The antiapoptotic gene bcl-2 prevents reactivation of the senescence program induced by the histone deacetylase inhibitor sodium butyrate in rat fibroblasts transformed by the oncogenes E1A and c-Ha-Ras

Abstract

The role of the gene bcl-2 conferring resistance to apoptosis in the activation of the cellular senescence program induced by the histone deacetylase inhibitor (HDACi) sodium butyrate (NaBut) has been studied in transformed rat fibroblasts. The work was carried out in the rat embryo fibroblast cell line transformed by the oncogenes E1A, cHa-Ras, and bcl-2 (ERasBcl cells) resistant to apoptosis. The parent line of E1A-and cHa-Ras-transformed cells (ERas cells) was used as a control. It has been shown that NaBut suppresses the proliferation of ERasBcl cells to a much lesser extent than do the control ERas cells, in spite of the delay in cell cycle progression in the G1 phase for both lines. NaBut-induced hypertrophy is less marked in ERasBcl cells than in ERas cells due to the lower level of activation of the mTORC1 complex controlling protein synthesis and ribosome biogenesis. The activation of mTORC1 was assessed from the phosphorylation of its targets: ribosomal protein S6 and the inhibitor of translation initiation factor eIF4E (4E-BP1). Investigation of the dynamics of the level of one of the major markers of autophagosome formation (protein LC3) has shown the transient character of NaBut-induced accumulation of lipid-bound form LC3-II marking autophagosome membranes in bcl-2-expressing transformants in contrast to the ERas line. In addition, in ERasBcl cells there was no activation of the senescence-associated β-galactosidase (the marker for senescent cells). The results obtained suggest that the high level of expression of bcl-2, which blocks apoptotic cell death, prevents the implementation of the NaBut-induced tumor-suppressive cellular senescence program.