Common Downstream Target Research Articles

Regulation of NF-κB induction by TCR/CD28

NF-κB family transcription factors are a common downstream target for inducible transcription mediated by many different cell-surface receptors, especially those receptors involved in inflammation and adaptive immunity. It is now clear that different classes of receptors employ different proximal signaling strategies to activate the common NF-κB signaling components, such as the IKK complex. For antigen receptors expressed by T and B cells, this pathway requires a complex of proteins including the proteins Carma1, Bcl10, and Malt1. Here, we discuss some of what is known about regulation of these proteins downstream of TCR/CD3 and co-stimulatory CD28 signaling. We also discuss another unique aspect of TCR-mediated NF-κB activation, i.e., the spatial restriction imposed on signaling events by the formation of the immunological synapse between a T cell and antigen-presenting cell presenting specific peptide/MHC.

Inhibition of Phosphodiesterases Leads to Prevention of the Mitochondrial Permeability Transition Pore Opening and Reperfusion Injury in Cardiac H9c2 Cells

We tested if inhibition of phosphodiesterases (PDEs) with IBMX (1-methyl-3-isobutylxanthine) can modulate the mitochondrial permeability transition pore (mPTP) opening by inactivating glycogen synthase kinase 3β (GSK-3β). H9c2 cells were exposed to 600μM H(2)O(2) for 20min to cause the mPTP opening. Mitochondrial membrane potential (ΔΨm) was assessed by imaging cells loaded with tetramethylrhodamine ethyl ester (TMRE). Cell viability was measured with propidium iodide (PI) fluorometry using a fluorescence reader. Ischemia/reperfusion injury was induced by exposing cells to ischemic solution for 90min followed by 30min of reperfusion. IBMX reduced loss of ΔΨm caused by H(2)O(2), indicating that inhibition of PDEs can prevent the mPTP opening. However, IBMX could not inhibit the pore opening in cells transfected with the constitutively active GSK-3β (GSK-3β-S9A) mutant, suggesting a critical role of GSK-3β in the action of IBMX. IBMX also reduced reperfusion injury in a GSK-3β dependent manner. In support, IBMX increased GSK-3β phosphorylation at Ser(9), an effect that was reversed by both the PKA inhibitor H89 and the PKG inhibitor KT5823. In support, IBMX activated both PKA and PKG. IBMX failed to prevent the loss of ΔΨm in the presence of H89 or PKA siRNA. Similarly, both KT5823 and PKG siRNA reversed the protective effect of IBMX. Inhibition of PDEs prevents the mPTP opening by inactivating GSK-3β through PKA and PKG. GSK-3β is a common downstream target of PKA and PKG. Inhibition of PDEs may be a useful approach to prevent reperfusion injury.

Neural cell adhesion molecule potentiates invasion and metastasis of melanoma cells through CAMP-dependent protein kinase and phosphatidylinositol 3-kinase pathways

Neural cell adhesion molecule (NCAM) has been implicated in tumor metastasis yet its function in melanoma progression remains unclear. Here, we demonstrate that stably silencing NCAM expression in mouse melanoma B16F0 cells perturbs their cellular invasion and metastatic dissemination in vivo. The pro-invasive function of NCAM is exerted via dual mechanisms involving both cAMP-dependent protein kinase (PKA) and phosphatidylinositol 3-kinase (PI3K) pathways. Pharmacologic inhibition of PKA and PI3K leads to impaired cellular invasion. In contrast, forced expression of constitutively activated Akt, the major downstream target of PI3K, restores the defective cellular invasiveness of NCAM knock-down (KD) B16F0 cells. Furthermore, attenuation of either PKA or Akt activity in NCAM KD cells is shown to affect their common downstream target, transcription factor cAMP response element binding protein (CREB), which in turn down-regulates mRNA expression of matrix metalloproteinase-2 (MMP-2), thus contributes to impaired cellular invasion and metastasis of melanoma cells. Together, these findings indicate that NCAM potentiates cellular invasion and metastasis of melanoma cells through stimulation of PKA and PI3K signaling pathways thus suggesting the potential implication of anti-NCAM strategy in melanoma treatment.

O9. Cross-talk between growth and differentiation pathways in cell fate determination in the developing brain

Proliferation of neural stem/progenitor cells (NSCs/NPCs) is closely linked to the inhibition of neuronal and glial differentiation. However, the molecular link between induction of cell cycle progression and inhibition of cell differentiation in NSCs/NPCs is poorly understood. Fibroblast growth factor 2 (FGF2) promotes proliferation of NSCs/NPCs while it inhibits their differentiation, which suggests that a molecular link between growth and differentiation pathways is functioning downstream of FGF2 signaling. We hypothesized that a component or components in the proliferative signaling pathway should also be involved in inhibition of NSCs/NPCs differentiation. We have found that the FGF2 signaling and the Wnt canonical pathway cooperate together, via inactivation of glycogen synthase kinase 3beta (GSK3beta) and subsequent induction of cyclin D1 expression, to promote proliferation of NSCs/NPCs. Interestingly, the GSK3beta inactivation-mediated beta-catenin accumulation in the nucleus is involved in the inhibition of neurogenesis from NSCs/NPCs by activation of hes1 and hes5 gene expression through the cooperation with a Notch pathway. As we have previously demonstrated, astrocyte differentiation from NSCs/NPCs is synergistically induced by a combination of LIF and BMP2. In this symposium, we also present our recent data showing that beta-catenin stabilization by a GSK3 beta inhibitor decreases the number of GFAP expressing astrocytes in the culture of NSCs/NPCs with LIF and BMP2. In addition, forced expression of cyclin D1, a common downstream target of FGF2 and Wnt signals, decreases the number of GFAP expressing astrocytes. We further show that knockdown of cyclin D1 relieves the inhibitory effect of the GSK3beta inhibitor. In conclusion, our findings indicate that cross-interactions among growth and differentiation pathways are important for the cell-fate determination in the developing brain.

Life span extension by resveratrol, rapamycin, and metformin: The promise of dietary restriction mimetics for an healthy aging

Life expectancy at the turn of the 20th century was 46 years on average worldwide and it is around 65 years today. The correlative increase in age-associated diseases incidence has a profound public health impact and is an important matter of concern for our societies. Aging is a complex, heterogeneous, and multifactorial phenomenon, which is the consequence of multiple interactions between genes and environment. In this review, we survey animals models that have been of great help for both investigating mechanism of aging and identifying molecules, which slow down the onset of age-related diseases. Resveratrol (RSV) is one of those. We will report evidences supporting RSV as a molecule that acts by mimicking the beneficial effects of dietary restriction, and may share common downstream targets with rapamycin and metformin. Although those molecules do not reveal all the secrets of the fountain of youth, they may help us maintaining the quality of life in the old age.

Phosphatidylinositol 4,5-bisphosphate-dependent regulation of the output in lobster olfactory receptor neurons

Transient receptor potential (TRP) channels often play a role in sensory transduction, including chemosensory transduction. TRP channels, a common downstream target of phosphoinositide (PI) signaling, can be modulated by exogenous phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2], phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] and/or diacylglycerol (DAG). Lobster olfactory receptor neurons (ORNs) express a TRP-related, non-selective, calcium/magnesium-permeable, sodium/calcium-gated cation (SGC) channel. Here we report that PIs regulate the function of the calcium-activated form of the lobster channel. Sequestering of endogenous PI(4,5)P2, either with an anti-PI(4,5)P2 antibody or by electrostatic screening with polyvalent cations, blocks the channel. Exogenous PI(3,4,5)P3 activates the channel independently of intracellular sodium and/or calcium. Exogenous non-hydrolysable DAG analogs fail to change the gating parameters of the channel, suggesting the channel is insensitive to DAG. Electrophysiological recording from lobster ORNs in situ using a panel of pharmacological tools targeting the key components of both PI and DAG metabolism (phospholipase C, phosphoinositide 4-kinase and DAG kinase) extend these findings to the intact ORN. PI(4,5)P2 depletion suppresses both the odorant-evoked discharge and whole-cell current of the cells, and does so possibly independently of DAG production. Collectively, our results argue that PIs can regulate output in lobster ORNs, at least in part through their action on the lobster SGC channel.

Abstract 1240: Functional deregulation of NF-kB and abnormal TNFa response in acute promyelocytic leukemia

Abstract Acute promyelocytic leukemia (APL) accounts for approximately 10% of acute myelogenous leukemia (AML) cases, and is characterized by accumulation of abnormal promyelocytes in patient bone marrow and peripheral blood. APL is associated with balanced chromosomal translocations involving retinoic acid receptor alpha (RARA), giving rise to fusion oncoproteins referred to as X-RARA. As deregulation of retinoid signaling is insufficient for leukemia development, our studies aim to determine other signaling pathways involved in APL by assessing the gene expression profiles and cell biology of X-RARA. We previously determined, using gene expression microarray analysis, common downstream targets of the variant APL fusion proteins NPM- and NuMA-RARA. We observed an over-representation of NF-κB target genes within this dataset. In these cells, a number of NF-κB target genes were commonly over-expressed. A subset of commonly deregulated genes were validated in our APL cell lines and 23 primary APL patient samples by real-time quantitative RT-PCR (RQ-PCR). 13/16 genes that were tested were significantly altered in APL compared to normal BM (n=11) p<0.05. The majority of these deregulated genes showed a progressive trend towards normal expression levels in post-treated samples. These data indicate defects in NF-κB-mediated gene expression in APL pathogenesis. We next examined NF-κB activity by assessing the expression levels of NF-κB target genes by quantitative real-time RT-PCR, in the presence and absence of TNFα. We observed that there was sustained activation of NF-κB in cells expressing NPM-RARA, as evidenced by the increased expression of NF-κB transcriptional target genes after induction by TNFα. Western analysis of protein derived from U937-NPM-RARA and NB4 cells demonstrated over-expression of NF-κB (p65) protein, as well as its transcriptional target IκBα. The increased pool of NF-κB localized to both the cytoplasm and the nucleus in U937-NPM-RARA cells as visualized by immunofluorescent confocal microscopy. Having observed deregulated expression of downstream targets of TNFα, we sought to examine the ability of X-RARA to confer resistance to TNF-mediated apoptosis. Our results in colony formation assays indicated that NPM-RARA expressing cells formed significantly more colonies, in the presence of 0-100 ng/mL TNFα, in a dose-dependent manner, compared to U937 control cells. These data suggested a greater ability on the part of NPM-RARA+ cells to survive and proliferate in the presence of TNFα. Our data provides the first evidence of the functional deregulation of the NF-κB-mediated signaling pathway and the TNFα response in cells expressing the variant APL fusion proteins. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1240.

Tbx3 improves the germ-line competency of induced pluripotent stem cells

Induced pluripotent stem (iPS) cells can be obtained through the introduction of defined factors into somatic cells1. The combination of Oct4, Sox2 and Klf4 (OSK) constitutes the minimal requirement for generating iPS cells from mouse embryonic fibroblasts (MEFs). These cells are thought to resemble embryonic stem cells (ESCs) based on global gene expression analyses; but, few studies have tested their ability and efficiency in contributing to chimerism, colonization of germ tissues, and most importantly, germ-line transmission and life-birth from iPS cells produced with tetraploid complementation. Through the genomic analyses of ESC genes that have roles in pluripotency and fusion-mediated somatic cell reprogramming, we identified Tbx3 as a transcription factor that significantly improves the quality of iPS cells. Induced-PS cells generated with OSK + Tbx3 (OSKT) are superior in both germ cell contribution to the gonads and germ-line transmission frequency. However, global gene expression profiling could not distinguish between OSK and OSKT iPS cells. Genome-wide ChIP-sequencing analysis of Tbx3 binding sites in ESCs suggests that Tbx3 regulates pluripotency-associated and reprogramming factors, in addition to sharing many common downstream regulatory targets with Oct4, Sox2, Nanog and Smad1. This study underscores the intrinsic qualitative differences between iPS cells generated by different methods and highlights the need to rigorously characterize iPS cells beyond in vitro studies.

Molecular Sequaele of Activin A-Dependent Osteoblast Inhibition in Myeloma.

Abstract 1789Poster Board I-815Understanding the pathogenesis of cancer-related bone disease is critical to the discovery of new therapies. The development of osteolytic lesions in multiple myeloma (MM) results from unopposed osteoclast activity due to decreased osteoblast (OB) function. We recently demonstrated that activin A contributes to MM-mediated OB inhibition. The availability of a clinical-grade activin A inhibitor that reduces tumor burden by restoring the bone structure in vivo, underscores the relevance of this pathway in the development of MM-bone disease. Here, we characterize the signaling pathway mediating OB inhibition by activin A. Activin A secretion by bone marrow stromal cells (BMSC) is enhanced in the presence of MM cells which was completely abrogated and using a transwell system. To identify the receptors and pathways involved in activin A secretion, we used neutralizing antibody against several integrins, CD40 and osteopontin. Only VLA4 neutralizing antibodies partially inhibited activin secretion by about 20% (range 10-30%, p<0.05). Since activin A promoter contains a cJUN-binding sequence, we explored the relations between JNK and activin. We show that upon MM cell binding to BMSC, stromal-derived JNK is phosphorylated and SP600125 (20 μM), a specific JNK inhibitor, impairs activin A secretion by BMSC both at basal conditions and in the presence of MM (40% and 54%, respectively; p<0.01). These results suggest that activin secretion requires JNK activation induced by cell-to-cell contact. We next investigated the mechanism underlying activin-mediated OB inhibition by assessing the activity of several signaling pathways critical to OB differentiation. First, we showed that activin A induces SMAD2 phosphorylation, while no effects were noted on SMAD1, β-catenin, pP65 and pERK. Then, using a doxycycline-inducible β-catenin system, we demonstrate that β-catenin activation overcomes activin A inhibition of OB differentiation. These results suggest that activin/SMAD2 and β-catenin modulate OB differentiation by affecting a common downstream target. We next evaluated the expression of two candidates, the transcription factors RUNX2 and DLX5. Only DLX5 expression was downregulated by exogenous activin A (5 fold decrease at 96 hours, p< 0.01). Specific inhibition of SMAD2 via shRNA-mediated knock-down upregulated basal DLX5 and ALP mRNA expression (1.5 and 4.7 fold increase respectively, p<0.05), and partially overcame activin A inhibitory effects. In turn, DLX5 knock-down abrogated OB differentiation without additive effects by exogenous activin A. The clinical relevance of DLX5 was confirmed by the strong correlation between its expression levels in BM biopsies from MM patients and activin A levels in BM serum. Finally, we demonstrate by in vitro and in-vivo studies that MM-mediated DLX5 inhibition is restored by treatment with RAP-011, the specific activin inhibitor. In conclusion, we show that MM cell engagement of BMSC enhances activin A secretion via adhesion-mediated JNK activation and activin A, in turn, inhibits osteoblast differentiation via SMAD2-dependent DLX5 downregulation. This study identifies a novel pathway relevant to OB differentiation and amenable to drug targeting. DisclosuresChauhan:Nereus Pharmaceuticals, Inc: Consultancy. Seehra:Acceleron Pharma: Employment. Anderson:Celgene : Research Funding; Novartis: Research Funding; Millennium: Research Funding. Scadden:Fate Therapeutics: Consultancy. Raje:Astrazeneca, Novartis, Celgene: Research Funding.

High Id1 Expression Is Associated with Poor Prognosis in 237 Patients with Acute Myeloid Leukemia.

Abstract 4687▪▪This icon denotes an abstract that is clinically relevant.Inhibitors of differentiation (Id) or DNA binding helix-loop-helix (HLH) proteins are a group of dominant inhibitors of basic HLH transcriptional factors, which act as positive regulators of cell growth or promote excessive proliferation, and also protect cells against drug-induced apoptosis in mammalians. Recently, Id1 has been identified as a common downstream target of several constitutively activated oncogenic tyrosine kinase(TK), such as FLT3/ITD, in leukemia cells. We analyzed Id1 expression as possible prognostic factor in 237 AML patients. High Id1 expression was associated with older age(p=0.009); and with Ftl3/ITD(p=0.003). However, 61% of the patients in the group of FLT3- AML were Id1+, suggesting that other TK are involved. In whole population, high Id1 expression independently predicted shorter disease free survival (DFS)(p=0.05), and overall survival (OS)(p=0.003). In the subgroup of young patients (age'60 years) with normal cytogenetic, Id1+ was, in multivariate analysis, associated with lower CR rates(p=0.02), shorter DFS(p=0.02) and OS(p=0.006).In conclusion our data provides a new molecular marker for refining the risk classification of AML especially in young patients with normal cytogenetic. Id1- patients with normal cytogenetic should be classified as favourable-risk leukemia. Id1, as a downstream target of constitutively activated TK, could be a suitable candidate for targeted therapy. Disclosures:No relevant conflicts of interest to declare.

High Id1 expression is associated with poor prognosis in 237 patients with acute myeloid leukemia

Inhibitors of differentiation (Id) are a group of dominant inhibitors of basic helix-loop-helix transcriptional factors, which promote excessive proliferation, and also protect cells against drug-induced apoptosis in mammalians. Recently, Id1 has been identified as a common downstream target of several constitutively activated oncogenic tyrosine kinase, such as FLT3 internal tandem duplication, in leukemia cells. We analyzed Id1 expression as possible prognostic factor in 237 acute myeloid leukemia (AML) patients. High Id1 expression was associated with older age (P = .009) and with FLT3 internal tandem duplication (P = .003). However, 61% of the patients in the group of FLT3(-) AML were Id1(+), suggesting that other tyrosine kinases are involved. In whole population, high Id1 expression independently predicted shorter disease-free survival (P = .05) and overall survival (P = .003). In young patients (age <OR= 60 years) with normal cytogenetics, Id1(+) was, in multivariate analysis, associated with lower complete remission rates (P = .02), shorter disease-free survival (P = .02), and overall survival (P = .006). In conclusion, our data provide a new molecular marker for refining the risk classification of AML, especially in young patients with normal cytogenetic. Id1(-) patients with normal cytogenetic should be classified as favorable-risk leukemia. Id1, as a downstream target of constitutively activated tyrosine kinase, could be a suitable candidate for targeted therapy.

Gardner's syndrome (familial adenomatous polyposis): a cilia-related disorder

Familial adenomatous polyposis (FAP) is an autosomal dominant form of intestinal polyposis and colorectal cancer caused by germ-line mutations in the adenomatous polyposis coli (APC) gene. The term Gardner's syndrome is used to describe extracolonic manifestations, such as osteomas, skin cysts, congenital hypertrophy of the retinal pigmented epithelium (CHRPE), and desmoid tumours (aggressive fibromatosis), that are especially prominent in families with FAP. We postulate that a ciliary dysfunction is the underlying pathogenetic mechanism of extraintestinal manifestations in patients with FAP. This postulation is based on the presence of common clinical manifestations (ie, cysts, retinal abnormalities, and fibrosis) in Gardner's syndrome and cilia-related disorders. Additionally, both APC and the cilia have degradation of beta-catenin as the common downstream target in the Wnt-signalling pathway. Mutations in APC causing Gardner's syndrome are clustered in a region encoding a series of amino-acid repeats responsible for the binding to beta-catenin. Proofs of principle that beta-catenin could be the key mediator of the ciliary disorder also rely in the findings that overexpression of beta-catenin induces polycystic kidney disease, and CHRPE phenotypes in animal models. Other candidates for the common link between Gardner's syndrome and cilia-related disorders are the APC-binding proteins: end-binding protein 1 (EB1) and kinesin-family-member 3a (KIF3a), both of which are ciliary proteins involved in intraflagellar transport. Finally, pathogenetic similarities between some ciliopathies and extraintestinal tumours in FAP suggest a cilia defect. Understanding extracolonic manifestations in the context of FAP as a ciliary disorder might add new therapeutic options for patients with Gardner's syndrome.

Convergent, not serial, striatal and pallidal circuits regulate opioid-induced food intake

Mu opioid receptor (MOR) signaling in the nucleus accumbens (NAcc) elicits marked increases in the consumption of palatable tastants. However, the mechanism and circuitry underlying this effect are not fully understood. Multiple downstream target regions have been implicated in mediating this effect but the role of the ventral pallidum (VP), a primary target of NAcc efferents, has not been well defined. To probe the mechanisms underlying increased consumption, we identified behavioral changes in rats' licking patterns following NAcc MOR stimulation. Because the temporal structure of licking reflects the physiological substrates modulating consumption, these measures provide a useful tool in dissecting the cause of increased consumption following NAcc MOR stimulation. Next, we used a combination of pharmacological inactivation and lesions to define the role of the VP in hyperphagia following infusion of the MOR-specific agonist [ d-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO) into the NAcc. In agreement with previous studies, results from lick microstructure analysis suggest that NAcc MOR stimulation augments intake through a palatability-driven mechanism. Our results also demonstrate an important role for the VP in normal feeding behavior: pharmacological inactivation of the VP suppresses baseline and NAcc DAMGO-induced consumption. However, this interaction does not occur through a serial circuit requiring direct projections from the NAcc to the VP. Rather, our results indicate that NAcc and VP circuits converge on a common downstream target that regulates food intake.

Thrombin as a common downstream target blocking both platelet and monocyte activation

Thromb Haemost 2009; 101: 220–221 Platelets play a pivotal role in the pathogenesis of thrombotic complications after percutaneous coronary interventions (PCI) (1). The use of optimal antiplatelet therapy is critical in reducing adverse events in this setting. Despite the efficacy of dual antiplatelet therapy in patients undergoing PCI, thrombo-ischaemic events and, in particular, stent thrombosis are frequent complications (2). High post-treatment platelet reactivity is associated with cardiovascular outcome after PCI (3) and coronary stent implantation (4). Different agents are currently in use for adjunctive anticoagulant treatment on top of adequate antiplatelet regimen during PCI. Traditionally, unfractionated heparin (UFH) has been the standard anticoagulant administered during coronary intervention. Enhanced platelet activation in vivo and ex vivo has been shown after UFH treatment (5, 6). Moreover, heparin does not suppress the transient increase in thromboxane biosynthesis associated with coronary angioplasty (7). Low-molecular-weight heparin (LMWH), in contrast, does not affect platelet activation in vivo and ex vivo after PCI (5, 8). Recently bivalirudin, a short-acting direct thrombin inhibitor, has been shown to be effective and safe in patients undergoing PCI (9), with reduced bleeding as compared with heparin. Reduced inhibition of adenosine diphosphate (ADP)-induced platelet aggregation at the time of PCI is associated with an increased risk for adverse thrombotic complications (10). Bivalirudin, given during PCI in patients pretreated with 600 mg of clopidogrel, is unlike UFH associated with further inhibition of platelet aggregation (11). A similar effect by bivalirudin was previously described on platelet P-selectin (12). Moreover, bivalirudin alone or coupled with clopidogrel may significantly down© 2009 Schattauer GmbH, Stuttgart

JNK-mediated Phosphorylation of Paxillin in Adhesion Assembly and Tension-induced Cell Death by the Adenovirus Death Factor E4orf4

The adenovirus type 2 Early Region 4 ORF4 (E4orf4) protein induces a caspase-independent death program in tumor cells involving changes in actin dynamics that are functionally linked to cell killing. Because an increase in myosin II-based contractility is needed for the death of E4orf4-expressing cells, we have proposed that alteration of cytoskeletal tension is part of the signals engaging the death pathway. Yet the mechanisms involved are poorly defined. Herein, we show that the Jun N-terminal kinase JNK is activated in part through a pathway involving Src, Rho, and ROCK (Rho kinase) and contributes to dysregulate adhesion dynamics and to kill cells in response to E4orf4. JNK supports the formation of atypically robust focal adhesions, which are bound to the assembly of the peculiar actomyosin network typifying E4orf4-induced cell death and which are required for driving nuclear condensation. Remarkably, the dramatic enlargement of focal adhesions, actin remodeling, and cell death all rely on paxillin phosphorylation at Ser-178, which is induced by E4orf4 in a JNK-dependent way. Furthermore, we found that Ser-178-paxillin phosphorylation is necessary to decrease adhesion turnover and to enhance the time residency of paxillin at focal adhesions, promoting its recruitment from an internal pool. Our results indicate that perturbation of tensional homeostasis by E4orf4 involves JNK-regulated changes in paxillin adhesion dynamics that are required to engage the death pathway. Moreover, our findings support a role for JNK-mediated paxillin phosphorylation in adhesion growth and stabilization during tension signaling.

Cooperative interaction of Nkx2.5 and Mef2c transcription factors during heart development

The interactions of diverse transcription factors mediate the molecular programs that regulate mammalian heart development. Among these, Nkx2.5 and the Mef2c regulate common downstream targets and exhibit striking phenotypic similarities when disrupted, suggesting a potential interaction during heart development. Co-immunoprecipitation and mammalian two-hybrid experiments revealed a direct molecular interaction between Nkx2.5 and Mef2c. Assessment of mRNA expression verified spatiotemporal cardiac coexpression. Finally, genetic interaction studies employing histological and molecular analyses showed that, although Nkx2.5(-/-) and Mef2c(-/-) individual mutants both have identifiable ventricles, Nkx2.5(-/-);Mef2c(-/-) double mutants do not, and that mutant cardiomyocytes express only atrial and second heart field markers. Molecular marker and cell death and proliferation analyses provide evidence that ventricular hypoplasia is the result of defective ventricular cell differentiation. Collectively, these data support a hypothesis where physical, functional, and genetic interactions between Nkx2.5 and Mef2c are necessary for ventricle formation.

UME6is a crucial downstream target of other transcriptional regulators of true hyphal development inCandida albicans

True hyphal growth of Candida albicans can be induced by several environmental conditions and contributes significantly to the high virulence of this pathogenic fungus. The transcriptional network that governs hyphal morphogenesis is complex, depends on several regulators and is not completely understood. Recently, CaUME6, a homolog of the Saccharomyces cerevisiae UME6 gene, has been shown to be required for hyphal elongation. In the present study, the C. albicans ume6Delta strain showed a complete defect in hyphae formation under all the growth conditions tested. UME6 was repressed by the Nrg1-Tup1 repressor in yeast-form cells but NRG1 was not repressed by Ume6p under hyphal growth conditions. Wild-type UME6 expression depended on each hyphal regulator tested, and ectopic UME6 expression in efg1Delta, cph1Delta and ras1Delta cells rescued the hyphal defects of these mutants under some hyphal growth conditions. Thus, UME6 is a common downstream target of regulators promoting hyphal development. Ectopic UME6 expression promoted both germ tube formation and hyphal elongation. The expression of all hyphae-specific genes investigated depended on UME6 expression. A model for transcriptional regulation of hyphal development and the role of Ume6p is proposed.

Elevated Expression of GPR34 and Its Association with a Novel Translocation T(X;14)(p11;q32) Involving IGHS and GPR34 in MALT Lymphoma.

MALT lymphoma is a genetically unique disorder and five mutually exclusive chromosomal translocations have been identified thus far in this disease: t(11;18), t(14;18), t(1;14), t(1;2) and t(3;14). Despite this genetic heterogeneity, all but one of the translocations affect the NF-κB signaling pathway, which is critical if not essential for antigen receptor mediated B- and T-cell activation and likely enhances MALT lymphoma growth. However, the known translocations are present in only 25% of cases suggesting that additional uncharacterized translocations exist. We used long-distance inverse polymerase chain reaction (LDI-PCR) technique to clone a novel IGH translocation partner in a 60-year-old female with a history of Sjogren's syndrome and primary MALT lymphoma involving the parotid gland. The breakpoint on chromosome 14 occurred within the IGHSA2 switch region while the breakpoint on chromosome X fell within Xp11.4. The breakpoint on chromosome Xp11.2 fell between two genes, GPR82 and GPR34, both of which code for orphan G-protein coupled receptors (GPCRs). The breakpoint also fell within and disrupted a larger gene called CASK (a membrane-associated guanylate kinase-MAGUK). To determine the prevalence of this translocation in MALT lymphoma we performed interphase FISH studies on 64 MALT lymphomas using a breakapart probe for GPR82. Only the index case had an abnormal split signal pattern. We next designed primers to perform real-time quantitative RT-PCR for the genes located on Xp11 and found that GPR34 RNA was highly expressed, a 49-fold increase, in the patient carrying the t(X;14)(p11.4;q32) translocation compared to a normal splenic B cell control. Expression of GPR82 and CASK RNA was similar between normal B cells and the patient carrying the t(X;14)(p11.4;q32) translocation. These data suggest that the GPR34 gene is dysregulated upon its translocation to the IGHSA2 switch region. We then measured GPR34 RNA expression in a panel of MALT lymphomas (n=12) and found that GPR34 was expressed at levels higher than that seen in normal B cells with an average increase of 11 fold, 9/11 of which had an expression lever greater than 3-fold over normal splenic B cells. In a gastric MALT lymphoma specimen arising in a 67-year-old male, we saw a 64 fold increase in GPR34 expression. Interphase FISH studies performed on this specimen showed an extra intact GPR34 signal but no translocation involving IGH or GPR34, suggesting that other mechanisms, including gene dosage effect, can upregulate GPR34. GPR34 RNA was also detected in other normal B cell populations and histologic subtypes of NHL but not to the extent seen in MALT lymphoma; values represent the expression of GPR34 normalized to β-actin and a normal B cell control (value of 1.0): t(X;14)(p11.4;q32) specimen, 49.0; MALT lymphoma, 11.0 (n=12); peripheral blood B cells, 0.48 (n=2); normal bone marrow B cells, 0.97 (n=3); follicular lymphoma, 2.47 (n=3); marginal zone B cell lymphoma, 2.47 (n=3); diffuse large cell lymphoma, 0.36, (n=3); mantle cell lymphoma, 2.67 (n=3); and multiple myeloma 0.52 (n=6). The receptor encoded by GPR34 is most similar to the PY2 receptor subfamily of GPCR and GPR34 mRNA transcripts are particularly abundant in mast cells while lower levels were detected in other immune cells including B cells. However, little is known about its natural ligand, biologic function, or the signaling cascades activated by its engagement. Because the NF-κB signaling pathway has been shown to be a common downstream target of MALT lymphoma translocations we first examined the impact of GPR34 expression on phosphorylation of Iκ-Bα. Transient expression of a YFP-GPR34 expression plasmid in HeLa cells results in increased phosphorylation of Iκ-Bα compared to the YFP control. Additionally, we observed increased phosphorylation of ERK1/2 in GPR34-expressing cells, however no change in phosphorylation of GSK3β was detected. In summary, these data identify a novel IGHS translocation partner in MALT lymphoma and suggest that dysregulation of GPR34 is commonly found in MALT lymphoma. Overexpression of GPR34 results in activation of the NF-κB and MAP kinase pathways and may be a novel mechanism by which MALT lymphoma occurs.

Overcoming an Energy Crisis?

See related article, pages 983–991 A prolonged period of ischemia leads to death of cardiac myocyte (myocardial infarction). In theory, quicker restoration of blood supply to the ischemic myocardium should reduce the extent of myocardial injury. However, reperfusion itself has the potential to exacerbate myocardial damage, a phenomenon known as reperfusion injury. Mitochondrial dysfunction plays a central role in mediating myocardial cell death by ischemia/reperfusion (IR). In particular, opening of the mitochondria permeability transition pore (mPTP) has been attributed to irreversible cell damage.1,2 Studies on the effects of preconditioning and postconditioning have revealed a number of signaling cascades that afford cardioprotection involving the mitochondria. Among them, inhibition of glycogen synthase kinase (GSK)-3 has been causatively related by many investigators to the protective effects of ischemic preconditioning,3,4 pharmacological preconditioning,5 anesthetic postconditioning,6 ischemic postconditioning,7 and many chemical cardioprotective interventions.8–13 However, some controversies exist regarding the involvement of GSK-3 inhibition in the ischemic preconditioning and postconditioning effects observed in mice.14 GSK-3 is a serine/threonine kinase, the activity of which is inhibited by phosphorylation induced by activation of upstream kinases. The activity of GSK-3β is decreased by ischemia because of phosphorylation of serine 9 through a phosphatidylinositol 3-kinase–dependent mechanism.4 Inhibition of GSK-3 during IR appears to be an important mechanism of myocardial adaptation because a number of cardioprotective agents use inhibition (phosphorylation) of mitochondrial GSK-3β as the common downstream target.15 We speculate that GSK-3 inhibitors either mimic preconditioning or ensure greater levels of GSK-3 inhibition during IR. However, an important question remains: How does GSK-3 inhibition achieve cardioprotection against ischemia? One proposed mechanism, endorsed by nearly all of the available literature in the field, is that GSK-3 inhibition may delay or suppress mPTP opening.3,6,11,12,15,16 However, a question remains as to how inhibition of …

ERK and p38 pathways regulate amino acid signalling

The ribosomal protein S6 kinase 1 (S6K1) is emerging as a common downstream target of signalling by hormones and nutrients such as insulin and amino acids. Here, we have investigated how amino acids signal through the S6K1 pathway. First, we found that a commercial anti-phospho-Thr389-S6K1 antibody detects an 80–90 kDa protein that is rapidly phosphorylated in response to amino acids. Unexpectedly, this phosphorylation was insensitive to both mTOR and PI-3 kinase inhibitors, and knockdown experiments showed that this protein was not S6K1. Looking for candidate targets of this phosphorylation, we found that amino acids stimulated phosphorylation of RSK and MSK kinases at residues that are homologous to Thr389 in S6K1. In turn, these phosphorylations required the activity of either p38 or ERK MAP kinases, which could compensate for each other. Moreover, we show that these MAP kinases are also needed for the amino acid-induced phosphorylation of S6K1 at Thr421/Ser424, as well as for that of S6K1 substrate, the S6 ribosomal protein. Consistent with these results, concomitant inhibition of p38 and ERK pathways also antagonised the well-known effects of amino acids on the process of autophagy. Altogether, these findings demonstrate a previously unknown role for MAP kinases in amino acid signalling.