Biomedical subjects

Daniel Jung

Publications and source records attributed to Daniel Jung.

6 recordsLinked to original sources

PubMed2006

c-Myc over-expression in Ramos Burkitt's lymphoma cell line predisposes to iron homeostasis disruption in vitro.

Burkitt's lymphoma is an aggressive B-cell neoplasm resulting from deregulated c-myc expression. We have previously shown that proliferation of Burkitt's lymphoma cell lines such as Ramos is markedly reduced by iron treatment. It has been shown that iron induces expression of c-myc which, owing to its transcriptional regulatory functions, regulates genes involved in iron metabolism. Transient enhancement of c-myc expression by iron could increase the expression of genes involved in iron incorporation, which could lead to an accumulation of intracellular free iron. Here, we have investigated whether cells with a high basal level of c-Myc were more likely to accumulate free iron. Our results suggest that the basal level of c-Myc in Ramos cells is twofold higher than what is seen in HL-60 cells. Moreover, in Ramos cells, where c-Myc is expressed at a high level, H-ferritin expression is down-regulated, transferrin receptor (CD71) expression is increased, and ferritin translation is inhibited. These modifications in iron metabolism, resulting from the strong basal expression of c-Myc, and amplified by iron addition, could lead to a disruption in homeostasis and consequently to growth arrest.

Antigens, CD↗

PubMed2006

Free radicals act as effectors in the growth inhibition and apoptosis of iron-treated Burkitt's lymphoma cells.

The addition of ferric citrate to Burkitt's lymphoma (BL) cell lines inhibits growth, leads to the accumulation of cells in the phase G(2)/M of the cell cycle and to the modulation of translocated c-myc expression. The increase in the labile iron pool (LIP) of iron-treated BL cells leads to cytotoxicity. Indeed, intracellular free iron catalyzes the formation of highly reactive compounds such as hydroxyl radicals and nitric oxide (NO) that damages macromolecular components of cells, eventually resulting in apoptosis. In this report, we have investigated the possible involvement of free radicals in the response of Ramos cells to iron. When added to Ramos cells, iron increased the intracellular levels of peroxide/peroxynitrite and NO. Moreover, the addition of free radicals scavengers (TROLOX and Carboxy-PTIO) neutralized the effects of iron on Ramos cells while addition of an NO donor or hydrogen peroxide (H2O2) to cells generated effects which partially mimicked those induced by iron addition. Collectively, our results suggest the involvement of free radicals as effectors in the iron specific growth inhibition of BL cells observed in vitro.

Apoptosis↗

PubMed2005

Iron specific growth inhibition of Burkitt's lymphoma cells in vitro, associated with a decrease in translocated c-myc expression.

The cellular proto-oncogene c-myc is an important transcription factor that plays a role in several cellular activities such as proliferation, differentiation, and apoptosis. It follows that regulation of c-myc expression is crucial for maintaining cell integrity. Amplification or translocation can convert this proto-oncogene into an activated oncogene, thereby deregulating c-myc expression. Changes in the expression of c-myc leading to malignant cell growth and tumor progression can also be triggered by extrinsic factors. It has been reported that iron can increase cell proliferation, mainly by stimulating DNA synthesis as well as by enhancing c-myc expression. Here, we studied the effect of iron on cells in which c-myc expression is deregulated by either chromosomal translocation or gene amplification. When added to Burkitt's lymphoma cell lines, iron markedly inhibits cell proliferation. This effect is mediated by a cell cycle arrest in G2/M, followed by an important decrease in c-myc expression, whereas no effect could be observed in a cell line harboring amplified c-myc. Moreover, the down-regulation of c-myc expression, which is independent from cell cycle blockade, leads to cell death by apoptosis. Collectively, our results suggest the existence of a novel iron-dependent cell cycle regulatory mechanism involving modulation of translocated c-myc gene expression.

Apoptosis↗

PubMed2005

Efficient gene transfer into normal human B lymphocytes with the chimeric adenoviral vector Ad5/F35.

The failure to efficiently introduce genes into normal cells such as human B lymphocytes limits the characterization of their function on cellular growth, differentiation and survival. Recent studies have shown that a new adenoviral vector Ad5/F35 can efficiently transduce human haematopoietic CD34+ progenitor cells. In this study, we compared the gene transfer efficiencies of the Ad5/F35 vector to that of the parental vector Ad5 in human B lymphocytes. Peripheral blood B cells obtained from healthy individuals were cultured in vitro using CD40-CD154 system. Normal B lymphocytes were infected with replication-defectives Ad5 and Ad5/F35, both containing the GFP reporter gene, and transduction efficiencies were monitored by flow cytometry. Ad5 was highly ineffective, infecting only about 5% of human B lymphocytes. In contrast, Ad5/F35 transduced up to 60% of human B lymphocytes and GFP expression could be detected for up to 5 days post infection. Importantly, physiology of B lymphocytes such as proliferation, viability and antibodies secretion were unaffected following Ad5/F35 transduction. Finally, we observed that memory B lymphocytes were more susceptible to Ad5/F35 infection than naïve B lymphocytes. Thus, our results demonstrate that the adenoviral vector Ad5/F35 is an efficient tool for the functional characterization of genes in B lymphopoiesis.

Adenoviruses, Human↗

PubMed2004

Maintenance of Epstein-Barr virus-derived episomal vectors in the murine Sp2/0 myeloma cell line is dependent upon exogenous expression of human EBP2.

Vectors carrying the origin of replication (oriP) and driving expression of the EBNA-1 protein from Epstein-Barr virus (EBV) replicate as extrachromosomal episomes in human cells. Whether these vectors can be maintained as episomes in murine cells is still controversial. Here we demonstrate that EBNA-1 expression alone was unable to maintain episomal expression of an EBV-based vector in the murine Sp2/0 cell line. However, we were able to obtain long-term episome maintenance in Sp2/0 cells after exogenously expressing human EBP2 by genetic engineering. Our results provide further evidence for the fundamental role of human EBP2 in episomal maintenance of EBV-based vectors. Moreover, we demonstrate that EBV-based vectors can be successfully used in cells presumably incompetent for episomal maintenance.

Animals↗

PubMed2002

Inducible expression of Bcl-XL restricts apoptosis resistance to the antibody secretion phase in hybridoma cultures.

B-cell hybridomas are widely used to produce monoclonal antibodies via large-scale cell culture. Unfortunately, these cells are highly sensitive to apoptotic death under conditions of nutrient deprivation observed at the plateau phase of batch cultures. Previous work has indicated that constitutive high-level expression of antiapoptotic genes in hybridoma cells could delay apoptosis, resulting in higher cell densities and prolonged viability. However, the constitutive high-level expression of antiapoptotic genes has been shown to have detrimental effects on genomic stability of other types of cultured cells. Inducible gene expression may be used to avoid this problem. In the present study, we first constructed an expression vector in which the promoter of a mammalian metallothionein (MT) gene drives the expression of bcl-XL in response to metal exposure. The vector was then used to exogenously control the expression of bcl-XL in D5 hybridoma cells. Our data show that stably transfected D5 cells (4G1.D9) expressed high levels of Bcl-X(L) following overnight exposure to ZnSO(4) concentrations (50 to 100 microM) that did not affect control cells. The level of Bcl-X(L) expressed after ZnSO(4) induction was sufficient to prevent apoptosis experimentally induced by cycloheximide and allowed 4G1.D9 cells to grow at higher densities and remain viable for prolonged periods in suboptimal culture conditions. The use of inducible bcl-XL expression permits extension of the viability of cultured B-cell hybridomas during the antibody secretion phase without the adverse genetic effects associated with constitutive long-term bcl-XL expression.

Animals↗