Publications (49) View all
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Article: Hyperosmotic stress regulates the distribution and stability of Myocardin-Related Transcription Factor, a key modulator of the cytoskeleton.
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ABSTRACT: Hyperosmotic stress initiates several adaptive responses, including the remodeling of the cytoskeleton. Besides maintaining structural integrity, the cytoskeleton has emerged as an important regulator of gene transcription. Myocardin-related transcription factor (MRTF), an actin-regulated co-activator of serum response factor is a major link between the actin skeleton and transcriptional control. We therefore investigated whether MRTF is regulated by hyperosmotic stress. Here we show that hypertonicity induces robust, rapid and transient translocation of MRTF from the cytosol to the nucleus in kidney tubular cells. We found that the hyperosmolarity-triggered MRTF translocation is mediated by the RhoA/Rho kinase (ROK) pathway. Moreover, the Rho guanine nucleotide exchange factor GEF-H1 is activated by hyperosmotic stress, and it is a key contributor to the ensuing RhoA activation and MRTF translocation, since siRNA-mediated GEF-H1 downregulation suppresses these responses. While the osmotically induced RhoA activation promotes nuclear MRTF accumulation, the concomitant activation of p38 MAP kinase mitigates this effect. Moderate hyperosmotic stress (600 mosM) drives MRTF-dependent transcription through the cis-element CArG box. Silencing or pharmacological inhibition of MRTF prevents the osmotic stimulation of CArG-dependent transcription, and renders the cells susceptible to osmotic shock-induced structural damage. Interestingly, strong hyperosmolarity promotes proteasomal degradation of MRTF, concomitant with apoptosis. Thus, MRTF is an osmosensitive and osmoprotective transcription factor, whose intracellular distribution is regulated by the GEF-H1/RhoA/ROK and p38 pathways. However, strong osmotic stress destabilizes MRTF, concomitant with apoptosis, implying that hyperosmotically induced cell death takes precedence over epithelial-myofibroblast transition, a potential consequence of MRTF-mediated phenotypic reprogramming.AJP Cell Physiology 10/2012; · 3.54 Impact Factor -
Article: Oxidant-induced TLR4 translocation in murine macrophages is Src kinase dependent
Critical Care 04/2012; 11:1-25. · 4.93 Impact Factor -
Article: Affinity precipitation of active Rho-GEFs using a GST-tagged mutant Rho protein (GST-RhoA(G17A)) from epithelial cell lysates.
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ABSTRACT: Proteins of the Rho family of small GTPases are central regulators of the cytoskeleton, and control a large variety of cellular processes, including cell migration, gene expression, cell cycle progression and cell adhesion. Rho proteins are molecular switches that are active in GTP-bound and inactive in GDP-bound state. Their activation is mediated by a family of Guanine-nucleotide Exchange Factor (GEF) proteins. Rho-GEFs constitute a large family, with overlapping specificities. Although a lot of progress has been made in identifying the GEFs activated by specific signals, there are still many questions remaining regarding the pathway-specific regulation of these proteins. The number of Rho-GEFs exceeds 70, and each cell expresses more than one GEF protein. In addition, many of these proteins activate not only Rho, but other members of the family, contributing further to the complexity of the regulatory networks. Importantly, exploring how GEFs are regulated requires a method to follow the active pool of individual GEFs in cells activated by different stimuli. Here we provide a step-by-step protocol for a method used to assess and quantify the available active Rho-specific GEFs using an affinity precipitation assay. This assay was developed a few years ago in the Burridge lab and we have used it in kidney tubular cell lines. The assay takes advantage of a "nucleotide free" mutant RhoA, with a high affinity for active GEFs. The mutation (G17A) renders the protein unable to bind GDP or GTP and this state mimics the intermediate state that is bound to the GEF. A GST-tagged version of this mutant protein is expressed and purified from E. coli, bound to glutathione sepharose beads and used to precipitate active GEFs from lysates of untreated and stimulated cells. As most GEFs are activated via posttranslational modifications or release from inhibitory bindings, their active state is preserved in cell lysates, and they can be detected by this assay. Captured proteins can be probed for known GEFs by detection with specific antibodies using Western blotting, or analyzed by Mass Spectrometry to identify unknown GEFs activated by certain stimuli.Journal of Visualized Experiments 01/2012; -
Article: Pre-B cell colony-enhancing factor (PBEF/Nampt/visfatin) primes neutrophils for augmented respiratory burst activity through partial assembly of the NADPH oxidase.
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ABSTRACT: Pre-B cell colony-enhancing factor ([PBEF] also known as Nampt/visfatin) is a pleiotropic 52-kDa cytokine-like molecule whose activity has been implicated in multiple inflammatory disease states. PBEF promotes polymorphonuclear neutrophil (PMN) proinflammatory function by inhibiting constitutive PMN apoptosis. We investigated whether PBEF activates or primes for PMN respiratory burst. We found that although PBEF did not activate respiratory burst on its own, it primed for increased reactive oxygen species generation through the NADPH oxidase. PBEF promoted membrane translocation of cytosolic NADPH oxidase subunits p40 and p47, but not p67, induced p40 phosphorylation on Thr(154), and activated the small GTPase Rac. Priming, translocation, and phosphorylation were dependent on activation of p38 and ERK MAPKs, but not of PI3K. Priming by PBEF occurred independent of its NAD-generating capacity because neither nicotinamide mononucleotide or NAD could recapitulate the effects, and a specific inhibitor of PBEF, APO-866, could not inhibit priming. Taken together, these results demonstrate that PBEF can prime for PMN respiratory burst activity by promoting p40 and p47 translocation to the membrane, and this occurs in a MAPK-dependent fashion.The Journal of Immunology 06/2011; 186(11):6474-84. · 5.79 Impact Factor -
Article: Altered inhibitory κBα expression in LPS-stimulated alveolar macrophages following resuscitated hemorrhagic shock.
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ABSTRACT: Patients resuscitated from hemorrhagic shock are at increased risk for the development of organ dysfunction, particularly acute respiratory distress syndrome. The "two-hit hypothesis" wherein shock/resuscitation (S/R) renders the immune system more responsive to subsequent inflammatory stimuli has been suggested as a major mechanism contributing to organ injury. Previous work has shown that S/R primes alveolar macrophages for increased nuclear factor κB (NF-κB) translocation in response to LPS, culminating in increased lung cytokine and chemokine production. Inhibitory κB (IκB) is known to be an important regulator of NF-κB activity. In this article, we investigated the effect of S/R on regulation of IκBα expression in response to LPS both in vitro and in vivo. Two discrete effects on IκB regulation were observed after S/R, which served to augment NF-κB activity. First, antecedent exposure of alveolar macrophages to S/R resulted in increased LPS-induced IκBα degradation through activation of upstream signaling, an effect that resulted in increased NF-κB translocation and cytokine-induced neutrophil chemoattractant gene expression. Second, cells recovered from rodents after S/R had reduced levels of IκB mRNA in response to LPS compared with sham/LPS treatment. This effect was primarily due to the ability of S/R to reverse the prolongation of IκB mRNA stability observed after LPS-alone treatment. Together, these effects on the important regulatory molecule IκB in the macrophage may contribute to the heightened inflammatory response observed after S/R.Shock (Augusta, Ga.) 02/2011; 35(2):171-7. · 2.87 Impact Factor
