Structural basis for the Nanos-mediated recruitment of the CCR4–NOT complex and translational repression

The RNA-binding proteins of the Nanos family play an essential role in germ cell development and survival in a wide range of metazoan species. They function by suppressing the expression of target mRNAs through the recruitment of effector complexes, which include the CCR4–NOT deadenylase complex. Here, we show that the three human Nanos paralogs (Nanos1–3) interact with the CNOT1 C-terminal domain and determine the structural basis for the specific molecular recognition. Nanos1–3 bind CNOT1 through a short CNOT1-interacting motif (NIM) that is conserved in all vertebrates and some invertebrate species. The crystal structure of the human Nanos1 NIM peptide bound to CNOT1 reveals that the peptide opens a conserved hydrophobic pocket on the CNOT1 surface by inserting conserved aromatic residues. The substitutions of these aromatic residues in the Nanos1–3 NIMs abolish binding to CNOT1 and abrogate the ability of the proteins to repress translation. Our findings provide the structural basis for the recruitment of the CCR4–NOT complex by vertebrate Nanos, indicate that the NIMs are the major determinants of the translational repression mediated by Nanos, and identify the CCR4–NOT complex as the main effector complex for Nanos function.     

K63-linked polyubiquitination of IRF1： an essential step in the IL-1 signaling cascade

Interleukin 1 （IL-1） is a pleiotropic cytokine that regulates immune and inflammatory responses by inducing the expression of a variety of pro-inflamma- tory cytokines and chemokines. IL-1 exerts its pro-inflammatory effects primarily by activating nuclear factor KB （NF-rB） and mitogen-activated protein kinases （MAPKs）. After binding to its receptor     

β-Catenin destruction complex-independent regulation of Hippo–YAP signaling by APC in intestinal tumorigenesis

Mutations in Adenomatous polyposis coli (APC) underlie familial adenomatous polyposis (FAP), an inherited cancer syndrome characterized by the widespread development of colorectal polyps. APC is best known as a scaffold protein in the β-catenin destruction complex, whose activity is antagonized by canonical Wnt signaling. Whether other effector pathways mediate APC''s tumor suppressor function is less clear. Here we report that activation of YAP, the downstream effector of the Hippo signaling pathway, is a general hallmark of tubular adenomas from FAP patients. We show that APC functions as a scaffold protein that facilitates the Hippo kinase cascade by interacting with Sav1 and Lats1. Consistent with the molecular link between APC and the Hippo signaling pathway, genetic analysis reveals that YAP is absolutely required for the development of APC-deficient adenomas. These findings establish Hippo–YAP signaling as a critical effector pathway downstream from APC, independent from its involvement in the β-catenin destruction complex.     

On the mechanism of genistein-induced activation of protein kinase A-dependent Cl– conductance in cardiac myocytes

Genistein, an inhibitor of protein tyrosine kinase (PTK), enhanced the activation of the cardiac isoform of the protein kinase A (PKA)-regulated cystic fibrosis transmembrane conductance regulator (CFTR) Cl^– conductance in guinea-pig ventricular cells. We examined the mechanism(s) underlying this excitatory action of genistein by using patch-clamp techniques. The CFTR Cl^– conductance, activated by isoproterenol (ISO, 10 nM; [Cl^–] 153 mM extracellular, 21 mM intracellular; 36 °C), was enhanced by 20 μM genistein. Daidzein, a structural analogue of genistein with little inhibitory action on PTK, also enhanced CFTR Cl^– currents. After maximal activation of the Cl^– conductance by a cocktail of adenosine 3’,5’-cyclic monophosphate, 3-isobutyl-1-methylxanthine and okadaic acid or vanadate plus forskolin in the pipette, genistein was no longer stimulatory but was rather slightly inhibitory at 100 μM. Direct exposure of myocytes to higher concentrations of genistein (50–100 μM) elicited outwardly rectifying currents with a reversal potential of –47 mV in the absence of ISO. In the presence of 50 μM H-89, a PKA inhibitor, genistein had no effect. Vanadate in the pipette at a concentration (100 μM) inhibiting phosphotyrosine phosphatases alone did not prevent the action of genistein. In contrast, no conductance was activated by tyrphostins B42 or 51 or lavendustin A, other PTK inhibitors. Genistein’s stimulation of cardiac CFTR Cl^– conductance appears to be independent of the PTK pathway and to be due to its direct interaction with CFTR Cl^– channels. Received: 22 January 1999 / Received after revision: 9 April 1999 / Accepted: 22 April 1999     

The emerging role of the Nrf2–Keap1 signaling pathway in cancer

The Nrf2 (nuclear factor erythroid 2 [NF-E2]-related factor 2 [Nrf2])–Keap1 (Kelch-like erythroid cell-derived protein with CNC homology [ECH]-associated protein 1) signaling pathway is one of the most important cell defense and survival pathways. Nrf2 can protect cells and tissues from a variety of toxicants and carcinogens by increasing the expression of a number of cytoprotective genes. As a result, several Nrf2 activators are currently being tested as chemopreventive compounds in clinical trials. Just as Nrf2 protects normal cells, studies have shown that Nrf2 may also protect cancer cells from chemotherapeutic agents and facilitate cancer progression. Nrf2 is aberrantly accumulated in many types of cancer, and its expression is associated with a poor prognosis in patients. In addition, Nrf2 expression is induced during the course of drug resistance. Collectively, these studies suggest that Nrf2 contributes to both intrinsic and acquired chemoresistance. This discovery has opened up a broad spectrum of research geared toward a better understanding of the role of Nrf2 in cancer. This review provides an overview of (1) the Nrf2–Keap1 signaling pathway, (2) the dual role of Nrf2 in cancer, (3) the molecular basis of Nrf2 activation in cancer cells, and (4) the challenges in the development of Nrf2-based drugs for chemoprevention and chemotherapy.     

ZnT-1 protects HL-1 cells from simulated ischemia–reperfusion through activation of Ras–ERK signaling

Activation of ERK signaling may promote cardioprotection from ischemia-reperfusion (I/R) injury. ZnT-1, a protein that confers resistance from zinc toxicity, was found to interact with Raf-1 kinase through its C-terminal domain, leading to downstream activation of ERK. In the present study, we evaluated the effects of ZnT-1 in cultured murine cardiomyocytes (HL-1 cells) that were exposed to simulated-I/R. Cellular injury was evaluated by lactate dehydrogenase (LDH) release and by staining for pro-apoptotic caspase activation. Overexpression of ZnT-1 markedly reduced LDH release and caspase activation following I/R. Knockdown of endogenous ZnT-1 augmented the I/R-induced release of LDH and increased caspase activation following I/R. Phospho-ERK levels were significantly increased following I/R in cells overexpressing ZnT-1, while knockdown of ZnT-1 reduced phospho-ERK levels. Pretreatment of cells with the MEK inhibitor PD98059 abolished the protective effect of ZnT-1 following I/R. Accordingly, a truncated form of ZnT-1 lacking the C-terminal domain failed to induce ERK activation and did not protect the cells from I/R injury. In contrast, expression of the C-terminal domain by itself was sufficient to induce ERK activation and I/R protection. Interestingly, the C-terminal of the ZnT-1 did not have protective effect against the toxicity of zinc. In the isolated rat heart, global ischemic injury rapidly increased the endogenous levels of ZnT-1. However, following reperfusion ZnT-1 levels were found to be decreased. Our findings indicate that ZnT-1 may have important role in the ischemic myocardium through its ability to interact with Raf-1 kinase.     

Protein kinase C-δ mediates sepsis-induced activation of complement 5a and urokinase-type plasminogen activator signaling in macrophages

Objective and design

Activations of the complement C5a (C5a) and the urokinase-type plasminogen activator (uPA) are commonly seen together during sepsis. However, the mechanism linking these two important pathways remains elusive.

Material, methods and treatment

We used the C57BL/6 J mice model of sepsis induced by cecal ligation puncture (CLP) procedure, injected anti-C5aR or rottlerin through the tail vein to neutralize C5aR or PKC-δ, and then isolated peritoneal macrophages. Total RNA was isolated from the cells and analyzed by quantitative PCR.

Results

Our study revealed that neutralizing C5aR markedly inhibited sepsis-induced uPA receptor (uPAR) expression and its downstream signaling in macrophage. Similarly, neutralizing uPAR suppressed sepsis activation of C5a signaling. Importantly, inhibition of PKC-δ largely blocked sepsis-induced expression of C5aR and uPAR.

Conclusions

Our study demonstrates a crosstalk between the complement C5a signaling and the fibrinolytic uPA pathways, which may depend on each other to maintain their expression and signaling, and reveals a central role of PKC-δ in mediating sepsis-induced activation of these pathways.     

Temporal activation of β-catenin signaling in the chondrogenic process of mesenchymal stem cells affects the phenotype of the cartilage generated

Adult mesenchymal stem cells (MSCs) are an attractive cell source for cartilage tissue engineering. In vitro predifferentiation of MSCs has been explored as a means to enhance MSC-based articular cartilage repair. However, there remain challenges to control and prevent the premature progression of MSC-derived chondrocytes to the hypertrophy. This study investigated the temporal effect of transforming growth factor (TGF)-β and β-catenin signaling co-activation during MSC chondrogenic differentiation and evaluated the influence of these predifferentiation conditions to subsequent phenotypic development of the cartilage. MSCs were differentiated in chondrogenic medium that contained either TGFβ alone, TGFβ with transient β-catenin coactivation, or TGFβ with continuous β-catenin coactivation. After in vitro differentiation, the pellets were transplanted into SCID mice. Both coactivation protocols resulted in the enhancement of chondrogenic differentiation of MSCs. Compared with TGFβ activation, transient coactivation of TGFβ-induction with β-catenin activation resulted in heightened hypertrophy and formed highly ossified tissues with marrow-like hematopoietic tissue in vivo. The continuous coactivation of the 2 signaling pathways, however, resulted in inhibition of progression to hypertrophy, marked by the suppression of type X collagen, Runx2, and alkaline phosphatase expression, and did not result in ossified tissue in vivo. Chondrocytes of the continuous co-activation samples secreted significantly more parathyroid hormone-related protein (PTHrP) and expressed cyclin D1. Our results suggest that temporal co-activation of the TGFβ signaling pathway with β-catenin can yield cartilage of different phenotype, represents a potential MSC predifferentiation protocol before clinical implantation, and has potential applications for the engineering of cartilage tissue.     

Acacetin inhibits expression of E-selectin on endothelial cells through regulation of the MAP kinase signaling pathway and activation of NF-κB

Abstract

Since E-selectin-mediated adhesion of leukocytes or tumor cells to the vascular endothelium is a key early event in the initiation of inflammatory response and cancer metastasis, E-selectin inhibition is thought to be a good target for therapeutic intervention. Several flavones have been shown to have anti-inflammatory and anticancer properties. In the present study, we investigated the effects of plant flavones on expression of E-selectin in human umbilical vein endothelial cells. Among 11 flavones, acacetin strongly inhibited TNF-α-induced E-selectin expression in HUVECs. Acacetin suppressed the TNF-α-induced phosphorylation of p38 but did not inhibit TNF-α-induced phosphorylations of JNK and ERK. Acacetin also inhibited the activation of NF-κB by stimulation with TNF-α. Furthermore, adhesion of monocytes to TNF-α-treated endothelial cells was inhibited by cotreatment with acacetin. These results suggest that acacetin inhibits the expression of E-selectin by regulation of the p38 MAPK signaling pathway and activation of NF-κB.     

ATR–Chk1–APC/CCdh1-dependent stabilization of Cdc7–ASK (Dbf4) kinase is required for DNA lesion bypass under replication stress

Cdc7 kinase regulates DNA replication. However, its role in DNA repair and recombination is poorly understood. Here we describe a pathway that stabilizes the human Cdc7–ASK (activator of S-phase kinase; also called Dbf4), its regulation, and its function in cellular responses to compromised DNA replication. Stalled DNA replication evoked stabilization of the Cdc7–ASK (Dbf4) complex in a manner dependent on ATR–Chk1-mediated checkpoint signaling and its interplay with the anaphase-promoting complex/cyclosome^Cdh1 (APC/C^Cdh1) ubiquitin ligase. Mechanistically, Chk1 kinase inactivates APC/C^Cdh1 through degradation of Cdh1 upon replication block, thereby stabilizing APC/C^Cdh1 substrates, including Cdc7–ASK (Dbf4). Furthermore, motif C of ASK (Dbf4) interacts with the N-terminal region of RAD18 ubiquitin ligase, and this interaction is required for chromatin binding of RAD18. Impaired interaction of ASK (Dbf4) with RAD18 disables foci formation by RAD18 and hinders chromatin loading of translesion DNA polymerase η. These findings define a novel mechanism that orchestrates replication checkpoint signaling and ubiquitin–proteasome machinery with the DNA damage bypass pathway to guard against replication collapse under conditions of replication stress.     

Genoarchitecture of the rostral hindbrain of a shark: basis for understanding the emergence of the cerebellum at the agnathan–gnathostome transition

The cerebellum is present in all extant gnathostomes or jawed vertebrates, of which cartilaginous fishes represent the most ancient radiation. Since the isthmic organizer induces the formation of the cerebellum, comparative genoarchitectonic analysis on the meso-isthmo-cerebellar region of cartilaginous fishes with respect to that of jawless vertebrates could reveal why the isthmic organizer acquires the ability to induce the formation of the cerebellum in gnathostomes. In the present work we analyzed the expression pattern of a variety of genes related to the cerebellar formation and patterning (ScOtx2, ScGbx2, ScFgf8, ScLmx1b, ScIrx1, ScIrx3,ScEn2, ScPax6 and ScLhx9) by in situ hybridization, and the distribution of Pax6 protein in the developing hindbrain of the shark Scyliorhinus canicula. The genoarchitectonic code in this species revealed high degree of conservation with respect to that of other gnathostomes. This resemblance may reveal the features of the ancestral condition of the gene network operating for specification of the rostral hindbrain patterning. Accordingly, the main subdivisions of the rostral hindbrain of S. canicula could be recognized. Our results support the existence of a rhombomere 0, identified as the ScFgf8/ScGbx2/ScEn2-positive and mainly negative ScIrx3 domain just caudal to the midbrain ScIrx1/ScOtx2/ScLmx1b-positive domain. The differential ScEn2 and Pax6 expression in the rhombomere 1 revealed anterior and posterior subdivisions. Interestingly, dissimilarities between S. canicula and lampreys (jawless vertebrates) were noted in the expression of Irx, Lhx and Pax genes, which could be part of significant gene network changes through evolution that caused the emergence of the cerebellum.     

Protein kinase Cδ is a critical component of Dectin-1 signaling in primary human monocytes

Zymosan, a mimic of fungal pathogens, and its opsonized form (ZOP) are potent stimulators of monocyte NADPH oxidase, resulting in the production of O(2)(.-), which is critical for host defense against fungal and bacterial pathogens and efficient immune responses; however, uncontrolled O(2)(.-) production may contribute to chronic inflammation and tissue injury. Our laboratory has focused on characterizing the signal transduction pathways that regulate NADPH oxidase activity in primary human monocytes. In this study, we examined the involvement of various pattern recognition receptors and found that Dectin-1 is the primary receptor for zymosan stimulation of O(2)(.-) via NADPH oxidase in human monocytes, whereas Dectin-1 and CR3 mediate the activation by ZOP. Further studies identified Syk and Src as important signaling components downstream of Dectin-1 and additionally identified PKCδ as a novel downstream signaling component for zymosan-induced O(2)(.-) as well as phagocytosis. Our results show that Syk and Src association with Dectin-1 is dependent on PKCδ activity and expression and demonstrate direct binding between Dectin-1 and PKCδ. Finally, our data show that PKCδ and Syk but not Src are required for Dectin-1-mediated phagocytosis. Taken together, our data identify Dectin-1 as the major PRR for zymosan in primary human monocytes and identify PKCδ as a novel downstream signaling kinase for Dectin-1-mediated regulation of monocyte NADPH oxidase and zymosan phagocytosis.     

TGF-β1/Smad signaling,MMP-14, and MSC markers in arterial injury: discovery of the molecular basis of restenosis

Transforming growth factor (TGF)-β1 has been suggested to be involved in the recruitment of mesenchymal stem cells (MSCs) following arterial injury, but the role of downstream signaling and the contribution of the recruited MSCs are still unknown. The release of latent TGF-β1 from latent TGF-binding protein (LTBP) by matrix metallopeptidase-14 (MMP-14) proteolysis was demonstrated, which contributed to neointima formation, but the relationship between MMP-14 and activated TGF-β1 in the process of restenosis has yet to be explored. In this study, we observed the change in expression and distribution of TGF-β1/Smad signaling pathway proteins, MMP-14, and MSC markers in the process of neointima formation using a rat model for balloon-induced carotid artery injury. We found that the increase in downstream Smad signaling was consistent with the elevation of TGF-β1 levels and MSCs accumulated at the lumen side of neointima. Furthermore, the activation of MMP-14 in the injured artery was preceded by the increase in TGF-β1 levels. Herein, we conclude that MMP-14 induces an elevation in the levels of TGF-β1/Smad signaling proteins in injured arteries, and that MSCs are recruited by TGF-β1/Smad signaling and MMP-14, possibly differentiating into vascular smooth muscle cell (VSMC)-like cells and VSMC via modulation of TGF-β1/Smads signaling and MMP-14.