Collagen gel overlay induces apoptosis of polarized cells in cultures: disoriented cell death

A histological study of mineralised tissue formation around implants with 3D culture of HMS0014 cells in Cellmatrix Type I-A collagen gel scaffold in vitro

We cultured HMS0014 Yub621b cells within a 3D collagen gel scaffold (Cellmatrix Type I-A) and aimed to study the fate and contribution of human bone-derived mesenchymal stem cells (MSCs) in the guided bone regeneration(GBR)-engineered tissue which has developed around the titanium (Ti) test dental implant (IP) in vitro. The light microscopy (LM) and transmission electron microscopy (TEM) results of the peri-IP tissue indicated that collagen fibrils of the Cellmatrix Type I-A gel were accumulated and fabricated to provide a 3D meshwork for proliferation and differentiation of the HMS0014 cells in the top (cell) layer; mineralisation of the GBR tissue had commenced since day 1 and became markedly deposited between days 7 and 14 of the experiment. TEM observation revealed sedimentation of cement line at the periphery of the interwoven Cellmatrix fibres and fibrils in the ECM scaffold of the GBR tissue; matrix vesicle-mediated and appositional collagen-mediated mineralisation were identified in the peri-IP ECM scaffold. The fine structure study of the plurimorphic osteoblast(Ob)-like osteogeneic cells demonstrated numerous membranous organelles related with vesicular trafficking, secretion and endocytosis in the cytoplasm; well-developed cytoskeleton networks and intercellular junctional complexes were also observed. The specimens on fluorescence immunohistochemistry (IHC) by confocal laser-scanning microscopy (LSM) showed the expression of LC3 and Cx43 associated with autophagic-lysosomal degeneration pathway and signal conduction mediated with gap junctions (GJS) in maintaining tissue homeostasis of the Ob-like cells which grew and degenerated in the 3D scaffold. Results from this in vitro study suggest that Ob-like HMS0014 cells actively regulate turnover of the peri-IP ECM to recapitulate the development and formation of osteoid tissue-engineered material which might contribute to augment osseointegration around the dental implant.

Mechanical properties of collagen gels derived from rats of different ages

In a previous study, we found that different collagen gels produced using collagen fibrils extracted from 1-, 4- and 8-month-old rat tails essentially influenced the morphogenesis of epithelial cells. More importantly, the youngest collagen gel induces the highest level of cell apoptosis. The objective of this study was to investigate mechanical properties of various collagen gels correlated to the rat ages. A rheometer and dynamic mechanical analyzer were used to measure shear and compressive properties of hydrated collagen gels. Experimental results obtained from both testing modes showed that older age-related collagen gels possessed a larger elastic modulus, possibly due to the enhanced cross-linking degree. The moduli obtained in shear mode were 1.4-2.7-times greater than those in compression. The results of shear test and compressive test consistently indicated the age of rats did have a statistically significant effect on mechanical properties of hydrated collagen gels.

Liver fibrosis protects mice from acute hepatocellular injury

BACKGROUND & AIMS

Development of fibrosis is part of the pathophysiologic process of chronic liver disease. Although it is considered deleterious, it also represents a form of tissue repair. Deposition of extracellular matrix changes the cellular environment of the liver; we investigated whether it increases resistance to noxious stimuli and the role of changes in intracellular signaling to hepatocytes in mediating this effect.

METHODS

Primary cultures of mouse hepatocytes were exposed to type I collagen (COL1); cell injury was assessed by morphologic and biochemical criteria. The expression of Bcl-2 family members was evaluated by immunoblot analyses. Activation of extracellular signal-regulated kinase (ERK) was assessed using phospho-specific antibodies. Liver fibrosis was induced by repeated administration of thioacetamide or carbon tetrachloride to mice; mice were then exposed to Fas antibodies.

RESULTS

Hepatocytes exposed to COL1 were more resistant to a variety of hepatotoxins, in a dose-dependent manner, and had lower levels of Bad, Bid, and Bax proapoptotic proteins compared with control hepatocytes. Activation of ERK1/2 was stronger and quicker in hepatocytes exposed to COL1. The MEK1/2 inhibitors U0126 and PD98059 reversed the protective effects of COL1 and the decrease in proapoptotic proteins. Hepatocytes isolated from ERK1(-/-) mice were insensitive to the protective effect of COL1. Fibrotic livers from wild-type mice had high levels of phospho-ERK1 and were resistant to Fas-induced cell death. ERK1(-/-) mice lost this effect.

CONCLUSIONS

Production of COL1 during liver fibrosis induces a hepatoprotective response that is mediated by activation of ERK1 signaling.

A computational approach to resolve cell level contributions to early glandular epithelial cancer progression

Background

Three-dimensional (3D) embedded cell cultures provide an appropriate physiological environment to reconstruct features of early glandular epithelial cancer. Although these are orders of magnitude simpler than tissues, they too are complex systems that have proven challenging to understand. We used agent-based, discrete event simulation modeling methods to build working hypotheses of mechanisms of epithelial 3D culture phenotype and early cancer progression. Starting with an earlier software analogue, we validated an improved in silico epithelial analogue (ISEA) for cardinal features of a normally developed MDCK cyst. A set of axiomatic operating principles defined simulated cell actions. We explored selective disruption of individual simulated cell actions. New framework features enabled recording detailed measures of ISEA cell activities and morphology.

Results

Enabled by a small set of cell operating principles, ISEA cells multiplied and self-organized into cyst-like structures that mimicked those of MDCK cells in a 3D embedded cell culture. Selective disruption of "anoikis" or directional cell division caused the ISEA to develop phenotypic features resembling those of in vitro tumor reconstruction models and cancerous tissues in vivo. Disrupting either process, or both, altered cell activity patterns that resulted in morphologically similar outcomes. Increased disruption led to a prolonged presence of intraluminal cells.

Conclusions

ISEA mechanisms, behaviors, and morphological properties may have biological counterparts. To the extent that in silico-to-in vitro mappings are valid, the results suggest plausible, additional mechanisms of in vitro cancer reconstruction or reversion, and raise potentially significant implications for early cancer diagnosis based on histology. Further ISEA development and use are expected to provide a viable platform to complement in vitro methods for unraveling the mechanistic basis of epithelial morphogenesis and cancer progression.

Collagen enhances compatibility and strength of glass ionomers

Glass ionomers have been used for perforation repair and retrograde filling where biointegration with periodontal tissue is required. Collagen has been demonstrated to promote cellular adhesion and enhance mineral tissue compressive strength. It was hypothesized that an appropriate concentration of collagen integrated into glass ionomer may improve both bio-compatibility and the mechanical properties of the material. By SEM and AFM, we discovered 70-nm granules appearing on the surfaces of glass-ionomer/collagen hybrids. Acid-etching revealed irregularly shaped particles interlinked by membrane-like sheets on the surface of the material with the typical 70-nm granules. WST-1 assay showed that acid-etching significantly enhanced the viability of attached gingival fibroblasts. However, the glass-ionomer/collagen hybrids' combined surface-etching outperformed other groups. The glass-ionomer/collagen hybrids presented enhanced compressive strength when integrated with 0.01% collagen, while higher concentrations of collagen compromised their mechanical property. In summary, collagen improved both the mechanical and biocompatible properties of glass ionomers. Further in vivo study is warranted.

Apoptotic mechanism of paclitaxel-induced cell death in human head and neck tumor cell lines

BACKGROUND

Paclitaxel (taxol) is clinically used to treat various human tumors. However, the cellular and molecular mechanism regarding apoptotic effect of paclitaxel on head and neck squamous cell carcinoma (HNSCC) remains elusive.

METHODS

The apoptotic effect and the mechanism of paclitaxel on FaDu hypopharyngeal cancer cell line, OEC-M1 gingival cancer cell line, and OC3 betel quid chewing-related buccal cancer cell lines were investigated by morphological observations, cell viability assay, flow cytometry assay and Western blotting methods.

RESULTS

Rounded-up cell number increased with membrane blebbing as the treatment of paclitaxel (50-500 nM) increased from 24 to 48 h among these cell lines. In cell viability assay, cell surviving rate significantly decreased from 87 to 27% as the dosage and duration of paclitaxel treatment increased (P < 0.05). Flow-cytometry analysis further demonstrated that 50 nM paclitaxel induced G2/M phase cell arrest among these cell lines within 8 h treatment, and then G2/M phase cell fraction significantly decreased as subG1 phase cell fraction significantly increased after 24 h treatment (P < 0.05), suggesting that cells underwent apoptosis. Furthermore, the activated caspases-8, -9, -3, -6 and poly ADP-ribose polymerase cleavage could all be significantly detected in FaDu, OEC-M1 and OC3 cells (P < 0.05).

CONCLUSION

Paclitaxel activated cell cycle arrest and caspase protein expressions to induce apoptosis in HNSCC cell lines.

Cell-generated forces influence the viability, metabolism and mechanical properties of fibroblast-seeded collagen gel constructs

The aim of this study was to investigate the influence of the endogenous forces generated by fibroblast-mediated contraction, using four individual collagen gel models that differed with respect to the ability of the cells to contract the gel. Human neonatal dermal fibroblasts were seeded in type I collagen and the gels were cast in a racetrack-shaped mould containing a removable central island. Two of the models were mechanically stressed (20 mm and 10 mm), as complete contraction was prevented by the presence of a central island. The central island was removed in the third model (released) and the final model was cast in a Petri dish and detached, allowing full multi-axial contraction (SR). Cell viability was maintained in the 10 mm, released and SR models over a 6 day culture period but localized regions of cell death were evident in the 20 mm model. Cell and collagen alignment was developed in the 20 mm and 10 mm models and to a lesser extent in the released model, but was absent in the SR model. Cell proliferation and collagen synthesis was lower in the 20 mm model compared to the other systems and there was evidence of enhanced matrix metalloproteinase production. The mechanical properties of the 20 mm model system were inferior to the 10 mm and released systems. The 10 mm model system induced a high level of cell and matrix orientation and may, therefore, represent the best option for tissue-engineered ligament repair involving an orientated fibroblast-seeded collagen gel.

Probing cellular microenvironments and tissue remodeling by atomic force microscopy

The function of cells is strongly determined by the properties of their extracellular microenvironment. Biophysical parameters like environmental stiffness and fiber orientation in the surrounding matrix are important determinants of cell adhesion and migration. Processes like tissue maintenance, wound repair, cancer cell invasion, and morphogenesis depend critically on the ability of cells to actively sense and remodel their surroundings. Pericellular proteolytic activity and adaptation of migration tactics to the environment are strategies to achieve this aim. Little is known about the distinct regulatory mechanisms that are involved in these processes. The system's critical biophysical and biochemical determinants are well accessible by atomic force microscopy (AFM), a unique tool for functional, nanoscale probing and morphometric, high-resolution imaging of processes in live cells. This review highlights common principles of tissue remodeling and focuses on application examples of different AFM techniques, for example elasticity mapping, the combination of AFM and fluorescence microscopy, the morphometric imaging of proteolytic activity, and force spectroscopy applications of single molecules or individual cells. To achieve a more complete understanding of the processes underlying the interaction of cells with their environments, the combination of AFM force spectroscopy experiments will be essential.

Activation of caspase-8 and Erk-1/2 in domes regulates cell death induced by confluence in MDCK cells

Under normal culture conditions, cells adhere to culture dish, spread out, proliferate, and finally cover all areas and reach confluence. During the confluent stage, cell proliferation ceases and differentiation is enhanced. Meanwhile, cell death also appears as the monolayer confluence proceeds. To delineate the mechanism of cell death induced by the confluent process, we employed Madin-Darby canine kidney (MDCK) cells. When approaching confluence, MDCK cells exhibited increase the levels of caspase-2 and enhanced the activity of caspase-8. Using various caspase inhibitors to block apoptosis, we found that only z-VAD-fmk and z-IETD-fmk can inhibit confluent cell death, indicating that confluent cell death is mediated by activation of caspase-8. Overexpression of Bcl-2 inhibited confluent cell death, suggesting the involvement of mitochondria-dependent pathway in confluent cell death. Interestingly, the activity of phospho-Erk (p-Erk) was initially decreased before confluence, but markedly increased after confluence. Immunofluorescence staining studies showed that p-Erk was expressed exclusively on dome-forming cells that underwent apoptosis. Treatment of confluent MDCK cells with PD98059 and UO126, the inhibitors of MEK, enhanced apoptosis as well as activity of caspase-8. These data indicate that elevation of p-Erk activity during confluence may serve to suppress confluent cell death. Taken together, activation of caspase-8 contributes to and results in confluent cell death, whereas elevated p-Erk activity serves to prevent confluent cell death by regulating activation of caspase-8.

Multiplex analysis of inflammatory signaling pathways using a high-content imaging system

This chapter describes a robust high-content cellular screening assay to simultaneously analyze the spatiotemporal activation of three different kinase-associated signaling pathways involving NF-kappaB, JNK, and p38, all of which are closely implicated in proliferative and proinflammatory responses. Signal transduction is dependent on the translocation of NF-kappaB p65 and phosphorylated c-Jun and p38 from the cytosol to the nucleus, and fluorescent immunolabeling was used to monitor changes in their cellular distribution. Cellular screening, data acquisition, and data interpretation were conducted on the ArrayScan HCS Reader (Cellomics Inc., Pittsburgh, PA). Assay adaptation to various cellular systems is feasible when sufficient separation of the nuclear and cytosolic compartment can be achieved and if cell adhesion properties permit proper attachment to the culture plates. Substitution of NF-kappaB p65 and phosphorylated forms of c-Jun and p38 as targets to analyze other translocating components is possible and is limited primarily by antibody specificity and the risk of fluorescent bleed-through between emission channels. Because assay validity is particularly confounded by inadequate spectral separation of the detection dyes in multicolor labeling assays, means of eliminating or counterbalancing staining artifacts are illustrated. Also, protocol parameter settings important for imaging and image processing are described, including object identification, image exposure settings, separation of cytosolic and nuclear regions, number of cells sufficient for analysis, and the use of gating thresholds critical for cell sorting and subpopulation analysis. This assay is a useful tool to investigate the interplay between signaling pathways and the mode of action, potency, and selectivity of compound inhibition of specific target molecules in a cellular context.

Deregulation of AP-1 proteins in collagen gel-induced epithelial cell apoptosis mediated by low substratum rigidity

In this study, we established that collagen gel, but not collagen gel coating, induced apoptosis exclusively in epithelial cell lines, which indicated that low substratum rigidity might trigger cell apoptosis. To confirm this, we used collagen gels with different rigidities due to cross-linking or physical disruption of collagen fibrils caused by sonication. We found that collagen gel-induced apoptosis was inversely correlated with substratum rigidity. Low substratum rigidity collagen gel-induced apoptosis was neither prevented by Bcl-2 overexpression nor preceded by mitochondrial release of cytochrome c. This suggested that the mitochondrial pathway was not involved in low substratum rigidity-induced apoptosis. Low substratum rigidity activated c-Jun N-terminal kinase (JNK) within 4 h, but it also rapidly down-regulated c-Jun within 1 h and triggered persistent aberrant expression of c-Fos for at least 24 h. Either reduced c-Jun expression or c-Fos overexpression induced apoptosis in several epithelial cells. Inhibiting low substratum rigidity-induced JNK activation prevented aberrant c-Fos expression but only partially blocked low substratum rigidity-induced apoptosis. Taking these results together, we conclude that low substratum rigidity collagen gel induced apoptosis in epithelial cells and that deregulated AP-1 proteins mediated that apoptosis, at least in part.

Increased collagen deposition and elevated expression of connective tissue growth factor in human thoracic aortic dissection

BACKGROUND

Thoracic aortic dissection (TAD) is characterized by dysregulated extracellular matrix. Little is known about the alterations of collagen and stimulators of collagen synthesis, eg, connective tissue growth factor (CTGF), in patients with TAD. In this study, we examined their roles in TAD.

METHODS AND RESULTS

Surgical specimens of the aortic wall of TAD patients (n=10) and controls (n=10) were tested for collagen types I and III and CTGF expression. When compared with controls, protein levels of type I and III collagen and CTGF were significantly increased by 3.2-, 3.7-, and 5.3-fold, respectively (P<0.05 for all). Similar patterns were shown in mRNA levels of type Ialpha and Ialpha2 collagen and CTGF. Using immunohistochemistry and trichrome staining, we also observed elevated levels of collagen in the aortic media and adventitia. Treatment with recombinant human CTGF increased collagen synthesis in cultured aortic smooth muscle cells in a dose- and time-dependent fashion, in which expression of collagens increased from 506+/-108 counts per minute to 2764+/-240 cpm by 50 ng/mL CTGF, and from 30+/-43 cpm to 429+/-102 cpm at 48 hours.

CONCLUSIONS

TAD patients exhibited significantly increased expression of aortic collagen types I and III as well as CTGF, which is likely to be responsible for the compromised aortic distensibility and systemic compliance. Because CTGF can increase collagen expression, CTGF may be a new target molecule in the pathogenesis and progression of TAD.

Regulation of epithelial tubule formation by Rho family GTPases

Previous work has established that the integrin signal transduction pathway plays an important role in the regulation of epithelial tubule formation. Furthermore, it has been demonstrated that Rho-kinase, an effector of the Rho signaling pathway, is an important downstream modulator of collagen-mediated renal and mammary epithelial tubule morphogenesis. In the present study, MDCK cells that expressed mutant dominant-negative, constitutively active Rho family GTPases were used to provide further insight into Rho-GTPase signaling and the regulation of epithelial tubule formation. Using collagen gel overlays on MDCK cells as a model system, we observed phosphorylated myosin light chain (pMLC) at the leading edge of migrating lamellipodia. This epithelial remodeling led to the formation of multicellular branching epithelial tubular structures with extensive tight junctions. However, in cells expressing dominant-negative RhoN19, MLC phosphorylation, epithelial remodeling, and tubule formation were inhibited. Instead, only small apical lumens with a solitary tight junctional ring were observed, providing further evidence that Rho signaling through Rho-kinase is important in the regulation of epithelial tubule formation. Because the present model for the Rho signaling pathway proposes that Rac plays a prominent but reciprocal role in cell regulation, experiments were conducted using cells that expressed constitutively active RacV12. When incubated with collagen gels, RacV12-expressing cells formed small apical lumens with simple tight junctions, suggesting that Rac1 signaling also has a prominent role in the regulation of epithelial morphogenesis. Complementary collagen gel overlay experiments with wild-type MDCK cells demonstrated that endogenous Rac1 activation levels decreased over a time course consistent with lamellipodia and tubule formation. Under these conditions, Rac1 was initially localized to the basolateral membrane. However, after epithelial remodeling, activated Rac1 was observed primarily in lamellipodia. These studies support a model in which Rac1 and RhoA are important modulators of epithelial tubule formation.

Function of discoidin domain receptor I in HGF-induced branching tubulogenesis of MDCK cells in collagen gel

Discoidin domain receptor I (DDR1) is a receptor tyrosine kinase (RTK) and serves as the receptor for collagen in addition to integrins. It has been well established that Madin-Darby canine kidney (MDCK) cells develop branching tubules in three-dimensional collagen gel in the presence of hepatocyte growth factor (HGF). MDCK cells normally express DDR1. However, the function of DDR1 in this in vitro model system has not been understood. We established stable-transfected MDCK cells harboring DDR1a, DDR1b, or dominant-negative (DN) DDR1 and cultured these transfectants in collagen gel with HGF (2 ng/ml) for the studies of branching tubule morphogenesis. Whether DDR1 played roles in cell growth, apoptosis, and migration was examined. We found that cells over-expressing DDR1a and DDR1b developed shorter tubules with fewer branches in collagen gel. In contrast, DN DDR1 over-expressed cells could not form tubule structure, but instead developed mostly cell aggregates with multiple long extended processes. Over-expression of DDR1a and 1b in MDCK cells resulted in reduction of cell growth when cells were cultured on collagen gel-coated dishes or collagen gel. On the other hand, DN DDR1 enhanced cell death on collagen gel, suggesting that DDR1 is involved in maintenance of cell survival. Moreover, over-expression of DDR1a and DDR1b markedly reduced collagen-induced migration capability, whereas DN DDR1 enhanced it, suggesting that DDR1a and 1b may serve as a negative regulator for alpha2beta1 integrin during migration on collagen substratum. These results indicate that DDR1 plays important role in regulation of HGF-induced branching tubulogenesis by modulating cell proliferation, survival, and cell migration.

Modulation of epithelial tubule formation by Rho kinase

We have developed a model system for studying integrin regulation of mammalian epithelial tubule formation. Application of collagen gel overlays to Madin-Darby canine kidney (MDCK) cells induced coordinated disassembly of junctional complexes that was accompanied by lamellipodia formation and cell rearrangement (termed epithelial remodeling). In this study, we present evidence that the Rho signal transduction pathway regulates epithelial remodeling and tubule formation. Incubation of MDCK cells with collagen gel overlays facilitated formation of migrating lamellipodia with membrane-associated actin. Inhibitors of myosin II and actin prevented lamellipodia formation, which suggests that actomyosin function was involved in regulation of epithelial remodeling. To determine this, changes in myosin II distribution, function, and phosphorylation were studied during epithelial tubule biogenesis. Myosin II colocalized with actin at the leading edge of lamellipodia thereby providing evidence that myosin is important in epithelial remodeling. This possibility is supported by observations that inhibition of Rho kinase, a regulator of myosin II function, alters formation of lamellipodia and results in attenuated epithelial tubule development. These data and those demonstrating myosin regulatory light-chain phosphorylation at the leading edge of lamellipodia strongly suggest that Rho kinase and myosin II are important modulators of epithelial remodeling. They support a hypothesis that the Rho signal transduction pathway plays a significant role in regulation of epithelial tubule formation.

Apical surface formation in MDCK cells: regulation by the serine/threonine kinase EMK1

It has recently become evident that basic mechanisms for the establishment of cell polarity are conserved between epithelial and nonepithelial systems. The vast catalogue of known gene products involved in various aspects of invertebrate and yeast cell polarity provides a repertoire of candidate proteins that can be tested for their roles in the organization of mammalian epithelia. Here, we describe cell biological approaches to study the development and maintenance of cell polarity in Mardin-Darby canine kidney (MDCK) cells, an established mammalian model cell line for simple epithelia. The assays allowed us to characterize the Caenorhabditis elegans PAR-1 homologue EMK1 as a novel regulator of apical surface formation in epithelial cells.

Rigidity of collagen fibrils controls collagen gel-induced down-regulation of focal adhesion complex proteins mediated by alpha2beta1 integrin

Previous studies have shown that collagen gel overlay induced selective proteolysis of focal adhesion complex proteins in Madin-Darby canine kidney (MDCK) cells. In this study, we examined whether morphological and biochemical changes were present in cells cultured on collagen gel. We found that focal adhesion complex proteins, including focal adhesion kinase (FAK), talin, paxillin, and p130cas, but not vinculin, were decreased within 1 h when MDCK cells were cultured on collagen gel. Collagen gel-induced selective decrease of focal adhesion proteins was observed in all lines of cells examined, including epithelial, fibroblastic, and cancer cells. Matrigel also induced selective down-regulation of focal adhesion proteins. However, cells cultured on collagen gel- or matrigel-coated dishes did not show any changes of focal adhesion proteins. These data suggest that the physical nature of the gel, i.e. the rigidity, is involved in the expression of focal adhesion proteins. The collagen gel-induced down-regulation of focal adhesion complex proteins was caused by reduction of protein synthesis and activation of proteases such as calpain. Overexpression of a dominant negative mutant of discoidin domain receptor 1 (DDR1) or FAK-related non-kinase (FRNK) did not prevent collagen gel-induced down-regulation of the focal adhesion complex protein, whereas an anti-alpha2beta1 integrin-neutralizing antibody completely blocked it. Taken together, our results indicate that the rigidity of collagen gel controls the expression of focal adhesion complex proteins, which is mediated by alpha2beta1 integrin but not DDR1.

A novel function of BCL-2 overexpression in regulatory volume decrease. Enhancing swelling-activated Ca(2+) entry and Cl(-) channel activity

The cellular function of the oncogene bcl-2, a key regulator of apoptosis, is still debated. The goal of this study was to explore the relationship between BCL-2 overexpression and cell volume regulation by using two independent models, Madin-Darby canine kidney (MDCK) cells stably transfected with BCL-2 and MDCK clones with inducible BCL-2 expression by the lac operator/repressor. BCL-2 overexpression enhanced the capability of regulatory volume decrease (RVD), a cellular defensive process against hypotonic stress. In various clones of MDCK cells, hypotonic stress induced an outwardly rectified Cl(-) current that was significantly up-regulated by BCL-2 overexpression. Other fundamental characteristics of this channel were similar among different MDCK clones, such as sensitivity to Cl(-) channel inhibitor, anion permeability, and time-dependent inactivation at more positive potential. Most importantly, BCL-2 overexpression up-regulates the swelling-activated Ca(2+) transient that is a critical signaling for normal RVD and the activation of swelling-activated Cl(-) channel in MDCK cells. BCL-2 overexpression also enhances the capacitative Ca(2+) entry that can be differentiated from the swelling-activated Ca(2+) transient by kinetic analysis and sensitivity to Gd(3+). Moreover, neutralization of endogenous BCL-2 by antibody blocks the normal RVD response and the activation of swelling-activated Cl(-) channel in human cervical cancer HT-3 cells. These results provide a new insight into the novel function of BCL-2 overexpression in the regulation of cell volume and ion flux.

Hepatocyte growth factor upregulates alpha2beta1 integrin in Madin-Darby canine kidney cells: implications in tubulogenesis

It has been well established that hepatocyte growth factor (HGF) induces branching tubule formation of Madin-Darby canine kidney (MDCK) cells cultured in collagen gel. Tubulogenesis per se requires the involvement of cell proliferation, migration, focalization proteolysis, cell-cell interaction and differentiation. However, signaling pathways and proteins involved in HGF-induced tubulogenesis by MDCK cells have not been thoroughly studied. Because cell-matrix interactions play important roles in tubulogenesis, we analyzed whether HGF altered the expression of extracellular matrix receptor (alpha2, alpha3, beta1 and alphavbeta3 integrin). We found that among those proteins examined, alpha2beta1 integrin levels were enhanced by HGF. HGF-induced upregulation of alpha2beta1 integrin was mediated via upregulation of alpha2 integrin mRNA abundance. Cycloheximide blocked the HGF-induced increase in alpha2 integrin mRNA expression. To understand the signaling pathways leading to an HGF-induced increase in alpha2beta1 integrin levels, PD98059 (MEK1 inhibitor), LY294002 (PI3-kinase inhibitor), and GF109203X (PKC inhibitor) were used. We found that PD98059 blocked the HGF-induced increase in alpha2beta1 integrin expression. Furthermore, 5E8 (specific anti-alpha2beta1 integrin antibody) was employed to elucidate the potential role of HGF-induced upregulation of alpha2beta1 integrin in branching morphogenesis. 5E8 did not alter HGF-induced scattering effects but disrupted HGF-induced branching tubulogenesis in collagen gel via inhibition of cell-cell interactions and growth. Taken together, HGF upregulates alpha2beta1 integrin expression via an indirect pathway, the results of which contribute to the regulation of cell-cell interactions and cell growth during branching morphogenesis in collagen gel.

Interactions between collagen IV and collagen-binding integrins in renal cell repair after sublethal injury

Recent studies demonstrate that collagen IV selectively promotes the repair of physiological processes in sublethally injured renal proximal tubular cells (RPTC). We sought to further define the mechanisms of cell repair by measuring the effects of toxicant injury and stimulation of repair by L-ascorbic acid-2-phosphate (AscP), exogenous collagen IV, or function-stimulating integrin antibodies on the expression and subcellular localization of collagen-binding integrins (CBI) in RPTC. Expression of CBI subunits alpha1, alpha2, and beta1 in RPTC was not altered on day 1 after sublethal injury by S-(1,2-dichlorovinyl)-L-cysteine (DCVC). On day 6, expression of alpha1 and beta1 subunits remained unchanged, whereas a 2.2-fold increase in alpha2 expression was evident in injured RPTC. CBI localization in control RPTC was limited exclusively to the basal membrane. On day 1 after injury, RPTC exhibited a marked inhibition of active Na(+) transport and a loss of cell polarity characterized by a decrease in basal CBI localization and the appearance of CBI on the apical membrane. On day 6 after injury, RPTC still exhibited marked inhibition of active Na(+) transport and localization of CBI to the apical membrane. However, DCVC-injured RPTC cultured in pharmacological concentrations of AscP (500 microM) or exogenous collagen IV (50 microg/ml) exhibited an increase in active Na(+) transport, relocalization of CBI to the basal membrane, and the disappearance of CBI from the apical membrane on day 6. Function-stimulating antibodies to CBI beta1 did not promote basal relocalization of CBI despite stimulating the repair of Na(+)/K(+)-ATPase activity on day 6 after injury. These data demonstrate that DCVC disrupts integrin localization and that physiological repair stimulated by AscP or collagen IV is associated with the basal relocalization of CBI in DCVC-injured RPTC. These data also suggest that CBI-mediated repair of physiological functions may occur independently of integrin relocalization.

Morphogenesis of MDCK cells in a collagen gel matrix culture under stromal adipocyte-epithelial cell interaction

BACKGROUND

The stromal-epithelial cell interaction is essential for epithelial morphogenesis. Recently, the specific stromal cell type adipocytes, which abundantly exist in perirenal adipose tissue, have been suggested to affect the biological behavior of some epithelial cell types. However, adipocyte-renal epithelial cell interaction remains unclear. We thus examined the effects of adipocytes on the morphogenesis of renal epithelial cells.

METHODS

The renal epithelial cell line, Madin-Darby canine kidney (MDCK), cells were cultured in three-dimensional collagen gel matrix with or without mature unilocular adipocytes. Cultures cells were examined by histochemistry, immunohistochemistry, and electron microscopy.

RESULTS

Adipocytes extensively promoted the tubule formation of MDCK cells in two different manners. In the first type, after approximately 20% of MDCK cells actively adhered to adipocytes; they organized double-cell structured tubules between the adipocytes and the gel, contacting directly with the entire surface of the adipocytes. In the second type, approximately 70% of MDCK cells apart from adipocytes also formed tubules that had no contact with adipocytes. The component cells of both tubule types at the apical side showed microvilli and peanut agglutinin lectin-positive stain. These cells at the basal side had the basal lamina and type IV collagen-positive stain.

CONCLUSIONS

These results indicate that the specific stromal cell type adipocytes cause MDCK cells to organize the well-polarized tubular structures in two different manners according to their direct and indirect interactions, suggesting that adipocytes may be involved in the regulatory mechanism of renal epithelial morphogenesis.

Collagen gel overlay induces two phases of apoptosis in MDCK cells

We previously demonstrated that collagen gel overlay induced cell remodeling to form lumen and apoptosis in Madin-Darby canine kidney cells. In the present study, we established that collagen gel overlay-induced apoptosis was initiated at areas exclusive of cell remodeling within 24 h (first phase) and extended into areas of cell remodeling within 48 h (second phase). Collagen gel overlay-induced apoptosis was accompanied by selective proteolysis of focal adhesion kinase (FAK), talin, p130cas, and c- src. Upon collagen gel overlay, FAK was initially degraded into a 90-kDa product during the first phase and subsequently into a 80-kDa product during the second phase. Collagen gel overlay-induced apoptosis of focal adhesion complex proteins and apoptosis of the first phase could be blocked only by a protease inhibitor cocktail. In addition, we found that both DEVD-fmk and ZVAD-fmk inhibited secondary proteolysis of FAK, but only ZVAD-fmk blocked collagen gel overlay-induced apoptosis of the second phase. Finally, collagen gel overlay-induced apoptosis and proteolysis of focal adhesion complex proteins were completely inhibited by the combination of protease inhibitor cocktail and ZVAD-fmk. Taken together, collagen gel overlay induces two phases of apoptosis; the first phase is dependent on proteolysis of focal adhesion complex proteins, and the second phase on activation of caspases.

Integrin regulation of cell-cell adhesion during epithelial tubule formation

The extracellular matrix plays an important role in regulation of epithelial development and organization. To determine more precisely the function of extracellular matrix in this process, the initial steps in collagen-mediated formation of epithelial tubules were studied using a model cell culture system. Previous studies have demonstrated that incubation of Madin-Darby canine kidney (MDCK) epithelial cells with a collagen gel overlay induces (beta)1 integrin-regulated epithelial remodeling accompanied by extensive cell rearrangements and formation of epithelial tubules. During epithelial remodeling there was extensive disruption of the epithelial junctional complex. Progressive opening of tight junctions was observed over 8 hours using transepithelial resistance measurements and immunofluorescence microscopy demonstrated that tight and adherens junction proteins were dispersed throughout the apical and basolateral membranes. Junction complex disruption allowed the formation of apical cell extensions and subsequent migration of selected cell sheets from the epithelial monolayer. Confocal microscopy demonstrated the presence of adherens junction (E-cadherin, (alpha)-catenin, (beta)-catenin, plakoglobin) and desmosomal (desmoplakin-1/2, plakoglobin) proteins on, and within, cell extensions demonstrating that cell junctions had undergone considerable disassembly. However, groups of cell extensions appeared to be associated by E-cadherin/catenin-mediated interactions. Association of E-cadherin/catenin complexes with the epithelial cytoskeleton was analyzed by differential detergent extraction. SDS-PAGE and immunoblot analysis demonstrated that adherens junction proteins were primarily cytoskeleton-associated in control cells. During integrin-regulated remodeling, there was a progressive reduction in the interaction of adherens junction proteins with the cytoskeleton suggesting that they play an important role in the maintenance of epithelial integrity. Since loss of transepithelial electrical resistance and disruption of junctional complexes were inhibited by an antifunctional integrin antibody, we propose that activation of integrin signaling pathways regulate junctional complex stability, cell-cell interactions and cell migration. These observations provide evidence that integrin-regulated MDCK epithelial tubule formation can serve as a model system for studying rearrangements of epithelial sheets which occur during development.

Age effect of type I collagen on morphogenesis of Mardin-Darby canine kidney cells

BACKGROUND

Mardin-Darby canine kidney (MDCK) cells cultured in hydrated collagen gels develop simple epithelial cysts or branching tubules, depending on the presence of hepatocyte growth factor (HGF). Constituents of extracellular matrix can modulate the morphogenesis of MDCK cells. Collagen is one of the few well-defined structural entities that display gross structural changes with aging. This study was conducted to delineate the effects of age-induced changes of collagen on the morphogenesis of MDCK cells cultured in collagen gel.

METHODS

We employed Y224 and MDCK clone II 3B5 cells to study cystogenesis and branching tubulogenesis, respectively. Cells were cultured in three-dimensional collagen gels prepared from 1-, 4-, 8-, and 16-month-old rat tail tendons, and their capacity to develop cysts or branching tubules was assessed. We also analyzed the compositions and physical structures of collagen of various ages.

RESULTS

Y224 cells developed generally larger spherical cysts in collagen gels prepared from rats that were more than four months old. The ratio of apoptosis of cells cultured in one-month-old collagen gel was markedly higher than in the gel of older ages. The results were consistent with the observations that collagen gel overlay-induced apoptosis of Y224 cells in one-month-old collagen was higher than that in older collagen. On the other hand, 3B5 cells exhibited a remarkable scattering morphology when cultured in one- or four-month-old collagen gel with HGF. In contrast, 3B5 cells exhibited more intercellular adhesion and were organized into branching tubule structures only in the collagen gel that was more than eight months old. The differences in morphogenesis could be explained by the observations that collagen of younger ages exerted markedly higher HGF-triggered migration capability than collagen of older ages.

CONCLUSIONS

Age-related alterations in collagen influence epithelial cell morphogenesis via regulation of cell apoptosis, proliferation, and/or motility.

Involvement of focal adhesion kinase in hepatocyte growth factor-induced scatter of Madin-Darby canine kidney cells

Focal adhesion kinase (FAK) has been implicated to play a critical role in integrin-mediated control of cell behavior. However, it is unclear whether FAK also participates in the regulation of growth factor-elicited cellular functions. In this study, we have demonstrated that although overexpression of FAK in Madin-Dardy canine kidney cells did not alter their growth property or ability to form tubules within collagen gel upon hepatocyte growth factor (HGF) stimulation, it apparently enhanced HGF-induced cell scattering. This enhancement was largely because of an increase in the third phase (i.e. cell migration) of cell scattering rather than the first two phases (i.e. cell spreading and cell-cell dissociation). Conversely, the expression of FAK-related nonkinase significantly ( approximately 60%) inhibited HGF-induced cell migration. Moreover, we have found that the effect of FAK on promoting HGF-induced cell motility was greatly dependent on cell-matrix interactions. We showed that HGF treatment selectively increased the expression of integrins alpha(2) and, to a lesser extent, alpha(3) in Madin-Dardy canine kidney cells and that a monoclonal antibody against integrin alpha(2) efficiently blocked HGF-enhanced cell migration on collagen. In our efforts to determine the mechanism by which FAK promotes HGF-induced cell migration, we found that FAK mutants deficient in phosphatidylinositol 3-kinase or p130(Cas) binding failed to promote HGF-induced cell migration. Interestingly, cells expressing a FAK mutant defective in Grb2 binding exhibited a rate of migration approximately 50% lower than that of cells expressing wild type FAK in response to HGF stimulation. Taken together, our results suggest a link between HGF-increased integrin expression, FAK activation, and enhanced cell motility and implicate a role for FAK in the facilitation of growth factor-induced cell motility.

Progelatinase A is produced and activated by rat hepatic stellate cells and promotes their proliferation

Activated hepatic stellate cells (HSCs) are a potential source of gelatinase A, which accumulates in fibrotic livers. Progelatinase A activation requires its binding to a complex of membrane-type matrix metalloproteinase (MT-MMP) and tissue inhibitor of metalloproteinases (TIMP)-2. These studies examine gelatinase A, MT1-MMP, and TIMP-2 synthesis by HSCs during activation in vitro and the potential role of gelatinase A in promoting HSC proliferation. Gelatinase A, MT1-MMP, and TIMP-2 messenger RNA (mRNA) were all upregulated in HSCs activated on plastic over 5 to 14 days. Gelatinase A expression was maximal at 7 days of culture, coinciding with the peak of HSC proliferation and the onset of procollagen I and alpha-smooth muscle actin (alpha-SMA) mRNA expression. Active forms of gelatinase A of 62 kd and 66 kd were secreted by activated HSCs and reached a maximum of 12.1% of total enzyme in 14-day culture supernatants. Treatment of HSCs with concanavalin A (con A) induced activation of MT1-MMP and enhanced secretion of activated gelatinase A, which reached a maximum of 44.4% of the total enzyme secreted into culture supernatants using 30 microgram/mL con A. [(14)C]-gelatin degradation assays confirmed the presence of gelatinolytic activity in activated HSC supernatants, which reached a maximum level at 7 days of culture. Antisense oligonucleotide inhibition of endogenous progelatinase A production, or the MMP inhibitor 1,10-phenanthroline inhibited (3)H-thymidine incorporation into HSC DNA by greater than 50%. We conclude that HSCs produce progelatinase A during activation in vitro and activate this enzyme coincident with MT1-MMP and TIMP-2 synthesis. Gelatinase A activity is required for maximal proliferation of HSCs in vitro suggesting this metalloproteinase is an autocrine proliferation factor for HSCs.

Suppression of ultraviolet irradiation-induced apoptosis by overexpression of focal adhesion kinase in Madin-Darby canine kidney cells

Focal adhesion kinase (FAK) has been implicated to play a role in suppression of apoptosis. In this study, we have demonstrated that UV irradiation induced cleavage of FAK and two of its interacting proteins Src and p130(Cas) in Madin-Darby canine kidney cells, concomitant with an increase in cell death. The cleavage of these proteins upon UV irradiation was completely inhibited by ZVAD-FMK, a broad range inhibitor of caspases, and apparently delayed by Bcl2 overexpression. To examine if FAK plays a role in suppressing UV-induced apoptosis, stable Madin-Darby canine kidney cell lines overexpressing FAK were established. Our results showed that a marked (30-40%) increase in cell survival upon UV irradiation was achieved by this strategy. In our efforts to determine the mechanism by which FAK transduces survival signals to the downstream, we found that a FAK mutant deficient in binding to phosphatidylinositol 3-kinase failed to promote cell survival. Moreover, the expression of the Src homology 3 domain of p130(Cas), which competed with endogenous p130(Cas) for FAK binding, abrogated the FAK-promoted cell survival. Together, these results suggest that the integrity of FAK and its binding to phosphatidylinositol 3-kinase and p130(Cas) are required for FAK to exert its antiapoptotic function.

Role of fibronectin deposition in cystogenesis of Madin-Darby canine kidney cells

BACKGROUND

Madin-Darby canine kidney (MDCK) cells cultured within collagen I gel exhibit clonal growth and form spherical multicellular cysts. The cyst-lining epithelial cells are polarized with the basolateral surface in contact with the collagen gel and the apical surface facing the lumen. To understand whether MDCK cysts construct the basal lamina, we characterized the composition of the extracellular matrix deposited by MDCK cysts. The cyst-lining cells produced an apparently incomplete basal lamina containing a discontinuous laminin substratum. In addition, the basal cell surface of the cyst was surrounded by a thick layer of fibronectin. This study was conducted to delineate the role of fibronectin deposition in cystogenesis.

METHODS

MDCK cells cultured in collagen gel were employed. We first used Arg-Gly-Asp (RGD) peptides containing disintegrin rhodostomin to disturb the interaction between fibronectin and the cell surface integrin. We then established several stable transfectants expressing the fibronectin antisense RNA and with which to directly examine the role of fibronectin in cystogenesis.

RESULTS

Rhodostomin markedly decreased the growth rates of the MDCK cyst, suggesting the importance of a normal interaction between fibronectin and integrins. The stable transfectants overexpressing the fibronectin antisense RNA exhibited relatively lower levels of fibronectin and markedly lower cyst growth rates than the control clone. The lower growth rate was correlated with an increase in collagen gel-induced apoptosis.

CONCLUSIONS

The results indicate that the deposition of fibronectin underlying the cyst-lining epithelium serves to prevent apoptosis induced by three-dimensional collagen gel cultures, and hence facilitates cyst growth of MDCK cells.

Collagens and atherosclerosis

Smooth muscle cells in the atherosclerotic lesions of diseased arteries produce new extracellular matrix, largely collagenous in nature, which is responsible in part for the occlusion of the vessel lumen by the atherosclerotic plaque. These smooth muscle cells express a different phenotype, responsive to growth factors, to that of the differentiated, nondividing contractile cell in the media. Specific collagens may be involved in the regulation of phenotype and in the migration of the cells to the site of lesion growth. Collagens may also be involved in the calcification of lesions, in the retention of low-density lipoprotein in the vessel wall and in smooth muscle cell survival. Glycation of collagen may promote atherogenesis. Effects as summarized in this short review, are not always, at first sight, consistent. The following points should be kept in mind, though, when considering the response of a cell to collagen. Any effect may be governed not just by the identity of the collagen type as such but by its state of polymerization: monomeric collagen, for instance, whether in solution or immobilized on plastic, may express different effects to the same collagen type when presented in its native polymerized state, e.g., as fibers. The precise identity of the cell and its location may be important: SMCs in secondary culture may not necessarily respond to any given collagen exactly as SMCs within the lesion or possess precisely the same properties, albeit both types are regarded as expressing the same (synthetic) phenotype. Effects may not necessarily be directly attributable to collagen, but to some other matrix constituent bound to collagen.

Bcl-2 overexpression prevents apoptosis-induced Madin-Darby canine kidney simple epithelial cyst formation

BACKGROUND

Madin-Darby canine kidney (MDCK) cells develop into simple epithelial cell cysts when cultured in type I collagen gel. We found that MDCK cells initially grow into multilayer cell aggregates and subsequently develop central lumen that contain apoptotic cells. We hypothesized that apoptosis might be essential for the formation of MDCK cysts.

METHODS

Using MDCK cells cultured in collagen gel as the experimental model, we investigated how renal cells organize to form cysts. To delineate the role of apoptosis in the process of cyst formation, MDCK cells were transfected with the bcl-2 gene. Characterization of apoptosis was studied by morphological and biochemical methods.

RESULTS

Bcl-2 overexpression conferred resistance to apoptosis. Cultured in collagen gel, Bcl-2 transfectants rarely formed a simple epithelial cyst, but instead remained as a multilayer cell aggregate containing central or multiple lumens, or even developing into branching structures.

CONCLUSIONS

Because Bcl-2 overexpression averts cyst cavitation, these data clearly indicate that apoptosis is an essential initial event for renal cyst formation.