A novel canine B-cell leukaemia cell line. Establishment, characterisation and sensitivity to chemotherapeutics

We established a new B-cell leukaemia cell line CLB70 from a dog with chronic lymphocytic leukaemia. This cell line is positive for CD20, CD45, CD79a, MHC class II, IgG, IgM; weakly positive for CD21; and negative for CD3, CD4, CD5, CD8, CD14, CD34, CD117. PCR for antigen receptor gene rearrangement (PARR) analysis revealed a biclonal immunoglobulin heavy chain (IgH) gene rearrangement and negative result for TCRγ. Western blot analysis of anti- and pro-apoptotic proteins showed increased expression of Bcl-2, Mcl-1, NF-kB, and Ras, and decreased expression of p53. CLB70 cells grow rapidly in vitro and are tumourigenic in nude mice. The CLB70 line is highly sensitive to doxorubicin, less sensitive to etoposide and imatinib, and resistant to piroxicam, celecoxib and dexamethasone. Our results indicate that CLB70 cells are derived from mature B-cells and they may be a useful tool for the development of new therapeutic strategies for both dogs and humans.

Immunophenotypic characterization of canine malignant lymphoma: a retrospective study of cases diagnosed in Poland Lower Silesia, over the period 2011-2013

Lymphoma is the most frequently diagnosed cancer of the canine haematopoietic system. In this study, the flow cytometry and polymerase chain reaction (PCR) analysis were used to characterize a series of canine lymphomas in detail. The aim of this study was to determine the incidence of B- and T-cell high-grade lymphomas and their immunophenotypic characterization in Lower Silesia, Poland. The results show that the frequency of each type of lymphoma is 71% for B-cell and 17% for T-cell lymphomas. In two cases the PCR techniques confirmed the presence of simultaneous double gene rearrangements of the BCR and TCR receptors.

Requirement for C-terminal end of fibroblast growth factor receptor 4 in translocation of acidic fibroblast growth factor to cytosol and nucleus

The ability of COS cells to bind and internalise acidic fibroblast growth factor (aFGF) was studied after transient transfection of the cells with wild-type and mutated fibroblast growth factor receptor 4. In one case the tyrosine kinase of the receptor was inactivated by a point mutation in the active site, whereas in other cases parts of the receptor were deleted to remove various parts of the cytoplasmic domain. In all cases the receptors were expressed at the cell surface at a high level and the cells bound labelled growth factor efficiently and internalised it by endocytosis. Translocation of externally added aFGF across cellular membranes to reach the cytosol and nucleus was measured as transport of labelled growth factor to the nuclear fraction obtained by centrifugation, by farnesylation of growth factor modified to carry a CAAX motif, and by phosphorylation of the growth factor at a site specific for protein kinase C. Whereas both full-length receptors (with and without an active kinase domain) facilitated translocation of the growth factor to the cytosol and nucleus, as assessed by these methods, the mutants of the receptor where the C terminus was deleted, were unable to do so. In contrast, a receptor containing only the 57 most C-terminal amino acids of the cytoplasmic domain in addition to the juxtamembrane, transmembrane and extracellular domains, was in fact able to mediate translocation of aFGF to the cytosol. These data indicate that information contained in the C terminus of the receptor is required for translocation.

Dependence of ricin toxicity on translocation of the toxin A-chain from the endoplasmic reticulum to the cytosol

Ricin acts by translocating to the cytosol the enzymatically active toxin A-chain, which inactivates ribosomes. Retrograde intracellular transport and translocation of ricin was studied under conditions that alter the sensitivity of cells to the toxin. For this purpose tyrosine sulfation of mutant A-chain in the Golgi apparatus, glycosylation in the endoplasmic reticulum (ER) and appearance of A-chain in the cytosolic fraction was monitored. Introduction of an ER retrieval signal, a C-terminal KDEL sequence, into the A-chain increased the toxicity and resulted in more efficient glycosylation, indicating enhanced transport from Golgi to ER. Calcium depletion inhibited neither sulfation nor glycosylation but inhibited translocation and toxicity, suggesting that the toxin is translocated to the cytosol by the pathway used by misfolded proteins that are targeted to the proteasomes for degradation. Slightly acidified medium had a similar effect. The proteasome inhibitor, lactacystin, sensitized cells to ricin and increased the amount of ricin A-chain in the cytosol. Anti-Sec61alpha precipitated sulfated and glycosylated ricin A-chain, suggesting that retrograde toxin translocation involves Sec61p. The data indicate that retrograde translocation across the ER membrane is required for intoxication.

Inability of the acidic fibroblast growth factor mutant K132E to stimulate DNA synthesis after translocation into cells

Acidic fibroblast growth factor (aFGF) is a potent mitogen. It acts through activation of specific cell surface receptors leading to intracellular tyrosine phosphorylation cascades, but several reports also indicate that aFGF enters cells and that it has an intracellular function as well. The aFGF(K132E) mutant binds to and activates fibroblast growth factor receptors equally strongly as the wild-type, but it is a poor mitogen. We demonstrate that aFGF(K132E) enters NIH 3T3 cells and is transported to the nuclear fraction like wild-type aFGF. A fusion protein of aFGF(K132E) and diphtheria toxin A-fragment (aFGF(K132E)-DT-A) and a similar fusion protein containing wild-type aFGF (aFGF-DT-A) were reconstituted with diphtheria toxin B-fragment. Both fusion proteins were translocated to the cytosol by the diphtheria toxin pathway and subsequently recovered from the nuclear fraction. Whereas translocation of aFGF-DT-A stimulated DNA synthesis in U2OSDR1 cells lacking functional fibroblast growth factor receptors, aFGF(K132E)-DT-A did not. The mutation disrupts a protein kinase C phosphorylation site in the growth factor making it unable to be phosphorylated. The data indicate that a defect in the intracellular action of aFGF(K132E) is the reason for its strongly reduced mitogenicity, possibly due to inability to be phosphorylated.

Expression of mutant dynamin inhibits toxicity and transport of endocytosed ricin to the Golgi apparatus

Endocytosis and intracellular transport of ricin were studied in stable transfected HeLa cells where overexpression of wild-type (WT) or mutant dynamin is regulated by tetracycline. Overexpression of the temperature-sensitive mutant dynG273D at the nonpermissive temperature or the dynK44A mutant inhibits clathrin-dependent endocytosis (Damke, H., T. Baba, A.M. van der Blieck, and S.L. Schmid. 1995. J. Cell Biol. 131: 69-80; Damke, H., T. Baba, D.E. Warnock, and S.L. Schmid. 1994. J. Cell Biol. 127:915-934). Under these conditions, ricin was endocytosed at a normal level. Surprisingly, overexpression of both mutants made the cells less sensitive to ricin. Butyric acid and trichostatin A treatment enhanced dynamin overexpression and increased the difference in toxin sensitivity between cells with normal and mutant dynamin. Intoxication with ricin seems to require toxin transport to the Golgi apparatus (Sandirg, K., and B. van Deurs. 1996. Physiol. Rev. 76:949-966), and this process was monitored by measuring the incorporation of radioactive sulfate into a modified ricin molecule containing a tyrosine sulfation site. The sulfation of ricin was much greater in cells expressing dynWT than in cells expressing dynK44A. Ultrastructural analysis using a ricin-HRP conjugate confirmed that transport to the Golgi apparatus was severely inhibited in cells expressing dynK44A. In contrast, ricin transport to lysosomes as measured by degradation of 125I-ricin was essentially unchanged in cells expressing dynK44A. These data demonstrate that although ricin is internalized by clathrin-independent endocytosis in cells expressing mutant dynamin, there is a strong and apparently selective inhibition of ricin transport to the Golgi apparatus. Also, in cells with mutant dynamin, there is a redistribution of the mannose-6-phosphate receptor.

Effect of mutation of cytoplasmic receptor domain and of genistein on transport of acidic fibroblast growth factor into cells

Acidic fibroblast growth factor (aFGF) binds to specific transmembrane receptors and is partly transported to a nuclear location. To study this transport we made a kinase-negative mutant of FGF receptor 4 as well as one where the major part of the cytoplasmic receptor domain was deleted, and expressed them in U2OSDr1 cells that lack functional FGF receptors. All receptors mediated endocytic uptake of aFGF. Translocation of the growth factor across cellular membranes was assayed using aFGF with a C-terminal CAAX-motif, which signals addition of a farnesyl group onto the protein once in the cytosol. CAAX-tagged aFGF was farnesylated when incubated with cells containing wild-type or kinase-negative receptors. It was not farnesylated in cells expressing the deleted receptor, or when the incubation was in the presence of genistein. aFGF incubated with cells transfected with wild-type or kinase-negative receptors, but not with the deleted receptor, was partly recovered from the nuclear fraction in the absence, but not in the presence of genistein. The data indicate that the cytoplasmic receptor domain, but not the active kinase, is required for transport of the growth factor into cells, and that genistein inhibits the process.

Retrograde transport of mutant ricin to the endoplasmic reticulum with subsequent translocation to cytosol

Translocation of ricin A chain to the cytosol has been proposed to take place from the endoplasmic reticulum (ER), but attempts to visualize ricin in this organelle have failed. Here we modified ricin A chain to contain a tyrosine sulfation site alone or in combination with N-glycosylation sites. When reconstituted with ricin B chain and incubated with cells in the presence of Na(2)(35)SO(4), the modified A chains were labeled. The labeling was prevented by brefeldin A and ilimaquinone, and it appears to take place in the Golgi apparatus. This method allows selective labeling of ricin molecules that have already been transported retrograde to this organelle. A chain containing C-terminal N-glycosylation sites became core glycosylated, indicating retrograde transport to the ER. In part of the toxin molecules, the A chain was released from the B chain and translocated to the cytosol. The finding that glycosylated A chain was present in the cytosol indicates that translocation takes place after transport of the toxin to the ER.

Stimulation of proliferation of a human osteosarcoma cell line by exogenous acidic fibroblast growth factor requires both activation of receptor tyrosine kinase and growth factor internalization

U2OS Dr1 cells, originating from a human osteosarcoma, are resistant to the intracellular action of diphtheria toxin but contain toxin receptors on their surfaces. These cells do not have detectable amounts of fibroblast growth factor receptors. When these cells were transfected with fibroblast growth factor receptor 4, the addition of acidic fibroblast growth factor to the medium induced tyrosine phosphorylation, DNA synthesis, and cell proliferation. A considerable fraction of the cell-associated growth factor was found in the nuclear fraction. When the growth factor was fused to the diphtheria toxin A fragment, it was still bound to the growth factor receptor and induced tyrosine phosphorylation but did not induce DNA synthesis or cell proliferation, nor was any fusion protein recovered in the nuclear fraction. On the other hand, when the fusion protein was associated with the diphtheria toxin B fragment to allow translocation to the cytosol by the toxin pathway, the fusion protein was targeted to the nucleus and stimulated both DNA synthesis and cell proliferation. In untransfected cells containing toxin receptors but not fibroblast growth factor receptors, the fusion protein was translocated to the cytosol and targeted to the nucleus, but in this case, it stimulated only DNA synthesis. These data indicate that the following two signals are required to stimulate cell proliferation in transfected U2OS Dr1 cells: the tyrosine kinase signal from the activated fibroblast growth factor receptor and translocation of the growth factor into the cell.

Translocation of cytosol of exogenous, CAAX-tagged acidic fibroblast growth factor

Acidic fibroblast growth factor (aFGF) added externally to cells has been proposed to enter the nucleus and stimulate DNA synthesis, but it has remained controversial whether or not exogenous aFGF has the capability of crossing cellular membranes. To test this, a novel principle to study translocation of proteins to the cytosol was developed by fusing a C-terminal farnesylation signal, a CAAX tag (C = Cys, A = an aliphatic amino acid, and X = any amino acid), onto aFGF. Farnesylation is only known to occur in the cytosol and possibly in the nucleus. When incubated with NIH3T3 cells overnight, about one-third of the cell-associated, CAAX-tagged growth factor was farnesylated, indicating that efficient translocation had taken place. Binding to specific FGF receptors was required for translocation to occur. Part of the farnesylated growth factor was found in the nuclear fraction. The data indicate that CAAX-tagged aFGF added externally to cells is able to cross cellular membranes and enter the cytosol and the nucleus.

Farnesylation of CaaX-tagged diphtheria toxin A-fragment as a measure of transfer to the cytosol

Diphtheria toxin binds to receptor-positive cells through its B-fragment, the toxin is then endocytosed, and the low pH in endosomes triggers the translocation of the enzymatically active A-fragment to the cytosol. A synchronous release of A-fragments into the cytosol can be induced by exposing cells with surface-bound toxin to low pH. We have used this protein translocation system to develop a novel method to study whether or not a protein is exposed to the cytosol. Protein farnesylation is a cytosolic modification signaled by a C-terminal CaaX motif, and to visualize the translocation process, we added a farnesylation signal to the toxin A-fragment. The A-fragment with an added CaaX motif was farnesylated within 1 h after exposure of cells with surface-bound toxin to low pH, and also A-fragment translocated from endosomes was quantitatively farnesylated. The results indicate that all cell-mediated reduction of the toxin implicates translocation of the A-fragment to the cytosol. The farnesylation was inhibited by lovastatin, the alkylating agent NEM, and the peptidomimetic farnesylation inhibitor B581. Farnesylated A-fragment partitioned preferentially into the detergent phase upon extraction with Triton X-114. Our data suggest that farnesylation of a CaaX tag is generally applicable as a cytosolic marker, and this strategy for monitoring protein transfer to the cytosol may have considerable potential for studying the transport to the cytosol of proteins added externally to cells.

Semiquantitative assay of human chorionic gonadotropin by a simple and fast immunofiltration technique

An immunofiltration technique for the semiquantitative assay of human chorionic gonadotropin (hCG) was applied in two versions, using different antibodies. One anti-beta hCG subunit was immobilized on a glass microfibre disc in the form of six radially located bars, and the dry disc was placed on a water-absorbing material in a plastic device. A second antibody labelled with horse radish peroxidase conjugate was used in solution. For the colour reaction a solution with tetramethylbenzidine and hydrogen peroxide was used. The number of blue bars appearing on the test disc depended on concentration range of human chorionic gonadotropin. The technique with the monoclonal antibodies, anti-beta hCG and anti-alpha hCG-horse radish peroxidase conjugate, was specific for intact human chorionic gonadotropin, while the technique with the rabbit antibodies, raised against synthetic fragment 122-145-beta hCG and beta hCG-horse radish peroxidase, was useful for both intact human chorionic gonadotropin and its beta-chain. Cross reactions with human lutropin and thyrotropin were negligible. Haemoglobin, urea and various tested drugs did not affect the assay. In the assay of human chorionic gonadotropin in the urine of pregnant women and in sera of patients with trophoblastic diseases, the results from the immunofiltration technique were in accordance with data obtained by classical ELISA and by two commercial kits.