Enhancement of vinculin synthesis by migrating stratified squamous epithelium

Age Dependent Changes in Corneal Epithelial Cell Signaling

The cornea is exposed daily to a number of mechanical stresses including shear stress from tear film and blinking. Over time, these stressors can lead to changes in the extracellular matrix that alter corneal stiffness, cell-substrate structures, and the integrity of cell-cell junctions. We hypothesized that changes in tissue stiffness of the cornea with age may alter calcium signaling between cells after injury, and the downstream effects of this signaling on cellular motility and wound healing. Nanoindentation studies revealed that there were significant differences in the stiffness of the corneal epithelium and stroma between corneas of 9- and 27-week mice. These changes corresponded to differences in the timeline of wound healing and in cell signaling. Corneas from 9-week mice were fully healed within 24 h. However, the wounds on corneas from 27-week mice remained incompletely healed. Furthermore, in the 27-week cohort there was no detectable calcium signaling at the wound in either apical or basal corneal epithelial cells. This is in contrast to the young cohort, where there was elevated basal cell activity relative to background levels. Cell culture experiments were performed to assess the roles of P2Y2, P2X7, and pannexin-1 in cellular motility during wound healing. Inhibition of P2Y2, P2X7, or pannexin-1 all significantly reduce wound closure. However, the inhibitors all have different effects on the trajectories of individual migrating cells. Together, these findings suggest that there are several significant differences in the stiffness and signaling that underlie the decreased wound healing efficacy of the cornea in older mice.

The Effect of Calcium and Glucose Concentration on Corneal Epithelial Cell Lines Differentiation, Proliferation, and Focal Adhesion Expression

It is known that culture media composition can affect cell behavior, morphology, and gene expression. However, in the case of corneal epithelial cells, the combined role of calcium and glucose concentration in media has not previously been examined. In this study, a human immortalized corneal epithelial cell line was used to examine the effect of glucose and calcium concentrations on these cells. Cell metabolic activity, cell growth curve analysis, and relative gene and protein expression of proliferative marker extracellular related kinase (ERK) were used to study proliferation. Corneal epithelial stem cell marker NP63 and mature epithelial marker cytokeratin 3 (CK3) were analyzed by using reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemistry. Focal adhesions were examined by using immunocytochemistry. Cells cultured in both low-glucose, high-calcium (LG-HC) media and high-glucose, low-calcium (HG-LC) media showed similar results in both RT-PCR and immunocytochemistry analysis. NP63 expression was significantly lower and CK3 expression was higher in these groups compared with cells cultured in commercial media. NP63 and CK3 expression was also analyzed by using immunocytochemistry, which confirmed these findings. The high-glucose, high-calcium-fed cells showed the lowest expression of all markers and no gene expression of CK3. This was deemed the most unsuitable media formulation for this cell line. Focal adhesion expression was the lowest in the high-calcium, high-glucose-fed cells, with the most even distribution of this among the commercial media group. Overall, this study showed that varying glucose and calcium concentrations can have significant effects on differentiation, proliferation, focal adhesions, and metabolic activity of this cell line. It seems that an LG-HC and HG-LC formulation were interchangeable with similar proliferative and differentiation effects.

The Role of Hypoxia in Corneal Extracellular Matrix Deposition and Cell Motility

The cornea is an excellent model tissue to study how cells adapt to periods of hypoxia as it is naturally exposed to diurnal fluxes in oxygen. It is avascular, transparent, and highly innervated. In certain pathologies, such as diabetes, limbal stem cell deficiency, or trauma, the cornea may be exposed to hypoxia for variable lengths of time. Due to its avascularity, the cornea requires atmospheric oxygen, and a reduction in oxygen availability can impair its physiology and function. We hypothesize that hypoxia alters membrane stiffness and the deposition of matrix proteins, leading to changes in cell migration, focal adhesion formation, and wound repair. Two systems-a 3D corneal organ culture model and polyacrylamide substrates of varying stiffness-were used to examine the response of corneal epithelium to normoxic and hypoxic environments. Exposure to hypoxia alters the deposition of the matrix proteins such as laminin and Type IV collagen. In addition, previous studies had shown a change in fibronectin after injury. Studies performed on matrix-coated acrylamide substrates ranging from 0.2 to 50 kPa revealed stiffness-dependent changes in cell morphology. The localization, number, and length of paxillin pY118- and vinculin pY1065-containing focal adhesions were different in wounded corneas and in human corneal epithelial cells incubated in hypoxic environments. Overall, these results demonstrate that low-oxygenated environments modify the composition of the extracellular matrix, basal lamina stiffness, and focal adhesion dynamics, leading to alterations in the function of the cornea. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc.

Epithelial cells exert differential traction stress in response to substrate stiffness

Epithelial wound healing is essential for maintaining the function and clarity of the cornea. Successful repair after injury involves the coordinated movements of cell sheets over the wounded region. While collective migration has been the focus of studies, the effects that environmental changes have on this form of movement are poorly understood. To examine the role of substrate compliancy on multi-layered epithelial sheet migration, we performed traction force and confocal microscopy to determine differences in traction forces and to examine focal adhesions on synthetic and biological substrates. The leading edges of corneal epithelial sheets undergo retraction or contraction prior to migration, and alterations in the sheet's stiffness are affected by the amount of force exerted by cells at the leading edge. On substrates of 30 kPa, cells exhibited greater and more rapid movement than on substrates of 8 kPa, which are similar to that of the corneal basement membrane. Vinculin and its phosphorylated residue Y1065 were prominent along the basal surface of migrating cells, while Y822 was prominent between neighboring cells along the leading edge. Vinculin localization was diffuse on a substrate where the basement membrane was removed. Furthermore, when cells were cultured on fibronectin-coated acrylamide substrates of 8 and 50 kPa and then wounded, there was an injury-induced phosphorylation of Y1065 and substrate dependent changes in the number and size of vinculin containing focal adhesions. These results demonstrate that changes in substrate stiffness affected traction forces and vinculin dynamics, which potentially could contribute to the delayed healing response associated with certain corneal pathologies.

A Proteomic Approach for Understanding the Mechanisms of Delayed Corneal Wound Healing in Diabetic Keratopathy Using Diabetic Model Rat

Diabetes mellitus is a widespread metabolic disorder, and long-term hyperglycemia in diabetics leads to diabetic keratopathy. In the present study, we used a shotgun liquid chromatography/mass spectrometry-based global proteomic approach using the cornea of streptozotocin-induced diabetic (STZ) rats to examine the mechanisms of delayed corneal wound healing in diabetic keratopathy. Applying a label-free quantitation method based on spectral counting, we identified 188 proteins that showed expression changes of >2.0-fold in the cornea of STZ rats. In particular, the level of lumican expression in the cornea of STZ rats was higher than that of the normal rats. In the cornea of the normal rat, the expression level of lumican was elevated during the wound healing process, and it returned to the same expression level as before cornea injury after the wound was healed completely. On the other hand, a high expression level of lumican in the cornea of STZ rats was still maintained even after the wound was healed completely. In addition, adhesion deficiency in corneal basal cells and Bowman’s membrane was observed in the STZ rat. Thus, abnormally overexpressed lumican may lead to adhesion deficiency in the cornea of STZ rats.

Effects of MMP12 on cell motility and inflammation during corneal epithelial repair

Corneal epithelial defects are a common cause of ocular morbidity and can result in corneal scarring if they do not heal properly. Matrix metalloproteinases (MMPs) are extracellular matrix proteinases that regulate multiple aspects of corneal repair. We have previously shown that MMP12 has a protective effect on corneal fibrosis through its regulation of neutrophil and macrophage infiltration and angiogenesis in a chemical injury model involving full thickness damage to the cornea. However, the role of MMP12 in injuries limited to the corneal epithelium is relatively unknown. This study investigates the reparative effects of MMP12 following isolated corneal epithelial injury. Using a corneal epithelial debridement injury model performed on corneas of wild-type (WT) mice, we show that Mmp12 is expressed early following corneal epithelial injury with highest expression levels at 8 h after injury and lower expression levels at 4 and 8 days after injury. We investigated whether MMP12 has an effect on the rate of epithelial repair and cell migration using in vivo and in vitro scratch assays performed on WT and Mmp12^-/- mice. We found that loss of MMP12 results in a slower scratch wound repair rate both in vivo and in vitro. We also found that corneas of Mmp12^-/- mice have decreased neutrophil infiltration following injury. Loss of MMP12, however, does not affect cell proliferation in the center of the wounds. These data support a role of MMP12 in promoting early repair processes following corneal epithelial injury by enhancing epithelial cell migration and neutrophil infiltration.

Purinoreceptor P2X7 Regulation of Ca(2+) Mobilization and Cytoskeletal Rearrangement Is Required for Corneal Reepithelialization after Injury

The process of wound healing involves a complex network of signaling pathways working to promote rapid cell migration and wound closure. Activation of purinergic receptors by secreted nucleotides plays a major role in calcium mobilization and the subsequent calcium-dependent signaling that is essential for proper healing. The role of the purinergic receptor P2X7 in wound healing is still relatively unknown. We demonstrate that P2X7 expression increases at the leading edge of corneal epithelium after injury in an organ culture model, and that this change occurs despite an overall decrease in P2X7 expression throughout the epithelium. Inhibition of P2X7 prevents this change in localization after injury and impairs wound healing. In cell culture, P2X7 inhibition attenuates the amplitude and duration of injury-induced calcium mobilization in cells at the leading edge. Immunofluorescence analysis of scratch-wounded cells reveals that P2X7 inhibition results in an overall decrease in the number of focal adhesions along with a concentration of focal adhesions at the wound margin. Live cell imaging of green fluorescent protein-labeled actin and talin shows that P2X7 inhibition alters actin cytoskeletal rearrangements and focal adhesion dynamics after injury. Together, these data demonstrate that P2X7 plays a critical role in mediating calcium signaling and coordinating cytoskeletal rearrangement at the leading edge, both of which processes are early signaling events necessary for proper epithelial wound healing.

Communication between corneal epithelial cells and trigeminal neurons is facilitated by purinergic (P2) and glutamatergic receptors

Previously, we demonstrated that nucleotides released upon mechanical injury to corneal epithelium activate purinergic (P2) receptors resulting in mobilization of a Ca²⁺ wave. However, the tissue is extensively innervated and communication between epithelium and neurons is critical and not well understood. Therefore, we developed a co-culture of primary trigeminal neurons and human corneal limbal epithelial cells. We demonstrated that trigeminal neurons expressed a repertoire of P2Yand P2X receptor transcripts and responded to P2 agonists in a concentration-dependent manner. Mechanical injuries to epithelia in the co-cultures elicited a Ca²⁺ wave that mobilized to neurons and was attenuated by Apyrase, an ectonucleotidase. To elucidate the role of factors released from each cell type, epithelial and neuronal cells were cultured, injured, and the wound media from one cell type was collected and added to the other cell type. Epithelial wound media generated a rapid Ca²⁺ mobilization in neuronal cells that was abrogated in the presence of Apyrase, while neuronal wound media elicited a complex response in epithelial cells. The rapid Ca²⁺ mobilization was detected, which was abrogated with Apyrase, but it was followed by Ca²⁺ waves that occurred in cell clusters. When neuronal wound media was preincubated with a cocktail of N-methyl-D-aspartate (NMDA) receptor inhibitors, the secondary response in epithelia was diminished. Glutamate was detected in the neuronal wound media and epithelial expression of NMDA receptor subunit transcripts was demonstrated. Our results indicate that corneal epithelia and neurons communicate via purinergic and NMDA receptors that mediate the wound response in a highly orchestrated manner.

Corneal epithelium expresses a variant of P2X(7) receptor in health and disease

Improper wound repair of the corneal epithelium can alter refraction of light resulting in impaired vision. We have shown that ATP is released after injury, activates purinergic receptor signaling pathways and plays a major role in wound closure. In many cells or tissues, ATP activates P2X(7) receptors leading to cation fluxes and cytotoxicity. The corneal epithelium is an excellent model to study the expression of both the full-length P2X(7) form (defined as the canonical receptor) and its truncated forms. When Ca(2+) mobilization is induced by BzATP, a P2X(7) agonist, it is attenuated in the presence of extracellular Mg(2+) or Zn(2+), negligible in the absence of extracellular Ca(2+), and inhibited by the competitive P2X7 receptor inhibitor, A438079. BzATP enhanced phosphorylation of ERK. Together these responses indicate the presence of a canonical or full-length P2X(7) receptor. In addition BzATP enhanced epithelial cell migration, and transfection with siRNA to the P2X(7) receptor reduced cell migration. Furthermore, sustained activation did not induce dye uptake indicating the presence of truncated or variant forms that lack the ability to form large pores. Reverse transcription-polymerase chain reaction and Northern blot analysis revealed a P2X(7) splice variant. Western blots identified a full-length and truncated form, and the expression pattern changed as cultures progressed from monolayer to stratified. Cross-linking gels demonstrated the presence of homo- and heterotrimers. We examined epithelium from age matched diabetic and non-diabetic corneas patients and detected a 4-fold increase in P2X(7) mRNA from diabetic corneal epithelium compared to non-diabetic controls and an increased trend in expression of P2X(7)variant mRNA. Taken together, these data indicate that corneal epithelial cells express full-length and truncated forms of P2X(7), which ultimately allows P2X(7) to function as a multifaceted receptor that can mediate cell proliferation and migration or cell death.

Albumin precursor and Hsp70 modulate corneal wound healing in an organ culture model

In order to investigate the role of albumin precursor and Hsp70 in corneal wound healing, we have analyzed the distribution of these proteins in wounded and non-wounded corneas of rabbits and the effects of topical applications of anti-albumin precursor and anti-Hsp70 antibodies on wound healing. Anti-albumin precursor and anti-Hsp70 antibodies were topically applied in healing corneal epithelium of rabbit eyes in organ culture. Corneas were allowed to heal in vitro for up to 120 h in serum-free medium with 5 and 10 μg/ml or without (migrating control) anti-albumin precursor/ or anti-Hsp70 antibodies. Fibronectin (Fb) (5 μg/ml) was used as a positive control. Immunofluorescence labelling was used to detect proteins in corneal epithelium at various time intervals following an epithelial defect. Delay in wound healing (p<0.005) was observed with 10 μg/ml anti-albumin antibody labelling. A similar pattern was observed when anti-fibronectin antibody (5 μg/ml) alone and in combination with anti-albumin (10 μg/ml) was ectopically added with wound closure occurring at 120 h. However with anti-Hsp70 antibody (5 μg/ml) slightly delayed (p<0.005) wound closure was observed at 96 h and considerable retardation >120 h with 10 μg/ml. Additionally, immunofluoresence showed a strong co-localization of Hsp70 and albumin precursor during the active phase of wound healing. The presence of albumin precursor and Hsp70 in the epithelial compartment of the cornea indicates a role for these proteins in modulating cell behavior such as epithelial growth, adhesion or regeneration, thus contributing to corneal epithelial wound healing.

Inhibitory effect of anti-aminopeptidase N/CD13 antibodies on fibroblast migration

Aminopeptidase N (APN)/CD13 is a widely expressed transmembrane ectoenzyme and has been implicated in a myriad of physiological processes that are specific to cell type and tissue origin, including cancer cell metastasis, angiogenesis, cholesterol uptake, apoptosis, and cell migration. Skin cells, in particular fibroblasts have a relatively high level of APN/CD13 expression. The migratory capacity of skin cells is critical for the outcome of wound repair, as successful wound healing requires timely re-epithelialization which involves reformation of epithelium over wound surface by migrating keratinocytes. While failure of keratinocytes to undergo proper migration leads to chronic non-healing wounds, the presence of excess fibroblasts may contribute to formation of hypertrophic scars and keloids. The aim of this study was to investigate the role of APN/CD13 in skin cell migration and explore its potential as a therapeutic target in wound healing. Our results show an elevated expression of APN/CD13 in fibroblasts on the edge of the wound compared to unwounded cells. The presence of anti-APN/CD13 antibodies WM15, 3D8, and H300 reduces the migratory activity of human dermal fibroblasts in a dose-dependent manner by 42, 21, and 28%, respectively. However, the antibodies have no effect on keratinocyte migration. Further, none of the anti-APN/CD13 antibodies used in this study has any antiproliferative and cytotoxic effect on primary human keratinocytes or fibroblasts when used at 10 μg/ml in vitro. The differential inhibition on the migratory capacity of fibroblasts and keratinocytes presents an opportunity for anti-APN/CD13 antibodies to be used as a therapeutic agent for high fibroblast cellularity seen in fibroproliferative disorders.

Adhesive mechanisms of the corneal epithelium

The corneal epithelium adheres to the stroma through a series of linked structures termed collectively the adhesion complex. These structures include; intermediate filaments (keratin filaments) which are linked to the hemidesmosome; the hemidesmosome; the anchoring filaments which extend from the membrane at the hemidesmosome through the lamina lucida to the lamina densa region of the basement membrane; the anchoring fibrils which insert into the basement membrane from the stromal side; and the anchoring plaque on which anchoring fibrils terminate distal from their insertion on the basement membrane. Upon wounding, basal cells of the corneal epithelium disassemble their hemidesmosomes. During migration, the membranes along the wound bed exhibit a different kind of adhesion junction, the focal contact. This junction is present primarily in cells of the leading edge of migration and may be the provisional adhesion junction used by epithelial sheet moving to cover a wound.

Changes in albumin precursor and heat shock protein 70 expression and their potential role in response to corneal epithelial wound repair

Many proteins displayed differential expression (either up- or down-regulation) when proteome of migrating and non-migrating epithelium was assessed using 2-DE and ESI-Q-TOF MS/MS. From the up-regulated set, we have identified for the first time a 69-kDa albumin precursor protein with four peptides sequences and 70-kDa heat shock protein (hsp70) with one peptide in the active phase of cell migration (48 h) during the healing process. Western blot analysis was used to further characterize these proteins at different phases (24, 48 and 72 h) of healing. An increase in the mRNA expression (measured using RT-PCR) in the active migration phase (48 h) for albumin precursor and hsp70 was also observed. Furthermore, co-immunoprecipitation studies with anti-albumin precursor and anti-hsp70 antibodies, followed by immunoblotting with anti-fibronectin antibody demonstrated a novel and biologically relevant interaction between albumin precursor protein and fibronectin in corneal epithelial wound healing but not with hsp70. The increased gene and protein expression of albumin and hsp70 during the active phase of cell migration (48 h) in the corneal epithelium suggests their possible role in corneal wound healing. These findings may have broader implications for developing therapeutic strategies for treating wound healing disorders.

Epithelial cell motility is triggered by activation of the EGF receptor through phosphatidic acid signaling

Phospholipase D catalyzes the hydrolysis of phosphatidylcholine to generate phosphatidic acid, and there is currently much interest in elucidating messenger functions for this molecule. We report here that wounding sheets of corneal epithelial and Madin Darby canine kidney cells induces strong activation of phospholipase D, and we provide evidence that activation is amplified through a positive feed-back loop. Short-chain analogues of phosphatidic acid induce motility robustly in corneal and other epithelial cell types. The effects of these analogues were not the result of their conversion to the corresponding diacylglycerol or lysophosphatidic acid, implying that phosphatidic acid acts directly on one or more cellular targets. Strikingly, phosphatidic acid signaling was found to stimulate the epidermal growth factor receptor (EGFR) through a transactivation process. Healing of wounds in sheets of corneal epithelial cells is absolutely dependent on epidermal growth factor receptor signaling, and the present data suggest that its activation is a result of wound-induced phospholipase D activation.

Immunomolecular mapping of adherens junction and desmosomal components in normal human epidermis

Adherens junctions (AJs) are cell-cell and cell-matrix junctions that are known to comprise the transmembrane and cytoplasmic components linked to the f-actin cytoskeleton. Although the presence of AJs han been confirmed in normal human epidermis, previous studies immunolocalizing AJ-related antigens have been controversial. The purpose of this study was to produce a more precise molecular mapping of AJs and their constituents in relation to desmosomes in normal human epidermal keratinocytes. Using an electron microscope (EM) method to optimally fix plasma membranes. AJ structures were typically seen as a narrowing of the intercellular space between two keratinocytes that was distinct from desmosomes and gap junctions. Such structures were consistently found more frequently in the upper epidermis than in the basal layer. Immunogold electron microscopy showed an absence of the AJ components (E-cadherin and beta-catenin) from desmosomal areas but they were present at interdesmosomal areas at sites of close membrane association. Conversely, the desmosomal components plakoglobin and plakophilin 1 were restricted only to the outer attachment plaque of the desmosome. These results further confirm that AJs have a distinct molecular composition and distribution from desmosomes and that they regularly occur between desmosomes along the keratinocyte plasma membrane to provide alternative cell-cell adhesion mechanisms.

Delay in migration of the corneal epithelium after incorporation of [3H]-mannose in organ cultures

PURPOSE

Corneal epithelial cell surface carbohydrate moieties influence migration during wound healing. The purpose of the present study was to investigate the incorporation of galactose and mannose sugar during corneal epithelial migration and their effect on the rate of wound healing.

METHODS

Organ cultures of non-migrating (n = 6) and migrating (n = 30) corneal epithelia were prepared. The incorporation of [3H]-galactose and [3H]-mannose was followed in the migrating samples after 18, 24, 48 and 72h incubation and at 18h in the non-migrating samples. Wound size was documented at the same intervals and the rate of healing was established.

RESULTS

The migrating corneal epithelium of the galactose and mannose treated samples incorporated more radioactive sugar than the non-migrating samples. Mannose incorporation decreased with time whereas the rate of healing was significantly delayed (41 +/- 0.01 microm/h) compared to galactose treated samples (63 +/- 0.01 microm/h) and controls (61 +/- 0.01 microm/h) during the active healing phase (18-48h). Galactose incorporation increased with time.

CONCLUSIONS

Incorporation of mannose sugar has an inhibitory effect on the rate of migration during the linear healing phase of the corneal epithelium.

Intercellular adhesion molecule-1 expression on human corneal epithelial outgrowth from limbal explant in culture

AIM

To investigate the relation between intercellular adhesion molecule (ICAM)-1 expression and cellular dynamics occurring concomitantly with epithelial cell movement.

METHODS

Outgrowing epithelial sheets of human corneal epithelial (HCE) cells from cultured limbal explants were examined by immunoperoxidase staining with anti-ICAM-1 monoclonal antibody. An adhesion assay was performed using the epithelial sheets of HCE cells and an Epstein-Barr virus (EVB) infected B cell lymphoma cell line (EVB(+)BJAB) expressing CD11a/CD18, a counter-receptor of ICAM-1. Also, the effect of calphostin C, a specific protein kinase C (PKC) inhibitor, on ICAM-1 expression on the outgrowing epithelial sheets of HCE cells was examined.

RESULTS

Strong positive staining for ICAM-1 was found predominantly on HCE cells in the marginal segment of the epithelial sheet, particularly on the cells at the leading edge. EBV(+)BJAB cells adhering to the HCE cells corresponded well to the area of ICAM-1 staining. Treatment of outgrowing epithelial sheets with calphostin C markedly decreased the ICAM-1 expression on the HCE cells.

CONCLUSION

ICAM-1 is actively expressed on HCE cells in the marginal segment of the outgrowing epithelial sheets where there is active movement mediated through a PKC dependent mechanism, suggesting the role of ICAM-1 in epithelial cell motility such as the spreading and migration of cells.

Epithelial repair: roles of extracellular matrix

PURPOSE

To review studies of the roles of extracellular matrix (ECM) metabolism in corneal epithelium during wound repair. Methods. 1) Alterations in the structure and composition of epithelial basement membrane during corneal epithelial healing were examined histologically and immunohistochemically. 2) The effects of procollagen and hyaluronan synthesis inhibitors on the spread of rabbit corneal epithelium were determined in organ culture. 3) Expression of keratan sulfate proteoglycan (KSPG) proteins in corneal epithelium was examined during repair after injury in wild-type and lumican-null mice.

RESULTS

1) Corneal epithelial basement membrane was transiently degraded and reassembled during tissue repair. Patterns of type IV collagen immunoreactivity were also transiently altered. The system of matrix metalloproteinase-tissue inhibitors of metalloproteinases may play an important role in the disassembly and reorganization of epithelial basement membrane. 2) Inhibitors of procollagen secretion and hyaluronan biosynthesis disrupted the spread of a corneal epithelial sheet in situ. 3) Among the corneal KSPG proteins examined, lumican was transiently expressed in migrating murine corneal epithelial cells. Anti-lumican antibody inhibited corneal epithelial resurfacing in organ culture. The absence of lumican was found to delay corneal epithelial wound healing in mice.

CONCLUSION

Extracellular matrix metabolism by the injured corneal epithelium is important in the repair process.

Expression of transcription factor AP-1 in rat lens epithelial cells during wound repair

We examined the spatial and temporal expression patterns of proteins and mRNAs of the components of transcription factor activator protein 1 (AP-1) to examine the activation pattern of lens epithelial cells during lens wound repair following an anterior capsular injury. One eye of adult Wistar rats (n = 106) were used. After making a lens anterior capsule incision with a hypodermic needle, the affected eye was enucleated 0 and 30 min, 1, 3, 5, 8, 10, 15, 20, 24 hr after injury. Forty six globes were processed for in situ hybridization with oligonucleotide probes for c-fos, fosB, c-jun, junB and junD mRNAs, and 60 globes were immunohistochemically analysed using anti-c-Fos and anti-c-Jun antibodies. Normal lens epithelial cells expressed mRNA signals for junD, but not for c-fos, fosB, c-jun, and junB. mRNAs for c-fos, fosB, c-jun, and junB were detected in the whole lens epithelium from the vicinity to the wound to the equator from 30 min to 8 hr post-injury with their peaks after 30 min to 1 hr, but were no longer detected at 10 hr or later. Expression of c-fos mRNA in the equatorial lens cells was more marked than that of c-jun mRNA. Immunohistochemistry showed that c-Fos protein was expressed in the lens epithelial cells in both the anterior and equatorial regions of the injured lens from 1 to 10 hr after injury, and was no longer detected at 12 hr. C-Jun protein was detected only in the equatorial lens cells from 1 to 5 hr after injury, and was no longer detected at 8 hr. Lens epithelial cells except those in the equatorial region did not express c-Jun protein. These findings indicate that transcriptional activation of lens epithelial cells is initiated in the very early phase after the lens injury, i.e. 30 min post-injury, suggesting that AP-1 may play important roles in regulating lens cell behavior during lens wound repair in rats.

Corneal epithelial wound healing

One of the important functions of the cornea is to maintain normal vision by refracting light onto the lens and retina. This property is dependent in part on the ability of the corneal epithelium to undergo continuous renewal. Epithelial renewal is essential because it enables this tissue to act as a barrier that protects the corneal interior from becoming infected by noxious environmental agents. Furthermore, the smooth optical properties of the corneal epithelial surface are sustained through this renewal process. The rate of renewal is dependent on a highly integrated balance between the processes of corneal epithelial proliferation, differentiation, and cell death. One experimental approach to characterize these three aspects of the renewal process has been to study the kinetics and dynamics of corneal re-epithelialization in a wound-healing model. This effort has employed in vivo and in vitro studies. From such studies it is evident that the appropriate integration and coordination of corneal epithelial proliferation, adhesion, migration, and cell demise is dependent on the actions of a myriad of cytokines. Our goal here is to provide an overview into how these mediators and environmental factors elicit control of cellular proliferation, adhesion, migration, and apoptosis. To this end we review the pertinent literature dealing with the receptor and the cell signaling events that are responsible for mediating cytokine control of corneal epithelial renewal. It is our hope that a better appreciation can be obtained about the complexity of the control processes that are responsible for assuring continuous corneal epithelial renewal in health and disease.

Injury and EGF mediate the expression of alpha6beta4 integrin subunits in corneal epithelium

Our goal was to evaluate the role of epidermal growth factor and injury on the expression of integrin subunits alpha6(alpha6) and beta4(beta4). An in vitro wound model was used to evaluate corneal wound repair and cellular migration. Primary rabbit corneal epithelial cell cultures were serum-starved and injured in the presence or absence of EGF or tyrphostin AG1478, an inhibitor of EGF receptor kinase activity. Repair was monitored morphologically and expression was analyzed using in situ hybridization and immunohistochemistry accompanied by confocal microscopy. The addition of EGF to cell cultures induced a dose-dependent increase in beta4 mRNA expression but the constitutive expression of alpha6 was several fold greater. In the wounded cultures there was a rapid change in expression at the edge of the wound that was enhanced with EGF. In our model there was an increase in beta4 and alpha6 protein in migrating cells. Changes in integrin expression were accompanied by a transient increase in activation of the EGF receptor. The addition of tyrphostin inhibited migration of cells and wound repair, the activation of the EGF receptor and phosphorylation of beta4 in the cytoplasm. These data indicate that the activation of the EGF receptor plays a critical role in the regulation of integrin receptors and the mediation of cellular migration.

Erk and PI-3 kinase are necessary for collagen binding and actin reorganization in corneal epithelia

PURPOSE

It was recently shown that phosphatidylinositol-(PI)3 kinase is upregulated in wounded rabbit corneal epithelia. Extracellular signal-regulated kinase (erk)-1 and -2 proteins and PI-3 kinase were activated in embryonic corneal epithelia after 1-hour stimulation by type I collagen. In the current investigation specific inhibitors of PI-3 kinase and mitogen-activated kinase-kinase (MEK-1 kinase) were used to determine the role of these signaling molecules in actin reorganization and collagen binding to isolated sheets of corneal epithelial tissue.

METHODS

Effects of specific PI-3 kinase and MEK-1 inhibitors (LY294002, PD98059, respectively) were investigated in embryonic corneal epithelial tissues. Avian embryonic corneal epithelia were isolated as tissue sheets, organ cultured in the presence of these specific inhibitors, and stimulated with type I collagen. The tissues were evaluated for collagen-stimulated actin reorganization, erk-1 and -2 and PI-3 kinase activity, total filamentous actin accumulation, and collagen binding.

RESULTS

The MEK-1 inhibitor PD98059 decreased erk-1 and -2 phosphorylation and blocked actin reorganization in a dose-dependent manner. The PI-3 kinase 85-kDa subunit was decreased 25% in LY294002-treated tissue, and collagen binding also decreased significantly in tissues treated with MEK-1 and PI-3 kinase inhibitors compared with control tissues. In addition, both inhibitors blocked actin cortical mat reorganization. CONCLUSIONS; PI-3 kinase and erk-1 and -2 signaling pathways are activated and necessary for collagen binding and integrin-mediated actin reorganization in embryonic avian corneal epithelium.

Role of lumican in the corneal epithelium during wound healing

Lumican regulates collagenous matrix assembly as a keratan sulfate proteoglycan in the cornea and is also present in the connective tissues of other organs and embryonic corneal stroma as a glycoprotein. In normal unwounded cornea, lumican is expressed by stromal keratocytes. Our data show that injured mouse corneal epithelium ectopically and transiently expresses lumican during the early phase of wound healing, suggesting a potential lumican functionality unrelated to regulation of collagen fibrillogenesis, e. g. modulation of epithelial cell adhesion or migration. An anti-lumican antibody was found to retard corneal epithelial wound healing in cultured mouse eyes. Healing of a corneal epithelial injury in Lum(-/-) mice was significantly delayed compared with Lum(+/-) mice. These observations indicate that lumican expressed in injured epithelium may modulate cell behavior such as adhesion or migration, thus contributing to corneal epithelial wound healing.

ECM-stimulated actin bundle formation in embryonic corneal epithelia is tyrosine phosphorylation dependent

Previous studies demonstrated that corneal epithelial cells isolated without basal lamina respond to extracellular matrix (ECM) in an actin dependent manner; the basal cell surface flattens and the actin cortical mat reorganizes. We hypothesize that the actin reorganization is initiated by intracellular signaling mechanisms that includes tyrosine phoshporylation and activation of the Rho, MAP kinase, and PI3 kinase signal transduction pathways. Our goals were to develop a morphological assay to test this hypothesis by answering the following questions: 1) Do the actin bundle formations in the cortical mat have the same configuration in response to different ECM molecules? 2) What is the minimum time ECM molecules need to be in contact with the tissue for the actin to reorganize? 3) Will blocking tyrosine phosphorylation inhibit reorganization of the actin? 4) Are known signal transduction proteins phosphorylated in response to soluble matrix molecules? The actin cortical mat demonstrated distinct bundle configurations in the presence of different ECM molecules. Soluble fibronectin accumulated at the basal cell surfaces 75-fold over 30 min in a clustered pattern. The cells need contact with ECM for a minimum of 10 min to reform the actin bundles at 2 hr. In contrast, two substances that bind to heptahelical receptors to stimulate the Rho pathway, bombesin and lysophosphatidic acid, reorganized the actin bundles in 15-30 min. Focal adhesion kinase, p190 Rho-GAP, tensin, and paxillin were tyrosine phosphorylated in response to soluble fibronectin, type I collagen, or laminin 1. Erk-1, erk-2, and PI3 kinase were activated after 1 hr stimulation by type I collagen. Herbimycin A blocked actin reorganization induced by ECM molecules. In conclusion, we have developed two morphological assays to examine the response of corneal epithelial cells to ECM molecules. In addition, actin bundle reorganization involved tyrosine phosphorylation, MAP kinase, and PI3 kinase activation.

Vinculin and cell-cell adhesion

Vinculin, a 117-kDa protein, is a constituent of adhesion plaques and adherence junctions in non-muscle cells. We investigated the role of vinculin on the physical strength of cell-cell adhesion by conducting disaggregation assays on aggregates of parental wild-type F9 mouse embryonal carcinoma cells (clone BIM), two vinculin-depleted F9 cell lines, gamma 227 and gamma 229, and a reconstituted gamma 229 cell line (R3) that re-express vinculin. Immunoblotting demonstrated that the four cell lines used in the study had similar expressions of the cell-cell adhesion molecule E-cadherin and associated membrane proteins alpha- and beta-catenin. Double immunofluorescence analysis showed that, in contrast to the vinculin-null cell lines. BIM and R3 cells expressed abundant vinculin at the cell margins in adhesion plaques and in cell-cell margins that also contained actin. Laminar flow assays showed that both the vinculin-positive and vinculin-negative cell aggregates that were formed in culture in the course of 24 to 48 hours largely remained intact despite the imposition of shear flow at high shear rates. Since laminar flow imposed on cell aggregates act to separate cells from each other, our data indicate that F9 cells that were adherent to a substrate formed strong cell-cell adhesion bonds independent of vinculin expression. On the other hand, aggregates of vinculin-depleted gamma 229 and gamma 227 cells that were formed in suspension during a two-hour static incubation at 37 degrees C were desegregated more easily with the imposition of shear flow than the BIM and R3 cell aggregates formed under identical conditions. Loss of vinculin was associated with a reduction in cell-cell adhesion strength only among those cells lacking contact to a substrate. Overall, the results indicate that vinculin is not needed for forming strong cell-cell adhesion bonds between neighboring carcinoma cells which are adherent to the basal lamina.

Towards a molecular definition of keratinocyte activation after acute injury to stratified epithelia

While in recent years we have come to increasingly appreciate the multifaceted role of skin, probably none of these novel contributions is as vital as its barrier function, inferred centuries ago. In human skin this function is fulfilled nearly entirely by the epidermis, a thin stratified squamous epithelium made up primarily of keratinocytes and located at the skin surface. Disruption of the integrity of epidermis triggers a homeostatic response involving blood-derived elements and resident skin cell types that is designed to rapidly restore a functional epithelial lining over the wound site. This article is focused on the process of recruitment of keratinocytes from intact skin tissue at the proximal wound edges to participate in re-epithelialization.

Differential effects of transforming growth factors on localization of adhesion complex proteins following corneal epithelial cell wounding

PURPOSE

The differential effects of transforming growth factor (TGF) alpha, beta 1 and beta 2 on the de novo localization of heparan sulfate proteoglycan, collagen type VII and laminin-1 to the adhesion complex were analyzed using an in vitro model of corneal epithelial cell wound healing.

METHODS

Bovine corneal explants were maintained in culture media containing either no growth factor or 1, 5, or 10 ng/ml TGF alpha, TGF beta 1 or TGF beta 2. After 24 or 48 hours in culture, cryostat sections of explants were processed for immunofluorescence microscopy using antibodies directed against heparan sulfate proteoglycan, collagen type VII or laminin-1.

RESULTS

A comparison of antibody labeling patterns and relative fluorescence intensity of antibody labeling to controls suggested that TGF alpha inhibits the spatial polarization of proteins into the reforming adhesion complex during early stages of wound healing. Both TGF beta 1 and beta 2 enhanced the linear localization of the three proteins to the site of the reforming adhesion complex. However, in our model TGF beta isoforms did not have identical functions. TGF beta 2 accelerated the temporal localization of collagen type VII to the adhesion complex, an effect which was not observed with TGF beta 1.

CONCLUSIONS

TGF beta, but not TGF alpha, may play an important role in corneal epithelial cell wound healing by accelerating the reformation of the adhesion complex and subsequent epithelial cell-extracellular matrix adhesion.

Upregulation of alpha 9 integrin and tenascin during epithelial regeneration after debridement in the cornea

Stratified epithelia are exposed to abrasive forces and are required to respond rapidly to injury to minimize fluid loss and the risk for microbial infection. Healing involves a cell migratory phase to reestablish barrier function and cell proliferation to restratify the epithelium. Cell migration during re-epithelialization involves cell sliding, termed sheet movement, during which cells retain their cell-cell junctions while dynamically altering their shape and cell-substrate interactions to permit movement across the exposed wound bed. Proteins of the integrin family of receptor molecules modulate cell shape, cell migration, and signal transduction in many cell types. In epithelial cells, integrins of the beta 1 family have been implicated in regulating cell proliferation and differentiation, alpha 9 beta b1 is one of the newer members of the integrin beta family and has been recently shown to function as a tenascin receptor. Although little is known about its function in vivo, studies in developing mouse cornea and eyelid suggest that it may play a role in epithelial differentiation. Using a debridement wound model in the mouse cornea, we show in this study that (a) in response to small debridement wounds that close without cell proliferation, alpha 9 integrin protein and mRNA are not induced during migration but are induced during restratification, (b) larger debridement wounds that require cell proliferation to generate the cells necessary for sheet movement result in a dramatic induction of alpha 9 protein and its mRNA during both migration and restratification, and (c) tenascin, an alpha 9 beta 1 ligand, accumulates beneath epithelial cells during restratification but not during cell migration. Therefore, alpha 9 integrin protein production and tenascin accumulation are dynamically regulated in response to corneal epithelial injury.

Role of matrix metalloproteinases in failure to re-epithelialize after corneal injury

Delayed re-epithelialization of the cornea after injury usually precedes stromal ulceration. Previous findings using a rat thermal injury model suggested that re-epithelialization is impeded by products of resident corneal cells, which destroy adhesive structures at the basement membrane zone. In this study, we provide additional evidence for this concept. Failure to re-epithelialize was found to correlate with an increase in the amounts of gelatinolytic matrix metalloproteinases present in the rat cornea. One of these gelatinases, gelatinase B, is synthesized by the resident corneal cells, and inhibitions of its synthesis correlated with inhibition of basement membrane dissolution. The matrix metalloproteinases collagenase and stromelysin are also synthesized by resident corneal cells in thermally injured corneas of rabbits, but the timing of bulk enzyme synthesis correlated more closely with deposition of repair tissue in the stroma than with failure to re-epithelialize. Nevertheless, in human corneas with repair defects, gelatinase B and collagenase are synthesized by cells in the basal layer of the epithelium directly adjacent to the basement membrane, suggesting that both could participate in dissolution of this structure. Importantly, treatment of thermally injured corneas with a synthetic inhibitor of matrix metalloproteinases significantly improved basement membrane integrity. These data support the concept that over-expression of matrix metalloproteinases by resident corneal cells impedes re-epithelialization after some types of corneal injury.

Expression of fos family and jun family proto-oncogenes during corneal epithelial wound healing

PURPOSE

While transformation of epithelial cells to a motile form is the first step in wound healing of the corneal epithelium, the migratory mechanism in these cells is not fully understood. We studied the expression of proto-oncogene mRNAs: c-fos; c-jun; fos B; jun B; jun D in injured corneal epithelium using in situ hybridization. Moreover, we examined immunolocalization of c-Fos and c-Jun protein products to elucidate the transcriptional activation prior to the onset of migration in corneal epithelium.

METHODS

An epithelial defect was made on one cornea of 60 Wistar rats. The affected eye was enucleated immediately (within 5 min) or was allowed to heal for 15, 30, 60, 90, 120 and 180 min. Frozen sections were processed for in situ hybridization with c-fos, c-jun, fos B, jun B and jun D mRNAs or were stained with anti-c-fos and anti-c-jun antibodies.

RESULTS

Fifteen min after the epithelial ablation, weak signals for c-fos and c-jun mRNAs were detected in the corneal epithelium surrounding the wound. These signals reached a peak 30 to 60 min after ablation, but were no longer evident at 120 min. Immunoreactivities for these proteins were also detected in the same area at 60 to 120 min after the epithelial ablation. Fos B mRNA was detected in the same region at 30 min after the ablation, and reached its peak after 30 to 60 min, but was no longer evident at 120 min. Jun B mRNA was detected in the epithelium around the defect 60 min after the ablation, later than the other proto-oncogenes, and reached its peak after 90 min. The message for jun D was detected in normal epithelium, and was not affected by wounding.

CONCLUSIONS

These findings indicate that transcriptional activation of epithelial cells is initiated in the early phase after epithelial ablation, before the cells start to migrate, and that these proto-oncogene products may play important roles in wound healing in corneal epithelium. The time lag of the peak of expression of these proto-oncogenes in this process.

Integrin expression on cell adhesion function and up-regulation of P125FAK and paxillin in metastatic renal carcinoma cells

Integrins from normal human renal cortex epithelial cells (RCEC) and from four renal carcinoma lines (metastatic Caki-1, non-metastatic Caki-2, metastatic ACHN, and non-metastatic 769-P) were compared by immunoprecipitation with specific anti-integrin antibodies. Integrin alpha 2 was present in normal RCEC, but absent in all four tumor lines. There was a 2.0-3.0 fold decrease of alpha 3 and beta 1 in localized tumor lines, and a further 5.0-7.0 fold decrease in metastatic lines over their expression in normal renal cells. No alpha V was detected in Caki-1 cells. The greatest adhesion of all cells occurred in the presence of a stimulatory anti-alpha 3 antibody, mediated by specific matrix proteins employed as substrates, while anti-beta 1 treatment dramatically inhibited cell attachment on collagen IV, plasma fibronectin, laminin and merosin substrates. In addition, the mRNA expression of focal adhesion kinase (p125FAK) and paxillin were up-regulated (2.0-2.5 fold increase) in the metastatic Caki-1 cells over normal RCEC. The alteration of integrin subunits alpha 2, alpha 3, alpha V, beta 1, as well as p125FAK and paxillin may contribute to the pathogenicity and/or metastatic propensity of renal epithelial tumors. The up-regulation of paxillin independently or in concert with p125FAK as shown in this study indicates its significant role as a potential marker of metastasis in renal carcinoma cells.

Targeted disruption of vinculin genes in F9 and embryonic stem cells changes cell morphology, adhesion, and locomotion

Vinculin, a major constituent of focal adhesions and zonula adherens junctions, is thought to be involved in linking the microfilaments to areas of cell-substrate and cell-cell contacts. To test the role of vinculin in cell adhesion and motility, we used homologous recombination to generate F9 embryonal carcinoma and embryonic stem cell clones homozygous for a disrupted vinculin gene. When compared to wild-type cells, vinculin-mutant cells displayed a rounder morphology and a reduced ability to adhere and spread on plastic or fibronectin. Decreased adhesion of the mutant cells was associated with a reduction in lamellipodial extensions, as observed by time-lapse video microscopy. The locomotive activities of control F9 and the vinculin-null cells were compared in two assays. Loss of vinculin resulted in a 2.4-fold increase in cell motility. These results demonstrate an important role for vinculin in determining cell shape, adhesion, surface protrusive activity, and cell locomotion.

Impact of altered actin gene expression on vinculin, talin, cell spreading, and motility

Previous studies have demonstrated a strong correlation between the expression of vinculin and the shape and motility of a cell (Rodriguez Fernandez et al., 1992a, b, 1993). This hypothesis was tested by comparing the expression of vinculin and talin with the motility of morphologically altered myoblasts. These mouse C2 myoblasts were previously generated by directly perturbing the cell cytoskeleton via the stable transfection of a mutant-form of the beta-actin gene (beta sm) and three different forms of the gamma-actin gene; gamma, gamma minus 3'UTR (gamma delta'UTR), and gamma minus intron III (gamma delta IVSIII) (Schevzov et al., 1992; Lloyd and Gunning, 1993). In the case of the beta sm and gamma-actin transfectants, a two-fold decrease in the cell surface area was coupled, as predicted, with a decrease in vinculin and talin expression. In contrast, the gamma delta IVSIII transfectants with a seven-fold decrease in the cell surface area showed an unpredicted slight increase in vinculin and talin expression and the gamma delta 3'-UTR transfectants with a slight increase in the cell surface area showed no changes in talin expression and a decrease in vinculin expression. We conclude that changes in actin gene expression alone can impact on the expression of vinculin and talin. Furthermore, we observed that these actin transfectants failed to show a consistent relationship between cell shape, motility, and the expression of vinculin. However, a relationship between talin and cell motility was found to exist, suggesting a role for talin in the establishment of focal contacts necessary for motility.

Distribution of F-actin, vinculin and integrin subunits (alpha 6 and beta 4) in response to corneal substrata

Our goal was to determine the early response of corneal epithelial cells to living modified stromal substrates. We examined the distribution of integrin subunits (alpha 6 and beta 4), vinculin and the organization of F-actin in epithelial cells after cell-matrix and cell-cell hypothesized that the distribution of proteins in the cell matrix attachment complex would be altered if the substrate was modified. Integrin subunits, alpha 6 and beta 4, were chosen as they play a role in cell matrix adhesion and adhesion site formation. Corneal epithelial cells were cultured from explants and seeded on three corneal substrates (a stroma containing an intact basal lamina, a cornea lacking a basal lamina and a cornea treated with alkali). After 3 h of incubation, the tissue was fixed and stained with monoclonal antibodies specific for vinculin and for the integrin subunits alpha 6 and beta 4. The organization of F-actin was assessed using rhodamine phalloidin. The localization of the proteins was recorded with confocal laser scanning microscopy. Filamentous actin delineated the lateral cell membranes of corneal epithelial cells. The organization of actin and distribution of vinculin and integrin subunits of epithelial cells cultured on stromal substrates containing a basal lamina mimicked a simple epithelial organization. In contrast, when cells are cultured on the substrate lacking a basal lamina and alkaline treated corneal substrates the distribution of the specific proteins examined was altered. Vinculin and alpha 6 were present along membranes of cells cultured on substrates lacking a basal lamina and were diffuse in cells cultured on the alkaline substrates. These studies demonstrate that changes in the distribution of adhesion and cytoskeletal proteins in response to different surfaces may contribute to the healing dynamics in different wounds.

Prolyl hydroxylase inhibitor and lysyl hydroxylase inhibitor inhibit spreading of corneal epithelium

BACKGROUND

The spreading of epithelium is critical in the healing of corneal wounds. Such epithelial spreading requires the continuous production of protein and glycoprotein. To determine whether collagen production is required for the spreading of corneal epithelium, we studied the effects of inhibitors for collagen production on spreading of corneal epithelium in vitro.

METHODS

We examined the effect of two proline analogs, L-azetidine 2-carboxylic acid and cis-hydroxyproline, a prolyl hydroxylase inhibitor, ethyl-3,4-dihydroxybenzoate, and a lysyl hydroxylase inhibitor, minoxidil, on the spreading of epithelium of organ-cultured rabbit cornea.

RESULTS

Both analogs and inhibitors inhibited epithelial spreading in a dose-dependent manner.

CONCLUSION

These observations indicate that collagen production may be involved in the spreading of corneal epithelium.

Talin: adherens junction protein is localized at the epidermal-dermal interface in skin

The interaction between cells of the epidermis and the basal lamina is important for the integrity of the skin. Several hereditary and acquired diseases show changes at the dermal-epidermal interface due to loss of adhesion between basal cells and the basement membrane. The structures mediating this interaction are hemidesmosomes, which have been extensively characterized by biochemical, molecular biologic, and morphologic techniques. Recently, however, a group of adhesion molecules that are distinct from hemidesmosomes and that mediate cell-matrix interactions was described in cultured fibroblasts, keratinocytes, and skin. These adhesion molecules, beta 1 integrins, have been shown to be present in the focal adhesion, a cell-matrix contact associated with microfilaments rather than intermediate filaments characteristic of hemidesmosomes. In cultured cells, integrins of the beta 1 family have been shown to be linked by a protein complex to actin filaments. In this study we describe the localization of talin, the binding protein for beta 1 integrins, and vinculin at the dermal-epidermal interface in skin with immunofluorescence and immunoblotting techniques. These data suggest the presence of a link between the cytoplasmic actin filament system in basal keratinocytes and the extracellular matrix.

Suppression of vinculin expression by antisense transfection confers changes in cell morphology, motility, and anchorage-dependent growth of 3T3 cells

The expression of vinculin, a major component of adhesion plaques and cell-cell junctions, is markedly modulated in cells during growth activation, differentiation, motility and cell transformation. The stimulation of quiescent cells by serum factors and the culturing of cells on highly adhesive matrices induce vinculin gene expression, whereas the transformation of fibroblast and epithelial cells often results in decreased vinculin expression (reviewed in Rodríguez Fernández, J. L., B. Geiger, D. Salomon, I. Sabanay, M. Zöller, and A. Ben-Ze'ev. 1992. J. Cell Biol. 119:427). To study the effect of reduced vinculin expression on cell behavior, 3T3 cells were transfected with an antisense vinculin cDNA construct, and clones displaying decreased vinculin levels down to 10-30% of control levels were isolated. These cells showed a round phenotype with smaller and fewer vinculin-positive plaques localized mostly at the cell periphery. In addition, they displayed an increased motility compared to controls, manifested by a faster closure of "wounds" introduced into the monolayer, and by the formation of longer phagokinetic tracks. Moreover, the antisense transfectants acquired a higher cloning efficiency and produced larger colonies in soft agar than the parental counterparts. The results demonstrate that the regulation of vinculin expression in cells can affect, in a major way, cell shape and motility, and that decreased vinculin expression can induce cellular changes reminiscent of those found in transformed cells.

Changes in the distribution of actin-associated proteins during epidermal wound healing

We have examined the distribution of actin filaments and a number of actin-associated proteins during human epidermal wound healing, using a suction blister model in which the epidermis is detached from the dermis, leaving the basement membrane intact. Filamentous actin was found in all the living epidermal layers before, during and after wound healing. alpha-actinin was also present in all the living layers of normal epidermis, but diffuse cytoplasmic staining was observed at the leading edge of migrating epidermis. Vinculin and talin were concentrated at the basement membrane prior to wounding, but were absent from the leading edge during wound healing. In normal epidermis, filamin and gelsolin showed a complementary distribution, with filamin most abundant in the basal layer and gelsolin most abundant suprabasally. The abundance of both proteins was reduced at the leading edge of migrating epidermis. All of the changes were transient, as the expression patterns returned to normal by 1 week after wounding, when the epidermis had reformed. The relevance of these changes to the process of keratinocyte migration is discussed.

Adherens junctions: demonstration in human epidermis

Adherens junctions are intercellular and cell-matrix junctions that, like desmosomes and hemidesmosomes, mediate adhesion of cells to each other or to matrix structures. These junctions have been detected recently in cultured human keratinocytes, indicating that they may be of importance in epidermis. To investigate the localization of adherens junctions in normal epidermis, we examined human epidermis, human oral mucosa, and monkey esophagus for the presence of vinculin, a major protein of the intracellular plaques of adherens junctions that is thought to be present in all adherens junctions. Western blot analysis demonstrated vinculin in extracts of epidermis. Immunohistochemistry of vinculin in these tissues displayed two distinct locations for adherens junctions: i) at the dermal-epidermal junction, and ii) in the region of cell-cell contacts in all layers of the epidermis. The location of vinculin in the region of the epidermal-dermal junction is reminiscent of the distribution of vinculin-containing focal contacts in cultured keratinocytes, and the intercellular staining of vinculin in epidermis is consistent with the presence of vinculin in adherens junctions in cultured keratinocytes at sites of cell-cell contact. These results demonstrate that adherens junctions are present in human epidermis, oral mucosa, and monkey esophagus. Vinculin-containing junctions in epidermis may be important in the pathogenesis of skin diseases involving alterations in intercellular integrity.

Restricted tissue distribution of a 37-kD possible adherens junction protein

A major polypeptide of M(r) 37,000 was purified from a desmosome-enriched citric acid-insoluble pellet of pig tongue epithelium. The polypeptide was solubilized from the 4-M urea-insoluble pellet with 9 M urea, and extracts were separated by carboxymethyl cellulose and gel filtration chromatography. The 37-kD protein was obtained in milligram quantities as a single band on two-dimensional gels in 30% yield after 21-fold purification from the citric acid-insoluble fraction. The protein is not glycosylated and has a pI of approximately 8.7. Although isolated from a fraction rich in desmosomes, the 37-kD protein is not a desmosomal protein. Indirect immunofluorescence analysis of frozen sections of tongue and other tissues demonstrated that antibodies raised to the 37-kD protein bound only to suprabasal cell layers at punctate regions of the periphery of the cell and was absent from most regions of epidermis, whereas antibodies to desmoplakins I and II, desmosomal proteins, bound similarly but in all epidermal layers. Immunoelectron microscopy localized the 37-kD protein to the cell periphery in regions between, but never in, desmosomes. By immunofluorescence, the 37-kD protein colocalized with actin as well as with vinculin and uvomorulin in oral tissues. Like the 37-kD protein, vinculin and uvomorulin were absent from the basal layer. Based on its appearance, localization, and solubility properties, the 37-kD protein is probably a component of adherens junctions; its restriction to suprabasal cells and exclusion from the epidermis are unique.

Suppression of tumorigenicity in transformed cells after transfection with vinculin cDNA

Transfection of chicken vinculin cDNA into two tumor cell lines expressing diminished levels of the endogenous protein, brought about a drastic suppression of their tumorigenic ability. The SV-40-transformed Balb/c 3T3 line (SVT2) contains four times less vinculin than the parental 3T3 cells, and the rat adenocarcinoma BSp73ASML has no detectable vinculin. Restoration of vinculin in these cells, up to the levels found in 3T3 cells, resulted in an apparent increase in substrate adhesiveness, a decrease in the ability to grow in soft agar, and suppression of their capacity to develop tumors after injection into syngeneic hosts or nude mice. These results suggest that vinculin, a cytoplasmic component of cell-matrix and cell-cell adhesions, may have a major suppressive effect on the transformed phenotype.