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Abstract Many oncogenes stimulate cell proliferation, but
some lead cells to programmed death (apoptosis). An
antiapoptotic function has been reported with activated Ha-ras
oncogene, but the apoptotic function of Ha-ras oncogene was
seldomly reported so far. A transformed cell line designated 7-4
cell (derived from mouse NIH/3T3 cell) containing an inducible
Ha-ras transgene and an E.coli lac I repressor gene has been
established in our laboratory. Under serum depleted condition
while Ha-ras oncogene was overexpressed, most of 7-4 cells
arrested at S-phase and subsequently died of apoptosis. In this
study, we showed that 7-4 cell apoptosis was not due to down-
regulation of endogenous bcl-2 and bcl-x expression. We also
demostrated that Ha-ras induced 7-4 cell apoptosis could be
inhibited by cycloheximide indicating that protein synthesis was
required in the process. Moreover, to explore the role of bcl-2
gene in Ha-ras induced cell apoptosis, the plasmid pC△j-bcl-2
encoding the human bcl-2 gene driven by an SV40 promoter was
transfected into 7-4 cells. Overexpression of bcl-2 gene
reversed the altered morphology and suppressed 7-4 cell
apoptosis, but did not affect Ha-ras gene expression, indicating
that bcl-2 action is not at the up-stream of Ha-ras gene
expression. Cell cycle analysis showed that 7-4 cell arrested at
S phase, and bcl-2 overexpression could prevent 7-4 cells
arresting at S phase. Our study also showed that the cell cycle
related kinase p34cdc2 protein expression level was not involved
in 7-4 cell apoptosis. Its influence may be at phosphorylation
level. Overexpression of bcl-2 gene alone in 7-4 cells was
insufficient for colony formation on soft agar, whereas combined
with Ha-ras gene overexpression enhanced the efficiency of
colony formation, indicating that overexpression of bcl-2 plus
Ha-ras increased the potency of cell transformation. On the
contrary, bcl-2 overexpression inhibited the tumor formation
induced by Ha-ras gene overexpression in BALB/c mice, and the
mechanism was unclear.
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