Papers by Enkhzol Malchinkhuu
Journal of Neurochemistry, Feb 9, 2011
Action mechanism of lipopolysaccharide (LPS), interleukin-1b (IL-1b), and lysophosphatidic acid (... more Action mechanism of lipopolysaccharide (LPS), interleukin-1b (IL-1b), and lysophosphatidic acid (LPA) to regulate motility, an important process of astrogliosis, was investigated in rat astrocytes. While LPA exerted no significant effect on the cell migration, the prior treatment of the cells with LPS or IL-1b resulted in the appearance of migration activity in response to LPA. The LPS induction of the migration response to LPA was associated with the production of IL-1b precursor protein and inhibited by the IL-1 receptor antagonist. The IL-1b treatment also allowed LPA to activate Rac1. The LPA-induced Rac1 activation and migration were inhibited by pertussis toxin, a small interfering RNA specific to LPA 1 receptors, and LPA 1 receptor antagonists, including Ki16425. However, the IL-1b treatment had no appreciable effect on LPA 1 receptor mRNA expression and LPA-induced activation of ERK, Akt, and proliferation. The induction of the migration response to LPA by IL-1b was inhibited by a constitutively active RhoA. Moreover, LPA significantly activated RhoA through the LPA 1 receptor in the control cells but not in the IL-1b-treated cells. These results suggest that IL-1b inhibits the LPA 1 receptormediated Rho signaling through the IL-1 receptor, thereby disclosing the LPA 1 receptor-mediated G i protein/Rac/migration pathway.
Carcinogenesis, Jan 7, 2009
Malignant ascites from pancreatic cancer patients has been reported to stimulate migration of pan... more Malignant ascites from pancreatic cancer patients has been reported to stimulate migration of pancreatic cancer cells through lysophosphatidic acid (LPA) and LPA 1 receptors. Indeed, ascitesand LPA-induced migration was inhibited by Ki16425, an LPA 1 and LPA 3 antagonist, in Panc-1 cells. Unexpectedly, however, in the presence of Ki16425, ascites and LPA inhibited cell migration in response to epidermal growth factor (EGF). The inhibitory migratory response to ascites and LPA was also observed in the cells treated with pertussis toxin (PTX), a G i protein inhibitor, and attenuated by a small interfering RNA (siRNA) specific to the LPA 2 receptor. The inhibitory LPA action was reversed by the regulators of G-protein signaling domain of p115RhoGEF, dominant-negative RhoA or C3 toxin. Indeed, LPA activated RhoA, which was attenuated by the siRNA against the LPA 2 receptor. Moreover, LP-105, an LPA 2 agonist, also inhibited EGF-induced migration in the PTX-treated cells. A similar inhibitory migration response through LPA 2 receptors was also observed in YAPC-PD, BxPC-3, CFPAC-1 and PK-1 pancreatic cancer cell lines. LPA also inhibited the invasion of Panc-1 cells in the PTX-treated cells in the in vitro Matrigel invasion assay. We conclude that LPA 2 receptors are coupled to the G 12/13 protein/Rho-signaling pathway, leading to the inhibition of EGF-induced migration and invasion of pancreatic cancer cells.
Molecular Biology of the Cell, Dec 15, 2009
The clarification of mechanisms that negatively regulate the invasive behavior of human glioma ce... more The clarification of mechanisms that negatively regulate the invasive behavior of human glioma cells is of great importance in order to find new methods of treatment. In this study, we have focused on the negative regulation of lysophosphatidic acid (LPA)-induced migration in glioma cells. Using small interference RNA and dominant-negative gene strategies in addition to pharmacological tools, we found that isoproterenol (ISO) and sphingosine-1-phosphate (S1P) negatively but differently regulate the LPA-induced migration. ISO-induced suppression of the migration of glioma cells occurs via  2-adrenergic receptor/cAMP/Epac/Rap1B/inhibition of Rac, whereas S1P has been shown to suppress the migration of the cells through S1P 2 receptor/Rho-mediated down-regulation of Rac1. The expression of tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is required for the inhibitory ISO-induced and Rap1B-mediated actions on the migration, Rac1 activation, and Akt activation in response to LPA. Thus, the PTENmediated down-regulation of phosphatidylinositol 3-kinase activity may be involved in the regulation of Rap1Bdependent inhibition of Rac1 activity. These findings suggest that there are at least two distinct inhibitory pathways, which are mediated by the S1P 2 receptor and  2-adrenergic receptor, to control the migratory, hence invasive, behavior of glioma cells.
Biochemical and Biophysical Research Communications, Feb 1, 2008
Sphingosine 1-phosphate (S1P) induced the inhibition of glioma cell migration. Here, we character... more Sphingosine 1-phosphate (S1P) induced the inhibition of glioma cell migration. Here, we characterized the signaling mechanisms involved in the inhibitory action by S1P. In human GNS-3314 glioblastoma cells, the S1P-induced inhibition of cell migration was associated with activation of RhoA and suppression of Rac1. The inhibitory action of S1P was recovered by a small interference RNA specific to S1P 2 receptor, a carboxyl-terminal region of Ga12 or Ga13, an RGS domain of p115RhoGEF, and a dominant-negative mutant of RhoA. The inhibitory action of S1P through S1P 2 receptors was also observed in both U87MG glioblastoma and 1321N1 astrocytoma cells, which have no protein expression of a phosphatase and tensin homolog deleted on chromosome 10 (PTEN). These results suggest that S1P 2 receptors/G 12/13-proteins/Rho signaling pathways mediate S1P-induced inhibition of glioma cell migration. However, PTEN, recently postulated as an indispensable molecule for the inhibition of cell migration, may not be critical for the S1P 2 receptor-mediated action in glioma cells.
Oncogene, Jun 20, 2005
A potential role for 1-oleoyl-sn-glycero-3-phosphate or lysophosphatidic acid (LPA) and sphingosi... more A potential role for 1-oleoyl-sn-glycero-3-phosphate or lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) in the regulation of malignant diseases has been widely considered. In this study, we found that in transformed astroglial cells, the expression profile of lysophospholipid receptor mRNA and the action modes of LPA and S1P on cell motility were changed: there was a change in the acquisition of the ability of LPA to stimulate cell migration and a change in the migratory response to S1P from stimulation through S1P 1 to inhibition through S1P 2. LPA-induced cell migration was almost completely inhibited by either pertussis toxin, LPA 1 receptor antagonists including Ki16425 (3-(4-[4-([1-(2-chlorophenyl)ethoxy]carbonyl amino)-3-methyl-5-isoxazolyl] benzylsulfonyl)propanoic acid) or an inhibitor of phosphatidylinositol 3-kinase (PI3K) wortmannin. The LPA-induced action was also suppressed, although incompletely, by several specific inhibitors for intracellular signaling pathways including Rac1, Cdc42, p38 mitogen-activated protein kinase (p38MAPK) and c-Jun terminal kinase (JNK), but not extracellular signalregulated kinase. Nearly complete inhibition of migration response to LPA, however, required simultaneous inhibition of both the p38MAPK and JNK pathways. Inhibition of Rac1 suppressed JNK but not p38MAPK, while the activity of p38MAPK was abolished by a dominantnegative form of Cdc42. These findings suggest that, in glioma cells, the PI3K/Cdc42/p38MAPK and PI3K/ Rac1/JNK pathways are equally important for LPA 1 receptor-mediated migration.
Molecular Pharmacology, Sep 18, 2003
For intracellular staining for IL-10 and FoxP3, cells were first stained with surface marker stai... more For intracellular staining for IL-10 and FoxP3, cells were first stained with surface marker staining Abs such as APC-B220 or APC-CD4 before overnight fixation and permeabilization and staining with anti-Foxp3-PE antibody according to the manufacturer's instructions (Mouse Regulatory T cell Staining kit, eBioscience). Cells were analyzed by flow cytometry using a FACScalibur (BD Pharmingen) with CELLQUEST software (BD Pharmingen). Mice and cells and cell manipulations. Knockout mice for Ebi3 and IL-10 were purchased from the Jackson Laboratory (Bar Harbor, ME). Splenocytes from B7-H1 KO mice were gift from Dr. Cornelia Bergmann (Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH). Mice, including Fas deficient LPR mice, were housed under pathogen-free conditions at the National Institute on Aging animal facility, Baltimore, MD. A drug resistant subset of MCF7 cells, MCF7D40, was a gift from Dr. Livio Malluci (King's College, UK), FS melanoma cells were a gift from Dr. Ashani Weeraratna (NIH, USA).Primary murine embryonic fibroblasts CD1 and DR4 (generated from mouse 17-18 day embryos) were a gift from Dr. Lioudmila Sharova (NIA/NIH) and used at the passage 4-6. Cells were grown in cRPMI (RPMI 1640 medium supplemented with 10% heat inactivated fetal bovine serum, plus 1 mM
Journal of Immunology, May 1, 2012
We have previously shown that breast cancer generates regulatory B cells (tBregs) to convert Treg... more We have previously shown that breast cancer generates regulatory B cells (tBregs) to convert Tregs and thereby to enable its metastasis. Thus, we decided to deplete tBregs using aCD20 antibody, a counterpart of the FDA approved strategy for the treatment of B cell malignancies (Rituximab). To our surprise, when tumor bearing mice were treated with αCD20 antibody, tumor progression was accelerated leading to increased lung metastasis. Thus, we hypothesized that tBregs may not be targeted by the antibody due to their low expression of CD20. Indeed, we found that B cell during their conversion to tBregs, downregulate their CD20 expression. Thus, tumor bearing mice treated with aCD20 antibody had enriched amounts of tBregs. We provide evidence that CD20 cannot be a target for the depletion of tBregs, explaining the failure of Rituximab to improve clinical outcomes in solid tumors. Instead, we developed an alternative strategy by in vivo targeting CpG through CXCR5 expressed by tBregs. We show that BLCArp-CpG inactivates tBregs, thereby reversing tumor metastasis. Taken together, suppressive B cells need to be controlled in solid tumors.
Vascular Pharmacology, May 1, 2009
Low-density lipoprotein (LDL) and lysophosphatidic acid (LPA), one of the lipid components of lip... more Low-density lipoprotein (LDL) and lysophosphatidic acid (LPA), one of the lipid components of lipoprotein, induced the DNA synthesis of coronary artery smooth muscle cells (CASMCs). The LDL-and LPA-induced DNA synthesis was markedly inhibited by the LPA receptor antagonist Ki16425, pertussis toxin, small interfering RNAs targeted for LPA 1 receptors, and a potent calcineurin inhibitor cyclosporine A. It has been reported that LDL and LPA induced a migration response in a manner sensitive to Ki16425, pertussis toxin, and a LPA 1 receptor-specific small interfering RNA. However, cyclosporine A was ineffective in inhibiting the migration response. Instead, an epidermal growth factor (EGF) receptor tyrosine kinase inhibitor markedly suppressed the migration response to LDL and LPA without having any significant effect on DNA synthesis. Thus, the LDLinduced stimulation of DNA synthesis and migration in CASMCs is mediated by its component LPA through LPA 1 receptors and G i/o-proteins. Ca 2+ /calcineurin pathways and transactivation of EGF receptors mediate LPA 1-receptor-induced DNA synthesis and migration, respectively.
Biochemical and Biophysical Research Communications, Aug 1, 2007
High-density lipoprotein (HDL)-associated sphingosine 1-phosphate mediates a variety of lipoprote... more High-density lipoprotein (HDL)-associated sphingosine 1-phosphate mediates a variety of lipoprotein-induced actions in vascular cell systems. However, it remains unknown whether extracellular S1P is associated with lipoproteins to exert biological actions in central nervous system. Human cerebrospinal fluid (CSF) induced rat astrocyte migration in a manner sensitive to S1P receptor antagonist VPC23019 and the migration activity was recovered in S1P fraction by thin-layer chromatography. Density-gradient separation of CSF revealed that the major S1P activity was detected in the HDL fraction. In conditioned medium of rat astrocytes cultured with sphingosine, the S1P activity was recovered again in the HDL fraction. The HDL fraction also induced migration of astrocytes and process retraction of oligodendrocytes in a manner similar to S1P. We concluded that S1P is accumulated in HDL-like lipoproteins in CSF and mediates some of lipoprotein-induced neural cell functions in central nervous system.
Biochemical Journal, Mar 15, 2003
It has been suggested that lipoproteins in the central nervous system are involved in the regulat... more It has been suggested that lipoproteins in the central nervous system are involved in the regulation of several neural functions independent of cholesterol metabolism as well as those related to lipid metabolism. We recently demonstrated that lipoproteins are carriers for sphingosine 1-phosphate (S1P). This raised the possibility that S1P mediates the neural cell functions induced by lipoproteins. In the current study, we examined the effects of plasma high-density lipoprotein (HDL) on astroglial cell functions, focusing especially on the role of the lipoprotein-associated S1P. In rat type I astrocytes or C6 glioma cells, similar to S1P, HDL stimulated DNA synthesis and mRNA expression of fibroblast growth factor-2, a potent neurotrophic factor, which was associated with the activation of extracellular signalregulated kinase (ERK) in a pertussis toxin-sensitive manner. The data from fractionation studies of HDL indicated that S1P may Abbreviations used : BrdU, 5-bromo-2h-deoxy-uridine ; [Ca 2 + ] i , cytoplasmic free Ca 2 + concentration ; CHO
Journal of Neurochemistry, Oct 11, 2007
Sphingosine 1-phosphate (S1P) is accumulated in lipoproteins, especially high-density lipoprotein... more Sphingosine 1-phosphate (S1P) is accumulated in lipoproteins, especially high-density lipoprotein (HDL), in plasma. However, it remains uncharacterized how extracellular S1P is produced in the CNS. The treatment of rat astrocytes with retinoic acid and dibutyryl cAMP, which induce apolipoprotein E (apoE) synthesis and HDL-like lipoprotein formation, stimulated extracellular S1P accumulation in the presence of its precursor sphingosine. The released S1P was present together with apoE particles in the HDL fraction. S1P release from astrocytes was inhibited by the treatment of the cells with glybenclamide or small interfering RNAs specific to ATP-binding cassette transporter A1 (ABCA1). Astrocytes from Abca1)/) mice also showed impairment of retinoic acid/dibutyryl cAMP-induced S1P release in association with the blockage of HDL-like lipoprotein formation. However, the formation of either apoE or lipoprotein itself was not sufficient, and additional up-regulation of ABCA1 was requisite to stimulate S1P release. We conclude that the S1P release from astrocytes is coupled with lipoprotein formation through ABCA1.
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Papers by Enkhzol Malchinkhuu