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

Delivery technologies for therapeutic targeting of fibronectin in autoimmunity and fibrosis applications

Fibronectin (FN) is a critical component of the extracellular matrix (ECM) contributing to various physiological processes, including tissue repair and immune response regulation. FN regulates various cellular functions such as adhesion, proliferation, migration, differentiation, and cytokine release. Alterations in FN expression, deposition, and molecular structure can profoundly impact its interaction with other ECM proteins, growth factors, cells, and associated signaling pathways, thus influencing the progress of diseases such as fibrosis and autoimmune disorders. Therefore, developing therapeutics that directly target FN or its interaction with cells and other ECM components can be an intriguing approach to address autoimmune and fibrosis pathogenesis.

A Selective Extracellular Matrix Proteomics Approach Identifies Fibronectin Proteolysis by A Disintegrin-like and Metalloprotease Domain with Thrombospondin Type 1 Motifs (ADAMTS16) and Its Impact on Spheroid Morphogenesis

Secreted and cell-surface proteases are major mediators of extracellular matrix (ECM) turnover, but their mechanisms and regulatory impact are poorly understood. We developed a mass spectrometry approach using a cell-free ECM produced in vitro to identify fibronectin (FN) as a novel substrate of the secreted metalloprotease ADAMTS16. ADAMTS16 cleaves FN between its (I)5 and (I)6 modules, releasing the N-terminal 30 kDa heparin-binding domain essential for FN self-assembly. ADAMTS16 impairs FN fibrillogenesis as well as fibrillin-1 and tenascin-C assembly, thus inhibiting formation of a mature ECM by cultured fibroblasts. Furthermore ADAMTS16 has a marked morphogenetic impact on spheroid formation by renal tubule-derived MDCKI cells. The N-terminal FN domain released by ADAMTS16 up-regulates MMP3, which cleaves the (I)5-(I)6 linker of FN similar to ADAMTS16, therefore creating a proteolytic feed-forward mechanism. Thus, FN proteolysis not only regulates FN turnover, but also FN assembly, with potential long-term consequences for ECM assembly and morphogenesis.

Pax8 controls thyroid follicular polarity through cadherin-16

Organization of epithelial cells during follicular lumen formation is crucial for thyroid morphogenesis and function of the thyroid gland; however, the molecular mechanisms underlying this are poorly understood. To investigate this process, we established three-dimensional (3D) epithelial culture model systems using Fischer rat thyroid (FRT) cells or murine primary thyrocytes that developed polarized spherical structures with a central lumen, mimicking thyroid follicles. Using microarray-based differential expression analysis of FRT cells grown under 2D or 3D conditions, followed by RNA-mediated interference (RNAi) and morphogenetic analysis, we identified a key role for the thyroid transcription factor Pax8 and its target cadherin-16 (Cdh16) in the generation of polarized follicle-like structures. Silencing Pax8 expression inhibited the acquisition of apical–basal membrane polarity and impaired lumen formation. Both laminin and β1-integrin (Itgb1) expression was reduced, and cell cytoskeleton polarized distribution was altered. Silencing Cdh16 expression also led to the formation of defective structures characterized by very low laminin expression at the follicle–matrix interface, downregulation of Itgb1, and unpolarized distribution of cell cytoskeleton. Our results demonstrate that Pax8 controls apical–basal follicular polarization and follicle formation through Cdh16.

Summary: Using a 3D culture model of thyroid morphogenesis, it is revealed that thyroid follicular cell polarity depends on the Pax8 transcription factor and is linked to the β1-integrin–laminin pathway through Cdh16.

1,4-Butanediol diglycidyl ether-cross-linked hyaluronan inhibits fibrosis in rat primary tenocytes by down-regulating autophagy modulation

Epidural fibrosis, an inevitable part of the postoperative healing process, is one of the important causes of failed back surgery syndrome after spinal surgery. The aim of this study was to examine the inhibitory effect of a novel material 1,4-butanediol diglycidyl ether-cross-linked hyaluronan (cHA) on fibrosis in primary tenocytes. cHA inhibited migration, cell proliferation, and suppressed the expression of fibronectin, but not transforming growth factor-β, in primary tenocytes. cHA significantly increased matrix metalloproteinase-3 but decreased collagen-1 and microtubule-associated protein light chain 3-II expression in a dose-dependent manner compared with control groups. We therefore concluded that suppressing autophagy activity may be involved in the anti-fibrotic effect of cHA in primary tenocytes. Further, cHA may have the potential for preventing epidural fibrosis and subsequent failed back syndrome in patients with laminectomy in the future.

Fabrication of Collagen Gel Hollow Fibers by Covalent Cross-Linking for Construction of Bioengineering Renal Tubules

Collagen, the most used natural biomacromolecule, has been extensively utilized to make scaffolds for cell cultures in tissue engineering, but has never been fabricated into the configuration of a hollow fiber (HF) for cell culture due to its poor mechanical properties. In this study, renal tubular cell-laden collagen hollow fiber (Col HF) was fabricated by dissolving sacrificial Ca-alginate cores from collagen shells strengthened by carbodiimide cross-linking. The inner/outer diameters of the Col HF were precisely controlled by the flow rates of core alginate/shell collagen solution in the microfluidic device. As found, the renal tubular cells self-assembled into renal tubules with diameters of 50-200 μm post to the culture in Col HF for 10 days. According to the 3D reconstructed confocal images or HE staining, the renal cells appeared as a tight tubular monolayer on the Col HF inner surface, sustaining more 3D cell morphology than the cell layer on the 2D flat collagen gel surface. Moreover, compared with the cultures in either a Transwell or polymer HF membrane, the renal tubules in Col HF exhibited at least 1-fold higher activity on brush border enzymes of alkaline phosphatase and γ-glutamyltransferase, consistent with their gene expressions. The enhancement occurred similarly on multidrug resistance protein 2 and glucose uptake. Such bioengineered renal tubules in Col HF will present great potential as alternatives to synthetic HF in both clinical use and pharmaceutical investigation.

Epithelial morphogenesis of MDCK cells in three-dimensional collagen culture is modulated by interleukin-8

Epithelial morphogenesis is dependent upon a variety of factors, many of which involve complex interactions between cells and their surrounding environments. We analyzed the patterns of differential gene expression associated with Madin-Darby canine kidney (MDCK) renal epithelial cells grown within a collagen gel in three-dimensional (3D) culture compared with those grown atop a collagen gel in two-dimensional (2D) culture. Under these conditions, MDCK cells spontaneously formed either hollow spherical cysts or flat monolayer sheets, respectively. Microarray analysis of gene expression revealed a twofold or greater expression difference in 732 gene sets from MDCK cysts compared with monolayers (false discovery rate or FDR-adjusted P values <0.05). Interleukin-8 (IL-8) was reproducibly found to be among the genes whose expression was most dramatically upregulated, and this behavior was verified through real-time PCR analysis. The level of IL-8 protein expression was significantly increased in 3D MDCK cultures compared with that detected in cells in 2D culture. Hepatocyte growth factor (HGF) induces MDCK cells in 3D culture to form linear tubule-like structures. We found that HGF stimulation caused MDCK cells in 3D culture to decrease the expression of IL-8 at both the mRNA and protein levels. Furthermore, the addition of recombinant IL-8 to HGF-stimulated 3D MDCK cultures was sufficient to partially reverse the tubulogenic effects of HGF, resulting in the formation of cystic structures. These data suggest that IL-8 participates in the formation of cystic structures by MDCK cells in 3D culture and that HGF may stimulate tubulogenesis through the suppression of IL-8.

Establishing epithelial glandular polarity: interlinked roles for ARF6, Rac1, and the matrix microenvironment

The depletion of ARF6 in epithelial cysts causes a striking inversion of glandular orientation. This requires temporal Rac1 inactivation and is accompanied in basement membrane cultures by improperly assembled laminins. In collagen I, these inverted cysts promote integrin-linked fibril linearization reminiscent of matrix remodeling in disease.

Epithelial cysts comprise the structural units of the glandular epithelium. Although glandular inversion in epithelial tumors is thought to be a potential mechanism for the establishment of metastatic disease, little is known about the morphogenic cues and signaling pathways that govern glandular polarity and organization. Using organotypic cultures of Madin-Darby canine kidney cells in reconstituted basement membrane, we show that cellular depletion of the small GTP-binding protein ARF6 promotes the formation of inverted cysts, wherein the apical cell membrane faces the cyst exterior, and the basal domain faces the central lumen, while individual cell polarity is maintained. These cysts are also defective in interactions with laminin at the cyst–matrix interface. This inversion of glandular orientation is accompanied by Rac1 inactivation during early cystogenesis, and temporal activation of Rac1 is sufficient to recover the normal cyst phenotype. In an unnatural collagen I microenvironment, ARF6-depleted, inverted epithelial cysts exhibit some loss of cell polarity, a marked increase in Rho activation and Rac1 inactivation, and striking rearrangement of the surrounding collagen I matrix. These studies demonstrate the importance of ARF6 as a critical determinant of glandular orientation and the matrix environment in dictating structural organization of epithelial cysts.

Plasma and cellular fibronectin: distinct and independent functions during tissue repair

Fibronectin (FN) is a ubiquitous extracellular matrix (ECM) glycoprotein that plays vital roles during tissue repair. The plasma form of FN circulates in the blood, and upon tissue injury, is incorporated into fibrin clots to exert effects on platelet function and to mediate hemostasis. Cellular FN is then synthesized and assembled by cells as they migrate into the clot to reconstitute damaged tissue. The assembly of FN into a complex three-dimensional matrix during physiological repair plays a key role not only as a structural scaffold, but also as a regulator of cell function during this stage of tissue repair. FN fibrillogenesis is a complex, stepwise process that is strictly regulated by a multitude of factors. During fibrosis, there is excessive deposition of ECM, of which FN is one of the major components. Aberrant FN-matrix assembly is a major contributing factor to the switch from normal tissue repair to misregulated fibrosis. Understanding the mechanisms involved in FN assembly and how these interplay with cellular, fibrotic and immune responses may reveal targets for the future development of therapies to regulate aberrant tissue-repair processes.

Requirement of focal adhesion kinase in branching tubulogenesis

We previously demonstrated that alpha3beta1 integrins are essential to hepatocyte growth factor (HGF)-independent branching tubulogenesis in Mardin-Darby Canine Kidney (MDCK) cells. However, the involvement of integrin downstream signaling molecules remains unclear. In the present study, we successfully isolated cell lines possessing different tubulogenic potentials from the MDCK cells; cyst clones (CA4, CA6) forming cystic structures when cultured in 0.3% type I collagen gel and mass clones (M610, M611, M612) forming aggregated masses. Cyst clones maintained cystic structure in 0.1% collagen gel, whereas mass clones spontaneously developed into tubules. Both clones exhibited various morphologies when cultured on a dish: cyst clones formed aggregated islands, while mass clones were more scattered and exhibited higher migration capacity. Among several focal adhesion machinery proteins examined, only the expression and phosphorylation level of focal adhesion kinase (FAK) in mass clones was higher than in cyst clones, while other proteins showed no obvious differences. However, overexpression of wild type FAK in CA6 cells did not facilitate branching tubule formation in 0.1% collagen gel. Targeted decrease in the expression level of FAK in M610 cells with the application of antisense cDNA resulted in a marked reduction of branching tubule formation in 0.1% collagen gel and showed a down-regulation of fibronectin assembly, which is known to promote tubulogenesis. In contrast, overexpression of wild type FAK in CA6 cells had no effect on fibronectin assembly. Taken together, our data demonstrates that FAK is required, but not sufficient for HGF-independent branching tubulogenesis in MDCK cells.

The C-terminal variable domain of LigB from Leptospira mediates binding to fibronectin

Adhesion through microbial surface components that recognize adhesive matrix molecules is an essential step in infection for most pathogenic bacteria. In this study, we report that LigB interacts with fibronectin (Fn) through its variable region. A possible role for LigB in bacterial attachment to host cells during the course of infection is supported by the following observations: (i) binding of the variable region of LigB to Madin-Darby canine kidney (MDCK) cells in a dose-dependent manner reduces the adhesion of Leptospira, (ii) inhibition of leptospiral attachment to Fn by the variable region of LigB, and (iii) decrease in binding of the variable region of LigB to the MDCK cells in the presence of Fn. Furthermore, we found a significant reduction in binding of the variable region of LigB to Fn using small interfering RNA (siRNA). Finally, the isothermal titration calorimetric results confirmed the interaction between the variable region of LigB and Fn. This is the first report to demonstrate that LigB binds to MDCK cells. In addition, the reduction of Fn expression in the MDCK cells, by siRNA, reduced the binding of LigB. Taken together, the data from the present study showed that LigB is a Fn-binding protein of pathogenic Leptospira spp. and may play a pivotal role in Leptospira-host interaction during the initial stage of infection.

Raf kinase inhibitor protein positively regulates cell-substratum adhesion while negatively regulating cell-cell adhesion

Raf kinase inhibitor protein (RKIP) regulates a number of cellular processes, including cell migration. Exploring the role of RKIP in cell adhesion, we found that overexpression of RKIP in Madin-Darby canine kidney (MDCK) epithelial cells increases adhesion to the substratum, while decreasing adhesion of the cells to one another. The level of the adherens junction protein E-cadherin declines profoundly, and there is loss of normal localization of the tight junction protein ZO-1, while expression of the cell-substratum adhesion protein beta1 integrin dramatically increases. The cells also display increased adhesion and spreading on multiple substrata, including collagen, gelatin, fibronectin and laminin. In three-dimensional culture, RKIP overexpression leads to marked cell elongation and extension of long membrane protrusions into the surrounding matrix, and the cells do not form hollow cysts. RKIP-overexpressing cells generate considerably more contractile traction force than do control cells. In contrast, RNA interference-based silencing of RKIP expression results in decreased cell-substratum adhesion in both MDCK and MCF7 human breast adenocarcinoma cells. Treatment of MDCK and MCF7 cells with locostatin, a direct inhibitor of RKIP and cell migration, also reduces cell-substratum adhesion. Silencing of RKIP expression in MCF7 cells leads to a reduction in the rate of wound closure in a scratch-wound assay, although not as pronounced as that previously reported for RKIP-knockdown MDCK cells. These results suggest that RKIP has important roles in the regulation of cell adhesion, positively controlling cell-substratum adhesion while negatively controlling cell-cell adhesion, and underscore the complex functions of RKIP in cell physiology.

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.

Simulating properties of in vitro epithelial cell morphogenesis

How do individual epithelial cells (ECs) organize into multicellular structures? ECs are studied in vitro to help answer that question. Characteristic growth features include stable cyst formation in embedded culture, inverted cyst formation in suspension culture, and lumen formation in overlay culture. Formation of these characteristic structures is believed to be a consequence of an intrinsic program of differentiation and de-differentiation. To help discover how such a program may function, we developed an in silico analogue in which space, events, and time are discretized. Software agents and objects represent cells and components of the environment. “Cells” act independently. The “program” governing their behavior is embedded within each in the form of axioms and an inflexible decisional process. Relationships between the axioms and recognized cell functions are specified. Interactions between “cells” and environment components during simulation give rise to a complex in silico phenotype characterized by context-dependent structures that mimic counterparts observed in four different in vitro culture conditions: a targeted set of in vitro phenotypic attributes was matched by in silico attributes. However, for a particular growth condition, the analogue failed to exhibit behaviors characteristic of functionally polarized ECs. We solved this problem by following an iterative refinement method that improved the first analogue and led to a second: it exhibited characteristic differentiation and growth properties in all simulated growth conditions. It is the first model to simultaneously provide a representation of nonpolarized and structurally polarized cell types, and a mechanism for their interconversion. The second analogue also uses an inflexible axiomatic program. When specific axioms are relaxed, growths strikingly characteristic of cancerous and precancerous lesions are observed. In one case, the simulated cause is aberrant matrix production. Analogue design facilitates gaining deeper insight into such phenomena by making it easy to replace low-resolution components with increasingly detailed and realistic components.

To gain new insights into how normal and abnormal epithelial cell (EC) morphogenesis occurs, Grant and colleagues designed, built, and studied a series of discrete event analogues capable of mimicking epithelial growth characteristics in four different culture conditions. The analogues use independent software agents and objects to represent cells and the two environment components. “Cells” interact with local components using an axiomatic decisional process deduced from experimental in vitro observations. During simulations, “cells” form stable structures that mimic counterparts in cell cultures: a set of targeted in vitro phenotypic attributes is matched by the analogue's phenotype. However, the foundational analogue failed to exhibit a behavior characteristic of functionally polarized ECs in stable structures. Iterative refinement solved the problem: the improved analogue is the first model to simultaneously provide a representation of nonpolarized and structurally polarized cell types, and a mechanism for their interconversion. Inflexible axiom application is essential to simulate normal attributes. Selectively changing an axiom or relaxing its application caused growths strikingly characteristic of cancerous and precancerous lesions. Gaining deeper insight into such phenomena can be achieved by replacing low-resolution components with increasingly detailed and realistic components.

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.

Specific lectins map the distribution of fibronectin and beta 1-integrin on living MDCK cells

The expression and dynamics of bound fibronectin and the sialylated integral membrane protein, beta 1-integrin, were analyzed on the apical membrane of living MDCK cells. Fibronectin was identified by its specific binding of fluorescent peanut agglutinin and sialylated beta 1-integrin by its binding of Sambucus nigra agglutinin. Confocal epifluorescence microscopy and laser scanning cytometry determined the distribution and abundance of binding sites of the two fluorescently labeled lectins. Both fibronectin and beta 1-integrin were restricted to specific regions uniformly distributed over the entire apical surface. Apical-surface fibronectin binding varied much more between cells than did the expression of beta 1-integrin. Sialylated beta 1-integrin colocalized >92% with membrane microplicae while fibronectin was unrelated to these surface structures. This lack of colocalization of the proteins was confirmed by double-labeling experiments. From the maturation dependence of the fibronectin-binding capacity and the differences in protein turnover times, it was evident that fibronectin did not bind to sialylated beta 1-integrin. Furthermore, desialylation of beta 1-integrin uncovered additional fibronectin receptors on the apical membrane. We conclude that these lectins permit tracking of two membrane-associated glycoproteins in living cells and that fibronectin binds only to desialylated beta 1-integrin on MDCK cells.

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.

Expression in Pichia pastoris and characterization by circular dichroism and NMR of rhodostomin

Rhodostomin (Rho) is a snake venom protein isolated from Calloselasma rhodostoma. Rho is a disintegrin that inhibits platelet aggregation by blocking the binding of fibrinogen to the integrin alpha(IIb)beta3 of platelets. Rho produced in Escherichia coli inhibited platelet aggregation with a K(I) value of 263 nM. Although functional, Rho produced in E. coli is misfolded based on our 2D and 3D NMR studies. In order to correct the folding problem, Rho was expressed in Pichia pastoris. The recombinant Rho expressed in P. pastoris inhibited platelet aggregation with a resulting K(I) value of 70 nM. This is the same potency as that of native Rho. CD analysis showed that the secondary structures of Rho are pH-independent and contain 3.5-7.9% alpha-helix, 48.2-50.5% beta-structures, and 42.3-47% coil. The sequential assignment and structure analysis of Rho were obtained using 2D and 3D 15N-edited NMR spectra. These results provide the first direct evidence that highly disulfide-bonded disintegrin can be expressed in P. pastoris with the correct fold. This evidence may serve as the basis for exploring the structure and function relationships as well as the dynamics of disintegrin and its variants.

Role of alpha(3)beta(1) integrin in tubulogenesis of Madin-Darby canine kidney cells

BACKGROUND

We isolated several Madin-Darby canine kidney (MDCK) subclones that exhibit different degrees of branching tubulogenesis in lower concentrations of collagen gel. The M634 clone formed cell aggregates in 0.3% collagen gel, but developed branching tubules vigorously in 0.1% collagen gel. In contrast, the Y224 clone formed cysts in 0.3% collagen gel and displayed fewer branching structures in 0.1% collagen gel. Morphologically, M634 cells exhibited higher levels of cell scattering as well as collagen-induced cell migration than Y224. We conducted this study to delineate the underlying mechanism of branching tubulogenesis in M634 cells.

METHODS

Components of the focal contact machinery were analyzed in both cell lines, including the extracellular matrix glycoproteins fibronectin, laminin, and vitronectin; cytoskeleton-associated elements alpha-actinin, talin, and vinculin; and receptors for extracellular matrix and alpha(2), alpha(3), alpha(5), alpha(v), beta(1), and beta(3) integrins. Furthermore, we established several stable transfectants of alpha(3) integrin antisense RNA in M634 cells to examine the role of alpha(3)beta(1) integrin in branching morphogenesis directly.

RESULTS

There were no obvious differences in levels of the focal adhesion complex proteins between M634 and Y224 cells, except that the content of the alpha(3) and beta1 integrins were 1.2- and 0.6-fold higher in M634 cells, respectively. The expression of alpha(3) integrin antisense RNA significantly lowered the levels of alpha(3) integrin mRNA and protein. The potential of cell scattering, migration, and branching tubulogenesis in M634 cells was inhibited according to the decrease in alpha(3) integrin expression.

CONCLUSION

Our data indicate that expression of alpha(3)beta(1) integrin regulates cell scattering, migration, and branching tubulogenesis of MDCK cells, possibly via adhesion to or serving as a signaling molecule for type I collagen.

Migration of Plasmodium sporozoites through cells before infection

Intracellular bacteria and parasites typically invade host cells through the formation of an internalization vacuole around the invading pathogen. Plasmodium sporozoites, the infective stage of the malaria parasite transmitted by mosquitoes, have an alternative mechanism to enter cells. We observed breaching of the plasma membrane of the host cell followed by rapid repair. This mode of entry did not result in the formation of a vacuole around the sporozoite, and was followed by exit of the parasite from the host cell. Sporozoites traversed the cytosol of several cells before invading a hepatocyte by formation of a parasitophorous vacuole, in which they developed into the next infective stage. Sporozoite migration through several cells in the mammalian host appears to be essential for the completion of the life cycle.

Role of fibronectin deposition in branching morphogenesis of Madin-Darby canine kidney cells

BACKGROUND

Madin-Darby canine kidney (MDCK) epithelial cells grown in collagen gels in the presence of hepatocyte growth factor (HGF) form branching tubules. The tubule-lining epithelial cells are polarized with the basolateral surface in contact with the collagen gel and the apical surface facing the lumen. To delineate whether MDCK branching tubules construct the basal lamina, we characterized the composition of the extracellular matrix deposited by MDCK tubules. The tubule-lining cells produced an apparently incomplete basal lamina containing a discontinuous laminin substratum. In addition, a thick layer of fibronectin surrounded the basal cell surface of the branching tubule. In an attempt to delineate the role of fibronectin deposition in branching morphogenesis, we conducted this study.

METHODS

MDCK cells cultured in collagen gel were employed. We first used arginine-glycine-aspartate peptides containing disintegrin rhodostomin to disturb the interactions between fibronectin and cell surface integrins. Furthermore, we established several stable transfectants expressing fibronectin antisense RNA to examine the role of fibronectin in branching morphogenesis directly.

RESULTS

Rhodostomin inhibited the formation of branching tubules. The transfectants expressing fibronectin antisense RNA exhibited relatively lower levels of synthesized fibronectin and markedly diminished growth rates of branching tubules than the control clone. An inhibition of branching morphogenesis induced by the overexpression of fibronectin antisense RNA was manifested by the decrease in cell growth rates and cell migration.

CONCLUSION

These results indicate that the deposition of fibronectin underlying the tubule-lining epithelium serves to enhance cell proliferation and migration, and hence facilitates the branching tubulogenesis of MDCK cells.

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.