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Acquiring oncogenes through horizontal transfer
By Bijal P. Trivedi

Acquisition of genes via horizontal transfer rather than by inheritance is frequently observed in bacteria. Now, Swedish researchers demonstrate that a similar phenomenon can occur between eucaryotic cells. Oncogenes from a dying cell can be transferred to a nearby cell via phagocytosis, a process through which one cell engulfs another. If the recipient cell is already genetically unstable, the newly acquired oncogenes can lead to tumor formation.

The researchers propose that this horizontal transfer of genes could be one route by which cells accumulate genetic abnormalities. The study also indicates that even after a cell dies, its genetic material—entire chromosomes in some cases—can be rescued by other cells.

The scientists mixed dying rat cells—carrying cancer-causing oncogenes—with mouse cells lacking p53, a tumor-suppressing gene. The p53-deficient cells developed tumor-like characteristics. The same experiment was done with mouse cells carrying p53. In contrast, however, the rat cells did not transform mouse cells carrying a healthy p53 gene, suggesting that the gene protected the cells from any acquired oncogenes. The research, led by Lars Holmgren, of the Cancer Center Karolinska Hospital in Stockholm, Sweden, appears in the current issue of the Proceedings of the National Academy of Sciences.

Holmgren and colleagues also report that in vitro, the acquired oncogenes were lost from the cells after a few generations. The oncogenes were only passed from one generation to the next if they were beneficial to the life of the cell. In vitro, the oncogenes conferred no advantage and were discarded.

However, when mouse cells lacking the p53 gene and carrying the oncogenes were implanted into live mice, the cells became tumorigenic and thrived. These cells retained the new oncogenes.

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Bergsmedh, A. et al. Horizontal transfer of oncogenes by uptake of apoptotic bodies. Proc Natl Acad Sci USA 98, 6407-6411 (May 22, 2001).

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