the surface of oocytes at mid and late gestation in estrogen-replete baboons and to the cytoplasm in late gestation after estrogen suppression. These results are the first to show that the fetal baboon oocyte expressed ezrin, SLC9A3R1, and alpha-actinin, and that these proteins were localized to the oocyte surface consistent with their role in microvilli development in epithelial cells. The current study also showed that the developmental increase in oocyte expression of alpha-actinin is regulated by estrogen and correlated with the estrogen-dependent increase in oocyte microvilli demonstrated previously. Therefore, we propose that development of oocyte microvilli requires expression of alpha-actinin and that expression of alpha-actinin and localization of ezrin-phosphate and SLC9A3R1 to the oocyte membrane are regulated by estrogen.

Disturbed colocalization of multidrug resistance protein 2 and radixin in human cholestatic liver diseases

BACKGROUND AND AIM

Endocytic retrieval of multidrug resistance protein 2 (MRP2) is closely associated with cholestasis and may be attributed to the disturbed linking of MRP2 and radixin, a cross-linker between actin filaments and membrane proteins. This study aimed to investigate the role of radixin in the altered localization of MRP2 in various human cholestatic liver diseases.

METHODS

Using immunofluorescence microscopy, we investigated the localization and expression of MRP2 and radixin in various cholestatic liver diseases, such as drug-induced liver injury, obstructive jaundice, primary sclerosing cholangitis and autoimmune hepatitis. Changes in localization and expression were analyzed using Scion Image (software).

RESULTS

In the icteric drug-induced liver injury, MRP2 was localized outside as well as inside of ZO-1 staining, indicating endocytic retrieval from the canalicular membrane into the pericanalicular compartments of the hepatocytes. The colocalization of MRP2 and radixin observed in the controls was disturbed, and MRP2 fluorescence disappeared in the canaliculi with disrupted radixin staining. Disturbed colocalization of MRP2 and radixin as well as endocytic retrieval of MRP2 was found in the poorly drained obstructive jaundice. When drainage was good, MRP2 was exclusively colocalized with radixin. Similar findings were observed in autoimmune hepatitis and primary sclerosing cholangitis. In the controls, the immunostaining intensity curves for MRP2 and radixin were steeply elevated in the canaliculi. The intensity curves for MRP2 and radixin were broadened in the icteric drug-induced liver injury and poorly drained obstructive jaundice, indicating endocytic retrieval into the hepatocytes. The peak fluorescence intensities for MRP2 and radixin decreased in the icteric liver.

CONCLUSION

Disturbed colocalization of MRP2 and radixin was common in various cholestatic liver diseases, which may be associated with endocytic retrieval of MRP2 due to failure in anchoring MRP2 in the canalicular membrane.

LC/MS identification of 12 intracellular cytoskeletal and inflammatory proteins from monocytes adherent on surface-adsorbed fibronectin-derived peptides

The extent and duration of the host response determines device efficacy, yet the mechanism is poorly understood. U937 promonocytic cells were cultured on peptide-adsorbed tissue-culture polystyrene to better understand surface-modulated intracellular events. Phosphotyrosine proteins were enriched by immunoprecipitation and analyzed by nanospray HPLC-coupled tandem mass spectrometry (LC/MS). Tyrosine-phosphorylated proteins were chosen based on physiological significance and previous densitometry results, which identified a set of proteins ranging from approximately 200 to approximately 23 kDa showing altered phosphorylation levels in response to various surface-adsorbed ligands and phosphorylation inhibitor AG18. Although LC/MS has been used for nearly a decade, its application to the field of biomaterials is relatively novel. Twelve intracellular proteins identified by nanospray LC/MS are potentially related to the host response. Eight of the twelve proteins are related to the cytoskeleton including: moesin, heat shock protein 90beta, alpha-tubulin, elongation factor 1alpha, beta actin, vimentin, plasminogen activator inhibitor 2, and heterogeneous ribonuclear protein A2. The remaining four proteins: high mobility group box 1, caspase recruitment domain 5, glycoprotein 96, and heterogeneous nuclear ribonucleoprotein D0 modulate inflammation. The specific effect each peptide has upon modulating the phosphorylation state of these proteins cannot be determined from this work; however, 12 viable targets have been identified for further investigation into the role each plays in the surface-mediated monocyte response.

Moesin helps to restrain synaptic growth at the Drosophila neuromuscular junction

The precise role of actin and actin-binding proteins in synaptic development is unclear. In Drosophila, overexpression of a dominant-negative NSF2 construct perturbs filamentous actin, which is associated with overgrowth of the NMJ, while co-expression of moesin, which encodes an actin binding protein, suppresses this overgrowth phenotype. These data suggest that Moesin may play a role in synaptic development at the Drosophila NMJ. To further investigate this possibility, we examined the influence of loss-of-function moesin alleles on the NSF2-induced overgrowth phenotype. We found that flies carrying P-element insertions that reduce moesin expression enhanced the NMJ overgrowth phenotype, indicating a role for Moesin in normal NMJ morphology. In addition to the NMJ overgrowth phenotype, expression of dominant-negative NSF2 is known to reduce the frequency of miniature excitatory junctional potentials and the amplitude of excitatory junctional potentials. We found that moesin coexpression did not restore the physiology of the mutant NSF2 phenotype. Together, our results demonstrate a role for moesin in regulating synaptic growth in the Drosophila NMJ and suggest that the effect of dominant-negative NSF2 on NMJ morphology and physiology may have different underlying molecular origins.

Remodeling of cellular cytoskeleton by the acid sphingomyelinase/ceramide pathway

The chemotherapeutic agent cisplatin is widely used in treatment of solid tumors. In breast cancer cells, cisplatin produces early and marked changes in cell morphology and the actin cytoskeleton. These changes manifest as loss of lamellipodia/filopodia and appearance of membrane ruffles. Furthermore, cisplatin induces dephosphorylation of the actin-binding protein ezrin, and its relocation from membrane protrusions to the cytosol. Because cisplatin activates acid sphingomyelinase (ASMase), we investigate here the role of the ASMase/ceramide (Cer) pathway in mediating these morphological changes. We find that cisplatin induces a transient elevation in ASMase activity and its redistribution to the plasma membrane. This translocation is blocked upon overexpression of a dominant-negative (DN) ASMase^S508A mutant and by a DN PKCδ. Importantly; knockdown of ASMase protects MCF-7 cells from cisplatin-induced cytoskeletal changes including ezrin dephosphorylation. Reciprocally, exogenous delivery of D-e-C₁₆-Cer, but not dihydro-C₁₆-Cer, recapitulates the morphotropic effects of cisplatin. Collectively, these results highlight a novel tumor suppressor property for Cer and a function for ASMase in cisplatin-induced cytoskeletal remodeling.

Defective endothelial nitric oxide synthase signaling is mediated by rho-kinase activation in rats with secondary biliary cirrhosis

In liver cirrhosis, down-regulation of endothelial nitric oxide synthase (eNOS) has been implicated as a cause of increased intrahepatic resistance. We investigated whether Rho-kinase activation is one of the molecular mechanisms involved in defective eNOS signaling in secondary biliary cirrhosis. Liver cirrhosis was induced by bile duct ligation (BDL). We measured mean arterial pressure (MAP), portal venous pressure (PVP), and hepatic tissue blood flow (HTBF) during intravenous infusion of saline (control), 0.3, 1, or 2 mg/kg/hour fasudil for 60 minutes. In BDL rats, 1 and 2 mg/kg/hour fasudil significantly reduced PVP by 20% compared with controls but had no effect on HTBF. MAP was significantly reduced in response to 2 mg/kg/hour fasudil. In the livers of BDL rats, 1 and 2 mg/kg/hour fasudil significantly suppressed Rho-kinase activity and significantly increased eNOS phosphorylation, compared with controls. Fasudil significantly reduced the binding of serine/threonine Akt/PKB (Akt) to Rho-kinase and increased the binding of Akt to eNOS. These results show in secondary biliary cirrhosis that (1) Rho-kinase activation with resultant eNOS down-regulation is substantially involved in the pathogenesis of portal hypertension and (2) Rho-kinase might interact with Akt and subsequently inhibit the binding of Akt to eNOS.

Megaintestine in claudin-15-deficient mice

BACKGROUND & AIMS

Claudins, the major components of tight junction (TJ) strands, which form paracellular barriers, consist of 24 family members, the combination of which determines the properties of TJ-based paracellular barriers. Here, we generated claudin-15-deficient (Cldn15(-/-)) mice to examine the ubiquitously expressed functions of claudin-15.

METHODS

We generated Cldn15(-/-) mice by the conventional gene-targeting strategy. Because the upper small intestine was enlarged in Cldn15(-/-) mice, we analyzed the phenotype from various angles regarding histology, physiology, and cell biology.

RESULTS

Cldn15(-/-) mice were born and grew normally with an enlarged upper small intestinal phenotype, megaintestine. Deficiency of claudin-15 did not cause a compensatory increase in the background expression of other types of claudins, claudin-1, -2, -3, -4, -7, -12, -18, -20, and -23, in the small intestine. Cldn15(-/-) mice showed enhanced proliferation of normal cryptic cells after weaning without diseased states such as polyps or cancer, resulting in megaintestine, in which the upper small intestine was approximately 2 times larger than normal in length and diameter. The number of transit-amplifying cells in crypts increased approximately 2-fold. Freeze-fracture electron microscopy revealed that deficiency of claudin-15 decreased the number of TJ strands, although the electric conductance was decreased in distal segments in Cldn15(-/-) jejunum, as compared with Cldn15(+/+) littermates.

CONCLUSIONS

Based on the specific roles of claudins in paracellular barrier formation without any direct role in cell proliferation, as previously shown in cultured epithelial cells, we propose that claudin-15-based formation of TJs to organize the microenvironment including ion conductance is important for normal-sized morphogenesis of the small intestine.

Cytochemical and ultrastructural study of anoikis and secondary necrosis in enterocytes detached in vivo

Detachment-induced apoptosis of enterocytes (anoikis) has not been investigated in vivo. Here we describe anoikis of fish enterocytes following detachment in a septicemia by Photobacterium damselae subsp. piscicida, or following injection of its exotoxin. The in vivo study was complemented with an ex vivo time-lapse analysis using conditions duplicating the in vivo situation. Linings of enterocytes detached from intestine mucosa dissociate into isolated enterocytes which undergo caspase 3-mediated anoikis with cell rounding, loss of polarization, condensation of chromatin and fragmentation of the nuclear envelope, early swelling of mitochondria with rupture of the outer membrane, and brush border disappearance. One mechanism for brush border loss was shedding of apoptotic bodies incorporating the apical part of the enterocyte. Brush border disappearance was also associated with disassembly of the F-actin microvillar core and involved re-absorption into the cell, or expansion and vesiculation followed by shedding of microvillar fragments. The enterocyte anoikis terminates by secondary necrosis and lysis due to lack of elimination by phagocytosis of apoptosing enterocytes. The conditions prevailing in vivo in the gut lumen accelerate enterocyte secondary necrosis. Our results underscore the importance of analyzing anoikis under conditions similar to those occurring in vivo.

The role of radixin in altered localization of canalicular conjugate export pump Mrp2 in cholestatic rat liver

AIM

Cholestasis has been associated with the endocytic retrieval of multidrug resistance protein 2 (Mrp2), but its mechanism is still unclear. Recent studies have indicated that radixin, a cross-linker between the actin filaments and membrane proteins, may be activated by phosphorylation and may be required for the canalicular localization of Mrp2.

METHODS

We investigated the role of radixin in the altered localization of Mrp2 in rat models of intrahepatic (ethinyl estradiol treatment) and extrahepatic (bile duct ligation) cholestasis using immunofluorescence microscopy. The changes in localization and expression were analyzed using Scion Image for Windows.

RESULTS

In both models, Mrp2 was localized outside as well as inside the ZO-1 staining, indicating partial dislocation from the canalicular membrane. In contrast to the steep elevation of the immunostaining intensity curves for Mrp2 in the controls, the corresponding curves in both models were broadened and flattened, confirming endocytic retrieval into the hepatocytes. Mrp2 and radixin were colocalized at the canalicular domain in the controls, whereas in both cholestatic rats they were dissociated at some canaliculi, indicating the disturbed colocalization of Mrp2 and radixin in cholestasis. The fluorescence of phosphorylated radixin, an active form of radixin, markedly decreased in both cholestatic models, which was supported by the reduced peak fluorescence intensities.

CONCLUSION

The disturbed colocalization of Mrp2 and radixin may contribute to the endocytic retrieval of Mrp2 in cholestasis due to the failure to anchor Mrp2 in the canalicular membrane, in which the phosphorylated radixin may play a major role.

Human immunodeficiency virus (HIV-1) Vpr induced downregulation of NHE1 induces alteration in intracellular pH and loss of ERM complex in target cells

Human immunodeficiency virus type 1 (HIV-1) Vpr is known to dysregulate host cellular functions through its interaction with cellular proteins. Using a protein array we assessed Vpr-mediated differential regulation of host cellular proteins expression. Results demonstrated that Vpr differentially regulated host factors that are involved in functions, such as cell proliferation, differentiation and apoptosis. One of the most highly downregulated proteins attained was the sodium hydrogen exchanger, isoform 1 (NHE1), which showed a significant (60%) decrease in HIV-1 Vpr(+) virus infected cells as compared to HIV-1 Vpr(-) virus infected control. NHE1 downregulation further led to acidification of cells and was directly correlated with loss of ezrin, radixin and moesin (ERM) protein complex and decreased AKT phosphorylation. Vpr-mediated NHE1 dyregulation is in part through GR pathway as GR antagonist, mifepristone reversed Vpr-induced NHE1 downregulation.

Programmed cell death in the larval salivary glands of Apis mellifera (Hymenoptera, Apidae)

The morphological and histochemical features of degeneration in honeybee (Apis mellifera) salivary glands were investigated in 5th instar larvae and in the pre-pupal period. The distribution and activity patterns of acid phosphatase enzyme were also analysed. As a routine,the larval salivary glands were fixed and processed for light microscopy and transmission electron microscopy.Tissue sections were subsequently stained with haematoxylin -eosin,bromophenol blue,silver,or a variant of the critical electrolyte concentration (CEC) method.Ultrathin sections were contrasted with uranyl acetate and lead citrate.Glands were processed for the histochemical and cytochemical localization of acid phosphatase,as well as biochemical assay to detect its activity pattern. Acid phosphatase activity was histochemically detected in all the salivary glands analysed.The cytochemical results showed acid phosphatase in vesicles, Golgi apparatus and lysosomes during the secretory phase and,additionally, in autophagic structures and luminal secretion during the degenerative phase. These findings were in agreement with the biochemical assay. At the end of the 5th instar, the glandular cells had a vacuolated cytoplasm and pyknotic nuclei, and epithelial cells were shed into the glandular lumen.The transition phase from the 5th instar to the pre-pupal period was characterized by intense vacuolation of the basal cytoplasm and release of parts of the cytoplasm into the lumen by apical blebbing; these blebs contained cytoplasmic RNA, rough endoplasmic reticule and, occasionally, nuclear material. In the pre-pupal phase, the glandular epithelium showed progressive degeneration so that at the end of this phase only nuclei and remnants of the cytoplasm were observed.The nuclei were pyknotic,with peripheral chromatin and blebs. The gland remained in the haemolymph and was recycled during metamorphosis. The programmed cell death in this gland represented a morphological form intermediate between apoptosis and autophagy.

After shrinkage apoptotic cells expose internal membrane-derived epitopes on their plasma membranes

Apoptosis and phagocytosis of apoptotic cells are crucial processes. At best the phagocytic machinery detects and swallows all apoptotic cells in a way that progression to secondary necrosis is avoided. Otherwise, inflammation and autoimmune diseases may occur. Most apoptotic cells are phagocytosed instantaneously in a silent fashion; however, some dying cells escape their clearance. If the cells are not cleared early, they lose membranes due to extensive shedding of membrane surrounded vesicles (blebbing) and shrink. It is unclear how apoptotic cells compensate their massive loss of plasma membrane. Here, we demonstrate that endoplasmic reticulum- (ER) resident proteins (calnexin, the KDEL receptor and a dysfunctional immunoglobulin heavy chain) were exposed at the surfaces of shrunken late apoptotic cells. Additionally, these cells showed an increased binding of lectins, which recognize sugar structures predominantly found as moieties of incompletely processed proteins in ER and Golgi. In addition the ER resident lipophilic ER-Tracker Blue-White DPX, and internal GM1 were observed to translocate to the cell surfaces during late apoptosis. We conclude that during blebbing of apoptotic cells the surface membrane loss is substituted by immature membranes from internal stores. This mechanism explains the simultaneous appearance of preformed recognition structures for several adaptor proteins known to be involved in clearance of dead cells.