|
|
By admin, on February 16th, 2012
J Biol Chem. 2012 Feb 9;
Choi HS, Su WM, Han GS, Plote D, Xu Z, Carman GM
The yeast Pah1p phosphatidate phosphatase, which catalyzes the penultimate step in the synthesis of triacylglycerol and plays a role in the transcriptional regulation of phospholipid synthesis genes, is a cytosolic enzyme that associates with the nuclear/endoplasmic reticulum membrane to catalyze the dephosphorylation of phosphatidate to yield diacylglycerol. Pah1p is phosphorylated on seven (Ser(110), Ser(114), Ser(168), Ser(602), Thr(723), Ser(744), and Ser(748)) sites that are targets for proline-directed proteins kinases. In this work, we showed that the seven sites are phosphorylated by Pho85p-Pho80p, a protein kinase-cyclin complex known to regulate a variety of cellular processes. The phosphorylation of recombinant Pah1p was time- and dose-dependent, and dependent on the concentrations of ATP (3.7 μM) and Pah1p (0.25 μM). Phosphorylation reduced (6-fold) the catalytic efficiency (Vmax/Km) of Pah1p and reduced (3-fold) its interaction (Kd) with liposomes. Alanine mutations of the seven sites ablated the inhibitory effect that Pho85p-Pho80p had on Pah1p activity and on the interaction with liposomes. Analysis of pho85Δ mutant cells, phosphate-starved wild type cells, and cells expressing phosphorylation-deficient forms of Pah1p indicated that loss of Pho85p-Pho80p phosphorylation reduced Pah1p abundance. In contrast, lack of Nem1p-Spo7p, the phosphatase complex that dephosphorylates Pah1p at the nuclear/endoplasmic reticulum membrane, stabilized Pah1p abundance. While loss of phosphorylation caused a decrease in abundance, a greater amount of Pah1p was associated with membranes when compared with phosphorylated enzyme, and the loss of phosphorylation allowed bypass of the Nem1p-Spo7p requirement for Pah1p function in the synthesis of triacylglycerol.
Original post:
Pho85p-Pho80p phosphorylation of yeast Pah1p phosphatidate phosphatase regulates its activity, location, abundance, and function in lipid metabolism.
By admin, on February 15th, 2012
Spermatogenesis. 2011 10; 1(4): 318-324
Lucas TF, Pimenta MT, Pisolato R, Lazari MF, Porto CS
In this review, we will present an overview of estrogen actions in the testis from immature and adult animals, with special emphasis on signaling mechanisms involved in the 17β-estradiol regulation of Sertoli cell function in immature rats. 17β-estradiol activates Sertoli cell proliferation in immature rats by a mechanism that involves the translocation of the estrogen receptors ESR1 and ESR2 to the plasma membrane, phosphorylation of epidermal growth factor receptor and activation of mitogen-activated protein kinase 3/1. Activation of the G protein-coupled estrogen receptor (GPER) also induces phosphorylation of mitogen-activated protein kinase 3/1 via epidermal growth factor receptor transactivation, which in turn increases expression of the antiapoptotic protein BCL2 and decreases the expression of proapoptotic protein BAX, indicating an antiapoptotic role of E2-GPER in immature rat Sertoli cells. In conclusion, ESRs and GPER can mediate rapid 17β-estradiol signaling in Sertoli cells, and modulate transcriptional events important for Sertoli cell function and maintenance of normal testis development and homeostasis. Our findings are important to clarify the role of estrogen in a critical period of testicular development and to direct further studies, which may contribute to better understand the causes of male infertility.
Here is the original post:
17β-estradiol signaling and regulation of Sertoli cell function.
By admin, on February 14th, 2012
J Cell Sci. 2012 Feb 10;
Liu M, Huang C, Polu SR, Schneiter R, Chang A
Sphingolipids are critical components of membranes and sphingolipid metabolites also serve as signaling molecules. Yeast Orm1 and Orm2 belong to a conserved family of ER membrane proteins that regulate serine palmitoyltransferase, catalyzing the first and rate-limiting step in sphingolipid synthesis. We now show that sphingolipid synthesis via Orm1 is a target of TOR signaling which regulates cell growth in response to nutritional signals. Orm1 phosphorylation is dependent on the Tap42-phosphatase complex which acts downstream of TOR protein kinase complex 1; in temperature-sensitive tap42-11 cells, impaired Orm1 phosphorylation occurs concomitantly with reduced sphingolipid synthesis. A second mechanism regulating sphingolipid synthesis is via controlling Orm2 protein level. Orm2 protein level responds to ER stress conditions, increasing when cells are treated with tunicamycin or DTT, agents that induce the unfolded protein response (UPR). The sphingolipid intermediates, long chain base and ceramide, are decreased when ORM2 is overexpressed, suggesting sphingolipid synthesis is repressed under ER stress conditions. Finally, in the absence of the Orms, the UPR is constitutively activated. Lipid dysregulation in the absence of the Orms may signal to the ER from the plasma membrane as UPR activation is dependent on a cell surface sensor and the MAPK cell wall integrity pathway. Thus, sphingolipid synthesis and the UPR are coordinately regulated.
See the rest here:
Regulation of sphingolipid synthesis via Orm1 and Orm2 in yeast.
By admin, on February 14th, 2012
J Cell Sci. 2012 Feb 10;
Liu M, Huang C, Polu SR, Schneiter R, Chang A
Sphingolipids are critical components of membranes and sphingolipid metabolites also serve as signaling molecules. Yeast Orm1 and Orm2 belong to a conserved family of ER membrane proteins that regulate serine palmitoyltransferase, catalyzing the first and rate-limiting step in sphingolipid synthesis. We now show that sphingolipid synthesis via Orm1 is a target of TOR signaling which regulates cell growth in response to nutritional signals. Orm1 phosphorylation is dependent on the Tap42-phosphatase complex which acts downstream of TOR protein kinase complex 1; in temperature-sensitive tap42-11 cells, impaired Orm1 phosphorylation occurs concomitantly with reduced sphingolipid synthesis. A second mechanism regulating sphingolipid synthesis is via controlling Orm2 protein level. Orm2 protein level responds to ER stress conditions, increasing when cells are treated with tunicamycin or DTT, agents that induce the unfolded protein response (UPR). The sphingolipid intermediates, long chain base and ceramide, are decreased when ORM2 is overexpressed, suggesting sphingolipid synthesis is repressed under ER stress conditions. Finally, in the absence of the Orms, the UPR is constitutively activated. Lipid dysregulation in the absence of the Orms may signal to the ER from the plasma membrane as UPR activation is dependent on a cell surface sensor and the MAPK cell wall integrity pathway. Thus, sphingolipid synthesis and the UPR are coordinately regulated.
Read the original post:
Regulation of sphingolipid synthesis via Orm1 and Orm2 in yeast.
By admin, on February 11th, 2012
J Immunol. 2012 Feb 8;
Lin Q, Liu Y, Moore DJ, Elizer SK, Veach RA, Hawiger J, Ruley HE
The expression of proinflammatory cytokines and chemokines in response to TCR agonists is regulated by the caspase-recruitment domain membrane-associated guanylate kinase 1 (CARMA1) signalosome through the coordinated assembly of complexes containing the BCL10 adaptor protein. We describe a novel mechanism to negatively regulate the CARMA1 signalosome by the “death” adaptor protein caspase and receptor interacting protein adaptor with death domain (CRADD)/receptor interacting protein-associated ICH-1/CED-3 homologous protein with a death domain. We show that CRADD interacts with BCL10 through its caspase recruitment domain and suppresses interactions between BCL10 and CARMA1. TCR agonist-induced interaction between CRADD and BCL10 coincides with reduction of its complex formation with CARMA1 in wild-type, as compared with Cradd-deficient, primary cells. Finally, Cradd-deficient spleen cells, CD4(+) T cells, and mice respond to T cell agonists with strikingly higher production of proinflammatory mediators, including IFN-γ, IL-2, TNF-α, and IL-17. These results define a novel role for CRADD as a negative regulator of the CARMA1 signalosome and suppressor of Th1- and Th17-mediated inflammatory responses.
The rest is here:
Cutting Edge: The "Death" Adaptor CRADD/RAIDD Targets BCL10 and Suppresses Agonist-Induced Cytokine Expression in T Lymphocytes.
By admin, on January 24th, 2012
By admin, on January 24th, 2012
By admin, on January 24th, 2012
By admin, on January 18th, 2012
J Biol Chem. 2012 Jan 13;
Chaudhri RA, Olivares-Navarrete R, Cuenca N, Hadadi A, Boyan BD, Schwartz Z
Protein kinase C (PKC) signaling can be activated rapidly by 17β-estradiol (E(2)) via non-traditional signaling in ERα-positive MCF7 and ERα-negative HCC38 breast cancer cells and is associated with tumorigenicity. Additionally, E(2) has been shown to elicit anti-apoptotic effects in cancer cells counteracting pro-apoptotic effects of chemotherapeuties. Supporting evidence suggests the existence of a membrane-associated ER that differs from the traditional receptors, ERα and ERβ. Our aim was to identify the ER responsible for rapid PKC activation and to evaluate downstream effects, such as proliferation, apoptosis and metastasis. RT-PCR, western blot, and immunofluorescence were used to determine presence of ER splice variants in multiple cell lines. E(2) effects on PKC activity were measured with and without ER blocking antibodies. Cell proliferation was determined by [(3)H]-thymidine incorporation, cell viability was measured by MTT, while apoptosis was determined by DNA fragmentation and TUNEL. Quantitative RT-PCR (qPCR) and sandwich ELISA were used to determine effects on metastatic factors. The role of membrane-dependent signaling in cancer cell invasiveness was examined using an in vitro assay. The results indicate the presence of an ERα splice variant, ERα36, in ERα-positive MCF7 and ERα-negative HCC38 breast cancer cells, which localized to plasma membranes and rapidly activated PKC in response to E(2), leading to deleterious effects such as enhancement of proliferation, protection against apoptosis, and enhancement of metastatic factors. These findings propose ERα36 as a novel target for the development of therapies that can prevent progression of breast cancer in the primary tumor as well as during metastasis.
See the rest here:
Membrane estrogen signaling enhances tumorigenesis and metastatic potential of breast cancer cells via estrogen receptor-α36 (ERα36).
By admin, on January 18th, 2012
J Biol Chem. 2012 Jan 13;
Chaudhri RA, Olivares-Navarrete R, Cuenca N, Hadadi A, Boyan BD, Schwartz Z
Protein kinase C (PKC) signaling can be activated rapidly by 17β-estradiol (E(2)) via non-traditional signaling in ERα-positive MCF7 and ERα-negative HCC38 breast cancer cells and is associated with tumorigenicity. Additionally, E(2) has been shown to elicit anti-apoptotic effects in cancer cells counteracting pro-apoptotic effects of chemotherapeuties. Supporting evidence suggests the existence of a membrane-associated ER that differs from the traditional receptors, ERα and ERβ. Our aim was to identify the ER responsible for rapid PKC activation and to evaluate downstream effects, such as proliferation, apoptosis and metastasis. RT-PCR, western blot, and immunofluorescence were used to determine presence of ER splice variants in multiple cell lines. E(2) effects on PKC activity were measured with and without ER blocking antibodies. Cell proliferation was determined by [(3)H]-thymidine incorporation, cell viability was measured by MTT, while apoptosis was determined by DNA fragmentation and TUNEL. Quantitative RT-PCR (qPCR) and sandwich ELISA were used to determine effects on metastatic factors. The role of membrane-dependent signaling in cancer cell invasiveness was examined using an in vitro assay. The results indicate the presence of an ERα splice variant, ERα36, in ERα-positive MCF7 and ERα-negative HCC38 breast cancer cells, which localized to plasma membranes and rapidly activated PKC in response to E(2), leading to deleterious effects such as enhancement of proliferation, protection against apoptosis, and enhancement of metastatic factors. These findings propose ERα36 as a novel target for the development of therapies that can prevent progression of breast cancer in the primary tumor as well as during metastasis.
The rest is here:
Membrane estrogen signaling enhances tumorigenesis and metastatic potential of breast cancer cells via estrogen receptor-α36 (ERα36).
By admin, on January 13th, 2012
Plant J. 2012 Jan 7;
Tanaka H, Osakabe Y, Katsura S, Mizuno S, Maruyama K, Kusakabe K, Mizoi J, Shinozaki K, Yamaguchi-Shinozaki K
Membrane-anchored receptor-like protein kinases (RLKs) recognize extracellular signals at the cell surface and activate the downstream signaling pathway by phosphorylating specific target proteins. We analyzed a receptor-like cytosolic kinase (RLCK), ARCK1, whose expression was induced by abiotic stress. ARCK1 belongs to the cysteine-rich repeat (CRR)-RLK subfamily and encodes a cytosolic protein kinase. The arck1 mutant showed higher sensitivity than the wild-type to ABA and osmotic stress during the postgerminative growth phase. CRK36, an abiotic stress-inducible RLK belonging to the CRR-RLK subfamily, was screened as an interacting factor with ARCK1 by co-expression analyses and a yeast two-hybrid system. CRK36 physically interacted with ARCK1 in plant cells and the kinase domain of CRK36 phosphorylated ARCK1 in vitro. We generated CRK36 RNAi transgenic plants and the transgenic plants with suppressed CRK36 expression showed higher sensitivity than arck1-2 to ABA and osmotic stress during the postgerminative growth phase. Microarray analysis using CRK36 RNAi plants revealed that the suppression of CRK36 up-regulates several ABA-responsive genes, such as LEAs, oleosin, ABI4, and ABI5. These results suggest that CRK36 and ARCK1 form a complex and negatively control ABA and osmotic stress signal transduction. © 2012 The Authors. The Plant Journal© 2012 Blackwell Publishing Ltd.
See original here:
Abiotic Stress-Inducible Receptor-Like Kinases Negatively Control ABA Signaling in Arabidopsis.
By admin, on January 3rd, 2012
FASEB J. 2011 Dec 30;
Mijouin L, Rosselin M, Bottreau E, Pizarro-Cerda J, Cossart P, Velge P, Wiedemann A
The Salmonella outer membrane protein Rck mediates a Zipper-like entry mechanism controlled by Rac, the Arp2/3 complex, and actin polymerization. However, little is known about the early steps leading to Rac activation and Rck-mediated internalization. The use of pharmacological inhibitors or PI 3-kinase dominant-negative mutant induced more than 80% less invasion without affecting attachment. Moreover, Rck-mediated internalization caused an increase in the association of p85 with at least one tyrosine-phosphorylated protein, indicating that class I PI 3-kinase activity was stimulated. We also report that this PI 3-kinase activity is essential for Rac1 activation. However, Rac recruitment at the Rck-mediated entry site was independent of its activation. Using a pharmacological approach or Akt-knockout cells, we also demonstrated that Akt was phosphorylated in response to Rck-mediated internalization as demonstrated by immunoblotting analysis and that all three Akt isoforms were required during this process. Overall, our results describe a signaling pathway involving tyrosine phosphorylation, class I PI 3-kinase, Akt activation, and Rac activation, leading to Rck-dependent Zipper entry. The specificity of this signaling pathway with regard to that of the type 3 secretion system, which is the other invasion process of Salmonella, is discussed.-Mijouin, L., Rosselin, M., Bottreau, E., Pizarro-Cerda, J., Cossart, P., Velge, P., Wiedemann, A. Salmonella Enteritidis Rck-mediated invasion requires activation of Rac1, which is dependent on the class I PI 3-kinases-Akt signaling pathway.
Here is the original post:
Salmonella Enteritidis Rck-mediated invasion requires activation of Rac1, which is dependent on the class I PI 3-kinases-Akt signaling pathway.
By admin, on December 28th, 2011
Int J Oncol. 2011 Dec 23;
Hwang SK, Minai-Tehrani A, Yu KN, Chang SH, Kim JE, Lee KH, Park J, Beck GR, Cho MH
Serine/threonine protein kinase B (PKB/Akt) is involved in cell survival and growth. Carboxyl-terminal modulator protein (CTMP), a novel Akt binding partner, prevents Akt activation at the plasma membrane in response to various stimuli, and thus possesses a tumor suppressor-like function. In a previous study, we have demonstrated that CTMP inhibits tumor progression by facilitating apoptosis in a mouse lung cancer model. However, the precise mechanism of CTMP-induced apoptosis remains to be elucidated. The present study was performed to examine the role of CTMP in mitochondrial-mediated apoptosis and regulation of mitochondrial function in human lung carcinoma cells. Our results showed that CTMP altered mitochondrial morphology and caused the release of cytochrome c by inhibiting OPA1 expression. Additionally, CTMP facilitated mitochondrial-mediated apoptosis by inhibiting heat-shock protein 27 and preventing cytochrome c interaction with Apaf-1. Our data suggest that CTMP may therefore play a critical role in mitochondrial-mediated apoptosis in lung cancer cells.
Originally posted here:
Carboxyl-terminal modulator protein induces apoptosis by regulating mitochondrial function in lung cancer cells.
By admin, on December 28th, 2011
Int J Oncol. 2011 Dec 23;
Hwang SK, Minai-Tehrani A, Yu KN, Chang SH, Kim JE, Lee KH, Park J, Beck GR, Cho MH
Serine/threonine protein kinase B (PKB/Akt) is involved in cell survival and growth. Carboxyl-terminal modulator protein (CTMP), a novel Akt binding partner, prevents Akt activation at the plasma membrane in response to various stimuli, and thus possesses a tumor suppressor-like function. In a previous study, we have demonstrated that CTMP inhibits tumor progression by facilitating apoptosis in a mouse lung cancer model. However, the precise mechanism of CTMP-induced apoptosis remains to be elucidated. The present study was performed to examine the role of CTMP in mitochondrial-mediated apoptosis and regulation of mitochondrial function in human lung carcinoma cells. Our results showed that CTMP altered mitochondrial morphology and caused the release of cytochrome c by inhibiting OPA1 expression. Additionally, CTMP facilitated mitochondrial-mediated apoptosis by inhibiting heat-shock protein 27 and preventing cytochrome c interaction with Apaf-1. Our data suggest that CTMP may therefore play a critical role in mitochondrial-mediated apoptosis in lung cancer cells.
Originally posted here:
Carboxyl-terminal modulator protein induces apoptosis by regulating mitochondrial function in lung cancer cells.
By admin, on December 24th, 2011
PLoS One. 2011; 6(12): e29260
Jongsma M, Matas-Rico E, Rzadkowski A, Jalink K, Moolenaar WH
Lysophosphatidic acid (LPA), a lipid mediator enriched in serum, stimulates cell migration, proliferation and other functions in many cell types. LPA acts on six known G protein-coupled receptors, termed LPA(1-6), showing both overlapping and distinct signaling properties. Here we show that, unexpectedly, LPA and serum almost completely inhibit the transwell migration of B16 melanoma cells, with alkyl-LPA(18∶1) being 10-fold more potent than acyl-LPA(18∶1). The anti-migratory response to LPA is highly polarized and dependent on protein kinase A (PKA) but not Rho kinase activity; it is associated with a rapid increase in intracellular cAMP levels and PIP3 depletion from the plasma membrane. B16 cells express LPA(2), LPA(5) and LPA(6) receptors. We show that LPA-induced chemorepulsion is mediated specifically by the alkyl-LPA-preferring LPA(5) receptor (GPR92), which raises intracellular cAMP via a noncanonical pathway. Our results define LPA(5) as an anti-migratory receptor and they implicate the cAMP-PKA pathway, along with reduced PIP3 signaling, as an effector of chemorepulsion in B16 melanoma cells.
Original post:
LPA Is a Chemorepellent for B16 Melanoma Cells: Action through the cAMP-Elevating LPA(5) Receptor.
By admin, on December 24th, 2011
PLoS One. 2011; 6(12): e29260
Jongsma M, Matas-Rico E, Rzadkowski A, Jalink K, Moolenaar WH
Lysophosphatidic acid (LPA), a lipid mediator enriched in serum, stimulates cell migration, proliferation and other functions in many cell types. LPA acts on six known G protein-coupled receptors, termed LPA(1-6), showing both overlapping and distinct signaling properties. Here we show that, unexpectedly, LPA and serum almost completely inhibit the transwell migration of B16 melanoma cells, with alkyl-LPA(18∶1) being 10-fold more potent than acyl-LPA(18∶1). The anti-migratory response to LPA is highly polarized and dependent on protein kinase A (PKA) but not Rho kinase activity; it is associated with a rapid increase in intracellular cAMP levels and PIP3 depletion from the plasma membrane. B16 cells express LPA(2), LPA(5) and LPA(6) receptors. We show that LPA-induced chemorepulsion is mediated specifically by the alkyl-LPA-preferring LPA(5) receptor (GPR92), which raises intracellular cAMP via a noncanonical pathway. Our results define LPA(5) as an anti-migratory receptor and they implicate the cAMP-PKA pathway, along with reduced PIP3 signaling, as an effector of chemorepulsion in B16 melanoma cells.
Excerpt from:
LPA Is a Chemorepellent for B16 Melanoma Cells: Action through the cAMP-Elevating LPA(5) Receptor.
|
