Protection against Nitric Oxide-Induced Apoptosis in Rat Mesangial Cells Demands Mitogen-Activated Protein Kinases and Reduced Glutathione

ABSTRACT Inflammatory diseases such as proliferative glomerulonephritis are associated with the production of nitric oxide (NO), which can initiate apoptotic/necrotic cell death. We studied the role of the p42/44 mitogen-activated protein kinases (MAPKs) and c-Jun N-terminal kinases1/2 (JNK1/2) in NO-evoked cytotoxicity in rat mesangial cells (MC). The NO donor S-nitrosoglutathione time-and concentration-dependently promoted apoptotic cell death as detected by JNK1/2 and caspase-3 activation as well as DNA fragmentation. By using Ro 318220, a JNK1/2 activator, we established a correlation between apoptosis and JNK1/2 activation. Apoptosis is antagonized by the addition of fetal calf serum or the simultaneous generation of NO and superoxide (O 2 Ϫ ), another biological inflammatory mediator. Fetal calf serum-induced protection required p42/44 MAPK activation as inhibition of the p42/44 MAPK pathway by the MAPK kinase-1 inhibitor PD 98059 attenuated MC protection. In contrast, cytoprotection by NO/O 2 Ϫ cogeneration demanded reduced glutathione but was p42/44 MAPK unrelated. Depletion of glutathione reversed NO/O 2 Ϫ -evoked survival to cell destruction and reinstalled JNK1/2 activity. In conclusion, different signal transduction pathways facilitate protection against NO-induced JNK1/2 activation and apoptosis in rat MC

Erioflorin stabilizes the tumor suppressor Pdcd4 by inhibiting its interaction with the E3-ligase β-TrCP1

Loss of the tumor suppressor Pdcd4 was reported for various tumor entities and proposed as a prognostic marker in tumorigenesis. We previously characterized decreased Pdcd4 protein stability in response to mitogenic stimuli, which resulted from p70S6K1-dependent protein phosphorylation, β-TrCP1-mediated ubiquitination, and proteasomal destruction. Following high-throughput screening of natural product extract libraries using a luciferase-based reporter assay to monitor phosphorylation-dependent proteasomal degradation of the tumor suppressor Pdcd4, we succeeded in showing that a crude extract from Eriophyllum lanatum stabilized Pdcd4 from TPA-induced degradation. Erioflorin was identified as the active component and inhibited not only degradation of the Pdcd4-luciferase-based reporter but also of endogenous Pdcd4 at low micromolar concentrations. Mechanistically, erioflorin interfered with the interaction between the E3-ubiquitin ligase β-TrCP1 and Pdcd4 in cell culture and in in vitro binding assays, consequently decreasing ubiquitination and degradation of Pdcd4. Interestingly, while erioflorin stabilized additional β-TrCP-targets (such as IκBα and β-catenin), it did not prevent the degradation of targets of other E3-ubiquitin ligases such as p21 (a Skp2-target) and HIF-1α (a pVHL-target), implying selectivity for β-TrCP. Moreover, erioflorin inhibited the tumor-associated activity of known Pdcd4- and IκBα-regulated αtranscription factors, that is, AP-1 and NF-κB, altered cell cycle progression and suppressed proliferation of various cancer cell lines. Our studies succeeded in identifying erioflorin as a novel Pdcd4 stabilizer that inhibits the interaction of Pdcd4 with the E3-ubiquitin ligase β-TrCP1. Inhibition of E3-ligase/target-protein interactions may offer the possibility to target degradation of specific proteins only as compared to general proteasome inhibition

Molecular actions of nitric oxide in mesangial cells

Nitric oxide (NO) is a widely recognized mediator of physiological and pathophysiological signal transmission. Its generation through L-arginine metabolism is relevant in the mesangium of the kidney where NO is produced by constitutive and inducible NOsynthase isoenzymes. Signaling is achieved through target interactions via redox and additive chemistry. In mesangial cells (MC), the outcome of these modifications promote on one side activation of soluble guanylyl cyclase while on the other side cytotoxicity is elicited. These contrasting situations are characterized by: 1) cGMP formation and signal propagation towards myosin light chain kinase, the effector system that regulates F-actin assembly, thereby affecting reversible relaxation/contraction of mesangial cells; and 2) initiation of morphological and biochemical alterations that are reminiscent of apoptosis such as chromatin condensation, p53 or Bax accumulation as well as caspase-3 activation. Off note, NO formation with concomitant initiation of apoptosis is efficiently antagonized by the simultaneous presence of superoxide (02-). We will recall the consequences that stem from a diffusion controlled NO/02- interaction thereby redirecting the apoptotic initiating activity of either NO or 02- towards protection. The crosstalk between cell destructive and protective signaling pathways, their activation or inhibition under the modulatory influence of NO will be discussed. Here we give examples of how NO elicits physiological and pathophysiological signal transmission in rat MC

GM-CSF in murine psoriasiform dermatitis : redundant and pathogenic roles uncovered by antibody-induced neutralization and genetic deficiency

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic, Th17-derived cytokine thought to critically contribute to the pathogenesis of diverse autoimmune diseases, including rheumatoid arthritis and psoriasis. Treatment with monoclonal antibodies that block GM-CSF activity is associated with favorable therapeutic effects in patients with rheumatoid arthritis. We evaluated the role of GM-CSF as a potential target for therapeutic interference in psoriasis using a combined pharmacologic and genetic approach and the mouse model of imiquimod-induced psoriasiform dermatitis (IMQPD). Neutralization of murine GM-CSF by an anti-GM-CSF antibody ameliorated IMQPD. In contrast, genetic deficiency in GM-CSF did not alter the course of IMQPD, suggesting the existence of mechanisms compensating for chronic, but not acute, absence of GM-CSF. Further investigation uncovered an alternative pathogenic pathway for IMQPD in the absence of GM-CSF characterized by an expanded plasmacytoid dendritic cell population and release of IFNα and IL-22. This pathway was not activated in wild-type mice during short-term anti-GM-CSF treatment. Our investigations support the potential value of GM-CSF as a therapeutic target in psoriatic disease. The discovery of an alternative pathogenic pathway for psoriasiform dermatitis in the permanent absence of GM-CSF, however, suggests the need for monitoring during therapeutic use of long-term GM-CSF blockade

ER-stress promotes VHL-independent degradation of hypoxia-inducible factors via FBXW1A/βTrCP

Abstract Metabolic adaptation and signal integration in response to hypoxic conditions is mainly regulated by hypoxia-inducible factors (HIFs). At the same time, hypoxia induces ROS formation and activates the unfolded protein response (UPR), indicative of endoplasmic reticulum (ER) stress. However, whether ER stress would affect the hypoxia response remains ill-defined. Here we report that feeding mice a high fat diet causes ER stress and attenuates the response to hypoxia. Mechanistically, ER stress promotes HIF-1α and HIF-2α degradation independent of ROS, Ca²⁺, and the von Hippel-Lindau (VHL) pathway, involving GSK3β and the ubiquitin ligase FBXW1A/βTrCP. Thereby, we reveal a previously unknown function of the GSK3β/HIFα/βTrCP1 axis in ER homeostasis and demonstrate that inhibition of the HIF-1 and HIF-2 response and genetic deficiency of GSK3β affects proliferation, migration, and sensitizes cells for ER stress promoted apoptosis. Vice versa, we show that hypoxia affects the ER stress response mainly through the PERK-arm of the UPR. Overall, we discovered previously unrecognized links between the HIF pathway and the ER stress response and uncovered an essential survival pathway for cells under ER stress

Erioflorin inhibits AP-1- and NF-κB-trancriptional activities.

<p>(A) HEK293 cells were co-transfected with an AP-1 <i>firefly</i> reporter and a <i>renilla</i> luciferase plasmid one day prior to experiments. Transfected cells were treated for 16 h with TPA (10 nM) with or without erioflorin (2.5 and 5 µM). Relative AP-1 activity was normalized to <i>renilla</i> luciferase and presented relative to TPA-only treated cells. (B) HEK293 cells were co-transfected with a NF-κB <i>firefly</i> reporter and a <i>renilla</i> luciferase plasmid one day prior to experiments. Transfected cells were treated for 16 h with TNFα (20 mg mL^–1) with or without erioflorin (2.5 and 5 µM). Relative NF-κB activity was normalized to <i>renilla</i> luciferase and presented relative to TNFα-only treated cells. All data are given as means ± SEM (n≥3, **p<0.01).</p

Erioflorin specifically inhibits E3-ligase β-TrCP1 activity.

<p>(A) HEK293 cells were treated with TNFα (20 ng mL^–1) for the indicated times with or without erioflorin (10 µM). (B) HEK293 cells were maintained under full medium conditions (10% serum) or serum deprived for 24 h following treatment with erioflorin (5 µM) for 8 h. (C) HEK293 cells were treated for 8 h with erioflorin (1.25–10 µM) or the prolyl-hydroxylase inhibitor dimethyloxallylglycine (DMOG, 1 µM). (D) HeLa cells were serum deprived for 48 h prior to treatment with erioflorin (10 µM) or the proteasome inhibitor MG132 (10 µM) for 8 h. Whole cell extracts were subjected to western analysis and probed with the indicated antibodies. Blots are representative for at least three independent experiments.</p