Cross talk between c-Met and epidermal growth factor receptor during retinal pigment epithelial wound healing

Cholinergic signaling via muscarinic M1 receptor confers resistance to docetaxel in prostate cancer

Docetaxel is the most commonly used chemotherapy for advanced prostate cancer (PC), including castration-resistant disease (CRPC), but the eventual development of docetaxel resistance constitutes a major clinical challenge. Here, we demonstrate activation of the cholinergic muscarinic M1 receptor (CHRM1) in CRPC cells upon acquiring resistance to docetaxel, which is manifested in tumor tissues from PC patients post- vs. pre-docetaxel. Genetic and pharmacological inactivation of CHRM1 restores the efficacy of docetaxel in resistant cells. Mechanistically, CHRM1, via its first and third extracellular loops, interacts with the SEMA domain of cMET and forms a heteroreceptor complex with cMET, stimulating a downstream mitogen-activated protein polykinase program to confer docetaxel resistance. Dicyclomine, a clinically available CHRM1-selective antagonist, reverts resistance and restricts the growth of multiple docetaxel-resistant CRPC cell lines and patient-derived xenografts. Our study reveals a CHRM1-dictated mechanism for docetaxel resistance and identifies a CHRM1-targeted combinatorial strategy for overcoming docetaxel resistance in PC.

Spatiotemporal roles of AMPK in PARP-1- and autophagy-dependent retinal pigment epithelial cell death caused by UVA

BACKGROUND

Although stimulating autophagy caused by UV has been widely demonstrated in skin cells to exert cell protection, it remains unknown the cellular events in UVA-treated retinal pigment epithelial (RPE) cells.

METHODS

Human ARPE-19 cells were used to measure cell viability, mitochondrial reactive oxygen species (ROS), mitochondrial membrane potential (MMP), mitochondrial mass and lysosomal mass by flow cytometry. Mitochondrial oxygen consumption rate (OCR) was recorded using Seahorse XF flux analyzer. Confocal microscopic images were performed to indicate the mitochondrial dynamics, LC3 level, and AMPK translocation after UVA irradiation.

RESULTS

We confirmed mitochondrial ROS production and DNA damage are two major features caused by UVA. We found the cell death is prevented by autophagy inhibitor 3-methyladenine and gene silencing of ATG5, and UVA induces ROS-dependent LC3II expression, LC3 punctate and TFEB expression, suggesting the autophagic death in the UVA-stressed RPE cells. Although PARP-1 inhibitor olaparib increases DNA damage, ROS production, and cell death, it also blocks AMPK activation caused by UVA. Interestingly we found a dramatic nuclear export of AMPK upon UVA irradiation which is blocked by N-acetylcysteine and olaparib. In addition, UVA exposure gradually decreases lysosomal mass and inhibits cathepsin B activity at late phase due to lysosomal dysfunction. Nevertheless, cathepsin B inhibitor, CA-074Me, reverses the death extent, suggesting the contribution of cathepsin B in the death pathway. When examining the role of EGFR in cellular events caused by UVA, we found that UVA can rapidly transactivate EGFR, and treatment with EGFR TKIs (gefitinib and afatinib) enhances the cell death accompanied by the increased LC3II formation, ROS production, loss of MMP and mass of mitochondria and lysosomes. Although AMPK activation by ROS-PARP-1 mediates autophagic cell death, we surprisingly found that pretreatment of cells with AMPK activators (A769662 and metformin) reverses cell death. Concomitantly, both agents block UVA-induced mitochondrial ROS production, autophagic flux, and mitochondrial fission without changing the inhibition of cathepsin B.

CONCLUSION

UVA exposure rapidly induces ROS-PARP-1-AMPK-autophagic flux and late lysosomal dysfunction. Pre-inducing AMPK activation can prevent cellular events caused by UVA and provide a new protective strategy in photo-oxidative stress and photo-retinopathy.

Myopia: Histology, clinical features, and potential implications for the etiology of axial elongation

Myopic axial elongation is associated with various non-pathological changes. These include a decrease in photoreceptor cell and retinal pigment epithelium (RPE) cell density and retinal layer thickness, mainly in the retro-equatorial to equatorial regions; choroidal and scleral thinning pronounced at the posterior pole and least marked at the ora serrata; and a shift in Bruch's membrane opening (BMO) occurring in moderately myopic eyes and typically in the temporal/inferior direction. The BMO shift leads to an overhang of Bruch's membrane (BM) into the nasal intrapapillary compartment and BM absence in the temporal region (i.e., parapapillary gamma zone), optic disc ovalization due to shortening of the ophthalmoscopically visible horizontal disc diameter, fovea-optic disc distance elongation, reduction in angle kappa, and straightening/stretching of the papillomacular retinal blood vessels and retinal nerve fibers. Highly myopic eyes additionally show an enlargement of all layers of the optic nerve canal, elongation and thinning of the lamina cribrosa, peripapillary scleral flange (i.e., parapapillary delta zone) and peripapillary choroidal border tissue, and development of circular parapapillary beta, gamma, and delta zone. Pathological features of high myopia include development of macular linear RPE defects (lacquer cracks), which widen to round RPE defects (patchy atrophies) with central BM defects, macular neovascularization, myopic macular retinoschisis, and glaucomatous/glaucoma-like and non-glaucomatous optic neuropathy. BM thickness is unrelated to axial length. Including the change in eye shape from a sphere in emmetropia to a prolate (rotational) ellipsoid in myopia, the features may be explained by a primary BM enlargement in the retro-equatorial/equatorial region leading to axial elongation.

The role of the PI3K/AKT signalling pathway in the corneal epithelium: recent updates

Phosphatidylinositol 3 kinase (PI3K)/AKT (also called protein kinase B, PKB) signalling regulates various cellular processes, such as apoptosis, cell proliferation, the cell cycle, protein synthesis, glucose metabolism, and telomere activity. Corneal epithelial cells (CECs) are the outermost cells of the cornea; they maintain good optical performance and act as a physical and immune barrier. Various growth factors, including epidermal growth factor receptor (EGFR) ligands, insulin-like growth factor 1 (IGF1), neurokinin 1 (NK-1), and insulin activate the PI3K/AKT signalling pathway by binding their receptors and promote antiapoptotic, anti-inflammatory, proliferative, and migratory functions and wound healing in the corneal epithelium (CE). Reactive oxygen species (ROS) regulate apoptosis and inflammation in CECs in a concentration-dependent manner. Extreme environments induce excess ROS accumulation, inhibit PI3K/AKT, and cause apoptosis and inflammation in CECs. However, at low or moderate levels, ROS activate PI3K/AKT signalling, inhibiting apoptosis and stimulating proliferation of healthy CECs. Diabetes-associated hyperglycaemia directly inhibit PI3K/AKT signalling by increasing ROS and endoplasmic reticulum (ER) stress levels or suppressing the expression of growth factors receptors and cause diabetic keratopathy (DK) in CECs. Similarly, hyperosmolarity and ROS accumulation suppress PI3K/AKT signalling in dry eye disease (DED). However, significant overactivation of the PI3K/AKT signalling pathway, which mediates inflammation in CECs, is observed in both infectious and noninfectious keratitis. Overall, upon activation by growth factors and NK-1, PI3K/AKT signalling promotes the proliferation, migration, and anti-apoptosis of CECs, and these processes can be regulated by ROS in a concentration-dependent manner. Moreover, PI3K/AKT signalling pathway is inhibited in CECs from individuals with DK and DED, but is overactivated by keratitis.

Circular gap forming device and two-dimensional area calculation for in vitro cell migration study

Cell wound healing assay is an important experimental technique for the detection of cell migration in vitro. At present, scratch on monolayer cells using a pipette tip is commonly used. However, it is difficult to guarantee the scratch with same width, and only the migration distance of a certain part is calculated. Therefore, the experimental method needs to be optimized. ATRA was used to treat hepa1-6 mouse hepatoma cells. Circular wound with diameter of 0.2 cm were formed by a circular gap forming device. The whole cell wound region could be captured under the microscope to observe cell migration. There are almost no crawling cells in the wound region. The migration capacity of hepa1-6 cells was evaluated by calculating the healing area. ATRA could significantly inhibit the migration of hepa1-6 cells. Compared with linear wound, the standard deviation of wound healing rate in the circular cell wound method is smaller. The circular cell wound method can ensure the dynamic observation of the same wound region, and calculate the healing area at the two-dimensional level with small error and high repetition rate. It is reliable and easy to operate, can be widely used in laboratory.

Proteomic and phosphoproteomic analyses identify liver-related signaling in retinal pigment epithelial cells during EMT

Epithelial-mesenchymal transition (EMT) of the retinal pigment epithelium (RPE) is associated with several blinding retinal diseases. Using proteomics and phosphoproteomics studies of human induced pluripotent stem cell-derived RPE monolayers with induced EMT, we capture kinase/phosphatase signaling cascades 1 h and 12 h after induction to better understand the pathways mediating RPE EMT. Induction by co-treatment with transforming growth factor β and tumor necrosis factor alpha (TGNF) or enzymatic dissociation perturbs signaling in many of the same pathways, with striking similarity in the respective phosphoproteomes at 1 h. Liver hyperplasia and hepatocyte growth factor (HGF)-MET signaling exhibit the highest overall enrichment. We also observe that HGF and epidermal growth factor signaling, two cooperative pathways inhibited by EMT induction, regulate the RPE transcriptional profile.

Single-Molecule Super-Resolution Microscopy Reveals Heteromeric Complexes of MET and EGFR upon Ligand Activation

Receptor tyrosine kinases (RTKs) orchestrate cell motility and differentiation. Deregulated RTKs may promote cancer and are prime targets for specific inhibitors. Increasing evidence indicates that resistance to inhibitor treatment involves receptor cross-interactions circumventing inhibition of one RTK by activating alternative signaling pathways. Here, we used single-molecule super-resolution microscopy to simultaneously visualize single MET and epidermal growth factor receptor (EGFR) clusters in two cancer cell lines, HeLa and BT-20, in fixed and living cells. We found heteromeric receptor clusters of EGFR and MET in both cell types, promoted by ligand activation. Single-protein tracking experiments in living cells revealed that both MET and EGFR respond to their cognate as well as non-cognate ligands by slower diffusion. In summary, for the first time, we present static as well as dynamic evidence of the presence of heteromeric clusters of MET and EGFR on the cell membrane that correlates with the relative surface expression levels of the two receptors.

Thiosemicarbazones suppress expression of the c-Met oncogene by mechanisms involving lysosomal degradation and intracellular shedding

Considering the role of proto-oncogene c-Met (c-Met) in oncogenesis, we examined the effects of the metastasis suppressor, N-myc downstream-regulated gene-1 (NDRG1), and two NDRG1-inducing thiosemicarbazone-based agents, Dp44mT and DpC, on c-Met expression in DU145 and Huh7 cells. NDRG1 silencing without Dp44mT and DpC up-regulated c-Met expression, demonstrating that NDRG1 modulates c-Met levels. Dp44mT and DpC up-regulated NDRG1 by an iron-dependent mechanism and decreased c-Met levels, c-Met phosphorylation, and phosphorylation of its downstream effector, GRB2-associated binding protein 1 (GAB1). However, incubation with Dp44mT and DpC after NDRG1 silencing or silencing of the receptor tyrosine kinase inhibitor, mitogen-inducible gene 6 (MIG6), decreased c-Met and its phosphorylation, suggesting NDRG1- and MIG6-independent mechanism(s). Lysosomal inhibitors rescued the Dp44mT- and DpC-mediated c-Met down-regulation in DU145 cells. Confocal microscopy revealed that lysosomotropic agents and the thiosemicarbazones significantly increased co-localization between c-Met and lysosomal-associated membrane protein 2 (LAMP2). Moreover, generation of c-Met C-terminal fragment (CTF) and its intracellular domain (ICD) suggested metalloprotease-mediated cleavage. In fact, Dp44mT increased c-Met CTF while decreasing the ICD. Dp44mT and a γ-secretase inhibitor increased cellular c-Met CTF levels, suggesting that Dp44mT induces c-Met CTF levels by increasing metalloprotease activity. The broad metalloprotease inhibitors, EDTA and batimastat, partially prevented Dp44mT-mediated down-regulation of c-Met. In contrast, the ADAM inhibitor, TIMP metallopeptidase inhibitor 3 (TIMP-3), had no such effect, suggesting c-Met cleavage by another metalloprotease. Notably, Dp44mT did not induce extracellular c-Met shedding that could decrease c-Met levels. In summary, the thiosemicarbazones Dp44mT and DpC effectively inhibit oncogenic c-Met through lysosomal degradation and metalloprotease-mediated cleavage.

Pathway Analysis Integrating Genome-Wide and Functional Data Identifies PLCG2 as a Candidate Gene for Age-Related Macular Degeneration

Purpose

Age-related macular degeneration (AMD) is the worldwide leading cause of blindness among the elderly. Although genome-wide association studies (GWAS) have identified AMD risk variants, their roles in disease etiology are not well-characterized, and they only explain a portion of AMD heritability.

Methods

We performed pathway analyses using summary statistics from the International AMD Genomics Consortium's 2016 GWAS and multiple pathway databases to identify biological pathways wherein genetic association signals for AMD may be aggregating. We determined which genes contributed most to significant pathway signals across the databases. We characterized these genes by constructing protein-protein interaction networks and performing motif analysis.

Results

We determined that eight genes (C2, C3, LIPC, MICA, NOTCH4, PLCG2, PPARA, and RAD51B) "drive" the statistical signals observed across pathways curated in the Kyoto Encyclopedia of Genes and Genomes (KEGG), Reactome, and Gene Ontology (GO) databases. We further refined our definition of statistical driver gene to identify PLCG2 as a candidate gene for AMD due to its significant gene-level signals (P < 0.0001) across KEGG, Reactome, GO, and NetPath pathways.

Conclusions

We performed pathway analyses on the largest available collection of advanced AMD cases and controls in the world. Eight genes strongly contributed to significant pathways from the three larger databases, and one gene (PLCG2) was central to significant pathways from all four databases. This is, to our knowledge, the first study to identify PLCG2 as a candidate gene for AMD based solely on genetic burden. Our findings reinforce the utility of integrating in silico genetic and biological pathway data to investigate the genetic architecture of AMD.

Heparin-Binding Epidermal Growth Factor-Like Growth Factor as a Critical Mediator of Tissue Repair and Regeneration

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family. It contains an EGF-like domain as well as a heparin-binding domain that allows for interactions with heparin and cell-surface heparan sulfate. Soluble mature HB-EGF, a ligand of human epidermal growth factor receptors 1 and 4, is cleaved from the membrane-associated pro-HB-EGF by matrix metalloproteinase or a disintegrin and metalloproteinase in a process called ectodomain shedding. Signaling through human epidermal growth factor receptors 1 and 4 results in a variety of effects, including cellular proliferation, migration, adhesion, and differentiation. HB-EGF levels increase in response to different forms of injuries as well as stimuli, such as lysophosphatidic acid, retinoic acid, and 17β-estradiol. Because it is widely expressed in many organs, HB-EGF plays a critical role in tissue repair and regeneration throughout the body. It promotes cutaneous wound healing, hepatocyte proliferation after partial hepatectomy, intestinal anastomosis strength, alveolar regeneration after pneumonectomy, neurogenesis after ischemic injury, bladder wall thickening in response to urinary tract obstruction, and protection against ischemia/reperfusion injury to many cell types. Additionally, innovative strategies to deliver HB-EGF to sites of organ injury or to increase the endogenous levels of shed HB-EGF have been attempted with promising results. Harnessing the reparatory properties of HB-EGF in the clinical setting, therefore, may produce therapies that augment the treatment of various organ injuries.

Fisetin inhibits epidermal growth factor-induced migration of ARPE-19 cells by suppression of AKT activation and Sp1-dependent MMP-9 expression

Purpose

Proliferative vitreoretinopathy (PVR) can result in abnormal migration of RPE cells. Fisetin is a naturally occurring compound that has been reported to have antitumor effects, but its effects on epidermal growth factor (EGF)-induced cell migration and the underlying mechanisms remain unclear.

Methods

Effects of fisetin on EGF-induced cell viability and migration were examined with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and in vitro migration assays. Reverse transcription-PCR (RT-PCR) and immunoblotting were performed to evaluate matrix metallopeptidase-9 (MMP-9) expression and activation of specificity protein-1 (Sp1) and protein kinase B (AKT) in ARPE-19 cells treated with EGF and with or without fisetin. Luciferase and chromatin immunoprecipitation (ChIP) assays were performed to examine Sp1 transcription activity and MMP-9 binding activity.

Results

Fisetin did not affect ARPE-19 cell viability and significantly inhibited the EGF-induced migration capacity of ARPE-19 cells. Furthermore, fisetin exerted an antimigratory effect and suppressed MMP-9 mRNA and protein expression. Treatment with EGF induced phosphorylation of AKT and expression of MMP-9 and Sp1. Fisetin combined with LY294002 (an inhibitor of AKT) prevented the EGF-induced migration involved in downregulation of Sp1 and MMP-9 expression. Luciferase and ChIP assays suggested that fisetin remarkably decreased the EGF-induced transcription activity of MMP-9 and Sp1 and inhibited EGF-mediated Sp1 from directly binding to the MMP-9 promoter in ARPE-19 cells.

Conclusions

Fisetin inhibited EGF-induced cell migration via modulation of AKT/Sp1-dependent MMP-9 transcriptional activity. Therefore, fisetin may be a potential agent in the treatment of migratory PVR diseases.

Both Autocrine Signaling and Paracrine Signaling of HB-EGF Enhance Ocular Neovascularization

OBJECTIVE

The incidence of blindness is increasing because of the increase in abnormal ocular neovascularization. Anti-VEGF (vascular endothelial growth factor) therapies have led to good results, although they are not a cure for the blindness. The purpose of this study was to determine what role HB-EGF (heparin-binding epidermal growth factor-like growth factor) plays in ocular angiogenesis.

APPROACH AND RESULTS

We examined the role played by HB-EGF in ocular neovascularization in 2 animal models of neovascularization: laser-induced choroidal neovascularization (CNV) and oxygen-induced retinopathy. We also studied human retinal microvascular endothelial cells in culture. Our results showed that the neovascularization was decreased in both the CNV and oxygen-induced retinopathy models in HB-EGF conditional knockout mice compared with that in wild-type mice. Moreover, the expressions of HB-EGF and VEGF were increased after laser-induced CNV and oxygen-induced retinopathy, and their expression sites were located around the neovascular areas. Exposure of human retinal microvascular endothelial cells to HB-EGF and VEGF increased their proliferation and migration, and CRM-197 (cross-reactive material-197), an HB-EGF inhibitor, decreased the HB-EGF-induced and VEGF-induced cell proliferation and migration. VEGF increased the expression of HB-EGF mRNA. VEGF-dependent activation of EGFR (epidermal growth factor receptor)/ERK1/2 (extracellular signal-regulated kinase 1/2) signaling and cell proliferation of endothelial cells required stimulation of the ADAM17 (a disintegrin and metalloprotease) and ADAM12. CRM-197 decreased the grades of the fluorescein angiograms and size of the CNV areas in marmoset monkeys.

CONCLUSIONS

These findings suggest that HB-EGF plays an important role in the development of CNV. Therefore, further investigations of HB-EGF are needed as a potential therapeutic target in the treatment of exudative age-related macular degeneration.

Stem Cell Secretome and Its Effect on Cellular Mechanisms Relevant to Wound Healing

Stem cells introduced to site of injury primarily act via indirect paracrine effects rather than direct cell replacement of damaged cells. This gives rise to understanding the stem cell secretome. In this study, in vitro studies demonstrate that the secretome activates the PI3K/Akt or FAK/ERK1/2 signaling cascades and subsequently enhances the proliferative and migratory abilities of various types of skin cells, such as fibroblasts, keratinocytes, and vascular epithelial cells, ultimately accelerating wound contraction. Indeed, inhibition of these signaling pathways with synthetic inhibitors resulted in the disruption of secretome-induced beneficial effects on various skin cells. In addition, major components of the stem cell secretome (EGF, basic FGF, and HGF) may be responsible for the acceleration of wound contraction. Stimulatory effects of these three prominent factors on wound contraction are achieved through the upregulation of PI3K/Akt or FAK/ERK1/2 activity. Overall, we lay the rationale for using the stem cell secretome in promoting wound contraction. In vivo wound healing studies are warranted to test the significance of our in vitro findings.

Lysosome trafficking is necessary for EGF-driven invasion and is regulated by p38 MAPK and Na+/H+ exchangers

Background

Tumor invasion through a basement membrane is one of the earliest steps in metastasis, and growth factors, such as Epidermal Growth Factor (EGF) and Hepatocyte Growth Factor (HGF), stimulate this process in a majority of solid tumors. Basement membrane breakdown is one of the hallmarks of invasion; therefore, tumor cells secrete a variety of proteases to aid in this process, including lysosomal proteases. Previous studies demonstrated that peripheral lysosome distribution coincides with the release of lysosomal cathepsins.

Methods

Immunofluorescence microscopy, western blot, and 2D and 3D cell culture techniques were performed to evaluate the effects of EGF on lysosome trafficking and cell motility and invasion.

Results

EGF-mediated lysosome trafficking, protease secretion, and invasion is regulated by the activity of p38 mitogen activated protein kinase (MAPK) and sodium hydrogen exchangers (NHEs). Interestingly, EGF stimulates anterograde lysosome trafficking through a different mechanism than previously reported for HGF, suggesting that there are redundant signaling pathways that control lysosome positioning and trafficking in tumor cells.

Conclusions

These data suggest that EGF stimulation induces peripheral (anterograde) lysosome trafficking, which is critical for EGF-mediated invasion and protease release, through the activation of p38 MAPK and NHEs. Taken together, this report demonstrates that anterograde lysosome trafficking is necessary for EGF-mediated tumor invasion and begins to characterize the molecular mechanisms required for EGF-stimulated lysosome trafficking.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3660-3) contains supplementary material, which is available to authorized users.

Suppressive effect of AMP-activated protein kinase on the epithelial-mesenchymal transition in retinal pigment epithelial cells

The epithelial-mesenchymal transition (EMT) in retinal pigment epithelial (RPE) cells plays a central role in the development of proliferative vitreoretinopathy (PVR). The purpose of this study was to investigate the effect of AMP-activated protein kinase (AMPK), a key regulator of energy homeostasis, on the EMT in RPE cells. In this study, EMT-associated formation of cellular aggregates was induced by co-stimulation of cultured ARPE-19 cells with tumor necrosis factor (TNF)-α (10 ng/ml) and transforming growth factor (TGF)-β₂ (5 ng/ml). 5-Aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR), a potent activator of AMPK, significantly suppressed TNF-α and TGF-β₂-induced cellular aggregate formation (p < 0.01). Dipyridamole almost completely reversed the suppressive effect of AICAR, whereas 5’-amino-5’-deoxyadenosine restored aggregate formation by approximately 50%. AICAR suppressed the downregulation of E-cadherin and the upregulation of fibronectin and α-smooth muscle actin by TNF-α and TGF-β₂. The levels of matrix metalloproteinase (MMP)-2, MMP-9, interleukin-6, and vascular endothelial growth factor were significantly decreased by AICAR. Activation of the mitogen-activated protein kinase and mammalian target of rapamycin pathways, but not the Smad pathway, was inhibited by AICAR. These findings indicate that AICAR suppresses the EMT in RPE cells at least partially via activation of AMPK. AMPK is a potential target molecule for the prevention and treatment of PVR, so AICAR may be a promising candidate for PVR therapy.

Visible-Light Optical Coherence Tomography Angiography for Monitoring Laser-Induced Choroidal Neovascularization in Mice

Purpose

This study sought to determine the earliest time-point at which evidence of choroidal neovascularization (CNV) could be detected with visible-light optical coherence tomography angiography (vis-OCTA) in a mouse model of laser-induced CNV.

Methods

Visible light-OCTA was used to study laser-induced CNV at different time-points after laser injury to monitor CNV development and measure CNV lesion size. Measurements obtained from vis-OCTA angiograms were compared with histopathologic measurements from isolectin-stained choroidal flatmounts.

Results

Choroidal neovascularization area measurements between the vis-OCTA system and isolectin-stained choroidal flatmounts were significantly different in area for days 2 to 4 postlaser injury, and were not significantly different in area for days 5, 7, and 14. Choroidal neovascularization area measurements taken from the stained flatmounts were larger than their vis-OCTA counterparts for all time-points. Both modalities showed a similar trend of CNV size increasing from the day of laser injury until a peak of day 7 postlaser injury and subsequently decreasing by day 14.

Conclusions

The earliest vis-OCTA can detect the presence of aberrant vessels in a mouse laser-induced CNV model is 5 days after laser injury. Visible light-OCTA was able to visualize the maximum of the CNV network 7 days postlaser injury, in accordance with choroidal flatmount immunostaining. Visible light-OCTA is a reliable tool in both detecting the presence of CNV development, as well as accurately determining the size of the lesion in a mouse laser-induced CNV model.

Oxidative stress affects retinal pigment epithelial cell survival through epidermal growth factor receptor/AKT signaling pathway

AIM

To investigate the cross-talk between oxidative stress and the epidermal growth factor receptor (EGFR)/AKT signaling pathway in retinal pigment epithelial (RPE) cells.

METHODS

Human RPE cell lines (ARPE-19 cell) were treated with different doses of epidermal growth factor (EGF) and hydrogen peroxide (H₂O₂). Cell viability was determined by a methyl thiazolyl tetrazolium assay. Cell proliferation was examined by a bromodeoxyuridine (BrdU) incorporation assay. EGFR/AKT signaling was detected by Western blot. EGFR localization was also detected by immunofluorescence. In addition, EGFR/AKT signaling was intervened upon by EGFR inhibitor (erlotinib), PI3K inhibitor (A66) and AKT inhibitor (MK-2206), respectively. H₂O₂-induced oxidative stress was blocked by antioxidant N-acetylcysteine (NAC).

RESULTS

EGF treatment increased ARPE-19 cell viability and proliferation through inducing phosphorylation of EGFR and AKT. H₂O₂ inhibited ARPE-19 cell viability and proliferation and also suppressed EGF-stimulated increase of RPE cell viability and proliferation by affecting the EGFR/AKT signaling pathway. EGFR inhibitor erlotinib blocked EGF-induced phosphorylation of EGFR and AKT, while A66 and MK-2206 only blocked EGF-induced phosphorylation of AKT. EGF-induced phosphorylation and endocytosis of EGFR were also affected by H₂O₂ treatment. In addition, antioxidant NAC attenuated H₂O₂-induced inhibition of ARPE-19 cell viability through alleviating reduction of EGFR, and phosphorylated and total AKT proteins.

CONCLUSION

Oxidative stress affects RPE cell viability and proliferation through interfering with the EGFR/AKT signaling pathway. The EGFR/AKT signaling pathway may be an important target in oxidative stress-induced RPE cell dysfunction.

Hepatocyte growth factor in physiology and infectious diseases

Hepatocyte growth factor (HGF) is a pleiotropic cytokine composed of an α-chain and a β-chain, and these chains contain four kringle domains and a serine protease-like structure, respectively. The receptor for HGF was identified as the c-met proto-oncogene product of transmembrane receptor tyrosine kinase. HGF-induced signaling through the receptor Met provokes dynamic biological responses that support morphogenesis, regeneration, and the survival of various cells and tissues, which includes hepatocytes, renal tubular cells, and neurons. Characterization of tissue-specific Met knockout mice has further indicated that the HGF-Met system modulates immune cell functions and also plays an inhibitory role in the progression of chronic inflammation and fibrosis. However, the biological actions that are driven by the HGF-Met pathway all play a role in the acquisition of the malignant characteristics in tumor cells, such as invasion, metastasis, and drug resistance in the tumor microenvironment. Even though oncogenic Met signaling remains the major research focus, the HGF-Met axis has also been implicated in infectious diseases. Many pathogens try to utilize host HGF-Met system to establish comfortable environment for infection. Their strategies are not only simply change the expression level of HGF or Met, but also actively hijack HGF-Met system and deregulating Met signaling using their pathogenic factors. Consequently, the monitoring of HGF and Met expression, along with real-time detection of Met activation, can be a beneficial biomarker of these infectious diseases. Preclinical studies designed to address the therapeutic significance of HGF have been performed on injury/disease models, including acute tissue injury, chronic fibrosis, and cardiovascular and neurodegenerative diseases. Likewise, manipulating the HGF-Met system with complete control will lead to a tailor made treatment for those infectious diseases.

A Novel Role of Spred2 in the Colonic Epithelial Cell Homeostasis and Inflammation

Rapid and adequate mucosal healing is important for a remission of ulcerative colitis (UC) patients. Here, we examined whether Spred2, a member of the Sprouty-related EVH1-domain-containing proteins that inhibit the Ras/Raf/ERK pathway, plays a role in colonic mucosal homeostasis and inflammation by using Spred2 knockout (KO) mice. We first detected increased epithelial cell proliferation and cadherin 1 expression in the colon of naïve Spred2 KO mice compared to wild-type mice. Interestingly, Spred2 KO mice were resistant to dextran sulfate sodium (DSS)-induced acute colitis as indicated by lower levels of body weight loss and disease activity index. Histologically, epithelial cell injury and inflammation were milder in the colonic mucosa of Spred2 KO mice on day 3 and almost undetectable by day 8. Experiments with bone chimeric mice indicated that Spred2-deficiency in non-hematopoietic cells was responsible for the reduced sensitivity to DSS. Finally, Spred2 KO mice developed significantly fewer tumors in response to azoxymethane plus DSS. Taken together, our results demonstrate, for the first time, that Spred2 plays an important role in the regulation of colonic epithelial cell proliferation and inflammation by potentially down-regulating the activation of ERK. Thus, Spred2 may be a new therapeutic target for the treatment of UC.

Mechanism of Resistance and Novel Targets Mediating Resistance to EGFR and c-Met Tyrosine Kinase Inhibitors in Non-Small Cell Lung Cancer

Tyrosine kinase inhibitors (TKIs) against EGFR and c-Met are initially effective when administered individually or in combination to non-small cell lung cancer (NSCLC) patients. However, the overall efficacies of TKIs are limited due to the development of drug resistance. Therefore, it is important to elucidate mechanisms of EGFR and c-Met TKI resistance in order to develop more effective therapies. Model NSCLC cell lines H1975 and H2170 were used to study the similarities and differences in mechanisms of EGFR/c-Met TKI resistance. H1975 cells are positive for the T790M EGFR mutation, which confers resistance to current EGFR TKI therapies, while H2170 cells are EGFR wild-type. Previously, H2170 cells were made resistant to the EGFR TKI erlotinib and the c-Met TKI SU11274 by exposure to progressively increasing concentrations of TKIs. In H2170 and H1975 TKI-resistant cells, key Wnt and mTOR proteins were found to be differentially modulated. Wnt signaling transducer, active β-catenin was upregulated in TKI-resistant H2170 cells when compared to parental cells. GATA-6, a transcriptional activator of Wnt, was also found to be upregulated in resistant H2170 cells. In H2170 erlotinib resistant cells, upregulation of inactive GSK3β (p-GSK3β) was observed, indicating activation of Wnt and mTOR pathways which are otherwise inhibited by its active form. However, in H1975 cells, Wnt modulators such as active β-catenin, GATA-6 and p-GSK3β were downregulated. Additional results from MTT cell viability assays demonstrated that H1975 cell proliferation was not significantly decreased after Wnt inhibition by XAV939, but combination treatment with everolimus (mTOR inhibitor) and erlotinib resulted in synergistic cell growth inhibition. Thus, in H2170 cells and H1975 cells, simultaneous inhibition of key Wnt or mTOR pathway proteins in addition to EGFR and c-Met may be a promising strategy for overcoming EGFR and c-Met TKI resistance in NSCLC patients.

Epidermal growth factor-stimulated Akt phosphorylation requires clathrin or ErbB2 but not receptor endocytosis

Upon ligand binding, the epidermal growth factor receptor (EGFR) activates signaling and undergoes endocytosis. EGFR signaling leading to Akt activation is impaired by perturbation of clathrin but not by inhibition of internalization through perturbation of dynamin. Clathrin may thus directly regulate receptor signaling at the cell surface.

Epidermal growth factor (EGF) binding to its receptor (EGFR) activates several signaling intermediates, including Akt, leading to control of cell survival and metabolism. Concomitantly, ligand-bound EGFR is incorporated into clathrin-coated pits—membrane structures containing clathrin and other proteins—eventually leading to receptor internalization. Whether clathrin might regulate EGFR signaling at the plasma membrane before vesicle scission is poorly understood. We compared the effect of clathrin perturbation (preventing formation of, or receptor recruitment to, clathrin structures) to that of dynamin2 (allowing formation of clathrin structures but preventing EGFR internalization) under conditions in which EGFR endocytosis is clathrin dependent. Clathrin perturbation by siRNA gene silencing, with the clathrin inhibitor pitstop2, or knocksideways silencing inhibited EGF-simulated Gab1 and Akt phosphorylation in ARPE-19 cells. In contrast, perturbation of dynamin2 with inhibitors or by siRNA gene silencing did not affect EGF-stimulated Gab1 or Akt phosphorylation. EGF stimulation enriched Gab1 and phospho-Gab1 within clathrin structures. ARPE-19 cells have low ErbB2 expression, and overexpression and knockdown experiments revealed that robust ErbB2 expression bypassed the requirement for clathrin for EGF-stimulated Akt phosphorylation. Thus clathrin scaffolds may represent unique plasma membrane signaling microdomains required for signaling by certain receptors, a function that can be separated from vesicle formation.

AMP-Activated Protein Kinase Regulates the Cell Surface Proteome and Integrin Membrane Traffic

The cell surface proteome controls numerous cellular functions including cell migration and adhesion, intercellular communication and nutrient uptake. Cell surface proteins are controlled by acute changes in protein abundance at the plasma membrane through regulation of endocytosis and recycling (endomembrane traffic). Many cellular signals regulate endomembrane traffic, including metabolic signaling; however, the extent to which the cell surface proteome is controlled by acute regulation of endomembrane traffic under various conditions remains incompletely understood. AMP-activated protein kinase (AMPK) is a key metabolic sensor that is activated upon reduced cellular energy availability. AMPK activation alters the endomembrane traffic of a few specific proteins, as part of an adaptive response to increase energy intake and reduce energy expenditure. How increased AMPK activity during energy stress may globally regulate the cell surface proteome is not well understood. To study how AMPK may regulate the cell surface proteome, we used cell-impermeable biotinylation to selectively purify cell surface proteins under various conditions. Using ESI-MS/MS, we found that acute (90 min) treatment with the AMPK activator A-769662 elicits broad control of the cell surface abundance of diverse proteins. In particular, A-769662 treatment depleted from the cell surface proteins with functions in cell migration and adhesion. To complement our mass spectrometry results, we used other methods to show that A-769662 treatment results in impaired cell migration. Further, A-769662 treatment reduced the cell surface abundance of β1-integrin, a key cell migration protein, and AMPK gene silencing prevented this effect. While the control of the cell surface abundance of various proteins by A-769662 treatment was broad, it was also selective, as this treatment did not change the cell surface abundance of the transferrin receptor. Hence, the cell surface proteome is subject to acute regulation by treatment with A-769662, at least some of which is mediated by the metabolic sensor AMPK.

Association between serum ligands and the skin toxicity of anti-epidermal growth factor receptor antibody in metastatic colorectal cancer

Skin toxicity is a known clinical signature used to predict the prognosis of anti-epidermal growth factor receptor (EGFR) antibody treatment in metastatic colorectal cancer (mCRC). There are no biological markers to predict skin toxicity before anti-EGFR antibody treatment in mCRC patients. Between August 2008 and August 2011, pretreatment serum samples were obtained from KRAS wild-type (WT) patients who received anti-EGFR antibody treatment. Serum levels of ligands were measured by ELISA. A total of 103 KRAS WT patients were enrolled in the study. Progression-free survival and overall survival of patients with a high grade (grade 2–3) of skin toxicity were significantly longer than those with a low grade (grade 0–1) of skin toxicity (median progression-free survival, 6.4 months vs 2.4 months, P < 0.001; median overall survival, 14.6 months vs 7.1 months, P = 0.006). There were significant differences in distribution of serum levels of epiregulin (EREG), amphiregulin (AREG), and hepatocyte growth factor (HGF) between groups of low/high grade of skin toxicity (P < 0.048, P < 0.012, P < 0.012, respectively). In addition, serum levels of HGF, EREG, and AREG were inversely proportional to grades of skin toxicity as determined by the Cochran–Armitage test (P = 0.019, P = 0.047, P = 0.021, respectively). Our study indicated that serum levels such as HGF, EREG, and AREG may be significant markers to predict the grade of skin toxicity and the prognosis of anti-EGFR antibody treatment, which contribute to improvement of the management of skin toxicity and survival time in mCRC patients.

c-Met and Other Cell Surface Molecules: Interaction, Activation and Functional Consequences

The c-Met receptor, also known as the HGF receptor, is one of the most studied tyrosine kinase receptors, yet its biological functions and activation mechanisms are still not fully understood. c-Met has been implicated in embryonic development and organogenesis, in tissue remodelling homeostasis and repair and in cancer metastasis. These functions are indicative of the many cellular processes in which the receptor plays a role, including cell motility, scattering, survival and proliferation. In the context of malignancy, sustained activation of c-Met leads to a signalling cascade involving a multitude of kinases that initiate an invasive and metastatic program. Many proteins can affect the activation of c-Met, including a variety of other cell surface and membrane-spanning molecules or receptors. Some cell surface molecules share structural homology with the c-Met extracellular domain and can activate c-Met via clustering through this domain (e.g., plexins), whereas other receptor tyrosine kinases can enhance c-Met activation and signalling through intracellular signalling cascades (e.g., EGFR). In this review, we provide an overview of c-Met interactions and crosstalk with partner molecules and the functional consequences of these interactions on c-Met activation and downstream signalling, c-Met intracellular localization/recycling and c-Met degradation.

The development of small molecule angiotensin IV analogs to treat Alzheimer's and Parkinson's diseases

Alzheimer's (AD) and Parkinson's (PD) diseases are neurodegenerative diseases presently without effective drug treatments. AD is characterized by general cognitive impairment, difficulties with memory consolidation and retrieval, and with advanced stages episodes of agitation and anger. AD is increasing in frequency as life expectancy increases. Present FDA approved medications do little to slow disease progression and none address the underlying progressive loss of synaptic connections and neurons. New drug design approaches are needed beyond cholinesterase inhibitors and N-methyl-d-aspartate receptor antagonists. Patients with PD experience the symptomatic triad of bradykinesis, tremor-at-rest, and rigidity with the possibility of additional non-motor symptoms including sleep disturbances, depression, dementia, and autonomic nervous system failure. This review summarizes available information regarding the role of the brain renin-angiotensin system (RAS) in learning and memory and motor functions, with particular emphasis on research results suggesting a link between angiotensin IV (AngIV) interacting with the AT4 receptor subtype. Currently there is controversy over the identity of this AT4 receptor protein. Albiston and colleagues have offered convincing evidence that it is the insulin-regulated aminopeptidase (IRAP). Recently members of our laboratory have presented evidence that the brain AngIV/AT4 receptor system coincides with the brain hepatocyte growth factor/c-Met receptor system. In an effort to resolve this issue we have synthesized a number of small molecule AngIV-based compounds that are metabolically stable, penetrate the blood-brain barrier, and facilitate compromised memory and motor systems. These research efforts are described along with details concerning a recently synthesized molecule, Dihexa that shows promise in overcoming memory and motor dysfunctions by augmenting synaptic connectivity via the formation of new functional synapses.

Normalization of wound healing and stem cell marker patterns in organ-cultured human diabetic corneas by gene therapy of limbal cells

Overexpression of c-met and suppression of matrix metalloproteinase-10 (MMP-10) and cathepsin F genes was previously shown to normalize wound healing, epithelial and stem cell marker patterns in organ-cultured human diabetic corneas. We now examined if gene therapy of limbal cells only would produce similar effects. Eight pairs of organ-cultured autopsy human diabetic corneas were used. One cornea of each pair was treated for 48 h with adenoviruses (Ad) harboring full-length c-met mRNA or a mixture (combo) of Ad with c-met and shRNA to MMP-10 and cathepsin F genes. Medium was kept at the limbal level to avoid transduction of central corneal epithelium. Fellow corneas received control Ad with EGFP gene. After additional 5 (c-met) or 10 days (combo) incubation, central corneal epithelial debridement with n-heptanol was performed, and wound healing times were determined microscopically. Corneal cryostat sections were immunostained for diabetic and putative limbal stem cell markers, α3β1 integrin, nidogen-1, fibronectin, laminin γ3 chain, ΔNp63α, keratins 14, 15, and 17, as well as for activated signaling intermediates, phosphorylated EGFR, Akt, and p38. Limbal c-met overexpression significantly accelerated healing of 8.5-mm epithelial wounds over EGFP controls (6.3 days vs. 9.5 days, p < 0.02). Combo treatment produced a similar result (6.75 days vs. 13.5 days, p < 0.03). Increased immunostaining vs. EGFP controls for most markers and signaling intermediates accompanied c-met gene or combo transduction. Gene therapy of limbal epithelial stem cell compartment has a beneficial effect on the diabetic corneal wound healing and on diabetic and stem cell marker expression, and shows potential for alleviating symptoms of diabetic keratopathy.

Squamosamide derivative FLZ protects retinal pigment epithelium cells from oxidative stress through activation of epidermal growth factor receptor (EGFR)-AKT signaling

Reactive oxygen species (ROS)-mediated retinal pigment epithelium (RPE) cell apoptosis is attributed to age-related macular degeneration (AMD) pathogenesis. FLZ, a novel synthetic squamosamide derivative from a Chinese herb, Annona glabra, has displayed significant cyto-protective activity. In the current study, we explored the pro-survival effect of FLZ in oxidative stressed-RPE cells and studied the underlying signaling mechanisms. Our results showed that FLZ attenuated hydrogen peroxide (H2O2)-induced viability decrease and apoptosis in the RPE cell line (ARPE-19 cells) and in primary mouse RPE cells. Western blotting results showed that FLZ activated AKT signaling in RPE cells. The AKT-specific inhibitor, MK-2206, the phosphoinositide 3-kinase (PI3K)/AKT pan inhibitor, wortmannin, and AKT1-shRNA (short hairpin RNA) depletion almost abolished FLZ-mediated pro-survival/anti-apoptosis activity. We discovered that epidermal growth factor receptor (EGFR) trans-activation mediated FLZ-induced AKT activation and the pro-survival effect in RPE cells, and the anti-apoptosis effect of FLZ against H2O2 was inhibited by the EGFR inhibitor, PD153035, or by EGFR shRNA-knockdown. In conclusion, FLZ protects RPE cells from oxidative stress through activation of EGFR-AKT signaling, and our results suggest that FLZ might have therapeutic values for AMD.

Crizotinib reduces the rate of dark adaptation in the rat retina independent of ALK inhibition

Crizotinib (Xalkori) is a tyrosine kinase inhibitor of both anaplastic lymphoma kinase (ALK) and mesenchymal-epithelial transition factor (c-Met). Though not predicted from standard nonclinical toxicological evaluation, visual disturbance became a frequently observed adverse event in humans. To understand the possible mechanism of this vision effect, an in vivo electroretinogram (ERG) study was conducted to assess retinal functional changes following oral administration of crizotinib. Immunohistochemical (IHC) staining of ALK and c-Met in the neural retinas of human, non-human primate, dog, rat, and mouse was used to aid in the animal model selection. ALK IHC staining was identified predominantly in the ganglion cell and inner nuclear layers of most species evaluated, in the inner plexiform layer in human and rodent, and in the nerve fiber layer in human and rat only. There was no apparent staining of any layer of the neural retina for c-Met in any of the species evaluated. ERG measurements identified a significant reduction in b-wave amplitude during the initial phase of dark adaptation in the crizotinib-treated rats. ERGs were also taken following oral administration of PF-06463922 (an ALK-selective inhibitor), for an understanding of potential kinase involvement. ERG effects were not observed in PF-06463922-treated animals when comparable exposures in the vitreous humor were achieved. Collectively, our results suggest that the ERG b-wave amplitude decreases during dark adaption following crizotinib administration may be related to signaling changes within the retina in rats, likely independent of ALK inhibition.

Selective impairment of a subset of Ran-GTP-binding domains of ran-binding protein 2 (Ranbp2) suffices to recapitulate the degeneration of the retinal pigment epithelium (RPE) triggered by Ranbp2 ablation

Retinal pigment epithelium (RPE) degeneration underpins diseases triggered by disparate genetic lesions, noxious insults, or both. The pleiotropic Ranbp2 controls the expression of intrinsic and extrinsic pathological stressors impinging on cellular viability. However, the physiological targets and mechanisms controlled by Ranbp2 in tissue homeostasis, such as RPE, are ill defined. We show that mice, RPE-cre::Ranbp2(-/-), with selective Ranbp2 ablation in RPE develop pigmentary changes, syncytia, hypoplasia, age-dependent centrifugal and non-apoptotic degeneration of the RPE, and secondary leakage of choriocapillaris. These manifestations are accompanied by the development of F-actin clouds, metalloproteinase-11 activation, deregulation of expression or subcellular localization of critical RPE proteins, atrophic cell extrusions into the subretinal space, and compensatory proliferation of peripheral RPE. To gain mechanistic insights into what Ranbp2 activities are vital to the RPE, we performed genetic complementation analyses of transgenic lines of bacterial artificial chromosomes of Ranbp2 harboring loss of function of selective Ranbp2 domains expressed in a Ranbp2(-/-) background. Among the transgenic lines produced, only Tg(RBD2/3*-HA)::RPE-cre::Ranbp2(-/-)-expressing mutations, which selectively impair binding of RBD2/3 (Ran-binding domains 2 and 3) of Ranbp2 to Ran-GTP, recapitulate RPE degeneration, as observed with RPE-cre::Ranbp2(-/-). By contrast, Tg(RBD2/3*-HA) expression rescues the degeneration of cone photoreceptors lacking Ranbp2. The RPE of RPE-cre::Ranbp2(-/-) and Tg(RBD2/3*-HA)::RPE-cre::Ranbp2(-/-) share proteostatic deregulation of Ran GTPase, serotransferrin, and γ-tubulin and suppression of light-evoked electrophysiological responses. These studies unravel selective roles of Ranbp2 and its RBD2 and RBD3 in RPE survival and functions. We posit that the control of Ran GTPase by Ranbp2 emerges as a novel therapeutic target in diseases promoting RPE degeneration.

The Hepatocyte Growth Factor (HGF)/Met Axis: A Neglected Target in the Treatment of Chronic Myeloproliferative Neoplasms?

Met is the receptor of hepatocyte growth factor (HGF), a cytoprotective cytokine. Disturbing the equilibrium between Met and its ligand may lead to inappropriate cell survival, accumulation of genetic abnormalities and eventually, malignancy. Abnormal activation of the HGF/Met axis is established in solid tumours and in chronic haematological malignancies, including myeloma, acute myeloid leukaemia, chronic myelogenous leukaemia (CML), and myeloproliferative neoplasms (MPNs). The molecular mechanisms potentially responsible for the abnormal activation of HGF/Met pathways are described and discussed. Importantly, inCML and in MPNs, the production of HGF is independent of Bcr-Abl and JAK2V617F, the main molecular markers of these diseases. In vitro studies showed that blocking HGF/Met function with neutralizing antibodies or Met inhibitors significantly impairs the growth of JAK2V617F-mutated cells. With personalised medicine and curative treatment in view, blocking activation of HGF/Met could be a useful addition in the treatment of CML and MPNs for those patients with high HGF/MET expression not controlled by current treatments (Bcr-Abl inhibitors in CML; phlebotomy, hydroxurea, JAK inhibitors in MPNs).

Amniotic fluid-borne hepatocyte growth factor protects rat pups against experimental necrotizing enterocolitis

Fetal swallowing of amniotic fluid, which contains numerous cytokines and growth factors, plays a key role in gut mucosal development. Preterm birth interrupts this exposure to amniotic fluid-borne growth factors, possibly contributing to the increased risk of necrotizing enterocolitis (NEC) in premature infants. We hypothesized that supplementation of formula feeds with amniotic fluid can provide amniotic fluid-borne growth factors and prevent experimental NEC in rat pups. We compared NEC-like injury in rat pups fed with infant formula vs. formula supplemented either with 30% amniotic fluid or recombinant hepatocyte growth factor (HGF). Cytokines/growth factors in amniotic fluid were measured by immunoassays. Amniotic fluid and HGF effects on enterocyte migration, proliferation, and survival were measured in cultured IEC6 intestinal epithelial cells. Finally, we used an antibody array to investigate receptor tyrosine kinase (RTK) activation and immunoblots to measure phosphoinositide 3-kinase (PI3K) signaling. Amniotic fluid supplementation in oral feeds protected rat pups against NEC-like injury. HGF was the most abundant growth factor in rat amniotic fluid in our panel of analytes. Amniotic fluid increased cell migration, proliferation, and cell survival in vitro. These effects were reproduced by HGF and blocked by anti-HGF antibody or a PI3K inhibitor. HGF transactivated several RTKs in IEC6 cells, indicating that its effects extended to multiple signaling pathways. Finally, similar to amniotic fluid, recombinant HGF also reduced the frequency and severity of NEC-like injury in rat pups. Amniotic fluid supplementation protects rat pups against experimental NEC, which is mediated, at least in part, by HGF.

Differentially expressed wound healing-related microRNAs in the human diabetic cornea

MicroRNAs are powerful gene expression regulators, but their corneal repertoire and potential changes in corneal diseases remain unknown. Our purpose was to identify miRNAs altered in the human diabetic cornea by microarray analysis, and to examine their effects on wound healing in cultured telomerase-immortalized human corneal epithelial cells (HCEC) in vitro. Total RNA was extracted from age-matched human autopsy normal (n=6) and diabetic (n=6) central corneas, Flash Tag end-labeled, and hybridized to Affymetrix® GeneChip® miRNA Arrays. Select miRNAs associated with diabetic cornea were validated by quantitative RT-PCR (Q-PCR) and by in situ hybridization (ISH) in independent samples. HCEC were transfected with human pre-miR™miRNA precursors (h-miR) or their inhibitors (antagomirs) using Lipofectamine 2000. Confluent transfected cultures were scratch-wounded with P200 pipette tip. Wound closure was monitored by digital photography. Expression of signaling proteins was detected by immunostaining and Western blot. Using microarrays, 29 miRNAs were identified as differentially expressed in diabetic samples. Two miRNA candidates showing the highest fold increased in expression in the diabetic cornea were confirmed by Q-PCR and further characterized. HCEC transfection with h-miR-146a or h-miR-424 significantly retarded wound closure, but their respective antagomirs significantly enhanced wound healing vs. controls. Cells treated with h-miR-146a or h-miR-424 had decreased p-p38 and p-EGFR staining, but these increased over control levels close to the wound edge upon antagomir treatment. In conclusion, several miRNAs with increased expression in human diabetic central corneas were found. Two such miRNAs inhibited cultured corneal epithelial cell wound healing. Dysregulation of miRNA expression in human diabetic cornea may be an important mediator of abnormal wound healing.

Enhanced wound healing, kinase and stem cell marker expression in diabetic organ-cultured human corneas upon MMP-10 and cathepsin F gene silencing

PURPOSE

Diabetic corneas overexpress proteinases including matrix metalloproteinase-10 (M10) and cathepsin F (CF). Our purpose was to assess if silencing M10 and CF in organ-cultured diabetic corneas using recombinant adenovirus (rAV)-driven small hairpin RNA (rAV-sh) would normalize slow wound healing, and diabetic and stem cell marker expression.

METHODS

Sixteen pairs of organ-cultured autopsy human diabetic corneas (four per group) were treated with rAV-sh. Proteinase genes were silenced either separately, together, or both, in combination (Combo) with rAV-driven c-met gene overexpression. Fellow control corneas received rAV-EGFP. Quantitative RT-PCR confirmed small hairpin RNA (shRNA) silencing effect. Ten days after transfection, 5-mm epithelial wounds were made with n-heptanol and healing time recorded. Diabetic, signaling, and putative stem cell markers were studied by immunofluorescence of corneal cryostat sections.

RESULTS

Proteinase silencing reduced epithelial wound healing time versus rAV-enhanced green fluorescent protein (EGFP) control (23% for rAV-shM10, 31% for rAV-shCF, and 36% for rAV-shM10 + rAV-shCF). Combo treatment was even more efficient (55% reduction). Staining patterns of diabetic markers (α₃β₁ integrin and nidogen-1), and of activated epidermal growth factor receptor and its signaling target activated Akt were normalized upon rAV-sh treatment. Combo treatment also restored normal staining for activated p38. All treatments, especially the combined ones, increased diabetes-altered staining for putative limbal stem cell markers, ΔNp63α, ABCG2, keratins 15 and 17, and laminin γ3 chain.

CONCLUSIONS

Small hairpin RNA silencing of proteinases overexpressed in diabetic corneas enhanced corneal epithelial and stem cell marker staining and accelerated wound healing. Combined therapy with c-met overexpression was even more efficient. Specific corneal gene therapy has a potential for treating diabetic keratopathy.

Alternative signaling pathways as potential therapeutic targets for overcoming EGFR and c-Met inhibitor resistance in non-small cell lung cancer

The use of tyrosine kinase inhibitors (TKIs) against EGFR/c-Met in non-small cell lung cancer (NSCLC) has been shown to be effective in increasing patient progression free survival (PFS), but their efficacy is limited due to the development of resistance and tumor recurrence. Therefore, understanding the molecular mechanisms underlying development of drug resistance in NSCLC is necessary for developing novel and effective therapeutic approaches to improve patient outcome. This study aims to understand the mechanism of EGFR/c-Met tyrosine kinase inhibitor (TKI) resistance in NSCLC. H2170 and H358 cell lines were made resistant to SU11274, a c-Met inhibitor, and erlotinib, an EGFR inhibitor, through step-wise increases in TKI exposure. The IC₅₀ concentrations of resistant lines exhibited a 4–5 and 11–22-fold increase for SU11274 and erlotinib, respectively, when compared to parental lines. Furthermore, mTOR and Wnt signaling was studied in both cell lines to determine their roles in mediating TKI resistance. We observed a 2–4-fold upregulation of mTOR signaling proteins and a 2- to 8-fold upregulation of Wnt signaling proteins in H2170 erlotinib and SU11274 resistant cells. H2170 and H358 cells were further treated with the mTOR inhibitor everolimus and the Wnt inhibitor XAV939. H358 resistant cells were inhibited by 95% by a triple combination of everolimus, erlotinib and SU11274 in comparison to 34% by a double combination of these drugs. Parental H2170 cells displayed no sensitivity to XAV939, while resistant cells were significantly inhibited (39%) by XAV939 as a single agent, as well as in combination with SU11274 and erlotinib. Similar results were obtained with H358 resistant cells. This study suggests a novel molecular mechanism of drug resistance in lung cancer.

Decorin inhibits angiogenic potential of choroid-retinal endothelial cells by downregulating hypoxia-induced Met, Rac1, HIF-1α and VEGF expression in cocultured retinal pigment epithelial cells

Choroidal neovascularization (CNV) is one of the most common causes of severe vision loss. Decorin, a multiple receptor tyrosine kinase inhibitor, has been recently shown to play an important regulatory role in angiogenic response. This study aims to investigate whether the overexpression of decorin in retinal pigment epithelial (RPE) cells under hypoxia alters the in vitro angiogenic ability of cocultured choroid-retinal endothelial cells and to explore the possible mechanisms involved. Human RPE cells (ARPE-19) were subjected to hypoxia with or without decorin pretreatment, and RNA interference technique was used to knock down the Met gene in ARPE-19 cells. Cell viability was determined using the Cell Counting Kit-8 assay. Expression of Met, Rac1 and hypoxia-inducible factor-1 alpha (HIF-1α) was evaluated by western blot and quantitative real-time polymerase chain reaction (qRT-PCR). Vascular endothelial growth factor (VEGF) expression was evaluated by enzyme-linked immunosorbent assay (ELISA) and qRT-PCR. We then constructed a recombinant lentiviral vector carrying the decorin gene to transduce ARPE-19 cells. The overexpression of decorin in transduced RPE cells was confirmed by qRT-PCR and western blot. The transduced RPE cells were then cocultured with rhesus macaque choroid-retinal endothelial cells (RF/6A) in a transwell coculture system to observe the effects of decorin overexpression in ARPE-19 cells on the proliferation, migration and tube formation of RF/6A cells. In response to hypoxia, the VEGF concentrations in the culture supernatants increased greatly at 24 and 48 h, and this effect was inhibited significantly and nearly equally in the presence of 50-200 nM decorin. Decorin pretreatment before hypoxia exposure effectively reduced the hypoxia-induced expression of Met, Rac1, HIF-1α and VEGF in ARPE-19 cells. Transfection of small interfering RNA against Met to ARPE-19 cells also resulted in significant downregulation of Rac1, HIF-1α and VEGF under hypoxia, and this effect was similar to that noted with decorin pretreatment alone or with their combination. Results from the coculture system showed that the overexpression of decorin in ARPE-19 cells significantly inhibited the proliferation, migration and tube formation of RF/6A cells. These results indicate that Met pathway activation plays an important role in the upregulation of VEGF in RPE cells under hypoxia. Decorin may interfere with angiogenesis by downregulating hypoxia-induced Met, Rac1, HIF-1α and VEGF expression in RPE cells, which suggests a potential strategy for the inhibition of CNV.

Hepatocyte growth factor-loaded biomaterials for mesenchymal stem cell recruitment

Human adult mesenchymal stem cells (MSC) can be readily harvested from bone marrow through aspiration. MSC are involved in tissue regeneration and repair, particularly in wound healing. Due to their high self-renewal capacity and excellent differentiation potential in vitro, MSC are ideally suited for regenerative medicine. The complex interactions of MSC with their environment and their influence on the molecular and functional levels are widely studied but not completely understood. MSC secrete, for example, hepatocyte growth factor (HGF), whose concentration is enhanced in wounded areas and which is shown to act as a chemoattractant for MSC. We produced HGF-loaded biomaterials based on collagen and fibrin gels to develop a recruitment system for endogenous MSC to improve wound healing. Here, we report that HGF incorporated into collagen or fibrin gels leads to enhanced and directed MSC migration in vitro. HGF-loaded biomaterials might be potentially used as in vivo wound dressings to recruit endogenous MSC from tissue-specific niches towards the wounded area. This novel approach may help to reduce costly multistep procedures of cell isolation, in vitro culture, and transplantation usually used in tissue engineering.

Enhanced PKCδ and ERK signaling mediate cell migration of retinal pigment epithelial cells synergistically induced by HGF and EGF

Proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR) are characterized by the development of epi-retinal membranes which may exert a tractional force on retina. A lot of inflammatory growth factors may disturb the local ocular cells such as retinal pigment epithelial (RPE) cells, causing them to migrate and proliferate in the vitreous cavity and ultimately forming the PVR membrane. In this study, the signal pathways mediating cell migration of RPE induced by growth factors were investigated. Hepatocyte growth factor (HGF), epidermal growth factor (EGF) or heparin-binding epidermal growth factor (HB-EGF) induced a greater extent of migration of RPE50 and ARPE19 cells, compared with other growth factors. According to inhibitor studies, migration of RPE cells induced by each growth factor was mediated by protein kinase C (PKC) and ERK (MAPK). Moreover, HGF coupled with EGF or HB-EGF had synergistic effects on cell migration and enhanced activation of PKC and ERK, which were attributed to cross activation of growth factor receptors by heterogeneous ligands. Furthermore, using the shRNA technique, PKCδ was found to be the most important PKC isozyme involved. Finally, vitreous fluids from PVR and PDR patients with high concentration of HGF may induce RPE cell migration in PKCδ- and ERK- dependent manner. In conclusion, migration of RPE cells can be synergistically induced by HGF coupled with HB-EGF or EGF, which were mediated by enhanced PKCδ activation and ERK phosphorylation.

Synergism of EGFR and c-Met pathways, cross-talk and inhibition, in non-small cell lung cancer

Background

c-Met and EGFR receptors are widely expressed on cancer cells; they are implicated in the development and progression of cancer through a plethora of effects on cell cycle progression, apoptosis, motility and metastasis and are potential targets for combination therapy. EGFR receptor tyrosine kinases are currently being targeted in a number of malignancies.

Methods

Apoptosis was studied by FACS analysis using propidium iodide. EGF and HGF signaling intermediates were studied by western blotting. Cell proliferation was determined by MTT assays. Cell motility was done by time lapse confocal microscopy.

Results

c-Met and EGFR were both expressed in A549, H1838, H2170, SW900, SW1573, H358, SKLU-1, and H1993 non small cell lung cancer (NSCLC) cell lines. Both EGF and HGF at 100 ng/ml in medium showed a synergistic effect on cell proliferation at 48–72 h as seen by a proliferation assay in A549, H1838, and SKMES cells. In A549 and H1838 cell lines, HGF (40 ng/ml) and EGF (5 ng/ml) induced synergistic phosphorylation on c-Met (Tyr 1003/1230/1234/1235). Additionally, synergistic phosphorylation of Akt (Ser-473) and phospho-ERK1+ERK2 (Thr202/Tyr204) was also seen indicating that EGF and HGF could induce synergistic phosphorylation of important signaling intermediates. Treatment with EGF and HGF at 100 ng/ml for 2 h also leads to an additive effect in inducing cell motility (especially membrane ruffling) in H1993 cells. A novel c-Met small molecule tyrosine kinase inhibitor SU11274 and EGFR tyrosine kinase inhibitors Tyrphostin AG1478 and gefitinib (Iressa) were tested to study their effect in combination on proliferation and apoptosis in lung cancer cells. Interestingly, a synergistic effect on inhibition of cell proliferation was seen in the presence of SU11274 and Tyrphostin AG1478. 0.5 µM Tyrphostin AG1478 and 2 µM SU11274 inhibited growth by 21% and 25%, respectively; a combination of both tyrosine kinase inhibitors inhibited growth by 65%. Interestingly, EGFR inhibitor (gefitinib, Iressa) and c-Met inhibitor (SU11274) also had a synergistic effect on apoptosis in H358 cells.

Conclusion

There was a synergistic effect of EGF and HGF on proliferation, downstream activation of signal transduction and an additive effect seen on motility. These studies show that a combination of HGF and EGF tyrosine kinase inhibitors on NSCLC, could potentially be targeted in a synergistic fashion.

Met interacts with EGFR and Ron in canine osteosarcoma

The receptor tyrosine kinase (RTK) Met is known to be over-expressed in canine osteosarcoma (OSA). In human cancers, the RTKs Met, epidermal growth factor receptor (EGFR) and Ron are frequently co-expressed and engage in heterodimerization, altering signal transduction and promoting resistance to targeted therapeutics. We found that EGFR and Ron are expressed in canine OSA cell lines and primary tissues, EGFR and Ron are frequently phosphorylated in OSA tumour samples, and Met is co-associated with EGFR and Ron in canine OSA cell lines. Transforming growth factor alpha (TGFα) and hepatocyte growth factor (HGF) stimulation induced amplification of ERK1/2 and STAT3 phosphorylation in OSA cells and Met was phosphorylated following TGFα stimulation providing evidence for receptor cross-talk. Lastly, treatment of OSA cells with combined gefitinib and crizotinib inhibited cell proliferation in an additive manner. Together, these data support the notion that Met, EGFR and Ron interact in OSA cells and as such, may represent viable targets for therapeutic intervention.

The expression and function of vascular endothelial growth factor in retinal pigment epithelial (RPE) cells is regulated by 4-hydroxynonenal (HNE) and glutathione S-transferaseA4-4

It is well established that 4-hydroxynonenal (HNE) plays a major role in oxidative stress-induced signaling and the toxicity of oxidants. Surprisingly our recent studies also demonstrate that low levels of HNE generated during oxidative stress promote cell survival mechanisms and proliferation. Since the expression and secretion of VEGF is known to be affected by Oxidative stress, during present studies, we have examined dose dependent effect of HNE on VEGF expression and secretion in a model of retinal pigment epithelial (RPE) cells in culture. Results of these studies showed that while inclusion of 0.1 μM HNE in the medium caused increased secretion of VEGF, its secretion and expression was significantly suppressed in the presence of >5 μM HNE in the media. These concentration dependent hormetic effects of HNE on VEGF secretion could be blocked by the over expression of GSTA4-4 indicating that these effects were specifically attributed to HNE and regulated by GSTA4-4. VEGF secreted into the media showed angiogenic properties as indicated by increased migration and tube formation of HUVEC in matrigel when grown in media from RPE cells treated with 1 μM HNE. The corresponding media from GSTA4-4 over expressing RPE cells had no effect on migration and tube formation of HUVEC in matrigel. These results are consistent with earlier studies showing that at low concentrations, HNE promotes proliferative mechanisms and suggest that HNE induces VEGF secretion from RPE cells that acts in a paracrine fashion to induce angiogenic signaling mechanism in the endothelial cells. These findings may suggest a role of HNE and GSTA4-4 in oxidative stress induced proliferative retinopathies.

Impaired epithelial wound healing and EGFR signaling pathways in the corneas of diabetic rats

PURPOSE. The purpose of the study was to investigate the effects of hyperglycemia on EGFR (epidermal growth factor receptor)-mediated wound response and signal transduction in the corneal epithelium of rats with type I diabetes mellitus (DM). METHODS. Corneal epithelia were removed from streptozotocin (STZ)- and weight-matched normal rats. Wound healing was monitored by fluorescein staining at 24 or 48 hours after epithelial debridement. Phosphorylation of EGFR, AKT, ERK, and BAD was determined by Western blot analysis. The distribution of phospho-AKT and proliferating cell nuclear antigen (PCNA) in rat corneas was examined by immunohistochemistry. Cell death was evaluated by TUNEL staining. RESULTS. A significant delay in corneal epithelial wound healing was observed 48 hours after wounding in the diabetic rats compared with the weight-matched control rats. In the DM rat corneas, epithelial cells demonstrated diminished responses to wounding, as assessed by the phosphorylation of EGFR and its downstream signaling molecules, AKT and ERK. Furthermore, although the distribution pattern of phospho-AKT suggested a role for AKT in epithelial migration and proliferation in the normoglycemic rat corneas, it was abrogated in the healing epithelia of the DM rats. Consistent with impaired AKT activity, the number of PCNA-stained cells was also greatly reduced in the healing corneas of the diabetic rats. Finally, decreases in pBAD (Ser(136) and Ser(112)) and increases in TUNEL-positive cells were observed in both the uninjured and healing corneal epithelia of the DM rats, but not of the control rats. CONCLUSIONS. In the corneas of SZT rats, EGFR-PI3K-AKT and ERK, as well as their downstream BAD signaling pathways in migratory epithelium, were altered, resulting in increased apoptosis, decreased cell proliferation, and delayed wound closure.

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.

Role of 4-hydroxynonenal in epidermal growth factor receptor-mediated signaling in retinal pigment epithelial cells

Lipid peroxidation (LPO) end-product 4-hydroxynonenal (4-HNE) has been implicated in the mechanism of retinopathy. Lately it has been shown that besides being cytotoxic, 4-HNE plays an important role in oxidative stress-induced signaling. In this study, we have investigated the effect of 4-HNE on epidermal growth factor receptor (EGFR)-mediated signaling, its potential functional consequences, and the regulatory role of the 4-HNE metabolizing isozymes, glutathione S-transferase A4-4 (GSTA4-4) on this signaling in retinal pigment epithelial (RPE) cells. Our results showed that consistent with its known toxicity at relatively higher concentrations, 4-HNE induced cell death in RPE. However, at lower concentrations (as low as 0.1 μM) 4-HNE triggered phosphorylation of EGFR and activation of its down stream signaling components ERK1/2 and Akt that are known to be involved in cell proliferation. These effects of 4-HNE on EGFR could be attenuated by the over expression of GSTA4-4 that reduces intracellular levels of 4-HNE. Our results also indicated that 4-HNE-induced activation of EGFR is a protective mechanism against oxidative stress because EGFR, MEK, and PI3K inhibitors potentiated the toxicity of 4-HNE and also inhibited wound healing in a RPE cell model. These studies suggest that as an initial response to oxidative stress, 4-HNE induces protective mechanism(s) in RPE cells through EGFR-mediated signaling.

Stromal cell-derived factor-1 is essential for photoreceptor cell protection in retinal detachment

Stromal cell-derived factor-1 (SDF-1) causes chemotaxis of CXCR4-expressing bone marrow-derived cells. SDF-1 is involved in the pathogenesis of various vascular diseases, including those of the eye. However, the role of SDF-1 in neuronal diseases is not completely understood. Here, we show higher SDF-1 levels in the vitreous humor of patients with retinal detachment (RD) compared with normal patients. SDF-1 correlated positively with the duration as well as the extent of RD. Furthermore, SDF-1 correlated significantly with levels of interleukin-6 and interleukin-8, but not with vascular endothelial growth factor. Western blot analysis results showed significant SDF-1 up-regulation in detached rat retinas compared with normal animals. Immunohistochemistry data showed that SDF-1 was co-localized with the glial cells of the detached retina. SDF-1 blockade with a neutralizing antibody increased photoreceptor cell loss and macrophage accumulation in the subretinal space. The retinal precursor cell line R28 expressed CXCR4. SDF-1 rescued serum starvation-induced apoptosis in R28 cells and enhanced their ability to participate in wound closure in a scratch assay. Our results indicate a surprising, protective role for SDF-1 in RD. This effect may be mediated directly or indirectly through other cell types.

EGFR/Met association regulates EGFR TKI resistance in breast cancer

Breast cancers show a lack of response to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), despite 30% of tumors expressing EGFR. The mechanism of this resistance is unknown; however, we have recently shown that Met kinase activity compensates for loss of EGFR kinase activity in cell culture models. Met has been implicated in the pathogenesis of breast tumors and therefore may cooperate with EGFR for tumor growth. Here we have found that EGFR phosphorylation and cell proliferation is in part regulated by Met expression. In addition, we found that Met constitutive phosphorylation occurred independent of the Met ligand hepatocyte growth factor (HGF). Ligand-independent Met phosphorylation is mediated by Met amplification, mutation, or overexpression and by Met interaction with other cell surface molecules. In SUM229 breast cancer cells, we found that Met was not amplified or mutated, however it was overexpressed. Met overexpression did not directly correlate with ligand-independent Met phosphorylation as the SUM229 cell line was the only Met expressing breast cancer line with constitutive Met phosphorylation. Interestingly, Met expression did correlate with EGFR expression and we identified an EGFR/Met complex via co-immunoprecipitation. However, we only observed Met constitutive phosphorylation when c-Src also was part of this complex. Ligand-independent phosphorylation of Met was decreased by down regulating EGFR expression or by inhibiting c-Src kinase activity. Lastly, inhibiting EGFR and Met kinase activities resulted in a synergistic decrease in cell proliferation, supporting the idea that EGFR and Met functionally, as well as physically interact in breast cancer cells to regulate response to EGFR inhibitors.