Analysis of the tumorigenic potential of common marmoset lymphoblastoid cells expressing a constitutively activated c-myc gene

Common Marmoset Cell Lines and Their Applications in Biomedical Research

Common marmosets (Callithrix jacchus; CMs) are small New World primates widely used in biomedical research. Early stages of such research often include in vitro experiments which require standardized and well-characterized CM cell cultures derived from different tissues. Despite the long history of laboratory work with CMs and high translational potential of such studies, the number of available standardized, well-defined, stable, and validated CM cell lines is still small. While primary cells and immortalized cell lines are mostly used for the studies of infectious diseases, biochemical research, and targeted gene therapy, the main current applications of CM embryonic stem cells and induced pluripotent stem cells are regenerative medicine, stem cell research, generation of transgenic CMs, transplantology, cell therapy, reproductive physiology, oncology, and neurodegenerative diseases. In this review we summarize the data on the main advantages, drawbacks and research applications of CM cell lines published to date including primary cells, immortalized cell lines, lymphoblastoid cell lines, embryonic stem cells, and induced pluripotent stem cells.

Transfection of the c-myc oncogene into normal Epstein-Barr virus-harboring B cells results in new phenotypic and functional features resembling those of Burkitt lymphoma cells and normal centroblasts

Activated c-myc gene was introduced into the cells of three normal Epstein-Barr virus (EBV)-positive lymphoblastoid B cell lines (LCL). The cells were monitored for the appearance of new phenotypic and functional features compared with the control LCL cells transfected with plasmid that did not contain the c-myc gene. The LCL-expressing c-myc constitutively did not arrest growth in low serum concentration. However, the cell number in the cultures failed to increase because of substantial cell death. Death was due to apoptosis as demonstrated by flow cytometric analysis of propidium iodide-stained cells, by typical DNA laddering in gel electrophoresis, and by the inspection of Giemsa-stained cell smears. Apoptosis was also induced by exposing the transfected cells to antibodies directed to the immunoglobulin mu chain (a-mu-ab) irrespective of the serum concentration in the culture. Exposure of the cells to CD40 ligand (CD40L) or CD40 monoclonal antibody prevented cell apoptosis. Upon transfection with c-myc, the LCL cells acquired a vacuolated morphology that was never observed in control cells. Moreover, the expression of CD10 and CD38 was upregulated, while that of CD39 and especially CD23 was downregulated. Unlike that observed in certain Burkitt lymphoma (BL) cell lines that share the same surface phenotype (CD10+CD38+CD23-CD39-), the c-myc-transfected cells expressed lymphocyte function-associated (LFA) 1, LFA-3, and intercellular adhesion molecule 1 and grew in large clumps rather than single-cell layers. Expression of CD10 and CD38 was particularly evident on the cells undergoing apoptosis, thus suggesting a correlation between the presence of these markers and the apoptotic process. Cells placed in conditions favoring in vitro apoptosis displayed downregulation of Bcl-2 protein. Bcl-2 expression was, however, upregulated when the cells were exposed to CD40L. These data indicate that the B cells expressing c-myc constitutively acquire some of the features of normal centroblasts and of BL cells, including the expression of CD10 and CD38, and the propensity to undergo apoptosis, which can be prevented by exposure to CD40L. Therefore, these cells can serve as a model system to study both BL lymphomagenesis as well as the process of B cell selection occurring in the germinal centers.

Effects of 50 Hz magnetic fields on C-myc transcript levels in nonsynchronized and synchronized human cells

The effects of 50 Hz electromagnetic fields (EMFs) on the expression of the c-myc oncogene, known to be involved in normal cell proliferation and possibly also in tumor processes, were investigated in nonsynchronized human lymphoid cells immortalized by Epstein-Barr virus. Viral injury to such cells makes them a good model for exploring the possible cancer-promoting effects of 50 Hz magnetic fields. Parallel experiments were conducted on human HL60 leukemic cells. Cells were exposed to sinusoidal 50 Hz EMFs at 10 microT or 1 mT for 20 min, 1 h, 24 h, or 72 h. Exposure was performed either immediately after refeeding or 1.5 h after refeeding. C-myc transcript values were assessed by Northern blot analysis and normalized to those of the noninducible gene GaPDH. No statistically significant difference between the c-myc transcript levels of control and exposed cells was found in lymphoid or leukemic cells under our experimental conditions, either after short exposures of 20 min and 1 h or after longer exposures of 24 and 72 h. Other experiments were carried out with pseudosynchronized cells in an attempt to establish whether cells were especially sensitive to 50 Hz magnetic field exposure in any particular phase of the cell cycle. Accordingly, cells were pseudosynchronized in G0/G1 by serum deprivation and exposed for 20 min to a 50 Hz magnetic field, at 10 microT for lymphoid cells and 1 mT for HL60 cells. No significant difference was observed between the c-myc transcript levels of control and exposed cells for either of the synchronized cell types. These results for synchronized cells correlated with those for nonsynchronized cells.