Download the Free Unbound MEDLINE PubMed App to your smartphone or tablet.
Available for iPhone, iPad, iPod touch, and Android.
Journal of molecular signaling [journal]
- TRAF molecules in cell signaling and in human diseases. [JOURNAL ARTICLE]
- J Mol Signal 2013 Jun 13; 8(1):7.
The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of intracellular proteins were originally identified as signaling adaptors that bind directly to the cytoplasmic regions of receptors of the TNF-R superfamily. The past decade has witnessed rapid expansion of receptor families identified to employ TRAFs for signaling. These include Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), T cell receptor, IL-1 receptor family, IL-17 receptors, IFN receptors and TGFbeta receptors. In addition to their role as adaptor proteins, most TRAFs also act as E3 ubiquitin ligases to activate downstream signaling events. TRAF-dependent signaling pathways typically lead to the activation of nuclear factor-kappaBs (NF-kappaBs), mitogen-activated protein kinases (MAPKs), or interferon-regulatory factors (IRFs). Compelling evidence obtained from germ-line and cell-specific TRAF-deficient mice demonstrates that each TRAF plays indispensable and non-redundant physiological roles, regulating innate and adaptive immunity, embryonic development, tissue homeostasis, stress response, and bone metabolism. Notably, mounting evidence implicates TRAFs in the pathogenesis of human diseases such as cancers and autoimmune diseases, which has sparked new appreciation and interest in TRAF research. This review presents an overview of the current knowledge of TRAFs, with an emphasis on recent findings concerning TRAF molecules in signaling and in human diseases.
- Ovarian cancer G protein coupled receptor 1 suppresses cell migration of MCF7 breast cancer cells via a Gα12/13-Rho-Rac1 pathway. [Journal Article]
- J Mol Signal 2013; 8(1):6.
Ovarian cancer G protein coupled receptor 1 (OGR1) mediates inhibitory effects on cell migration in human prostate and ovarian cancer cells. However, the mechanisms and signaling pathways that mediate these inhibitory effects are essentially unknown.MCF7 cell line was chosen as a model system to study the mechanisms by which OGR1 regulates cell migration, since it expresses very low levels of endogenous OGR1. Cell migratory activities were assessed using both wound healing and transwell migration assays. The signaling pathways involved were studied using pharmacological inhibitors and genetic forms of the relevant genes, as well as small G protein pull-down activity assays. The expression levels of various signaling molecules were analyzed by Western blot and quantitative PCR analysis.Over-expression of OGR1 in MCF7 cells substantially enhanced activation of Rho and inhibition of Rac1, resulting in inhibition of cell migration. In addition, expression of the Gα12/13 specific regulator of G protein signaling (RGS) domain of p115RhoGEF, but not treatment with pertussis toxin (PTX, a Gαi specific inhibitor), could abrogate OGR1-dependent Rho activation, Rac1 inactivation, and inhibition of migration in MCF7 cells. The bioactive lipids tested had no effect on OGR1 function in cell migration.Our data suggest, for the first time, that OGR1 inhibits cell migration through a Gα12/13 -Rho-Rac1 signaling pathway in MCF7 cells. This pathway was not significantly affected by bioactive lipids and all the assays were conducted at constant pH, suggesting a constitutive activity of OGR1. This is the first clear delineation of an OGR1-mediated cell signaling pathway involved in migration.
- NFAT5 in cellular adaptation to hypertonic stress - regulations and functional significance. [Journal Article]
- J Mol Signal 2013; 8(1):5.
The Nuclear Factor of Activated T Cells-5 (NFAT5), also known as OREBP or TonEBP, is a member of the nuclear factors of the activated T cells family of transcription factors. It is also the only known tonicity-regulated transcription factor in mammals. NFAT5 was initially known for its role in the hypertonic kidney inner medulla for orchestrating a genetic program to restore the cellular homeostasis. Emerging evidence, however, suggests that NFAT5 might play a more diverse functional role, including a pivotal role in blood pressure regulation and the development of autoimmune diseases. Despite the growing significance of NFAT5 in physiology and diseases, our understanding of how its activity is regulated remains very limited. Furthermore, how changes in tonicities are converted into functional outputs via NFAT5 remains elusive. Therefore, this review aims to summarize our current knowledge on the functional roles of NFAT5 in osmotic stress adaptation and the signaling pathways that regulate its activity.
- Aggressive neuroblastomas have high p110alpha but low p110delta and p55alpha/p50alpha protein levels compared to low stage neuroblastomas. [Journal Article]
- J Mol Signal 2013; 8(1):4.
The phosphoinositide 3-kinase (PI3K)/Akt pathway is involved in neuroblastoma development where Akt/PKB activation is associated with poor prognosis. PI3K activity subsequently activates Akt/PKB, and as mutations of PI3K are rare in neuroblastoma and high levels of PI3K subunit p110delta is associated with favorable disease with low p-Akt/PKB, the levels of other PI3K subunits could be important for Akt activation.Protein levels of Type IA PI3K catalytic and regulatory subunits were investigated together with levels of phosphorylated Akt/PKB and the PI3K negative regulator PTEN in primary neuroblastoma tumors. Relation between clinical markers and protein levels were evaluated through t-tests.We found high levels of p-Akt/PKB correlating to aggressive disease and p-Akt/PKB (T308) showed inverse correlation to PTEN levels. The regulatory isomers p55alpha/p50alpha showed higher levels in favorable neuroblastoma as compared with aggressive neuroblastoma. The PI3K-subunit p110alpha was found mainly in advanced tumors while p110delta showed higher levels in favorable neuroblastoma.Activation of the PI3K/Akt pathway is seen in neuroblastoma tumors, however the contribution of the different PI3K isoforms is unknown. Here we show that p110alpha is preferentially expressed in aggressive neuroblastomas, with high p-Akt/PKB and p110delta is mainly detected in favorable neuroblastomas, with low p-Akt/PKB. This is an important finding as PI3K-specific inhibitors are suggested for enrollment in treatment of neuroblastoma patients.
- Determinants at the N- and C-termini of Gα12 required for activation of Rho-mediated signaling. [Journal Article]
- J Mol Signal 2013; 8(1):3.
Heterotrimeric guanine nucleotide binding proteins of the G12/13 subfamily, which includes the α-subunits Gα12 and Gα13, stimulate the monomeric G protein RhoA through interaction with a distinct subset of Rho-specific guanine nucleotide exchange factors (RhoGEFs). The structural features that mediate interaction between Gα13 and RhoGEFs have been examined in crystallographic studies of the purified complex, whereas a Gα12:RhoGEF complex has not been reported. Several signaling responses and effector interactions appear unique to Gα12 or Gα13, despite their similarity in amino acid sequence.To comprehensively examine Gα12 for regions involved in RhoGEF interaction, we screened a panel of Gα12 cassette substitution mutants for binding to leukemia-associated RhoGEF (LARG) and for activation of serum response element mediated transcription.We identified several cassette substitutions that disrupt Gα12 binding to LARG and the related p115RhoGEF. These Gα12 mutants also were impaired in activating serum response element mediated signaling, a Rho-dependent response. Most of these mutants matched corresponding regions of Gα13 reported to contact p115RhoGEF, but unexpectedly, several RhoGEF-uncoupling mutations were found within the N- and C-terminal regions of Gα12. Trypsin protection assays revealed several mutants in these regions as retaining conformational activation. In addition, charge substitutions near the Gα12 N-terminus selectively disrupted binding to LARG but not p115RhoGEF.Several structural aspects of the Gα12:RhoGEF interface differ from the reported Gα13:RhoGEF complex, particularly determinants within the C-terminal α5 helix and structurally uncharacterized N-terminus of Gα12. Furthermore, key residues at the Gα12 N-terminus may confer selectivity for LARG as a downstream effector.
- Caspase-3 mediated release of SAC domain containing fragment from Par-4 is necessary for the sphingosine-induced apoptosis in Jurkat cells. [Journal Article]
- J Mol Signal 2013; 8(1):2.
Prostate apoptosis response-4 (Par-4) is a tumor-suppressor protein that selectively activates and induces apoptosis in cancer cells, but not in normal cells. The cancer specific pro-apoptotic function of Par-4 is encoded in its centrally located SAC (Selective for Apoptosis induction in Cancer cells) domain (amino acids 137-195). The SAC domain itself is capable of nuclear entry, caspase activation, inhibition of NF-κB activity, and induction of apoptosis in cancer cells. However, the precise mechanism(s) of how the SAC domain is released from Par-4, in response to apoptotic stimulation, is not well explored.In this study, we demonstrate for the first time that sphingosine (SPH), a member of the sphingolipid family, induces caspase-dependant cleavage of Par-4, leading to the release of SAC domain containing fragment from it. Par-4 is cleaved at the EEPD131G site on incubation with caspase-3 in vitro, and by treating cells with several anti-cancer agents. The caspase-3 mediated cleavage of Par-4 is blocked by addition of the pan-caspase inhibitor z-VAD-fmk, caspase-3 specific inhibitor Ac-DEVD-CHO, and by introduction of alanine substitution for D131 residue. Moreover, suppression of SPH-induced Akt dephosphorylation also abrogated the caspase dependant cleavage of Par-4.Evidence provided here shows that Par-4 is cleaved by caspase-3 during SPH-induced apoptosis. Cleavage of Par-4 leads to the generation of SAC domain containing fragment which may possibly be essential and sufficient to induce or augment apoptosis in cancer cells.
- Consequences of nongenomic actions of estradiol on pathogenic genital tract response. [Journal Article]
- J Mol Signal 2013; 8(1):1.
ABSTRACT:Estradiol is a steroid hormone that regulates the structure and function of the female reproductive system. In addition to its genomic effects, which are mediated by activated nuclear receptors, estradiol elicits a variety of rapid signaling events independently of transcriptional or genomic regulation. These nongenomic actions influence the milieu of the genital tract, which changes the ability of pathogens to infect the genital tract. This review discusses our current knowledge regarding the mechanisms and relevance of nongenomic estradiol signaling in the genital tract that could change the ability of pathogens to invade epithelial cells. PubMed was searched through January 1980 for papers related to estradiol actions in the ovary, fallopian tube, uterus and cervix. The mechanisms conveying these rapid effects consist of a multitude of signaling molecules and include cross-talk with slower transcriptional actions. The nongenomic actions of estradiol that influence the infectious abilities of pathogens occur either directly on the genital tract cells or indirectly by modulating the local and systemic immune systems. Additional in-depth characterization of the response is required before the normal and pathological reproductive functions of the nongenomic estradiol pathway can be targeted for pharmacological intervention.
- Defining regulatory and phosphoinositide-binding sites in the human WIPI-1 β-propeller responsible for autophagosomal membrane localization downstream of mTORC1 inhibition. [Journal Article]
- J Mol Signal 2012; 7(1):16.
ABSTRACT:Autophagy is a cytoprotective, lysosomal degradation system regulated upon induced phosphatidylinositol 3-phosphate (PtdIns(3)P) generation by phosphatidylinositol 3-kinase class III (PtdIns3KC3) downstream of mTORC1 inhibition. The human PtdIns(3)P-binding β-propeller protein WIPI-1 accumulates at the initiation site for autophagosome formation (phagophore), functions upstream of the Atg12 and LC3 conjugation systems, and localizes at both the inner and outer membrane of generated autophagosomes. In addition, to a minor degree WIPI-1 also binds PtdIns(3,5)P2. By homology modelling we earlier identified 24 evolutionarily highly conserved amino acids that cluster at two opposite sites of the open Velcro arranged WIPI-1 β-propeller.By alanine scanning mutagenesis of 24 conserved residues in human WIPI-1 we define the PtdIns-binding site of human WIPI-1 to critically include S203, S205, G208, T209, R212, R226, R227, G228, S251, T255, H257. These amino acids confer PtdIns(3)P or PtdIns(3,5)P2 binding. In general, WIPI-1 mutants unable to bind PtdIns(3)P/PtdIns(3,5)P2 lost their potential to localize at autophagosomal membranes, but WIPI-1 mutants that retained PtdIns(3)P/PtdIns(3,5)P2 binding localized at Atg12-positive phagophores upon mTORC1 inhibition. Both, downregulation of mTOR by siRNA or cellular PtdIns(3)P elevation upon PIKfyve inhibition by YM201636 significantly increased the localization of WIPI-1 at autophagosomal membranes. Further, we identified regulatory amino acids that influence the membrane recruitment of WIPI-1. Exceptional, WIPI-1 R110A localization at Atg12-positive membranes was independent of autophagy stimulation and insensitive to wortmannin. R112A and H185A mutants were unable to bind PtdIns(3)P/PtdIns(3,5)P2 but localized at autophagosomal membranes, although in a significant reduced number of cells when compared to wild-type WIPI-1.We identified amino acids of the WIPI-1 β-propeller that confer PtdIns(3)P or PtdIns(3,5)P2 binding (S203, S205, G208, T209, R212, R226, R227, G228, S251, T255, H257), and that regulate the localization at autophagosomal membranes (R110, R112, H185) downstream of mTORC1 inhibition.
- NADPH oxidase mediates the oxygen-glucose deprivation/reperfusion-induced increase in the tyrosine phosphorylation of the N-methyl-D-aspartate receptor NR2A subunit in retinoic acid differentiated SH-SY5Y Cells. [Journal Article]
- J Mol Signal 2012; 7(1):15.
ABSTRACT:Evidence exists that oxidative stress promotes the tyrosine phosphorylation of N-methyl-D-aspartate receptor (NMDAR) subunits during post-ischemic reperfusion of brain tissue. Increased tyrosine phosphorylation of NMDAR NR2A subunits has been reported to potentiate receptor function and exacerbate NMDAR-induced excitotoxicity. Though the effect of ischemia on tyrosine phosphorylation of NMDAR subunits has been well documented, the oxidative stress signaling cascades mediating the enhanced tyrosine phosphorylation of NR2A subunits remain unclear.We report that the reactive oxygen species (ROS) generator NADPH oxidase mediates an oxidative stress-signaling cascade involved in the increased tyrosine phosphorylation of the NR2A subunit in post-ischemic differentiated SH-SY5Y neuroblastoma cells. Inhibition of NADPH oxidase attenuated the increased tyrosine phosphorylation of the NMDAR NR2A subunit, while inhibition of ROS production from mitochondrial or xanthine oxidase sources failed to dampen the post-ischemic increase in tyrosine phosphorylation of the NR2A subunit. Additionally, inhibition of NADPH oxidase blunted the interaction of activated Src Family Kinases (SFKs) with PSD-95 induced by ischemia/reperfusion. Lastly, inhibition of NADPH oxidase also markedly reduced cell death in post-ischemic SH-SY5Y cells stimulated by NMDA.These data indicate that NADPH oxidase has a key role in facilitating NMDAR NR2A tyrosine phosphorylation via SFK activation during post-ischemic reperfusion.
- The roles played by highly truncated splice variants of G protein-coupled receptors. [Journal Article]
- J Mol Signal 2012; 7(1):13.