Down-regulation of Cbl-b by bufalin results in up-regulation of DR4/DR5 and sensitization of TRAIL-induced apoptosis in breast cancer cells

Purpose

TNF-related apoptosis-inducing ligand (TRAIL) is a potential cancer therapeutic agent that preferentially induces apoptosis in cancer cells. However, breast cancer cells are generally resistant to TRAIL. Bufalin is a major active ingredient of the traditional Chinese medicine ChanSu. The present study aimed to assess the synergistic effect of bufalin and TRAIL and elucidate the underlying mechanisms in breast cancer cells.

Methods

Cell proliferation and apoptosis were measured by MTT assay and flow cytometry, respectively. The expression of proteins was assayed by flow cytometry and/or Western blotting. Transfection studies were used to determine the involvement of DR4, DR5 and Cbl-b in the synergistic effect of bufalin and TRAIL.

Results

MCF-7 and MDA-MB-231 cells were resistant to TRAIL. Both cell lines were dramatically sensitized to TRAIL-induced apoptosis by bufalin. Further experiments indicated that bufalin up-regulated DR4 and DR5, activated ERK, JNK and p38 MAPK and down-regulated Cbl-b. Blocking the up-regulation of DR4 and DR5 by siRNA rendered cells less sensitive to apoptosis induced by the combination of bufalin and TRAIL. Inhibition of the activation of ERK, JNK and p38 MAPK by specific inhibitors attenuated DR4 and DR5 up-regulation. Moreover, down-regulation of Cbl-b by shRNA led to stronger activation of ERK, JNK and p38 MAPK, more up-regulation of DR4 and DR5, and a stronger synergistic effect of bufalin and TRAIL.

Conclusions

Bufalin enhanced TRAIL-induced apoptosis by up-regulating the expression of DR4 and DR5. Bufalin-induced down-regulation of Cbl-b contributed to the up-regulation of DR4 and DR5, which might be partially mediated by the activation of ERK, JNK and p38 MAPK.     

Sphingosine kinase 1 regulates mucin production via ERK phosphorylation

Our previous report showed that inhibition of sphingosine kinase (SphK) ameliorates eosinophilic inflammation and mucin production in a mouse asthmatic model. To clarify the role of SphK in airway mucin production, we utilized the mouse asthmatic model and found that both SphK and MUC5AC expression were increased and co-localized in airway epithelium. Next we cultured normal human bronchial epithelial cells in an air–liquid interface and treated with IL-13 to induce their differentiation into goblet cells. We found that SphK1 and MUC5AC expression was increased by IL-13 treatment at both protein and mRNA levels, whereas SphK2 expression was not changed. N,N-dimethylsphingosine (DMS), a potent SphK inhibitor, decreased MUC5AC expression up-regulated by IL-13 treatment. Furthermore, DMS inhibited IL-13-induced ERK1/2 phosphorylation but neither p38 MAPK nor STAT6 phosphorylation. These results suggest that SphK1 is involved in MUC5AC production induced by IL-13 upstream of ERK1/2 phosphorylation, and independent of STAT6 phosphorylation.     

HOXA10 Promotes Cell Invasion and MMP-3 Expression Via TGFβ2-Mediated Activation of the p38 MAPK Pathway in Pancreatic Cancer Cells

Background

HOXA10 is closely related to tumor progression in many human cancers. However, the role of HOXA10 in pancreatic cancer remains unclear. The aim of this study was to determine the involvement of HOXA10 in pancreatic cancer cell invasion and migration.

Methods

The effect of HOXA10 on the invasion and migration of pancreatic cancer cells was assessed by invasion and migration assays. The protein of transforming growth factor beta-2 (TGFβ2) was neutralized by TGFβ2 blocking antibody. The activation of p38 was inhibited by SB239063.

Results

HOXA10 could promote the invasion and migration of pancreatic cancer cells. Knockdown of HOXA10 decreased the expressions of TGFβ2 and matrix metallopeptidase-3 (MMP-3) and suppressed the activation of p38. Conversely, overexpression of HOXA10 increased the levels of TGFβ2 and MMP-3. Further experiments identified that TGFβ2 contributed to the HOXA10-promoted invasion and migration and regulated MMP-3 expression and p38 activation. Additionally, inhibition of p38 suppressed cell invasion and MMP-3 expression in pancreatic cancer cells.

Conclusions

HOXA10 promotes cell invasion and MMP-3 expression of pancreatic cancer cells via TGFβ2-p38 MAPK pathway. Thus, HOXA10 could be a useful target for the treatment of pancreatic cancer.     

Overexpression of galectin-3 enhances migration of colon cancer cells related to activation of the K-Ras–Raf–Erk1/2 pathway

Background

Galectin-3 has been independently correlated with malignant behavior in human colon cancer. The involvement of galectin-3 in the invasiveness of colon cancer cells remains to be determined. We investigated whether galectin-3 was involved in the colon cancer cell migration mediated by certain kinase pathways.

Methods

We studied 2 colon cancer cell lines (DLD-1 and Caco2) and clinical samples. Immunostaining and Western blotting were used to analyze the expression of galectin-3 in vitro and in the clinical samples. Short hairpin RNA and overexpression of galectin-3 were used to study loss- and gain-of-function in a wound-healing assay and a Transwell migration assay, and Western blotting was used to study the Ras–Raf signaling pathway.

Results

Galectin-3 was expressed at lower levels in DLD-1 than in Caco2 cells. The lower galectin-3 level in DLD-1 cells was associated with decreased cell migration, in comparison with that of Caco2 cells. Overexpression of galectin-3 increased the migration rate of DLD-1, while knockdown of galectin-3 decreased the migration. Overexpression of galectin-3 was correlated with increased lamellipodia formation and distal lung localization in a mouse model. The galectin-3 enhancement of DLD-1 cell migration was mediated by K-Ras, Raf and Erk1/2 pathway activation, but not the H-Ras, p38, or JNK activation.

Conclusions

Galectin-3 plays an important role in regulating colon cancer cell migration and potential distal localization. The galectin-3 enhancement of cell migration is mediated through the K-Ras–Raf–Erk1/2 pathway. Specific targeting of the K-Ras–Raf–Erk1/2 pathway may be useful for treating colon cancers associated with increased galectin-3 expression.     

Exendin-4 protects pancreatic beta cells from palmitate-induced apoptosis by interfering with GPR40 and the MKK4/7 stress kinase signalling pathway

Aims/hypothesis

The mechanisms of the protective effects of exendin-4 on NEFA-induced beta cell apoptosis were investigated.

Methods

The effects of exendin-4 and palmitate were evaluated in human and murine islets, rat insulin-secreting INS-1E cells and murine glucagon-secreting alpha-TC1-6 cells. mRNA and protein expression/phosphorylation were measured by real-time RT-PCR and immunoblotting or immunofluorescence, respectively. Small interfering (si)RNAs for Ib1 and Gpr40 were used. Cell apoptosis was quantified by two independent assays. Insulin release was assessed with an insulin ELISA.

Results

Exposure of human and murine primary islets and INS-1E cells, but not alpha-TC1-6 cells, to exendin-4 inhibited phosphorylation of the stress kinases, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), and prevented apoptosis in response to palmitate. Exendin-4 increased the protein content of islet-brain 1 (IB1), an endogenous JNK blocker; however, siRNA-mediated reduction of IB1 did not impair the ability of exendin-4 to inhibit JNK and prevent apoptosis. Exendin-4 reduced G-protein-coupled receptor 40 (GPR40) expression and inhibited palmitate-induced phosphorylation of mitogen-activated kinase kinase (MKK)4 and MKK7. The effects of exendin-4 were abrogated in the presence of the protein kinase A (PKA) inhibitors, H89 and KT5720. Knockdown of GPR40, as well as use of a specific GPR40 antagonist, resulted in diminished palmitate-induced JNK and p38 MAPK phosphorylation and apoptosis. Furthermore, inhibition of JNK and p38 MAPK activity prevented palmitate-induced apoptosis.

Conclusions/interpretation

Exendin-4 counteracts the proapoptotic effects of palmitate in beta cells by reducing GPR40 expression and inhibiting MKK7- and MKK4-dependent phosphorylation of the stress kinases, JNK and p38 MAPK, in a PKA-dependent manner.     

Lipopolysaccharide-Induced Toll-Like Receptor 4 Signaling in Cancer Cells Promotes Cell Survival and Proliferation in Hepatocellular Carcinoma

Background

Recent studies have shown that toll-like receptor 4 (TLR4) is involved in hepatocarcinogenesis. However, the significance of TLR4 signaling in cancer development and progression remains unclear.

Aim

The purpose of this study was to investigate the role of TLR4 in cancer cell survival and proliferation in hepatocellular carcinoma (HCC).

Methods

Fifty-three HCC and ten normal liver specimens were analyzed by immunohistochemistry, and three cell lines (HL-7702, PLC/PRF/5 and HepG2) were used for in vitro studies. Lipopolysaccharide (LPS), a specific ligand of TLR4, was used to activate TLR4 signaling. The effects of LPS-TLR4 signaling on cell survival, proliferation and invasion were examined. Specific inhibitors of NF-κB and MAPK (JNK, ERK and p38) signaling pathways were used to explore the role of each pathway in LPS-TLR4 signaling.

Results

TLR4 was overexpressed in HCC cell lines and in human HCC tissues, where it correlated with Ki-67 expression. LPS-induced activation of TLR4 signaling promoted cancer cell survival and proliferation. LPS-TLR4 signaling was associated with regulation on the activation of NF-κB and MAPK signaling pathways. LPS-TLR4-induced activation of ERK and JNK signaling promotes cell proliferation through regulating Bax translocation to mitochondria. Activation of NF-κB and p38 mediates cytotoxicity of LPS, and inhibition on these two pathways promotes cell proliferation in HCC cells.

Conclusion

Our results indicate that TLR4 signaling in cancer cells promotes cell survival and proliferation in HCC.     

Lentiviral vector-mediated down-regulation of IL-17A receptor in hepatic stellate cells results in decreased secretion of IL-6

AIM: To investigate the mechanism of interleukin (IL)-6 secretion through blocking the IL-17A/IL-17A recepto (IL-17RA) signaling pathway with a short hairpin RNA (shRNA) in hepatic stellate cells (HSCs) in vitro . METHODS: HSCs were derived from the livers of adul male Sprague-Dawley rats. IL-6 expression was evalu ated using real-time quantitative polymerase chain reaction and enzyme linked immunosorbent assay. The phosphorylation activity of p38 mitogen activated pro tein kinases (MAPK) and extracellular regulated pro tein kinases (ERK) 1/2 upon induction by IL-17A and suppression by IL-17RA shRNA were examined using Western blotting.RESULTS: IL-6 expression induced by IL-17A was significantly increased compared to control in HSCs (P 0.01 in a dose-dependent manner). Suppression of IL17RA using lentiviral-mediated shRNA inhibited IL-6 expression induced by IL-17A compared to group with only IL-17A treatment (1.44 ± 0.17 vs 4.07 ± 0.43, P 0.01). IL-17A induced rapid phosphorylation of p38 MAPK and ERK1/2 after 5 min exposure, and showed the strongest levels of phosphorylation of p38 MAPK and ERK1/2 at 15 min in IL-17A-treated HSCs. IL-6 mRNA expression induced by IL-17A (100 ng/mL) for 3 h exposure was inhibited by preincubation with specific inhibitors of p38 MAPK (SB-203580) and ERK1/2 (PD-98059) compared to groups without inhibitors preincubation (1.67 ± 0.24, 2.01 ± 0.10 vs 4.08 ± 0.59, P 0.01). Moreover, lentiviral-mediated IL-17RA shRNA 1 inhibited IL-17A-induced IL-6 mRNA expression compared to random shRNA in HSCs (1.44 ± 0.17 vs 3.98 ± 0.68, P 0.01). Lentiviral-mediated IL17RA shRNA 1 inhibited phosphorylation of p38 MAPK and ERK1/2 induced by 15 min IL-17A (100 ng/mL) exposure. CONCLUSION: Down-regulation of the IL-17RA receptor by shRNA decreased IL-6 expression induced by IL-17A via p38 MAPK and ERK1/2 phosphorylation in HSCs. Suppression of IL-17RA expression may be a strategy to reduce the inflammatory response induced by IL-17A in the liver.     

SphK1对结肠癌lovo细胞的增殖、迁移和凋亡的影响

目的:探讨鞘胺醇激酶1(SphK1)对结肠癌lovo细胞增殖、迁移和凋亡的影响及其作用机制.方法:培养人结肠癌lovo细胞株,实验分3组:对照组、PMA组和DMS组.PMA组加入佛波醇-12-豆蔻酸酯-13-乙酸酯(PMA,100nmol/L),DMS组加入N,N-二甲基鞘胺醇(DMS,50μmol/L),对照组加入等量的培养基.采用MTT法和克隆形成实验检测细胞生长增殖的变化,流式细胞术检测细胞凋亡,Tranwell小室模型观察细胞迁移能力的变化,RT-PCR检测mRNA的表达,Westernblot检测蛋白的表达.结果:PMA显著促进细胞的增殖、迁移并抑制细胞的凋亡,DMS则显著抑制细胞的增殖、迁移并促进细胞的凋亡(对照组、PMA组和DMS组的细胞增殖活力:0.71±0.03vs1.05±0.05vs0.46±0.04;克隆形成率:1.32%±0.26%vs2.17%±0.17%vs0.73%±0.13%;凋亡率:16.25%vs9.15%vs32.58%;迁移细胞数:72.19±3.36vs98.46±6.25vs40.48±4.27;均P<0.05).PMA显著促进黏着斑激酶(FAK)的活性和表达,相反DMS则抑制FAK的活性和表达[对照组、PMA组和DMS组FAKmRNA的表达强度:0.151±0.008vs0.212±0.014vs0.114±0.021;蛋白:0.332±0.022vs0.374±0.029vs0.296±0.018;磷酸化FAK(p-FAKTyr397)蛋白:0.186±0.032vs0.234±0.017vs0.112±0.023;均P<0.05].结论:SphK1可促进lovo细胞的增殖和迁移能力并抑制细胞的凋亡,其机制可能是通过激活FAK通路而发挥作用.     

Butein inhibits ethanol-induced activation of liver stellate cells through TGF-β, NFκB, p38, and JNK signaling pathways and inhibition of oxidative stress

Background

Butein has been reported to prevent and partly reverse liver fibrosis in vivo; however, the mechanisms of its action are poorly understood. We, therefore, aimed to determine the antifibrotic potential of butein.

Methods

We assessed the influence of the incubation of hepatic stellate cells (HSCs) and hepatoma cells (HepG2) with butein on sensitivity to ethanol- or acetaldehyde-induced toxicity; the production of reactive oxygen species (ROS); the expression of markers of HSC activation, including smooth muscle α-actin (α-SMA) and procollagen I; and the production of transforming growth factor-β1 (TGF-β1), metalloproteinases-2 and -13 (MMP-2and MMP-13), and tissue inhibitors of metalloproteinases (TIMPs). The influence of butein on intracellular signals in HSCs; i.e., nuclear factor-κB (NFκB), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (p38 MAPK) induced by ethanol was estimated.

Results

Butein protected HSCs and HepG2 cells against ethanol toxicity by the inhibition of ethanol- or acetaldehyde-induced production of ROS when cells were incubated separately or in co-cultures; butein also inhibited HSC activation measured as the production of α-SMA and procollagen I. As well, butein downregulated ethanol- or acetaldehyde-induced HSC migration and the production of TGF-β, TIMP-1, and TIMP-2; decreased the activity of MMP-2; and increased the activity of MMP-13. In ethanol-induced HSCs, butein inhibited the activation of the p38 MAPK and JNK transduction pathways as well as significantly inhibiting the phosphorylation of NF κB inhibitor (IκB) and Smad3.

Conclusions

The results indicated that butein inhibited ethanol- and acetaldehyde-induced activation of HSCs at different levels, acting as an antioxidant and inhibitor of ethanol-induced MAPK, TGF-β, and NFκB/IκB transduction signaling; this result makes butein a promising agent for antifibrotic therapies.     

Cotransfection of Survivin and CD44v3 Short Hairpin RNAs Affects Proliferation, Apoptosis, and Invasiveness of Colorectal Cancer

Introduction

Colorectal cancer is one of the common malignant tumors in humans, and the incidence rate is gradually increasing year by year. Survivin and CD44v3 are ideal targets for gene therapy due to their overexpression in colorectal cells. Studies show that downregulation of survivin could promote apoptosis and depress proliferation, and reduction of CD44v3 expression could inhibit tumor invasive capacity. It is difficult to achieve satisfactory curative effect.

Objective

In this study, we use survivin and CD44v3 short hairpin RNAs (shRNA) combined transfection into colorectal cancer cell line SW480 to investigate its effects on the cell apoptosis, proliferation and invasiveness.

Methods

ShRNA plasmids targeting survivin and CD44v3 were singly or co-transfected into SW480 cells.

Results

The co-transfection group exhibited the most significant inhibitory effect on cell growth (P < 0.05) and the highest apoptosis rate (P < 0.05). In addition, the invasive capacity in the co-transfected group was the least. The tumor inhibition rate of the cotransfected group in xenograft tumor mice was significantly higher than other groups (P < 0.05). Moreover, the microvessel density of the co-transfected group was significantly decreased compared with other groups (P < 0.05).

Conclusion

These results suggest combined transfection of survivin shRNA and CD44v3 shRNA may produce a synergistic effect on gene therapy in colorectal cancer.     

阿托伐他汀通过抑制ERK/MAPK信号通路改善H2O2诱导的血管内皮细胞损伤的机制研究

目的探究阿托伐他汀通过调节ERK/MAPK信号通路改善H₂O₂诱导的血管内皮细胞损伤的作用机制。方法体外培养人脐静脉内皮细胞(HUVECs),分为空白对照组、模型组(H₂O₂处理)、阿托伐他汀组(阿托伐他汀+H₂O₂)、U0126组(ERK/MAPK信号通路抑制剂U0126+H₂O₂)、阿托伐他汀+LM22B-10组(阿托伐他汀和ERK/MAPK信号通路激活剂LM22B-10+H₂O₂)。采用MTT法、AO/EB染色法分别检测各组细胞活性、凋亡率;用酶联免疫吸附法检测各组细胞乳酸脱氢酶(LDH)、丙二醛(MDA)、超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)含量;荧光法检测活性氧簇(ROS)水平;Western blot法检测各组细胞中ERK1/2、p-ERK1/2、p38 MAPK、p-p38 MAPK蛋白表达。结果与空白对照组比较,模型组细胞增殖活性、SOD和GSH-Px含量降低,细胞凋亡率、LDH、MDA和ROS水平增加,p-ERK1/2/ERK1/2、p-p38 MAPK/p38 MAPK蛋白表达比值上调(P均<0.05)。与模型组比较,阿托伐他汀组细胞增殖活性、SOD和GSH-Px含量升高,细胞凋亡率、LDH、MDA和ROS水平降低,且p-ERK1/2/ERK1/2、p-p38 MAPK/p38 MAPK蛋白表达比值下调(P均<0.05)。与阿托伐他汀组比较,阿托伐他汀+LM22B-10组细胞增殖活性、SOD和GSH-Px含量降低,凋亡率、LDH、MDA和ROS水平升高,同时p-ERK1/2/ERK1/2、p-p38 MAPK/p38 MAPK蛋白表达比值上调(P均<0.05)。结论阿托伐他汀能够改善H₂O₂诱导的血管内皮细胞损伤,其机制与抑制ERK/MAPK信号通路进而降低ROS介导的血管内皮细胞凋亡和氧化应激损伤有关。     

Predictive value of sphingosine kinase 1 expression in neoadjuvant treatment of breast cancer

Purpose

Sphingolipids play important roles in apoptosis and cell proliferation. Sphingosine kinase 1 (SphK1) expression has a prognostic impact in primary breast cancer, but its predictive value is currently unknown.

Methods

A total of 112 breast cancer specimens from a prospective neoadjuvant chemotherapy trial (GeparDuo) were studied. Using tissue microarrays of pre-treatment core cut biopsies, we determined the expression of SphK1 by immunohistochemistry. The upper quartile of the cohort according to an immune reactive score of SphK1 was used as cutoff for high expression.

Results

We observed a larger number of samples with high SphK1 expression among ER-negative cancers (36.8 vs. 20.5 % among ER-positive cancers; Fisher test p = 0.073). Eighteen of the 112 patients demonstrated a pathological complete response. A significant predictive value for pathological complete response was observed for ER negativity (p = 0.003), young age (p = 0.037), and high tumor grade (p = 0.049). An increased pCR rate was observed in tumors with high SphK1 expression within the luminal subtype (26.7 vs. 5.8 %; Fisher test p = 0.040). No significant difference in survival was detected according to SphK1 expression.

Conclusions

Our results suggest that SphK1 may be a predictive factor for pCR after neoadjuvant treatment in luminal type breast cancers and warrants further investigation.     

The RhoA/ROCK pathway mediates high glucose‐induced cardiomyocyte apoptosis via oxidative stress,JNK, and p38MAPK pathways

Aims

To understand the roles of the RhoA/ROCK and mitogen‐activated protein kinase (MAPK) pathways in high glucose (HG)‐induced apoptosis and oxidative stress in cardiomyocytes.

Materials and methods

Neonatal rat cardiomyocytes were cultured in Dulbecco's modified Eagle's medium, supplemented with 5.5 or 30 mmol/L D‐glucose, in the presence or absence of fasudil (50 or 100 μM), SB203580, SP600125, or PD98059 (10 μM, respectively). The percentage of early apoptotic cardiomyocytes was evaluated using flow cytometry. The superoxide dismutase activity and malondialdehyde contents in the cellular supernatants were measured. The Bax and Bcl‐2 mRNA levels were determined by quantitative real‐time PCR. Phosphorylation of myosin phosphatase target subunit 1 (MYPT1), p38MAPK, JNK, and ERK as well as the protein levels of Bax, Bcl‐2, and cleaved caspase‐3 was analysed by Western blot.

Results

Fasudil, SB203580, and SP600125 effectively inhibited the HG‐induced early apoptosis increase and decreased Bax mRNA expression, the Bax/Bcl‐2 protein expression ratio, and cleaved caspase‐3 protein levels in the cardiomyocytes; this was accompanied by upregulation of the Bcl‐2 mRNA. Moreover, fasudil markedly increased the superoxide dismutase activity level and suppressed the elevation in HG‐induced malondialdehyde content and the phosphorylation of MYPT1, p38MAPK and JNK.

Conclusions

The RhoA/ROCK pathway mediates HG‐induced cardiomyocyte apoptosis via oxidative stress and activation of p38MAPK and JNK in neonatal rats in vitro. Fasudil effectively ameliorates HG‐induced cardiomyocyte apoptosis by suppressing oxidative stress and the p38MAPK and JNK pathways.     

Acid exposure activates the mitogen-activated protein kinase pathways in Barrett's esophagus

BACKGROUND & AIMS: To explore mechanisms whereby acid reflux might contribute to carcinogenesis in Barrett's esophagus (BE) we studied: (1) the effects of acid on the mitogen-activated protein kinase (MAPK) pathways, cell proliferation, and apoptosis in a Barrett's adenocarcinoma cell line (SEG-1); and (2) the ability of acid to activate the MAPK pathways in vivo in patients with BE. METHODS: SEG-1 cells were exposed to acidic media for 3 minutes, and the activities of 3 MAPKs (ERK, p38, and JNK) were determined. Proliferation was assessed using flow cytometry; cell growth and apoptosis were assessed using cell counts and an apoptosis ELISA assay. MAPK activation was studied in biopsy specimens taken from patients with BE before and after esophageal perfusion for 3 minutes with 0.1N HCl. RESULTS: Acid-exposed SEG-1 cells exhibited a significant increase in proliferation and total cell numbers, and a significant decrease in apoptosis. These effects were preceded by a rapid increase in the activities of ERK and p38, and a delayed increase in JNK activity. PD 98059 abolished the acid-induced increase in G0/G1 and decrease in subG0 phases of the cell cycle. Both SB 203580 and DN-JNK 1/2 inhibited the acid-induced progression from G0/G1 to G2/M. The acid-induced decrease in apoptosis was abolished by inhibition of either ERK or p38. In the patients, acid exposure significantly increased the activity of p38 in the metaplastic epithelium. CONCLUSIONS: Acid increases proliferation and survival, and decreases apoptosis in SEG-1 cells by activating the MAPK pathways. Acid also activates the MAPK pathways in BE in vivo. These findings suggest that acid might contribute to carcinogenesis in BE through activation of MAPK pathways.     

Urokinase-type plasminogen activator (uPA) modulates monocyte-to-macrophage differentiation and prevents Ox-LDL-induced macrophage apoptosis

Objective

Monocyte-to-macrophage differentiation and macrophage death play a pivotal role in atherogenesis. uPA and its receptor uPAR are expressed in atherosclerotic lesion macrophages and contribute to atherosclerosis progression. In the present study we investigated the effect and mechanisms of action of uPA on monocyte-to-macrophage differentiation and on macrophage apoptotic death.

Methods and results

The number of mouse peritoneal macrophages (MPM) harvested from uPAR-deficient (uPAR^−/−) mice was significantly lower by 30% in comparison to control C57BL/6 mice. In vitro, uPA intensified PMA-induced THP-1 monocyte differentiation, as determined by increased expression of the macrophage marker CD36. This effect was mediated via G1 arrest, downregulation of G2/S phase and inhibition of PMA-induced cell death. uPA attenuated MonoMac6 (MM6) macrophage-like cell line apoptosis induced by oxidized LDL (Ox-LDL) and by thapsigargin (inhibitor of sarco-endoplasmic reticulum Ca²⁺-ATPase), but not by staurosporine (protein kinase inhibitor), suggesting that uPA antiapoptotic activity is Ca²⁺-independent, but involves a kinase activation. The antiapoptotic activity of uPA was dependent on the presence of uPAR, and it involved ERK1/2 activation-dependent downregulation of the proapoptotic protein Bim in macrophages stimulated with Ox-LDL.

Conclusions

The present study demonstrates, for the first time, that uPA stimulates the differentiation of monocytes into macrophages and attenuates Ox-LDL-induced macrophage apoptotic death via ERK1/2 activation-dependent Bim downregulation. These processes may result in prolonged macrophage survival in the lesion, increased lesion cellularity, and eventually necrosis, which accelerates lesion development.     

Urokinase Receptor Orchestrates the Plasminogen System in Airway Epithelial Cell Function

Purpose

The plasminogen system plays many roles in normal epithelial cell function, and components are elevated in diseases, such as cancer and asthma. The relative contribution of each component to epithelial function is unclear. We characterized normal cell function in airway epithelial cells with increased expression of selected pathway components.

Methods

BEAS-2B R1 bronchial epithelial cells stably overexpressing membrane urokinase plasminogen activator receptor (muPAR), soluble spliced uPAR (ssuPAR), the ligand (uPA) or inhibitors (PAI1 or PAI2), were characterized for pathway expression. Cell function was examined using proliferation, apoptosis, and scratch wound assays. A549 alveolar epithelial cells overexpressing muPAR were similarly characterized and downstream plasmin activity, MMP-1, and MMP-9 measured.

Results

Elevated expression of individual components led to changes in the plasminogen system expression profile, indicating coordinated regulation of the pathway. Increased muPAR expression augmented wound healing rate in BEAS-2B R1 and attenuated repair in A549 cells. Elevated expression of other system components had no effect on cell function in BEAS-2B R1 cells. This is the first study to investigate activity of the splice variant ssuPAR, with results suggesting that this variant plays a limited role in epithelial cell function in this model.

Conclusions

Our data highlight muPAR as the critical molecule orchestrating effects of the plasminogen system on airway epithelial cell function. These data have implications for diseases, such as cancer and asthma, and suggest uPAR as the key therapeutic target for the pathway in approaches to alter epithelial cell function.