Hepatocyte growth factor induces MDCK cell morphogenesis without causing loss of tight junction functional integrity

Using Microfluidics to Align Matrix Architecture and Generate Chemokine Gradients Promotes Directional Branching in a Model of Epithelial Morphogenesis

The mechanical cue of fiber alignment plays a key role in the development of various tissues in the body. The ability to study the effect of these stimuli in vitro has been limited previously. Here, we present a microfluidic device capable of intrinsically generating aligned fibers using the microchannel geometry. The device also features tunable interstitial fluid flow and the ability to form a morphogen gradient. These aspects allow for the modeling of complex tissues and to differentiate cell response to different stimuli. To demonstrate the abilities of our device, we incorporated luminal epithelial cysts into our device and induced growth factor stimulation. We found the mechanical cue of fiber alignment to play a dominant role in cell elongation and the ability to form protrusions was dependent on cadherin-3. Together, this work serves as a springboard for future potential with these devices to answer questions in developmental biology and complex diseases such as cancers.

Fosgonimeton, a Novel Positive Modulator of the HGF/MET System, Promotes Neurotrophic and Procognitive Effects in Models of Dementia

All types of dementia, including Alzheimer's disease, are debilitating neurodegenerative conditions marked by compromised cognitive function for which there are few effective treatments. Positive modulation of hepatocyte growth factor (HGF)/MET, a critical neurotrophic signaling system, may promote neuronal health and function, thereby addressing neurodegeneration in dementia. Here, we evaluate a series of novel small molecules for their ability to (1) positively modulate HGF/MET activity, (2) induce neurotrophic changes and protect against neurotoxic insults in primary neuron culture, (3) promote anti-inflammatory effects in vitro and in vivo, and (4) reverse cognitive deficits in animal models of dementia. Through screening studies, the compound now known as fosgonimeton-active metabolite (fosgo-AM) was identified by use of immunocytochemistry to be the most potent positive modulator of HGF/MET and was selected for further testing. Primary hippocampal neurons treated with fosgo-AM showed enhanced synaptogenesis and neurite outgrowth, supporting the neurotrophic effects of positive modulators of HGF/MET. Additionally, fosgo-AM protected against neurotoxic insults in primary cortical neuron cultures. In vivo, treatment with fosgo-AM rescued cognitive deficits in the rat scopolamine amnesia model of dementia. Although fosgo-AM demonstrated several procognitive effects in vitro and in vivo, a prodrug strategy was used to enhance the pharmacological properties of fosgo-AM, resulting in the development of fosgonimeton (ATH-1017). The effect of fosgonimeton on cognition was confirmed in a lipopolysaccharide (LPS)-induced neuroinflammatory mouse model of dementia. Together, the results of these studies support the potential of positive modulators of HGF/MET to be used as novel therapeutics and suggest the drug candidate fosgonimeton might protect against neurodegeneration and be therapeutic in the management of Alzheimer's disease and other types of dementia.

Resveratrol Suppresses Prostate Cancer Epithelial Cell Scatter/Invasion by Targeting Inhibition of Hepatocyte Growth Factor (HGF) Secretion by Prostate Stromal Cells and Upregulation of E-cadherin by Prostate Cancer Epithelial Cells

Cancer mortality is primarily attributed to metastasis and the resulting compromise of organs secondary to the initial tumor site. Metastasis is a multi-step process in which the tumor cells must first acquire a migratory phenotype and invade through the surrounding tissue for spread to distant organs in the body. The ability of malignant cells to migrate and breach surrounding tissue/matrix barriers is among the most daunting challenges to disease management for men in the United States diagnosed with prostate cancer (CaP), especially since, at diagnosis, a high proportion of patients already have occult or clinically-detectable metastasis. The interaction between hepatocyte growth factor (HGF) secreted by the stroma, with its receptor c-Met located in the epithelium, must occur for epithelial CaP cells to become migratory. We studied the effects of grape-derived phytochemical resveratrol on the transition of epithelial tumor cells from sedentary to a mobile, penetrant phenotype. A time lapse microscopy assay was used to monitor the acquisition of the migratory phenotype by resveratrol. The results show that resveratrol inhibits HGF-mediated interaction between the stroma and epithelium and suppresses epithelial CaP cell migration by attenuating the control of epithelial-to-mesenchymal transition (EMT).

c-Met expression and activity in urogenital cancers - novel aspects of signal transduction and medical implications

C-Met is a receptor tyrosine kinase with multiple functions throughout embryonic development, organogenesis and wound healing and is expressed in various epithelia. The ligand of c-Met is Hepatocyte Growth Factor (HGF) which is secreted among others by mesenchymal stroma/stem (MSC) cells.

Physiological c-Met functions are centred around processes that underly cellular motility and invasive growth. Aberrant c-Met expression and activity is observed in numerous cancers and makes major contributions to cell malignancy. Importantly, HGF/c-Met signaling is crucial in the context of communication between cancer cells and the the tumor stroma.

Here, we review recent findings on roles of dysregulated c-Met in urogenital tumors such as cancers of the urinary bladder, prostate, and ovary. We put emphasis on novel aspects of cancer-associated c-Met expression regulation on both, HGF-dependent and HGF-independent non-canonical mechanisms. Moreover, this review focusses on c-Met-triggered signalling with potential relevance for urogenital oncogenesis, and on strategies to specifically inhibit c-Met activity.

Grainyhead-like 2 inhibits the coactivator p300, suppressing tubulogenesis and the epithelial-mesenchymal transition

GRHL2 suppresses EMT to give a default epithelial phenotype. GRHL2 inhibits this process through the histone acetyltransferase coactivator p300, repressing the partial EMT and preventing induction of MMPs. The results demonstrate novel roles for p300 and GRHL2 in promoting or suppressing EMT in morphogenesis and tumor progression.

Developmental morphogenesis and tumor progression require a transient or stable breakdown of epithelial junctional complexes to permit programmed migration, invasion, and anoikis resistance, characteristics endowed by the epithelial–mesenchymal transition (EMT). The epithelial master-regulatory transcription factor Grainyhead-like 2 (GRHL2) suppresses and reverses EMT, causing a mesenchymal–epithelial transition to the default epithelial phenotype. Here we investigated the role of GRHL2 in tubulogenesis of Madin–Darby canine kidney cells, a process requiring transient, partial EMT. GRHL2 was required for cystogenesis, but it suppressed tubulogenesis in response to hepatocyte growth factor. Surprisingly, GRHL2 suppressed this process by inhibiting the histone acetyltransferase coactivator p300, preventing the induction of matrix metalloproteases and other p300-dependent genes required for tubulogenesis. A 13–amino acid region of GRHL2 was necessary for inhibition of p300, suppression of tubulogenesis, and interference with EMT. The results demonstrate that p300 is required for partial or complete EMT occurring in tubulogenesis or tumor progression and that GRHL2 suppresses EMT in both contexts through inhibition of p300.

HGF/c-Met signaling promotes liver progenitor cell migration and invasion by an epithelial-mesenchymal transition-independent, phosphatidyl inositol-3 kinase-dependent pathway in an in vitro model

Oval cells constitute an interesting hepatic cell population. They contribute to sustain liver regeneration during chronic liver damage, but in doing this they can be target of malignant conversion and become tumor-initiating cells and drive hepatocarcinogenesis. The molecular mechanisms beneath either their pro-regenerative or pro-tumorigenic potential are still poorly understood. In this study, we have investigated the role of the HGF/c-Met pathway in regulation of oval cell migratory and invasive properties. Our results show that HGF induces c-Met-dependent oval cell migration both in normal culture conditions and after in vitro wounding. HGF-triggered migration involves F-actin cytoskeleton reorganization, which is also evidenced by activation of Rac1. Furthermore, HGF causes ZO-1 translocation from cell-cell contact sites to cytoplasm and its concomitant activation by phosphorylation. However, no loss of expression of cell-cell adhesion proteins, including E-cadherin, ZO-1 and Occludin-1, is observed. Additionally, migration does not lead to cell dispersal but to a characteristic organized pattern in rows, in turn associated with Golgi compaction, providing strong evidence of a morphogenic collective migration. Besides migration, HGF increases oval cell invasion through extracellular matrix, a process that requires PI3K activation and is at least partly mediated by expression and activation of metalloproteases. Altogether, our findings provide novel insights into the cellular and molecular mechanisms mediating the essential role of HGF/c-Met signaling during oval cell-mediated mouse liver regeneration.

Spatially restricted hyaluronan production by Has2 drives epithelial tubulogenesis in vitro

Generation of branched tubes from an epithelial bud is a fundamental process in development. We hypothesized that induction of hyaluronan synthase (Has) and production of hyaluronan (HA) drives tubulogenesis in response to morphogenetic cytokines. Treatment of J3B1A mammary cells with transforming growth factor-β1 or renal MDCK and mCCD-N21 cells with hepatocyte growth factor induced strong and specific expression of Has2. Immunostaining revealed that HA was preferentially produced at the tips of growing tubules. Inhibition of HA production, either by 4-methylumbelliferone (4-MU) or by Has2 mRNA silencing, abrogated tubule formation. HA production by J3B1A and mCCD-N21 cells was associated with sustained activation of ERK and S6 phosphorylation. However, silencing of either CD44 or RHAMM (receptor for HA-mediated motility), the major HA receptors, by RNA interference, did not alter tubulogenesis, suggesting that this process is not receptor-mediated.

Spatiotemporal control of gene expression using microfluidics

Accurate spatiotemporal regulation of genetic expression and cell microenvironment are both essential to epithelial morphogenesis during development, wound healing and cancer. In vivo, this is achieved through the interplay between intrinsic cellular properties and extrinsic signals. Amongst these, morphogen gradients induce specific concentration- and time-dependent gene expression changes that influence a target cell's fate. As systems biology attempts to understand the complex mechanisms underlying morphogenesis, the lack of experimental setup to recapitulate morphogen-induced patterning in vitro has become limiting. For this reason, we developed a versatile microfluidic-based platform to control the spatiotemporal delivery of chemical gradients to tissues grown in Petri dishes. Using this setup combined with a synthetic inducible gene expression system, we were able to restrict a target gene's expression within a confluent epithelium to bands of cells as narrow as four cell diameters with a one cell diameter accuracy. Applied to the targeted delivery of growth factor gradients to a confluent epithelium, this method further enabled the localized induction of epithelial-mesenchymal transitions and associated morphogenetic changes. Our approach paves the way for replicating in vitro the morphogen gradients observed in vivo to determine the relative contributions of known intrinsic and extrinsic factors in differential tissue patterning, during development and cancer. It could also be readily used to spatiotemporally control cell differentiation in ES/iPS cell cultures for re-engineering of complex tissues. Finally, the reversibility of the microfluidic chip assembly allows for pre- and post-treatment sample manipulations and extends the range of patternable samples to animal explants.

Hepatocyte growth factor enhances the barrier function in primary cultures of rat brain microvascular endothelial cells

The effects of hepatocyte growth factor (HGF) on barrier functions were investigated by a blood-brain barrier (BBB) in vitro model comprising a primary culture of rat brain capillary endothelial cells (RBEC). In order to examine the response of the peripheral endothelial cells to HGF, human umbilical vascular endothelial cells (HUVEC) and human dermal microvascular endothelial cells (HMVEC) were also treated with HGF. HGF decreased the permeability of RBEC to sodium fluorescein and Evans blue albumin, and dose-dependently increased transendothelial electrical resistance (TEER) in RBEC. HGF altered the immunochemical staining pattern of F-actin bands and made ZO-1 staining more distinct on the linear cell borders in RBEC. In contrast, HGF increased sodium fluorescein and Evans blue albumin permeability in HMVEC and HUVEC, and decreased TEER in HMVEC. In HMVEC, HGF reduced cortical actin bands and increased stress fiber density, and increased the zipper-like appearance of ZO-1 staining. Western blot analysis showed that HGF significantly increased the amount of ZO-1 and VE-cadherin. HGF seems to act on the BBB to strengthen BBB integrity. These findings indicated that cytoskeletal rearrangement and cell-cell adhesion, such as through VE-cadherin and ZO-1, are candidate mechanisms for the influence of HGF on the BBB. The possibility that HGF has therapeutic significance in protecting the BBB from damage needs to be considered.

Molecular mechanisms regulating the establishment of hepatocyte polarity during human hepatic progenitor cell differentiation into a functional hepatocyte-like phenotype

The correct functioning of hepatocytes requires the establishment and maintenance of hepatocyte polarity. However, the mechanisms regulating the generation of hepatocyte polarity are not completely understood. The differentiation of human fetal hepatic progenitor cells (hFHPCs) into functional hepatocytes provides a powerful in vitro model system for studying the molecular mechanisms governing hepatocyte development. In this study, we used a two-stage differentiation protocol to generate functional polarized hepatocyte-like cells (HLCs) from hFHPCs. Global gene expression profiling was performed on triplicate samples of hFHPCs, immature-HLCs and mature-HLCs. When the differential gene expression was compared based on the differentiation stage, a number of genes were identified that might be essential for establishing and maintaining hepatocyte polarity. These genes include those that encode actin filament-binding protein, protein tyrosine kinase activity molecules, and components of signaling pathways, such as PTK7, PARD3, PRKCI and CDC42. Based on known and predicted protein-protein interactions, the candidate genes were assigned to networks and clustered into functional categories. The expression of several of these genes was confirmed using real-time RT-PCR. By inactivating genes using small interfering RNA, we demonstrated that PTK7 and PARD3 promote hepatic polarity formation and affect F-actin organization. These results provide unique insight into the complex process of polarization during hepatocyte differentiation, indicating key genes and signaling molecules governing hepatocyte differentiation.

Desmoglein 3 acting as an upstream regulator of Rho GTPases, Rac-1/Cdc42 in the regulation of actin organisation and dynamics

Desmoglein 3 (Dsg3), a member of the desmoglein sub-family, serves as an adhesion molecule in desmosomes. Our previous study showed that overexpression of human Dsg3 in several epithelial lines induces formation of membrane protrusions, a phenotype suggestive of Rho GTPase activation. Here we examined the interaction between Dsg3 and actin in detail and showed that endogenous Dsg3 colocalises and interacts with actin, particularly the junctional actin in a Rac1-dependent manner. Ablation of Rac1 activity by dominant negative Rac1 mutant (N17Rac1) or the Rac1 specific inhibitor (NSC23766) directly disrupts the interaction between Dsg3 and actin. Assembly of the junctional actin at the cell borders is accompanied with enhanced levels of Dsg3, while inhibition of Dsg3 by RNAi results in profound changes in the organisation of actin cytoskeleton. In accordance, overexpression of Dsg3 results in a remarkable increase of Rac1 and Cdc42 activities and to a lesser extent, RhoA. The enhancements in Rho GTPases are accompanied by the pronounced actin-based membrane structures such as lamellipodia and filopodia, enhanced rate of actin turnover and cell polarisation. Together, our results reveal an important novel function for Dsg3 in promoting actin dynamics through regulating Rac1 and Cdc42 activation in epithelial cells.

Hepatocyte growth factor (HGF) regulates blood-testis barrier (BTB) in adult rats

We have studied the effects of HGF on BTB dynamics in adult rats. We demonstrate that, at stages VII-VIII of the epithelium wave when germ cells traverse the BTB, HGF reduces the levels of occludin and influences its distribution pattern and assembling. Moreover, we report that, at stages VII-VIII, HGF significantly increases the amount of active TGF-β and the amount of uPA present in the tubules. For the first time we report that, in the same stages, HGF reduces the amount of actin present in the BTB region, in which occludin levels are highest, and modifies the morphology of the actin cytoskeleton network. At the level of maximal intensity of occludin fluorescence, we report that HGF also modifies the colocalization of occludin and actin. Lastly, we demonstrate that HGF is maximally expressed at stages VII-VIII, whereas its levels fall in the subsequent stages.

Systemic administration of naked plasmid encoding HGF attenuates puromycin aminonucleoside-induced damage of murine glomerular podocytes

Podocyte injury is considered to play important roles in the pathogenesis of human glomerular disease. There is accumulating evidence suggesting that hepatocyte growth factor (HGF) elicits preventive activity for glomerular cells in animal models of chronic renal diseases. In this study, we demonstrated that delivery of a naked plasmid vector encoding the human HGF gene into mice by a hydrodynamic-based in vivo gene transfection approach markedly reduced proteinuria and attenuated podocyte injury in a mouse model induced by puromycin aminonucleoside (PAN) injection. Systemic administration by rapid injection via the tail vein of a naked plasmid containing HGF cDNA driven under a cytomegalovirus promoter (pCMV-HGF) produced a remarkable level of human HGF protein in the circulation. Tissue distribution studies suggested that the kidney expressed a high level of the HGF transgene. Meanwhile, compared with tubules and interstitium, a higher level of exogenous HGF protein was detected in the glomeruli. Administration of pCMV-HGF dramatically abated the urine albumin excretion and podocyte injury in PAN nephropathy in mice. Exogenous expression of HGF produced evidently beneficial effects, leading to restoration of Wilms' tumor-1 (WT1) and α-actinin-4 expression and attenuation of ultrastructural damage of the podocytes. In vitro, HGF not only restored WT1 and α-actinin-4 expression but also inhibited albumin leakage of podocytes incubated with PAN in a Transwell culture chamber. These results suggest that HGF might provide a novel strategy for amelioration of podocyte injury.

Hepatocyte Growth Factor stimulated cell scattering requires ERK and Cdc42-dependent tight junction disassembly

The mechanism by which Hepatocyte Growth Factor (HGF) induces tight junction disassembly prior to cell scattering is largely unknown. Here, we show that HGF stimulates rapid loss of the TJ assembly protein Par6 from the TJ in an Erk-dependent manner. Erk activation by HGF is found to mediate the interaction of Par6 with GTP-loaded Cdc42. The Cdc42 GTPase activating protein cdGAP is shown to interact with Pkcζ at baseline and prevent Par6-Cdc42 association. Erk, by phosphorylating cdGAP at threonine776, can inhibit the GAP activity, thereby increasing Par6-Cdc42 association and TJ disassembly. Our findings reveal a novel pathway for regulating HGF signaling to the Par proteins through Erk-cdGAP, resulting in TJ disassembly and cell scattering.

Normalization of wound healing and diabetic markers in organ cultured human diabetic corneas by adenoviral delivery of c-Met gene

Purpose. Diabetic corneas display altered basement membrane and integrin markers, increased expression of proteinases, decreased hepatocyte growth factor (HGF) receptor, c-met proto-oncogene, and impaired wound healing. Recombinant adenovirus (rAV)-driven c-met overexpression in human organ-cultured corneas was tested for correction of diabetic abnormalities. Methods. Forty-six human corneas obtained postmortem from 23 donors with long-term diabetes (5 with diabetic retinopathy) were organ cultured and transduced with rAV-expressing c-met gene (rAV-cmet) under the cytomegalovirus promoter at approximately 10(8) plaque-forming units per cornea for 48 hours. Each control fellow cornea received control rAV (rAV expressing the beta-galactosidase gene or vector alone). After an additional 4 to 5 days of incubation, 5-mm epithelial wounds were created with n-heptanol, and healing was monitored. The corneas were analyzed afterward by immunohistochemistry and Western blot analysis. Signaling molecule expression and role was examined by immunostaining, phosphokinase antibody arrays, Western blot analysis, and inhibitor analysis. Results. rAV-cmet transduction led to increased epithelial staining for c-met (total, extracellular, and phosphorylated) and normalization of the patterns of select diabetic markers compared with rAV-vector-transduced control fellow corneas. Epithelial wound healing time in c-met-transduced diabetic corneas decreased twofold compared with rAV-vector-transduced corneas and became similar to normal. c-Met action apparently involved increased activation of p38 mitogen-activated protein kinase. c-Met transduction did not change tight junction protein patterns, suggesting unaltered epithelial barrier function. Conclusions. rAV-driven c-met transduction into diabetic corneas appears to restore HGF signaling, normalize diabetic marker patterns, and accelerate wound healing. c-Met gene therapy could be useful for correcting human diabetic corneal abnormalities.

Overexpression of DPAGT1 leads to aberrant N-glycosylation of E-cadherin and cellular discohesion in oral cancer

Cancer cells are frequently characterized by aberrant increases in protein N-glycosylation and by disruption of E-cadherin-mediated adherens junctions. The relationship between altered N-glycosylation and loss of E-cadherin adhesion in cancer, however, remains unclear. Previously, we reported that complex N-glycans on the extracellular domains of E-cadherin inhibited the formation of mature adherens junctions. Here, we examined whether dysregulated N-glycosylation was one of the underlying causes for cellular discohesion in oral cancer. We show that dense cultures of human salivary epidermoid carcinoma A253 cells exhibited elevated expression of DPAGT1, the gene that initiates protein N-glycosylation. Overexpression of DPAGT1 correlated with the production of E-cadherin-bearing complex N-glycans in nascent adherens junctions. Partial inhibition of DPAGT1 with small interfering RNA reduced the complex N-glycans of E-cadherin and increased the abundance of alpha-catenin and stabilizing proteins in adherens junctions. This was associated with the assembly of functional tight junctions. The inverse relationship between DPAGT1 expression and intercellular adhesion was a feature of oral squamous cell carcinoma. Oral squamous cell carcinomas displayed overexpression of DPAGT1 that correlated with diminished localization of E-cadherin and alpha-catenin at the sites of adherens junctions. Our studies show for the first time that DPAGT1 is an upstream regulator of E-cadherin N-glycosylation status and adherens junction composition and suggest that dysregulation of DPAGT1 causes disturbances in intercellular adhesion in oral cancer.

Hepatocyte growth factor modulates Sertoli-Sertoli tight junction dynamics

In mammalian testes Sertoli cells form tight junctions whose function is fundamental for the maintenance of a normal spermatogenesis. Hepatocyte growth factor (HGF) is a cytokine influencing the cellular tight junctions either in normal or in tumor cells. We have previously demonstrated that HGF is expressed in the rat testis and influences many functional activities of somatic and germ cells. We now report that HGF decreases the levels of testicular occludin and influences the position of the molecule in the tight junctions as demonstrated by confocal microscopy analysis. In fact in the presence of the factor occludin was mainly localized in the suprabasal region of the tubules whereas in its absence occludin was prevalently localized in the basal region. Occludin production is known to be regulated by different cytokines including TGFbeta. We have investigated the role of HGF in the regulation of the levels of TGFbeta and we report that HGF significantly increases the amount of the active fraction of the factor without affecting the amount of the total TGFbeta. Urokinase type plasminogen activator (uPA) is closely related with the tight junctions and is one of the molecules able to activate the inactive TGF-beta. We found that HGF significantly increases the amount of uPA present in the testis suggesting that HGF regulates the amount of active TGFbeta via uPA levels. In conclusion we report that in the testis HGF regulates Sertoli-Sertoli tight junctions inducing a reduction and redistribution of occludin possibly modulating the levels of uPA and active TGFbeta.

Innate Immunity in the Female Reproductive Tract: Role of Sex Hormones in Regulating Uterine Epithelial Cell Protection Against Pathogens

The mucosal immune system in the upper female reproductive tract is uniquely prepared to maintain a balance between the presence of commensal bacteria, sexually transmitted bacterial and viral pathogens, allogeneic spermatozoa, and an immunologically distinct fetus. At the center of this dynamic system are the epithelial cells that line the Fallopian tubes, uterus, cervix and vagina. Epithelial cells provide a first line of defense that confers continuous protection, by providing a physical barrier as well as secretions containing bactericidal and virucidal agents. In addition to maintaining a state of ongoing protection, these cells have evolved to respond to pathogens, in part through Toll-like receptors (TLRs), to enhance innate immune protection and, when necessary, to contribute to the initiation of an adaptive immune response. Against this backdrop, epithelial cell innate and adaptive immune function is modulated to meet the constraints of procreation. The overall goal of this review is to focus on the dynamic role of epithelial cells in the upper reproductive tract, with special emphasis on the uterus, to define the unique properties of these cells as they maintain homeostasis in preparation for successful fertilization and pregnancy while at the same time confer protection against sexually transmitted infections, which threaten to compromise women's reproductive health and survival. By understanding the nature of this protection and the ways in which innate and adaptive immunity are regulated by sex hormones, these studies provide the opportunity to contribute to the foundation of information essential for ensuring reproductive health.

beta-Catenin and actin reorganization in HGF/SF response of ST14A cells

Hepatocyte growth factor/scatter factor (HGF/SF) is a pleiotropic factor that activates proliferation, differentiation, and migration of various cell types. Its action is mediated by c-Met, a receptor endowed with tyrosine kinase activity that activates complex signaling cascades and mediates diverse cell responses. Although HGF action was first demonstrated in epithelial cells, expression of HGF and c-Met receptor has also been described in developing and adult mammalian brain. In the developing central nervous system, areas of HGF and c-Met expression are coincident with the migratory pathway of precursor cells. In the present article we report that the interaction between c-Met and HGF/SF in striatal progenitor ST14A cells triggers a signaling cascade that induces modification of cell morphology, with decreased cell-cell interactions and increased cell motility; in particular, we analyzed the reorganization of the actin cytoskeleton and the delocalization of beta-catenin and N-cadherin. The testing of other neurotrophic factors (NGF, BDNF, NT3, and CNTF) showed that the observed modifications were peculiar to HGF. We show that phosphoinositide 3-kinase inhibitor treatment, which blocks cell scattering induced by HGF/SF, does not abolish actin and beta-catenin redistribution. The effects of HGF/SF on primary spinal cord cell cultures were also investigated, and HGF/SF was found to have a possible motogenic effect on these cells. The data reported suggest that HGF could play a role in the early steps of neurogenesis as a motogenic factor.

The third dimension bridges the gap between cell culture and live tissue

Moving from cell monolayers to three-dimensional (3D) cultures is motivated by the need to work with cellular models that mimic the functions of living tissues. Essential cellular functions that are present in tissues are missed by 'petri dish'-based cell cultures. This limits their potential to predict the cellular responses of real organisms. However, establishing 3D cultures as a mainstream approach requires the development of standard protocols, new cell lines and quantitative analysis methods, which include well-suited three-dimensional imaging techniques. We believe that 3D cultures will have a strong impact on drug screening and will also decrease the use of laboratory animals, for example, in the context of toxicity assays.

Tyrosine phosphorylated Par3 regulates epithelial tight junction assembly promoted by EGFR signaling

The conserved polarity complex, comprising the partitioning-defective (Par) proteins Par3 and Par6, and the atypical protein kinase C, functions in various cell-polarization events and asymmetric cell divisions. However, little is known about whether and how external stimuli-induced signals may regulate Par3 function in epithelial cell polarity. Here, we found that Par3 was tyrosine phosphorylated through phosphoproteomic profiling of pervanadate-induced phosphotyrosine proteins. We also demonstrated that the tyrosine phosphorylation event induced by multiple growth factors including epidermal growth factor (EGF) was dependent on activation of Src family kinase (SFK) members c-Src and c-Yes. The tyrosine residue 1127 (Y1127) of Par3 was identified as the major EGF-induced phosphorylation site. Moreover, we found that Y1127 phosphorylation reduced the association of Par3 with LIM kinase 2 (LIMK2), thus enabling LIMK2 to regulate cofilin phosphorylation dynamics. Substitution of Y1127 for phenylalanine impaired the EGF-induced Par3 and LIMK2 dissociation and delayed epithelial tight junction (TJ) assembly considerably. Collectively, these data suggest a novel, phosphotyrosine-dependent fine-tuning mechanism of Par3 in epithelial TJ assembly controlled by the EGF receptor-SFK signaling pathway.

Cell and fibronectin dynamics during branching morphogenesis

Branching morphogenesis is a dynamic developmental process shared by many organs, but the mechanisms that reorganize cells during branching morphogenesis are not well understood. We hypothesized that extensive cell rearrangements are involved, and investigated cell migration using two-color confocal time-lapse microscopy to image cell and extracellular-matrix dynamics in developing salivary glands. We labeled submandibular salivary gland (SMG) epithelial cells with green fluorescent protein and matrix with fluorescent fibronectin. Surprisingly, we observed substantial, rapid and relatively random migration of individual epithelial cells during branching morphogenesis. We predicted that cell migration would decrease after formation of acini and, indeed, found that rapid cell movements do not occur in SMG from newborn mice. However, in embryonic SMG epithelial cells, we observed an absence of choreographed cell migration, indicating that patterned cell migration alone cannot explain the highly ordered process of branching morphogenesis. We therefore hypothesized a role for directional fibronection assembly in branching. Washout and pulse-chase experiments revealed that older fibronectin accumulates at the base of the clefts and translocates inwards as a wedge, with newer fibronectin assembling behind it. These findings identify a new mechanism for branching morphogenesis involving directional fibronectin translocation superimposed on individual cell dynamics.

Met-Independent Hepatocyte Growth Factor-mediated regulation of cell adhesion in human prostate cancer cells

BACKGROUND

Prostate cancer cells communicate reciprocally with the stromal cells surrounding them, inside the prostate, and after metastasis, within the bone. Each tissue secretes factors for interpretation by the other. One stromally-derived factor, Hepatocyte Growth Factor (HGF), was found twenty years ago to regulate invasion and growth of carcinoma cells. Working with the LNCaP prostate cancer progression model, we found that these cells could respond to HGF stimulation, even in the absence of Met, the only known HGF receptor. The new HGF binding partner we find on the cell surface may help to clarify conflicts in the past literature about Met expression and HGF response in cancer cells.

METHODS

We searched for Met or any HGF binding partner on the cells of the PC3 and LNCaP prostate cancer cell models, using HGF immobilized on agarose beads. By using mass spectrometry analyses and sequencing we have identified nucleolin protein as a novel HGF binding partner. Antibodies against nucleolin (or HGF) were able to ameliorate the stimulatory effects of HGF on met-negative prostate cancer cells. Western blots, RT-PCR, and immunohistochemistry were used to assess nucleolin levels during prostate cancer progression in both LNCaP and PC3 models.

RESULTS

We have identified HGF as a major signaling component of prostate stromal-conditioned media (SCM) and have implicated the protein nucleolin in HGF signal reception by the LNCaP model prostate cancer cells. Antibodies that silence either HGF (in SCM) or nucleolin (on the cell surfaces) eliminate the adhesion-stimulatory effects of the SCM. Likewise, addition of purified HGF to control media mimics the action of SCM. C4-2, an LNCaP lineage-derived, androgen-independent human prostate cancer cell line, responds to HGF in a concentration-dependent manner by increasing its adhesion and reducing its migration on laminin substratum. These HGF effects are not due to shifts in the expression levels of laminin-binding integrins, nor can they be linked to expression of the known HGF receptor Met, as neither LNCaP nor clonally-derived C4-2 sub-line contain any detectable Met protein. Even in the absence of Met, small GTPases are activated, linking HGF stimulation to membrane protrusion and integrin activation. Membrane-localized nucelolin levels increase during cancer progression, as modeled by both the PC3 and LNCaP prostate cancer progression cell lines.

CONCLUSION

We propose that cell surface localized nucleolin protein may function in these cells as a novel HGF receptor. Membrane localized nucleolin binds heparin-bound growth factors (including HGF) and appears upregulated during prostate cancer progression. Antibodies against nucleolin are able to ameliorate the stimulatory effects of HGF on met-negative prostate cancer cells. HGF-nucleolin interactions could be partially responsible for the complexity of HGF responses and met expression reported in the literature.

Ligand-of-Numb protein X is an endocytic scaffold for junctional adhesion molecule 4

Junctional adhesion molecule 4 (JAM4) is a cell adhesion molecule that interacts with a tight junction protein, membrane-associated guanylate kinase inverted 1 (MAGI-1). Our previous studies suggest that JAM4 is implicated in the regulation of paracellular permeability and the signalings of hepatocyte growth factor. In this study, we performed yeast two-hybrid screening to search for an unidentified JAM4-binding protein and obtained one isoform of Ligand-of-Numb protein X1 (LNX1), LNXp70, that is an interactor of Numb. Ligand-of-Numb protein X1 is expressed in kidney glomeruli and intestinal epithelial cells, where JAM4 is also detected. Immunoprecipitation from kidney lysates supports the in vivo interaction of proteins. Biochemical studies reveal that JAM4 directly binds the second PDZ domain of LNX1 through its carboxyl terminus. Junctional adhesion molecule 4, LNX1 and Numb form a tripartite complex in vitro and are partially colocalized in heterologous cells. Ligand-of-Numb protein X1 facilitates endocytosis of JAM4 and is involved in transforming growth factor beta -induced redistribution of JAM4 in mammary epithelial cells. Experiments using dominant-negative constructs and RNA interference insure that Numb is necessary for the LNX1-mediated endocytosis of JAM4. All these findings indicate that LNX1 provides an endocytic scaffold for JAM4 that is implicated in the reorganization of cell junctions.

Microbial strategies to target, cross or disrupt epithelia

Epithelia are highly organized structures adapted to protect the underlying tissues from external aggressions, including microbial infections. Consequently, pathogens have evolved various strategies to target directly or indirectly intercellular junctions and/or components that maintain the structure of epithelia. Interestingly, some extracellular pathogens secrete enzymes that modify the extracellular part of junction components. Others produce toxins that are endocytosed and act from the inside of the cell to disrupt epithelial junctions. Other pathogens may directly inject into cells factors that are targeted to and destabilize the junctions, or that interact with signaling cascades that affect junction stability. Finally invasive bacteria or viruses may, by entering into cells, destabilize the junctions by targeting junction components directly or by inducing a series of events that lead to chemokine secretion, polymorphonuclear recruitment and inflammation.

Extracellular Signal-regulated Kinases 1/2 Control Claudin-2 Expression in Madin-Darby Canine Kidney Strain I and II Cells

The tight junction of the epithelial cell determines the characteristics of paracellular permeability across epithelium. Recent work points toward the claudin family of tight junction proteins as leading candidates for the molecular components that regulate paracellular permeability properties in epithelial tissues. Madin-Darby canine kidney (MDCK) strain I and II cells are models for the study of tight junctions and based on transepithelial electrical resistance (TER) contain "tight" and "leaky" tight junctions, respectively. Overexpression studies suggest that tight junction leakiness in these two strains of MDCK cells is conferred by expression of the tight junction protein claudin-2. Extracellular signal-regulated kinase (ERK) 1/2 activation by hepatocyte growth factor treatment of MDCK strain II cells inhibited claudin-2 expression and transiently increased TER. This process was blocked by the ERK 1/2 inhibitor U0126. Transfection of constitutively active mitogen-activated protein kinase/extracellular signal-regulated kinase kinase into MDCK strain II cells also inhibited claudin-2 expression and increased TER. MDCK strain I cells have higher levels of active ERK 1/2 than do MDCK strain II cells. U0126 treatment of MDCK strain I cells decreased active ERK 1/2 levels, induced expression of claudin-2 protein, and decreased TER by approximately 20-fold. U0126 treatment also induced claudin-2 expression and decreased TER in a high resistance mouse cortical collecting duct cell line (94D). These data show for the first time that the ERK 1/2 signaling pathway negatively controls claudin-2 expression in mammalian renal epithelial cells and provide evidence for regulation of tight junction paracellular transport by alterations in claudin composition within tight junction complexes.

Hepatocyte growth factor regulation of uterine epithelial cell transepithelial resistance and tumor necrosis factor alpha release in culture

Underlying stromal cells are essential for the normal development of epithelial cells (ECs) at mucosal surfaces. Recent studies from our laboratory have shown that uterine stromal cells regulate EC integrity, measured as transepithelial resistance (TER) as well as tumor necrosis factor (TNF) alpha alpha secretion by ECs in culture. Using stromal cells in coculture with polarized ECs grown on inserts, we found that stromal cells produce soluble mediators that increase TER and decrease TNFalpha secretion. The purpose of the present study was to identify the mechanisms whereby stromal cells exert their effects on uterine epithelium. We report that hepatocyte growth factor (HGF), a known mesenchymal growth factor that mediates EC proliferation, increases TER but, at the same time, decreases apical TNFalpha release. When ECs and/or stromal cells were incubated with anti-HGF or anti-HGF receptor (HGFR) antibody before HGF, the effects of HGF were blocked. These findings indicate that ECs express the HGFR at their basolateral surfaces and that HGFR mediates the effects of HGF on TER and TNFalpha. Neutralization of stromal cell secretions with antibodies for HGF and HGFR demonstrate that stromal-derived HGF is the mediator of EC TER. In contrast, neither anti-HGF antibody nor HGFR antibody had any effect on stromal cell-induced decreases in TNFalpha secretion. From these results, we conclude that stromal cell regulation of EC TER is mediated through the secretion of stromal HGF. Furthermore, because neutralization of stromal media failed to affect TNFalpha secretion, these findings suggest that other growth factors, in addition to HGF, affect EC cytokine production.

Gene expression alterations during HGF-induced dedifferentiation of a renal tubular epithelial cell line (MDCK) using a novel canine DNA microarray

Hepatocyte growth factor (HGF) elicits a broad spectrum of biological activities, including epithelial cell dedifferentiation. One of the most widely used and best-studied polarized epithelial cell lines is the Madin-Darby canine kidney (MDCK) cell line. Here, we describe and validate the early response of polarized monolayers of MDCK cells stimulated with recombinant HGF using a novel canine DNA microarray designed to query 12,473 gene sequences. In our survey, eight genes previously implicated in the HGF signaling pathway were differentially regulated, demonstrating that the system was responsive to HGF. Also identified were 117 genes not previously known to be involved in the HGF pathway. The results were confirmed by real-time PCR or Western blot analysis for 38 genes. Of particular interest were the large number of differentially regulated genes encoding small GTPases, proteins involved in endoplasmic reticulum translation, proteins involved in the cytoskeleton, the extracellular matrix, and the hematopoietic and prostaglandin systems.