Rar. Hurta et Ja. Wright, ORNITHINE DECARBOXYLASE GENE-EXPRESSION IS ABERRANTLY REGULATED VIA THE CAMP SIGNAL-TRANSDUCTION PATHWAY IN MALIGNANT H-RAS TRANSFORMED-CELL LINES, Journal of cellular physiology, 161(2), 1994, pp. 383-391
We have tested the hypothesis that H-ras transformed cells contain alt
erations in signal pathways important in controlling the expression of
ornithine decarboxylase (ODC), the highly regulated rate-limiting act
ivity in the biosynthesis of polyamines. Mouse 10T1/2 fibroblasts and
a series of 10T1/2 H-ras transformed cell lines were treated with stim
ulators of cAMP synthesis (forskolin and cholera toxin), a biologicall
y stable analogue of cAMP (8-bromo-cAMP), and an inhibitor of cAMP deg
radation (3-isobutyl-1-methylxanthine). Elevations in ODC gene express
ion were noted in H-ras transformed cells that were not observed in pa
rental 10T1/2 fibroblasts. The forskolin-mediated effects were not det
ected with 1,9-dideoxyforskolin, a compound structurally related to fo
rskolin, which does not activate adenyl cyclase. The effects observed
with cholera toxin were not detected when cells were treated with the
purified subunits of this compound, indicating that the toxin-induced
effects were cAMP-specific. Actinomycin D treatment prior to forskolin
exposure reduced the elevation observed in ODC gene expression indica
ting the involvement of the transcriptional process. Furthermore, we o
bserved that cycloheximide treatment of malignant but not benign H-ras
transformed cells significantly elevated ODC message level. Treatment
of malignant cells with both cycloheximide and forskolin together res
ulted in a further additive elevation in ODC message, but a similar tr
eatment of benign tumor cells reduced the forskolin-mediated increase
in ODC message. In addition, treatment of H-ras transformed cells with
the tumor promoter, 12-0-tetradecanoylphorbol-13-acetate (TPA) led to
an elevation in ODC mRNA levels not observed in parental 10T1/2 fibro
blasts. However, an increase in ODC message levels was observed in par
ental 10T1/2 cells treated with a combination of TPA and forskolin. Ex
posure of H-ras transformed cells to TPA and forskolin together led to
further pronounced increases in ODC message when compared to treatmen
t with TPA or forskolin alone. These results demonstrate aberrant regu
lation of signal pathways involved in controlling ODC gene expression
in H-ras transformed cells and provide further insight into the altere
d growth regulatory program associated with malignant transformation.
(C) 1994 Wiley-Liss, Inc.