Requirement for Pak3 in Rac1-induced organization of actin and myosin during Drosophila larval wound healing

Aloesin-loaded chitosan/cellulose-based scaffold promotes skin tissue regeneration

Skin wound healing and regeneration is very challenging across the world as simple or acute wounds can be transformed into chronic wounds or ulcers due to foreign body invasion, or diseases like diabetes or cancer. The study was designed to develop a novel bioactive scaffold, by loading aloesin to chitosan-coated cellulose scaffold, to cure full-thickness skin wounds. The physiochemical characterization of the scaffold was carried out using scanning electron microscopy (SEM) facilitated by energy-dispersive spectrophotometer (EDS), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). The results indicated the successful coating of chitosan and aloesin on cellulose without any physical damage. The drug release kinetics confirmed the sustained release of aloesin by showing a cumulative release of up to 88 % over 24 h. The biocompatibility of the aloesin-loaded chitosan/cellulose (AlCsCFp) scaffold was evaluated by the WST-8 assay that confirmed the significantly increased adherence and proliferation of fibroblasts on the AlCsCFp scaffold. The in vivo wound healing study showed that both 0.05 % and 0.025 % AlCsCFp scaffolds have significantly higher wound closure rates (i.e. 88.2 % and 95.6 % approximately) as compared to other groups. This showed that novel composite scaffold has a wound healing ability. Furthermore, histological and gene expression analysis demonstrated that the scaffold also induced cell migration, angiogenesis, re-epithelialization, collagen deposition, and tissue granulation formation. Thus, it is concluded that the aloesin-loaded chitosan/cellulose-based scaffold has great therapeutic potential for being used in wound healing applications in the clinical setting in the future.

The Drosophila tumour suppressor Lgl and Vap33 activate the Hippo pathway through a dual mechanism

The tumour suppressor, Lethal (2) giant larvae [Lgl; also known as L(2)gl], is an evolutionarily conserved protein that was discovered in the vinegar fly Drosophila, where its depletion results in tissue overgrowth and loss of cell polarity. Lgl links cell polarity and tissue growth through regulation of the Notch and the Hippo signalling pathways. Lgl regulates the Notch pathway by inhibiting V-ATPase activity via Vap33. How Lgl regulates the Hippo pathway was unclear. In this current study, we show that V-ATPase activity inhibits the Hippo pathway, whereas Vap33 acts to activate Hippo signalling. Vap33 physically and genetically interacts with the actin cytoskeletal regulators RtGEF (Pix) and Git, which also bind to the Hippo protein (Hpo) and are involved in the activation of the Hippo pathway. Additionally, we show that the ADP ribosylation factor Arf79F (Arf1), which is a Hpo interactor, is involved in the inhibition of the Hippo pathway. Altogether, our data suggest that Lgl acts via Vap33 to activate the Hippo pathway by a dual mechanism: (1) through interaction with RtGEF, Git and Arf79F, and (2) through interaction and inhibition of the V-ATPase, thereby controlling epithelial tissue growth.

Underlying mechanisms that ensure actomyosin-mediated directional remodeling of cell-cell contacts for multicellular movement: Tricellular junctions and negative feedback as new aspects underlying actomyosin-mediated directional epithelial morphogenesis: Tricellular junctions and negative feedback as new aspects underlying actomyosin-mediated directional epithelial morphogenesis

Actomyosin (actin-myosin II complex)-mediated contractile forces are central to the generation of multifaceted uni- and multi-cellular material properties and dynamics such as cell division, migration, and tissue morphogenesis. In the present article, we summarize our recent researches addressing molecular mechanisms that ensure actomyosin-mediated directional cell-cell junction remodeling, either shortening or extension, driving cell rearrangement for epithelial morphogenesis. Genetic perturbation clarified two points concerning cell-cell junction remodeling: an inhibitory mechanism against negative feedback in which actomyosin contractile forces, which are well known to induce cell-cell junction shortening, can concomitantly alter actin dynamics, oppositely leading to perturbation of the shortening; and tricellular junctions as a point that organizes extension of new cell-cell junctions after shortening. These findings highlight the notion that cells develop underpinning mechanisms to transform the multi-tasking property of actomyosin contractile forces into specific and proper cellular dynamics in space and time.

Inhibition of negative feedback for persistent epithelial cell-cell junction contraction by p21-activated kinase 3

Actin-mediated mechanical forces are central drivers of cellular dynamics. They generate protrusive and contractile dynamics, the latter of which are induced in concert with myosin II bundled at the site of contraction. These dynamics emerge concomitantly in tissues and even each cell; thus, the tight regulation of such bidirectional forces is important for proper cellular deformation. Here, we show that contractile dynamics can eventually disturb cell–cell junction contraction in the absence of p21-activated kinase 3 (Pak3). Upon Pak3 depletion, contractility induces the formation of abnormal actin protrusions at the shortening junctions, which causes decrease in E-cadherin levels at the adherens junctions and mislocalization of myosin II at the junctions before they enough shorten, compromising completion of junction shortening. Overexpressing E-cadherin restores myosin II distribution closely placed at the junctions and junction contraction. Our results suggest that contractility both induces and perturbs junction contraction and that the attenuation of such perturbations by Pak3 facilitates persistent junction shortening.

Actin and myosin operate at cell–cell junctions during junctional shortening. Here the authors show that prolonged actomyosin contractility can compromise junctional shortening, and that Pak3 is required for attenuation of abnormal active protrusive structure and thus keeps junction contraction, appropriate E-cadherin distribution, and junction shortening in Drosophila.

Suppression of spastin Mutant Phenotypes by Pak3 Loss Implicates a Role for Reactive Glia in AD-HSP

Neurodegenerative mechanisms due to mutations in spastin currently center on neuronal defects, primarily in microtubule and endomembrane regulation. Spastin loss in Drosophila larvae compromises neuronal microtubule distribution, alters synaptic bouton morphology, and weakens synaptic transmission at glutamatergic neuromuscular junction (NMJ) synapses. Pak3, a p21-activated kinase that promotes actin polymerization and filopodial projections, is required for these spastin mutant defects; animals lacking both genes have normal NMJs. Here we show that Pak3 is expressed in central and peripheral glial populations, and reduction of Pak3 specifically in subperineurial glial cells is sufficient to suppress the phenotypes associated with spastin loss. Subperineurial glia in the periphery ensheathe motor neuron axons and have been shown to extend actin-based projections that regulate synaptic terminals during normal NMJ development. We find that these subperineurial glial projections are Pak3-dependent and nearly twice as frequent in spastin mutants, while in Pak3, spastin double mutants, neither glial projections nor synaptic defects are observed. Spastin deficiency thus increases Pak3-dependent subperineurial glia activity, which is in turn required for neuronal defects. Our results demonstrate a central role for Pak3-mediated, altered glial behavior in the neuronal defects due to spastin loss, and suggest that a similar reactive glia-mediated mechanism may underlie human AD-HSP pathogenesis.

NED416, a novel synthetic Sirt1 activator, promotes cutaneous wound healing via the MAPK/Rho pathway

Cutaneous wound healing is a highly complex biological process involving major events such as cell migration, angiogenesis, and tissue development. Sirtuin 1 (Sirt1) and its regulators have been suggested to play a role in cell migration and tissue repair. The aim of the present study was to determine the effects of a novel Sirt1 activator, the piper amide derivative (E)-3-(2,4-dichlorophenyl)-N-phenylacrylamide, also known as NED416, on cutaneous wound healing. The effects of NED416 on Sirt1 activity, Sirt1 expression, and angiogenesis were measured in skin and endothelial cells (epidermal keratinocytes, dermal fibroblasts and vascular endothelial cells) using a Sirt1 activity assay kit, western blot analysis and tube formation assays, respectively. The effects of NED416 on the rate of wound closure and collagen deposition were measured via H&E staining and Masson's trichrome staining, respectively. Levels of migration-related [Rac1, cell division cycle 42 (Cdc42) and α-p21-activated kinase] and mitogen-activated protein kinase (MAPK) signaling pathway proteins were measured in hairless mice via western blot analysis. NED416 significantly increased Sirt1 activity in dermal fibroblasts and epidermal keratinocytes to a greater extent than resveratrol, leading to increased cell migration and angiogenesis through Rac1/Cdc42 and ERK/JNK activation. Furthermore, NED416 accelerated wound closure, macrophage infiltration, and epithelium and collagen formation in vivo. The present study demonstrated a role of Sirt1 in cutaneous wound healing, and suggested that NED416 as a Sirt1 activator is more potent than resveratrol in promoting wound healing through Rac1/Cdc42 and MAPK signaling without toxicity, thus serving as a promising candidate for treatment.

Interplay between integrins and PI4P5K Sktl is crucial for cell polarization and reepithelialisation during Drosophila wound healing

Phosphatidylinositol(4,5)-bisphosphate [PI(4,5)P2] regulates cell adhesion and actin dynamics during cell migration. PI(4,5)P2 binds various components of the cell adhesion machinery, but how these processes affect migration of the epithelial cell sheet is not well understood. Here, we report that PI(4,5)P2 and Sktl, the kinase that converts PI4P to PI(4,5)P2, are both localized to the rear side of cells during wound healing of the Drosophila larval epidermis. The Sktl localization requires JNK pathway activation and integrins, but not PVR. The sktl knockdown epidermis displays strong defects in would closure, reminiscent of the JNK-depleted epidermis, and shows severe disruption of cell polarity, as determined by myosin II localization. Sktl and βPS integrin colocalize at the rear side of cells forming the trailing edge during wound healing and the two are inter-dependent in that the absence of one severely disrupts the rear localization of the other. These results strongly suggest that the JNK pathway regulates the rear localization of Sktl and integrins and the interplay between Sktl and integrins sets up cell polarity, which is crucial for reepithelialisation during wound healing.

Casein kinase 1α decreases β-catenin levels at adherens junctions to facilitate wound closure in Drosophila larvae

Skin wound repair is essential to restore barrier function and prevent infection after tissue damage. Wound-edge epidermal cells migrate as a sheet to close the wound. However, it is still unclear how cell-cell junctions are regulated during wound closure (WC). To study this, we examined adherens junctions during WC in Drosophila larvae. β-Catenin is reduced at the lateral cell-cell junctions of wound-edge epidermal cells in the early healing stages. Destruction complex components, including Ck1α, GSK3β and β-TrCP, suppress β-catenin levels in the larval epidermis. Tissue-specific RNAi targeting these genes also caused severe WC defects. The Ck1αRNAi -induced WC defect is related to adherens junctions because loss of either β-catenin or E-cadherin significantly rescued this WC defect. In contrast, TCFRNAi does not rescue the Ck1αRNAi -induced WC defect, suggesting that Wnt signaling is not related to this defect. Direct overexpression of β-catenin recapitulates most of the features of Ck1α reduction during wounding. Finally, loss of Ck1α also blocked junctional E-cadherin reduction around the wound. Our results suggest that Ck1α and the destruction complex locally regulate cell adhesion to facilitate efficient wound repair.

Protein kinases involved in epidermal barrier formation: The AKT family and other animals

Formation of a stratified epidermis is required for the performance of the essential functions of the skin; to act as an outside-in barrier against the access of microorganisms and other external factors, to prevent loss of water and solutes via inside-out barrier functions and to withstand mechanical stresses. Epidermal barrier function is initiated during embryonic development and is then maintained throughout life and restored after injury. A variety of interrelated processes are required for the formation of a stratified epidermis, and how these processes are both temporally and spatially regulated has long been an aspect of dermatological research. In this review, we describe the roles of multiple protein kinases in the regulation of processes required for epidermal barrier formation.

Crawling wounded: molecular genetic insights into wound healing from Drosophila larvae

For animals, injury is inevitable. Because of this, organisms possess efficient wound healing mechanisms that can repair damaged tissues. However, the molecular and genetic mechanisms by which epidermal repair is accomplished remain poorly defined. Drosophila has become a valuable model to study epidermal wound healing because of the comprehensive genetic toolkit available in this organism and the similarities of wound healing processes between Drosophila and vertebrates. Other reviews in this Special Issue cover wound healing assays and pathways in Drosophila embryos, pupae and adults, as well as regenerative processes that occur in tissues such as imaginal discs and the gut. In this review, we will focus on the molecular/genetic control of wound-induced cellular processes such as inflammation, cell migration and epithelial cell-cell fusion in Drosophila larvae. We will give a brief overview of the three wounding assays, pinch, puncture, and laser ablation, and the cellular responses that ensue following wounding. We will highlight the actin regulators, signaling pathways and transcriptional mediators found so far to be involved in larval epidermal wound closure and what is known about how they act. We will also discuss wound-induced epidermal cell-cell fusion and possible directions for future research in this exciting system.

Aloesin from Aloe vera accelerates skin wound healing by modulating MAPK/Rho and Smad signaling pathways in vitro and in vivo

BACKGROUND

Cutaneous wound healing is a complex process involving various regulatory factors at the molecular level. Aloe vera is widely used for cell rejuvenation, wound healing, and skin moisturizing.

HYPOTHESIS/PURPOSE

This study aimed to investigate the effects of aloesin from Aloe vera on cutaneous wound healing and mechanisms involved therein.

STUDY DESIGN

This study consisted of both in vitro and in vivo experiments involving skin cell lines and mouse model to demonstrate the wound healing effects of aloesin by taking into account several parameters ranging from cultured cell migration to wound healing in mice.

METHODS

The activities of Smad signaling molecules (Smad2 and Smad3), MAPKs (ERK and JNK), and migration-related proteins (Cdc42, Rac1, and α-Pak) were assessed after aloesin treatment in cultured cells (1, 5 and 10µM) and mouse skin (0.1% and 0.5%). We also monitored macrophage recruitment, secretion of cytokines and growth factors, tissue development, and angiogenesis after aloesin treatment using IHC analysis and ELISAs.

RESULTS

Aloesin increased cell migration via phosphorylation of Cdc42 and Rac1. Aloesin positively regulated the release of cytokines and growth factors (IL-1β, IL-6, TGF-β1 and TNF-α) from macrophages (RAW264.7) and enhanced angiogenesis in endothelial cells (HUVECs). Aloesin treatment accelerated wound closure rates in hairless mice by inducing angiogenesis, collagen deposition and granulation tissue formation. More importantly, aloesin treatment resulted in the activation of Smad and MAPK signaling proteins that are key players in cell migration, angiogenesis and tissue development.

CONCLUSION

Aloesin ameliorates each phase of the wound healing process including inflammation, proliferation and remodeling through MAPK/Rho and Smad signaling pathways. These findings indicate that aloesin has the therapeutic potential for treating cutaneous wounds.

Spatiotemporal regulation of cell fusion by JNK and JAK/STAT signaling during Drosophila wound healing

Cell-cell fusion is widely observed during development and disease, and imposes a dramatic change on participating cells. Cell fusion should be tightly controlled, but the underlying mechanism is poorly understood. Here, we found that the JAK/STAT pathway suppressed cell fusion during wound healing in the Drosophila larval epidermis, restricting cell fusion to the vicinity of the wound. In the absence of JAK/STAT signaling, a large syncytium containing a 3-fold higher number of nuclei than observed in wild-type tissue formed in wounded epidermis. The JAK/STAT ligand-encoding genes upd2 and upd3 were transcriptionally induced by wounding, and were required for suppressing excess cell fusion. JNK (also known as Basket in flies) was activated in the wound vicinity and activity peaked at ∼8 h after injury, whereas JAK/STAT signaling was activated in an adjoining concentric ring and activity peaked at a later stage. Cell fusion occurred primarily in the wound vicinity, where JAK/STAT activation was suppressed by fusion-inducing JNK signaling. JAK/STAT signaling was both necessary and sufficient for the induction of βPS integrin (also known as Myospheroid) expression, suggesting that the suppression of cell fusion was mediated at least in part by integrin protein.

Juglone ameliorates skin wound healing by promoting skin cell migration through Rac1/Cdc42/PAK pathway

Skin cell regeneration and wound healing are key processes in the recovery from skin injuries. Rapid cell migration and regeneration of skin cells lead to faster and better healing of wounded skin. In the present study, we aimed to investigate the wound healing potential of juglone, a naturally occurring Pin1 inhibitor found in walnuts. Cultured skin cells (NHDF and HaCaT) and hairless mice were treated with juglone after wound creation to examine its effects on cell migration and wound healing rate. The expressions of cell migration related proteins (Rac1, Cdc42, and α-PAK), collagen deposition, and angiogenesis were analyzed. Juglone treatment resulted in faster rate of growth and migration and recovered cell morphology, particularly at a concentration of 5 µM, in skin cells compared to the untreated group. In vivo experiments showed that mice treated with juglone showed faster wound healing rate with better skin morphology and collagen deposition than the vehicle group. Furthermore, juglone increased the activation and/or expression of Cdc42, Rac1, and α-pak in HaCaT cells, and resulted in enhanced angiogenesis in endothelial cells (HUVECs). Juglone also activated MAPKs signaling by activation of ERK, JNK, and p38 proteins. Taken together, these data suggest that juglone may be a potential candidate for wound healing and skin regeneration which ameliorates wound healing mainly by promoting skin cell migration through Rac1/Cdc42/PAK pathway.

P21-Activated Kinase Inhibitors FRAX486 and IPA3: Inhibition of Prostate Stromal Cell Growth and Effects on Smooth Muscle Contraction in the Human Prostate

Prostate smooth muscle tone and hyperplastic growth are involved in the pathophysiology and treatment of male lower urinary tract symptoms (LUTS). Available drugs are characterized by limited efficacy. Patients' adherence is particularly low to combination therapies of 5α-reductase inhibitors and α1-adrenoceptor antagonists, which are supposed to target contraction and growth simultaneously. Consequently, molecular etiology of benign prostatic hyperplasia (BPH) and new compounds interfering with smooth muscle contraction or growth in the prostate are of high interest. Here, we studied effects of p21-activated kinase (PAK) inhibitors (FRAX486, IPA3) in hyperplastic human prostate tissues, and in stromal cells (WPMY-1). In hyperplastic prostate tissues, PAK1, -2, -4, and -6 may be constitutively expressed in catecholaminergic neurons, while PAK1 was detected in smooth muscle and WPMY-1 cells. Neurogenic contractions of prostate strips by electric field stimulation were significantly inhibited by high concentrations of FRAX486 (30 μM) or IPA3 (300 μM), while noradrenaline- and phenylephrine-induced contractions were not affected. FRAX486 (30 μM) inhibited endothelin-1- and -2-induced contractions. In WPMY-1 cells, FRAX486 or IPA3 (24 h) induced concentration-dependent (1-10 μM) degeneration of actin filaments. This was paralleled by attenuation of proliferation rate, being observed from 1 to 10 μM FRAX486 or IPA3. Cytotoxicity of FRAX486 and IPA3 in WPMY-1 cells was time- and concentration-dependent. Stimulation of WPMY-1 cells with endothelin-1 or dihydrotestosterone, but not noradrenaline induced PAK phosphorylation, indicating PAK activation by endothelin-1. Thus, PAK inhibitors may inhibit neurogenic and endothelin-induced smooth muscle contractions in the hyperplastic human prostate, and growth of stromal cells. Targeting prostate smooth muscle contraction and stromal growth at once by a single compound is principally possible, at least under experimental conditions.

Rho family GTPase functions in Drosophila epithelial wound repair

Epithelial repair in the Drosophila embryo is achieved through 2 dynamic cytoskeletal machineries: a contractile actomyosin cable and actin-based cellular protrusions. Rho family small GTPases (Rho, Rac, and Cdc42) are cytoskeletal regulators that control both of these wound repair mechanisms. Cdc42 is necessary for cellular protrusions and, when absent, wounds are slow to repair and never completely close. Rac proteins accumulate at specific regions in the wound leading edge cells and Rac-deficient embryos exhibit slower repair kinetics. Mutants for both Rho1 and its effector Rok impair the ability of wounds to close by disrupting the leading-edge actin cable. Our studies highlight the importance of these proteins in wound repair and identify a downstream effector of Rho1 signaling in this process.

Pak3 regulates apical-basal polarity in migrating border cells during Drosophila oogenesis

Group cell migration is a highly coordinated process that is involved in a number of physiological events such as morphogenesis, wound healing and tumor metastasis. Unlike single cells, collectively moving cells are physically attached to each other and retain some degree of apical-basal polarity during the migratory phase. Although much is known about direction sensing, how polarity is regulated in multicellular movement remains unclear. Here we report the role of the protein kinase Pak3 in maintaining apical-basal polarity in migrating border cell clusters during Drosophila oogenesis. Pak3 is enriched in border cells and downregulation of its function impedes border cell movement. Time-lapse imaging suggests that Pak3 affects protrusive behavior of the border cell cluster, specifically regulating the stability and directionality of protrusions. Pak3 functions downstream of guidance receptor signaling to regulate the level and distribution of F-actin in migrating border cells. We also provide evidence that Pak3 genetically interacts with the lateral polarity marker Scribble and that it regulates JNK signaling in the moving border cells. Since Pak3 depletion results in mislocalization of several apical-basal polarity markers and overexpression of Jra rescues the polarity of the Pak3-depleted cluster, we propose that Pak3 functions through JNK signaling to modulate apical-basal polarity of the migrating border cell cluster. We also observe loss of apical-basal polarity in Rac1-depleted border cell clusters, suggesting that guidance receptor signaling functions through Rac GTPase and Pak3 to regulate the overall polarity of the cluster and mediate efficient collective movement of the border cells to the oocyte boundary.

Induction of focal adhesions and motility in Drosophila S2 cells

In this study, normally immotile S2 cells are engineered to induce the formation of focal adhesions and cell motility by the transfection of a single gene encoding an integrin subunit. It is demonstrated that the focal adhesions recruit expected components and exhibit mechanosensitive behavior on integrin-ligand substrates of different stiffnesses.

Focal adhesions are dynamic structures that interact with the extracellular matrix on the cell exterior and actin filaments on the cell interior, enabling cells to adhere and crawl along surfaces. We describe a system for inducing the formation of focal adhesions in normally non–ECM-adherent, nonmotile Drosophila S2 cells. These focal adhesions contain the expected molecular markers such as talin, vinculin, and p130Cas, and they require talin for their formation. The S2 cells with induced focal adhesions also display a nonpolarized form of motility on vitronectin-coated substrates. Consistent with findings in mammalian cells, the degree of motility can be tuned by changing the stiffness of the substrate and was increased after the depletion of PAK3, a p21-activated kinase. A subset of nonmotile, nonpolarized cells also exhibited focal adhesions that rapidly assembled and disassembled around the cell perimeter. Such cooperative and dynamic fluctuations of focal adhesions were decreased by RNA interference (RNAi) depletion of myosin II and focal adhesion kinase, suggesting that this behavior requires force and focal adhesion maturation. These results demonstrate that S2 cells, a cell line that is well studied for cytoskeletal dynamics and readily amenable to protein manipulation by RNAi, can be used to study the assembly and dynamics of focal adhesions and mechanosensitive cell motility.

Rapid clearance of epigenetic protein reporters from wound edge cells in Drosophila larvae does not depend on the JNK or PDGFR/VEGFR signaling pathways

The drastic cellular changes required for epidermal cells to dedifferentiate and become motile during wound closure are accompanied by changes in gene transcription, suggesting corresponding alterations in chromatin. However, the epigenetic changes that underlie wound-induced transcriptional programs remain poorly understood partly because a comprehensive study of epigenetic factor expression during wound healing has not been practical. To determine which chromatin modifying factors might contribute to wound healing, we screened publicly available fluorescently-tagged reporter lines in Drosophila for altered expression at the wound periphery during healing. Thirteen reporters tagging seven different proteins showed strongly diminished expression at the wound edge. Three downregulated proteins, Osa, Kismet, and Spt6, are generally associated with active chromatin, while four others, Sin3A, Sap130, Mi-2, and Mip120, are associated with repressed chromatin. In all cases reporter down regulation was independent of the Jun N-terminal Kinase and Pvr pathways, suggesting that novel signals control reporter clearance. Taken together, our results suggest that clearance of chromatin modifying factors may enable wound edge cells to rapidly and comprehensively change their transcriptional state following tissue damage.

Polyploidization and cell fusion contribute to wound healing in the adult Drosophila epithelium

BACKGROUND

Reestablishing epithelial integrity and biosynthetic capacity is critically important following tissue damage. The adult Drosophila abdominal epithelium provides an attractive new system to address how postmitotic diploid cells contribute to repair.

RESULTS

Puncture wounds to the adult Drosophila epidermis close initially by forming a melanized scab. We found that epithelial cells near the wound site fuse to form a giant syncytium, which sends lamellae under the scab to re-epithelialize the damaged site. Other large cells arise more peripherally by initiating endocycles and becoming polyploid, or by cell fusion. Rac GTPase activity is needed for syncytium formation, while the Hippo signaling effector Yorkie modulates both polyploidization and cell fusion. Large cell formation is functionally important because when both polyploidization and fusion are blocked, wounds do not re-epithelialize.

CONCLUSIONS

Our observations indicate that cell mass lost upon wounding can be replaced by polyploidization instead of mitotic proliferation. We propose that large cells generated by polyploidization or cell fusion are essential because they are better able than diploid cells to mechanically stabilize wounds, especially those containing permanent acellular structures, such as scar tissue.

p21-activated kinase 3 (PAK3) is an AP-1 regulated gene contributing to actin organisation and migration of transformed fibroblasts

Activating Protein 1 (AP-1) plays a vital role in cell proliferation, differentiation and apoptosis. While de-regulation of AP-1 has been linked to many cancers, little is known regarding its downstream transcriptional targets that associate with cellular transformation. Previous studies identified PAK3, a serine/threonine kinase, as a potential AP-1 target gene. PAK3 has been implicated in a variety of pathological disorders and over-expression of other PAK-family members has been linked to cancer. In this study, we investigate AP-1 regulation of PAK3 expression and the role of PAK3 in cJun/AP-1-associated cellular transformation. Our results showed elevated PAK3 expression at both the mRNA and protein level in cJun-over-expressing Rat1a fibroblasts, as well as in transformed human fibroblasts. Elevated PAK3 expression in cJun/AP-1 over-expressing cells associated with a significant increase in PAK3 promoter activation. This increased promoter activity was lost when a single putative Jun binding site, which can bind AP-1 directly both in vitro and in vivo, was mutated. Further, inhibition of PAK3 using siRNA showed a regression in the cell morphology, migratory potential and actin organisation associated with AP-1 transformed cells. Our study is a first to describe a role for AP-1 in regulating PAK3 expression and suggest that PAK3 is an AP-1 target required for actin organization and migration observed in transformed cells.