Platelet-derived growth factor-BB and lysophosphatidic acid distinctly regulate hepatic myofibroblast migration through focal adhesion kinase

Lysophosphatidic acid as a regulator of endometrial connective tissue growth factor and prostaglandin secretion during estrous cycle and endometrosis in the mare

Background

Equine endometrosis is a chronic degenerative condition, described as endometrial fibrosis that forms in the stroma, under the basement membrane and around the endometrial glands. The role of lysophosphatidic acid (LPA) in the development of tissue fibrosis varies depending on the organ, and its profibrotic role in mare endometrosis remains unclear. The study aimed to establish the endometrial presence of LPA and its receptors (LPAR1–4), together with its effects on connective tissue growth factor (CTGF) and prostaglandins (PG) secretion from equine endometrium under physiological (estrous cycle), or pathological conditions (endometrosis). Mare endometria in the mid-luteal phase (n = 5 for each category I, IIA, IIB, III of Kenney and Doig) and in the follicular phase (n = 5 for each category I, IIA, III and n = 4 for IIB) were used. In experiment 1, the levels of LPA, LPAR1–4 mRNA level and protein abundance were investigated in endometria at different stages of endometrosis. In experiment 2, the in vitro effect of LPA (10^− 9 M) on the secretion of CTGF and PGs from endometrial tissue explants at different stages of endometrosis were determined.

Results

Endometrial LPA concentration was higher in the mid-luteal phase compared to the follicular phase in category I endometrium (P < 0.01). There was an alteration in endometrial concentrations of LPA and LPAR1–4 protein abundance in the follicular phase at different stages of endometrosis (P < 0.05). Additionally, LPA increased the secretion of PGE₂ from category I endometrium in both phases of the estrous cycle (P < 0.05). The effect of LPA on the secretion of CTGF and PGF_2α from endometrial tissue was altered depending on different stages of endometrosis (P < 0.05).

Conclusion

Our data indicate that endometrosis disturbs proper endometrial function and is associated with altered endometrial LPA concentration, its receptor expression and protein abundance, PGE₂/PGF_2α ratio, and CTGF secretion in response to LPA. These changes could influence several physiological events occurring in endometrium in mare during estrous cycle and early pregnancy.

Lysophosphatidic acid (LPA) as a pro-fibrotic and pro-oncogenic factor: a pivotal target to improve the radiotherapy therapeutic index

Radiation-induced fibrosis is widely considered as a common but forsaken phenomenon that can lead to clinical sequela and possibly vital impairments. Lysophosphatidic acid is a bioactive lipid involved in fibrosis and probably in radiation-induced fibrosis as suggested in recent studies. Lysophosphatidic acid is also a well-described pro-oncogenic factor, involved in carcinogenesis processes (proliferation, survival, angiogenesis, invasion, migration). The present review highlights and summarizes the links between lysophosphatidic acid and radiation-induced fibrosis, lysophosphatidic acid and radioresistance, and proposes lysophosphatidic acid as a potential central actor of the radiotherapy therapeutic index. Besides, we hypothesize that following radiotherapy, the newly formed tumour micro-environment, with increased extracellular matrix and increased lysophosphatidic acid levels, is a favourable ground to metastasis development. Lysophosphatidic acid could therefore be an exciting therapeutic target, minimizing radio-toxicities and radio-resistance effects.

Characterization of the properties of a selective, orally bioavailable autotaxin inhibitor in preclinical models of advanced stages of liver fibrosis

BACKGROUND AND PURPOSE

Autotaxin (ATX) is a secreted phospholipase which hydrolyses lysophosphatidylcholine to generate lysophosphatidic acid (LPA). The extracellular signalling molecule LPA exerts its biological actions through activation of six GPCRs expressed in various cell types including fibroblasts. Multiple preclinical studies using knockout animals, LPA receptor antagonists or ATX inhibitors have provided evidence for a potential role of the ATX/LPA axis in tissue fibrosis. Despite growing evidence for a correlation between ATX levels and the degree of fibrosis in chronic liver diseases, including viral hepatitis and hepatocellular carcinoma, the role of ATX in non-alcoholic steatohepatitis (NASH) remains unclear.

EXPERIMENTAL APPROACH

The relevance of ATX in the pathogenesis of liver fibrosis was investigated by oral administration of Ex_31, a selective ATX inhibitor, in a 10 week model of carbon tetrachloride-induced liver injury and in a 14 week model of choline-deficient amino acid-defined diet-induced liver injury in rats.

KEY RESULTS

Oral administration of Ex_31, a selective ATX inhibitor, at 15 mg·kg^-1 twice daily in therapeutic intervention mode resulted in efficient ATX inhibition and more than 95% reduction in plasma LPA levels in both studies. Treatment with Ex_31 had no effect on biomarkers of liver function, inflammation, or fibrosis and did not result in histological improvements in diseased animals.

CONCLUSIONS AND IMPLICATIONS

Our findings question the role of ATX in the pathogenesis of hepatic fibrosis and the potential of small molecule ATX inhibitors for the treatment of patients with NASH and advanced stages of liver fibrosis.

Focal Adhesion Kinase Regulates Hepatic Stellate Cell Activation and Liver Fibrosis

Understanding the underlying molecular mechanisms of liver fibrosis is important to develop effective therapy. Herein, we show that focal-adhesion-kinse (FAK) plays a key role in promoting hepatic stellate cells (HSCs) activation in vitro and liver fibrosis progression in vivo. FAK activation is associated with increased expression of α-smooth muscle actin (α-SMA) and collagen in fibrotic live tissues. Transforming growth factor beta-1 (TGF-β1) induces FAK activation in a time and dose dependent manner. FAK activation precedes the α-SMA expression in HSCs. Inhibition of FAK activation blocks the α-SMA and collagen expression, and inhibits the formation of stress fibers in TGF-β1 treated HSCs. Furthermore, inhibition of FAK activation significantly reduces HSC migration and small GTPase activation, and induces apoptotic signaling in TGF-β1 treated HSCs. Importantly, FAK inhibitor attenuates liver fibrosis in vivo and significantly reduces collagen and α-SMA expression in an animal model of liver fibrosis. These data demonstrate that FAK plays an essential role in HSC activation and liver fibrosis progression, and FAK signaling pathway could be a potential target for liver fibrosis.

Platelet-Derived Growth Factor in the Ovarian Follicle Attracts the Stromal Cells of the Fallopian Tube Fimbriae

During human ovulation, the fallopian tube fimbriae must move to the ovulation site to catch the oocyte. As the tissue-of-origin of the majority of ovarian high-grade serous carcinoma (HGSC), the fallopian tube fimbriae carrying a precursor cancer lesion may also approach the ovulatory site for metastasis. We hypothesize that platelet-derived growth factor (PDGF) in mature follicle fluid (FF) attracts the migration of PDGFR-expressing fimbriae toward the ovulating follicle. We observed that more PDGFR-β was expressed in the distal part than in the proximal parts of the fallopian tube, particularly in stromal cells in the lamina propria. The stromal cells, but not the epithelial cells, from normal fimbriae and fallopian tube HGSC were highly chemotactic to mature FF. The chemotactic activities were positively correlated with PDGF-BB and estradiol levels in FF and were abolished by a blocking antibody of PDGFR-β and by tyrosine kinase inhibitor imatinib. When PDGF-BB/AB was depleted from the FF, more than 80% of chemotaxis activities were diminished. This study suggests an ovarian follicle-directed and PDGF-dependent attraction of fallopian tube fimbriae before ovulation. The same mechanism may also be crucial for the ovarian homing of HGSC, which largely originates in the fimbriae.

Role of sphingosine 1-phosphate and lysophosphatidic acid in fibrosis

This review highlights an emerging role for sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) in many different types of fibrosis. Indeed, both LPA and S1P are involved in the multi-process pathogenesis of fibrosis, being implicated in promoting the well-established process of differentiation of fibroblasts to myofibroblasts and the more controversial epithelial-mesenchymal transition and homing of fibrocytes to fibrotic lesions. Therefore, targeting the production of these bioactive lysolipids or blocking their sites/mechanisms of action has therapeutic potential. Indeed, LPA receptor 1 (LPA(1)) selective antagonists are currently being developed for the treatment of fibrosis of the lung as well as a neutralising anti-S1P antibody that is currently in Phase 1 clinical trials for treatment of age related macular degeneration. Thus, LPA- and S1P-directed therapeutics may not be too far from the clinic. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Amelioration of dermal fibrosis by genetic deletion or pharmacologic antagonism of lysophosphatidic acid receptor 1 in a mouse model of scleroderma

OBJECTIVE

Scleroderma (systemic sclerosis [SSc]), is characterized by progressive multiorgan fibrosis. We recently implicated lysophosphatidic acid (LPA) in the pathogenesis of pulmonary fibrosis. The purpose of the present study was to investigate the roles of LPA and two of its receptors, LPA₁ and LPA₂, in dermal fibrosis in a mouse model of SSc.

METHODS

Wild type (WT), and LPA₁-knockout (KO) and LPA₂-KO mice were injected subcutaneously with bleomycin or phosphate buffered saline (PBS) once daily for 28 days. Dermal thickness, collagen content, and numbers of cells positive for α-smooth muscle actin (α-SMA) or phospho-Smad2 were determined in bleomycin-injected and PBS-injected skin. In separate experiments, a novel selective LPA₁ antagonist AM095 or vehicle alone was administered by oral gavage to C57BL/6 mice that were challenged with 28 daily injections of bleomycin or PBS. AM095 or vehicle treatments were initiated concurrently with, or 7 or 14 days after, the initiation of bleomycin and PBS injections and continued to the end of the experiments. Dermal thickness and collagen content were determined in injected skin.

RESULTS

The LPA₁ -KO mice were markedly resistant to bleomycin-induced increases in dermal thickness and collagen content, whereas the LPA₂-KO mice were as susceptible as the WT mice. Bleomycin-induced increases in dermal α-SMA+ and phospho-Smad2+ cells were abrogated in LPA₁-KO mice. Pharmacologic antagonism of LPA₁ with AM095 significantly attenuated bleomycin-induced dermal fibrosis when administered according to either a preventive regimen or two therapeutic regimens.

CONCLUSION

These results suggest that LPA/LPA₁ pathway inhibition has the potential to be an effective new therapeutic strategy for SSc, and that LPA₁ is an attractive pharmacologic target in dermal fibrosis.

Vascular involvement in systemic sclerosis (scleroderma)

Systemic sclerosis (SSc) is an acquired multiorgan connective tissue disease with variable mortality and morbidity dictated by clinical subset type. The etiology of the basic disease and pathogenesis of the systemic autoimmunity, fibrosis, and fibroproliferative vasculopathy are unknown and debated. In this review, the spectrum of vascular abnormalities and the options currently available to treat the vascular manifestations of SSc are discussed. Also discussed is how the hallmark pathologies (ie, how autoimmunity, vasculopathy, and fibrosis of the disease) might be effected and interconnected with modulatory input from lysophospholipids, sphingosine 1-phosphate, and lysophosphatidic acid.

Lysophosphatidic acid-activated Cl- current activity in human systemic sclerosis skin fibroblasts

OBJECTIVES

SSc (scleroderma) is an often fatal disease characterized by widespread tissue fibrosis. Fibroblasts play a key role in SSc-associated fibrosis. This study was designed to determine: (i) whether fibroblasts isolated from skin of patients with SSc have increased lysophosphatidic acid-activated Cl- current (IClLPA) activity vs healthy controls; (ii) whether myofibroblast differentiation is involved in SSc skin fibrosis; and (iii) whether SSc fibroblasts have different proliferation rates vs controls.

METHODS

Skin biopsies were taken from involved and uninvolved skin of SSc patients and controls. Whole-cell perforated patch-clamping was used to measure IClLPA activity in fibroblasts isolated and cultured from these biopsies. Western blotting was used to measure α-smooth muscle actin (α-SMA). Proliferation was measured using a colorimetric assay.

RESULTS

Fibroblasts cultured from SSc skin show significantly increased IClLPA activity following LPA exposure compared with control skin fibroblasts. α-SMA protein was significantly increased in cultured SSc skin fibroblasts vs controls. No significant differences in proliferation rates were found.

CONCLUSIONS

Elevated IClLPA activity is a hallmark of SSc skin fibroblasts. Blocking IClLPA activation may be a new therapeutic approach for treating SSc-associated fibrosis.

New insights into the mechanism of fibroblast to myofibroblast transformation and associated pathologies

Myofibroblasts are a differentiated cell type essential for wound healing, participating in tissue remodeling following insult. Myofibroblasts are typically activated fibroblasts, although they can also be derived from other cell types, including epithelial cells, endothelial cells, and mononuclear cells. In most organ systems, cell signals initiated following tissue-specific insult or during the metastatic process lead to differentiation of fibroblasts or other precursor cells to the myofibroblast phenotype. In addition to their beneficial and necessary role in wound healing, myofibroblasts also contribute to a number of pathologies, primarily fibrotic processes and tumor invasiveness. This review explores both traditional and nontraditional concepts of myofibroblast differentiation in the cornea, skin, heart, and other tissues, as well as some of the pathologies associated with myofibroblast activities.

Origin and function of tumor stroma fibroblasts

Tumor development is critically dependent on the formation of a supporting stroma consisting of neovasculature, inflammatory cells and activated fibroblasts. Activated fibroblasts present a heterogeneous cell population not only in regard to the expression of marker molecules but also to their origin and molecular signaling properties. The plasticity of this cell type is pointed out by the multiple transdifferentiation events that lead to the generation of activated fibroblasts which can arise from resting fibroblasts, epithelial and endothelial cells as well as from mesenchymal stem cells. Cellular in vitro and in vivo experiments have changed the perspective of fibroblasts from passive "bystanders" in the tumor microenvironment to that of important drivers of tumor progression. Here, we describe the multiple origins of fibroblast recruitment to the tumor tissue as well as the function of activated fibroblasts during tumor initiation, progression, metastasis and anti-VEGF resistance. The identification of markers present in activated fibroblasts as well as a better understanding how these cells influence other tumor compartments has led to the clinical development of anti-tumor therapies.

Combined lysophosphatidic acid/platelet-derived growth factor signaling triggers glioma cell migration in a tenascin-C microenvironment

The antiadhesive extracellular matrix molecule tenascin-C abrogates cell spreading on fibronectin through competitive inhibition of syndecan-4, thereby preventing focal adhesion kinase (FAK) activation and triggering enhanced proteolytic degradation of both RhoA and tropomyosin 1 (TM1). Here, we show that simultaneous signaling by lysophosphatidic acid (LPA) and platelet-derived growth factor (PDGF) initiates glioma cell spreading and migration through syndecan-4-independent activation of paxillin and FAK and by stabilizing expression of RhoA, TM1, TM2, and TM3. By using gene silencing methods, we show that paxillin, TM1, TM2, and TM3 are essential for LPA/PDGF-induced cell spreading on a fibronectin/tenascin-C (FN/TN) substratum. LPA/PDGF-induced cell spreading and migration on FN/TN depends on phosphatidylinositol 3-kinase, RhoKinase, and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1/2 but is independent of phospholipase C and Jun kinase. RNA microarray data reveal expression of tenascin-C, PDGFs, LPA, and the respective receptors in several types of cancer, suggesting that the TN/LPA/PDGF axis exists in malignant tumors. These findings may in turn be relevant for diagnostic or therapeutic applications targeting cancer.

Cancer-derived lysophosphatidic acid stimulates differentiation of human mesenchymal stem cells to myofibroblast-like cells

Lysophosphatidic acid (LPA) is enriched in ascites of ovarian cancer patients and is involved in growth and invasion of ovarian cancer cells. Accumulating evidence suggests cancer-associated myofibroblasts play a pivotal role in tumorigenesis through secreting stromal cell-derived factor-1 (SDF-1). In the present study, we demonstrate that LPA induces expression of alpha-smooth muscle actin (alpha-SMA), a marker for myofibroblasts, in human adipose tissue-derived mesenchymal stem cells (hADSCs). The LPA-induced expression of alpha-SMA was completely abrogated by pretreatment of the cells with Ki16425, an antagonist of LPA receptors, or by silencing LPA(1) or LPA(2) isoform expression with small interference RNA (siRNA). LPA elicited phosphorylation of Smad2/3, and siRNA-mediated depletion of endogenous Smad2/3 or adenoviral expression of Smad7, an inhibitory Smad, abrogated the LPA induced expression of alpha-SMA and phosphorylation of Smad2/3. LPA-induced secretion of transforming growth factor (TGF)-beta1 in hADSCs, and pretreatment of the cells with SB431542, a TGF-beta type I receptor kinase inhibitor, or anti-TGF-beta1 neutralizing antibody inhibited the LPA-induced expression of alpha-SMA and phosphorylation of Smad2. Furthermore, ascites from ovarian cancer patients or conditioned medium from ovarian cancer cells induced expression of alpha-SMA and phosphorylation of Smad2, and pretreatment of the cells with Ki16425 or SB431542 abrogated the expression of alpha-SMA and phosphorylation of Smad2. In addition, LPA increased the expression of SDF-1 in hADSCs, and pretreatment of the cells with Ki16425 or SB431562 attenuated the LPA-stimulated expression of SDF-1. These results suggest that cancer-derived LPA stimulates differentiation of hADSCs to myofibroblast-like cells and increases SDF-1 expression through activating autocrine TGF-beta1-Smad signaling pathway.

Lysophosphatidic acid modulates the healing responses of human periodontal ligament fibroblasts and enhances the actions of platelet-derived growth factor

BACKGROUND

Platelet-derived growth factor (PDGF) has been used to promote healing in many in vitro and in vivo models of periodontal regeneration. PDGF interacts extensively with lysophosphatidic acid (LPA). We recently showed that LPA modulates the responses of human gingival fibroblasts to PDGF. The objectives of this study were as follows: 1) to evaluate the basic interactions of LPA with primary human periodontal ligament fibroblasts (PDLFs) alone and with PDGF-BB for promoting PDLF growth and migration; 2) to determine the effects in an in vitro oral wound-healing model; and 3) to identify the LPA receptors (LPARs) expressed by PDLF.

METHODS

PDLF regenerative responses were measured using 1 and 10 microM LPA in the absence or presence of 1 or 10 ng/ml PDGF. Cell proliferation was determined by 5-bromo-2'-deoxyuridine (BrdU) immunohistochemistry and by cell counting. Migration responses were measured using a microchemotaxis chamber. PDLFs were grown to confluence on glass slides, a 3-mm-wide wound was mechanically inflicted, and wound fill on days 4, 6, and 9 was reported. PDLF LPAR expression was determined using Western blotting.

RESULTS

PDLFs exhibited proliferative and chemotactic responses to LPA; these responses were enhanced when LPA and PDGF were present together. LPA plus PDGF elicited complete wound fill. PDLFs express the LPARs LPA(1), LPA(2), and LPA(3).

CONCLUSIONS

To our knowledge, this study provides the first evidence that LPA stimulates human PDLF wound healing responses and interacts positively with PDGF to regulate these actions. These results suggest that LPA and its receptors play important modulatory roles in PDLF regenerative biology.

Different profiles of Ca2+ responses to endothelin-1 and PDGF in liver myofibroblasts during the process of cell differentiation

BACKGROUND AND PURPOSE

Hepatic stellate cells play an important role in liver fibrosis but little is known about liver myofibroblasts located around the central vein and in the portal area. In this study, intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured to assess the response to endothelin-1 (ET-1), platelet derived growth factor (PDGF) and ATP in rat liver myofibroblasts.

EXPERIMENTAL APPROACH

Rat liver myofibroblasts were compared in 'quiescent' (cultured on Matrigel-coated dishes) and 'activated' (cultured on non-coated plastic dishes) conditions. [Ca(2+)](i) was measured with the fluorescent dye fura-2 and mRNA for ET-1, PDGF and their receptors by RT-PCR.

KEY RESULTS

ET-1 increased [Ca(2+)](i) in quiescent cells but not in activated cells, whereas PDGF-BB increased [Ca(2+)](i) in activated cells but not in quiescent cells. However, there was no difference between responses to ATP in quiescent or activated cells. ET-1 (in quiescent cells), PDGF-BB (in activated cells) and ATP (in both cells) all induced transient increases in [Ca(2+)](i) in the absence of extracellular Ca(2+) (with EGTA), indicating the involvement of Ca(2+) release from intracellular Ca(2+) stores. The sustained increase in [Ca(2+)](i) in the presence of external Ca(2+) in activated cells (ATP and PDGF) was significantly reduced by nicardipine, a L-type Ca(2+) channel blocker, but not in quiescent cells (ATP and ET-1).

CONCLUSIONS AND IMPLICATIONS

The different pharmacological profiles of [Ca(2+)](i)-response in quiescent and activated myofibroblasts suggest that ET-1 and PDGF contribute differently to myofibroblast activation during the process of liver fibrosis.

Focal adhesion kinase protein levels in gut epithelial motility

Mucosal healing requires migration and proliferation. Most studies of focal adhesion kinase (FAK), a protein that regulates motility, proliferation, and apoptosis, have focused on rapid phosphorylation. We reported lower FAK protein levels in motile Caco-2 colon cancer cells and postulated that this reduction in FAK available for activation might impact cell migration and mucosal healing. Therefore, total and active FAK (FAK(397)) immunoreactivity was assessed at the migrating fronts of human Caco-2 and rat IEC-6 intestinal epithelial cells. Caco-2 and IEC-6 motility, quantitated as migration into linear or circular wounds, was examined following FAK protein inhibition by small interfering RNA (siRNA). FAK protein stability and mRNA expression were ascertained by cycloheximide decay, RT-PCR, and in situ hybridization in static and migrating Caco-2 cells. Cells at the migrating front of Caco-2 and IEC-6 monolayers exhibited lower immunostaining for both total and activated FAK than cells immediately behind the front. Western blot analysis also demonstrated diminished FAK protein levels in motile cells by >/=30% in both the differential density seeding and multiple scrape models. siRNA FAK protein inhibition enhanced motility in both the linear scrape (20% in Caco-2) and circular wound (16% in Caco-2 and 19% in IEC-6 cells) models. FAK protein degradation did not differ in motile and static Caco-2 cells and was unaffected by FAK(397) phosphorylation, but FAK mRNA was lower in migrating Caco-2 cells. Thus FAK protein abundance appears regulated at the mRNA level during gut epithelial cell motility and may influence epithelial cell migration coordinately with signals that modify FAK phosphorylation.

Focal adhesion kinase and Src phosphorylations in HGF-induced proliferation and invasion of human cholangiocarcinoma cell line, HuCCA-1

AIM: To study the role of focal adhesion kinase (FAK) and its association with Src in hepatocyte growth factor (HGF)-induced cell signaling in cholangiocarcinoma progression.

METHODS: Previously isolated HuCCA-1 cells were re-characterized by immunofluorescent staining and reverse transcriptase-polymerase chain reaction assay for the expression of cytokeratin 19, HGF and c-Met mRNA. Cultured HuCCA-1 cells were treated with HGF and determined for cell proliferation and invasion effects by MTT and invasion assays. Western blotting, immunop-recipitation, and co-immunoprecipitation were also performed to study the phosphorylation and interaction of FAK and Src. A novel Src inhibitor (AZM555130) was applied in cultures to investigate the effects on FAK phosphorylation inhibition and on cell proliferation and invasion.

RESULTS: HGF enhanced HuCCA-1 cell proliferation and invasion by mediating FAK and Src phosphorylations. FAK-Src interaction occurred in a time-dependent manner that Src was proved to be an upstream signaling molecule to FAK. The inhibitor to Src decreased FAK phosphorylation level in correlation with the reduction of cell proliferation and invasion.

CONCLUSION: FAK plays a significant role in signaling pathway of HGF-responsive cell line derived from cholangiocarcinoma. Autophosphorylated Src, induced by HGF, mediates Src kinase activation, which subsequently phosphorylates its substrate, FAK, and signals to cell proliferation and invasion.

Transactivation of the epidermal growth factor receptor mediates muscarinic stimulation of focal adhesion kinase in intestinal epithelial cells

We have previously shown that the Gq protein coupled receptor (GqPCR) agonist, carbachol (CCh), transactivates and recruits epidermal growth factor receptor (EGFr)-dependent signaling mechanisms in intestinal epithelial cells. Increasing evidence suggests that GqPCR agonists can also recruit focal adhesion-dependent signaling pathways in some cell types. Therefore, the aim of the present study was to investigate if CCh stimulates activation of the focal adhesion-associated protein, focal adhesion kinase (FAK), in intestinal epithelia and, if so, to examine the signaling mechanisms involved. Experiments were carried out on monolayers of T84 cells grown on permeable supports. CCh rapidly induced tyrosine phosphorylation of FAK in T84 cells. This effect was accompanied by phosphorylation of another focal adhesion-associated protein, paxillin, and association of FAK with paxillin. CCh-stimulated FAK phosphorylation was inhibited by a chelator of intracellular Ca2+, BAPTA/AM (20 microM), and was mimicked by thapsigargin (2 microM), which mobilizes intracellular Ca2+ in a receptor-independent fashion. CCh also induced association of FAK with the EGFr and FAK phosphorylation was attenuated by an EGFr inhibitor, tyrphostin AG1478, and an inhibitor of Src family kinases, PP2. The actin cytoskeleton disruptor, cytochalasin D (20 microM), abolished FAK phosphorylation in response to CCh but did not alter CCh-induced EGFr or ERK MAPK activation. In summary, these data demonstrate that agonists of GqPCRs have the ability to induce FAK activation in intestinal epithelial cells. GqPCR-induced FAK activation is mediated by via a pathway involving transactivation of the EGFr and alterations in the actin cytoskeleton.

Effect of interleukin-10 and platelet-derived growth factor on expressions of matrix metalloproteinases-2 and tissue inhibitor of metalloproteinases-1 in rat fibrotic liver and cultured hepatic stellate cells

AIM

To examine the expressions of matrix metalloproteinases-2 (MMP-2) and tissue inhibitor of metalloproteinases-1 (TIMP-1) in rat fibrotic liver and in normal rat hepatic stellate cells, and to investigate the changes in their expressions in response to treatment with interleukin-10 (IL-10) and platelet-derived growth factor (PDGF).

METHODS

Rat models of CCl4-induced hepatic fibrosis were established and the liver tissues were sampled from the rats with or without IL-10 treatment, and also from the control rats. The expressions of MMP-2 and TIMP-1 in liver tissues were detected by S-P immunohistochemistry, and their expression intensities were evaluated in different groups. Hepatic stellate cells (HSCs) were isolated from normal rat and cultured in vitro prior to exposure to PDGF treatment or co-treatment with IL-10 and PDGF. MMP-2 and TIMP-1 levels were measured by semi-quantitative reverse transcriptional polymerase chain reaction (RT-PCR).

RESULTS

CCl4- induced rat hepatic fibrosis models were successfully established. The positive expressions of MMP-2 and TIMP-1 increased obviously with the development of hepatic fibrosis, especially in untreated model group (84.0% and 92.0%, P<0.01). The positive signals decreased significantly following IL-10 treatment (39.3% and 71.4%, P<0.01 and P<0.05) in a time-dependent manner. TIMP-1 mRNA in PDGF-treated group was significantly increased time-dependently in comparison with that of the control group, but PDGF did not obviously affect MMP-2 expression. No difference was noted in TIMP-1 and MMP-2 expressions in HSCs after IL-10 and PDGF treatment (P>0.05).

CONCLUSION

MMP-2 and TIMP-1 expressions increase in liver tissues with the development of fibrosis, which can be inhibited by exogenous IL-10 inhibitor. PDGF induces the up-regulation of TIMP-1 but not MMP-2 in the HSCs. IL-10 inhibits TIMP-1 and MMP-2 expressions in HSCs induced by PDGF.

Lysophosphatidic Acid Stimulates Ovarian Cancer Cell Migration via a Ras-MEK Kinase 1 Pathway

Lysophosphatidic acid (LPA) is present at high concentrations in ascites and plasma of ovarian cancer patients. Studies conducted in experimental models demonstrate that LPA promotes ovarian cancer invasion/metastasis by up-regulating protease expression, elevating protease activity, and enhancing angiogenic factor expression. In this study, we investigated the effect of LPA on ovarian cancer migration, an essential component of cancer cell invasion. LPA stimulates both chemotaxis and chemokinesis of ovarian cancer cells and LPA-stimulated cell migration is G(I) dependent. Moreover, constitutively active H-Ras enhances ovarian cancer cell migration, whereas dominant negative H-Ras blocks LPA-stimulated cell migration, suggesting that Ras works downstream of G(i) to mediate LPA-stimulated cell migration. Interestingly, H-Ras mutants that specifically activate Raf-1, Ral-GDS, or phosphatidylinositol 3'-kinase are unable to significantly enhance ovarian cancer cell migration, suggesting that a Ras downstream effector distinct from Raf-1, Ral-GDS, and phosphatidylinositol 3'-kinase is responsible for LPA-stimulated cell migration. In this article, we demonstrate that LPA activates mitogen-activated protein kinase kinase 1 (MEKK1) in a G(i)-Ras-dependent manner and that MEKK1 activity is essential for LPA-stimulated ovarian cancer cell migration. Inhibitors that block MEKK1 downstream pathways, including MEK1/2, MKK4/7, and nuclear factor-kappa B pathways, do not significantly alter LPA-stimulated cell migration. Instead, LPA induces the redistribution of focal adhesion kinase to focal contact regions of the cytoplasm membrane, and this event is abolished by pertussis toxin, dominant negative H-Ras, or dominant negative MEKK1. Our studies thus suggest that the G(i)-Ras-MEKK1 signaling pathway mediates LPA-stimulated ovarian cancer cell migration by facilitating focal adhesion kinase redistribution to focal contacts.

Rho and p38 MAP kinase signaling pathways mediate LPA-stimulated hepatic myofibroblast migration

Although hepatic myofibroblast migration plays a key role in the liver's injury response, the signal transduction pathways mediating the migration of this cell type are uncertain. Recently, we reported that lysophosphatidic acid (LPA) stimulates the migration of hepatic myofibroblasts. The goal of this study was to test the hypothesis that rho and p38 MAP kinase signaling pathways mediate LPA-stimulated hepatic myofibroblast migration. We measured migration, myosin regulatory light chain and p38 MAP kinase phosphorylation, and contractile force generation by human hepatic myofibroblasts. LPA stimulated migration in a dose-dependent and saturable manner that was partially blocked by Y-27632, a rho-associated kinase inhibitor, as well as by SB-202190, a p38 MAP kinase inhibitor. LPA also induced myosin regulatory light chain phosphorylation and contractile force generation in a Y-27632 dependent, and SB-202190 independent fashion. Moreover, LPA stimulated a dose-dependent and saturable phosphorylation of p38 MAP kinase, which was not altered by Y-27632 or C3 transferase, a rho inactivator. These novel results suggest that LPA stimulates hepatic myofibroblast migration via distinct pathways that signal through rho and p38 MAP kinase.