| 1. |
- Tingström, Anders, et al.
(författare)
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Distribution and dynamics of cell surface-associated cellCAM 105 in cultured rat hepatocytes
- 1989
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Ingår i: Experimental Cell Research. - : Elsevier BV. - 1090-2422 .- 0014-4827. ; 185:1, s. 132-142
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Tidskriftsartikel (refereegranskat)abstract
- The cellular location of cellCAM 105 was studied by indirect immunofluorescence microscopy of primary rat hepatocytes grown in monolayer culture. Staining corresponding to cellCAM 105 was seen both in cell-cell contact areas and on the upper surfaces of the cells. In the cell-cell contact areas the antigen was not accessible to the antibodies unless the cells were either permeabilized with detergent or incubated in a calcium-free medium. Removal of calcium from the medium caused the cells to separate from each other. Within a few minutes wide intercellular clefts were formed, and upon further incubation the cells became stellate-shaped and finally remained in contact with each other only via thin cellular processes. These processes were cellCAM 105-positive and at sites where they attached to the bodies of the contracted cells a granular fluorescence pattern appeared. After 24-48 h of culture, intercellular channels resembling bile canaliculi were sometimes formed in the hepatocyte monolayers. The membranes of these intercellular channels were stained for cellCAM 105. After culture for several days the hepatocytes lost their polygonal shape and gradually acquired a more fibroblast-like morphology. This morphological change was accompanied by a decrease in cellCAM 105-specific fluorescence, both in the cell-cell contact areas and on the free cell surfaces.
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| 2. |
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| 3. |
- Imreh, Gabriela, et al.
(författare)
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ER retention may play a role in sorting of the nuclear pore membrane protein POM121
- 2003
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Ingår i: Experimental Cell Research. - 0014-4827 .- 1090-2422. ; 284:2, s. 173-184
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Tidskriftsartikel (refereegranskat)abstract
- Integral membrane proteins of the nuclear envelope (NE) are synthesized on the rough endoplasmic reticulum (ER) and following free diffusion in the continuous ER/NE membrane system are targeted to their proper destinations due to interactions of specific domains with other components of the NE. By studying the intracellular distribution and dynamics of a deletion mutant of an integral membrane protein of the nuclear pores, POM121, which lacks the pore-targeting domain, we investigated if ER retention plays a role in sorting of integral membrane proteins to the nuclear envelope. A nascent membrane protein lacking sorting determinants is believed to diffuse laterally in the continuous ER/NE lipid bilayer and expected to follow vesicular traffic to the plasma membrane. The GFP-tagged deletion mutant, POM121(1-129)-GFP, specifically distributed within the ER membrane, but was completely absent from the Golgi compartment and the plasma membrane. Experiments using fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) demonstrated that despite having very high mobility within the whole ER network (D = 0.41 +/- 0.11 mum(2)/s) POM121(1-129)-GFP was unable to exit the ER. It was also not detected in post-ER compartments of cells incubated at 15degreesC. Taken together, these experiments show that amino acids 1-129 of POM121 are able to retain GFP in the ER membrane and suggest that this retention occurs by a direct mechanism rather than by a retrieval mechanism. Our data suggest that ER retention might be important for sorting of POM121 to the nuclear pores.
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| 4. |
- Lennartsson, Johan, et al.
(författare)
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Identification of Tyr900 in the kinase domain of c-Kit as a Src-dependent phosphorylation site mediating interaction with c-Crk
- 2003
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Ingår i: Experimental Cell Research. - 0014-4827 .- 1090-2422. ; 288:1, s. 110-118
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Tidskriftsartikel (refereegranskat)abstract
- We have previously demonstrated that ligand-stimulation of c-Kit induces phosphorylation of Tyr568 and Tyr570 in the juxtamembrane region of the receptor, leading to recruitment, phosphorylation and activation of members of the Src family of tyrosine kinases. In this paper, we demonstrate that members of the Src family of tyrosine kinases are able to phosphorylate c-Kit selectively on one particular tyrosine residue, Tyr900, located in the second part of the tyrosine kinase domain. In order to identify potential docking partners of Tyr900, a synthetic phosphopeptide corresponding to the amino acid sequence surrounding Tyr900 was used as an affinity matrix. By use of MALDI-TOF mass spectrometry, CrkII was identified as a protein that specifically bound to Tyr900 in a phosphorylation dependent manner, possibly via the p85 subunit of PI3-kinase. Expression of a mutant receptor where Tyr900 had been replaced with a phenylalanine residue (Y900F) resulted in a receptor with reduced ability to phosphorylate CrkII. Together these data support a model where c-Src phosphorylates the receptor, thereby creating docking sites for SH2 domain containing proteins, leading to recruitment of Crk to the receptor.
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| 5. |
- Melhus, Håkan, et al.
(författare)
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Retinol-binding protein and transthyretin expressed in HeLa cells form a complex in the endoplasmic reticulum in both the absence and the presence of retinol
- 1991
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Ingår i: Experimental Cell Research. - 0014-4827 .- 1090-2422. ; 197:1, s. 119-124
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Tidskriftsartikel (refereegranskat)abstract
- To establish a suitable experimental system for studies of the interaction of retinol-binding protein (RBP) with transthyretin (TTR) we have expressed the corresponding cDNAs in HeLa cells. To investigate whether complex formation might occur already in the endoplasmic reticulum (ER), the C-terminal ER retention signal, KDEL, was attached to TTR. The tetrameric TTR-KDEL fusion protein was retained in the ER of HeLa cells. When RBP was co-expressed with TTR-KDEL, RBP was retained intracellularly. A cDNA-encoding purpurin, a protein which is 50% identical to RBP, was then expressed together with TTR-KDEL. Purpurin was not retained intracellularly and did not bind to TTR coupled to Sepharose. The effect of the vitamin A status on the secretion of TTR and RBP was examined. While TTR expressed alone was not retained intracellularly, TTR was retained in vitamin A-deficient cells when co-expressed with RBP. Addition of retinol stimulated rapid secretion of both proteins. These results demonstrate that TTR can form a complex with RBP in the ER. The data suggest that RBP and TTR are secreted as a complex.
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| 6. |
- Rennel, Emma, et al.
(författare)
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Regulation of endothelial cell differentiation and transformation by H-Ras
- 2003
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Ingår i: Experimental Cell Research. - 0014-4827 .- 1090-2422. ; 291:1, s. 189-200
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Tidskriftsartikel (refereegranskat)abstract
- Angiogenesis is regulated by growth factors which activate tyrosine kinase receptors leading to the activation of a number of intracellular signaling pathways. The specific function of H-Ras during FGF-2 stimulated endothelial cell differentiation, defined as invasive growth and formation of branching networks in fibrin gels, was investigated by using conditionally immortalized endothelial cell lines induced to express H-Ras mutants. Expression of inhibitory N17Ras did not impair differentiation in response to FGF-2 and TNF-alpha. The farnesyltransferase inhibitor FTI-277 inhibited farnesylation of Ras but did not inhibit differentiation of human microvascular endothelial cells or mouse brain endothelial cells. In contrast, activated V12Ras inhibited endothelial cell differentiation and cells displayed a transformed phenotype with an increased rate of proliferation and loss of contact inhibited growth. Furthermore, V12Ras expressing endothelial cells grew as solid tumors when injected subcutaneously into mice. Our data suggest that, in endothelial cells, H-Ras activity is not required for differentiation. However, this activity must be tightly regulated as aberrant activity can disturb the ability of endothelial cells to undergo differentiation.
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| 7. |
- Siwicki, Jan Konrad, et al.
(författare)
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Telomere maintenance and cell cycle regulation in spontaneously immortalized T-cell lines from Nijmegen breakage syndrome patients
- 2003
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Ingår i: Experimental Cell Research. - 0014-4827 .- 1090-2422. ; 287:1, s. 178-189
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Tidskriftsartikel (refereegranskat)abstract
- Nijmegen breakage syndrome (NBS) is a rare genetic instability syndrome associated with a high incidence of lymphoid malignancies. The NBS1 protein has been implicated in telomere biology suggesting that cells from NBS patients might have deficient telomere maintenance capacity. In this study we characterized spontaneously immortalized T-cell lines derived from three NBS patients regarding growth characteristics, telomere biology, expression of cell-cycle regulators, and response to DNA damage to understand the role of NBS1 in the immortalization process. In all the NBS T-cell lines the acquisition of an immortal phenotype was associated with telomere length stabilization, high telomerase activity, and increased mRNA expression of the catalytic subunit of telomerase (hTERT), together with c-myc up-regulation. Our findings provide evidence that telomere length maintenance was intact in the T lymphocytes in the absence of a full-length NBS protein, presumably due to the presence of an alternatively transcribed NBS protein of 70 kDa. Normal protein expression patterns for pRb and p53 in all the immortal lines coincided with altered expression of some cell-cycle proteins as well as with an impaired G1/S arrest after gamma irradiation, despite a seemingly normal p53/p21 pathway. The here described, spontaneously immortalized NBS derived T-cell lines can be useful in future analysis of the biologic effects in the NBS.
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| 8. |
- Tågerud, Sven, et al.
(författare)
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Receptor-mediated uptake of horseradish peroxidase in innervated and denervated skeletal muscle
- 1985
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Ingår i: Experimental Cell Research. - : Elsevier BV. - 0014-4827 .- 1090-2422. ; 160:1, s. 95-105
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Tidskriftsartikel (refereegranskat)abstract
- The in vitro uptake of [3H]inulin and horseradish peroxidase (HRP) has been studied in innervated and 6 days denervated extensor digitorum longus muscle of the mouse. Both markers were taken up at a higher rate in denervated muscle. The increase in uptake after denervation was, however, larger for HRP than for [3H]inulin. After 2 h incubation at 37 °C, pH 7.3, in the presence of equimolar concentrations of HRP and [3H]inulin (approx. 2.1 μM), the uptake of HRP was approx. 8 times as great as the uptake of [3H]inulin in the same innervated muscles. In denervated muscle the HRP uptake was approx. 19 times as great as the [3H]inulin uptake in the same muscles. Various possible explanations of these differences in uptake have been considered and tested experimentally. [3H]Inulin uptake in skeletal muscle has previously been shown to obey bulk kinetics. The present investigation shows the HRP uptake to obey saturation kinetics. The HRP uptake shows dependency on divalent cations and is reduced if incubation is carried out at pH 6.4. The uptake of HRP, when used at a low, non-saturating concentration (10 μg/ml approx. 0.25 μM), is inhibited 60% by yeast mannan (0.1 mg/ml), ribonuclease B (0.1 mg/ml, approx. 7.4 μM), mannose (30 mM), monodansylcadaverine (1 mM), chloroquine (100 μM), trifluoperazine (25 μM) or maleic acid (2 mM). It is concluded that HRP is taken up in innervated and denervated skeletal muscle by a process of receptor-mediated endocytosis and that this uptake is under neurotrophic control.
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| 9. |
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| 10. |
- Ageberg, Malin, et al.
(författare)
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Inhibition of geranylgeranylation mediates sensitivity to CHOP-induced cell death of DLBCL cell lines.
- 2011
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Ingår i: Experimental Cell Research. - : Elsevier BV. - 1090-2422 .- 0014-4827. ; 317, s. 1179-1191
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Tidskriftsartikel (refereegranskat)abstract
- Prenylation is a post-translational hydrophobic modification of proteins, important for their membrane localization and biological function. The use of inhibitors of prenylation has proven to be a useful tool in the activation of apoptotic pathways in tumor cell lines. Rab geranylgeranyl transferase (Rab GGT) is responsible for the prenylation of the Rab family. Overexpression of Rab GGTbeta has been identified in CHOP refractory diffuse large B cell lymphoma (DLBCL). Using a cell line- based model for CHOP resistant DLBCL, we show that treatment with simvastatin, which inhibits protein farnesylation and geranylgeranylation, sensitises DLBCL cells to cytotoxic treatment. Treatment with the farnesyl transferase inhibitor, FTI-277, or the geranylgeranyl transferase I inhibitor, GGTI-298, indicates that the reduction in cell viability was restricted to inhibition of geranylgeranylation. In addition, treatment with BMS1, a combined inhibitor of farnesyl transferase and Rab GGT, resulted in a high cytostatic effect in WSU-NHL cells, demonstrated by reduced cell viability and decreased proliferation. Co-treatment of BMS1 or GGTI-298 with CHOP showed synergistic effects with regard to markers of apoptosis. We propose that inhibition of protein geranylgeranylation together with conventional cytostatic therapy is a potential novel strategy for treating patients with CHOP refractory DLBCL.
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