ANTIAPOPTOTIC ONCOGENE bcl-2 INDUCES A PROGRAM OF SENESCENCE IN E1A + c-Ha-ras-TRANSFORMANTS TREATED
WITH ADRIAMYCIN
A. M. Nelyudova,1 S. G. Zubova, N. D. Aksenov, V. A. Pospelov, T. V. Pospelova
Institute of Cytology RAS, St. Petersburg, Russia;
1 e-mail: annanelioudova@hotmail.com
Introduction of bcl-2 gene in E1A + ñ-ßà-ras-transformed rat embryo fibroblasts, which are unable
to be arrested after damaging influences and possess high proapoptotic sensitivity, results not only in suppression of cell
death but also in re-establishment of cell cycle block following DNA damage and serum starvation. Flow cytometry showed that
E1A + c-Ha-ras + bcl-2-transformants treated with DNA-intercalator adriamycin are capable of being arrested at Gi/S boundary for
a long time (for less than 5 days). According to the growth curve data, the number of Bcl-2-overexpressing cells remanins
constant for a week of cultivation with adriamycin. Clonogenic efficacy of E1A + c-Ha-ras + bcl-2-cells is brought to no already
in 16 h after adriamycin addition. Apoptotic death, revealed by oligonucleosomic fragmentation of DNA, as well as cell death,
occurring due to mitotic catastrophe, after adriamycin treatment are almost absent in Bcl-2-overexpressing transformants, as
compared with parental E1A + c-Ha-ras-transformants. Bcl-2 introduction in E1A + c-Ha-ras-transformants is accompanied by a rise
of SA β-Gal (Senescence Associated β-Galactosidase) activity, which is commonly considered to be a marker of cell
senescence. Adriamycin treatment of E1A + c-Ha-ras + bcl-2-transformants results in a much higher rise in SA β-Gal activity,
as compared with untreated cells. Co-immunoprecipitation experiments demonstrated the introduction of Bcl-2 to result in
formation of Bcl-2 complexes with early region E1A oncoproducts, which are thought to be responsible for proapoptotic
susceptibility of E1A-expressing transformants. The data obtained lead to suggestion that bcl-2 transfer to
E1A + c-Ha-ras-transformants may induce a switch from the cell death program on the program of senescence after DNA damage, due,
presumably, to Bcl-2 interaction with the apoptosis activator the viral oncoprotein E1A.
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