Loss of LSR affects epithelial barrier integrity and tumor xenograft growth of CaCo-2 cells

An Updated View on the Cellular Uptake and Mode-of-Action of Clostridioides difficile Toxins

Research on the human gut pathogen Clostridioides (C.) difficile and its toxins continues to attract much attention as a consequence of the threat to human health posed by hypervirulent strains. Toxin A (TcdA) and Toxin B (TcdB) are the two major virulence determinants of C. difficile. Both are single-chain proteins with a similar multidomain architecture. Certain hypervirulent C. difficile strains also produce a third toxin, namely binary toxin CDT (C. difficile transferase). C. difficile toxins are the causative agents of C. difficile-associated diseases (CDADs), such as antibiotics-associated diarrhea and pseudomembranous colitis. For that reason, considerable efforts have been expended to unravel their molecular mode-of-action and the cellular mechanisms responsible for their uptake. Many of these studies have been conducted in European laboratories. Here, we provide an update on our previous review (Papatheodorou et al. Adv Exp Med Biol, 2018) on important advances in C. difficile toxins research.

Anti-lipolysis-stimulated lipoprotein receptor monoclonal antibody as a novel therapeutic agent for endometrial cancer

Background

Endometrial cancer (EC) is a common gynecologic malignancy and patients with advanced and recurrent EC have a poor prognosis. Although chemotherapy is administered for those patients, the efficacy of current chemotherapy is limited. Therefore, it is necessary to develop novel therapeutic agents for EC. In this study, we focused on lipolysis-stimulated lipoprotein receptor (LSR), a membrane protein highly expressed in EC cells, and developed a chimeric chicken–mouse anti-LSR monoclonal antibody (mAb). This study investigated the antitumor effect of an anti-LSR mAb and the function of LSR in EC.

Methods

We examined the expression of LSR in 228 patients with EC using immunohistochemistry and divided them into two groups: high-LSR (n = 153) and low-LSR groups (n = 75). We developed a novel anti-LSR mAb and assessed its antitumor activity in an EC cell xenograft mouse model. Pathway enrichment analysis was performed using protein expression data of EC samples. LSR-knockdown EC cell lines (HEC1 and HEC116) were generated by transfected with small interfering RNA and used for assays in vitro.

Results

High expression of LSR was associated with poor overall survival (hazard ratio: 3.53, 95% confidence interval: 1.35–9.24, p = 0.01), advanced stage disease (p = 0.045), deep myometrial invasion (p = 0.045), and distant metastasis (p < 0.01). In EC with deep myometrial invasion, matrix metalloproteinase (MMP) 2 was highly expressed along with LSR. Anti-LSR mAb significantly inhibited the tumor growth in EC cell xenograft mouse model (tumor volume, 407.1 mm³versus 726.3 mm³, p = 0.019). Pathway enrichment analysis identified the mitogen-activated protein kinase (MAPK) pathway as a signaling pathway associated with LSR expression. Anti-LSR mAb suppressed the activity of MAPK in vivo. In vitro assays using EC cell lines demonstrated that LSR regulated cell proliferation, invasion, and migration through MAPK signaling, particularly MEK/ERK signaling and membrane-type 1 MMP (MT1-MMP) and MMP2. Moreover, ERK1/2-knockdown suppressed cell proliferation, invasion, migration, and the expression of MT1-MMP and MMP2.

Conclusions

Our results suggest that LSR contributes to tumor growth, invasion, metastasis, and poor prognosis of EC through MAPK signaling. Anti-LSR mAb is a potential therapeutic agent for EC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09789-6.

Mechanisms and modeling of wound repair in the intestinal epithelium

The intestinal epithelial barrier is susceptible to injury from insults, such as ischemia or infectious disease. The epithelium's ability to repair wounded regions is critical to maintaining barrier integrity. Mechanisms of intestinal epithelial repair can be studied with models that recapitulate the in vivo environment. This review focuses on in vitro injury models and intestinal cell lines utilized in such systems. The formation of artificial wounds in a controlled environment allows for the exploration of reparative physiology in cell lines modeling diverse aspects of intestinal physiology. Specifically, the use of intestinal cell lines, IPEC-J2, Caco-2, T-84, HT-29, and IEC-6, to model intestinal epithelium is discussed. Understanding the unique systems available for creating intestinal injury and the differences in monolayers used for in vitro work is essential for designing studies that properly capture relevant physiology for the study of intestinal wound repair.

Lipolysis-Stimulated Lipoprotein Receptor Impairs Hepatocellular Carcinoma and Inhibits the Oncogenic Activity of YAP1 via PPPY Motif

Purpose

Lipolysis-stimulated lipoprotein receptor (LSR) is a type I single-pass transmembrane protein which is mainly expressed in the liver. In this study, we investigated if and how LSR is involved in the carcinogenesis of hepatocellular carcinoma (HCC).

Experimental Design

To evaluate if LSR was abnormally expressed in human HCC tissues, and how its expression was associated with the survival probability of patients, we obtained data from Gene Expression Omnibus and The Cancer Genome Atlas Program. To investigate if and how LSR regulates tumor growth, we knocked down and overexpressed LSR in human HCC cell lines. In addition, to evaluate the interaction between LSR and yes-associated protein1 (YAP1), we mutated LSR at PPPY motif, a binding site of YAP1.

Results

Totally, 454 patients were enrolled in the present study, and high expression of LSR significantly decreased the probability of death. Knockdown of LSR significantly increased the expansion of HCC cells and significantly promoted tumor growth. In addition, downregulation of LSR increased the nuclear accumulation and transcriptional function of YAP1. Conversely, overexpression of LSR impairs this function of YAP1 and phosphorylates YAP1 at serine 127. Of note, mutation of LSR at the PPPY motif could block the interaction between LSR and YAP1, and restore the transcriptional ability of YAP1.

Conclusions

The present study suggests that LSR binds to YAP1 via the PPPY motif. Thus, LSR increases the phosphorylation of YAP1 and impairs the growth of HCC. This highlights that targeting LSR might be a promising therapeutic strategy for HCC.

Effects of Lipolysis-Stimulated Lipoprotein Receptor on Tight Junctions of Pancreatic Ductal Epithelial Cells in Hypertriglyceridemic Acute Pancreatitis

Objective

We investigated the effects of lipolysis-stimulated lipoprotein receptor (LSR) on the tight junctions (TJs) of pancreatic ductal epithelial cells (PDECs) in hypertriglyceridemic acute pancreatitis (HTGAP).

Methods

Sprague-Dawley rats were fed standard rat chow or a high-fat diet and injected with sodium taurocholate to obtain normal and HTGAP rats, respectively. Serum triglyceride (TG) levels, pathological changes, TJ proteins in the pancreas, and TJ ultrastructure of PDECs were assessed. LSR overexpression (OE) and knockdown (KD) HPDE6-C7 models were designed and cultured in a high-fat environment. Protein levels were quantified by Western blotting. Cell monolayer permeability was detected using FITC-Dextran.

Results

Serum TG concentration and pancreatic scores were higher in the HTGAP group than in the normal group. Among the TJ proteins, LSR protein expression was significantly lower in the HTGAP group than in the acute pancreatitis (AP) group. Tricellulin (TRIC) expression in the pancreatic ductal epithelia was higher in the HTGAP group than in the AP group. The HTGAP group had lower TJ protein levels, wider intercellular space, and widespread cellular necrosis with disappearance of cell junction structures. In the cell study, TJ proteins were downregulated and the cellular barrier was impaired by palmitic acid (PA), which was reversed by LSR-OE, whereas LSR-KD downregulated the TJ proteins and aggravated PA-induced cellular barrier impairment.

Conclusions

Hypertriglyceridemia downregulates the TJ proteins in PDECs, which may impair the pancreatic ductal mucosal barrier function. LSR regulation can change the effects of HTG on cellular barrier function by upregulating the TJ proteins.

The Roles of Tricellular Tight Junction Protein Angulin-1/Lipolysis-Stimulated Lipoprotein Receptor (LSR) in Endometriosis and Endometrioid-Endometrial Carcinoma

Tight junction proteins play roles beyond permeability barriers functions and control cell proliferation and differentiation. The relation between tight junctions and the signal transduction pathways affects cell growth, invasion and migration. Abnormality of tight junction proteins closely contributes to epithelial mesenchymal transition (EMT) and malignancy of various cancers. Angulin-1/lipolysis-stimulated lipoprotein receptor (LSR) forms tricellular contacts that has a barrier function. Downregulation of angulin-1/LSR correlates with the malignancy in various cancers, including endometrioid-endometrial carcinoma (EEC). These alterations have been shown to link to not only multiple signaling pathways such as Hippo/YAP, HDAC, AMPK, but also cell metabolism in ECC cell line Sawano. Moreover, loss of angulin-1/LSR upregulates claudin-1, and loss of apoptosis stimulating p53 protein 2 (ASPP2) downregulates angulin-1/LSR. Angulin-1/LSR and ASPP2 concentrate at both midbody and centrosome in cytokinesis. In EEC tissues, angulin-1/LSR and ASPP2 are reduced and claudin-2 is overexpressed during malignancy, while in the tissues of endometriosis changes in localization of angulin-1/LSR and claudin-2 are seen. This review highlights how downregulation of angulin-1/LSR promotes development of endometriosis and EEC and discusses about the roles of angulin-1/LSR and its related proteins, including claudins and ASPP2.

Angulin-1 (LSR) Affects Paracellular Water Transport, However Only in Tight Epithelial Cells

Water transport in epithelia occurs transcellularly (aquaporins) and paracellularly (claudin-2, claudin-15). Recently, we showed that downregulated tricellulin, a protein of the tricellular tight junction (tTJ, the site where three epithelial cells meet), increased transepithelial water flux. We now check the hypothesis that another tTJ-associated protein, angulin-1 (alias lipolysis-stimulated lipoprotein receptor, LSR) is a direct negative actuator of tTJ water permeability depending on the tightness of the epithelium. For this, a tight and an intermediate-tight epithelial cell line, MDCK C7 and HT-29/B6, were stably transfected with CRISPR/Cas9 and single-guide RNA targeting angulin-1 and morphologically and functionally characterized. Water flux induced by an osmotic gradient using 4-kDa dextran caused water flux to increase in angulin-1 KO clones in MDCK C7 cells, but not in HT-29/B6 cells. In addition, we found that water permeability in HT-29/B6 cells was not modified after either angulin-1 knockout or tricellulin knockdown, which may be related to the presence of other pathways, which reduce the impact of the tTJ pathway. In conclusion, modulation of the tTJ by knockout or knockdown of tTJ proteins affects ion and macromolecule permeability in tight and intermediate-tight epithelial cell lines, while the transepithelial water permeability was affected only in tight cell lines.

Pyk2 inhibitor prevents epithelial hyperpermeability induced by HMGB1 and inflammatory cytokines in Caco-2 cells

The non-receptor protein tyrosine kinase 2β (Pyk2) phosphorylated tricellular tight junction (tTJ) molecules angulin-1/LSR and tricellulin (TRIC) and the inhibitor PF-431396 (PF43) suppress angulin-1/LSR and TRIC recruitment to tTJs. The disruption of the intestinal epithelial barrier by high mobility group box 1 (HMGB1) and the inflammatory cytokines TNFα and IFNγ contributes to downregulation of angulin-1/LSR and TRIC in 2.5D culture of Caco-2 cells as a novel model of inflammatory bowel disease (IBD). In the present study, to investigate the roles of Pyk2 phosphorylated angulin-1/LSR and TRIC in the intestinal epithelial barrier, 2D and 2.5D cultures of Caco-2 cells were treated with the Pyk2 inhibitor PF-43 with or without HMGB1, inflammatory cytokines TNFα and IFNγ. Treatment with PF-43 increased expression of angulin-1/LSR, phosphorylated AMPK and phosphorylated MAPK and decreased that of phosphorylated JNK, with upregulation of the epithelial barrier and cellular metabolism measured as basal oxygen consumption rate (OCR) and ATP production in 2D culture. Treatment with PF-43 prevented the downregulation of the epithelial barrier by HMGB1 and inflammatory cytokines in 2D culture. Treatment with PF-43 prevented the epithelial hyperpermeability induced by HMGB1 and inflammatory cytokines in 2.5D culture. In 2.5D culture, treatment with PF-43 inhibited the decreases of angulin-1/LSR, TRIC, pJNK, pAMPK and pMAPK induced by HMGB1 and the inflammatory cytokines. Treatment with PF-43 inhibited in part the induced phosphorylation of the serine of angulin-1/LSR and TRIC. Pyk2 inhibitor PF-43 may have potential for use in therapy for IBD via its actions with regard to phosphorylated tTJs and cellular metabolism.

LSR Promotes Cell Proliferation and Invasion in Lung Cancer

The lipolysis-stimulated lipoprotein receptor (LSR) displays an important regulatory role in cancer. However, the association between LSR and lung cancer is still elusive. Here, the candidate oncogene LSR on Ch.9q was obtained and assessed by bioinformatics analysis of The Cancer Genome Atlas (TCGA) dataset of lung cancer. We conducted clinical pathology and survival analysis based on the lung cancer database. We assessed the biological effects of LSR in lung cancer cells on cell proliferation. Our data indicated that LSR was upregulated in lung cancer cells. Meanwhile, LSR was identified in this study to be a poor prognostic factor, and its high expression exhibited relations with grades, stages, and nodal metastasis status. Using in vitro analysis, our data revealed that LSR could promote lung cancer progression by regulating cell proliferation, migration, and invasion. In our study, our data demonstrated that LSR was a tumor promoter for lung cancer and was a potential biomarker and target for lung cancer prognosis and treatment.

The cytotoxic effect of Clostridioides difficile pore-forming toxin CDTb

Clostridioides (C.) difficile is clinically highly relevant and produces several AB-type protein toxins, which are the causative agents for C. difficile-associated diarrhea and pseudomembranous colitis. Treatment with antibiotics can lead to C. difficile overgrowth in the gut of patients due to the disturbed microbiota. C. difficile releases large Rho/Ras-GTPase glucosylating toxins TcdA and TcdB, which are considered as the major virulence factors for C. difficile-associated diseases. In addition to TcdA and TcdB, C. difficile strains isolated from severe cases of colitis produce a third toxin called CDT. CDT is a member of the family of clostridial binary actin ADP-ribosylating toxins and consists of two separate protein components. The B-component, CDTb, binds to the receptor and forms a complex with and facilitates transport and translocation of the enzymatically active A-component, CDTa, into the cytosol of target cells by forming trans-membrane pores through which CDTa translocates. In the cytosol, CDTa ADP-ribosylates G-actin causing depolymerization of the actin cytoskeleton and, eventually, cell death. In the present study, we report that CDTb exhibits a cytotoxic effect in the absence of CDTa. We show that CDTb causes cell rounding and impairs cell viability and the epithelial integrity of CaCo-2 monolayers in the absence of CDTa. CDTb-induced cell rounding depended on the presence of LSR, the specific cellular receptor of CDT. The isolated receptor-binding domain of CDTb was not sufficient to cause cell rounding. CDTb-induced cell rounding was inhibited by enzymatically inactive CDTa or a pore-blocker, implying that CDTb pores in cytoplasmic membranes contribute to cytotoxicity.

LSR promotes epithelial ovarian cancer cell survival under energy stress through the LKB1-AMPK pathway

Lipolysis-stimulated lipoprotein receptor (LSR), also known as a component of tricellular tight junctions, is highly expressing in epithelial ovarian cancer (EOC). However, the biological role of LSR in EOC cells remains unclear. In this study, we evaluated liver kinase B1 (LKB1) mediated AMP-activated protein kinase (AMPK) activity and investigated the effect of LSR on EOC cell survival under energy stress. LSR increased the levels of phospho-AMPKα at Thr172 and phospho-acetyl-CoA carboxylase (ACC) at Ser79 via LKB1-AMPK pathway in glucose deprivation in vitro. The increase of P-AMPKα (Thr172) and P-ACC (Ser79) was also detected in tumor microenvironment in vivo. Meanwhile, LSR promoted LKB1 localization at the cell membrane of EOC cells. By cell survival analysis, LSR attenuated glucose deprivation-induced cell death in EOC cells in vitro. Our results suggest that LSR promotes EOC cell survival and tumor growth through the LKB1-AMPK pathway.

Increase in Epithelial Permeability and Cell Metabolism by High Mobility Group Box 1, Inflammatory Cytokines and TPEN in Caco-2 Cells as a Novel Model of Inflammatory Bowel Disease

High mobility group box 1 protein (HMGB1) is involved in the pathogenesis of inflammatory bowel disease (IBD). Patients with IBD develop zinc deficiency. However, the detailed roles of HMGB1 and zinc deficiency in the intestinal epithelial barrier and cellular metabolism of IBD remain unknown. In the present study, Caco-2 cells in 2D culture and 2.5D Matrigel culture were pretreated with transforming growth factor-β (TGF-β) type 1 receptor kinase inhibitor EW-7197, epidermal growth factor receptor (EGFR) kinase inhibitor AG-1478 and a TNFα antibody before treatment with HMGB1 and inflammatory cytokines (TNFα and IFNγ). EW-7197, AG-1478 and the TNFα antibody prevented hyperpermeability induced by HMGB1 and inflammatory cytokines in 2.5D culture. HMGB1 affected cilia formation in 2.5D culture. EW-7197, AG-1478 and the TNFα antibody prevented the increase in cell metabolism induced by HMGB1 and inflammatory cytokines in 2D culture. Furthermore, ZnSO₄ prevented the hyperpermeability induced by zinc chelator TPEN in 2.5D culture. ZnSO₄ and TPEN induced cellular metabolism in 2D culture. The disruption of the epithelial barrier induced by HMGB1 and inflammatory cytokines contributed to TGF-β/EGF signaling in Caco-2 cells. The TNFα antibody and ZnSO₄ as well as EW-7197 and AG-1478 may have potential for use in therapy for IBD.

HMGB1 enhances epithelial permeability via p63/TGF-β signaling in lung and terminal bronchial epithelial cells

High mobility group box 1 (HMGB1) is involved in the induction of airway inflammation and injury in patients with chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). HMGB1 increased by transforming growth factor-β1 (TGF-β1), impairs airway epithelial barrier function in the lung. In the present study, to investigate how HMGB1 affects the barrier of normal human lung epithelial (HLE) cells, monolayer cells (2D culture) and bronchial-like spheroid cells (2.5 D Matrigel culture), which have lumen formation, were pretreated with TGF-β type I receptor kinase inhibitor EW-7197 before treatment with HMGB1. In 2D culture, treatment with HMGB1 decreased expression of angulin-1/LSR, TRIC and CLDN-1, -4, -7 and increased that of CLDN-2. Pretreatment with EW-7197 prevented the changes of all tight junction molecules induced by HMGB1. In 2.5D Matrigel culture, treatment with HMGB1 induced permeability of FITC-dextran (FD-4) into the lumen, whereas pretreatment with EW-7197 prevented the hyperpermeability of FD-4 into the lumen caused by HMGB1. In 2.5D Matrigel culture, knockdown of transcription factor p63 prevented the hyperpermeability induced by HMGB1 as well as pretreatment with EW-7197. In the 2D culture of HLE cells with HMGB1, knockdown of p63 increased the level of angulin-1/LSR and CLDN-4, while pretreatment with EW-7197 enhanced the increase of CLDN-4 induced by knockdown of p63. Immunohistochemical analysis of IPF, CLDN-2, HMGB1 and p63 revealed that their levels were higher in the regenerative epithelium of the terminal bronchial region than in normal epithelium. HMGB1 induces epithelial permeability of HLE cells via p63/TGF-β signaling in normal lung and IPF.

Improved micro-impedance spectroscopy to determine cell barrier properties

The goal of this study was to determine whether the Tethapod system, which was designed to determine the impedance properties of lipid bilayers, could be used for cell culture in order to utilise micro-impedance spectroscopy to examine further biological applications. To that purpose we have used normal epithelial cells from kidney (RPTEC) and a kidney cancer cell model (786-O). We demonstrate that the Tethapod system is compatible with the culture of 10,000 cells seeded to grow on a small area gold measurement electrode for several days without affecting the cell viability. Furthermore, the range of frequencies for EIS measurements were tuned to examine easily the characteristics of the cell monolayer. We demonstrate significant differences in the paracellular resistance pathway between normal and cancer kidney epithelial cells. Thus, we conclude that this device has advantages for the study of cultured cells that include (i) the configuration of measurement and reference electrodes across a microfluidic channel, and (ii) the small surface area of 6 parallel measurement electrodes (2.1 mm2) integrated in a microfluidic system. These characteristics might improve micro-impedance spectroscopy measurement techniques to provide a simple tool for further studies in the field of the patho-physiology of biological barriers.

HMGB1-downregulated angulin-1/LSR induces epithelial barrier disruption via claudin-2 and cellular metabolism via AMPK in airway epithelial Calu-3 cells

A non-histone chromatin-associated protein, high mobility group box 1 (HMGB1), which impairs the airway epithelial barrier, is involved in the induction of airway inflammation in patients with allergy, asthma, chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis (IPF). Tricellular tight junctions (tTJs) form at the convergence of bicellular tight junctions (bTJs). Angulin-1/lipolysis-stimulated lipoprotein receptor (LSR) is a novel molecule present at tricellular contacts and contributes to the epithelial barrier and cellular metabolism. Adenosine monophosphate-activated protein kinase (AMPK) is a central metabolic regulator and has a reciprocal association with TJs. In the present study, to examine how HMGB1 contributes to airway epithelial barrier disruption and the cellular metabolism indicated as mitochondrial respiration, bronchial epithelial Calu-3 cells were transfected with siRNAs of angulin-1/LSR or treated with HMGB1 and the relationship between HMGB1 and angulin-1/LSR was investigated. Knockdown of angulin-1/LSR upregulated the expression of the tight junction molecule claudin-2, AMPK activity, and mitochondrial respiration, and downregulated the epithelial barrier. Treatment with HMGB1 downregulated angulin-1/LSR expression and the epithelial barrier, and upregulated claudin-2 expression, AMPK activity and mitochondrial respiration. Treatment with EW-7197, a transforming growth factor-β (TGF-β) type I receptor kinase inhibitor, prevented all the effects of HMGB1 in Calu-3 cells. HMGB1-downregulated angulin-1/LSR induced epithelial barrier disruption via claudin-2 and cellular metabolism via AMPK in airway epithelial Calu-3 cells. The effects of HMGB1 contribute to TGF-β signaling and EW-7197 shows potential for use in therapy for HMGB1-induced airway inflammation.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

Receptor-Binding and Uptake of Binary Actin-ADP-Ribosylating Toxins

Binary actin-ADP-ribosylating toxins (e.g., Clostridium botulinum C2 toxin or Clostridium perfringens iota toxin ) consist of two separate proteins: An ADP-ribosyltransferase, which modifies actin thereby inhibiting actin polymerization, and a binding component that forms heptamers after proteolytic activation. While C2 toxin interacts with carbohydrate structures on host cells, the group of iota-like toxins binds to lipolysis-stimulated lipoprotein receptor (LSR). Here, we review LSR and discuss the role and function of LSR in interaction of iota-like toxins with host cells.

Towards embedding Caco-2 model of gut interface in a microfluidic device to enable multi-organ models for systems biology

Background

A cancer cell line originating from human epithelial colorectal adenocarcinoma (Caco-2 cells) serves as a high capacity model for a preclinical screening of drugs. Recent need for incorporating barrier tissue into multi-organ chips calls for inclusion of Caco-2 cells into microperfused environment.

Results

This article describes a series of systems biology insights obtained from comparing Caco-2 models cells grown as conventional 2D layer and in a microfluidic chip. When basic electrical parameters of Caco-2 monolayers were evaluated using impedance spectrometry and MTT assays, no differences were noted. On the other hand, the microarray profiling of mRNAs and miRNAs revealed that grows on a microfluidic chip leads to the change in the production of specific miRNA, which regulate a set of genes for cell adhesion molecules (CAMs), and provide for more complete differentiation of Caco-2 monolayer. Moreover, the sets of miRNAs secreted at the apical surface of Caco-2 monolayers grown in conventional 2D culture and in microfluidic device differ.

Conclusions

When integrated into a multi-tissue platform, Caco-2 cells may aid in generating insights into complex pathophysiological processes, not possible to dissect in conventional cultures.

Mutations in the Drosophila tricellular junction protein M6 synergize with RasV12 to induce apical cell delamination and invasion

Complications from metastasis are responsible for the majority of cancer-related deaths. Despite the outsized medical impact of metastasis, remarkably little is known about one of the key early steps of metastasis: departure of a tumor cell from its originating tissue. It is well documented that cellular delamination in the basal direction can induce invasive behaviors, but it remains unknown if apical cell delamination can induce migration and invasion in a cancer context. To explore this feature of cancer progression, we performed a genetic screen in Drosophila and discovered that mutations in the protein M6 synergize with oncogenic Ras to drive invasion following apical delamination without crossing a basement membrane. Mechanistically, we observed that M6-deficient Ras^V12 clones delaminate as a result of alterations in a Canoe-RhoA-myosin II axis that is necessary for both the delamination and invasion phenotypes. To uncover the cellular roles of M6, we show that it localizes to tricellular junctions in epithelial tissues where it is necessary for the structural integrity of multicellular contacts. This work provides evidence that apical delamination can precede invasion and highlights the important role that tricellular junction integrity can play in this process.

Guanylate binding protein-1-mediated epithelial barrier in human salivary gland duct epithelium

Guanylate-binding protein-1 (GBP-1) is an interferon-inducible large GTPase involved in the epithelial barrier at tight junctions. To investigate the role of GBP-1 in the epithelial barrier, primary human salivary gland duct epithelial cells were treated with the the proinflammatory cytokines IFNγ, IL-1β, TNFα and the growth factor TGF-β. Treatment with IFNγ, IL-1β, or TNFα markedly enhanced GBP-1 and the epithelial barrier function, and induced not only CLDN-7 but also the tricellular tight junction molecule lipolysis-stimulated lipoprotein receptor (LSR). Knockdown of GBP-1 by its siRNA induced endocytosis of tight junction molecules, and prevented the increases of CLDN-7 and LSR with the upregulation of the epithelial barrier function induced by treatment with IFNγ or TNFα. Treatment with a PKCα inhibitor induced expression of GBP-1, CLDN-7 and LSR and enhanced the epithelial barrier function. In almost intact salivary gland ducts from patients with IgG4-related disease (IgG4-RD) indicated significant infiltration of IgG-positive plasma cells, expression of GBP-1, CLDN-7 and LSR was increased. These findings indicated that GBP-1 might play a crucial role in barrier function of normal human salivary gland duct epithelium and perform a preventive role in the duct epithelium of IgG4-RD disease.

Binary Clostridium difficile toxin (CDT) - A virulence factor disturbing the cytoskeleton

Clostridium difficile infection causes antibiotics-associated diarrhea and pseudomembranous colitis. Major virulence factors of C. difficile are the Rho-glucosylating toxins TcdA and TcdB. In addition, many, so-called hypervirulent C. difficile strains produce the binary actin-ADP-ribosylating toxin CDT. CDT causes depolymerization of F-actin and rearrangement of the actin cytoskeleton. Thereby, many cellular functions, which depend on actin, are altered. CDT disturbs the dynamic balance between actin and microtubules in target cells. The toxin increases microtubule polymerization and induces the formation of microtubule-based protrusions at the plasma membrane of target cells. Moreover, CDT causes a redistribution of vesicles from the basolateral side to the apical side, where extracellular matrix proteins are released. These processes may increase the adherence of clostridia to target cells. Here, we review the effects of the action of CDT on the actin cytoskeleton and on the microtubule system.