scholarly journals Multiple Signaling Pathways Regulate Cell Surface Expression and Activity of the Excitatory Amino Acid Carrier 1 Subtype of Glu Transporter in C6 Glioma

1998 ◽  
Vol 18 (7) ◽  
pp. 2475-2485 ◽  
Author(s):  
Karen E. Davis ◽  
Dean J. Straff ◽  
Edward A. Weinstein ◽  
Peter G. Bannerman ◽  
Dana M. Correale ◽  
...  
Keyword(s):  
Amino Acid ◽  
Cell Surface ◽  
Signaling Pathways ◽  
Excitatory Amino Acid ◽  
Surface Expression ◽  
C6 Glioma ◽  
Cell Surface Expression ◽  
Multiple Signaling ◽  
Amino Acid Carrier ◽  
Expression And Activity

Defects of the Tpo-Receptor, Mpl, Caused by Mutations Found in CAMT Patients.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2181-2181
Author(s):  
Marloes R. Tijssen ◽  
Franca di Summa ◽  
Sonja Van den Oudenrijn ◽  
Carlijn Voermans ◽  
C.Ellen Van der Schoot ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Amino Acid ◽  
Cell Surface ◽  
Cell Line ◽  
Mrna Level ◽  
K562 Cells ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Amino Acid Substitutions ◽  
Bhk Cells

Abstract Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare disorder that presents with severe thrombocytopenia and absence of megakaryocytes in the bone marrow. The disease may develop into bone marrow aplasia. In vitro, CD34-positive hematopoietic progenitor cells from CAMT patients did not show any megakaryocyte formation in a Tpo-driven expansion culture. We and others found genetic defects in the gene encoding the Tpo receptor, c-mpl (Van den Oudenrijn et al., Br J Haematol.2002, 117: 390–398 and Ballmaier et al., Ann N Y Acad Sci.2003, 996: 17–25). In our patients, we found four mutations that predicted amino-acid substitutions, of which three in the extracellular domain; Arg102Pro, Pro136His and Arg257Cys, and one in the intracellular signaling domain (Pro635Leu), which may result in either defective Tpo-binding and/or signaling. To investigate this, we transfected full-length Mpl (wt and mutants) into the erythroleukemic cell line K562 and truncated Mpl (encompassing the extracellular domain; wt and mutants) into Baby Hamster Kidney (BHK) cells. In the K562 cells, the mRNA level (RQ-PCR) of the Pro136His mutant was severely decreased compared to the wt transfectant, while the mRNA level of the other mutants was comparable to that of wt. On Western blot, wt Mpl migrated as two, presumably differently glycosylated, bands of 75 kD and 72 kD. The mutants showed an altered migration pattern, which might result from differences in glycosylation. With the Pro635Leu mutant lower signals were obtained when equal amounts of total protein were loaded. Since the Mpl mRNA level was comparable to that of wt, this suggests a higher level of protein degradation. Upon transfection of the Arg102Pro and the Arg257Cys mutants in BHK cells, we observed that these mutants did not gain endo-H resistency, which suggests an aberrant processing of these mutant Mpls through the Golgi apparatus and retention in the ER. However, in cell fractionation experiments with surface-biotinylated K562 cells, biotinylated wt Mpl and mutant Mpl (except Pro136His) could be detected. Apparently, in K562 cells, the amino-acid substitutions do not impair membrane expression completely. To examine whether the mutant receptors were still able to signal after Tpo incubation, K562 cells were serum-starved and subsequently stimulated with 50 ng/ml rhTpo for 5 to 30 minutes. All mutants, including Pro136His, showed increased ERK phosphorylation after 5 minutes. To summarize, the Pro136His mutant is hardly expressed in the K562 expression model, presumably because of instability of the mRNA, but is still able to induce signaling. In contrast to the results obtained in the BHK model, the Arg102Pro and Arg257Cys mutants, showed cell-surface expression in the K562 cell line. The obtained cell-surface expression in the K562 model may have been significantly increased compared to the in vivo situation on hematopoietic stem cells, because of artificially induced efficient expression. Finally, with a super-physiological concentration of rhTpo, we obtained evidence that all Mpl mutants were able to signal upon Tpo binding. Whether impaired signaling by the Mpl mutants in the presence of physiological levels of Tpo may contribute to the development of CAMT, will be investigated.

scholarly journals Cyclic AMP Increases Cell Surface Expression of Functional Na,K-ATPase Units in Mammalian Cortical Collecting Duct Principal Cells

2001 ◽  
Vol 12 (2) ◽  
pp. 255-264 ◽  
Author(s):  
Sandrine Gonin ◽  
Georges Deschênes ◽  
Frank Roger ◽  
Marcelle Bens ◽  
Pierre-Yves Martin ◽  
...  
Keyword(s):  
Cyclic Amp ◽  
Cell Surface ◽  
Atpase Activity ◽  
Cultured Cells ◽  
Collecting Duct ◽  
Brefeldin A ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Cortical Collecting Duct ◽  
Expression And Activity

Cyclic AMP (cAMP) stimulates the transport of Na+ and Na,K-ATPase activity in the renal cortical collecting duct (CCD). The aim of this study was to investigate the mechanism whereby cAMP stimulates the Na,K-ATPase activity in microdissected rat CCDs and cultured mouse mpkCCDc14 collecting duct cells. db-cAMP (10−3 M) stimulated by 2-fold the activity of Na,K-ATPase from rat CCDs as well as the ouabain-sensitive component of 86Rb+ uptake by rat CCDs (1.7-fold) and cultured mouse CCD cells (1.5-fold). Pretreatment of rat CCDs with saponin increased the total Na,K-ATPase activity without further stimulation by db-cAMP. Western blotting performed after a biotinylation procedure revealed that db-cAMP increased the amount of Na,K-ATPase at the cell surface in both intact rat CCDs (1.7-fold) and cultured cells (1.3-fold), and that this increase was not related to changes in Na,K-ATPase internalization. Brefeldin A and low temperature (20°C) prevented both the db-cAMP-dependent increase in cell surface expression and activity of Na,K-ATPase in both intact rat CCDs and cultured cells. Pretreatment with the intracellular Ca2+chelator bis-(o-aminophenoxy)-N,N,N′,N′-tetraacetic acid also blunted the increment in cell surface expression and activity of Na,K-ATPase caused by db-cAMP. In conclusion, these results strongly suggest that the cAMP-dependent stimulation of Na,K-ATPase activity in CCD results from the translocation of active pump units from an intracellular compartment to the plasma membrane.

scholarly journals Adenovirus RIDαβ Complex Inhibits Lipopolysaccharide Signaling without Altering TLR4 Cell Surface Expression

2006 ◽  
Vol 80 (13) ◽  
pp. 6378-6386 ◽  
Author(s):  
Fernando Delgado-Lopez ◽  
Marshall S. Horwitz
Keyword(s):  
Signal Transduction ◽  
Cell Surface ◽  
Signaling Pathways ◽  
Interleukin 1 ◽  
Mechanistic Explanation ◽  
Surface Expression ◽  
Receptor Internalization ◽  
Cell Surface Receptor ◽  
Cell Surface Expression ◽  
Down Regulation

ABSTRACT The transmembrane heterotrimer complex 10.4K/14.5K, also known as RID (for “receptor internalization and degradation”), is encoded by the adenovirus E3 region, and it down-regulates the cell surface expression of several unrelated receptors. We recently showed that RID expression correlates with down-regulation of the cell surface expression of the tumor necrosis factor (TNF) receptor 1 in several human cells. This observation provided the first mechanistic explanation for the inhibition of TNF alpha-induced chemokines by RID. Here we analyze the immunoregulatory activities of RID on lipopolysaccharide (LPS) and interleukin-1 beta (IL-1β)-mediated responses. Although both signaling pathways are strongly inhibited by RID, the chemokines up-regulated by IL-1β stimulation are only marginally inhibited. In addition, RID inhibits signaling induced by LPS without affecting the expression of the LPS receptor Toll-like receptor 4, demonstrating that RID need not target degradation of the receptor to alter signal transduction. Taken together, our data demonstrate the inhibitory effect of RID on two additional cell surface receptor-mediated signaling pathways involved in inflammatory processes. The data suggest that RID has intracellular targets that impair signal transduction and chemokine expression without evidence of receptor down-regulation.

scholarly journals The Predominant Activation of Alternative Signaling Pathways Explains the Differential Propensity of Different c-Mpl Gain-of-Function Mutations to Promote Myeloproliferative Malignancies

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 1578-1578
Author(s):  
Clemens Stockklausner ◽  
Christin Maria Duffert ◽  
Nicole Dickemann ◽  
Anne Christine Klotter ◽  
Isabelle Nadine Kuhlee ◽  
...  
Keyword(s):  
Cell Surface ◽  
Signaling Pathways ◽  
Plasma Levels ◽  
Feedback Loop ◽  
Receptor Gene ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Negative Feedback Loop ◽  
Gain Of Function ◽  
Functional Analyses

Abstract Thrombopoiesis is tightly regulated by the binding of thrombopoietin (THPO) to its receptor c-Mpl that leads to the clearance of THPO from the plasma thus establishing a negative feedback loop. Several mutations in the c-Mpl receptor gene have been linked to a gain-of-function resulting in thrombocytosis. We focused on a comparison of gain-of-function mutation in the extracellular part of the c-Mpl receptor, where ligand binding and receptor dimerization occur, with the S505N, W515K and W515L mutations in the transmembrane and juxtamembrane region, respectively. Interestingly, the latter mutations are known to also promote myeloproliferative malignancies and AML, whereas the P106L mutation causes hereditary thrombocytosis without a known predisposition to hematologic malignancies. We have now performed functional analyses of these gain-of-function mutations to address the question of how the different propensity to induce malignancy can be explained. We first analyzed the post-translational processing of the normal and the P106L mutated receptor in comparison to the receptors carrying the S505N, W515K and W515L mutations in transfected HeLa and BA/F3 cells. The normal and the S505N, W515K and W515L mutated c-Mpl receptors were properly glycosylated during their transport through the Golgi apparatus, whereas the P106L mutated receptor did not enter the Golgi and was not fully glycosylated. The plasma membrane expression, assayed by confocal microscopy and FACS, of the S515N, W515K and W515L mutated receptors was comparable to the normal receptor, whereas the P106L mutated receptor was not detectable on the cell surface. Functional analyses of the THPO/c-Mpl signaling pathways in THPO stimulated c-Mpl transfected BA/F3 cells showed activation of the ERK1/2 pathway in all mutants but only weaker activation of the PI3K/m-TOR and Stat3/5 signaling pathways for the P106L mutant. By contrast, cells transfected with the normal receptor gene and the S505N, W515K and W515L c-Mpl mutants showed predominant up-regulation of the PI3K/m-TOR and Stat3/5 pathways. These results show that (1) the activation of c-Mpl by THPO does not absolutely require surface expression of the receptor (2) different c-Mpl gain-of-function mutations activate separable downstream pathways and (3) the predominant activation of the PI3K/m-TOR and Stat3/5 pathways correlates with the propensity to induce hematopoietic malignancy. Further, it is interesting to note that the c-Mpl P106L gain-of-function mutant is known to cause 10 to 20-fold elevated thrombopoietin (THPO) plasma levels in patients and is shown here not to be properly glycosylated and transported to the cell surface. By contrast, patients with the other gain-of-function mutations analyzed here show normal or even reduced THPO plasma concentrations and normal post-translational processing and cell surface expression. In conclusion, we propose that c-Mpl gain-of-function mutations exert their effect by predominantly activating either the PI3K/m-TOR and Stat3/5 or the ERK signaling pathways and that the predominant activation of PI3K/m-TOR and Stat3/5 correlates with the propensity to induce malignancy. Furthermore, THPO clearance and maintenance of the negative feedback loop regulating THPO plasma levels, but not signaling activity of the c-Mpl receptor necessarily require proper glycosylation, intracellular trafficking and cell surface expression. Disclosures No relevant conflicts of interest to declare.

Two Different β3 Cysteine Substitutions Alter αIIbβ3 Maturation and Result in Glanzmann Thrombasthenia

2002 ◽  
Vol 88 (07) ◽  
pp. 104-110 ◽  
Author(s):  
S. Milet-Marsal ◽  
C. Breillat ◽  
O. Peyruchaud ◽  
P. Nurden ◽  
R. Combrié ◽  
...  
Keyword(s):  
Amino Acid ◽  
Cell Surface ◽  
Transient Expression ◽  
Double Mutant ◽  
Direct Sequencing ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Homozygous Mutation ◽  
Glanzmann Thrombasthenia ◽  
Exon 10

SummaryWe report the defects responsible for Glanzmann thrombasthenia in two patients showing traces of abnormally migrating platelet β3 in immunoblotting. Using PCR-SSCP and direct sequencing, we identified a novel homozygous mutation in exon 10 of the β3 gene of patient 1 which gave a C457 to Y amino acid substitution. A C542 to R substitution in β3 of patient 2 was previously reported by us. These cysteines are present in EGF-domains 1 and 3 respectively of β3. We therefore constructed mutants carrying substitutions on cysteine residues in each of the first three EGF domains of β3, C457, C495 and C542 respectively. Transient expression of these mutants in COS-7 cells, including the C542 and C547 double mutant, proved that disulfide disruption directly affects cell surface expression of the integrin. We then showed by metabolic (35S) labeling and Endo-H glycosidase treatment that these substitutions strongly affected complex maturation within the cell.

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