Non-classical export of epimorphin and its adhesion to alphav-integrin in regulation of epithelial morphogenesis

The Janus-faced functions of Apolipoproteins L in membrane dynamics

The functions of human Apolipoproteins L (APOLs) are poorly understood, but involve diverse activities like lysis of bloodstream trypanosomes and intracellular bacteria, modulation of viral infection and induction of apoptosis, autophagy, and chronic kidney disease. Based on recent work, I propose that the basic function of APOLs is the control of membrane dynamics, at least in the Golgi and mitochondrion. Together with neuronal calcium sensor-1 (NCS1) and calneuron-1 (CALN1), APOL3 controls the activity of phosphatidylinositol-4-kinase-IIIB (PI4KB), involved in both Golgi and mitochondrion membrane fission. Whereas secreted APOL1 induces African trypanosome lysis through membrane permeabilization of the parasite mitochondrion, intracellular APOL1 conditions non-muscular myosin-2A (NM2A)-mediated transfer of PI4KB and APOL3 from the Golgi to the mitochondrion under conditions interfering with PI4KB-APOL3 interaction, such as APOL1 C-terminal variant expression or virus-induced inflammatory signalling. APOL3 controls mitophagy through complementary interactions with the membrane fission factor PI4KB and the membrane fusion factor vesicle-associated membrane protein-8 (VAMP8). In mice, the basic APOL1 and APOL3 activities could be exerted by mAPOL9 and mAPOL8, respectively. Perspectives regarding the mechanism and treatment of APOL1-related kidney disease are discussed, as well as speculations on additional APOLs functions, such as APOL6 involvement in adipocyte membrane dynamics through interaction with myosin-10 (MYH10).

Role of syntaxin3 an apical polarity protein in poorly polarized keratinocytes: regulation of asymmetric barrier formations in the skin epidermis

The skin epidermis exhibits an asymmetric structure composed of multilayered keratinocytes and those in the outer layers form two-way physical barriers, cornified cell envelope (CCE), and tight junctions (TJs). While undifferentiated keratinocytes in the basal layer continuously deliver daughter cells outward, which undergo successive differentiation with losing their polarized characteristics, they retain the expression of several polarity proteins. In the present study, we revealed that the t-SNARE protein syntaxin3, a critical element for the formation of the apical compartment in simple epithelial cells, is required to confer the ability to organize the physical barriers on "poorly polarized" keratinocytes in epidermal outer layers. HaCaT keratinocytes with genetic ablation of syntaxin3 readily succumbed to hydrogen peroxide-induced cell death. Additionally, they lost the ability to organize TJ and CCE structures, accompanied by notable downregulation of transglutaminase1 and caspase14 (a cornification regulator) expression. These syntaxin3-knockout cells appeared to restore oxidative stress tolerance and functional TJ formation ability, in response to the inducible re-expression of exogenous syntaxin3. While plausible mechanisms underlying these phenomena remain unclear, syntaxin3, an apical polarity protein in the simple epithelia, has emerged as a potentially crucial element for barrier formation in poorly polarized keratinocytes in polarized epidermal tissue.

Syntaxin4, P-cadherin, and CCAAT enhancer binding protein β as signaling elements in the novel differentiation pathway for cultured embryonic stem cells

Pluripotent stem cells possess the potential to differentiate into all three germ layers. However, upon removal of the stemness factors, pluripotent stem cells, such as embryonic stem cells (ESCs), exhibit EMT-like cell behavior and lose stemness signatures. This process involves the membrane translocation of the t-SNARE protein syntaxin4 (Stx4) and the expression of the intercellular adhesion molecule P-cadherin. The forced expression of either of these elements induces the emergence of such phenotypes even in the presence of stemness factors. Interestingly, extracellular Stx4, but not P-cadherin, appears to induce a significant upregulation of the gastrulation-related gene brachyury, along with a slight upregulation of the smooth muscle cell-related gene ACTA2 in ESCs. Furthermore, our findings reveal that extracellular Stx4 plays a role in preventing the elimination of CCAAT enhancer binding protein β (C/EBPβ). Notably, the forced overexpression of C/EBPβ led to the downregulation of brachyury and a significant upregulation of ACTA2 in ESCs. These observations suggest that extracellular Stx4 contributes to early mesoderm induction while simultaneously activating an element that alters the differentiation state. The fact that a single differentiation cue can elicit multiple differentiation responses may reflect the challenges associated with achieving sensitive and directed differentiation in cultured stem cells.

Extracellular epimorphin impairs expression and processing of profilaggrin in HaCaT keratinocytes

The expression and processing of filaggrin, a filament-associated protein in the skin epidermis, is closely associated with keratinocyte cornification. The large precursor profilaggrin (Pro-FLG) is initially detected at the granular layer in keratohyalin granules, subsequently processed into 10 to 12 filaggrin monomers (mFLGs) for keratin assembly, and ultimately degraded into smaller peptides that behave as natural moisturizing factor (NMF) at the outermost epidermis. We previously reported that epimorphin (EPM) extruded upon external stimuli severely perturbs epidermal terminal differentiation. Using HaCaT keratinocytes with inducible expression and recombinant EPM and FLG, we investigated the effect of extracellular EPM on the expression profile of filaggrin. As expression and processing of Pro-FLG in primary keratinocytes are accompanied with apoptotic cell death, we employed HaCaT keratinocytes that grow and express filaggrin mRNA in standard culture medium. In response to ectopic stimulation with extracellular EPM, Pro-FLG expression decreased with elimination of keratohyalin granules in the cells, with filaggrin mRNA remained constant and profilaggrin processing was not accelerated. Additionally, using a recombinant form of mFLG engineered for intracellular localization, we found that extracellular EPM hindered proteolytic cleavage of mFLG for production of NMF. Taken together, extracellularly extruded EPM, an epidermal cornification blocker, not only decreases Pro-FLG expression but also reduces the production of NMF in HaCaT keratinocytes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-022-00566-8.

Plasma membrane flipping of Syntaxin-2 regulates its inhibitory action on insulin granule exocytosis

Enhancing pancreatic β-cell secretion is a primary therapeutic target for type-2 diabetes (T2D). Syntaxin-2 (Stx2) has just been identified to be an inhibitory SNARE for insulin granule exocytosis, holding potential as a treatment for T2D, yet its molecular underpinnings remain unclear. We show that excessive Stx2 recruitment to raft-like granule docking sites at higher binding affinity than pro-fusion syntaxin-1A effectively competes for and inhibits fusogenic SNARE machineries. Depletion of Stx2 in human β-cells improves insulin secretion by enhancing trans-SNARE complex assembly and cis-SNARE disassembly. Using a genetically-encoded reporter, glucose stimulation is shown to induce Stx2 flipping across the plasma membrane, which relieves its suppression of cytoplasmic fusogenic SNARE complexes to promote insulin secretion. Targeting the flipping efficiency of Stx2 profoundly modulates secretion, which could restore the impaired insulin secretion in diabetes. Here, we show that Stx2 acts to assist this precise tuning of insulin secretion in β-cells, including in diabetes.

Cooperation of membrane-translocated syntaxin4 and basement membrane for dynamic mammary epithelial morphogenesis

Mammary epithelia undergo dramatic morphogenesis after puberty. During pregnancy, luminal epithelial cells in ductal trees are arranged to form well-polarized cystic structures surrounded by a myoepithelial cell layer, an active supplier of the basement membrane (BM). Here, we identified a novel regulatory mechanism involved in this process by using a reconstituted BM-based three-dimensional culture and aggregates of a model mouse cell line, EpH4, that had either been manipulated for inducible expression of the t-SNARE protein syntaxin4 in intact or signal peptide-connected forms, or that were genetically deficient in syntaxin4. We found that cells extruded syntaxin4 upon stimulation with the lactogenic hormone prolactin, which in turn accelerated the turnover of E-cadherin. In response to extracellular expression of syntaxin4, cell populations that were less affected by the BM actively migrated and integrated into the cell layer facing the BM. Concurrently, the BM-facing cells, which were simultaneously stimulated with syntaxin4 and BM, acquired unique epithelial characteristics to undergo dramatic cellular arrangement for cyst formation. These results highlight the importance of the concerted action of extracellular syntaxin4 extruded in response to the lactogenic hormone and BM components in epithelial morphogenesis.

Membrane-tethered syntaxin-4 locally abrogates E-cadherin function and activates Smad signals, contributing to asymmetric mammary epithelial morphogenesis

Spatial and temporal epithelial-mesenchymal transition (EMT) is a critical event for the generation of asymmetric epithelial architectures. We found that only restricted cell populations in the morphogenic mammary epithelia extrude syntaxin-4, a plasmalemmal t-SNARE protein, and that epithelial cell clusters with artificial heterogenic presentation of extracellular syntaxin-4 undergo asymmetric morphogenesis. A previous study revealed that inducible expression of cell surface syntaxin-4 causes EMT-like cell behaviors in the clonal mammary epithelial cells, where laminin-mediated signals were abolished so that cells readily succumb to initiate EMT. The present study added new mechanistic insight into syntaxin-4-driven EMT-like cell behaviors. Extracellular syntaxin-4 directly perturbs E-cadherin-mediated epithelial cell-cell adhesion and activates Smad signals. We found that the epithelial cells activated Smad2/3 upon induction of expression of extracellular syntaxin-4, leading to the upregulation of certain transcriptional targets of these TGF-β signaling mediators. Intriguingly, however, mRNA expression of canonical EMT initiators, such as Snail and Slug, was unchanged. In addition, E-cadherin protein was steeply decreased, yet its transcriptional expression remained constant for a couple of days. We found that extracellular syntaxin-4 directly bound to E-cadherin and sequestered β-catenin from cell-cell contact sites, perturbing intercellular adhesive property. The functional ablation of E-cadherin by syntaxin-4 was further validated by L cells with stably expressing E-cadherin, in which cells shows intercellular adhesive property solely by E-cadherin. These results underline the role of local exportation of syntaxin-4 for onset of complex epithelial morphogenesis.

Homogeneous pancreatic cancer spheroids mimic growth pattern of circulating tumor cell clusters and macrometastases: displaying heterogeneity and crater-like structure on inner layer

PURPOSE

Pancreatic cancer 3D in vitro models including multicellular tumor spheroid (MCTS), single cell-derived tumor spheroid (SCTS), tissue-derived tumor spheroid, and organotypic models provided powerful platforms to mimic in vivo tumor. Recent work supports that circulating tumor cell (CTC) clusters are more efficient in metastasis seeding than single CTCs. The purpose of this study is to establish 3D culture models which can mimic single CTC, monoclonal CTC clusters, and the expansion of macrometastases.

METHODS

Seven pancreatic ductal adenocarcinoma cell lines were used to establish MCTS and SCTS using hanging drop and ultra-low attachment plates. Spheroid immunofluorescence staining, spheroid formation assay, immunoblotting, and literature review were performed to investigate molecular biomarkers and the morphological characteristics of pancreatic tumor spheroids.

RESULTS

Single cells experienced different growth patterns to form SCTS, like signet ring-like cells, blastula-like structures, and solid core spheroids. However, golf ball-like hollow spheroids could also be detected, especially when DanG and Capan-1 cells were cultivated with fibroblast-conditioned medium (p < 0.05). The size of golf ball-like hollow spheroids hardly grew after getting matured. Only DanG and Capan-1 could establish SCTS- and MCTS-derived hollow spheroids using hanging drop plates and ultra-low attachment plates. Other PDA cell lines could also establish tumor spheroid with hanging drop plates by adding methylated cellulose. Tumor spheroids derived from pancreatic cancer cell line DanG possessed asymmetrically distributed proliferation center, immune-checkpoint properties. ß-catenin, Ki-67, and F-actin were active surrounding the crater-like structure distributing on the inner layer of viable rim cover of the spheroids, which was relevant to well-differentiated tumor cells.

CONCLUSIONS

It is possible to establish 3D CTC cluster models from homogenous PDA cell lines using hanging drop and ultra-low attachment plates. PDA cell line displays its own intrinsic properties or heterogeneity. The mechanism of formation of the crater-like structure as well as golf ball-like structure needs further exploration.

Membrane translocation of t-SNARE protein syntaxin-4 abrogates ground-state pluripotency in mouse embryonic stem cells

Embryonic stem (ES) and induced pluripotent stem (iPS) cells are attractive tools for regenerative medicine therapies. However, aberrant cell populations that display flattened morphology and lose ground-state pluripotency often appear spontaneously, unless glycogen synthase kinase 3β (GSK3β) and mitogen-activated protein kinase kinase (MEK1/2) are inactivated. Here, we show that membrane translocation of the t-SNARE protein syntaxin-4 possibly is involved in this phenomenon. We found that mouse ES cells cultured without GSK3β/MEK1/2 inhibitors (2i) spontaneously extrude syntaxin-4 at the cell surface and that artificial expression of cell surface syntaxin-4 induces appreciable morphological changes and mesodermal differentiation through dephosphorylation of Akt. Transcriptome analyses revealed several candidate elements responsible for this, specifically, an E-to P-cadherin switch and a marked downregulation of Zscan4 proteins, which are DNA-binding proteins essential for ES cell pluripotency. Embryonic carcinoma cell lines F9 and P19CL6, which maintain undifferentiated states independently of Zscan4 proteins, exhibited similar cellular behaviors upon stimulation with cell surface syntaxin-4. The functional ablation of E-cadherin and overexpression of P-cadherin reproduced syntaxin-4-induced cell morphology, demonstrating that the E- to P-cadherin switch executes morphological signals from cell surface syntaxin-4. Thus, spontaneous membrane translocation of syntaxin-4 emerged as a critical element for maintenance of the stem-cell niche.

Extracellularly Extruded Syntaxin-4 Binds to Laminin and Syndecan-1 to Regulate Mammary Epithelial Morphogenesis

Epithelial morphogenesis in the mammary gland proceeds as a consequence of complex cell behaviors including apoptotic cell death and epithelial-mesenchymal transition (EMT); the extracellular matrix (ECM) protein laminin is crucially involved. Syntaxins mediate intracellular vesicular fusion, yet certain plasmalemmal members have been shown to possess latent extracellular functions. In this study, the extracellular subpopulation of syntaxin-4, extruded in response to the induction of differentiation or apoptosis in mammary epithelial cells, was detected. Using a tetracycline-repressive transcriptional system and clonal mammary epithelial cells, SCp2, we found that the expression of cell surface syntaxin-4 elicits EMT-like cell behaviors. Intriguingly, these cells did not up-regulate key transcription factors associated with the canonical EMT such as snail, slug, or twist, and repressed translation of E-cadherin. Concurrently, the cells completely evaded the cellular aggregation/rounding triggered by a potent EMT blocker laminin-111. We found that the recombinant form of syntaxin-4 not only bound to laminin but also latched onto the glycosaminoglycan (GAG) side chains of syndecan-1, a laminin receptor that mediates epithelial morphogenesis. Thus, temporal extracellular extrusion of syntaxin-4 emerged as a novel regulatory element for laminin-induced mammary epithelial cell behaviors. J. Cell. Biochem. 118: 686-698, 2017. © 2016 Wiley Periodicals, Inc.

HIV and HCV Co-Culture Promotes Profibrogenic Gene Expression through an Epimorphin-Mediated ERK Signaling Pathway in Hepatic Stellate Cells

Accelerated fibrosis in patients co-infected with hepatitis C virus (HCV) and human immunodeficiency virus (HIV) has been a major cause of mortality in the highly active anti-retroviral therapy (HAART) era. However, the role of co-infection in accelerating the progression of liver fibrosis, particularly with regard to the effects of co-infection on hepatic stellate cells (HSCs), remains unclear. We hypothesized that HIV and HCV induce liver fibrosis synergistically by altering the regulation of epimorphin production, and thereby indirectly alter HSC function. Here, we examined the effects of epimorphin on HSC proliferation and invasion, and the changes in fibrogenesis-related gene activity in HSCs (LX2) in the presence of inactivated CXCR4-tropic HIV and HCV (JFH1). The combination of HIV and HCV significantly increased epimorphin expression, which increased the proliferation and invasion capabilities of HSCs. Epimorphin also induced the expression of profibrogenic tissue inhibitor of metalloproteinase 1 (TIMP1) in an extracellular signal-regulated kinase (ERK)-dependent manner. These data indicated that the effects of HIV/HCV co-infection on hepatic fibrosis might be mediated in part by EPM. Strategies to limit the expression of EPM might represent a novel therapeutic approach to prevent the progression of hepatic fibrosis during HIV/HCV co-infection.

Regulation of epithelial-mesenchymal transition in breast cancer cells by cell contact and adhesion

Epithelial-mesenchymal transition (EMT) is a physiological program that is activated during cancer cell invasion and metastasis. We show here that EMT-related processes are linked to a broad and conserved program of transcriptional alterations that are influenced by cell contact and adhesion. Using cultured human breast cancer and mouse mammary epithelial cells, we find that reduced cell density, conditions under which cell contact is reduced, leads to reduced expression of genes associated with mammary epithelial cell differentiation and increased expression of genes associated with breast cancer. We further find that treatment of cells with matrix metalloproteinase-3 (MMP-3), an inducer of EMT, interrupts a defined subset of cell contact-regulated genes, including genes encoding a variety of RNA splicing proteins known to regulate the expression of Rac1b, an activated splice isoform of Rac1 known to be a key mediator of MMP-3-induced EMT in breast, lung, and pancreas. These results provide new insights into how MMPs act in cancer progression and how loss of cell-cell interactions is a key step in the earliest stages of cancer development.

Extracellularly Extruded Syntaxin-4 Is a Potent Cornification Regulator of Epidermal Keratinocytes

In the skin epidermis, keratinocytes undergo anchorage-dependent cornification, which gives rise to stratified multilayers, each with a distinct differentiation feature. The active formation of the cornified cell envelope (CCE), an important element in the skin barrier, occurs in keratinocytes of the upper epidermal layers and impacts their terminal differentiation. In the present study, we identified the extracellularly extruded syntaxin-4 as a potent differentiation regulator of epidermal keratinocytes. We found that differentiation stimuli led to the acceleration of syntaxin-4 exposure at the keratinocyte cell surface and that the artificial control of extracellular syntaxin-4, either by the forced expression of several syntaxin-4 mutants with structural alterations at the putative functional core site (AIEPQK), or by using antagonistic circular peptides containing this core sequence, dramatically influenced the CCE formation, with spatial misexpression of TGase1 and involucrin. We also found that the topical application of a peptide that exerted the most prominent antagonistic activity for syntaxin-4, named ST4n1, evidently prevented the formation of the hyperplastic and hyperkeratotic epidermis generated by physical irritation in HR-1 mice skin. Collectively, these results demonstrate that extracellularly extruded syntaxin-4 is a potent regulator of CCE differentiation, and that ST4n1 has potential as a clinically applicable reagent for keratotic skin lesions.

CCAAT/enhancer binding protein beta (C/EBPβ) isoform balance as a regulator of epithelial-mesenchymal transition in mouse mammary epithelial cells

Activation of the epithelial-mesenchymal transition (EMT) program promotes cell invasion and metastasis, and is reversed through mesenchymal-epithelial transition (MET) after formation of distant metastases. Here, we show that an imbalance of gene products encoded by the transcriptional factor C/EBPβ, LAP (liver-enriched activating protein) and LIP (liver-enriched inhibitory protein), can regulate both EMT- and MET-like phenotypic changes in mouse mammary epithelial cells. By using tetracycline repressive LIP expression constructs, we found that SCp2 cells, a clonal epithelial line of COMMA1-D cells, expressed EMT markers, lost the ability to undergo alveolar-like morphogenesis in 3D Matrigel, and acquired properties of benign adenoma cells. Conversely, we found that inducible expression of LAP in SCg6 cells, a clonal fibroblastic line of COMMA1-D cells, began to express epithelial keratins with suppression of proliferation. The overexpression of the C/EBPβ gene products in these COMMA1-D derivatives was suppressed by long-term cultivation on tissue culture plastic, but gene expression was maintained in cells grown on Matrigel or exposed to proteasome inhibitors. Thus, imbalances of C/EBPβ gene products in mouse mammary epithelial cells, which are affected by contact with basement membrane, are defined as a potential regulator of metastatic potential.

Milk secretion: The role of SNARE proteins

During lactation, polarized mammary epithelial secretory cells (MESCs) secrete huge quantities of the nutrient molecules that make up milk, i.e. proteins, fat globules and soluble components such as lactose and minerals. Some of these nutrients are only produced by the MESCs themselves, while others are to a great extent transferred from the blood. MESCs can thus be seen as a crossroads for both the uptake and the secretion with cross-talks between intracellular compartments that enable spatial and temporal coordination of the secretion of the milk constituents. Although the physiology of lactation is well understood, the molecular mechanisms underlying the secretion of milk components remain incompletely characterized. Major milk proteins, namely caseins, are secreted by exocytosis, while the milk fat globules are released by budding, being enwrapped by the apical plasma membrane. Prolactin, which stimulates the transcription of casein genes, also induces the production of arachidonic acid, leading to accelerated casein transport and/or secretion. Because of their ability to form complexes that bridge two membranes and promote their fusion, SNARE (Soluble N-ethylmaleimide-Sensitive Factor Attachment Protein Receptor) proteins are involved in almost all intracellular trafficking steps and exocytosis. As SNAREs can bind arachidonic acid, they could be the effectors of the secretagogue effect of prolactin in MESCs. Indeed, some SNAREs have been observed between secretory vesicles and lipid droplets suggesting that these proteins could not only orchestrate the intracellular trafficking of milk components but also act as key regulators for both the coupling and coordination of milk product secretion in response to hormones.

Epimorphin deletion inhibits polyposis in the Apcmin/+ mouse model of colon carcinogenesis via decreased myofibroblast HGF secretion

Interactions between the epithelium and surrounding mesenchyme/stroma play an important role in normal gut morphogenesis, the epithelial response to injury, and epithelial carcinogenesis. The tumor microenvironment, composed of stromal cells including myofibroblasts and immune cells, regulates tumor growth and the cancer stem cell niche. Deletion of epimorphin (Epim), a syntaxin family member expressed in myofibroblasts and macrophages, results in partial protection from colitis and from inflammation-induced colon cancer in mice. We sought to determine whether epimorphin deletion protects from polyposis in the Apcmin/+ mouse model of intestinal carcinogenesis. Epim-/- mice were crossed to Apcmin/+ mice; Apcmin/+ and Apcmin/+/Epim-/- mice were killed at 3 mo of age. Polyp numbers and sizes were quantified in small intestine and colon, and gene expression analyses for pathways relevant to epithelial carcinogenesis were performed. Primary myofibroblast cultures were isolated, and expression and secretion of selected growth factors from Apcmin/+ and Apcmin/+/Epim-/- myofibroblasts were examined by ELISA. Small bowel polyposis was significantly inhibited in Apcmin/+/Epim-/- compared with Apcmin/+ mice. Apcmin/+/Epim-/- compared with Apcmin/+ polyps and adjacent uninvolved intestinal mucosa had increased transforming growth factor-β (TGF-β) expression and signaling with increased P-Smad2/3 expression. Myofibroblasts isolated from Apcmin/+/Epim-/- vs. Apcmin/+ mice had markedly decreased hepatocyte growth factor (HGF) expression and secretion. We concluded that Epim deletion inhibits polyposis in Apcmin/+ mice, associated with increased mucosal TGF-β signaling and decreased myofibroblast HGF expression and secretion. Our data suggest that Epim deletion reduces tumorigenicity of the stromal microenvironment.

Epimorphin-induced MET sensitizes ovarian cancer cells to platinum

Distinctive genotypic and phenotypic features of ovarian cancer via epithelial-mesenchymal transition (EMT) have been correlated with drug resistance and disease recurrence. We investigated whether therapeutic reversal of EMT could re-sensitize ovarian cancer cells (OCCs) to existing chemotherapy. We report that epimorphin, a morphogenic protein, has pivotal control over mesenchymal versus epithelial cell lineage decision of the putative OCCs. Exposure to epimorphin induced morphological changes reminiscent of mesenchymal-to-epithelial transition (MET), but in a dose dependent manner, i.e., at 10 µg/mL of epimorphin cells obtain a more mesenchymal-like morphology while at 20 µg/mL of epimorphin cells display an epithelial morphology. The latter changes were accompanied by suppression of mesenchymal markers, such as vimentin (∼8-fold↓, p<0.02), Twist1 (∼7-fold↓, p<0.03), dystroglycan (∼4-fold↓, p<0.01) and palladin (∼3-fold↓, p<0.01). Conversely, significant elevations of KLF4 (∼28-fold↑, p<0.002), β-catenin (∼6-fold↑, p<0.004), EpCAM (∼6-fold↑, p<0.0002) and occludin (∼15-fold↑, p<0.004) mRNAs as part of the commitment to the epithelial cell lineage were detected in response to 20 µg/mL of exogenous epimorphin. Changes in occludin mRNA levels were accompanied by a parallel, albeit weaker expression at the protein level (∼5-fold↑, p<0.001). Likewise, acquisition of epithelial-like properties, including mucin1, CK19, and β-catenin gene expression, was also obtained following epimorphin treatment. Further, MMP3 production was found to be reduced whereas laminin secretion was strongly amplified upon epimorphin-induced MET. These results suggest there is a dosage window for actions of epimorphin on cellular differentiation, wherein it can either suppress or enhance epithelial differentiation of OCCs. Importantly, induction of epithelial-like phenotypes by epimorphin led to an enhanced sensitivity to carboplatin. Overall, we demonstrate that epimorphin can revert OCCs away from their mesenchymal phenotype and toward an epithelial phenotype, thereby enhancing their sensitivity to a front-line chemotherapeutic agent.

Epimorphin is a novel regulator of the progesterone receptor isoform-a

Epimorphin/syntaxin-2 is a membrane-tethered protein localized extracellularly (Epim) and intracellularly (Stx-2). The extracellular form Epim stimulates morphogenic processes in a range of tissues, including in murine mammary glands where its overexpression in luminal epithelial cells is sufficient to drive hyperplasia and neoplasia. We analyzed WAP-Epim transgenic mice to gain insight into how Epim promotes malignancy. Ectopic overexpression of Epim during postnatal mammary gland development led to early side-branching onset, precocious bud formation, and increased proliferation of mammary epithelial cells. Conversely, peptide-based inhibition of Epim function reduced side branching. Because increased side branching and hyperplasia occurs similarly in mice upon overexpression of the progesterone receptor isoform-a (Pgr-a), we investigated whether Epim exhibits these phenotypes through Pgr modulation. Epim overexpression indeed led to a steep upregulation of both total Pgr mRNA and Pgr-a protein levels. Notably, the Pgr antagonist RU486 abrogated Epim-induced ductal side branching, mammary epithelial cell proliferation, and bud formation. Evaluation of Epim signaling in a three-dimensional ex vivo culture system showed that its action was dependent on binding to its extracellular receptor, integrin-αV, and on matrix metalloproteinase 3 activity downstream of Pgr-a. These findings elucidate a hitherto unknown transcriptional regulator of Pgr-a, and shed light on how overexpression of Epim leads to malignancy.

PI3K regulates branch initiation and extension of cultured mammary epithelia via Akt and Rac1 respectively

The tree-like architecture of the mammary gland is generated by branching morphogenesis, which is regulated by many signals from the microenvironment. Here we examined how signaling downstream of phosphoinositide 3-kinase (PI3K) regulates different steps of mammary branching using three-dimensional culture models of the mammary epithelial duct. We found that PI3K was required for both branch initiation and elongation. Activated Akt was enhanced at branch initiation sites where its negative regulator, PTEN, was blocked by signaling via Sprouty2 (SPRY2); inhibiting Akt prevented branch initiation. The pattern of SPRY2 expression, and thus of Akt activation and branch initiation, was controlled by mechanical signaling from endogenous cytoskeletal contractility. In contrast, activated GTP-bound Rac1 localized to the leading edge of nascent branches and was required for branch elongation. These data suggest that the PI3K network integrates mechanical and biochemical signaling to control branching morphogenesis of mammary epithelial cells.

Phosphatidylserine externalization and membrane blebbing are involved in the nonclassical export of FGF1

The mechanisms of nonclassical export of signal peptide-less proteins remain insufficiently understood. Here, we demonstrate that stress-induced unconventional export of FGF1, a potent and ubiquitously expressed mitogenic and proangiogenic protein, is associated with and dependent on the formation of membrane blebs and localized cell surface exposure of phosphatidylserine (PS). In addition, we found that the differentiation of promonocytic cells results in massive FGF1 release, which also correlates with membrane blebbing and exposure of PS. These findings indicate that the externalization of acidic phospholipids could be used as a pharmacological target to regulate the availability of FGF1 in the organism.

Integrins in mammary development

Integrins are ubiquitously expressed major cell surface receptors for extracellular matrix. Integrin interaction with their extracellular ligands triggers activation of the intracellular signaling pathways that control cell shape, motility, proliferation, survival, cell-type-specific gene expression. In this review, we summarize recent studies analyzing contribution of integrins to the control of the mammary morphogenesis and differentiation, function and maintenance of mammary stem and progenitor cells and resume the data from mouse models revealing the contribution of the integrin-mediated signaling to mammary tumorigenesis.

Regulation of non-classical FGF1 release and FGF-dependent cell transformation by CBF1-mediated notch signaling

FGF1, a widely expressed proangiogenic factor involved in tissue repair and carcinogenesis, is released from cells through a non-classical pathway independent of endoplasmic reticulum and Golgi. Although several proteins participating in FGF1 export were identified, genetic mechanisms regulating this process remained obscure. We found that FGF1 export and expression are regulated through Notch signaling mediated by transcription factor CBF1 and its partner MAML. The expression of a dominant negative (dn) form of CBF1 in 3T3 cells induces transcription of FGF1 and sphingosine kinase 1 (SphK1), which is a component of FGF1 export pathway. dnCBF1 expression stimulates the stress-independent release of transduced FGF1 from NIH 3T3 cells and endogenous FGF1 from A375 melanoma cells. NIH 3T3 cells transfected with dnCBF1 form colonies in soft agar and produce rapidly growing highly angiogenic tumors in nude mice. The transformed phenotype of dnCBF1 transfected cells is efficiently blocked by dn forms of FGF receptor 1 and S100A13, which is a component of FGF1 export pathway. FGF1 export and acceleration of cell growth induced by dnCBF1 depend on SphK1. Similar to dnCBF1, dnMAML transfection induces FGF1 expression and release, and accelerates cell proliferation. The latter effect is strongly decreased in FGF1 null cells. We suggest that the regulation of FGF1 expression and release by CBF1-mediated Notch signaling can play an important role in tumor formation.

Role of epimorphin in bile duct formation of rat liver epithelial stem-like cells: involvement of small G protein RhoA and C/EBPβ

Epimorphin/syntaxin 2 is a high conserved and very abundant protein involved in epithelial morphogenesis in various organs. We have shown recently that epimorphin (EPM), a protein exclusively expressed on the surface of hepatic stellate cells and myofibroblasts of the liver, induces bile duct formation of hepatic stem-like cells (WB-F344 cells) in a putative biophysical way. Therefore, the aim of this study was to present some of the molecular mechanisms by which EPM mediates bile duct formation. We established a biliary differentiation model by co-culture of EPM-overexpressed mesenchymal cells (PT67(EPM)) with WB-F344 cells. Here, we showed that EPM could promote WB-F344 cells differentiation into bile duct-like structures. Biliary differentiation markers were also elevated by EPM including Yp, Cx43, aquaporin-1, CK19, and gamma glutamyl transpeptidase (GGT). Moreover, the signaling pathway of EPM was analyzed by focal adhesion kinase (FAK), extracellular regulated kinase 1/2 (ERK1/2), and RhoA Western blot. Also, a dominant negative (DN) RhoA-WB-F344 cell line (WB(RhoA-DN)) was constructed. We found that the levels of phosphorylation (p) of FAK and ERK1/2 were up-regulated by EPM. Most importantly, we also showed that RhoA is necessary for EPM-induced activation of FAK and ERK1/2 and bile duct formation. In addition, a dual luciferase-reporter assay and CHIP assay was performed to reveal that EPM regulates GGT IV and GGT V expression differentially, possibly mediated by C/EBPβ. Taken together, these data demonstrated that EPM regulates bile duct formation of WB-F344 cells through effects on RhoA and C/EBPβ, implicating a dual aspect of this morphoregulator in bile duct epithelial morphogenesis.

Epimorphin promotes human hepatocellular carcinoma invasion and metastasis through activation of focal adhesion kinase/extracellular signal-regulated kinase/matrix metalloproteinase-9 axis

The high incidence rate of hepatocellular carcinoma (HCC) is mainly the result of frequent metastasis and tumor recurrence. Unfortunately, the underlying molecular mechanisms driving HCC metastasis are still not fully understood. It has been demonstrated that tumor stroma cells contribute to primary tumor growth and metastasis. Within the HCC environment, activated hepatic stellate cells (HSCs) can release a number of molecules and enhance cancer cell proliferation and invasiveness in a paracrine manner. Here, for the first time, we demonstrate that epimorphin (EPM; also called syntaxin-2), an extracellular protein, is strongly elevated in activated HSCs within tumor stroma. We show that knockdown of EPM expression in HSCs substantially abolishes their effects on cancer cell invasion and metastasis. Ectopic expression of EPM in HCC cancer cells enhances their invasiveness; we demonstrate that the cells expressing EPM have markedly increased metastasis potential. Furthermore, EPM-mediated invasion and metastasis of cancer cells is found to require up-regulation of matrix metalloproteinase-9 (MMP-9) through the activation of focal adhesion kinase (FAK)/extracellular signal-regulated kinase (ERK) axis.

CONCLUSION

Our results show that EPM, secreted by activated HSCs within HCC stroma, promotes invasion and metastasis of cancer cells by activating MMP-9 expression through the FAK-ERK pathway.

A polymorphism in the integrin αV subunit gene affects the progression of primary biliary cirrhosis in Japanese patients

BACKGROUND

Accumulating evidence indicates that multiple genetic factors are involved in the pathogenesis of primary biliary cirrhosis (PBC). The aim of this study was to investigate whether polymorphisms of the integrin αV subunit gene (ITGAV), a component of integrin αVβ6, which plays an important role in the process of fibrosis, are associated with susceptibility to the onset and/or progression of PBC.

METHODS

In the primary study, eight tag single nucleotide polymorphisms (SNPs) in ITGAV were analyzed by polymerase chain reaction (PCR)-restriction fragment length polymorphism, direct DNA sequencing, or high-resolution melting curve analysis in 309 Japanese patients with PBC who were registered in the National Hospital Organization Study Group for Liver Disease in Japan (PBC cohort I) and 293 gender-matched healthy Japanese volunteers (control subjects). For the replication study, 35 PBC patients who progressed to end-stage hepatic failure and underwent liver transplantation (PBC cohort II) were also analyzed.

RESULTS

Three tag SNPs (rs3911238, rs10174098, and rs1448427) in ITGAV were significantly associated with the severe progression of PBC, but not with susceptibility to the onset of PBC, in the primary study (PBC cohort I). Among these SNPs, rs1448427 was also significantly associated with the severe progression to end-stage hepatic failure in the replication study of PBC patients who underwent liver transplantation (PBC cohort II).

CONCLUSIONS

ITGAV is a genetic determinant for the severe progression of PBC in Japanese patients. Genetic polymorphisms of ITGAV may be useful for identifying high-risk Japanese PBC patients, including those who will require liver transplantation, at the time of initial diagnosis.

A culture system for the live analysis of successive developmental processes and the morphological control of mammalian vertebral cartilage

The mesoderm-derived segmental somite differentiates into dermomyotome and sclerotome, the latter of which undergoes vertebrogenesis to spinal cartilage and ultimately to vertebral bones. However, analysis and manipulation of the developing mammalian vertebrae in the same embryo has been infeasible because of their placental-dependent embryogenesis. Here, we report a novel culture system of the mouse embryonic tailbud, by which the developmental processes of mammalian vertebral cartilage are traceable and manipulatable in the same sample. The anaplastic segmental somites/sclerotomes in the tailbud of 13 gestational day (g.d.) embryo that are structurally continuous to the vertebral column underwent progressive vertebrogenesis when (1) the ectoderm-derived nascent epidermis was microsurgically removed prior to cultivation, and (2) the sample was incubated at the air-medium interface. After cultivation for 5 days, the size and shape of the instructed vertebral cartilage showed features comparable to well-differentiated body vertebra along with the expression of the cartilage marker collagen type II, suggesting that aggressive differentiation of the sclerotomal cell lineage was achieved. In the presence of recombinant bone morphogenic protein (BMP) and Noggin, or adenoviral particles for extracellular epimorphin, dramatic alteration of the vertebral morphology ensued in the explants. Thus, this model system provides an approach to study the detailed molecular mechanisms of mammalian vertebrogenesis and enables pretreatment strategies of precartilagious fragments for improving the efficacy of subsequent transplantation.

Involvement of epimorphin in the repair of experimental renal fibrosis in mice

Interaction between epithelial cells and mesenchymal cells is essential in normal organ morphogenesis and in tissue repair after injury. Epimorphin, a mesenchymal protein that regulates epithelial morphogenesis through epithelial-mesenchymal interactions, has recently attracted attention as an important modulator of tissue repair. In this study we analyzed the role of epimorphin in renal fibrosis. We first found a progressive increase in epimorphin expression corresponding to the progression of renal fibrosis in mice with unilateral ureteral obstruction (UUO). To determine whether this expression has a role in the repair or progression of renal fibrosis, we analyzed a model of renal fibrosis repair, the UUO-release (UUO-R) model. Epimorphin expression was increased at 3 and 7 days after the UUO-R rather than on the day of release, but was decreased at 21 days after the release. Inhibition of endogenous epimorphin with anti-epimorphin antibody (MC-1) significantly delayed the repair of fibrosis. When compared with normal-IgG-injected mice, MC-1-injected mice showed significantly decreased renal matrix metalloproteinase (MMP)-2 and MMP-9 expressions by western blotting and increased expression of TGF-beta and collagen-I mRNA by real-time RT-PCR. Recombinant epimorphin induced prominent increases in MMP-2 and MMP-9 activities in the culture media of renal interstitial fibroblasts in vitro. These findings indicate that epimorphin has a pivotal role in the repair of renal fibrosis by modulating both extracellular matrix (ECM) degradation and its production.

Epimorphin deletion protects mice from inflammation-induced colon carcinogenesis and alters stem cell niche myofibroblast secretion

Epithelial-mesenchymal interactions regulate normal gut epithelial homeostasis and have a putative role in inflammatory bowel disease and colon cancer pathogenesis. Epimorphin is a mesenchymal and myofibroblast protein with antiproliferative, promorphogenic effects in intestinal epithelium. We previously showed that deletion of epimorphin partially protects mice from acute colitis, associated with an increase in crypt cell proliferation. Here we explored the potential therapeutic utility of modulating epimorphin expression by examining the effects of epimorphin deletion on chronic inflammation-associated colon carcinogenesis using the azoxymethane/dextran sodium sulfate (AOM/DSS) model. We found that mice in which epimorphin expression was absent had a marked reduction in incidence and extent of colonic dysplasia. Furthermore, epimorphin deletion in myofibroblasts altered the morphology and growth of cocultured epithelial cells. Loss of epimorphin affected secretion of soluble mesenchymal regulators of the stem cell niche such as Chordin. Importantly, IL-6 secretion from LPS-treated epimorphin-deficient myofibroblasts was completely inhibited, and stromal IL-6 expression was reduced in vivo. Taken together, these data show that epimorphin deletion inhibits chronic inflammation-associated colon carcinogenesis in mice, likely as a result of increased epithelial repair, decreased myofibroblast IL-6 secretion, and diminished IL-6-induced inflammation. Furthermore, we believe that modulation of epimorphin expression may have therapeutic benefits in appropriate clinical settings.

Epimorphin regulates bile duct formation via effects on mitosis orientation in rat liver epithelial stem-like cells

Understanding how hepatic precursor cells can generate differentiated bile ducts is crucial for studies on epithelial morphogenesis and for development of cell therapies for hepatobiliary diseases. Epimorphin (EPM) is a key morphogen for duct morphogenesis in various epithelial organs. The role of EPM in bile duct formation (DF) from hepatic precursor cells, however, is not known. To address this issue, we used WB-F344 rat epithelial stem-like cells as model for bile duct formation. A micropattern and a uniaxial static stretch device was used to investigate the effects of EPM and stress fiber bundles on the mitosis orientation (MO) of WB cells. Immunohistochemistry of liver tissue sections demonstrated high EPM expression around bile ducts in vivo. In vitro, recombinant EPM selectively induced DF through upregulation of CK19 expression and suppression of HNF3alpha and HNF6, with no effects on other hepatocytic genes investigated. Our data provide evidence that EPM guides MO of WB-F344 cells via effects on stress fiber bundles and focal adhesion assembly, as supported by blockade EPM, beta1 integrin, and F-actin assembly. These blockers can also inhibit EPM-induced DF. These results demonstrate a new biophysical action of EPM in bile duct formation, during which determination of MO plays a crucial role.

Protein folding does not prevent the nonclassical export of FGF1 and S100A13

Newly synthesized proteins are usually exported through the endoplasmic reticulum (ER) and Golgi due to the presence in their primary sequence of a hydrophobic signal peptide that is recognized by the ER translocation system. However, some secreted proteins lack a signal peptide and are exported independently of ER-Golgi. Fibroblast growth factor (FGF)1 is included in this group of polypeptides, as well as S100A13 that is a small calcium-binding protein critical for FGF1 export. Classically secreted proteins are transported into ER in their unfolded states. To determine the role of protein tertiary structure in FGF1 export through the cell membrane, we produced the chimeras of FGF1 and S100A13 with dihydrofolate reductase (DHFR). The specific DHFR inhibitor, aminopterin, prevents its unfolding. We found that aminopterin did not inhibit the release of FGF1:DHFR and S100A13:DHFR. Thus, FGF1 and S100A13 can be exported in folded conformation.

Single proteins might have dual but related functions in intracellular and extracellular microenvironments

The maintenance of organ homeostasis and the control of an appropriate response to environmental alterations require the intimate coordination of cellular functions and tissue organization. An important component of this coordination could be provided by proteins that can have distinct but linked functions on both sides of the plasma membrane. We present a model that proposes that unconventional secretion provides a mechanism through which single proteins can integrate complex tissue functions.

Homology with vesicle fusion mediator syntaxin-1a predicts determinants of epimorphin/syntaxin-2 function in mammary epithelial morphogenesis

We have shown that branching morphogenesis of mammary ductal structures requires the action of the morphogen epimorphin/syntaxin-2. Epimorphin, originally identified as an extracellular molecule, is identical to syntaxin-2, an intracellular molecule that is a member of the extensively investigated syntaxin family of proteins that mediate vesicle trafficking. We show here that, although epimorphin/syntaxin-2 is highly homologous to syntaxin-1a, only epimorphin/syntaxin-2 can stimulate mammary branching morphogenesis. We construct a homology model of epimorphin/syntaxin-2 based on the published structure of syntaxin-1a, and we use this model to identify the structural motif responsible for the morphogenic activity. We identify four residues located within the cleft between helices B and C that differ between syntaxin-1a and epimorphin/syntaxin-2; through site-directed mutagenesis of these four amino acids, we confer the properties of epimorphin for cell adhesion, gene activation, and branching morphogenesis onto the inactive syntaxin-1a template. These results provide a dramatic demonstration of the use of structural information about one molecule to define a functional motif of a second molecule that is related at the sequence level but highly divergent functionally.

Candida albicans cell wall proteins

The Candida albicans cell wall maintains the structural integrity of the organism in addition to providing a physical contact interface with the environment. The major components of the cell wall are fibrillar polysaccharides and proteins. The proteins of the cell wall are the focus of this review. Three classes of proteins are present in the candidal cell wall. One group of proteins attach to the cell wall via a glycophosphatidylinositol remnant or by an alkali-labile linkage. A second group of proteins with N-terminal signal sequences but no covalent attachment sequences are secreted by the classical secretory pathway. These proteins may end up in the cell wall or in the extracellular space. The third group of proteins lack a secretory signal, and the pathway(s) by which they become associated with the surface is unknown. Potential constituents of the first two classes have been predicted from analysis of genome sequences. Experimental analyses have identified members of all three classes. Some members of each class selected for consideration of confirmed or proposed function, phenotypic analysis of a mutant, and regulation by growth conditions and transcription factors are discussed in more detail.

Cell-surface and mitotic-spindle RHAMM: moonlighting or dual oncogenic functions?

Tumor cells use a wide variety of post-translational mechanisms to modify the functional repertoire of their transcriptome. One emerging but still understudied mechanism involves the export of cytoplasmic proteins that then partner with cell-surface receptors and modify both the surface-display kinetics and signaling properties of these receptors. Recent investigations demonstrate moonlighting roles for the proteins epimorphin, FGF1, FGF2, PLK1 and Ku80, to name a few, during oncogenesis and inflammation. Here, we review the molecular mechanisms of unconventional cytoplasmic-protein export by focusing on the mitotic-spindle/hyaluronan-binding protein RHAMM, which is hyper-expressed in many human tumors. Intracellular RHAMM associates with BRCA1 and BARD1; this association attenuates the mitotic-spindle-promoting activity of RHAMM that might contribute to tumor progression by promoting genomic instability. Extracellular RHAMM-CD44 partnering sustains CD44 surface display and enhances CD44-mediated signaling through ERK1 and ERK2 (ERK1/2); it might also contribute to tumor progression by enhancing and/or activating the latent tumor-promoting properties of CD44. The unconventional export of proteins such as RHAMM is a novel process that modifies the roles of tumor suppressors and promoters, such as BRCA1 and CD44, and might provide new targets for therapeutic intervention.

Secretion without Golgi

A growing number of proteins devoid of signal peptides have been demonstrated to be released through the non-classical pathways independent of endoplasmic reticulum and Golgi. Among them are two potent proangiogenic cytokines FGF1 and IL1alpha. Stress-induced transmembrane translocation of these proteins requires the assembly of copper-dependent multiprotein release complexes. It involves the interaction of exported proteins with the acidic phospholipids of the inner leaflet of the cell membrane and membrane destabilization. Not only stress, but also thrombin treatment and inhibition of Notch signaling stimulate the export of FGF1. Non-classical release of FGF1 and IL1alpha presents a promising target for treatment of cardiovascular, oncologic, and inflammatory disorders.

Depletion of apical transport proteins perturbs epithelial cyst formation and ciliogenesis

Epithelial cells are vital for maintaining the complex architecture and functions of organs in the body. Directed by cues from the extracellular matrix, cells polarize their surface into apical and basolateral domains, and connect by extensive cell-cell junctions to form tightly vowen epithelial layers. In fully polarized cells, primary cilia project from the apical surface. Madin-Darby canine kidney (MDCK) cells provide a model to study organization of cells as monolayers and also in 3D in cysts. In this study retrovirus-mediated RNA interference (RNAi) was used to generate a series of knockdowns (KDs) for proteins implicated in apical transport: annexin-13, caveolin-1, galectin-3, syntaxin-3, syntaxin-2 and VIP17 and/or MAL. Cyst cultures were then employed to study the effects of these KDs on epithelial morphogenesis. Depletion of these proteins by RNAi stalled the development of the apical lumen in cysts and resulted in impaired ciliogenesis. The most severe ciliary defects were observed in annexin-13 and syntaxin-3 KD cysts. Although the phenotypes demonstrate the robustness of the formation of the polarized membrane domains, they indicate the important role of apical membrane biogenesis in epithelial organization.

Epimorphin, a morphogenic protein, induces proteases in rodent hepatocytes through NF-kappaB

BACKGROUND/AIMS

Epimorphin, expressed by hepatic stellate cells in the liver, directs normal morphogenesis in various organs. The aim of this study was to clarify the mechanism by which epimorphin functions as a morphogen in vitro.

METHODS

Male Balb/c mice and Sprague-Dawley rats were used. First, we explored the relationship between epimorphin expression and distribution of protease-positive cells in carbon tetrachloride-induced acute liver injury. We then examined protease levels in cultured hepatocytes and signal transduction of epimorphin. Finally, we determined the requirement for proteases and NF-kappaB in spheroid formation induced by epimorphin.

RESULTS

Epimorphin expression was enhanced in injured areas during late recovery phase, in which protease-positive hepatocytes were localized adjacent to epimorphin-expressing cells. In vitro, epimorphin induced matrix metalloproteinase (MMP) 9, MMP 3 and urokinase type plasminogen activator (uPA) in hepatocytes. NF-kappaB mediated these protease expressions in hepatocytes. These proteases were required for epimorphin-induced and Matrigel induced spheroid. An epimorphin-neutralizing antibody also blocked spheroid formation on Matrigel, which contained epimorphin. In addition, NF-kappaB activation was also required for spheroid formation.

CONCLUSION

Epimorphin elicits hepatocyte spheroids by inducing proteases in rodent hepatocytes through NF-kappaB.