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An inducible 212 cell line was established from NIH3T3 cells
using Escherichia coli lactose regulatory system to regulate Ha-
ras oncogene expression. But basal level expression of Ha-ras
oncogene was always detectable in 212 cells without induction.
To improve the strengency of repression, a 7-4 cell line was
established using a Stratagene repressor gene with a nuclear
localization signal (NLS) outside the tetramer formation
region. However, basal level expression of Ha-ras oncogene was
still detectable in 7-4 cells. Activation of Ha-ras oncogene in
7-4 cell line suppressed gelsolin gene mRNA expression
accompained with cells'' rounding up. Additionally, the mRNA and
protein levels of .alpha.-actinin decreased only in 7-4 cell
line. On contrary, the mRNA level of vimentin gene increased in
7-4 and 212 cell lines. Ha-ras oncogene expression decreased
after removal of Isopropyl-.beta.-D-thiogalactoside (IPTG) and
the mRNA levels of .alpha.-actinin, gelsolin and vimentin genes
correspondently reversed to their normal levels, indicating the
close relationship among Ha-ras oncogene and these cytoskeleton
-related genes. Cell cycle study show that only 7-4 cells were
arrested at S phase when they were cultured in medium
containing 0.2% serum with Ha-ras oncogene overexpression. The
chromosome numbers were compared in both cell lines. It
increased in 212 cells but decreased in 7-4 cells. Moreover,
short period Ha-ras oncogene overexpression caused minor
changes of the chromosome modal numbers in both cell lines. In
this study, the findings of : 1). the arrestng of cell cycle in
7-4 cell line could lead to the investigation of the role of Ha-
ras oncogene between cell proliferation and cell death. 2).
the changes of chromosome modal mumbers could be used to study
the mechanism of DNA instability caused by Ha-ras oncogene
overexpression.
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