Thrombin stimulates RPE cell proliferation by promoting c-Fos-mediated cyclin D1 expression

Transcriptome analysis reveals key transcription factors and pathways of polian vesicle associated with cell proliferation in Vibrio splendidus-challenged Apostichopus japonicus

Polian vesicle is thought to produce coelomocytes and contribute to the sea cucumber's immune system. Our previous work has indicated that polian vesicle was responsible for cell proliferation at 72 h post pathogenic challenge. However, the transcription factors related to the activation of effector factors and the molecular process behind this remained unknown. In this study, to reveal the early functions of polian vesicle in response to the microbe, a comparative transcriptome sequencing of polian vesicle in V. splendidus-challenged Apostichopus japonicus, including normal group (PV 0 h), pathogen challenging for 6 h (PV 6 h) and 12 h (PV 12 h) was performed. Compared PV 0 h to PV 6 h, PV 0 h to PV 12 h, and PV 6 h to PV 12 h, we found 69, 211, and 175 differentially expressed genes (DEGs), respectively. KEGG enrichment analysis revealed the DEGs, including several transcription factors such as fos, FOS-FOX, ATF2, egr1, KLF2, and Notch3 between PV 6 h and PV 12 h were consistently enriched in MAPK, Apelin and Notch3 signaling pathways related to cell proliferation compared with that in PV 0 h. Important DEGs involved in cell growth were chosen, and their expression patterns were almost the same as the transcriptome profile analysis by qPCR. Protein interaction network analysis indicated that two DEGs of fos and egr1 were probably significant as key candidate genes controlling cell proliferation and differentiation in polian vesicle after pathogenic infection in A. japonicus. Overall, our analysis demonstrates that polian vesicles may play an essential role in regulating proliferation via transcription factors-mediated signaling pathway in A. japonicus and provide new insights into hematopoietic modulation of polian vesicles in response to pathogen infection.

Thrombin-activated PAR1 membrane expression is regulated by Rab11a-RCP complex dissociation

PAR1 activation by thrombin promotes intracellular signaling leading to RPE cell transformation, proliferation, and migration, characteristic of fibroproliferative eye diseases. Due to the cleavage of PAR1 N-terminal domain, carried by thrombin, the arrest of PAR1 signaling is achieved by transport into lysosomes and degradation. Recent findings suggest that the GTPase Rab11a in conjunction with its effector RCP may direct PAR1 to lysosomes. Hereby we demonstrate that thrombin-induced PAR1 internalization and lysosomal targeting requires the disassembly of the Rab11a/RCP complex, and that this process depends on thrombin-induced intracellular calcium increase and calpain activation. These findings unveil a novel mechanism that regulates thrombin activated PAR1 internalization and degradation.

Identification of genes and genetic networks associated with BAG3‑dependent cell proliferation and cell survival in human cervical cancer HeLa cells

Bcl‑2‑associated athanogene (BAG) 3, is a member of the BAG protein family and a known co‑chaperone of heat shock protein (HSP) 70. BAG3 serves a role in regulating a variety of cellular functions, including cell growth, proliferation and cell death including apoptosis. BAG3 is a stress‑inducible protein, however the constitutive expression level of BAG3 is increased in cancer cells compared with healthy cells. Recent proteomics technology combined with bioinformatics has revealed that BAG3 participates in an interactome with a number of proteins other than its typical partner HSP70. The functional types represented in the interactome included nucleic acid binding proteins and transcription factors, as well as chaperones, which indicated that overexpression of BAG3 may contribute to proliferation and cell survival through the alteration of gene transcription. While an increasing number of studies have addressed the function of BAG3 as a co‑chaperone protein, BAG3‑dependent alteration of gene transcription has not been studied extensively. The present study established two BAG3 knockout human cervical cancer HeLa cell clones and addressed the role of BAG3 in cell proliferation and survival through gene transcription, using DNA microarray‑based transcriptome analysis and bioinformatics. The present study also identified two genetic networks associated with 'cellular growth and proliferation' and 'cell death and survival', which are dysregulated in the absence of BAG3, and may therefore be linked to BAG3 overexpression in cancer. These findings provide a molecular basis for understanding of BAG3‑dependent cell proliferation and survival from the aspect of alteration of gene expression.

Reduction of CRKL expression in patients with partial DiGeorge syndrome is associated with impairment of T-cell functions

BACKGROUND

Partial DiGeorge syndrome (pDGS) is caused by deletion of the 22q11.2 region. Within this region lies CrK-like (CRKL), a gene encoding an adapter protein belonging to the Crk family that is involved in the signaling cascade of IL-2, stromal cell-derived factor 1α, and type I interferon. Although recurrent infections can be observed in patients with deletion of chromosome 22 syndrome, the immune pathogenesis of this condition is yet not fully understood.

OBJECTIVE

We aimed to investigate the role of CRKL in T-cell functional responses in patients affected with pDGS.

METHODS

Protein expression levels and phosphorylation of CRKL were evaluated in patients with pDGS. T-cell functional assays in vitro and gene-silencing experiments were also performed.

RESULTS

CRKL protein expression, as well as its phosphorylation, were reduced in all patients with pDGS, especially on IL-2 stimulation. Moreover, T cells presented impaired proliferation and reduced IL-2 production on anti-CD3/CD28 stimulation and decreased c-Fos expression. Finally, CRKL silencing in Jurkat T cells resulted in impaired T-cell proliferation and reduced c-Fos expression.

CONCLUSIONS

The impaired T-cell proliferation and reduction of CRKL, phosphorylated CRKL, and c-Fos levels suggest a possible role of CRKL in functional deficiencies of T cells in patients with pDGS.

VEGF/VEGFR2 Signaling Regulates Germ Cell Proliferation in vitro and Promotes Mouse Testicular Regeneration in vivo

Vascular endothelial growth factor (VEGF) plays fundamental roles in testicular development; however, its function on testicular regeneration remains unknown. The objective of this study was to explore the roles VEGF/VEGFR2 signaling plays in mouse germ cells and in mouse testicular regeneration. VEGF and the VEGFR2 antagonist SU5416 were added to culture medium to evaluate their effects on spermatogonial stem cell line (C18-4 cells) proliferation. Testicular cells obtained from newborn male ICR mice were grafted into the dorsal region of male BALB/c nude mice. VEGF and SU5416 were injected into the graft sites to assess the effects of the VEGF and VEGFR2 signaling pathways on testicular reconstitution. The grafts were analyzed after 8 weeks. We found that VEGF promoted C18-4 proliferation in vitro, indicating its role in germ cell survival. HE staining revealed that seminiferous tubules were reconstituted and male germ cells from spermatogonia to spermatids could be observed in testis-like tissues 8 weeks after grafting. A few advantaged male germ cells, including spermatocytes and spermatids, were found in SU5416-treated grafts. Moreover, VEGF enhanced the expression of genes specific for male germ cells and vascularization in 8-week grafts, whereas SU5416 decreased the expression of these genes. SU5416-treated grafts had a lower expression of MVH and CD31, indicating that blockade of VEGF/VEGFR2 signaling reduces the efficiency of seminiferous tubule reconstitution. Collectively, these data suggest that VEGF/VEGFR2 signaling regulates germ cell proliferation and promotes testicular regeneration via direct action on germ cells and the enhancement of vascularization.

Analysis of the ways and methods of signaling pathways in regulating cell cycle of NIH3T3 at transcriptional level

BACKGROUND

To analyze the ways and methods of signaling pathways in regulating cell cycle progression of NIH3T3 at transcriptional level, we modeled cell cycle of NIH3T3 and found that G1 phase of NIH3T3 cell cycle was at 5-15 h after synchronization, S phase at 15-21 h, G2 phase at 21-22 h, M phase at 22-25 h.

RESULTS

Mouse Genome 430 2.0 microarray was used to detect the gene expression profiles of the model, and results showed remarkable changes in the expressions of 64 cell cycle genes and 960 genes associated with other physiological activity during the cell cycle of NIH3T3. For the next step, IPA software was used to analyze the physiological activities, cell cycle genes-associated signal transduction activities and their regulatory roles of these genes in cell cycle progression, and our results indicated that the reported genes were involved in 17 signaling pathways in the regulation of cell cycle progression. Newfound genes such as PKC, RAS, PP2A, NGR and PI3K etc. belong to the functional category of molecular mechanism of cancer, cyclins and cell cycle regulation HER-2 signaling in breast cancer signaling pathways. These newfound genes could promote DNA damage repairment and DNA replication progress, regulate the metabolism of protein, and maintain the cell cycle progression of NIH3T3 modulating the reported genes CCND1 and C-FOS.

CONCLUSION

All of the aforementioned signaling pathways interacted with the cell cycle network, indicating that NIH3T3 cell cycle was regulated by a number of signaling pathways.

The influences of purple sweet potato anthocyanin on the growth characteristics of human retinal pigment epithelial cells

Background

Anthocyanins have been proven to be beneficial to the eyes. However, information is scarce about the effects of purple sweet potato (Ipomoea batatas, L.) anthocyanin (PSPA), a class of anthocyanins derived from purple sweet potato roots, on visual health.

Objective

The aim of this study was to investigate whether PSPA could have influences on the growth characteristics (cellular morphology, survival, and proliferation) of human retinal pigment epithelial (RPE) cells, which perform essential functions for the visual process.

Methods

The RPE cell line D407 was used in the present study. The cytotoxicity of PSPA was assessed by MTT assay. Then, cellular morphology, viability, cell cycle, Ki67expression, and PI3K/MAPK activation of RPE cells treated with PSPA were determined.

Results

PSPA exhibited dose-dependent promotion of RPE cell proliferation at concentrations ranging from 10 to 1,000 µg/ml. RPE cells treated with PSPA demonstrated a predominantly polygonal morphology in a mosaic arrangement, and colony-like cells displayed numerous short apical microvilli and typical ultrastructure. PSPA treatment also resulted in a better platform growing status, statistically higher viability, an increase in the S-phase, and more Ki67+ cells. However, neither pAkt nor pERK were detected in either group.

Conclusions

We found that PSPA maintained high cell viability, boosted DNA synthesis, and preserved a high percentage of continuously cycling cells to promote cell survival and division without changing cell morphology. This paper lays the foundation for further research about the damage-protective activities of PSPA on RPE cells or human vision.

The FOS transcription factor family differentially controls trophoblast migration and invasion

Extravillous trophoblast invasion is a fundamental component of human placentation. Invading trophoblast cells promote blood flow to the conceptus by actively remodeling the uterine vasculature. The extent of trophoblast invasion is tightly regulated; aberrant invasion is linked with several obstetrical complications. However, the transcriptional networks responsible for controlling the extent of trophoblast invasion are not well defined. Previous studies have identified high levels of FOS (FOS, FOSB, FOS-like (FOSL) 1, and FOSL2) proteins in extravillous trophoblast cells. These proteins form part of the activating protein-1 (AP-1) transcription factor complex and are implicated in regulating gene networks controlling cellular invasion in diverse biological systems. Therefore, we hypothesized that FOS family proteins play a role in regulating trophoblast invasion. We assessed expression of FOS family proteins in trophoblast cell lines and human placentae at different gestational ages. FOS, FOSB, and FOSL1 proteins were robustly increased in trophoblast cells subject to wound-based migration assays as well as Matrigel-based invasion assays. FOS knockdown resulted in cessation of proliferation and an induction of migration and invasion concomitant with robust expression of matrix metalloproteinase (MMP) 1, MMP3, and MMP10. Conversely, FOSL1 knockdown abrogated trophoblast migration and invasion and inhibited the production of MMP1, MMP3, and MMP10. In human placenta, FOS was expressed in proximal anchoring villi in conjunction with phospho-ERK. FOSL1 was temporally expressed only in the distal-most extravillous trophoblast cells, which represent a migratory cell population. Therefore, FOS and FOSL1 exert opposing effects on trophoblast invasion.

Photocoagulation of human retinal pigment epithelial cells in vitro: evaluation of necrosis, apoptosis, cell migration, cell proliferation and expression of tissue repairing and cytoprotective genes

Aims

Sight-threatening diabetic retinopathy has been treated with photocoagulation for decades but the mechanisms behind the beneficial clinical effects are poorly understood. One target of irradiation and a potential player in this process is the retinal pigment epithelium (RPE). Here we establish an in vitro model for photocoagulation of human RPE cells.

Methods

ARPE-19 cells were exposed to photocoagulation and studied at various time points up to 168h. Lesion morphology, necrosis and apoptosis were investigated by light microscopy; LIVE/DEAD staining and measurements of lactate dehydrogenase activity; and TUNEL- and ELISA-based quantification of DNA fragments, respectively. Cell migration and proliferation were explored using docetaxel and mitomycin C; temporal and spatial changes in proliferation were assessed by confocal immunofluorescence of proliferating cell nuclear antigen. Gene expression was measured by qPCR.

Results

Photocoagulation of ARPE-19 resulted in denaturation of proteins and reproducible lesion formation. A transient peak in necrosis, followed by a peak in apoptosis was observed in cells within the lesions at 6h and 24h, respectively after photocoagulation. Cell proliferation was depressed during the first hours after photocoagulation, back to control levels at 24h and augmented in the following days. These effects were not limited to cells in the lesions, but also evident in neighbouring cells. Changes in cell proliferation during lesion repair were preceded by changes in cell migration. Altered mRNA expression of genes previously implicated in the regulation of cell proliferation (FOS, IL-1β, IL-8, HMGA2), migration and tissue repairing (TGFBR2, ADAMTS6, TIMP3, CTGF) was observed, as well as increased expression of the alarmin IL33 and the cytoprotective gene HSPA6.

Conclusions

Using a laser system and experimental settings that comply with standards used in clinical practice, we have established a suitable model for in vitro photocoagulation of human RPE cells to isolate their contribution to the beneficial effects of laser treatment.

Thrombin induces slug-mediated E-cadherin transcriptional repression and the parallel up-regulation of N-cadherin by a transcription-independent mechanism in RPE cells

The proliferation, directional migration to the vitreous and epithelial-mesenchymal transition (EMT) of quiescent, differentiated retinal pigment epithelium (RPE) cells is a major feature in the development of proliferative vitreoretinopathy (PVR) following exposure of the immuno-privileged eye niche to serum components, thrombin among them. We have previously documented thrombin induction of RPE cell proliferation and migration. We here analyzed the effect of thrombin on the E/N cadherin switch, a hallmark of EMT. Results show that thrombin induces the specific repression of epithelial E-cadherin gene transcription, alongside with the up-regulation of mesenchymal N-cadherin protein in RPE cells. We demonstrate, for the first time, that thrombin induces E-cadherin repression by stimulating snail-2 (SLUG) transcription factor expression, and the concomitant up-regulation of N-cadherin through the transcription-independent increase in protein translation promoted by PI3K/PKC-ζ/mTOR signaling. Our present findings suggest that the activation of protease-activated receptor-1 (PAR-1) by thrombin induces EMT of RPE cells, further supporting a central role for thrombin in PVR pathogenesis.

ERK1/2-dependent activation of mTOR/mTORC1/p70S6K regulates thrombin-induced RPE cell proliferation

Epithelial-mesenchymal transition (EMT), proliferation and migration of RPE cells characterize the development of proliferative vitreoretinopathy (PVR) and other fibro-proliferative eye diseases leading to blindness. A common event in these pathologies is the alteration of the BRB which allows the interaction of RPE cells with thrombin, a pro-inflammatory protease contained in serum. Thrombin promotion of cytoskeletal reorganization, proliferation, and migration has been reported in different cell types, although the molecular mechanisms involved in these processes remain poorly understood. Our previous work demonstrated that thrombin promotes RPE cell proliferation, cytoskeletal remodeling and migration, hallmark processes in the development of PVR. Thrombin induction of RPE cell proliferation requires PI3K, PDK1, and Akt/PKB (Akt) signaling leading to cyclin D1 gene expression. Since Akt functions as an upstream activator of mechanistic target of rapamycin complex 1 (mTORC1) and is also a downstream target for mTORC2, the aim of this work was to determine whether mTOR is involved in thrombin-induced RPE cell proliferation by regulating cyclin D1 expression in immortalized rat RPE-J cell line. Results demonstrate that thrombin-induced cyclin D1 expression and cell proliferation require Akt-independent phosphorylation/activation of mTOR at Ser 2448 mediated by PI3K/PKC-ζ/ERK1/2 signaling, concomitant to Akt-dependent activation of p70S6K carried by mTORC1.

Bradykinin-mediated cell proliferation depends on transactivation of EGF receptor in corneal fibroblasts

In previous studies, bradykinin (BK) has been shown to induce cell proliferation through BK B2 receptor (B2R) via p42/p44 MAPK in Statens Seruminstitut Rabbit Corneal Cells (SIRCs). In addition to this pathway, EGFR transactivation pathway has been implicated in linking a variety of G-protein coupled receptors to MAPK cascades. Here, we further investigate whether these transactivation mechanisms participating in BK-induced cell proliferation in SIRCs. Using an immunofluorescence staining and RT-PCR, we initially characterize that SIRCs were corneal fibroblasts and predominantly expressed B2R by BK. Inhibition of p42/p44 MAPK by the inhibitors of Src, EGFR, and Akt or transfection with respective siRNAs prevents BK-induced DNA synthesis in SIRCs. The mechanisms underlying these responses were mediated through phosphorylation of Src and EGFR via the formation of Src/EGFR complex which was attenuated by PP1 and AG1478. Moreover, BK-induced p42/p44 MAPK and Akt activation was mediated through EGFR transactivation, which was diminished by the inhibitors of MMP-2/9 and heparin-binding EGF-like factor (HB-EGF). Finally, increased nuclear translocation of Akt and p42/p44 MAPK turns on early gene expression leading to cell proliferation. These results suggest that BK-induced cell proliferation is mediated through c-Src-dependent transactivation of EGFR via MMP2/9-dependent pro-HB-EGF shedding linking to activation of Akt and p42/p44 MAPK in corneal fibroblasts.

New insights into the regulation of myosin light chain phosphorylation in retinal pigment epithelial cells

The retinal pigment epithelium (RPE) plays an essential role in the function of the neural retina and the maintenance of vision. Most of the functions displayed by RPE require a dynamic organization of the acto-myosin cytoskeleton. Myosin II, a main cytoskeletal component in muscle and non-muscle cells, is directly involved in force generation required for organelle movement, selective molecule transport within cell compartments, exocytosis, endocytosis, phagocytosis, and cell division, among others. Contractile processes are triggered by the phosphorylation of myosin II light chains (MLCs), which promotes actin-myosin interaction and the assembly of contractile fibers. Considerable evidence indicates that non-muscle myosin II activation is critically involved in various pathological states, increasing the interest in studying the signaling pathways controlling MLC phosphorylation. Particularly, recent findings suggest a role for non-muscle myosin II-induced contraction in RPE cell transformation involved in the establishment of numerous retinal diseases. This review summarizes the current knowledge regarding myosin function in RPE cells, as well as the signaling networks leading to MLC phosphorylation under pathological conditions. Understanding the molecular mechanisms underlying RPE dysfunction would improve the development of new therapies for the treatment or prevention of different ocular disorders leading to blindness.

MEK-ERK and heparin-susceptible signaling pathways are involved in cell-cycle entry of the wound edge retinal pigment epithelium cells in the adult newt

The onset mechanism of proliferation in mitotically quiescent retinal pigment epithelium (RPE) cells is still obscure in humans and newts, although it can be a clinical target for manipulating both retinal diseases and regeneration. To address this issue, we investigated factors or signaling pathways involved in the first cell-cycle entry of RPE cells upon retinal injury using a newt retina-less eye-cup culture system in which the cells around the wound edge of the RPE exclusively enter the cell cycle. We found that MEK-ERK signaling is necessary for their cell-cycle entry, and signaling pathways whose activities can be modulated by heparin, such as Wnt-, Shh-, and thrombin-mediated pathways, are capable of regulating the cell-cycle entry. Furthermore, we found that the cells inside the RPE have low proliferation competence even in the presence of serum, suggesting inversely that a loss of cell-to-cell contact would allow the cells to enter the cell cycle.

Apo- and holo-lactoferrin stimulate proliferation of mouse crypt cells but through different cellular signaling pathways

Lactoferrin (Lf), an iron-binding glycoprotein in human milk, plays an important role in intestinal epithelial cell proliferation, but the underlying molecular mechanisms remain unknown. Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinases (ERK) and the phosphoinositide 3-kinase (PI3K) cascades are chief pathways controlling cell proliferation. We hypothesized that Lf stimulates proliferation of intestinal epithelial cells by activating ERK and PI3K signaling cascades and that lactoferrin receptor (LfR) is involved in these processes. Confocal microscopy showed that LfR is expressed and localized at the plasma membrane of mouse crypt cells isolated from 7 to 10 days old pups, specifically binding both iron-free Lf (apo-Lf) and iron-saturated Lf (holo-Lf). Using the BrdU assay, we observed that apo-Lf had a stronger stimulatory effect than holo-Lf on proliferation of crypt cells. Both function-blocking antibody against LfR and MEK inhibitor (U0126) resulted in inhibitory effects on apo-Lf-induced cell proliferation, whereas PI3K inhibitor (LY294002) significantly decreased both apo- and holo-Lf-induced proliferation. Although both apo- and holo-Lf up-regulated transcription of cyclin D1, an effector of ERK1/2 and PI3K/Akt signaling cascades, only apo-Lf initiated ERK1/2 signaling and both apo- and holo-Lf were capable of activating the PI3K/Akt signaling pathway. Function-blocking antibody against LfR and LfR siRNA inhibited apo-Lf induced activation of the ERK1/2 signaling pathway, suggesting that LfR is involved in apo-Lf induced activation of the ERK1/2, but not the PI3K signaling pathway. In conclusion, apo-Lf and holo-Lf stimulate intestinal proliferation but through different signaling pathways.

Mature peripheral RPE cells have an intrinsic capacity to proliferate; a potential regulatory mechanism for age-related cell loss

BACKGROUND

Mammalian peripheral retinal pigmented epithelium (RPE) cells proliferate throughout life, while central cells are senescent. It is thought that some peripheral cells migrate centrally to correct age-related central RPE loss.

METHODOLOGY/PRINCIPAL FINDINGS

We ask whether this proliferative capacity is intrinsic to such cells and whether cells located centrally produce diffusible signals imposing senescence upon the former once migrated. We also ask whether there are regional differences in expression patterns of key genes involved in these features between the centre and the periphery in vivo and in vitro. Low density RPE cultures obtained from adult mice revealed significantly greater levels of proliferation when derived from peripheral compared to central tissue, but this significance declined with increasing culture density. Further, exposure to centrally conditioned media had no influence on proliferation in peripheral RPE cell cultures at the concentrations examined. Central cells expressed significantly higher levels of E-Cadherin revealing a tighter cell adhesion than in the peripheral regions. Fluorescence-labelled staining for E-Cadherin, F-actin and ZO-1 in vivo revealed different patterns with significantly increased expression on central RPE cells than those in the periphery or differences in junctional morphology. A range of other genes were investigated both in vivo and in vitro associated with RPE proliferation in order to identify gene expression differences between the centre and the periphery. Specifically, the cell cycle inhibitor p27(Kip1) was significantly elevated in central senescent regions in vivo and mTOR, associated with RPE cell senescence, was significantly elevated in the centre in comparison to the periphery.

CONCLUSIONS

These data show that the proliferative capacity of peripheral RPE cells is intrinsic and cell-autonomous in adult mice. These differences between centre and periphery are reflected in distinct patterns in junctional markers. The regional proliferation differences may be inversely dependent to cell-cell contact.

Thrombin promotes actin stress fiber formation in RPE through Rho/ROCK-mediated MLC phosphorylation

The retinal pigment epithelium (RPE) forms the outer blood-retina barrier (BRB). Most retinal diseases involve BRB breakdown, whereupon thrombin contained in serum directly contacts the RPE. Thrombin is known to promote actin stress fiber formation, an important determinant in eye diseases involving the epithelial-mesenchymal transition (EMT) and migration of RPE cells, such as proliferative vitreoretinopathy. We analyzed thrombin effect on signaling pathways leading to myosin light chain (MLC) phosphorylation and actin stress fiber formation in primary cultures of rat RPE cells, in order to support a role for thrombin in RPE transdifferentiation. MLC phosphorylation was measured by Western blot; actin cytoskeleton was visualized using immunofluorescent phalloidin, and Rho GTPase activation was assessed by ELISA. We showed that thrombin/PAR-1 induces the time- and dose-dependent phosphorylation of MLC through the activation of Rho/ROCK and myosin light chain kinase (MLCK). ROCK increased phospho-MLC by phosphorylating MLC and by inhibiting MLC phosphatase. Thrombin effect was abolished by the ROCK inhibitor Y-27632, whereas MLCK inhibitor ML-7 and PLC-β inhibitor U73122 attenuated MLC phosphorylation by ≈50%, suggesting the activation of MLCK by PLC-β-mediated calcium increase. Additionally, thrombin-induced MLC phosphorylation was blocked by the inhibitory PKCζ pseudosubstrate, wortmannin, and LY294002, indicating IP(3)/PKCζ involvement in the control of MLC phosphorylation. Moreover, we demonstrated that thrombin effect on MLC induces actin stress fiber formation, since this effect was prevented by inhibiting the pathways leading to MLC phosphorylation. We conclude that thrombin stimulation of MLC phosphorylation and actin stress fiber formation may be involved in thrombin-induced RPE cell transformation subsequent to BRB dysfunction.

Thrombin stimulates RPE cell motility by PKC-zeta- and NF-kappaB-dependent gene expression of MCP-1 and CINC-1/GRO chemokines

Retinal pigment epithelial cells (RPE) are the major cell type involved in the pathogenesis of proliferative vitreoretinopathy (PVR), which involves the epithelial-mesenchymal transition, proliferation, and directional migration of transformed RPE cells to the vitreous upon RPE exposure to serum components, thrombin among them. Although the aqueous humor and vitreous of PVR patients contain high levels of chemokines, their possible involvement in PVR development has not been explored. We here analyzed the effect of thrombin on chemokine gene expression and its correlation with RPE cell migration using rat RPE cells in culture as a model system. We demonstrated that thrombin induces RPE cell migration through the dose-dependent stimulation of MCP1 and GRO expression/release, and the autocrine activation of CXCR-2 and CCR-2 chemokine receptors. Whereas inhibition of CXCR2 by Sb-225002 and of CCR2 by Rs-504393 partially prevented hirudin-sensitive cell migration, the joint inhibition of these receptors abolished thrombin effect, suggesting the contribution of distinct but coincident mechanisms. Thrombin effects were not modified by Ro-32-0432 inhibition of conventional/novel PKC isoenzymes or by the MAPkinase pathway inhibitor U0126. MCP1 and GRO expression/secretion, and cell migration were completely prevented by the inhibitory PKC-zeta pseudosubstrate and by the nuclear factor-kappa B (NF-kappaB) inhibitor BAY11-7082, but not by wortmannin inhibition of PI3K. Results show that signaling pathways leading to RPE cell migration differ from the MEK-ERK-PI3K-mediated promotion RPE of cell proliferation, both of which concur at the activation of PKC-zeta.