Migration of retinal pigment epithelium cells in vitro is regulated by protein kinase C

12-O-tetradecanoylphorbol-13-acetate Reduces Activation of Hepatic Stellate Cells by Inhibiting the Hippo Pathway Transcriptional Coactivator YAP

Although protein kinase C (PKC) regulates various biological activities, including cell proliferation, differentiation, migration, tissue remodeling, gene expression, and cell death, the antifibrotic effect of PKC in myofibroblasts is not fully understood. We investigated whether 12-O-tetradecanoylphorbol-13-acetate (TPA), a PKC activator, reduced the activation of hepatic stellate cells (HSCs) and explored the involvement of the Hippo pathway transcriptional coactivator YAP. We analyzed the effect of TPA on the proliferation and expression of α-smooth muscle actin (SMA) in the LX-2 HSC line. We also analyzed the phosphorylation of the Hippo pathway molecules YAP and LATS1 and investigated YAP nuclear translocation. We examined whether Gö 6983, a pan-PKC inhibitor, restored the TPA-inhibited activities of HSCs. Administration of TPA decreased the growth rate of LX-2 cells and inhibited the expression of α-SMA and collagen type I alpha 1 (COL1A1). In addition, TPA induced phosphorylation of PKCδ, LATS1, and YAP and inhibited the nuclear translocation of YAP compared with the control. These TPA-induced phenomena were mostly ameliorated by Gö 6983. Our results indicate that PKCδ exerts an antifibrotic effect by inhibiting the Hippo pathway in HSCs. Therefore, PKCδ and YAP can be used as therapeutic targets for the treatment of fibrotic diseases.

Repeated Injection of Methotrexate into Silicone Oil-Filled Eyes for Grade C Proliferative Vitreoretinopathy: A Pilot Study

PURPOSE

To evaluate the effects of repeated intra-silicone oil (SO) injections of methotrexate (MTX) on the outcomes of surgery for rhegmatogenous retinal detachment (RRD) with grade C proliferative vitreoretinopathy (PVR-C).

METHODS

In this prospective pilot case series, eyes with RRD and PVR-C underwent pars plana vitrectomy and intraocular injection of SO. At the conclusion of the procedure, 250 µg of MTX was injected into the SO-filled vitreous cavity. Intra-SO injection was repeated at weeks 3 and 6; the minimum follow-up period was 6 months. The main outcome measure was retinal reattachment rate.

RESULTS

Eleven eyes of 11 patients (mean age, 52.73 ± 18.01 years) were included. The mean follow-up period was 9 ± 3 months (range, 6-15 months). Total retinal detachment with anterior and/or posterior PVR-C was present in all eyes before surgery. Mean preoperative best-corrected visual acuity (BCVA) was 2.62 ± 0.04 logMAR. All operated eyes exhibited retinal reattachment posterior to the equator during the follow-up period. Mean postoperative BCVA was significantly improved to 1.02 ± 0.51 logMAR (p = 0.003). No ocular or systemic side effects were observed.

CONCLUSION

Repeated intra-SO injection of MTX as an adjunctive therapy for RRD complicated by PVR showed promising results and was not associated with adverse effects. Further studies are needed to confirm its possible beneficial effects on the final anatomic and functional outcomes in these cases.

PKCζ-dependent upregulation of p27kip1 contributes to oxidative stress induced retinal pigment epithelial cell multinucleation

Retinal pigment epithelial (RPE) cells increase in size and multinucleate during aging. We have shown using human and mouse cell lines that oxidised photoreceptor outer segments (oxPOS)-induced cytokinesis failure is related to RPE cell multinucleation, although the underlying mechanism remains unknown. This study investigated the role of the PKC pathway in oxPOS-induced RPE multinucleation using ARPE19 cells. oxPOS treatment promoted PKC activity and upregulated the mRNA expression of PKC α, δ, ζ, ι and μ. Inhibition of PKCα with Gö6976 resulted in a 33% reduction of multinucleate ARPE19 cells, whereas inhibition of PKCζ with Gö6983 led to a 50% reduction in multinucleate ARPE19 cells. Furthermore, oxPOS treatment induced a PKCζ-dependent upregulation of the Cdk inhibitor p27kip1, its inhibition using A2CE reduced oxPOS-induced ARPE19 multinucleation. Our results suggest that oxPOS-induced ARPE19 cytokinesis failure is, at least in part, due to the upregulation of p27kip1 through activating the PKC, particularly PKCζ pathway. Targeting the PKCζ-p27kip1 signalling axis may be a novel approach to restore RPE repair capacity during aging.

The Effect of PKCα on the Light Response of Rod Bipolar Cells in the Mouse Retina

PURPOSE

Protein kinase C α (PKCα) is abundantly expressed in rod bipolar cells (RBCs) in the retina, yet the physiological function of PKCα in these cells is not well understood. To elucidate the role of PKCα in visual processing in the eye, we examined the effect of genetic deletion of PKCα on the ERG and on RBC light responses in the mouse.

METHODS

Immunofluorescent labeling was performed on wild-type (WT), TRPM1 knockout, and PKCα knockout (PKC-KO) retina. Scotopic and photopic ERGs were recorded from WT and PKC-KO mice. Light responses of RBCs were measured using whole-cell recordings in retinal slices from WT and PKC-KO mice.

RESULTS

Protein kinase C alpha expression in RBCs is correlated with the activity state of the cell. Rod bipolar cells dendrites are a major site of PKCα phosphorylation. Electroretinogram recordings indicated that loss of PKCα affects the scotopic b-wave, including a larger peak amplitude, longer implicit time, and broader width of the b-wave. There were no differences in the ERG a- or c-wave between PKCα KO and WT mice, indicating no measurable effect of PKCα in photoreceptors or the RPE. The photopic ERG was unaffected consistent with the lack of detectable PKCα in cone bipolar cells. Whole-cell recordings from RBCs in PKC-KO retinal slices revealed that, compared with WT, RBC light responses in the PKC-KO retina are delayed and of longer duration.

CONCLUSIONS

Protein kinase C alpha plays an important modulatory role in RBCs, regulating both the peak amplitude and temporal properties of the RBC light response in the rod visual pathway.

The inhibitory effect of small interference RNA protein kinase C-alpha on the experimental proliferative vitreoretinopathy induced by dispase in mice

Aim

To evaluate the effects of small interference RNA protein kinase C-alpha (siRNA-PKCα) on experimental proliferative vitreoretinopathy (PVR) induced by dispase in mice.

Methods

C57BL/6 mice PVR models (4–6 weeks old) were induced by intravitreal injection of dispase and then equally divided into six groups. After 1 week, the five treatment groups received 2 μL, intravitreal injections of siRNA-PKCα at a concentration of 250 nM, 500 nM, 750 nM, 1000 nM, and 1500 nM, respectively, while the negative control group received 2 μL of 500 nM no-silencing siRNA. SiRNA-PKCα was transfected by a square wave electroporator. Postoperative ophthalmic observations of lens clarity and the fundus of the eyes were performed periodically. The eyeballs of the mice were enucleated and imbedded in optimal cutting temperature to perform histological and immunofluorescence analysis at the end of a 4-week observation period.

Results

Four weeks after the siRNA-PKCα injections, there are 100% lens dissolution and 100% PVR in the 250 nM group and 70%, 70%, 70%, and 50% PVR in the 500 nM, 750 nM, 1000 nM, and 1500 nM groups, respectively, which is significantly different from the negative group. Abnormalities in fundus appearance were related to the concentrations of siRNA-PKCα; a higher concentration of siRNA-PKCα resulted in a more normal fundus. Histological sections by hematoxylin-eosin staining of the eyes support the clinical observation. Immunofluorescence analysis showed that RPE65, glutamine synthase, glial acidic fibrillary protein, and α-smooth muscle actin were increasing in the retina with the decreasing concentration of siRNA-PKCα, indicating that intraocular siRNA-PKCα can partly inhibit changes of markers for glia cells, fibroblast cells, retinal pigment epithelium cells, and Müller cells in the process of PVR.

Conclusion

Gene therapy with siRNA-PKCα could effectively inhibit PVR in mice and provide us with a novel therapeutic target on PVR.

Activation of PKCβII by PMA facilitates enhanced epithelial wound repair through increased cell spreading and migration

Rapid repair of epithelial wounds is essential for intestinal homeostasis, and involves cell proliferation and migration, which in turn are mediated by multiple cellular signaling events including PKC activation. PKC isoforms have been implicated in regulating cell proliferation and migration, however, the role of PKCs in intestinal epithelial cell (IEC) wound healing is still not completely understood. In the current work we used phorbol 12-myristate 13-acetate (PMA), a well recognized agonist of classical and non-conventional PKC subfamilies to investigate the effect of PKC activation on IEC wound healing. We found that PMA treatment of wounded IEC monolayers resulted in 5.8±0.7-fold increase in wound closure after 24 hours. The PMA effect was specifically mediated by PKCβII, as its inhibition significantly diminished the PMA-induced increase in wound closure. Furthermore, we show that the PKCβII-mediated increase in IEC wound closure after PMA stimulation was mediated by increased cell spreading/cell migration but not proliferation. Cell migration was mediated by PKCβII dependent actin cytoskeleton reorganization, enhanced formation of lamellipodial extrusions at the leading edge and increased activation of the focal adhesion protein, paxillin. These findings support a role for PKCβII in IEC wound repair and further demonstrate the ability of epithelial cells to migrate as a sheet thereby efficiently covering denuded surfaces to recover the intestinal epithelial barrier.

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.

Protein kinase Cα downregulation via siRNA-PKCα released from foldable capsular vitreous body in cultured human retinal pigment epithelium cells

We previously found that downregulation of protein kinase Cα (PKCα) can inhibit retinal pigment epithelium (RPE) cell proliferation involved in the development of proliferative vitreoretinopathy (PVR). In this study, we tested whether PKCα could be downregulated via small interfering RNA (siRNA)-PKCα released from foldable capsular vitreous body (FCVB) in cultured human RPE cells. SiRNA-PKCα content, determined by ultraviolet (UV) spectrophotometer, was released from FCVB containing 200, 300, 400, 500, and 600 nm siRNA-PKCα in a time-dependent manner from 1 to 96 hours and a dose-dependent manner at five concentrations. The content (y) had a good linear relationship with time (x), especially in the 600 nm siRNA-PKCα group (y = 16.214x, R² = 0.9809). After treatment with siRNA-PKCα released from FCVBs, the PKCα was significantly decreased by RT-PCR, Western blot, and immunofluorescence analysis in RPE cells. These results indicate that PKCα was significantly downregulated by siRNA-PKCα released from FCVB in human RPE cells and provide us with a new avenue to prevent PVR.

Integrin alpha5beta1 mediates attachment, migration, and proliferation in human retinal pigment epithelium: relevance for proliferative retinal disease

PURPOSE

The aim of this study was to determine the expression and localization of integrin alpha5beta1 in human retinal pigment epithelium (RPE) and its ability to modulate RPE cell attachment, proliferation, migration, and F-actin cytoskeleton distribution.

METHODS

Expression and localization of alpha5beta1 were analyzed on human RPE by immunoblot/immunofluorescence. Polarized secretion of fibronectin was measured. RPE attachments to different substrates were determined using cell attachment screening kits. BrdU incorporation and wound-healing assays were used to test hfRPE proliferation and migration. F-actin cytoskeleton was visualized with phalloidin.

RESULTS

Integrin alpha5beta1 was detected in native adult and fetal human RPE. The alpha5-subunit is predominantly localized at the apical membrane of hfRPE, whereas the beta1-subunit is uniformly detected at the apical/basolateral membranes. The authors also found that hfRPE cultures secrete significant amounts of fibronectin to the apical bath. JSM6427, a specific integrin alpha5beta1 antagonist, significantly inhibited hfRPE cell attachment to fibronectin, but not laminin, or collagen I or IV. JSM6427 also showed a strong inhibitory effect on bFGF, PDGF-BB, and serum-induced cell migration and proliferation. Furthermore, JSM6427 induced significant disruption of the F-actin cytoskeleton of dividing RPE cells but had no effect on quiescent cells.

CONCLUSIONS

The apical localization of alpha5beta1 and the secretion of fibronectin to the apical bath suggest the presence of an autocrine loop that can guide the migration of RPE. The strong inhibitory effects of JSM6427 on human RPE cell attachment, proliferation, and migration is probably mediated by F-actin cytoskeletal disruption in proliferating cells and suggests a potential clinical use of this compound in proliferative retinopathies.

Involvement of protein kinase C in phagocytosis of human retinal pigment epithelial cells and induction of matrix metalloproteinase secretion

Protein kinase C (PKC) is involved in cell activation. We investigated PKC-mediated pathways and secretion of matrix metalloproteinases (MMPs) in phagocytosis by human retinal pigment epithelial cells (RPE). We used time-resolved fluorometry for europium-labeled microsphere uptake and gel zymography to assay the influence of PKC modulators. PKC inhibitors blocked phagocytosis by RPE. ARPE-19, a human RPE-cell line, showed reduced secretion of MMP-2, although MMP-9 secretion by PKC activation was conserved in both cell types, namely in the primary RPEs and in the RPE-cell line. Particle uptake by RPE cells requires activation of PKC; the use of PKC inhibitors as new anticancer drugs may possibly cause ocular side-effects.

Expression of protein kinase C isoforms in cultured human retinal pigment epithelial cells

BACKGROUND

Protein kinase C (PKC) is involved in both physiological and pathophysiological processes and plays an important role in signal transduction. The present studies were designed to examine the 12 isoforms (PKCalpha, PKCbetaI, PKCbetaII, PKCgamma, PKCdelta, PKCepsilon, PKCeta, PKCtheta, PKCmu, PKCxi, PKClambda and PKCiota) of PKC expressed in cultured human retinal pigment epithelium (RPE) cells.

METHODS

Human RPE cells were investigated for 12 PKC isoforms at the mRNA, protein and cellular levels by reverse transcription (RT)-PCR, Western blot analysis and laser scanning confocal microscope (LSCM), respectively.

RESULTS

RT-PCR and Western blot analyses showed similar results for specific PKC isoforms in that both revealed that PKCalpha, PKCbetaI, PKCbetaII, PKCdelta, PKCepsilon, PKCtheta, PKCmu, PKCxi, PKClambda and PKCiota, but not PKCgamma and PKCeta, were constantly expressed in RPE cells, with the exception of PKCbetaI at the protein level. Confocal microscopy showed that ten PKC isoforms - PKCalpha, PKCbetaI, PKCbetaII, PKCdelta, PKCepsilon, PKCtheta, PKCxi, PKCiota, PKClambda and PKCmu - appeared almost exclusively in the cytoplasm of the cells. However, PKCgamma and PKCeta were not detected by staining.

CONCLUSIONS

This study characterized the expression pattern of all 12 PKC isoforms and showed that ten of these (PKCalpha, PKCbetaI, PKCbetaII, PKCdelta, PKCepsilon, PKCtheta, PKCmu, PKCxi, PKClambda and PKCiota) are present in cultured human RPE cells. This identification provides the first step towards elucidating their roles in RPE cell proliferation.

The adenomatous polyposis coli protein: the Achilles heel of the gut epithelium

The Adenomatous Polyposis coli (APC) gene is mutated or lost in most colon cancers, and the APC protein has emerged as a multifunctional protein that is not only involved in the Wnt-regulated degradation of -catenin, but also regulates cytoskeletal proteins and thus plays a role in cell migration, cell adhesion, and mitosis. The gut epithelium is uniquely dependent on an intricate balance between a number of fundamental cellular processes including migration, differentiation, adhesion, apoptosis, and mitosis. In this review, I discuss the molecular mechanisms that govern the various functions of APC and their relationship to the role of APC in colon cancer.

Uveal Melanocytes Produce Matrix Metalloproteinases-2 and -9 In Vitro

The purpose of the present study was to investigate the expression of matrix metalloproteinase (MMP)-2 and MMP-9 by cultured human uveal melanocytes, and to test the effects of 12-O-tetradecanoyl-phorbol-13-acetate on the expression of these MMPs. Gelatin zymography of conditioned culture medium from four cultures of human uveal melanocytes (two cultures of iridal melanocytes and two cultures of choroidal melanocytes) detected MMP-2 (72 kDa) and a relatively small amount of MMP-9 (92 kDa), both in the latent form. RT-PCR analysis revealed the MMP-2 mRNA and MMP-9 mRNA in cultured uveal melanocytes. Addition of 12-O-tetradecanoyl-phorbol-13-acetate (10 ng/ml) to the culture medium caused an increase of production of MMP-2 and MMP-9 by cultured uveal melanocytes, and also stimulated the transcription of MMP-2 and MMP-9 of these cells.

Actin-dependent, retrograde motility of surface-attached beads and aggregating pigment granules in dissociated teleost retinal pigment epithelial cells

Teleost retinal pigment epithelial (RPE) cells contain pigment granules within apical projections which undergo actin-dependent, bi-directional motility. Dissociated RPE cells in culture attach to the substrate and extend apical projections in a radial array from the central cell body. Pigment granules within projections can be triggered to aggregate or disperse by the presence or absence of 1 mM cAMP. Aminated, fluorescent latex beads attached to the dorsal surface of apical projections and moved in the retrograde direction, towards the cell body. Bead rates on RPE cells with aggregating or fully aggregated pigment granules were 2.2 +/- 0.5 and 2.6 +/- 0.2 microm/min (mean +/- SEM), respectively, similar to rates of aggregating (retrograde) pigment granule movement (2.0 +/- 0.4 microm/min). Bead rates were slightly slower on cells with fully dispersed or dispersing pigment granules (1.5 +/- 0.1 and 1.5 +/- 0.4 microm/min). Movements of surface-attached beads and aggregating pigment granules were closely correlated in the distal portions of apical projections, but were more independent of each other in proximal regions of the projections. The actin disrupting drug, cytochalasin D (CD), reversibly halted retrograde bead movements, suggesting that motility of surface-attached particles is actin-dependent. In contrast, the microtubule depolymerizing drug, nocodazole, had no effect on retrograde bead motility. The similar characteristics and actin-dependence of retrograde bead movements and aggregating pigment granules suggest a correlation between these two processes.

Involvement of the muscarinic acetylcholine receptor in inhibition of cell migration

Activation of G protein-coupled receptors is known to stimulate cell migration, but receptor-mediated signals inhibiting cell migration have not been identified. We investigated the ability of transfected human M(3) muscarinic acetylcholine receptors (mAChR) to regulate the migration of Chinese hamster ovary (CHO) cells. Single cells migrated on colloidal gold applied to fibronectin-coated plates, and videomicroscopy was used to measure cell spreading and migration. Activation of M(3) mAChR with the agonist carbachol was found to inhibit cell migration, whereas direct activation of protein kinase C (PKC) with PMA was found to stimulate migration. The amount of cell adhesion and spreading was found to be equivalent for carbachol- and PMA-treated cells. Selective inactivation of conventional PKC isoforms with Go6976 (C(24)H(18)N(4)O) abolished the PMA-mediated increase in cell migration. In contrast, the mAChR-mediated decrease in migration was not altered by Go6976, but was abolished when both novel and conventional PKC isoforms were inactivated by calphostin C or chelerythrine. These findings suggest involvement of conventional PKC isoforms in the stimulation of migration and of novel PKC isoforms in the inhibition of migration. Carbachol- but not PMA-treated cells exhibited an elongated morphology reminiscent of migrating cells that cannot detach their trailing edges from the substratum. Similarly, carbachol-treated cells detached less readily from fibronectin than control or PMA-treated cells when integrin activity was diminished by the chelation of Ca(2+) and Mg(2+). Finally, the carbachol-induced diminution of cell detachment was preserved after inhibition of the conventional PKC isoforms with Go6976, but was abrogated by treatment with either calphostin C or chelerythrine. These findings suggest that mAChR activation diminishes the ability of cells to detach from the substratum, resulting in diminished migration. This is in contrast to the direct activation of PKC with PMA, which stimulates migration.

Intracellular signaling pathway of FGF-2-modulated corneal endothelial cell migration during wound healing in vitro

After wounding, the corneal endothelium heals primarily by migration of adjacent cells into the denuded wound area. In this study, it has been attempted to identify elements of the intracellular signaling pathway activated through basic Fibroblast Growth Factor (FGF-2)- and Protein Kinase C (PKC)-modulated migration, using specific inhibitors and stimulators of second messengers in a cell culture model. Bovine corneal endothelial cells (BCEC) were grown to confluency and experiments performed with first passage cells under serum-free conditions. A central circular 'wound' was made with a specially designed trephine. In different experiments, cells were incubated with either FGF-2 (10 ng ml(-1)), pertussis toxin (PTX; 1-50 ng ml(-1)), phorbol 12-myristate 13-acetate (PMA; 50 ng ml(-1)), 2,4'-di-bromoacetophenone (DAP; 5 microM), 1-(5-iosquinolinesulphonyl)-2-methyl-piperazine dihydrochloride (H7; 10 microM), indomethacin (5 ng ml(-1)), nordihydroguaiaretic acid (NDGA; 10 ng ml(-1)), 2-(4-morpholinyl)-8-pheny-4H-1-benzopyran-4-one (LY294002; 10 microM) or different combinations of these agents. Unsupplemented cultures served as controls. Migration was quantitated by counting the cells inside the denuded area in one randomly chosen section from the wound edge 72 hr after wounding. Cell toxicity was determined with the trypan blue exclusion test. Results were statistically analysed by Student's t-test. FGF-2 and PMA (a protein kinase C activator) both stimulated migration of endothelial cells at 2.2- and 3.1-fold, respectively. The PLA(2) inhibitor DAP and the PKC inhibitor H7 both significantly reduced PMA-stimulated migration to control levels but had no effect (DAP) or even stimulated (H7) FGF-2-modulated migration. PTX did not affect FGF-2-stimulated migration. The phosphoinositol (3)-kinase inhibitor LY294002 significantly reduced FGF-2-mediated stimulation of endothelial migration similar to the rate of control cultures. LY294002 had no effect when applied together with PMA. The cyclooxygenase inhibitor indomethacin did not influence migration rates of the cells added either alone or in combination with PMA and FGF-2, respectively. The lipoxygenase inhibitor NDGA significantly reduced the number of migrating cells in cultures with no other supplements, or of those supplemented with either PMA or FGF-2. FGF-2-induced endothelial migration in vitro is not dependent on PKC/PLA(2) or pertussis-toxin sensitive G-protein pathways but rather requires activation of a phosphoinositol (3)-kinase-like enzyme and/or arachidonic acid release with subsequent liberation of lipoxygenase products. Independent of FGF-2, PKC is a major intracellular effector of corneal endothelial migration activity after wounding and stimulates migration via the PLA(2)-dependent generation of lipoxygenase metabolites.

Effect of thalidomide, octreotide, and prednisolone on the migration and proliferation of RPE cells in vitro

PURPOSE

The retinal pigment epithelium (RPE) is involved in the pathogenesis of age-related macular degeneration. The purpose of this study was to assess the effect of thalidomide, octreotide, and prednisolone on the proliferation and migration of bovine RPE cells in vitro.

METHODS

The migration assay was performed in double-chamber-wells separated by a membrane filter with 8 microm pores. Cells were allowed to migrate vertically for 7 hr, afterwards the cells on both filtersides were fixed, stained, and the migrated cells were counted. To examine RPE proliferation, bovine RPE cells were seeded subconfluently followed by an incubation with octreotide, thalidomide or prednisolone in a concentration gradient for 24 hr. Stimulation or inhibition of DNA synthesis was measured by [(3)H]-thymidine incorporation. Statistical analysis was performed with the paired student's t-test.

RESULTS

Statistically significant (p < 0.05) inhibition of RPE cell proliferation was measured for thalidomide at a concentration of 10-50 microg/ml, for octreotide at a concentration of 5 x 10(-4) and 5 x 10(-5) M, and for prednisolone at a concentration of 250 and 500 microg/ml as compared to the negative control. RPE cell migration was significantly (p < 0.05) inhibited by thalidomide at a concentration of 10 microg/ml, by octreotide at a concentration of 5 x 10(-5) M, and also by prednisolone at a concentration of 500 microg/ml as compared to the negative control.

CONCLUSIONS

Although the main effect of thalidomide, octreotide, and prednisolone when treating patients with choroidal neovascular membranes is probably related to the inhibition of angiogenesis it should be kept in mind that these substances may additionally inhibit RPE proliferation and migration.

The antidepressant hypericin inhibits progression of experimental proliferative vitreoretinopathy

PURPOSE

Hypericin, a polycyclic dione used as an antidepressant, has been shown to inhibit the protein kinase C (PKC) pathway. Many of the pathologic responses found in proliferative vitreoretinopathy (PVR) are dependent upon PKC. Therefore, we studied the effect of hypericin on the treatment of experimental PVR.

METHODS

PVR was induced in pigmented rabbits by intravitreal injection of 50,000 rabbit conjunctival fibroblasts after vitrectomy. Subsequently, the eyes received an intravitreal injection of either balanced salt solution (BSS, 0.1 mL) (group A, control) or hypericin (0.1 mL) in doses of 1 muM (group B), 10 muM (group C), and 100 muM (group D). The eyes were examined ophthalmoscopically on days 1, 3, 7, 14, and 28 after surgery and the stage of PVR was evaluated (0 to V). The effect of hypericin on retinal morphology and function was also determined for the eyes injected with 100 muM hypericin with no fibroblasts by light microscopy and electroretinogram (ERG).

RESULTS

In the control eyes, the retina was detached after 5 days, membranes had formed on and beneath it, and the PVR had progressed to higher stages over time. In the eyes injected with hypericin, the PVR also progressed; however, the severity of PVR on each day was lower than that in control eyes on that day. PVR was significantly inhibited in groups C and D as compared with the control eyes after day 5 (P < 0.05). Histological examination of the hypericin-treated control eyes disclosed no morphological change, and ERG analysis revealed no significant functional change.

CONCLUSIONS

Intravitreal injection of hypericin is a safe and effective means of reducing experimental PVR.

Verapamil inhibits proliferation, migration and protein kinase C activity in human retinal pigment epithelial cells

The effects of three calcium channel blockers, verapamil, diltiazem and nifedipine, were examined on in vitro proliferation and migration of human retinal pigment epithelial cells. Human retinal pigment epithelial cells were seeded in Dulbecco's modified essential medium with 10% fetal bovine serum and different concentrations of the three calcium channel blockers. After 3 days of treatment, cell proliferation was determined by cell counting and by [3H]-thymidine uptake. Cell viability was determined with trypan blue exclusion. For determination of cell migration, retinal pigment epithelial cells were grown to confluence and then growth-inhibited with mitomycin C. After a 3 mm zone was denuded, the cells were treated with different concentrations of the calcium channel antagonists. After 24 hr, the cells that had migrated over the wound edge were counted. To determine the involvement of protein kinase C in the verapamil effect, its activity was measured in both verapamil-treated and untreated cells. Verapamil dose dependently inhibited serum-induced proliferation of retinal pigment epithelial cells, when measured by cell number (IC50 14.6 microM) or [3H]-thymidine incorporation (IC50 11.3 microM). At concentrations of 15 microM and below, there was no effect on cell viability, as determined by morphology and trypan blue exclusion. Diltiazem inhibited cell proliferation at a concentration of 100 microM; however, 100 microM nifedipine had no effect. Verapamil showed a significant inhibition of serum-induced migration in the range of 10 microM to 0.1 microM. The IC50 of the inhibition of retinal pigment epithelial cell proliferation and migration by verapamil is significantly higher than that seen for effects on calcium channel blockage. Eight micromolar verapamil reversibly inhibited total protein kinase-C activity in retinal pigment epithelial cells suggesting the possibility that the drug may act by inhibiting the protein kinase-C pathway. These data suggest the potential of the calcium channel blocker verapamil as a pharmacological modulator of disorders such as proliferative vitreoretinopathy in which there is increased retinal pigment epithelial cell proliferation and migration.

Differential translocation of protein kinase C isozymes by phorbol esters, EGF, and ANG II in rat liver WB cells

The protein kinase C (PKC) family represents an important group of enzymes whose activation is associated with their translocation from the cytosol to different cellular membranes. In this study, the spatial distribution of PKC-alpha, -delta and -epsilon in rat liver epithelial (WB) cells has been examined by Western blot analysis after subcellular fractionation. Cytosolic, membrane, nuclear, and cytoskeletal fractions were obtained from cells stimulated with phorbol 12-myristate 13-acetate (PMA), angiotensin II (ANG II), or epidermal growth factor (EGF). PMA caused most of the PKC-alpha, -delta and -epsilon initially present in the cytosol to be transported to the membrane and nuclear fractions. In contrast, both ANG II and EGF induced only a minor translocation of PKC-alpha to the membrane fraction but caused a statistically significant membrane-directed movement of PKC-delta and -epsilon. Translocation of PKC-delta and -epsilon to the nucleus induced by ANG II and EGF was transient and quantitatively smaller than that induced by PMA. PKC-delta and -epsilon were present in the cytoskeleton of resting cells, but although PMA, ANG II, and EGF caused some changes in their content, these were variable, suggesting that the cytoskeleton fraction was heterogeneous. PKC depletion inhibited ANG II-induced mitogenesis and the sustained activation of Raf-1 and extracellular regulated protein kinase (ERK). However, although PKC depletion inhibited EGF-induced mitogenesis, the maximum EGF-induced activation of the ERK pathway was only slightly retarded. We hypothesize that PKC-delta and -epsilon are involved in mitogenesis via both ERK-dependent and ERK-independent mechanisms. These results support the notion that specific PKC isozymes exert spatially defined effects by virtue of their directed translocation to distinct intracellular sites.

Mitogen-activated protein kinase activation mediates PDGF-directed migration of RPE cells

Growth factor-directed migration is a critical component of the wound healing response although little is known about the signaling pathways involved. We examined the effect of inhibiting the mitogen-activated protein kinase (MAPK) pathway on platelet-derived growth factor (PDGF) and fibronectin-induced cell migration of human retinal pigment epithelial (RPE) cells. Using transwell cell-culture chambers, the effect of PDGF-BB (10-50 ng/ml) and fibronectin on components of migration was measured with or without the MAPK pathway inhibitor PD98059 (10-30 microM) MAPK activation of serum-starved cells by PDGF-BB was demonstrated by an immunoprecipitation/kinase assay and by immunohistochemistry using antibody specific for phosphorylated MAPK. PDGF-BB (10 ng/ml) stimulated MAPK activity in RPE (10 min) and its nuclear localization (1 h). PD98059 inhibited the activation of MAPK by PDGF-BB or serum. PDGF-BB stimulated RPE chemokinesis, chemotaxis, and haptotaxis; chemokinesis was additively increased and chemotaxis synergistically increased by the presence of a fibronectin substratum. PD98059 potently inhibited fibronectin-induced haptotaxis and PDGF-BB-induced chemotaxis but inhibited chemokinesis only at higher PDGF-BB (50 ng/ml) concentrations in the presence of fibronectin substratum. These results demonstrate that MAPK is critically involved in multiple components of RPE migration in vitro and suggest the potential of targeting MAPK to inhibit RPE migration in vivo.

A phospholipase D and protein kinase C inhibitor blocks the spreading of murine mammary adenocarcinoma cells altering f-actin and beta1-integrin point contact distribution

Spreading is a critical process involved in motility and growth of tumor cells during the metastatic cascade. Focal adhesion kinase, src-proteins and PKC have been reported to participate in the regulation of cytoskeleton organization in both normal and transformed cells during spreading. The role of other signaling enzymes such as PLD and PAP has not been studied during spreading in tumor cells. We now show that the spreading of murine mammary adenocarcinoma LM3 cells was significantly reduced by n-butanol, a PLD and PKC inhibitor, with a maximal inhibition of 54% (p < 0.001) in both the presence and absence of serum, as measured by phase-contrast microscopy. PMA only stimulated cell spreading over the control in the absence of serum and n-butanol inhibition was completely reversed by PMA treatment in both conditions. PA, the product of PLD activity, stimulated LM3 cell spreading and the same effect was observed with staurosporine. Spreading was enhanced when cells were seeded on collagen-IV- or fibronectin-coated surfaces and n-butanol could inhibit both integrin-derived signals. Cell spreading inhibition correlated with the absence of f-actin bundles and fewer beta1-integrin point contacts as determined by double immunofluorescence microscopy. In addition, n-butanol inhibited the proliferation of LM3 cells in the presence of serum (p < 0.01). These results suggest that beta1-integrin and f-actin/point contact assembly, involved in spreading and proliferation, require the participation of PLD-PKC regulatory pathways in LM3 cells.

Vitamin E succinate inhibits proliferation and migration of retinal pigment epithelial cells in vitro: therapeutic implication for proliferative vitreoretinopathy

BACKGROUND

Retinal pigment epithelial (RPE) cells play an important role in proliferative vitreoretinopathy (PVR). Vitamin E succinate is an ester form of a potent biological antioxidant, vitamin E, and has unique effects on various cells. We examined the effect of vitamin E succinate on proliferation and migration of cultured bovine RPE cells, since these are critical steps in the development of PVR.

METHODS

Bovine RPE cells were cultured in minimal essential medium (MEM) containing 10% fetal calf serum (MEM-10). Cells were incubated with MEM-10 containing 25 microM vitamin E, vitamin E succinate, butylated hydroxytoluene (BHT) or d-mannitol. Cell proliferation was assessed by counting cell numbers on days 2, 4 and 6. 3H-Thymidine uptake was also examined in RPE cells incubated with various forms of vitamin E-- vitamin E, vitamin E succinate, Trolox, gamma-tocopherol, vitamin E acetate, vitamin E phosphate, vitamin E nicotinate--or antioxidants-- BHT or d-mannitol (25 microM each). RPE cell migration was studied as follows: A small area (5 x 15 mm) of confluent cultured RPE cells was denuded using a straight razor blade and incubation was continued for 20 h with MEM-10 containing vitamin E, vitamin E succinate, gamma-tocopherol or BHT. The number of cells that migrated into the denuded area from the wound edge in each microscopic field (x20) was counted and expressed as a percentage of control (MEM-10 alone).

RESULTS

The antioxidants, vitamin E and BHT, stimulated RPE cell proliferation and 3H-thymidine incorporation compared with the control, while vitamin E succinate significantly inhibited both proliferation and 3H-thymidine uptake (IC50, 23 microM). Other forms of vitamin E or d-mannitol had no effect. Neither vitamin E nor BHT had a significant effect on RPE cell migration (108.2% and 112.6% of control, respectively), but vitamin E succinate inhibited migration (58.3%). Cell viability, assessed by the trypan blue dye exclusion test, was not impaired by a 3-day incubation with 50 microM of vitamin E succinate.

CONCLUSIONS

An ester form of a physiological antioxidant, vitamin E succinate, inhibits RPE cell proliferation and migration without causing cellular toxicity. These findings suggest its therapeutic potential for the pharmacological treatment of PVR.