Rac upregulates tissue inhibitor of metalloproteinase-1 expression by redox-dependent activation of extracellular signal-regulated kinase signaling

Hypoxia-induced preadipocyte factor 1 expression in human lung fibroblasts through ERK/PEA3/c-Jun pathway

Background

Several studies have reported that hypoxia plays a pathological role in severe asthma and tissue fibrosis. Our previous study showed that hypoxia induces A disintegrin and metalloproteinase 17 (ADAM17) expression in human lung fibroblasts. Moreover, preadipocyte factor 1 (Pref-1) is cleaved by ADAM17, which participates in adipocyte differentiation. Furthermore, Pref­1 overexpression is involved in tissue fibrosis including liver and heart. Extracellular signal-regulated kinase (ERK) could active downstram gene expression through polyoma enhancer activator 3 (PEA3) phosphorylation. Studies have demonstrated that PEA3 and activator protein 1 (AP-1) play crucial roles in lung fibrosis, and the Pref-1 promoter region contains PEA3 and AP-1 binding sites as predicted. However, the roles of ERK, PEA3, and AP-1 in hypoxia-stimulated Pref-1 expression in human lung fibroblasts remain unknown.

Methods

The protein expression in ovalbumin (OVA)-induced asthmatic mice was performed by immunohistochemistry and immunofluorescence. The protein expression or the mRNA level in human lung fibroblasts (WI-38) was detected by western blot or quantitative PCR. Small interfering (si) RNA was used to knockdown gene expression. The collaboration with PEA3 and c-Jun were determined by coimmunoprecipitation. Translocation of PEA3 from the cytosol to the nucleus was observed by immunocytochemistry. The binding ability of PEA3 and AP-1 to Pref-1 promoter was assessed by chromatin immunoprecipitation.

Results

Pref-1 and hypoxia-inducible factor 1α (HIF-1α) were expressed in the lung sections of OVA-treated mice. Colocalization of PEA3 and Fibronectin was detected in lung sections from OVA-treated mice. Futhermore, Hypoxia induced Pref­1 protein upregulation and mRNA expression in human lung fibroblasts (WI­38 cells). In 60 confluent WI-38 cells, hypoxia up-regulated HIF-1α and Pref-1 protein expression. Moreover, PEA3 small interfering (si) RNA decreased the expression of hypoxia-induced Pref­1 in WI­38 cells. Hypoxia induced PEA3 phosphorylation, translocation of PEA3 from the cytosol to the nucleus, PEA3 recruitment and AP-1 binding to the Pref­1 promoter region, and PEA3-luciferase activity. Additionally, hypoxia induced c-Jun-PEA3 complex formation. U0126 (an ERK inhibitor), curcumin (an AP­1 inhibitor) or c-Jun siRNA downregulated hypoxia-induced Pref-1 expression.

Conclusions

These results implied that ERK, PEA3, and AP­1 participate in hypoxia­induced Pref­1 expression in human lung fibroblasts.

Up-Regulation of Tiam1 Promotes the Radioresistance of Laryngeal Squamous Cell Carcinoma Through Activation of the JNK/ATF-2 Signaling Pathway

Purpose

Our previous study has revealed that T-lymphoma invasion and metastasis-inducing factor 1 (Tiam1) overexpression are significantly associated with aggressive behavior and poor prognosis in patients with laryngeal squamous cell carcinoma (LSCC). However, the influence of Tiam1 in the radioresistance of LSCC and its mechanism have never been elucidated.

Materials and Methods

Western blotting was used to confirm the relationship between Tiam1 and the JNK/ATF-2 signaling pathway. To explore the specific functions of Tiam1 and JNK/ATF-2 signaling pathway on the proliferation and apoptosis of LSCC after radiation, cloning formation assay and flow cytometry were conducted in vitro, and the experiments on a xenograft mouse model and TUNEL assay were performed in vivo.

Results

Western blotting indicated that Tiam1 can regulate the JNK/ATF-2 signaling pathway through the influence of the activity of JNK and ATF-2. Up-regulation of Tiam1 could promote proliferation and inhibit apoptosis of LSCC after radiation both in vitro and in vivo. Moreover, the down-regulation of the JNK/ATF-2 signaling pathway reduced the radioresistance of LSCC caused by Tiam1 up-regulation.

Conclusion

These results suggest that the up-regulation of Tiam1 expression can promote the radioresistance of LSCC through activation of the JNK/ATF-2 signaling pathway.

Induction of Connective Tissue Growth Factor Expression by Hypoxia in Human Lung Fibroblasts via the MEKK1/MEK1/ERK1/GLI-1/GLI-2 and AP-1 Pathways

Several reports have indicated that hypoxia, GLI, and connective tissue growth factor (CTGF) contribute to pulmonary fibrosis in idiopathic pulmonary fibrosis. We investigated the participation of mitogen-activated protein kinase kinase (MEK) kinase 1 (MEKK1)/MEK1/ERK1/GLI-1/2 and activator protein-1 (AP-1) signaling in hypoxia-induced CTGF expression in human lung fibroblasts. Hypoxia time-dependently increased CTGF expression, which was attenuated by the small interfering RNA (siRNA) of GLI-1 (GLI-1 siRNA) and GLI-2 (GLI-2 siRNA) in both human lung fibroblast cell line (WI-38) and primary human lung fibroblasts (NHLFs). Moreover, GLI-1 siRNA and GLI-2 siRNA attenuated hypoxia-induced CTGF-luciferase activity, and the treatment of cells with hypoxia induced GLI-1 and GLI-2 translocation. Furthermore, hypoxia-induced CTGF expression was reduced by an MEK inhibitor (PD98059), MEK1 siRNA, ERK inhibitor (U0126), ERK1 siRNA, and MEKK1 siRNA. Both PD98059 and U0126 significantly attenuated hypoxia-induced CTGF-luciferase activity. Hypoxia time-dependently increased MEKK1, ERK, and p38 MAPK phosphorylation. Moreover, SB203580 (a p38 MAPK inhibitor) also apparently inhibited hypoxia-induced CTGF expression. The treatment of cells with hypoxia induced ERK, GLI-1, or GLI-2 complex formation. Hypoxia-induced GLI-1 and GLI-2 translocation into the nucleus was significantly attenuated by U0126. In addition, hypoxia-induced ERK Tyr204 phosphorylation was impeded by MEKK1 siRNA. Moreover, hypoxia-induced CTGF-luciferase activity was attenuated by cells transfected with AP-1 site mutation in a CTGF construct. Exposure to hypoxia caused a time-dependent phosphorylation of c-Jun, but not of c-Fos. Chromatin immunoprecipitation (ChIP) revealed that hypoxia induced the recruitment of c-Jun, GLI-1, and GLI-2 to the AP-1 promoter region of CTGF. Hypoxia-treated cells exhibited an increase in α-smooth muscle actin (α-SMA) and collagen production, which was blocked by GLI-1 siRNA and GLI-2 siRNA. Overall, these data implied that the MEKK1/MEK1/ERK1/GLI-1/GLI-2, and AP-1 pathways mediated hypoxia-induced CTGF expression in human lung fibroblasts. Furthermore, GLI-1 and GLI-2 found to be involved in hypoxia-induced α-SMA and collagen expression.

CXCL12 induces connective tissue growth factor expression in human lung fibroblasts through the Rac1/ERK, JNK, and AP-1 pathways

CXCL12 (stromal cell-derived factor-1, SDF-1) is a potent chemokine for homing of CXCR4+ fibrocytes to injury sites of lung tissue, which contributes to pulmonary fibrosis. Overexpression of connective tissue growth factor (CTGF) plays a critical role in pulmonary fibrosis. In this study, we investigated the roles of Rac1, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and activator protein-1 (AP-1) in CXCL12-induced CTGF expression in human lung fibroblasts. CXCL12 caused concentration- and time-dependent increases in CTGF expression and CTGF-luciferase activity. CXCL12-induced CTGF expression was inhibited by a CXCR4 antagonist (AMD3100), small interfering RNA of CXCR4 (CXCR4 siRNA), a dominant negative mutant of Rac1 (RacN17), a mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor (PD98059), a JNK inhibitor (SP600125), a p21-activated kinase inhibitor (PAK18), c-Jun siRNA, and an AP-1 inhibitor (curcumin). Treatment of cells with CXCL12 caused activations of Rac1, Rho, ERK, and c-Jun. The CXCL12-induced increase in ERK phosphorylation was inhibited by RacN17. Treatment of cells with PD98059 and SP600125 both inhibited CXCL12-induced c-Jun phosphorylation. CXCL12 caused the recruitment of c-Jun and c-Fos binding to the CTGF promoter. Furthermore, CXCL12 induced an increase in α-smooth muscle actin (α-SMA) expression, a myofibroblastic phenotype, and actin stress fiber formation. CXCL12-induced actin stress fiber formation and α-SMA expression were respectively inhibited by AMD3100 and CTGF siRNA. Taken together, our results suggest that CXCL12, acting through CXCR4, activates the Rac/ERK and JNK signaling pathways, which in turn initiates c-Jun phosphorylation, and recruits c-Jun and c-Fos to the CTGF promoter and ultimately induces CTGF expression in human lung fibroblasts. Moreover, overexpression of CTGF mediates CXCL12-induced α-SMA expression.

Connective tissue growth factor induces collagen I expression in human lung fibroblasts through the Rac1/MLK3/JNK/AP-1 pathway

Connective tissue growth factor (CTGF) plays an important role in lung fibrosis. In this study, we investigated the role of Rac1, mixed-lineage kinase 3 (MLK3), c-Jun N-terminal kinase (JNK), and activator protein-1 (AP-1) in CTGF-induced collagen I expression in human lung fibroblasts. CTGF caused concentration- and time-dependent increases in collagen I expression. CTGF-induced collagen I expression was inhibited by the dominant negative mutant (DN) of Rac1 (RacN17), MLK3DN, MLK3 inhibitor (K252a), JNK1DN, JNK2DN, a JNK inhibitor (SP600125), and an AP-1 inhibitor (curcumin). Treatment of cells with CTGF caused activation of Rac1, MLK3, JNK, and AP-1. The CTGF-induced increase in MLK3 phosphorylation was inhibited by RacN17. Treatment with RacN17 and the MLK3DN inhibited CTGF-induced JNK phosphorylation. CTGF caused increases in c-Jun phosphorylation and the recruitment of c-Jun and c-Fos to the collagen I promoter. Furthermore, stimulation of cells with the CTGF resulted in increases in AP-1-luciferase activity; this effect was inhibited by Rac1N17, MLK3DN, JNK1DN, and JNK2DN. Moreover, CTGF-induced α-smooth muscle actin (α-SMA) expression was inhibited by the procollagen I small interfering RNA (siRNA). These results suggest for the first time that CTGF acting through Rac1 activates the MLK3/JNK signaling pathway, which in turn initiates AP-1 activation and recruitment of c-Jun and c-Fos to the collagen I promoter and ultimately induces collagen I expression in human lung fibroblasts.

CaMKII in the cardiovascular system: sensing redox states

The multifunctional Ca(2+)- and calmodulin-dependent protein kinase II (CaMKII) is now recognized to play a central role in pathological events in the cardiovascular system. CaMKII has diverse downstream targets that promote vascular disease, heart failure, and arrhythmias, so improved understanding of CaMKII signaling has the potential to lead to new therapies for cardiovascular disease. CaMKII is a multimeric serine-threonine kinase that is initially activated by binding calcified calmodulin (Ca(2+)/CaM). Under conditions of sustained exposure to elevated Ca(2+)/CaM, CaMKII transitions into a Ca(2+)/CaM-autonomous enzyme by two distinct but parallel processes. Autophosphorylation of threonine-287 in the CaMKII regulatory domain "traps" CaMKII into an open configuration even after Ca(2+)/CaM unbinding. More recently, our group identified a pair of methionines (281/282) in the CaMKII regulatory domain that undergo a partially reversible oxidation which, like autophosphorylation, prevents CaMKII from inactivating after Ca(2+)/CaM unbinding. Here we review roles of CaMKII in cardiovascular disease with an eye to understanding how CaMKII may act as a transduction signal to connect pro-oxidant conditions into specific downstream pathological effects that are relevant to rare and common forms of cardiovascular disease.

Rac1-mediated mitochondrial H2O2 generation regulates MMP-9 gene expression in macrophages via inhibition of SP-1 and AP-1

Aberrant matrix deposition is a hallmark of pulmonary fibrosis and is characterized by an imbalance between matrix deposition and degradation. We have previously shown that mice harboring a conditional deletion of the GTP-binding protein, Rac1, in macrophages are protected from asbestos-induced pulmonary fibrosis. To investigate the contribution of aberrant matrix degradation, we addressed the role of Rac1 in regulating expression of macrophage-specific MMP-9 (matrix metalloproteinase-9). We found that MMP-9 gene transcription was significantly greater in Rac1 null macrophages. Deletion and mutational analysis of the MMP-9 promoter revealed that both SP-1 and AP-1 are essential for MMP-9 transcription. Overexpression of constitutive active Rac1 (V12) revealed that H(2)O(2) was derived from the mitochondria. Rac1-induced H(2)O(2) generation down-regulated MMP-9 gene transcription, whereas catalase overexpression in WT cells enhanced MMP-9 expression. SP-1 interacted directly with both c-Jun and c-Fos, and H(2)O(2) decreased this binding, suggesting that SP-1 and AP-1 function cooperatively to regulate MMP-9 transcription. Rac1-mediated H(2)O(2) inhibited the ERK MAPK, which was essential for activation of SP-1 and AP-1. ERK activation and MMP-9 expression were recovered by overexpressing catalase or transfecting siRNA for the mitochondrial iron-sulfur protein, Rieske. These observations were recapitulated in vivo. MMP-9 mRNA was higher in alveolar macrophages isolated from Rac1 null mice and wild type mice given catalase. Rac1 regulates MMP-9 transcription via mitochondrial H(2)O(2) generation, providing a potential mechanism by which Rac1 null mice fail to develop pulmonary fibrosis.

The "two-faced" effects of reactive oxygen species and the lipid peroxidation product 4-hydroxynonenal in the hallmarks of cancer

Reacytive Oxygen Species (ROS) have long been considered to be involved in the initiation, progression and metastasis of cancer. However, accumulating evidence points to the benefical role of ROS. Moreover, ROS production, leading to apoptosis, is the mechanism by which many chemotherapeutic agents can act. Beside direct actions, ROS elicit lipid peroxidation, leading to the production of 4-hydroxynoneal (HNE). Interestingly, HNE also seems to have a dual behaviour with respect to cancer. In this review we present recent literature data which outline the "two-faced" character of oxidative stress and lipid peroxidation in carcinogenesis and in the hallmarks of cancer.

A dynamic pathway for calcium-independent activation of CaMKII by methionine oxidation

Calcium/calmodulin (Ca2+/CaM)-dependent protein kinase II (CaMKII) couples increases in cellular Ca2+ to fundamental responses in excitable cells. CaMKII was identified over 20 years ago by activation dependence on Ca2+/CaM, but recent evidence shows that CaMKII activity is also enhanced by pro-oxidant conditions. Here we show that oxidation of paired regulatory domain methionine residues sustains CaMKII activity in the absence of Ca2+/CaM. CaMKII is activated by angiotensin II (AngII)-induced oxidation, leading to apoptosis in cardiomyocytes both in vitro and in vivo. CaMKII oxidation is reversed by methionine sulfoxide reductase A (MsrA), and MsrA-/- mice show exaggerated CaMKII oxidation and myocardial apoptosis, impaired cardiac function, and increased mortality after myocardial infarction. Our data demonstrate a dynamic mechanism for CaMKII activation by oxidation and highlight the critical importance of oxidation-dependent CaMKII activation to AngII and ischemic myocardial apoptosis.

Natural dietary anti-cancer chemopreventive compounds: redox-mediated differential signaling mechanisms in cytoprotection of normal cells versus cytotoxicity in tumor cells

Many dietary phytochemicals exhibit health-beneficial effects including prevention of diseases such as cancer, as well as neurological, cardiovascular, inflammatory, and metabolic diseases. Evolutionarily, herbivorous and omnivorous animals have been ingesting plants. This interaction between "animal-plant" ecosystems has resulted in an elaborate system of detoxification and defense mechanisms evolved by animals including humans. Mammalian cells, including human cells, respond to these dietary phytochemicals by "non-classical receptor sensing" mechanisms of electrophilic chemical-stress typified by "thiol-modulated" cellular signaling events primarily leading to the gene expression of pharmacologically beneficial effects, but sometimes unwanted cytotoxicity also. Our laboratory has been studying two groups of dietary phytochemical cancer-chemopreventive compounds (isothiocyanates and polyphenols), which are effective in chemical-induced, as well as genetically-induced, animal carcinogenesis models. These compounds typically generate "cellular stress" and modulate gene expression of phase II detoxifying/antioxidant enzymes. Electrophiles, reactive oxygen species, and reactive nitrogen species are known to act as second messengers in the modulation of many cellular signaling pathways leading to gene expression changes and pharmacological responses. Redox-sensitive transcription factors such as nuclear factor-E2-related factor 2 (Nrf2), AP-1, NF-kappaB, to cite a few examples, sense and transduce changes in the cellular redox status and modulate gene expression responses to oxidative and electrophilic stresses, presumably via sulfhydryl modification of critical cysteine residues found on these proteins and/or other upstream redox-sensitive molecular targets. In the current review, we will explore dietary cancer chemopreventive phytochemicals, discuss the link between oxidative/electrophilic stresses and the redox circuitry, and consider different redox-sensitive transcription factors. We will also discuss the kelch-like erythroid Cap'n'Collar homologue-associated protein 1 (Keap1)-Nrf2 axis in redox signaling of induction of phase II detoxifying/antioxidant defense mechanisms, an important target and preventive strategy for normal cells against carcinogenesis, and the converse inhibition of cell growth/inflammatory signaling pathways that would confer therapeutic intervention in many types of cancers. Finally, we will summarize the Nrf2 paradigm in gene expression, the pharmacotoxicogenomic relevance of redox-sensitive Nrf2, and the redox regulation of cell death mechanisms.