AUF-1 mediates inhibition by nitric oxide of lipopolysaccharide-induced matrix metalloproteinase-9 expression in cultured astrocytes

Hypoxic Effects on Matrix Metalloproteinases' Expression in the Tumor Microenvironment and Therapeutic Perspectives

The tumor microenvironment (TME) is characterized by an acidic pH and low oxygen concentrations. Hypoxia induces neoplastic cell evasion of the immune surveillance, rapid DNA repair, metabolic reprogramming, and metastasis, mainly as a response to the hypoxic inducible factors (HIFs). Likewise, cancer cells increase matrix metalloproteinases' (MMPs) expression in response to TME conditions, allowing them to migrate from the primary tumor to different tissues. Since HIFs and MMPs are augmented in the hypoxic TME, it is easy to consider that HIFs participate directly in their expression regulation. However, not all MMPs have a hypoxia response element (HRE)-HIF binding site. Moreover, different transcription factors and signaling pathways activated in hypoxia conditions through HIFs or in a HIF-independent manner participate in MMPs' transcription. The present review focuses on MMPs' expression in normal and hypoxic conditions, considering HIFs and a HIF-independent transcription control. In addition, since the hypoxic TME causes resistance to anticancer conventional therapy, treatment approaches using MMPs as a target alone, or in combination with other therapies, are also discussed.

Expression Profile of Six RNA-Binding Proteins in Pulmonary Sarcoidosis

BACKGROUND

Sarcoidosis is characterised by up-regulation of cytokines and chemokine ligands/receptors and proteolytic enzymes. This pro-inflammatory profile is regulated post-transcriptionally by RNA-binding proteins (RBPs). We investigated in vivo expression of six RBPs (AUF1, HuR, NCL, TIA, TIAR, PCBP2) and two inhibitors of proteolytic enzymes (RECK, PTEN) in pulmonary sarcoidosis and compared it to the expression in four control groups of healthy individuals and patients with other respiratory diseases: chronic obstructive pulmonary disease (COPD), asthma and idiopathic interstitial pneumonias (IIPs).

METHODS

RT-PCR was used to quantify the mRNAs in bronchoalveolar (BA) cells obtained from 50 sarcoidosis patients, 23 healthy controls, 30 COPD, 19 asthmatic and 19 IIPs patients. Flow cytometry was used to assess intracellular protein expression of AUF1 and HuR in peripheral blood T lymphocytes (PBTLs) obtained from 9 sarcoidosis patients and 6 healthy controls.

RESULTS

Taking the stringent conditions for multiple comparisons into consideration, we consistently observed in the primary analysis including all patients regardless of smoking status as well as in the subsequent sub-analysis limited for never smokers that the BA mRNA expression of AUF1 (p<0.001), TIA (p<0.001), NCL (p<0.01) and RECK (p<0.05) was decreased in sarcoidosis compared to healthy controls. TIA mRNA was also decreased in sarcoidosis compared to both obstructive pulmonary diseases (COPD and asthma; p<0.001) but not compared to IIPs. There were several positive correlations between RECK mRNA and RBP mRNAs in BA cells. Also sarcoidosis CD3+, CD4+ and CD8+ PBTLs displayed lower mean fluorescence intensity of AUF1 (p≤0.02) and HuR (p≤0.03) proteins than control healthy PBTLs.

CONCLUSION

mRNA expressions of three RBPs (AUF1, TIA and NCL) and their potential target mRNA encoding RECK in BA cells and additionally protein expression of AUF1 and HuR in PBTLs were down-regulated in our sarcoidosis patients compared to healthy individuals. Its significance, e.g. for stability of mRNAs encoding pro-inflammatory factors, should be further explored in sarcoidosis.

Targeted mRNA Decay by RNA Binding Protein AUF1 Regulates Adult Muscle Stem Cell Fate, Promoting Skeletal Muscle Integrity

Following skeletal muscle injury, muscle stem cells (satellite cells) are activated, proliferate, and differentiate to form myofibers. We show that mRNA-decay protein AUF1 regulates satellite cell function through targeted degradation of specific mRNAs containing 3' AU-rich elements (AREs). auf1(-/-) mice undergo accelerated skeletal muscle wasting with age and impaired skeletal muscle repair following injury. Satellite cell mRNA analysis and regeneration studies demonstrate that auf1(-/-) satellite cell self-renewal is impaired due to increased stability and overexpression of ARE-mRNAs, including cell-autonomous overexpression of matrix metalloprotease MMP9. Secreted MMP9 degrades the skeletal muscle matrix, preventing satellite-cell-mediated regeneration and return to quiescence. Blocking MMP9 activity in auf1(-/-) mice restores skeletal muscle repair and maintenance of the satellite cell population. Control of ARE-mRNA decay by AUF1 represents a mechanism for adult stem cell regulation and is implicated in human skeletal muscle wasting diseases.

Nitric oxide-matrix metaloproteinase-9 interactions: biological and pharmacological significance--NO and MMP-9 interactions

Nitric oxide (NO) and matrix metalloproteinase 9 (MMP-9) levels are found to increase in inflammation states and in cancer, and their levels may be reciprocally modulated. Understanding interactions between NO and MMP-9 is of biological and pharmacological relevance and may prove crucial in designing new therapeutics. The reciprocal interaction between NO and MMP-9 have been studied for nearly twenty years but to our knowledge, are yet to be the subject of a review. This review provides a summary of published data regarding the complex and sometimes contradictory effects of NO on MMP-9. We also analyse molecular mechanisms modulating and mediating NO-MMP-9 interactions. Finally, a potential therapeutic relevance of these interactions is presented.

Inhibition of matrix metalloproteinases-2/-9 transiently reduces pre-oligodendrocyte loss during lipopolysaccharide- but not tumour necrosis factor-alpha-induced inflammation in fetal ovine glial culture

To determine whether increased matrix metalloproteinase (MMP) proteolytic activity plays a pathological role in infection/inflammation-induced preterm brain injury, primary cultures of preterm (day 90 of gestation; term 145 days) fetal ovine mixed glia were exposed to 24-96 h of lipopolysaccharide (LPS, 1 μg/ml) or tumour necrosis factor-α (TNF-α, 100 ng/ml). MMP-2 mRNA levels were significantly increased after TNF-α (96 h) and LPS exposure (48 and 96 h), and MMP-9 mRNA levels were significantly increased at 48 and 96 h after TNF-α. On zymography, the active form of secreted MMP-2 was significantly increased 24 h after LPS, but not TNF-α. Both active and latent forms of MMP-9 gelatinolytic activity were significantly increased by TNF-α (96 h) and LPS (72 and 96 h). On reverse zymography, inhibitory activity of TIMP-1 but not TIMP-2 was significantly increased by TNF-α and LPS. SB-3CT-mediated MMP-2 and MMP-9 inhibition transiently reduced LPS-induced oligodendrocyte cell death but had no effect during TNF-α exposure. Collectively, these observations suggest a limited, transient effect of MMPs on immature white matter damage associated with infection but not TNF-α-mediated inflammation.

NFATc3 promotes Ca(2+) -dependent MMP3 expression in astroglial cells

Increase in intracellular calcium ([Ca(2+) ]i ) is a key mediator of astrocyte signaling, important for activation of the calcineurin (CN)/nuclear factor of activated T cells (NFAT) pathway, a central mediator of inflammatory events. We analyzed the expression of matrix metalloproteinase 3 (Mmp3) in response to increases in [Ca(2+) ]i and the role of the CN/NFAT pathway in this regulation. Astrocyte Mmp3 expression was induced by overexpression of a constitutively active form of NFATc3, whereas other MMPs and tissue inhibitor of metalloproteinases (TIMP) were unaffected. Mmp3 mRNA and protein expression was also induced by calcium ionophore (Io) and 2'(3')-O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (Bz-ATP) and Mmp3 upregulation was prevented by the CN inhibitor cyclosporin A (CsA). Ca(2+) -dependent astrocyte Mmp3 expression was also inhibited by actinomycin D, and a Mmp3 promoter luciferase reporter was efficiently activated by increased [Ca(2+) ]i , indicating regulation at the transcriptional level. Furthermore, Ca(2+) /CN/NFAT dependent Mmp3 expression was confirmed in pure astrocyte cultures derived from neural stem cells (Ast-NSC), demonstrating that the induced Mmp3 expression occurs in astrocytes, and not microglial cells. In an in vivo stab-wound model of brain injury, MMP3 expression was detected in NFATc3-positive scar-forming astrocytes. Because [Ca(2+) ]i increase is an early event in most brain injuries, these data support an important role for Ca(2+) /CN/NFAT-induced astrocyte MMP3 expression in the early neuroinflammatory response. Understanding the molecular pathways involved in this regulation could provide novel therapeutic targets and approaches to promoting recovery of the injured brain.

Microglia are the major source of TNF-α and TGF-β1 in postnatal glial cultures; regulation by cytokines, lipopolysaccharide, and vitronectin

Damage to the central nervous system (CNS) leads to increased production of TNF-α and TGF-β1 cytokines that have pro- or anti-inflammatory actions, respectively. To define whether astrocytes or microglia express these cytokines, prior studies have used mixed glial cultures (MGC) to represent astrocytes, thought these results are inevitably complicated by the presence of contaminating microglia within MGC. To clarify the cellular source of these cytokines, here we employed a recently described method of preparing microglia-free astrocyte cultures, in which neural stem cells (NSC) are differentiated into astrocytes. Using ELISA to quantify cytokine production in three types of glial culture: MGC, pure microglia or pure astrocytes, this showed that microglia but not astrocytes, produce TNF-α, and that this expression is increased by LPS, IFN-γ, and to a lesser extent by vitronectin, but decreased by TGF-β1. In contrast, TGF-β1 was produced by microglia and astrocytes, though at 10-fold higher levels by microglia. TGF-β1 expression in microglia was increased by vitronectin and to a lesser extent by TNF-α and LPS, but astrocyte TGF-β1 expression was not regulated by any factor tested. In summary, our data reveal that microglia, not astrocytes are the major source of TNF-α and TGF-β1 in postnatal glial cultures, and that microglial production of these antagonistic cytokines is tightly regulated by cytokines, LPS, and vitronectin.

Role of transcription factor Sp1 and RNA binding protein HuR in the downregulation of Dr+ Escherichia coli receptor protein decay accelerating factor (DAF or CD55) by nitric oxide

We previously reported that nitric oxide (NO) reduces the rate of bacteremia and maternal mortality in pregnant rats with uterine infection by Escherichia coli expressing the Dr Fimbria (Dr(+) ). The epithelial invasion of Dr(+) E. coli is dependent on the expression level of its cellular receptor decay accelerating factor (DAF). NO reduces the rate of bacteremia by downregulating the expression of DAF. In this study, we elucidated the role of transcription factor Sp1 and RNA binding protein HuR in the downregulation of human DAF by NO. We generated a series of deletion mutant constructs of DAF gene 5'-untranslated region and mapped the NO-response region upstream to the core promoter region of the DAF gene. One of the several Sp1 binding sites in the DAF 5'-untranslated region was located within the NO-response region. The binding of Sp1 to this site was inhibited by NO. Furthermore, NO also promoted the degradation of DAF mRNA. The 3'-untranslated region of DAF harbors an AU-rich element and this element destabilized the mRNA transcript. NO promoted the rapid degradation of DAF mRNA by inhibiting the binding of mRNA stabilizing protein HuR to this AU-rich region. The inhibition of binding of HuR to the AU-rich region was due to the S-nitrosylation of one or more cysteine residues by NO. Thus, these data reveal the molecular mediators of transcriptional and post-transcriptional regulation of DAF by NO with implications in pathophysiology related to DAF.

Nitric oxide-mediated regulation of β-amyloid clearance via alterations of MMP-9/TIMP-1

Fibrillar amyloid plaques are largely composed of amyloid-beta (Aβ) peptides that are metabolized into products, including Aβ1-16, by proteases including matrix metalloproteinase 9 (MMP-9). The balance between production and degradation of Aβ proteins is critical to amyloid accumulation and resulting disease. Regulation of MMP-9 and its endogenous inhibitor tissue inhibitor of metalloproteinase (TIMP)-1 by nitric oxide (NO) has been shown. We hypothesize that nitric oxide synthase (NOS2) protects against Alzheimer's disease pathology by increasing amyloid clearance through NO regulation of MMP-9/TIMP-1 balance. We show NO-mediated increased MMP-9/TIMP-1 ratios enhanced the degradation of fibrillar Aβ in vitro, which was abolished when silenced for MMP-9 protein translation. The in vivo relationship between MMP-9, NO and Aβ degradation was examined by comparing an Alzheimer's disease mouse model that expresses NOS2 with a model lacking NOS2. To quantitate MMP-9 mediated changes, we generated an antibody recognizing the Aβ1-16 fragment, and used mass spectrometry multi-reaction monitoring assay for detection of immunoprecipitated Aβ1-16 peptides. Aβ1-16 levels decreased in brain lysates lacking NOS2 when compared with strains that express human amyloid precursor protein on the NOS2 background. TIMP-1 increased in the APPSwDI/NOS2(-/-) mice with decreased MMP activity and increased amyloid burden, thereby supporting roles for NO in the regulation of MMP/TIMP balance and plaque clearance.

A modified in vitro method to obtain pure astrocyte cultures induced from mouse hippocampal neural stem cells using clonal expansion

The aim of the present study was to produce astrocyte cultures of high purity from mouse hippocampal neural stem cells and to compare their in vitro properties with those isolated from enriched mixed glial cultures prepared from mouse hippocampus, which are commonly contaminated by microglia. We produced primary cultures of newborn mouse hippocampal neural stem cells, which have the potential to differentiate into astrocytes, neurons, and oligodendrocytes. We produced monoclonal neural stem cell colonies by limiting dilution. We induced astrocyte differentiation by plating the colonies on poly-L: -lysine and culturing them in induction medium consisting of minimum essential medium/F12 supplemented with 10% fetal bovine serum and 100 ng/ml ciliary neurotrophic factor. We then further purified the cells by differential adherence and shaking at a constant temperature, followed by a second round of limiting dilution. Immunocytochemistry for glial fibrillary acidic protein showed that our method yielded 99.4 ± 0.5% pure astrocytes, whereas traditionally enriched mixed glial cultures yielded 94.2 ± 2% pure astrocytes. Induced cells resembled primary astrocyte cultures in functional properties such as cell proliferation rates and lack of tumorigenicity and p53, and expression of epidermal growth factor receptor, bystin, and nitric oxygen synthase. Our novel method of culture and purification of neural stem cells can therefore be used routinely for the primary culture of highly purified astrocytes from mouse hippocampus.

Modulation of neoplastic gene regulatory pathways by the RNA-binding factor AUF1

The mRNA-binding protein AUF1 regulates the expression of many key players in cancer including proto-oncogenes, regulators of apoptosis and the cell cycle, and pro-inflammatory cytokines, principally by directing the decay kinetics of their encoded mRNAs. Most studies support an mRNA-destabilizing role for AUF1, although other findings suggest additional functions for this factor. In this review, we explore how changes in AUF1 isoform distribution, subcellular localization, and post-translational protein modifications can influence the metabolism of targeted mRNAs. However, several lines of evidence also support a role for AUF1 in the initiation and/or development of cancer. Many AUF1-targeted transcripts encode products that control pro- and anti-oncogenic processes. Also, overexpression of AUF1 enhances tumorigenesis in murine models, and AUF1 levels are enhanced in some tumors. Finally, signaling cascades that modulate AUF1 function are deregulated in some cancerous tissues. Together, these features suggest that AUF1 may play a prominent role in regulating the expression of many genes that can contribute to tumorigenic phenotypes, and that this post-transcriptional regulatory control point may be subverted by diverse mechanisms in neoplasia.

Nitric oxide in vascular endothelial growth factor-induced focal angiogenesis and matrix metalloproteinase-9 activity in the mouse brain

BACKGROUND AND PURPOSE

Vascular endothelial growth factor (VEGF) can induce matrix metalloproteinase (MMP)-9 activities and focal angiogenesis. We hypothesized that VEGF activation of cerebral MMP-9 would require nitric oxide participation.

METHODS

We compared the in vivo effects of: (1) N(G)-monomethyl-l-arginine, a nonspecific nitric oxide synthase inhibitor; (2) L-N(6)-(1-iminoethyl)lysine, an inducible nitric oxide synthase selective inhibitor; and (3) doxycycline, a known nonspecific inhibitor of MMP in the mouse brain, using in situ zymography and endothelial marker CD31. 3-nitrotyrosine was used as a surrogate for nitric oxide activity. Inflammatory cell markers CD68 and MPO were used to confirm leukocyte infiltration.

RESULTS

VEGF-stimulated MMP-9 activity expressed primarily around cerebral microvessels. N(G)-monomethyl-l-arginine suppressed cerebral angiogenesis (P<0.05), especially those microvessels associated with MMP-9 activation (P<0.02) induced by VEGF, comparable to the effect of doxycycline. L-N(6)-(1-iminoethyl)lysine showed similar inhibitory effects. 3-nitrotyrosine confirmed nitric oxide levels in the brain. Compared with the lacZ control, VEGF increased inflammatory cell infiltration, especially macrophages, in the induced brain angiogenic focuses.

CONCLUSIONS

Inhibition of nitric oxide production decreased MMP-9 activity and focal angiogenesis in the VEGF-stimulated brain. Both specific and nonspecific inhibition of nitric oxide synthase resulted in similar reductions, suggesting that VEGF-stimulated cerebral MMP activity and angiogenesis are predominantly mediated through inducible nitric oxide synthase, a specific nitric oxide synthase isoform mediating inflammatory responses.

Diffusion-weighted magnetic resonance imaging reversal by gene knockdown of matrix metalloproteinase-9 activities in live animal brains

The involvement of matrix metalloproteinase-9 (MMP-9) activities in the development of abnormal water diffusion in the brain after cardiac arrest is not fully understood. We used magnetic resonance imaging to determine the correlation between MMP-9 activity and the mechanism of abnormal water diffusion after global cerebral ischemia (GCI)-induced brain damage in C57black6 mice. We induced GCI in mice by occluding both carotid arteries for 60 min, then allowing reperfusion. We labeled a short DNA that targets mmp-9 mRNA activity [phosphorothioate-modified oligodeoxynucleotide (sODN)-mmp9] or a control probe without intracellular target (sODN-Ran) with iron-based MR contrast agent [superparamagnetic iron oxide nanoparticle (SPION)-mmp9 or SPION-Ran] or fluorescein isothiocyanate (FITC)-sODN-mmp9 or FITC-sODN-Ran; we then delivered these probes by intracerebroventricular infusion or intraperitoneal injection within 3 h of reperfusion. At low dose (120 pmol/kg) the SPION-mmp9 probe was retained at significant levels in the striatum and cortex of living brains 10 h after GCI. Probe retention was validated by similar elevation of mmp-9 mRNA and antigens in postmortem samples taken from regions that exhibited GCI-induced hyperintensity in diffusion-weighted imaging, and a significant reduction in apparent diffusion coefficient (rADC, p = 0.0006, n = 12). At a higher dose (120 nmol/kg), the FITC-sODN-mmp9 probe revealed significant knockdown of MMP-9 activity, per zymography, and a reversal of striatal rADC (p = 0.004, n = 6). These observations were not duplicated in the control group. We conclude that expression of mmp-9 mRNA is associated with abnormal ADC after GCI.

A novel method to establish microglia-free astrocyte cultures: comparison of matrix metalloproteinase expression profiles in pure cultures of astrocytes and microglia

Increased matrix metalloproteinase (MMP) proteolytic activity contributes to the pathogenesis of many neuroinflammatory and neurodegenerative conditions in the CNS. To fully understand this process, it is important to define the MMP expression profile of specific cell types, including the CNS-resident cells astrocytes and microglia. While previous studies have characterized astrocyte MMP expression by using mixed glial cultures, these results are likely complicated by the presence of contaminating microglia within these cultures. In the current study, we sought to clarify this complexity, by taking a novel approach to prepare pure astrocyte cultures entirely devoid of microglia, by promoting neural stem cell (NSC) differentiation into astrocytes. The MMP expression profile of mixed glial cultures, neurosphere-derived astrocytes, and pure microglia was characterized by RNase protection assay. This revealed that MMP gene expression is largely cell-type specific. Astrocytes constitutively expressed MMP-11, MMP-14, and MMP-2 and showed induction of MMP-3 in response to IL-1beta but did not respond to lipopolysaccharide (LPS). In contrast, microglia constitutively expressed high levels of MMP-12 and showed strong induction of MMP-9 and MMP-14 in response to LPS. Gelatin zymography confirmed that LPS and TNF-alpha induced strong expression of MMP-9 in microglia but not astrocytes. In summary, these studies demonstrate that neurosphere-derived astrocytes represent an attractive alternative system in which to study astrocyte behavior in vitro. Using this system, we have shown that astrocytes and microglia express distinct sets of MMP genes and that microglia, not astrocytes, are the major source of MMP-9 in response to LPS or TNF-alpha.

Inhibition of poly(ADP-ribose) polymerase-1 by arsenite interferes with repair of oxidative DNA damage

Arsenic enhances skin tumor formation when combined with other carcinogens, including UV radiation (UVR). In this study we report that low micromolar concentrations of arsenite synergistically increases UVR-induced oxidative DNA damage in human keratinocytes as detected by 8-hydroxyl-2'-deoxyguanine (8-OHdG) formation. Poly(ADP-ribose) polymerase-1 (PARP-1) is involved in base excision repair, a process that repairs 8-OHdG lesions. Arsenite suppresses UVR-induced PARP-1 activation in a concentration-dependent manner. Inhibition of PARP-1 activity by 3-aminobenzamide or small interfering RNA silencing of PARP-1 expression significantly increases UVR-induced 8-OHdG formation, suggesting that inhibition of PARP-1 activity by arsenite contributes to oxidative DNA damage. PARP-1 is a zinc finger protein, and mass spectrometry analysis reveals that arsenite can occupy a synthetic apopeptide representing the first zinc finger of PARP-1 (PARPzf). When the PARPzf peptide is preincubated with Zn(II) followed by incubation with increasing concentrations of arsenite, the ZnPARPzf signal is decreased while the AsPARPzf signal intensity is increased as a function of arsenite dose, suggesting a competition between zinc and arsenite for the same binding site. Addition of Zn(II) abolished arsenite enhancement of UVR-stimulated 8-OHdG generation and restored PARP-1 activity. Our findings demonstrate that arsenite inhibits oxidative DNA damage repair and suggest that interaction of arsenite with the PARP-1 zinc finger domain contributes to the inhibition of PARP-1 activity by arsenite. Arsenite inhibition of poly(ADP-ribosyl)ation is one likely mechanism for the reported co-carcinogenic activities of arsenic in UVR-induced skin carcinogenesis.

Low concentration of arsenite exacerbates UVR-induced DNA strand breaks by inhibiting PARP-1 activity

Epidemiological studies have associated arsenic exposure with many types of human cancers. Arsenic has also been shown to act as a co-carcinogen even at low concentrations. However, the precise mechanism of its co-carcinogenic action is unknown. Recent studies indicate that arsenic can interfere with DNA-repair processes. Poly(ADP-ribose) polymerase (PARP)-1 is a zinc-finger DNA-repair protein, which can promptly sense DNA strand breaks and initiate DNA-repair pathways. In the present study, we tested the hypothesis that low concentrations of arsenic could inhibit PAPR-1 activity and so exacerbate levels of ultraviolet radiation (UVR)-induced DNA strand breaks. HaCat cells were treated with arsenite and/or UVR, and then DNA strand breaks were assessed by comet assay. Low concentrations of arsenite ( Collapse

Key Words

• arsenic
• parp-1
• dna damage repair
• dna strand break
• comet assay
• ros
• carcinogenesis

Collapse

MESH Headings

• Arsenites/toxicity
• Benzamides/pharmacology
• Carcinogens/toxicity
• Cell Line
• Chlorides/pharmacology
• Comet Assay
• DNA Breaks
• Dose-Response Relationship, Drug
• Enzyme Inhibitors/toxicity
• Humans
• Keratinocytes/drug effects
• Keratinocytes/enzymology
• Keratinocytes/radiation effects
• Poly (ADP-Ribose) Polymerase-1
• Poly(ADP-ribose) Polymerase Inhibitors
• Poly(ADP-ribose) Polymerases/genetics
• Poly(ADP-ribose) Polymerases/metabolism
• RNA Interference
• RNA, Small Interfering
• Reactive Oxygen Species/metabolism
• Sodium Compounds/toxicity
• Transfection
• Ultraviolet Rays
• Zinc Compounds/pharmacology

Collapse

Grants

• R01 ES012938-01 NIEHS NIH HHS
• P30 ES012072 NIEHS NIH HHS
• P30 ES-012072 NIEHS NIH HHS
• R01 ES015826 NIEHS NIH HHS
• R01 ES015826-01A1 NIEHS NIH HHS
• P30 CA118100 NCI NIH HHS
• R01 ES012938 NIEHS NIH HHS

Collapse

Affiliation(s)

Xu-Jun Qin Program of Toxicology, College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131-0001, USA
Laurie G Hudson
Wenlan Liu
Graham S Timmins
Ke Jian Liu

Collapse

Dual actions involved in arsenite-induced oxidative DNA damage

Arsenic is a recognized human carcinogen, but the mechanism of carcinogenesis is not well understood. Oxidative stress and inhibition of DNA damage repair have been postulated as potential carcinogenic actions of arsenic. The present study tests the hypothesis that arsenite not only induces oxidative stress but also inhibits the activity of the DNA base excision repair protein, poly(ADP-ribose) polymerase-1 (PARP-1), leading to exacerbation of the oxidative DNA damage induced by arsenic. HaCat cells were treated with arsenite for 24 h before measuring 8-hydroxyl-2'-deoxyguanosine (8-OHdG), PARP-1 activity, and reactive oxygen species (ROS). Zinc supplementation and PARP-1 siRNA were used to increase or decrease, respectively, the PARP-1 protein's physiological function. At high concentrations (10 microM or higher), arsenite greatly induced oxidative DNA damage, as indicated by 8-OHdG formation. At lower concentrations (1 microM), arsenite did not produce detectable 8-OHdG, but was still able to effectively inhibit PARP-1 activity. Zinc supplementation reduced the formation of 8-OHdG, restored the PARP-1 activity inhibited by arsenite, but did not decrease ROS production. SiRNA knockdown of PARP-1 did not affect the 8-OHdG level induced by arsenic, while it greatly increased the 8-OHdG level produced by hydrogen peroxide indicating that PARP-1 is a molecular target of arsenite. Our findings demonstrate that in addition to inducing oxidative stress at higher concentrations, arsenite can also inhibit the function of a key DNA repair protein, PARP-1, even at very low concentrations, thus exacerbating the overall oxidative DNA damage produced by arsenite, and potentially, by other oxidants as well.

Nitric oxide and vascular remodeling: Spotlight on the kidney

Extracellular matrix (ECM) remodeling with successive tissue fibrosis is a key feature of chronic cardiovascular diseases, including atherosclerosis and restenosis. The atherogenic changes underlying these pathologies result from chronification of an acute repair response towards injurious and inflammatory stimuli. Thereby functional tissue is replaced by excessive ECM deposition. In the kidney, impaired remodeling is a major cause of perivascular, interstitial, and glomerular fibrosis but also a common complication of chronic hypertension. Experimental evidence points to the matrix metalloproteases (MMPs) and their intrinsic inhibitors, the tissue inhibitors of MMPs as key mediators of atherogenic and fibrotic pathologies. Mechanistically, a deregulation in ECM turnover tightly correlates with an increased production and release of proinflammatory and profibrotic factors including interleukin-1beta, transforming growth factor beta, angiotensin II, and reactive oxygen species. Unlike these factors the pleiotropic messenger molecule nitric oxide (NO) by acting as the major physiological vasodilator has emerged as one of the most atheroprotective factors. However, under inflammatory conditions NO does acquire proatherogenic and profibrotic properties thereby exacerbating tissue fibrosis. In this review, the mechanisms underlying both opposing properties of NO on perivascular ECM remodeling will exemplarily be discussed for renal fibrosis with a particular focus on the MMPs and intrinsic protease inhibitors.

mRNA stability control: a clandestine force in normal and malignant hematopoiesis

This review addresses the scope of influence of mRNA decay on cellular functions and its potential role in normal and malignant hematopoiesis. Evidence is emerging that leukemic oncogenes and hematopoietic cytokines interact with mRNA decay pathways. These pathways can co-regulate functionally related genes through specific motifs in the 3'-untranslated region of targeted transcripts. The steps that link external stimuli to transcript turnover are not fully understood, but include subcellular relocalization or post-transcriptional modification of specific transcript-stabilizing or -destabilizing proteins. Improper functioning of these regulators of mRNA turnover can impede normal cellular differentiation or promote cancers. By delineating how subsets of transcripts decay in synchrony during normal hematopoiesis, it may be possible to determine whether this post-transcriptional regulatory pathway is hijacked in leukemogenesis.