HGF- and KGF-induced activation of PI-3K/p70 s6 kinase pathway in corneal epithelial cells: its relevance in wound healing

Corneal injury repair and the potential involvement of ZEB1

The cornea, consisting of three cellular and two non-cellular layers, is the outermost part of the eyeball and frequently injured by external physical, chemical, and microbial insults. The epithelial-to-mesenchymal transition (EMT) plays a crucial role in the repair of corneal injuries. Zinc finger E-box binding homeobox 1 (ZEB1), an important transcription factor involved in EMT, is expressed in the corneal tissues. It regulates cell activities like migration, transformation, and proliferation, and thereby affects tissue inflammation, fibrosis, tumor metastasis, and necrosis by mediating various major signaling pathways, including transforming growth factor (TGF)-β. Dysfunction of ZEB1 would impair corneal tissue repair leading to epithelial healing delay, interstitial fibrosis, neovascularization, and squamous cell metaplasia. Understanding the mechanism underlying ZEB1 regulation of corneal injury repair will help us to formulate a therapeutic approach to enhance corneal injury repair.

Elucidating the mechanism of corneal epithelial cell repair: unraveling the impact of growth factors

The repair mechanism for corneal epithelial cell injuries encompasses migration, proliferation, and differentiation of corneal epithelial cells, and extracellular matrix remodeling of the stromal structural integrity. Furthermore, it involves the consequential impact of corneal limbal stem cells (LSCs). In recent years, as our comprehension of the mediating mechanisms underlying corneal epithelial injury repair has advanced, it has become increasingly apparent that growth factors play a pivotal role in this intricate process. These growth factors actively contribute to the restoration of corneal epithelial injuries by orchestrating responses and facilitating specific interactions at targeted sites. This article systematically summarizes the role of growth factors in corneal epithelial cell injury repair by searching relevant literature in recent years, and explores the limitations of current literature search, providing a certain scientific basis for subsequent basic research and clinical applications.

Modulating Growth Factor Receptor Signaling to Promote Corneal Epithelial Homeostasis

The corneal epithelium is the first anatomical barrier between the environment and the cornea; it is critical for proper light refraction onto the retina and prevents pathogens (e.g., bacteria, viruses) from entering the immune-privileged eye. Trauma to the highly innervated corneal epithelium is extremely painful and if not resolved quickly or properly, can lead to infection and ultimately blindness. The healthy eye produces its own growth factors and is continuously bathed in tear fluid that contains these proteins and other nutrients to maintain the rapid turnover and homeostasis of the ocular surface. In this article, we review the roles of growth factors in corneal epithelial homeostasis and regeneration and some of the limitations to their use therapeutically.

Knockout of c-Cbl/Cbl-b slows c-Met trafficking resulting in enhanced signaling in corneal epithelial cells

In many cell types, the E3 ubiquitin ligases c-Cbl and Cbl-b induce ligand-dependent ubiquitylation of the hepatocyte growth factor (HGF)-stimulated c-Met receptor and target it for lysosomal degradation. This study determines whether c-Cbl/Cbl-b are negative regulators of c-Met in the corneal epithelium (CE) and if their inhibition can augment c-Met-mediated CE homeostasis. Immortalized human corneal epithelial cells were transfected with Cas9 only (Cas9, control cells) or with Cas9 and c-Cbl/Cbl-b guide RNAs to knockout each gene singularly (-c-Cbl or -Cbl-b cells) or both genes (double KO [DKO] cells) and monitored for their responses to HGF. Cells were assessed for ligand-dependent c-Met ubiquitylation via immunoprecipitation, magnitude, and duration of c-Met receptor signaling via immunoblot and receptor trafficking by immunofluorescence. Single KO cells displayed a decrease in receptor ubiquitylation and an increase in phosphorylation compared to control. DKO cells had no detectable ubiquitylation, had delayed receptor trafficking, and a 2.3-fold increase in c-Met phosphorylation. Based on the observed changes in receptor trafficking and signaling, we examined HGF-dependent in vitro wound healing via live-cell time-lapse microscopy in control and DKO cells. HGF-treated DKO cells healed at approximately twice the rate of untreated cells. From these data, we have generated a model in which c-Cbl/Cbl-b mediate the ubiquitylation of c-Met, which targets the receptor through the endocytic pathway toward lysosomal degradation. In the absence of ubiquitylation, the stimulated receptor stays phosphorylated longer and enhances in vitro wound healing. We propose that c-Cbl and Cbl-b are promising pharmacologic targets for enhancing c-Met-mediated CE re-epithelialization.

Epidermal Growth Factor Receptor Expression in the Corneal Epithelium

A properly functioning cornea is critical to clear vision and healthy eyes. As the most anterior portion of the eye, it plays an essential role in refracting light onto the retina and as an anatomical barrier to the environment. Proper vision requires that all layers be properly formed and fully intact. In this article, we discuss the role of the epidermal growth factor receptor (EGFR) in maintaining and restoring the outermost layer of the cornea, the epithelium. It has been known for some time that the addition of epidermal growth factor (EGF) promotes the restoration of the corneal epithelium and patients using EGFR inhibitors as anti-cancer therapies are at increased risk of corneal erosions. However, the use of EGF in the clinic has been limited by downregulation of the receptor. More recent advances in EGFR signaling and trafficking in corneal epithelial cells have provided new insights in how to overcome receptor desensitization. We examine new strategies for overcoming the limitations of high ligand and receptor expression that alter trafficking of the ligand:receptor complex to sustain receptor signaling.

KGF Is Delivered to Inflammatory and Induces the Epithelial Hyperplasia in Trinitrobenzene Sulfonic Acid-Induced Ulcerative Colitis Rats

Introduction

KGF-modified MSCs can promote the repair of spinal cord injury and pulmonary fibrosis injury in rats. However, the effect of KGF-modified MSCs on UC rats is unclear. We aimed to explore the therapeutic effect and possible mechanism of KGF gene-modified MSCs on trinitrobenzene sulfonic acid (TNBS)-induced UC rats.

Methods

The lentivirus-mediated KGF gene was introduced into bone marrow MSCs of male rats. Female SD rats were induced to establish a UC model by TNBS. Untreated MSCs, MSCs carrying empty vectors (MSCs-vec) or MSCs carrying KGF gene (MSCs-KGF) were transplanted into UC rats by tail vein injection.

Results

Significantly high expression of KGF was observed in the intestinal tissues of the MSCs-KGF group. Compared with the challenged control group, the DAI score, CMDI score and TDI score of the MSCs group, MSCs-vec group and MSCs-KGF group were markedly lower. Treatment with MSCs obviously promoted the expression of claudin-1 and PCNA in intestinal tissues of UC rats. Simultaneously, compared with the challenged control group, the levels of TNF-α, IL-6 and IL-8 in the intestinal tissues of the MSCs groups were significantly decreased, while the levels of IL-10 were significantly increased. Most importantly, we found that MSCs-KGF significantly improved colonic morphology and tissue damage and inflammation in UC rats compared with MSCs and MSCs-vec. Further analysis showed that MSCs-KGF clearly promoted phosphorylation of PI3K and Akt and inhibited nuclear translocation of NF-κB in intestinal tissues of UC rats.

Discussion

MSCs, especially KGF-modified MSCs, can improve colonic tissue damage in UC rats by promoting intestinal epithelial cell proliferation and reducing colonic inflammatory response, which may be related to activation of PI3K/Akt pathway and inhibition of NF-κB activation.

Isolation and Characterization of a Human Fetal Mesenchymal Stem Cell Population: Exploring the Potential for Cell Banking in Wound Healing Therapies

Various cell-based therapies are in development to address chronic and acute skin wound healing, for example for burns and trauma patients. An off-the-shelf source of allogeneic dermal cells could be beneficial for innovative therapies accelerating the healing in extensive wounds where the availability of a patient’s own cells is limited. Human fetal-derived dermal fibroblasts (hFDFs) show high in vitro division rates, exhibit low immunological rejection properties, and present scarless wound healing in the fetus, and previous studies on human fetal tissue-derived cell therapies have shown promising results on tissue repair. However, little is known about cell lineage stability and cell differentiation during the cell expansion process, required for any potential therapeutic use. We describe an isolation method, characterize a population, and investigate its potential for cell banking and thus suitability as a potential product for cell grafting therapies. Our results show hFDFs and a bone marrow-derived mesenchymal stem cell (BM-MSC) line shared identification markers and in vitro multilineage differentiation potential into osteogenic, chondrogenic, and adipogenic lineages. The hFDF population exhibited similar cell characteristics as BM-MSCs while producing lower pro-inflammatory cytokine IL-6 levels and higher levels of the wound healing factor hepatocyte growth factor. We demonstrate in vitro differentiation of hFDFs, which may be a problem in maintaining long-term lineage stability, potentially limiting their use for cell banking and therapy development.

Effects of HGF and KGF gene silencing on vascular endothelial growth factor and its receptors in rat ultraviolet radiation‑induced corneal neovascularization

Hepatocyte growth factor (HGF) and keratinocyte growth factor (KGF), two paracrine growth factors, modulate corneal epithelial cell metabolism, apoptosis and survival. Vascular endothelial growth factor (VEGF) serves as a proangiogenic factor in corneal neovascularization (CNV), which is a major cause of vision impairment and corneal blindness. The aim of the present study was to evaluate the ability of HGF and KGF to influence VEGF and its receptor, kinase insert domain receptor (Flk‑1) in corneal injury and CNV in rats induced by ultraviolet radiation (UVR). An UVR‑induced corneal injury rat model was successfully established to characterize the expression patterns of KGF, HGF, VEGF and Flk‑1 in corneal tissues. Corneal epithelial cells were extracted and treated with small interfering RNAs (siRNAs) targeting KGF, HGF or both (si‑KGF, si‑HGF or si‑HGF/KGF). The effects of HGF and KGF were examined through detection of the expression of KGF, HGF, VEGF and Flk‑1, and the evaluation of cell proliferation, cell cycle and cell apoptosis. The expression levels of KGF, HGF, VEGF and Flk‑1 in corneal tissues were increased in the rat model. In the cell experiments, the transfection of si‑HGF/KGF resulted in reductions in VEGF, Flk‑1, KGF and HGF. In addition, decreased cell proliferation and elevated cell apoptosis were found in the corneal epithelial cells from the rat model following KGF and HGF gene silencing. Taken together, these findings suggest that HGF and KGF gene silencing inhibits UVR‑induced corneal epithelial proliferation and CNV and may function as novel targets for corneal wound healing.

The role of hepatocyte growth factor in corneal wound healing

Hepatocyte growth factor (HGF) is a glycoprotein produced by mesenchymal cells and operates as a key molecule for tissue generation and renewal. During corneal injury, HGF is primarily secreted by stromal fibroblasts and promotes epithelial wound healing in a paracrine manner. While this mesenchymal-epithelial interaction is well characterized in various organs and the cornea, the role of HGF in corneal stromal and endothelial wound healing is understudied. In addition, HGF has been shown to play an anti-fibrotic role by inhibiting myofibroblast generation and subsequent production of a disorganized extracellular matrix and tissue fibrosis. Therefore, HGF represents a potential therapeutic tool in numerous organs in which myofibroblasts are responsible for tissue scarring. Corneal fibrosis can be a devastating sequela of injury and can result in corneal opacification and retrocorneal membrane formation leading to severe vision loss. In this article, we concisely review the available literature regarding the role of HGF in corneal wound healing. We highlight the influence of HGF on cellular behaviors in each corneal layer. Additionally, we suggest the possibility that HGF may represent a therapeutic tool for interrupting dysregulated corneal repair processes to improve patient outcomes.

Optimization of Corneal Epithelial Progenitor Cell Growth on Bombyx mori Silk Fibroin Membranes

Scaffolds prepared from silk fibroin derived from cocoons of the domesticated silkworm moth Bombyx mori have demonstrated potential to support the attachment and growth of human limbal epithelial (HLE) cells in vitro. In this study, we attempted to further optimize protocols to promote the expansion of HLE cells on B. mori silk fibroin- (BMSF-) based scaffolds. BMSF films were initially coated with different extracellular matrix proteins and then analysed for their impact on corneal epithelial cell adhesion, cell morphology, and culture confluency. Results showed that collagen I, collagen III, and collagen IV consistently improved HCE-T cell adherence, promoted an elongated cell morphology, and increased culture confluency. By contrast, ECM coating had no significant effect on the performance of primary HLE cells cultured on BMSF films. In the second part of this study, primary HLE cells were grown on BMSF films in the presence of medium (SHEM) supplemented with keratinocyte growth factor (KGF) and the Rho kinase inhibitor, Y-27632. The results demonstrated that SHEM medium supplemented with KGF and Y-27632 dramatically increased expression of corneal differentiation markers, keratin 3 and keratin 12, whereas expression of the progenitor marker, p63, did not appear to be significantly influenced by the choice of culture medium.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Fibroblast growth factor receptor 2 (FGFR2) is required for corneal epithelial cell proliferation and differentiation during embryonic development

Fibroblast growth factors (FGFs) play important roles in many aspects of embryonic development. During eye development, the lens and corneal epithelium are derived from the same surface ectodermal tissue. FGF receptor (FGFR)-signaling is essential for lens cell differentiation and survival, but its role in corneal development has not been fully investigated. In this study, we examined the corneal defects in Fgfr2 conditional knockout mice in which Cre expression is activated at lens induction stage by Pax6 P0 promoter. The cornea in LeCre, Fgfr2^loxP/loxP mice (referred as Fgfr2^CKO) was analyzed to assess changes in cell proliferation, differentiation and survival. We found that Fgfr2^CKO cornea was much thinner in epithelial and stromal layer when compared to WT cornea. At embryonic day 12.5–13.5 (E12.5–13.5) shortly after the lens vesicle detaches from the overlying surface ectoderm, cell proliferation (judged by labeling indices of Ki-67, BrdU and phospho-histone H3) was significantly reduced in corneal epithelium in Fgfr2^CKO mice. At later stage, cell differentiation markers for corneal epithelium and underlying stromal mesenchyme, keratin-12 and keratocan respectively, were not expressed in Fgfr2^CKO cornea. Furthermore, Pax6, a transcription factor essential for eye development, was not present in the Fgfr2^CKO mutant corneal epithelial at E16.5 but was expressed normally at E12.5, suggesting that FGFR2-signaling is required for maintaining Pax6 expression in this tissue. Interestingly, the role of FGFR2 in corneal epithelial development is independent of ERK1/2-signaling. In contrast to the lens, FGFR2 is not required for cell survival in cornea. This study demonstrates for the first time that FGFR2 plays an essential role in controlling cell proliferation and differentiation, and maintaining Pax6 levels in corneal epithelium via ERK-independent pathways during embryonic development.

The role of endogenous epidermal growth factor receptor ligands in mediating corneal epithelial homeostasis

PURPOSE

To provide a comprehensive study of the biological role and therapeutic potential of six endogenous epidermal growth factor receptor (EGFR) ligands in corneal epithelial homeostasis.

METHODS

Kinetic analysis and dose response curves were performed by using in vitro and in vivo wound-healing assays. Biochemical assays were used to determine receptor expression and activity. Human tears were collected and quantitatively analyzed by multianalyte profiling for endogenous EGFR ligands.

RESULTS

Epidermal growth factor receptor ligands improved wound closure and activated EGFR, but betacellulin (BTC) was the most efficacious promoter of wound healing in vitro. In contrast, only epidermal growth factor (EGF) promoted wound healing in vivo. Human tears from 25 healthy individuals showed EGFR ligands at these average concentrations: EGF at 2053 ± 312.4 pg/mL, BTC at 207 ± 39.4 pg/mL, heparin-binding EGF at 44 ± 5.8 pg/mL, amphiregulin at 509 ± 28.8 pg/mL, transforming growth factor-α at 84 ± 19 pg/mL, and epiregulin at 52 ± 15 pg/mL.

CONCLUSIONS

Under unwounded conditions, only EGF was present at concentrations near the ligand's Kd for the receptor, indicating it is the primary mediator of corneal epithelial homeostasis. Other ligands were present but at concentrations 11- to 7500-fold less their Kd, preventing significant ligand binding. Further, the high levels of EGF and its predicted binding preclude receptor occupancy by exogenous ligand and can explain the discrepancy between the in vitro and in vivo data. Therefore, therapeutic use of EGFR ligands may be unpredictable and impractical.

Regulation of Cdc42 expression and signaling is critical for promoting corneal epithelial wound healing

PURPOSE

Cdc42, a member of Rho GTPases (guanosine triphosphatases), participates in cytokine- and growth factor-controlled biological functions in mammalian tissues. Here, we examined Cdc42 role in corneal epithelial wound healing and the influence of hepatocyte, keratinocyte, and epidermal growth factor (HGF, KGF, and EGF)-mediated signaling on Cdc42.

METHODS

Epithelial wounds were created on the corneas of live rabbits by complete debridement and in rabbit corneal epithelial primary cultures through scratch injury. Cdc42 expression in cultures was suppressed using Cdc42 siRNA. Cdc42 activation was determined by pull-down assays with PAK-agarose beads. Cdc42 expression was analyzed by immunoblotting and immunofluorescence. Association of Cdc42 with cell-cycle proteins was identified by immunoprecipitation.

RESULTS

In rabbit corneas, significant increase in Cdc42 expression that occurred 2 to 4 days after the injury coincided with wound closure, and by 8 days the expression reached near basal levels. Silencing of Cdc42 expression in cultures caused inhibition of wound closure as a result of 60% to 75% decrease in epithelial migration and growth. HGF, KGF, and EGF increased Cdc2 expression, activation, and its phosphorylation on ser71. Inhibition of growth factor-mediated PI-3K signaling resulted in the downregulation of Cdc42 expression and its phosphorylation. Increased association of cell-cycle proteins p27(kip) and cyclin-dependent kinase 4 (CDK4) with Cdc42; and phosphorylated Cdc42 with plasma membrane leading edges was also observed in the presence of growth factors.

CONCLUSIONS

Cdc42 is an important regulator of corneal epithelial wound repair. To promote healing, Cdc42 may interact with receptor tyrosine kinase-activated signaling cascades that participate in cell migration and cell-cycle progression.

Involvement of pigment epithelium-derived factor, docosahexaenoic acid and neuroprotectin D1 in corneal inflammation and nerve integrity after refractive surgery

Alterations in corneal innervations result in impaired corneal sensation, severe dry eye and damage to the epithelium that may in turn lead to corneal ulcers, melting and perforation. These alterations can occur after refractive surgery. We have discovered that pigment epithelium-derived factor (PEDF) plus docosahexaenoic acid (DHA or the docosanoid bioactive neuroprotectin D1 (NPD1)) induces nerve regeneration after corneal surgery that damages the stromal nerves. We found that PEDF is released from corneal epithelial cells after injury, and when DHA is provided to the cells it stimulates the biosynthesis of NPD1 by an autocrine mechanism. The combination of PEDF plus DHA also decreased the production of leukotriene B4 (LTB4), a neutrophil chemotactic factor, thereby decreasing the inflammation induced after corneal damage. These studies suggest that PEDF plus DHA and its derivative NPD1 hold promise as a future treatment to restore a healthy cornea after nerve damage.

Interleukin-18 augments growth ability of primary human melanocytes by PTEN inactivation through the AKT/NF-κB pathway

Normal human skin relies on melanocytes to provide photoprotection and thermoregulation by producing melanin. The growth and behavior of melanocytes are controlled by many factors. Interleukin-18 (IL-18) is expressed in both immune and non-immune cells and participates in the adjustment of multitude cellular functions. Nonetheless, the regulative roles of IL-18 in melanogenesis and growth of melanocytes have not been explored. The present study was conducted to investigate the effects of IL-18 on melanocytes and elucidate the underlying mechanisms. We proved that IL-18 increased the tyrosinase activity and melanin content in normal human foreskin-derived epidermal melanocytes (NHEM). Treatment with IL-18 (20 ng/ml) enhanced the expression of c-Kit, microphtalmia-associated transcription factor (MITF) and its downstream tyrosinase-related protein 1 (TRP-1), and TRP-2. In addition, IL-18 induced NHEM migration at concentration of 20 ng/ml. These results indicated a promotive action of IL-18 on melanogenesis in NHEM. Our data revealed that IL-18 stimulated ERK1/2 and NF-κB activation, improved p-Akt, p70 S6K and anti-apoptotic Bcl-2 levels, and deactivated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in NHEM. Besides, IL-18 increased level of PTEN phosphorylation to protect NHEM from damage induced by H(2)O(2). These results in vitro showed the accommodation of IL-18 in melanocytes growth. Therefore, we suggested an important regulating action of IL-18 to melanogenesis and cell growth ability of skin melanocytes.

Phospholipase C/Protein Kinase C pathway is essential for corneal re-epithelialization induced by Ap(4)A

PURPOSE

We have previously demonstrated the importance of P2Y(2) receptors in the corneal re-epithelialization effect triggered by diadenosine tetraphosphate (Ap(4)A). In addition, we have also shown the ERK1/2 and ROCK-I activation in Ap(4)A-wound repair response. Phospholipase C/Protein Kinase C (PLC/PKC) pathway activation has been suggested as a molecular mechanism of growth factors-modulated corneal cell migration and P2Y(2) agonists. Hence, the aim of this study is to investigate the role of PLC/PKC cascade in the modification of re-epithelialization rate triggered by Ap(4)A in an established corneal epithelial cell line (Statens Seruminstitut rabbit cornea [SIRC] cells).

METHODS

In wounded confluent SIRC cell monolayers and in the presence or absence of Ap(4)A 100 μM, a group of PLC/PKC inhibitors (U73122 3 μM, Staurosporine 1 nM and Bisindolylmaleimide-I 10 μM) and activator (PDBU 1 μM) were assayed and the migration rate was evaluated. Also, the activation of ERK1/2 and ROCK-I was examined by Western blot assay after treatment with or without Ap(4)A, U73122, Staurosporine, Bisindolylmaleimide-I and PDBU.

RESULTS

Pre-treatment of wounded SIRC cells with PLC/PKC inhibitors significantly diminished the Ap(4)A-stimulated cell migration rate. Furthermore, PLC/PKC inhibitors also reduced ERK1/2 phosphorylation and ROCK-I activation triggered by Ap(4)A.

CONCLUSIONS

The present study shows the involvement of PLC/PKC pathway in the activation of ERK1/2 and ROCK-I downstream signal transduction pathways stimulated by Ap(4)A/P2Y(2) receptor during corneal epithelial wound repair.

EGF stimulates lipoxin A4 synthesis and modulates repair in corneal epithelial cells through ERK and p38 activation

PURPOSE

To investigate the effect of epidermal growth factor (EGF) on lipoxin A4 (LXA4) synthesis and how it regulates corneal epithelial wound healing through mitogen-activated kinases, extracellular regulated kinase (ERK) 1/2, and p38.

METHODS

Rabbit corneal epithelial (RCE) cells were stimulated with EGF or LXA4 at different times. In some experiments, cells were pretreated with 12/15-lipoxygenase (12/15-LOX) inhibitor cinnamyl-3,4-dihydroxy-α-cyanocinnamate (CDC), ERK1/2 inhibitor PD98059, or p38 inhibitor SB203580. For wound-healing experiments, corneas from rabbits and 12/15-LOX (ALOX-15)-deficient mice were injured by epithelial removal and maintained in organ culture in the presence of EGF or LXA4 with or without inhibitors. Epithelial cell proliferation was assayed by immunofluorescence with Ki67 and cell counting. Scrape migration assays were performed in 6-well plates. LXA4 synthesis was analyzed by liquid chromatography-tandem mass spectrometry analysis.

RESULTS

EGF activated ERK1/2 and p38 in RCE cells in a sustained manner. EGF activation was partially inhibited by CDC. EGF and LXA4 increased corneal epithelial wound closure. ERK1/2 inhibition with PD98059 or p38 with SB203580 blocked the effect of LXA4 on wound healing. ALOX-15 corneas displayed inhibition of epithelial wound closure promoted by EGF, whereas LXA4 stimulation induced similar wound closure in wild-type and knockout mice. EGF-stimulated LXA4 synthesis in RCE cells was inhibited by CDC or the EGF receptor antagonist AG1478.

CONCLUSIONS

These results demonstrate that EGF-stimulated epithelial wound healing is partially mediated through a 12/15-LOX-LXA4 pathway, and activation of ERK1/2 and p38 is required for LXA4 action.

Hepatocyte growth factor and keratinocyte growth factor enhance IL-1-induced IL-8 secretion through different mechanisms in Caco-2 epithelial cells

A variety of cytokines have been detected in inflamed intestinal mucosal tissues, including the pro-inflammatory cytokine, interleukin-1 (IL-1), along with growth factors involved in wound healing processes such as proliferation and cell migration. However, little is known about how IL-1 and growth factors interact with intestinal epithelial cells to regulate the production of inflammatory cytokines such as interleukin-8 (IL-8). Previously, we have shown that hepatocyte growth factor (HGF) could significantly enhance IL-1-stimulated IL-8 secretion by the Caco-2 colonic epithelial cell line, yet HGF, by itself, did not stimulate IL-8 secretion. In this report, a second growth factor, keratinocyte growth factor (KGF), was also found to significantly enhance IL-1-induced IL-8 secretion by Caco-2 cells, yet KGF, by itself, also had no effect. Simultaneous addition of both IL-1 and KGF was also required for the enhancing effect. Treatment of the Caco-2 cells with wortmannin or triciribine suppressed the enhancing effect of HGF, suggesting that the effect was mediated by signaling through phosphatidylinositol-3-kinase (PI3K) and the kinase AKT. The enhancing effect of KGF was not affected by wortmannin, but was suppressed by triciribine, suggesting that the effect of KGF was through a PI3K-independent activation of AKT. These results suggest that the growth factors HGF and KGF may play a role in enhancing IL-1-stimulated production of IL-8 by epithelial cells during mucosal inflammations. However, the mechanism by which the growth factors enhance the IL-1 response may be through different initial signaling pathways.

Keratinocyte growth factor promotes preadipocyte proliferation via an autocrine mechanism

Keratinocyte growth factor (KGF; also known as FGF-7) is a well-characterized paracrine growth factor for tissue growth and regeneration. However, its role in adipose tissue, which is known to undergo tremendous expansion in obesity, is virtually unknown. Given that we previously identified KGF as one of the up-regulated growth factors in adipose tissue of an early-life programmed rat model of visceral obesity, the present study was undertaken to examine the hypothesis that KGF promotes adipogenesis. Using 3T3-L1 and rat primary preadipocytes as in vitro model systems, we demonstrated that (1) KGF stimulated preadipocyte proliferation in a concentration-dependent manner with a maximal effect at 2.5 ng/ml (approximately 2-fold increase); (2) KGF mRNA was highly expressed in rat adipocytes and preadipocytes as well as 3T3-L1 cells; (3) treatment of preadipocytes with a neutralizing antibody against KGF and siRNA-mediated knockdown of KGF led to a 50% reduction in their proliferative capacity; (4) KGF activated the protein kinase Akt, and the PI3 kinase inhibitor LY294002 blocked KGF stimulation of preadipocyte proliferation; and (5) KGF did not promote differentiation of preadipocytes to mature adipocytes. Together, these results reveal adipocytes and their precursor cells as novel sites of KGF production. Importantly, they also demonstrate that KGF promotes preadipocyte proliferation by an autocrine mechanism that involves activation of the PI3K/Akt signaling pathway. Aberrant KGF expression may have consequences not only for normal adipose tissue growth but also for the pathogenesis of obesity.

Novel therapeutic strategies for acute lung injury induced by lung damaging agents: the potential role of growth factors as treatment options

The increasing threat from terrorism has brought attention to the possible use of toxic industrial compounds (TICs) and other lung-damaging agents as weapons against civilian populations. The way in which these agents could be used favours the development of generic countermeasures. Improved medical countermeasures would increase survivability and improve the quality of recovery of lung damaged casualties. It is evident that there is a dearth of therapeutic regimes available to treat those forms of lung damage that currently require intensive care management. It is quite possible that mass casualties from a terrorist incident or major industrial accident involving the release of large quantities of inhaled TICs would place a severe burden on already scarce intensive care facilities. The development of effective pharmacological approaches to assist the recovery of casualties suffering from acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) may improve the prognosis of such patients (which is currently poor) and would ideally be used as a means of preventing subjects from developing the pulmonary oedema characteristic of ALI/ARDS. Many promising candidate pharmacological treatments have been evaluated for the treatment of ALI/ARDS, but their clinical value is often debatable. Thus, despite improvements in ventilation strategies, pharmacological intervention for ALI/ARDS remains problematical. A new approach is clearly required for the treatment of patients with severely compromised lungs. Whilst the pathology of ALI/ARDS associated with exposure to a variety of agents is complex, numerous experimental studies suggest that generic therapeutic intervention directed at approaches that aim to upregulate repair of the damaged alveolar blood/air barrier of the lung may be of value, particularly with respect to chemical-induced injury. To this end, keratinocyte growth factor (KGF), epithelial growth factor (EGF) and basic fibroblast growth factor (bFGF) are emerging as the most important candidates. Hepatocyte growth factor (HGF) does not have epithelial specificity for lung tissue. However, the enhanced effects of combinations of growth factors, such as the synergistic effect of HGF upon vascular endothelial growth factor (VEGF)-mediated endothelial cell activity, and the combined effect of HGF and KGF in tissue repair should be investigated, particularly as the latter pair of growth factors are frequently implicated in processes associated with the repair of lung damage. Synergistic interactions also occur between trefoil factor family (TFF) peptides and growth factors such as EGF. TFF peptides are most likely to be of value as a short term therapeutic intervention strategy in stimulating epithelial spreading activities which allow damaged mucosal surfaces to be rapidly covered by epithelial cells.

Expression of semaphorin 3A in the rat corneal epithelium during wound healing

The neural guidance protein semaphorin 3A (Sema3A) is expressed in corneal epithelial cells of the adult rat. We have now further investigated the localization of Sema3A in the normal rat corneal epithelium as well as changes in its expression pattern during wound healing after central corneal epithelial debridement. The expression pattern of Sema3A was compared with that of the tight-junction protein zonula occludens-1 (ZO-1), the gap-junction protein connexin43 (Cx43), or the cell proliferation marker Ki67. Immunofluorescence analysis revealed that Sema3A was present predominantly in the membrane of basal and wing cells of the intact corneal epithelium. The expression of Sema3A at the basal side of basal cells was increased in the peripheral epithelium compared with that in the central region. Sema3A was detected in all layers at the leading edge of the migrating corneal epithelium at 6h after central epithelial debridement. The expression of Sema3A was markedly up-regulated in the basal and lateral membranes of columnar basal cells apparent in the thickened, newly healed epithelium at 1 day after debridement, but it had largely returned to the normal pattern at 3 days after debridement. The expression of ZO-1 was restricted to superficial epithelial cells and remained mostly unchanged during the wound healing process. The expression of Cx43 in basal cells was down-regulated at the leading edge of the migrating epithelium but was stable in the remaining portion of the epithelium. Ki67 was not detected in basal cells of the central epithelium at 1 day after epithelial debridement, when Sema3A was prominently expressed. Immunoblot analysis showed that the abundance of Sema3A in the central cornea was increased 1 day after epithelial debridement, whereas that of ZO-1 or Cx43 remained largely unchanged. This increase in Sema3A expression was accompanied by up-regulation of the Sema3A coreceptor neuropilin-1. Our observations have thus shown that the expression of Sema3A is increased markedly in basal cells of the newly healed corneal epithelium, and that this up-regulation of Sema3A is not associated with cell proliferation. They further suggest that Sema3A might play a role in the regulation of corneal epithelial wound healing.

The growth-promoting effect of KGF on limbal epithelial cells is mediated by upregulation of ΔNp63α through the p38 pathway

Corneal epithelial stem cells are thought to reside in the limbus, the transition zoon between cornea and conjunctiva. Keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF) are two paracrine factors that regulate the proliferation, migration and differentiation of the limbal epithelial cells; however, the underlying mechanisms are still poorly understood. In an ex vivo limbal explant culture, we found that KGF is a more potent growth stimulator for the epithelial outgrowth than HGF. Immunofluorescence studies of the epithelial outgrowth from cells treated with HGF or KGF showed similar expression patterns of keratin-3 and keratin-14. Interestingly, p63 was highly expressed in KGF-treated limbal epithelial sheets but not in those treated with HGF. Kinase inhibitor studies showed that induction of ΔNp63α expression by KGF is mediated via the p38 pathway. The effect of KGF on limbal epithelial outgrowth was significantly reduced when endogenous ΔNp63α was suppressed, suggesting that KGF-induced limbal epithelial outgrowth is dependent on the expression of ΔNp63α. Our findings strongly suggest that limbal keratocytes regulate limbal epithelial cell growth and differentiation through a KGF paracrine loop, with ΔNp63α expression as one of the downstream targets.

Neuroprotectin D1 synthesis and corneal nerve regeneration after experimental surgery and treatment with PEDF plus DHA

PURPOSE

This study was conducted to define whether pigment epithelial-derived growth factor (PEDF), together with docosahexaenoic acid (DHA), enhances the synthesis of neuroprotectin D1 (NPD1) and the regeneration of corneal nerves damaged after surgery.

METHODS

Corneal stromal dissection was performed in the left eyes of adult New Zealand rabbits treated with DHA+PEDF, PEDF, or DHA for 6 weeks. In vivo confocal images of the corneas were obtained at 2, 4, and 8 weeks, and nerve areas were quantified. At 8 weeks after treatment, corneas were stained with tubulin betaIII antibody, and the epithelial nerve area and the sub-basal and stromal nerve plexus were quantified. At 1 week and 2 weeks after treatment, lipids were extracted from corneas, and the synthesis of NPD1 was analyzed by mass spectrometry. Epithelial cell density was quantified by confocal microscopy 8 weeks after surgery.

RESULTS

In vivo confocal images at 2 and 4 weeks after surgery showed a 2.5-fold increase in corneal nerve area in PEDF+DHA-treated animals compared with control animals. Increased nerve surface areas in epithelia, subepithelia, and stroma were observed in rabbits treated for 8 weeks with PEDF+DHA. PEDF or DHA alone did not produce a significant increase. NPD1 synthesis peaked at 1 week and was four times higher in the PEDF+DHA-treated group than in the controls.

CONCLUSIONS

PEDF+DHA promotes the regeneration of corneal nerves. Neurotrophin-mediated NPD1 synthesis is suggested to precede nerve regeneration by demonstration of its accumulation upon addition of DHA and PEDF at earlier time points. Therefore, this signaling mechanism upregulates corneal nerve regeneration and may be targeted in neurotrophic keratitis, dry eye after refractive surgery, and other corneal diseases.

Growth factors and corneal epithelial wound healing

In this article, we briefly review recent findings in the effects of growth factors including the EGF family, KGF, HGF, IGF, insulin, and TGF-beta on corneal epithelial wound healing. We discuss the essential role of EGFR in inter-receptor cross-talk in response to wounding in corneal epithelium and bring forward a concept of "alarmins" to the field of wound healing research.

Inhibition of p38 MAPK facilitates ex vivo expansion of skin epithelial progenitor cells

Ex vivo expansion of skin epithelial stem cells has long attracted great interest because of the potential utilization in transplantation and gene therapy. The use of cultured stem or progenitor cells was limited by the lack of applicable culturing system with both satisfactory expansion efficacy and well suppressed differentiation ex vivo. The p38 mitogen-activated protein kinase (MAPK) pathways are responsible for cell growth and differentiation process. We investigated the function of p38 inhibitor SB203580 in the ex vivo expansion of skin epithelial progenitor cells by comparing media with or without addition of this inhibitor. Our results showed that the culturing medium with murine 3T3 feeder layers added with 10 microM SB203580 was more effective in promoting clonal growth of human skin epithelial progenitors or stem cells than the conventional medium without SB203580. The clone initial day in cells treated with 10 microM SB203580 came 2 d earlier with higher colony formation efficiency. The skin epithelial progenitor cells treated with 10 microM SB203580 formed clones that were uniformly smaller in size, longer in sustained proliferation, shorter in clone doubling time, higher in S-phase cells percentage, and lower in levels of differentiation markers such as K10 along with higher levels of stem-cell-associated markers such as p63, K15, and ABCG2 than those cultured in the conventional medium. Collectively, these results indicate that the p38 MAPK pathways inhibitor SB203580 can be used as a culture medium additive that helps to achieve more effective ex vivo expansion of skin epithelial progenitor cells.

Specific signaling cascades involved in cell spreading during healing of micro-wounded gastric epithelial monolayers

Mechanisms that specifically modulate cell spreading and/or cell migration following epithelial wounding are poorly understood. Using micro-wounded human gastric epithelial monolayers, we show herein that EGF and TGFalpha maximally increase spreading of epithelial sheets under a cell proliferation-independent mechanism. Treatment of confluent HGE-17 cells with the phosphatidylinositol 3-kinase inhibitor, LY294002, and the epidermal growth factor receptor inhibitor, PD153035, strongly reduced basal and TGFalpha-stimulated cell spreading. While pharmacological inhibition of pp60src-kinase activity also attenuated basal epithelial spreading, addition of the mTOR/p70S6K inhibitor rapamycin or a specific siRNA targeting ILK sequence did not affect the kinetic rates of wound closure. Epithelial wound healing was initiated by actin purse-string contraction followed by lamellae formation. Conversely, disruption of actin and tubulin stability with cytochalasin D and nocodazole, respectively, inhibited epithelial sheet spreading. Finally, antibodies directed against the alpha3 integrin subunit, but not against the alpha6 or alpha2 subunits, attenuated epithelial sheet spreading as well as lamellae formation. In conclusion, the current investigation establishes that EGF/TGFalpha and the alpha3beta1 integrin, pp60c-src, EGFR and PI3K pathways are mainly associated with the cell spreading of the restitution process during healing of human gastric epithelial wounds.

Association of protein tyrosine phosphatases (PTPs)-1B with c-Met receptor and modulation of corneal epithelial wound healing

PURPOSE

The purpose of this study was to investigate the expression and activity of protein tyrosine phosphatases (PTPs) in epithelium during corneal wound healing and to investigate how PTPs regulate activation of the c-Met receptor and the receptor's proximal signaling.

METHODS

Rabbit corneas were injured by gentle scraping of the surface, leaving the limbal epithelium intact, and epithelium was collected at 1, 2, 3, and 7 days after injury. In organ culture models, epithelium was removed and corneas were incubated with hepatocyte growth factor (HGF), with or without the PTP inhibitor bpV(phen), and the PI-3K inhibitors wortmannin and LY294002. Human corneal epithelial (HCE) cells were stimulated with HGF with or without bpV(phen). Total cell lysates and cytosolic and membrane fractions were analyzed by Western blot. PTP activities were measured with specific substrates. PTP1B and SHP-2 genes were knocked down by interference RNA (siRNA).

RESULTS

PTP activity and expression increased during wound healing. The most abundant were SHP-2, PTP1B, and PTEN. HGF activated the c-Met receptor in HCE cells up to 30 minutes and was downregulated by 2 hours. Inhibition of PTPs increased HGF-promoted wound healing, HGF-activated phosphorylation of c-Met, and its downstream signal PI-3K/Akt, but not ERK1/2 or p70S6K. PTP1B and SHP-2 were bound to the c-Met. Part of the c-Met was colocalized in the endoplasmic reticulum with PTP1B. PTP1B phosphorylation increased when the c-Met receptor was deactivated, and gene knockdown of PTP1B increased c-Met activation. SHP-2 phosphorylation and binding to c-Met was higher during receptor activation, and SHP-2 gene silencing decreased receptor phosphorylation.

CONCLUSIONS

Inhibition of PTP activity mimics the effect of HGF by activating the PI-3K/Akt signal involved in wound healing. PTP1B and SHP-2 are bound to the c-Met receptor to control its activity. Although the binding of PTP1B increases when there is a decrease in c-Met activation and acts as a negative regulator of the receptor, the increased binding and phosphorylation of SHP-2 coincide with maximal stimulation of c-Met, acting as a positive regulator.

ERK1/2 mediate wounding- and G-protein-coupled receptor ligands-induced EGFR activation via regulating ADAM17 and HB-EGF shedding

PURPOSE

Previous studies have shown that wounding of human corneal epithelial cells (HCECs) results in the release of G-protein-coupled receptor ligands such as ATP and lysophosphatidic acid (LPA), which in turn transactivate epidermal growth factor (EGF) receptor (EGFR) through ectodomain shedding of heparin-binding EGF-like growth factor (HB-EGF). In the present study, the role of extracellular signal-regulated kinases 1/2 (ERK1/2) in regulating EGFR transactivation was investigated.

METHODS

SV40-immortalized HCECs were wounded or stimulated with ATP and LPA. EGFR and ADAM17 activation was analyzed by immunoprecipitation followed by Western blot analysis with phospho-tyrosine or phospho-serine antibodies, respectively. Phosphorylation of ERK and AKT was analyzed by Western blot analysis. HB-EGF shedding was assessed by measuring the release of alkaline phosphatase (AP) in a stably transfected human corneal epithelial (THCE) cell line expressing HB-EGF-AP. ADAM17 and ERK interaction was determined by coimmunoprecipitation.

RESULTS

Early, but not late, ERK1/2 phosphorylation in response to wounding, LPA, and ATP was EGFR independent, but sensitive to the inhibitors of calcium influx, protein kinase C and Src kinase. Wounding-, LPA-, and ATP-induced HB-EGF shedding and EGFR activation were attenuated by the MAPK/ERK kinase (MEK) inhibitors PD98059 and U0126, as well as by ADAM10 and -17 inhibitors. ADAM17 was found to be physically associated with active ERK and phosphorylated at serine residues in an ERK-dependent manner in wounded cells.

CONCLUSIONS

Taken together, our data suggest that in addition to functioning as an EGFR downstream effector, ERK1/2 also mediates ADAM-dependent HB-EGF shedding and subsequent EGFR transactivation in response to a variety of stimuli, including wounding and GPCR ligands.

Coordinating cell proliferation and migration in the lens and cornea

Migration is a complex process for epithelial tissues, because the epithelium must move as an intact sheet to preserve its barrier function. The requirement for structural integrity is met by coupling cell-to-matrix and cell-to-cell adhesion at the cellular level, and by coordinating cell proliferation and cell migration in the tissue as a whole. Proliferation is suppressed at the migrating cell front, allowing cells in this region to remain tightly packed while advancing rapidly. At the same time, proliferation is enhanced in a region behind the advancing cell front to expand the epithelial cell sheet. This review considers the extracellular signals and intracellular signaling pathways that regulate these processes in the lens and corneal epithelium, with emphasis on the commonalities that link these tissues.

Elf5 is an epithelium-specific, fibroblast growth factor-sensitive transcription factor in the embryonic lung

Fibroblast growth factor (FGF) signaling has been shown to be essential for many aspects of normal lung development. To determine epithelial targets of FGF signaling, we cultured embryonic day (E) 11.5 mouse lungs for 24 hr in the presence or absence of the FGF receptor antagonist SU5402, which inhibited branching morphogenesis. Affymetrix gene chip analysis of treated and control epithelia identified several genes regulated by FGF signaling, including Elf5, a member of the Epithelial-specific Ets family of transcription factors. SU5402 reduced Elf5 expression in mesenchyme-free cultures of E12.5 epithelium, demonstrating that the inhibition was direct. In situ hybridization revealed that Elf5 had a dynamic pattern of expression during lung development. We found that expression of Elf5 was induced by FGF7 and FGF10, ligands that primarily bind FGFR2b. To further define the pathways by which FGFs activate Elf5 expression, we cultured E11.5 lung tips in the presence of compounds to inhibit FGF receptors (SU5402), PI3-Kinase/Akt-mediated signaling (LY294002), and MAP Kinase/Erk-mediated signaling (U0126). We found that SU5402 and LY294002 significantly reduced Elf5 expression, whereas U0126 had no effect. LY294002 also reduced Elf5 expression in cultures of purified epithelium. Finally, pAkt was coexpressed with Elf5 in the proximal epithelial airways of E17.5 lungs. These results demonstrate that Elf5 is an FGF-sensitive transcription factor in the lung with a dynamic pattern of expression and that FGF regulation of Elf5 by means of FGFR2b occurs through the PI3-Kinase/Akt pathway.

Protein kinase C alpha and epsilon differentially modulate hepatocyte growth factor-induced epithelial proliferation and migration

Protein kinase C (PKC) isoenzymes require membrane translocation for physiological activation. We have recently shown that the growth factors such as epidermal growth factor and hepatocyte growth factor (HGF), but not keratinocyte growth factor (KGF), regulate PKCalpha activation to promote epithelial wound healing [Sharma, G.D., Ottino, P., Bazan, H.E.P., 2005. Epidermal and hepatocyte growth factors, but not keratinocyte growth factor, modulate protein kinase C alpha translocation to the plasma membrane through 15(S)-hydroxyeicosatetraenoic acid synthesis. J. Biol. Chem. 280, 7917--924]. Protein kinase C alpha (PKCalpha) and protein kinase C epsilon (PKCvarepsilon) are two differentially regulated isoenzymes. While PKCalpha requires Ca(2+) for its activation, PKEvarepsilon is Ca(2+) independent. However, growth factor-induced activation of these enzymes and their specific regulation of epithelial migration and proliferation have not been explored. In the present study, we overexpressed PKCvarepsilon fused to green fluorescent protein to examine its translocation in real-time to the plasma membrane in living human corneal epithelial cells. Stimulation with HGF and KGF demonstrated translocation of PKCvarepsilon to the plasma membrane. Because HGF activates both PKCs, this growth factor was used to stimulate wound healing. PKCalpha or PKCvarepsilon-genes were knocked down individually without affecting the basal expression of the other PKC isoforms. Gene knockdown of PKCalpha significantly inhibited HGF-stimulated proliferation of human corneal epithelial cells. In contrast, PKCvarepsilon-gene-silencing severely impaired the HGF-stimulated migratory ability of human corneal epithelial cells. When migrating epithelial cells in the cornea wound bed after injury were transfected with specific PKCalpha- or PKCvarepsilon-siRNA, there was a significant delay in wound healing. Corneal wound healing stimulated with HGF in similar conditions was also inhibited. On the other hand, overexpression of PKCalpha or PKCvarepsilon-genes fused with green fluorescent protein in migrating corneal epithelium accelerated repair of the epithelial defect. Our findings demonstrate that PKCalpha and PKCvarepsilon modulate different stages of wound healing stimulated by HGF and contribute to epithelial repair by playing selective regulatory roles in epithelial proliferation and migration, both crucial to corneal wound healing.

Investigating transcriptional regulation of Prdx6 in mouse liver cells

Prdx6, a unique member of the peroxiredoxin family of antioxidants, is highly expressed in liver and protects cells from oxidative damage by reducing H2O2 and various lipid peroxides. We investigated the transcriptional regulation of Prdx6 in the H2.35 mouse hepatocyte cell line and sought to determine the mechanism of basal and induced expression. We found that Prdx6 expression is down-regulated upon serum deprivation and subsequently induced in a time-dependent manner in response to KGF, TNF-alpha, dexamethasone, and H2O2. Inhibitors of both PKC and MEK largely prevented Prdx6 induction by KGF and, to a lesser extent, TNF-alpha. Interestingly, inhibition of NF-kappaB led to a marked increase in Prdx6 regulation in the absence or presence of inducers, suggesting a normal role for NF-kappaB in Prdx6 suppression. Using reporter constructs from the mouse gene, we found that the first 160 bp of the proximal promoter was sufficient for low levels of expression, and expression increased sixfold with 1200 bp of the proximal promoter. These regions were not, however, sufficient to mediate up-regulation by the known Prdx6 inducers in our system. Together, these data support multiple pathways of Prdx6 regulation and reveal important promoter regions that mediate its transcriptional regulation.

Lysophosphatidic acid promoting corneal epithelial wound healing by transactivation of epidermal growth factor receptor

PURPOSE

To identify the underlying mechanisms by which lipid mediator lysophosphatidic acid (LPA) acts as a growth factor in stimulating extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3'-kinase (PI3K) during corneal epithelial wound healing.

METHODS

Epithelial debridement wounds in cultured porcine corneas and scratch wounds in an epithelial monolayer of SV40-immortalized human corneal epithelial (THCE) cells were allowed to heal in the presence or absence of an epidermal growth factor receptor (EGFR) inhibitor (tyrphostin AG1478), a matrix metalloproteinase inhibitor (GM6001), or a heparin-binding EGF-like growth factor (HB-EGF) antagonist (CRM197) with or without LPA. EGFR activation was analyzed by immunoprecipitation using EGFR antibodies and Western blotting with phosphotyrosine antibodies. Phosphorylation of ERK and AKT (a major substrate of PI3K) was analyzed by Western blotting with antibodies specific to the phosphorylated proteins. Wound- and LPA-induced shedding of HB-EGF was assessed by measuring the release of alkaline phosphatase (AP) in a stable THCE cell line that expressed HB-EGF with AP inserted in the heparin-binding site.

RESULTS

In organ and cell culture models, LPA enhanced corneal epithelial wound healing. LPA-stimulated and spontaneous wound closure was attenuated by AG1478, GM6001, or CRM197. Consistent with the effects on epithelial migration, these inhibitors, as well as the Src kinase inhibitor (PP2), retarded LPA-induced activation of EGFR and its downstream effectors ERK and AKT in THCE cells. Unlike exogenously added HB-EGF, LPA stimulated moderate EGFR phosphorylation; the level of phosphorylated EGFR was similar to that induced by wounding. However, LPA appeared to prolong wound-induced EGFR signaling. The release of HB-EGF assessed by AP activity increased significantly in response to wounding, LPA, or both, and the release of HB-EGF-AP induced by LPA was inhibited by PP2 and GM6001.

CONCLUSIONS

LPA accelerates corneal epithelial wound healing through its ability to induce autocrine HB-EGF signaling. Transactivation of EGFR by LPA represents a convergent signaling pathway accessible to stimuli such as growth factors and ligands of G-protein-coupled receptors in response to pathophysiological challenge in human corneal epithelial cells.

Wound-induced ATP release and EGF receptor activation in epithelial cells

We have shown previously that wounding of human corneal epithelial (HCE) cells resulted in epidermal growth factor receptor (EGFR) transactivation through ectodomain shedding of heparin-binding EGF-like growth factor (HB-EGF). However, the initial signal to trigger these signaling events in response to cell injury remains elusive. In the present study, we investigated the role of ATP released from the injured cells in EGFR transactivation in HCE cells as well as in BEAS 2B cells, a bronchial epithelial cell line. Wounding of epithelial monolayer resulted in the release of ATP into the culture medium. The wound-induced rapid activation of phosphatidylinositol-3-kinase (PI3K) and extracellular signal-regulated kinase (ERK) pathways in HCE cells was attenuated by eliminating extracellular ATP, ADP and adenosine. The nonhydrolyzable ATP analog ATP-gamma-S induced rapid and sustained EGFR activation that depended on HB-EGF shedding and ADAM (a disintegrin and metalloproteinase). Targeting pathways leading to HB-EGF shedding and EGFR activation attenuated ATP-gamma-S-enhanced closure of small scratch wounds. The purinoceptor antagonist reactive blue 2 decreased wound closure and attenuated ATP-gamma-S induced HB-EGF shedding. Taken together, our data suggest that ATP, released upon epithelial injury, acts as an early signal to trigger cell responses including an increase in HB-EGF shedding, subsequent EGFR transactivation and its downstream signaling, resulting in wound healing.

Epidermal growth factor receptor-dependent PI3K-activation promotes restitution of wounded human gastric epithelial monolayers

Restitution is a crucial event during the healing of superficial injury of the gastric mucosa involving epithelial cell sheet movement into the damaged area. We demonstrated that growth factors promote the restitution of human gastric epithelial cells. However, the intracellular signaling pathways that transmit extracellular cues as well as regulate basal and growth factor-stimulated gastric epithelial cell migration are still unclear. Herein, confluent human gastric epithelial cell monolayers (HGE-17) or primary cultures of gastric epithelial cells were wounded with a razor blade and the migration response was analyzed in presence or absence of TGFalpha or of pharmacological inhibitors of signaling proteins. Kinase activation profile analysis and phase-contrast microscopy were also performed in parallel. We report that ERK1/2 and Akt activities are rapidly stimulated following wounding of HGE-17 cells. Treatment of confluent HGE-17 cells or primary cultures of gastric epithelial cells with the phosphatidylinositol 3-kinase inhibitor LY294002, but not the MEK1 inhibitor, PD98059, significantly inhibits basal and TGFalpha-induced migration following wounding. Conversely, treatment of wounded HGE-17 cells with phosphatidylinositol(3,4,5)-triphosphate is sufficient to stimulate basal cell migration by 235%. In addition, pp60c-src kinase activity and tyrosine phosphorylation of epidermal growth factor receptors (EGFR) are also rapidly enhanced after wounding and pharmacological inhibition of both these activities strongly attenuates basal and TGFalpha-induced migration as well as Akt phosphorylation levels. In conclusion, the present results indicate that EGFR-dependent PI3K activation promotes restitution of wounded human gastric epithelial monolayers.

SRC-family tyrosine kinases in wound- and ligand-induced epidermal growth factor receptor activation in human corneal epithelial cells

PURPOSE

The authors have previously demonstrated that wounding of human corneal epithelial cells (HCECs) transactivates epidermal growth factor (EGF) receptor (EGFR) and its downstream signaling pathways and that this EGFR signaling is required for epithelial wound healing. In this study, the authors sought to identify the underlying mechanisms for EGFR transactivation in response to wounding in HCECs.

METHODS

SV40-immortalized HCEC (THCE) monolayer was wounded and allowed to heal in the presence or absence of a selective inhibitor of the Src family kinases PP2 and EGFR ligand heparin-binding EGF-like growth factor (HB-EGF). Wound closure was monitored by photographing of the injury immediately or 24 hours after wounding. Activation of EGFR in THCE cells and in primary HCECs was analyzed by immunoprecipitation of EGFR, followed by Western blotting with phosphotyrosine antibody. Phosphorylation of extracellular signal-regulated kinase (ERK), AKT (a major substrate of phosphatidylinositol 3'-kinase [PI3K]), Src at tyrosine Y416, and EGFR at Y845 was analyzed by Western blotting with antibodies specific to phosphorylated proteins. Effects of PP2 on THCE cell migration were determined by Boyden chamber migration assay.

RESULTS

Among several inhibitors tested, PP2 blocked wound-induced EGFR phosphorylation in THCE cells. PP2 at 12.5 microM effectively inhibited EGFR transactivation in response to wounding and to the phosphorylation of ERK and AKT in THCE cells and primary HCECs. Consistent with the inhibition of EGFR transactivation, PP2 also attenuated epithelial migration and wound closure with or without exogenously added HB-EGF. PP2 at a concentration as high as 50 microM exhibited no effects on HB-EGF induced ERK phosphorylation. On the other hand, AKT phosphorylation was much more sensitive to PP2 than ERK or EGFR phosphorylation because 3.13 microM PP2 effectively inhibited wound- or HB-EGF-induced AKT phosphorylation.

CONCLUSIONS

These results suggest that Src kinase mediates wound-induced EGFR transactivation and participates in a pathway to activate the PI3K-AKT pathway downstream of EGFR in HCECs.

KGF induces lipogenic genes through a PI3K and JNK/SREBP-1 pathway in H292 cells

Lipid synthesis is required for cell growth and is subject to pharmacologic regulation. Keratinocyte growth factor (KGF) stimulates proliferation and lipogenesis in H292 cells, a pulmonary epithelial cancer cell line, but the signaling pathways are not known. KGF stimulated the expression of the transcription factors sterol-regulatory element binding protein-1 (SREBP-1), CCAAT/enhancer binding protein alpha (C/EBPalpha), and C/EBPdelta and two key enzymes involved in lipogenesis, FAS and stearoyl coenzyme A desaturase-1 (SCD-1). We found that KGF induced rapid activation of Akt, p70 S6K, JNK, and extracellular signal-regulated (ERK). Induction of SREBP-1, SCD-1, and FAS by KGF was inhibited by the JNK inhibitor SP600125 and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 but not by the ERK inhibitor PD98059. Using FAS and SCD-1-luciferase promoter constructs, we observed that KGF stimulated the transcription of these promoters and that exogenous cholesterol inhibited the induction. Mutation of the SREBP-1 binding site in the SCD-1 promoter abolished the effect of KGF on SCD-1 transcription. In addition, overexpression of active SREBP-1 directly stimulated SCD-1 and FAS. Conversely, adenovirus-mediated overexpression of a dominant negative form of SREBP-1 inhibited the KGF effect on FAS and SCD-1 expression. In summary, we conclude that KGF requires both PI3K and JNK signaling pathways to induce SREBP-1, which in turn induces SCD-1 and FAS expression in H292 cells.

Hepatocyte growth factor and keratinocyte growth factor regulation of epithelial and stromal corneal wound healing

PURPOSE

To investigate the effects of hepatocyte growth factor (HGF) and keratinocyte growth factor (KGF) on early wound healing in the corneal epithelium and stroma.

SETTING

Cell and Molecular Biology Unit, Department of Optometry and Vision Sciences, Cardiff University, and the Cardiff Institute of Tissue Engineering and Repair, Cardiff, United Kingdom.

METHODS

Corneal keratocyte cell cultures and wounded corneal organ cultures (both maintained in serum-free conditions) were treated with 0.1 to 100 ng/mL of HGF or KGF for up to 5 days. Cell cultures were assessed for proliferation, migration, and differentiation into myofibroblasts. Organ cultures were used to evaluate the effect of HGF and KGF on reepithelialization following a wound, epithelial morphology and stratification, keratocyte numbers directly beneath the wounded area, and differentiation into myofibroblasts.

RESULTS

The 2 growth factors had opposite effects on the rate of reepithelialization, with HGF delaying and KGF accelerating epithelial coverage of the wound. Morphologic assessment showed that both growth factors affected the stratification and differentiation of the epithelium. Both factors stimulated proliferation of keratocytes in serum-free cell culture, although neither induced the appearance of myofibroblasts. This was in contrast to wounded organ cultures treated with 100 ng/mL HGF, in which large numbers of myofibroblasts were observed under the wound. Control corneas and those receiving KGF contained very few myofibroblasts. Keratocyte repopulation of the denuded area under the wound was enhanced in the presence of HGF but decreased in response to KGF.

CONCLUSIONS

Hepatocyte growth factor and KGF appeared to have potent and often opposite effects on epithelial and stromal cells following a wound. Hepatocyte growth factor was more detrimental than KGF, resulting in an aberrant epithelium and mass differentiation of keratocytes into myofibroblasts. Inhibition of HGF may be an appropriate therapeutic intervention in the case of persistent epithelial defects and to prevent fibrosis following a corneal stromal wound such as can occur after refractive surgery.

FGFR2b signaling regulates ex vivo submandibular gland epithelial cell proliferation and branching morphogenesis

Branching morphogenesis of mouse submandibular glands is regulated by multiple growth factors. Here, we report that ex vivo branching of intact submandibular glands decreases when either FGFR2 expression is downregulated or soluble recombinant FGFR2b competes out the endogenous growth factors. However, a combination of neutralizing antibodies to FGF1, FGF7 and FGF10 is required to inhibit branching in the intact gland, suggesting that multiple FGF isoforms are required for branching. Exogenous FGFs added to submandibular epithelial rudiments cultured without mesenchyme induce distinct morphologies. FGF7 induces epithelial budding, whereas FGF10 induces duct elongation, and both are inhibited by FGFR or ERK1/2 signaling inhibitors. However, a PI3-kinase inhibitor also decreases FGF7-mediated epithelial budding, suggesting that multiple signaling pathways exist. We immunolocalized FGF receptors and analyzed changes in FGFR, FGF and MMP gene expression to identify the mechanisms of FGF-mediated morphogenesis. FGFR1b and FGFR2b are present throughout the epithelium,although FGFR1b is more highly expressed around the periphery of the buds and the duct tips. FGF7 signaling increases FGFR1b and FGF1expression, and MMP2 activity, when compared with FGF10, resulting in increased cell proliferation and expansion of the epithelial bud, whereas FGF10 stimulates localized proliferation at the tip of the duct. FGF7- and FGF10-mediated morphogenesis is inhibited by an MMP inhibitor and a neutralizing antibody to FGF1, suggesting that both FGF1 and MMPs are essential downstream mediators of epithelial morphogenesis. Taken together,our data suggests that FGFR2b signaling involves a regulatory network of FGFR1b/FGF1/MMP2 expression that mediates budding and duct elongation during branching morphogenesis.

An optimised protocol for the production of autologous serum eyedrops

BACKGROUND

Serum eyedrops have been successfully used in the treatment of severe dry eye, persistent epithelial defects and other severe ocular surface disorders. A number of clinical studies showed a variable efficacy of this approach, but the parameters for the production of this blood product varied significantly. In order to establish an optimised protocol for the production of serum eyedrops, we examined the effect of various clotting times, centrifugation forces, types of diluent and dilutions on the concentration of growth factors, fibronectin, and vitamins in serum and tested the epitheliotrophic capacity of these serum modifications in a cell culture model of human SV-40-immortalised corneal epithelial cells (HCE-T).

METHODS

Serum samples were prepared with a clotting time of 20, 60 or 120 min, a centrifugation force of 500 xg or 3,000 xg, and diluted with BSS or isotonic saline. The concentrations of EGF, TGF-beta1, PDGF-AB, FGF, HGF, fibronectin, vitamin A and vitamin E in these samples were evaluated with ELISA and HPLC. HCE-T cells were incubated for 24, 48, 72, 96 and 144 h with 100, 50, 25, 12.5, 6.25 and 3.125% serum in diluent, and cell proliferation, migration and differentiation were evaluated by means of a luminescence-based ATP assay, a colony-dispersion assay and scanning electron microscopy.

RESULTS

Using a longer clotting time resulted in an increased concentration of all the epitheliotrophic factors examined in serum; the difference was statistically significant for EGF, TGF-beta1 and HGF. Increasing the g force of centrifugation from 500 xg to 3,000 xg resulted in significantly less TGF-beta1, but more EGF and vitamin A. Cell proliferation was better supported by serum prepared with 3,000 xg and diluted with BSS. Serum prepared with a longer clotting time yielded better cell migration and differentiation.

CONCLUSION

Clotting time, centrifugation and diluents have a significant impact on the composition and epitheliotrophic effects of serum. A long clotting time (>or=120 min), a sharp centrifugation (3,000 xg for 15 min) and dilution with BSS improve the ability of serum eyedrops to support proliferation, migration and differentiation of corneal epithelial cells.

KGF-induced motility of breast cancer cells is dependent on Grb2 and Erk1,2

Breast cancer metastasis is directly associated with breast cancer cell motility. Using a cell culture wounding model, we have demonstrated that keratinocyte growth factor (KGF) enhanced the motility of estrogen receptor-positive breast cancer cells. However, the mechanisms by which KGF enhanced motility of breast cancer cells are not known. In the present study, we report that KGF-induced motility requires intact tyrosine kinase signaling since genistein, a tyrosine kinase inhibitor, led to decreased motility of breast cancer cells mediated by KGF. Using cDNA microarrays, we previously found that KGF increased the expression of Grb2 mRNA by 2 3-fold. Since Grb2 plays an important role in tyrosine kinase signaling, we examined the involvement of Grb2 in KGF-induced motility. Down-regulation of Grb2 protein expression inhibited KGF-induced motility. Since Grb2 is known to regulate Erk1,2 and Akt kinase activities we determined whether these downstream proteins may be vital to KGF-induced motility. Inhibiting the activation of Erk1,2 by PD98059 suppressed KGF-induced motility whereas inhibiting the activation of Akt by wortmannin did not affect KGF-induced motility. In conclusion, these results indicate that KGF mediated signal transduction employs Grb2 to transduce the tyrosine kinase signals resulting in the activation of Erk1,2 and breast cancer cell motility.

Epidermal and Hepatocyte Growth Factors, but Not Keratinocyte Growth Factor, Modulate Protein Kinase Cα Translocation to the Plasma Membrane through 15(S)-Hydroxyeicosatetraenoic Acid Synthesis

Activation of protein kinase C (PKC) involves its recruitment to the membrane, where it interacts with its activator(s). We expressed PKCalpha fused to green fluorescent protein and examined its real time translocation to the plasma membrane in living human corneal epithelial cells. Upon 10 min of stimulation with epidermal and hepatocyte growth factors (EGF and HGF), PKCalpha translocated to the plasma membrane. Keratinocyte growth factor did not stimulate PKCalpha translocation up to 1 h after stimulation. Pretreatment with the 15-lipoxygenase metabolite, 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), followed by EGF or HGF, produced faster translocation of PKCalpha detectable at 2 min. However, the same concentration of 15(S)-HETE alone did not stimulate translocation. 15(S)-Hydroperoxyeicosatetraenoic acid and 5(S)-HETE did not affect growth factor-induced translocation of PKCalpha. PD153035, a specific inhibitor of tyrosine kinase activity of the EGF receptor, completely blocked PKCalpha translocation induced by EGF. PD98059, a specific MEK inhibitor, significantly inhibited EGF- and HGF-mediated PKCalpha translocation, which was reversed by addition of 15(S)-HETE. Phosphorylation of ERK1/2 by EGF was followed by phosphorylation of cytosolic phospholipase A(2) (cPLA(2)), and blocking ERK1/2 inhibited cPLA(2) activation. Immunofluorescence demonstrated translocation of p-cPLA(2) to plasma and nuclear membranes as early as 2 min. This may further increase arachidonic acid release from membrane phospholipid pools and increase the intracellular pool of HETEs. In fact, in cells prelabeled with [(3)H]arachidonic acid, EGF stimulated synthesis of 15(S)-HETE in the cytosolic fraction. 15(S)-HETE also reversed the effect of LOX inhibitor on EGF-mediated cell proliferation. Our results indicate that 15(S)-HETE is an intracellular second messenger that facilitates translocation of PKCalpha to the membrane and elucidate a mechanism that plays a regulatory role in cell proliferation crucial to corneal wound healing.

Role of ErbB2 in Corneal Epithelial Wound Healing

PURPOSE

Human corneal epithelial cells (HCECs) were functionally depleted of erbB2 to elucidate its role in epidermal growth factor (EGF) receptor (EGFR) activation-dependent cell migration.

METHODS

The retrovirus pBabe-5R, which encodes an erbB2 single-chain antibody with an endoplasmic reticulum (ER)-targeting sequence, and control pBabe-puro were used to infect THCE cells (an SV40-immortalized HCEC line). Several cell lines expressing 5R were selected along with a pBabe-puro control line. The depletion of erbB2 was verified by cell surface biotinylation of proteins, followed by streptavidin precipitation and subsequent detection of erbB2 by immunoblot analysis. Activation of erbBs was analyzed by immunoprecipitation using the phosphotyrosine antibody pY20, followed by Western blot analysis with erbB1 or erbB2 antibodies. Phosphorylation of extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3'-kinase (PI3K) was analyzed by Western blot with antibodies specific to phosphorylated proteins. Effects of erbB2 depletion on heparin-binding EGF-like growth factor (HB-EGF)-induced cell migration were determined by Boyden chamber migration assay and by scratch wound assay.

RESULTS

Wounding induced erbB2 tyrosine phosphorylation. Expression of 5R encoding an erbB2 single-chain antibody with an endoplasmic reticulum-targeting sequence depleted the cell surface expression of erbB2 in HCECs. Wounding resulted in a rapid increase in the phosphorylation of erbB1 in both 5R-expressing and control cells, whereas wound-induced erbB2 phosphorylation in 5R-expressing cells was not detectable. Depletion of functional erbB2 attenuated the healing of scratch wounds in the presence of HB-EGF and impaired both chemotactic migration stimulated by HB-EGF and haptotactic migration toward a fibronectin-collagen I (3:1; FNC) coating mix. Expression of 5R affected both the intensity and the duration of wound-induced, EGFR-elicited ERK and PI3K activation. Inhibition of ERK and PI3K pathways in cultured porcine corneas impaired ex vivo epithelial wound healing.

CONCLUSIONS

ErbB2 serves as a critical component that couples erbB receptor tyrosine kinase to the migration machinery of corneal epithelial cells.

Keratinocyte growth factor/fibroblast growth factor 7, a homeostatic factor with therapeutic potential for epithelial protection and repair

Keratinocyte growth factor (KGF) is a paracrine-acting, epithelial mitogen produced by cells of mesenchymal origin. It is a member of the fibroblast growth factor (FGF) family, and acts exclusively through a subset of FGF receptor isoforms (FGFR2b) expressed predominantly by epithelial cells. The upregulation of KGF after epithelial injury suggested it had an important role in tissue repair. This hypothesis was reinforced by evidence that intestinal damage was worse and healing impaired in KGF null mice. Preclinical data from several animal models demonstrated that recombinant human KGF could enhance the regenerative capacity of epithelial tissues and protect them from a variety of toxic exposures. These beneficial effects are attributed to multiple mechanisms that collectively act to strengthen the integrity of the epithelial barrier, and include the stimulation of cell proliferation, migration, differentiation, survival, DNA repair, and induction of enzymes involved in the detoxification of reactive oxygen species. KGF is currently being evaluated in clinical trials to test its ability to ameliorate severe oral mucositis (OM) that results from cancer chemoradiotherapy. In a phase 3 trial involving patients who were treated with myeloablative chemoradiotherapy before autologous peripheral blood progenitor cell transplantation for hematologic malignancies, KGF significantly reduced both the incidence and duration of severe OM. Similar investigations are underway in patients being treated for solid tumors. On the basis of its success in ameliorating chemoradiotherapy-induced OM in humans and tissue damage in a variety of animal models, additional clinical applications of KGF are worthy of investigation.

Keratinocyte Growth Factor Stimulates Alveolar Type II Cell Proliferation through the Extracellular Signal–Regulated Kinase and Phosphatidylinositol 3-OH Kinase Pathways

Keratinocyte growth factor (KGF or FGF-7) stimulates alveolar type II cell proliferation, but little is known about the signaling pathways involved. We investigated the role of the ERK (p42/44 mitogen activated protein [MAP] kinase) and phosphatidylinositol 3-OH kinase (PI3 kinase) pathways on alveolar type II cell proliferation and differentiation. Rat type II cells were cultured on tissue culture plastic and Matrigel in the presence or absence of KGF and specific chemical inhibitors PD98059, LY294002, and rapamycin at various concentrations. Proliferation was measured by thymidine incorporation and DNA quantitation, and differentiation was measured by expression of surfactant protein A and alkaline phosphatase. We demonstrate that KGF activates distal effectors of the PI3 kinase pathway, PKB/Akt, and p70S6 kinase, as well as p42/44 MAP kinase proteins. Inhibition of these pathways with PD98059, LY294002, or rapamycin inhibited type II cell proliferation but had no significant effect on differentiation. KGF did not activate the c-Jun kinase or p38 MAP kinase pathways. We conclude that the p42/44 MAP kinase and PI3 kinase pathways are important in regulating alveolar type II cell proliferation in response to KGF.

EGF stimulates growth by enhancing capacitative calcium entry in corneal epithelial cells

In rabbit corneal epithelial cells (RCEC), we determined whether capacitative calcium entry (CCE) mediates the mitogenic response to epidermal growth factor, EGF. [Ca2+]i was measured with single-cell fluorescence imaging of fura2-loaded RCEC. EGF (5 ng/ml) maximally increased [Ca2+]i 4.4-fold. Following intracellular store (ICS) calcium depletion in calcium-free medium with 10 microM cyclopiazonic acid (CPA) (endoplasmic reticulum calcium ATPase inhibitor), calcium addback elicited plasma membrane Ca2+ influx as a result of activation of plasma membrane store operated channel (SOC) activity. Based on Mn2+ quench measurements of fura2 fluorescence, 5 ng/ml EGF enhanced such influx 2.3-fold, whereas with Rp-cAMPS (protein kinase A inhibitor) plus EGF it increased by 5.3-fold. In contrast, SOC activation was blocked with 100 microM 2-aminoethyldiphenylborate (2-APB, store-operated channel inhibitor). During exposure to either 50 microM UO126 (MEK-1/2 inhibitor) or 10 microM forskolin (adenylate cyclase activator), 5 ng/ml EGF failed to affect [Ca2+]i. RT-PCR detected gene expression of: 1) transient receptor potential (TRP) protein isoforms 1, 3, 4, 6 and 7; 2) IP3R isoforms 1-3. Immunocytochemistry, in conjunction with confocal and immunogold electron microscopy, detected plasma membrane localization of TRP4 expression. Inhibition of CCE with 2-APB and/or CPA, eliminated the 2.5-fold increase in intracellular [3H]-thymidine incorporation induced by EGF. Taken together, CCE in RCEC mediates the mitogenic response to EGF. EGF induces CCE through its stimulation of Erkl/2 activity, whereas PKA stimulation suppresses these effects of EGF. TRP4 may be a component of plasma membrane SOC activity, which is stimulated by ICS calcium depletion.

Role of protein kinase C in arginine vasopressin-stimulated ERK and p70S6 kinase phosphorylation

We previously showed in rat renal glomerular mesangial cells, that arginine vasopressin (AVP)-stimulated cell proliferation was mediated by epidermal growth factor receptor (EGF-R) transactivation, and activation (phosphorylation) of ERK1/2 and p70S6 kinase (Ghosh et al. [2001]: Am J Physiol Renal Physiol 280:F972-F979]. In this paper, we extend these observations and show that different protein kinase C (PKC) isoforms play different roles in mediating AVP-stimulated ERK1/2 and p70S6 kinase phosphorylation and cell proliferation. AVP treatment for 0-60 min stimulated the serine/threonine phosphorylation of PKC isoforms alpha, delta, epsilon, and zeta. The activation of PKC was dependent on EGF-R and phosphatidylinositol 3-kinase (PI3K) activation. In addition, inhibition of conventional and novel PKC isoforms by chronic (24 h) exposure to phorbol 12-myristate 13-acetate (PMA) inhibited AVP-induced activation of ERK and p70S6 kinase as well as EGF-R phosphorylation. Rottlerin, a specific inhibitor of PKCdelta, inhibited both ERK and p70S6 kinase phosphorylation and cell proliferation. In contrast, a PKCepsilon translocation inhibitor decreased ERK1/2 activation without affecting p70S6 kinase or cell proliferation, while a dominant negative PKCzeta (K281W) cDNA delayed p70S6 kinase activation without affecting ERK1/2. On the other hand, Gö6976, an inhibitor of conventional PKC isoforms, did not affect p70S6 kinase, but stimulated ERK1/2 phosphorylation without affecting cell proliferation. Our results indicate that PKCdelta plays an important role in AVP-stimulated ERK and p70S6 kinase activation and cell proliferation.

Hepatocyte growth factor exerts a proliferative effect on oval cells through the PI3K/AKT signaling pathway

Hepatocyte growth factor (HGF) is a potent mitogen for a variety of cells including hepatocytes. While rat oval cells are supposed to be one of hepatic stem cells, biological effects of HGF on oval cells and their relevant signal transduction pathways remain to be determined. We sought to investigate them on OC/CDE22 rat oval cells, which are established from the liver of rats fed a choline-deficient/DL-ethionine-supplemented diet. The oval cells were cultured on fibronectin-coated dishes and stimulated with recombinant HGF, transforming growth factor-alpha (TGF-alpha), and thrombopoietin (TPO) under the serum-free medium condition. HGF treatment enhanced [3H]thymidine incorporation into oval cells in a dose-dependent manner. On the contrary, treatment with TGF-alpha or TPO had no significant effects on [3H]thymidine incorporation into the oval cells. c-Met protein was phosphorylated at the tyrosine residues after the HGF treatment. AKT, extracellular signal-regulated kinase 1/2 (ERK1/2), and p70(s6k) were simultaneously activated after the HGF stimulation, peaking at 30min after the treatment. The activation of AKT, p70(s6k), and ERK1/2 induced by HGF was abolished by pre-treatment with LY294002, a phosphoinositide 3-OH kinase (PI3K) inhibitor, and U0126, a mitogen-activated protein kinase/ERK kinase (MEK) inhibitor, respectively. When the cells were pre-treated with LY294002 prior to the HGF stimulation, the proliferative action of HGF was completely abrogated, implying that the PI3K/AKT signaling pathway is responsible for the biological effect of HGF. These in vitro data indicate that HGF exerts a proliferative action on hepatic oval cells via activation of the PI3K/AKT signaling pathway.