The HMG-CoA reductase inhibitor simvastatin activates the protein kinase Akt and promotes angiogenesis in normocholesterolemic animals

Recent studies suggest that statins can function to protect the vasculature in a manner that is independent of their lipid-lowering activity. We show here that statins rapidly activate the protein kinase Akt/PKB in endothelial cells. Accordingly, simvastatin enhanced phosphorylation of the endogenous Akt substrate endothelial nitric oxide synthase (eNOS), inhibited apoptosis and accelerated vascular structure formation in vitro in an Akt-dependent manner. Similar to vascular endothelial growth factor (VEGF) treatment, both simvastatin administration and enhanced Akt signaling in the endothelium promoted angiogenesis in ischemic limbs of normocholesterolemic rabbits. Therefore, activation of Akt represents a mechanism that can account for some of the beneficial side effects of statins, including the promotion of new blood vessel growth.

A dimeric 14-3-3 protein is an essential cofactor for Raf kinase activity

cRaf-1 is a mitogen-activated protein kinase that is the main effector recruited by GTP-bound Ras in order to activate the MAP kinase pathway. Inactive Raf is found in the cytosol in a complex with Hsp90, Hsp50 (Cdc37) and the 14-3-3 proteins. GTP-bound Ras binds Raf and is necessary but not sufficient for the stable activation of Raf that occurs in response to serum, epidermal growth factor, platelet-derived growth factor or insulin. These agents cause a two- to threefold increase in overall phosphorylation of Raf on serine/threonine residues, and treatment of cRaf-1 with protein (serine/threonine) phosphatases can deactivate it, at least partially. The role of 14-3-3 proteins in the regulation of Raf's kinase activity is uncertain and is investigated here. Active Raf can be almost completely deactivated in vitro by displacement of 14-3-3 using synthetic phosphopeptides. Deactivation can be substantially reversed by addition of purified recombinant bacterial 14-3-3; however, Raf must have been previously activated in vivo to be reactivated by 14-3-3 in vitro. The ability of 14-3-3 to support Raf activity is dependent on phosphorylation of serine residues on Raf and on the integrity of the 14-3-3 dimer; mutant monomeric forms of 14-3-3, although able to bind Raf in vivo, do not enable Raf to be activated in vivo or restore Raf activity after displacement of 14-3-3 in vitro. The 14-3-3 protein is not required to induce dimerization of Raf. We propose that dimeric 14-3-3 is needed both to maintain Raf in an inactive state in the absence of GTP-bound Ras and to stabilize an active conformation of Raf produced during activation in vivo.

Vascular endothelial growth factor/vascular permeability factor augments nitric oxide release from quiescent rabbit and human vascular endothelium

BACKGROUND

Vascular endothelial growth factor (VEGF)/ vascular permeability factor (VPF) is an endothelial cell (EC) mitogen. This feature is considered central to the documented role of VEGF/VPF in promoting angiogenesis. More recent evidence suggests that VEGF/VPF may also serve a "maintenance" function, modulating various aspects of EC biology. In the present study, we sought to determine the extent to which VEGF/VPF may stimulate the release of NO from normal ECs.

METHODS AND RESULTS

VEGF/VPF produced a dose-dependent rise in NO concentration ([NO]) from vascular segments of rabbit thoracic aorta, pulmonary artery, and inferior vena cava. In comparison to stimulation with acetylcholine, the onset of increased [NO] after administration of VEGF/VPF was slower, reaching a maximum value after 8 minutes. Preincubation of the aortic segments with L-arginine raised by twofold both baseline [NO] and [NO] stimulated by addition of 2.5 micrograms/mL VEGF/VPF. Removal of CaCl2 from the Krebs solution, disruption of the endothelium, and administration of NG-monomethyl-L-arginine abrogated the stimulatory effect of 10 micrograms/mL VEGF/VPF. Similar findings were documented with an NO-specific polarographic electrode to measure NO released from cultured human umbilical vein ECs.

CONCLUSIONS

VEGF/VPF stimulates production of NO from rabbit and human ECs. This finding (1) constitutes inferential evidence for the presence of functional VEGF/VPF receptors on quiescent endothelium of the adult rabbit as well as human ECs and (2) supports the notion that putative maintenance functions of VEGF/VPF may include regulation of baseline synthesis and/or release of EC NO.

Ras activation of the Raf kinase: tyrosine kinase recruitment of the MAP kinase cascade

A continuing focus of our work has been an effort to understand the signal transduction pathways through which insulin achieves its cellular actions. In the mid-1970s, we and others observed that insulin promoted an increase in Ser/Thr phosphorylation of a subset of cellular proteins. This finding was unanticipated, inasmuch as nearly all of the actions of insulin then known appeared to result from protein dephosphorylation. In fact, nearly 15 years elapsed before any physiologic response to insulin attributable to stimulated (Ser/Thr) phosphorylation was established. Nevertheless, based on the hypothesis that insulin-stimulated Ser/Thr phosphorylation reflected the activation of protein (Ser/Thr) kinases downstream of the insulin receptor, we sought to detect and purify these putative, insulin-responsive protein (Ser/Thr) kinases. Our effort was based on the presumption that an understanding of the mechanism for their activation would provide an entry into the biochemical reactions through which the insulin receptor activated its downstream effectors. To a degree that, in retrospect, is surprising, this goal was accomplished, much in the way originally envisioned. It is now well known that receptor tyrosine kinases (RTKs) recruit a large network of protein (Ser/Thr) kinases to execute their cellular programs. The first of these insulin-activated protein kinase networks to be fully elucidated was the Ras-Raf-mitogen-activated protein kinase (MAPK) cascade. This pathway is a central effector of cellular differentiation in development; moreover, its inappropriate and continuous activation provides a potent promitogenic force and is a very common occurrence in human cancers. Conversely, this pathway contributes minimally, if at all, to insulin's program of metabolic regulation. Nevertheless, the importance of the Ras-MAPK pathway in metazoan biology and human malignancies has impelled us to an ongoing analysis of the functions and regulation of Ras and Raf. This chapter will summarize briefly the way in which work from this and other laboratories on insulin signaling led to the discovery of the mammalian MAP kinase cascade and, in turn, to the identification of unique role of the Raf kinases in RTK activation of this protein (Ser/Thr) kinase cascade. We will then review in more detail current understanding of the biochemical mechanism through which the Ras proto-oncogene, in collaboration with the 14-3-3 protein and other protein kinases, initiates activation of the Raf kinase.

Fluorous mixture synthesis: a fluorous-tagging strategy for the synthesis and separation of mixtures of organic compounds

The solution-phase synthesis of organic compounds as mixtures rather than in individual pure form offers efficiency advantages that are negated by the difficulty in separating and identifying the components of the final mixture. Here, a strategy for mixture synthesis that addresses these separation and identification problems is presented. A series of organic substrates was tagged with a series of fluorous tags of increasing fluorine content. The compounds were then mixed, and multistep reactions were conducted to make enantiomers or analogs of the natural product mappicine. The resulting tagged products were then demixed by fluorous chromatography (eluting in order of increasing fluorine content) to provide the individual pure components of the mixture, which were detagged to release the final products.

The JAK inhibitor tofacitinib suppresses synovial JAK1-STAT signalling in rheumatoid arthritis

OBJECTIVE

Tofacitinib is an oral Janus kinase (JAK) inhibitor for the treatment of rheumatoid arthritis (RA). The pathways affected by tofacitinib and the effects on gene expression in situ are unknown. Therefore, tofacitinib effects on synovial pathobiology were investigated.

METHODS

A randomised, double-blind, phase II serial synovial biopsy study (A3921073; NCT00976599) in patients with RA with an inadequate methotrexate response. Patients on background methotrexate received tofacitinib 10 mg twice daily or placebo for 28 days. Synovial biopsies were performed on Days -7 and 28 and analysed by immunoassay or quantitative PCR. Clinical response was determined by disease activity score and European League Against Rheumatism (EULAR) response on Day 28 in A3921073, and at Month 3 in a long-term extension study (A3921024; NCT00413699).

RESULTS

Tofacitinib exposure led to EULAR moderate to good responses (11/14 patients), while placebo was ineffective (1/14 patients) on Day 28. Tofacitinib treatment significantly reduced synovial mRNA expression of matrix metalloproteinase (MMP)-1 and MMP-3 (p<0.05) and chemokines CCL2, CXCL10 and CXCL13 (p<0.05). No overall changes were observed in synovial inflammation score or the presence of T cells, B cells or macrophages. Changes in synovial phosphorylation of signal transducer and activator of transcription 1 (STAT1) and STAT3 strongly correlated with 4-month clinical responses (p<0.002). Tofacitinib significantly decreased plasma CXCL10 (p<0.005) at Day 28 compared with placebo.

CONCLUSIONS

Tofacitinib reduces metalloproteinase and interferon-regulated gene expression in rheumatoid synovium, and clinical improvement correlates with reductions in STAT1 and STAT3 phosphorylation. JAK1-mediated interferon and interleukin-6 signalling likely play a key role in the synovial response.

TRIAL REGISTRATION NUMBER

NCT00976599.

Oligomerization activates c-Raf-1 through a Ras-dependent mechanism

The c-Raf-1 proto-oncoprotein is a Ras-GTP-regulated protein kinase that associates in situ with 14-3-3 proteins, which are naturally dimeric. In COS cells, recombinant Raf is found in oligomeric assemblies. To examine whether induced oligomerization can alter Raf kinase activity, sequences encoding the FK506-binding protein FKBP12 were fused to the amino terminus of c-Raf-1, introducing a binding site for FK506. Oligomerization of recombinant FKBP-Raf in situ, induced by the addition of the dimeric FK506 derivative FK1012A, activated Raf kinase activity at least half as well as epidermal growth factor (EGF). As with EGF, activation of FKBP-Raf by FK1012A is entirely Ras-GTP dependent. Thus oligomerization of Raf per se promotes Raf activation through a Ras-dependent mechanism.

Acute modulation of endothelial Akt/PKB activity alters nitric oxide-dependent vasomotor activity in vivo

The serine/threonine protein kinase Akt (protein kinase B) phosphorylates endothelial cell nitric oxide synthase (eNOS) and enhances its ability to generate nitric oxide (NO). Because NO is an important regulator of vasomotor tone, we investigated whether Akt can regulate endothelium-dependent vasomotion in vivo using a rabbit femoral artery model of gene transfer. The endothelium of isolated femoral arteries was infected with replication-defective adenoviral constructs expressing beta-galactosidase, constitutively-active Akt (myr-Akt), or dominant-negative Akt (dn-Akt). Femoral arteries transduced with myr-Akt showed a significant increase in resting diameter and blood flow, as assessed by angiography and Doppler flow measurements, respectively. L-NAME, an eNOS inhibitor, blocked myr-Akt-mediated vasodilatation. In contrast, endothelium-dependent vasodilatation in response to acetylcholine was attenuated in vessels transduced with dn-Akt, although these vessels showed normal responses to nitroglycerin, an endothelium-independent vasodilator. Similarly, relaxation of murine aorta ex vivo in response to acetylcholine, but not nitroglycerin, was inhibited by transduction of dn-Akt to the endothelium. These data provide evidence that Akt functions as key regulator of vasomotor tone in vivo.

A new symmetrodont mammal from China and its implications for mammalian evolution

A new symmetrodont mammal has been discovered in the Mesozoic era (Late Jurassic or Early Cretaceous period) of Liaoning Province, China. Archaic therian mammals, including symmetrodonts, are extinct relatives of the living marsupial and placental therians. However, these archaic therians have been mostly documented by fragmentary fossils. This newfossil taxon, represented by a nearly complete postcranial skeleton and a partial skull with dentition, is the best-preserved symmetrodont mammal yet discovered. It provides a new insight into the relationships of the major lineages of mammals and the evolution of the mammalian skeleton. Our analysis suggests that this new taxon represents a part of the early therian radiation before the divergence of living marsupials and placentals; that therians and multituberculates are more closely related to each other than either group is to other mammalian lineages; that archaic therians lacked the more parasagittal posture of the forelimb of most living therian mammals; and that archaic therians, such as symmetrodonts, retained the primitive feature of a finger-like promontorium (possibly with a straight cochlea) of the non-therian mammals. The fully coiled cochlea evolved later in more derived therian mammals, and is therefore convergent to the partially coiled cochlea of monotremes.

Actin-binding protein-280 binds the stress-activated protein kinase (SAPK) activator SEK-1 and is required for tumor necrosis factor-alpha activation of SAPK in melanoma cells

SEK-1, a dual specificity protein kinase that serves as one of the immediate upstream activators of the stress-activated protein kinases (SAPKs), associates specifically with the actin-binding protein, ABP-280, in vitro and in situ. SEK-1 binds to the carboxyl-terminal rod segment of ABP-280, upstream of the ABP carboxyl-terminal dimerization domain. Activation of SEK-1 in situ increases the SEK-1 activity bound to ABP-280 without changing the amount of SEK-1 polypeptide bound. The influence of ABP-280 on SAPK regulation was evaluated in human melanoma cells that lack ABP-280 expression, and in stable transformants of these cells expressing wild type ABP, or an actin-binding but dimerization-deficient mutant ABP (ABPDeltaCT109). ABP-280-deficient cells show an activation of SAPK in response to most stimuli that is comparable to that seen in ABP-280-replete cells; ABP-280-deficient cells, however, fail to show the brisk tumor necrosis factor-alpha (TNF-alpha) activation of SAPK seen in ABP-replete cells and have an 80% reduction in SAPK activation by lysophosphatidic acid. Expression of the dimerization-deficient mutant ABP-280 fails to correct the defective SAPK response to lysophosphatidic acid, but essentially normalizes the TNF-alpha activation of SAPK. Thus, a lack of ABP-280 in melanoma cells causes a defect in the regulation of SAPK that is selective for TNF-alpha and is attributable to the lack of ABP-280 polypeptide itself rather than to the disordered actin cytoskeleton that results therefrom. ABP-280 participates in TNF-alpha signal transduction to SAPKs, in part through the binding of SEK-1.

Generation of constitutively active recombinant caspases-3 and -6 by rearrangement of their subunits

Caspases play a major role in the transduction of the apoptotic signal and execution of apoptosis in mammalian cells. Ectopic overexpression of the short prodomain caspases-3 and -6 precursors in mammalian cells does not induce apoptosis. This is due to their inability to undergo autocatalytic processing/activation and suggests that they depend on the long prodomain caspases for activation. To investigate directly the apoptotic activity of these two caspases in vivo, we engineered constitutively active recombinant caspases-3 and -6 precursors. This was achieved by making contiguous precursor caspases-3 and -6 molecules, which have their small subunits preceding their large subunits. Unlike their wild type counterparts, these recombinant molecules were capable of autocatalytic processing in an in vitro translation reaction, suggesting that they are catalytically active. They were also capable of autoprocessing and inducing apoptosis in vivo independent of the upstream caspases. Furthermore, their autocatalytic and apoptotic activities were inhibited by the pancaspase inhibitor z-VAD-fluoromethylketone, but not by CrmA or Bcl-2, thus directly demonstrating that the targets of inhibition of apoptosis by CrmA and Bcl-2 are upstream of caspases-3 and -6. Since caspases-3 and -6 are the most downstream executioners of apoptosis, the constitutively active versions of these caspases could be used at very low concentrations in gene therapy model systems to induce apoptosis in target tissues or tumors.

Genetic diversity of hantaviruses isolated in china and characterization of novel hantaviruses isolated from Niviventer confucianus and Rattus rattus

The antigenic and genetic properties of 46 hantaviruses from China, 13 from patients, 23 from rodents, and 10 from unknown hosts, were compared with those of other hantaviruses. The viruses were classified as either Hantaan (HTN) or Seoul (SEO) viruses. A phylogenetic analysis of the partial M (300 bp) and S (around 485 bp) genomes of HTN viruses identified nine distinct genetic subtypes, one consisting of isolates from Korea. The SEO viruses were divided into five genetic subtypes, although they had less variability than the HTN subtypes. There was a correlation between the subtype and province of origin for four subtypes of HTN viruses, confirming geographical clustering. Hantaan virus NC167 isolated from Niviventer confucianus and SEO virus Gou3 isolated from Rattus rattus were the basal clades in each virus. The phylogenetic trees constructed from the entire S and M segments suggested that NC167 was introduced to N. confucianus in a host-switching event. The reactivity of a panel of 35 monoclonal antibodies was almost exactly the same in NC167 and a representative HTN virus and in Gou3 and a representative SEO virus. However, there was a one-way cross-neutralization between them. These results confirm the varied nature of Murinae-associated hantaviruses in China.

Cingulate cortex synaptic terminal proteins and neural cell adhesion molecule in schizophrenia

The neuronal organization and patterns of afferent innervation are abnormal in the cingulate cortex in schizophrenia, and associated changes in synaptic terminals could be present. A panel of monoclonal antibodies was defined with biochemical and fusion protein studies as detecting syntaxin (antibody SP6), synaptophysin (antibody SP4) and synaptosomal-associated protein-25 (antibody SP12). These antibodies and a polyclonal antibody reactive with neural cell adhesion molecule were used to investigate the cingulate cortex in schizophrenia. Immunocytochemistry indicated that syntaxin immunoreactivity had a considerably wider distribution than synaptophysin. Overall, multivariate analysis indicated increased synaptic terminal protein immunoreactivity in schizophrenia compared to controls (P=0.004). Controlled for age and post mortem interval, syntaxin immunoreactivity was significantly elevated in schizophrenia (P=0.004), and neural cell adhesion molecule immunoreactivity was also elevated (P=0.05). The neural cell adhesion molecule to synaptophysin ratio was increased (P=0.005), possibly indicating the presence of less mature synapses in schizophrenia. Elevated syntaxin immunoreactivity is consistent with increased glutamatergic afferents to the cingulate cortex in schizophrenia, and combined with the neural cell adhesion molecule to synaptophysin ratio results suggests that synaptic function in this region in schizophrenia may be abnormal.

IL6 derived from cancer-associated fibroblasts promotes chemoresistance via CXCR7 in esophageal squamous cell carcinoma

Various factors and cellular components in the tumor microenvironment are key drivers associated with drug resistance in many cancers. Here, we analyzed the factors and molecular mechanisms involved in chemoresistance in patients with esophageal squamous cell carcinoma (ESCC). We found that interleukin 6 (IL6) derived mainly from cancer-associated fibroblasts played the most important role in chemoresistance by upregulating C-X-C motif chemokine receptor 7 (CXCR7) expression through signal transducer and activator of transcription 3/nuclear factor-κB pathway. CXCR7 knockdown resulted in the inhibition of IL6-induced proliferation and chemoresistance. In addition, CXCR7 silencing significantly decreased gene expression associated with stemness, chemoresistance and epithelial-mesenchymal transition and suppressed the proliferation ability of ESCC cells in three-dimensional culture systems and angiogenesis assay. In clinical samples, ESCC patients with high expression of CXCR7 and IL6 presented a significantly worse overall survival and progression-free survival upon receiving cisplatin after operation. These results suggest that the IL6-CXCR7 axis may provide a promising target for the treatment of ESCC.

Structural and functional characterization of human CXCR4 as a chemokine receptor and HIV-1 co-receptor by mutagenesis and molecular modeling studies

The human CXC chemokine receptor 4 (CXCR4) is a receptor for the chemokine stromal cell-derived factor (SDF-1alpha) and a co-receptor for the entry of specific strains of human immunodeficiency virus type I (HIV-1). CXCR4 is also recognized by an antagonistic chemokine, the viral macrophage inflammatory protein II (vMIP-II) encoded by human herpesvirus type VIII. SDF-1alpha or vMIP-II binding to CXCR4 can inhibit HIV-1 entry via this co-receptor. An approach combining protein structural modeling and site-directed mutagenesis was used to probe the structure-function relationship of CXCR4, and interactions with its ligands SDF-1alpha and vMIP-II and HIV-1 envelope protein gp120. Hypothetical three-dimensional structures were proposed by molecular modeling studies of the CXCR4.SDF-1alpha complex, which rationalize extensive biological information on the role of CXCR4 in its interactions with HIV-1 envelope protein gp120. With site-directed mutagenesis, we have identified that the amino acid residues Asp (D20A) and Tyr (Y21A) in the N-terminal domain and the residue Glu (E268A) in extracellular loop 3 (ECL3) are involved in ligand binding, whereas the mutation Y190A in extracellular loop 2 (ECL2) impairs the signaling mediated by SDF-1alpha. As an HIV-1 co-receptor, we found that the N-terminal domain, ECL2, and ECL3 of CXCR4 are involved in HIV-1 entry. These structural and mutational studies provide valuable information regarding the structural basis for CXCR4 activity in chemokine binding and HIV-1 viral entry, and could guide the design of novel targeted inhibitors.

Intracoronary, adenovirus-mediated Akt gene transfer in heart limits infarct size following ischemia-reperfusion injury in vivo

BACKGROUND

Previous data have shown that enhanced Akt signaling inhibits cardiac myocyte apoptosis in vitro and in vivo. To elucidate the contribution of apoptosis to the pathogenesis of the infarct, we investigated whether intra-coronary Akt gene delivery could reduce gross infarct size following ischemia/reperfusion injury.

METHODS AND RESULTS

Replication-defective adenoviral constructs encoding a myristoylated, constitutively-active form of Akt (myrAkt) or beta -galactosidase were delivered to rat hearts by intracoronary perfusion. Twenty-four h after gene transduction, hearts in both groups underwent 45 min of ischemia followed by 4 h of reperfusion. A third group of animals also underwent ischemia-reperfusion injury but were not transduced with an adenoviral vector. The proportion of the left ventricle at risk was not different among the experimental groups. However, infarct size as a proportion of the area at risk was significantly lower in myrAkt-treated group than in the beta -galactosidase treated group or in the control group that was not subject to intracoronary perfusion (myrAkt=20.9+/-2.7%v beta -galactosidase=56.1+/-3.9% and control=46.2+/-4.6%, P<0.05), as was infarct size as a proportion of the total left ventricle (myrAkt=11.4+/-3.2 v beta -galactosidase=32. 9+/-3.3 and control=23.5+/-3.0, P<0.05).

CONCLUSIONS

These data demonstrate that Akt signaling limits infarct size following ischemia/reperfusion injury and they indicate that the activation of this pathway may be useful in protecting against myocardial loss in the diseased heart.

Calcium regulation of skeletal muscle thin filament motility in vitro

Using an in vitro motility assay, we have investigated Ca2+ regulation of individual, regulated thin filaments reconstituted from rabbit fast skeletal actin, troponin, and tropomyosin. Rhodamine-phalloidin labeling was used to visualize the filaments by epifluorescence, and assays were conducted at 30 degrees C and at ionic strengths near the physiological range. Regulated thin filaments exhibited well-regulated behavior when tropomyosin and troponin were added to the motility solutions because there was no directed motion in the absence of Ca2+. Unlike F-actin, the speed increased in a graded manner with increasing [Ca2+], whereas the number of regulated thin filaments moving was more steeply regulated. With increased ionic strength, Ca2+ sensitivity of both the number of filaments moving and their speed was shifted toward higher [Ca2+] and was steepest at the highest ionic strength studied (0.14 M gamma/2). Methylcellulose concentration (0.4% versus 0.7%) had no effect on the Ca2+ dependence of speed or number of filaments moving. These conclusions hold for five different methods used to analyze the data, indicating that the conclusions are robust. The force-pCa relationship (pCa = -log10[Ca2+]) for rabbit psoas skinned fibers taken under similar conditions of temperature and solution composition (0.14 M gamma/2) paralleled the speed-pCa relationship for the regulated filaments in the in vitro motility assay. Comparison of motility results with the force-pCa relationship in fibers suggests that relatively few cross-bridges are needed to make filaments move, but many have to be cycling to make the regulated filament move at maximum speed.

An intact Raf zinc finger is required for optimal binding to processed Ras and for ras-dependent Raf activation in situ

The function of the c-Raf-1 zinc finger domain in the activation of the Raf kinase was examined by the creation of variant zinc finger structures. Mutation of Raf Cys 165 and Cys 168 to Ser strongly inhibits the Ras-dependent activation of c-Raf-1 by epidermal growth factor (EGF). Deletion of the Raf zinc finger and replacement with a homologous zinc finger from protein kinase C gamma (PKC gamma) (to give gamma/Raf) also abrogates EGF-induced activation but enables a vigorous phorbol myristate acetate (PMA)-induced activation. PMA activation of gamma/Raf does not require endogenous Ras or PKCs and probably occurs through a PMA-induced recruitment of gamma/Raf to the plasma membrane. The impaired ability of EGF to activate the Raf zinc finger variants in situ is attributable, at least in part, to a major decrement in their binding to Ras-GTP; both Raf zinc finger variants exhibit decreased association with Ras (V12) in situ upon coexpression in COS cells, as well as diminished binding in vitro to immobilized, processed COS recombinant Ras(V12)-GTP. In contrast, Raf binding to unprocessed COS or prokaryotic recombinant Ras-GTP is unaffected by Raf zinc finger mutation. Thus, the Raf zinc finger contributes an important component to the overall binding to Ras-GTP in situ, through an interaction between the zinc finger and an epitope on Ras, distinct from the effector loop, that is present only on prenylated Ras.

Effect of waterborne copper exposure on growth, hepatic enzymatic activities and histology in Synechogobius hasta

The present study was conducted to determine growth, hepatic enzymatic activities and histology in Synechogobius hasta exposed to waterborne copper concentrations of 0 (control), 0.15 and 0.3 mg Cu/l, respectively, for 15 days, and explore whether waterborne copper exposure could induce the fatty liver syndrome for the fish species. Growth (WG and SGR) declined, but HSI increased in S. hasta with increasing waterborne copper levels (P<0.05). Waterborne copper exposure also significantly increased lipid content and reduced protein content in both whole body and liver, and increased copper accumulation in whole body and vertebrae. Copper exposure changed hepatic enzymatic activities (SOD, CAT, SDH, PK, LDH, LPL and HL) and increased hepatic lipid peroxidation level, impaired the histological structure of the gill and liver in S. hasta. Thus, our study demonstrated for the first time that waterborne Cu exposure could induce fatty liver syndrome in fish.

Inactivation of AMPK alters gene expression and promotes growth of prostate cancer cells

AMP-activated protein kinase (AMPK) serves as a fuel-sensing enzyme that is activated by binding of AMP and subsequent phophorylation by upstream kinases such as the tumor suppressor LKB1, when cells sense an increase in the ratio of AMP to ATP. Acute activation of AMPK stimulates fatty acid oxidation to generate more ATP and simultaneously inhibits ATP-consuming processes including fatty acid and protein syntheses, thereby preserving energy for acute cell surviving program, while the chronic activation leads to inhibition of cell growth. The goal of the present study is to explore the mechanisms by which AMPK regulates cell growth. Toward this end, we established stable cell lines by introducing a dominant negative mutant of AMPK α1 subunit or its shRNA into the prostate cancer C4-2 cells and other cells, or wild type LKB1 into the lung adenocarcinoma A549 and breast MB-MDA-231 cancer cells, both of which lack functional LKB1. Our results showed that the inhibition of AMPK accelerated cell proliferation and promoted malignant behavior such as increased cell migration and anchorage-independent growth. This was associated with decreased G1 population, downregulation of p53 and p21, and upregulation of S6K, IGF-1 and IGF1R. Conversely, treatment of the C4-2 cells with 5-aminoimidazole-4-carboxamide 1-Dribonucleoside (AICAR), a prototypical AMPK activator, caused opposite changes. In addition, our study using microarray and RT-PCR revealed that AMPK regulated gene expression involved in tumor cell growth and survival. Thus, our study provides novel insights into the mechanisms of AMPK action in cancer cells and presents AMPK as an ideal drug target for cancer therapy.

AP180 and AP-2 interact directly in a complex that cooperatively assembles clathrin

Clathrin-coated vesicles are involved in protein and lipid trafficking between intracellular compartments in eukaryotic cells. AP-2 and AP180 are the resident coat proteins of clathrin-coated vesicles in nerve terminals, and interactions between these proteins could be important in vesicle dynamics. AP180 and AP-2 each assemble clathrin efficiently under acidic conditions, but neither protein will assemble clathrin efficiently at physiological pH. We find that there is a direct, clathrin-independent interaction between AP180 and AP-2 and that the AP180-AP-2 complex is more efficient at assembling clathrin under physiological conditions than is either protein alone. AP180 is phosphorylated in vivo, and in crude vesicle extracts its phosphorylation is enhanced by stimulation of casein kinase II, which is known to be present in coated vesicles. We find that recombinant AP180 is a substrate for casein kinase II in vitro and that its phosphorylation weakens both the binding of AP-2 by AP180 and the cooperative clathrin assembly activity of these proteins. We have localized the binding site for AP-2 to amino acids 623-680 of AP180. The AP180/AP-2 interaction can be disrupted by a recombinant AP180 fragment containing the AP-2 binding site, and this fragment also disrupts the cooperative clathrin assembly activity of the AP180-AP-2 complex. These results indicate that AP180 and AP-2 interact directly to form a complex that assembles clathrin more efficiently than either protein alone. Phosphorylation of AP180, by modulating the affinity of AP180 for AP-2, may contribute to the regulation of clathrin assembly in vivo.

Induction of acetylcholine receptor gene expression by ARIA requires activation of mitogen-activated protein kinase

Transcription of genes encoding nicotinic acetylcholine receptor (AChR) subunits (alpha, beta, gamma or epsilon, and delta) is highest in nuclei localized to the synaptic region of the muscle, which contributes to maintain a high density of AChRs at the postjunctional membrane. ARIA (AChR inducing activity) is believed to be the trophic factor utilized by motor neurons to stimulate AChR synthesis in the subsynaptic area. To elucidate the signaling mechanism initiated by ARIA, we established stable C2C12 cell lines carrying the nuclear lacZ gene under the control of the mouse epsilon subunit promoter or chicken alpha subunit promoter. ARIA stimulated tyrosine phosphorylation of erbB proteins in these C2C12 cells within 15 s with a peak at 5 min. Immediately following tyrosine phosphorylation of erbB proteins, mitogen-activated protein (MAP) kinase was activated which occurred within 30 s and peaked at 8 min after ARIA stimulation. Concomitantly, expression of AChR genes was induced by ARIA. ARIA-induced AChR subunit transgene expression was observed only in differentiated myotubes and not in myoblasts, suggesting that downstream signaling component(s) are regulated in a manner dependent on the myogenic program. Inhibition of the MAP kinase activity by using a specific MAP kinase kinase inhibitor or by overexpressing dominant negative mutants of Raf or MAP kinase kinase attenuated or abolished the ARIA-induced activation of AChR alpha and epsilon subunit gene expression. These results indicate that regulation of AChR gene expression by ARIA in C2C12 cells requires activation of the MAP kinase signaling pathway.