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Molecular and Cellular Biology, December 1998, p. 7020-7029, Vol. 18, No. 12
Unité de Virologie Humaine, Institut
National de la Santé et de la Recherche Médicale
(INSERM-U412), Ecole Normale Supérieure, 69364 Lyon Cedex 07, France,1 and
Sylvius Laboratories,
Leiden University Medical Center, 2300 RA Leiden, The
Netherlands2
Received 18 May 1998/Returned for modification 1 July 1998/Accepted 4 September 1998
ATF2 belongs to the bZIP family of transcription factors and
controls gene expression via 8-bp ATF/CREB motifs either as a homodimer
or as a heterodimer
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Transcription Factor ATF2 Cooperates with v-Jun To
Promote Growth Factor-Independent Proliferation In Vitro and Tumor
Formation In Vivo
for instance, with Jun
but has never been shown
to be directly involved in oncogenesis. Experiments were designed to
evaluate a possible role of ATF2 in oncogenesis in chick embryo
fibroblasts (CEFs) in the presence or absence of v-Jun. We found that
(i) forced expression of ATF2 cannot alone cause transformation, (ii)
overexpression of ATF2 plus v-Jun specifically stimulates v-Jun-induced
growth in medium with a reduced amount of serum, and (iii) the
efficiency of low-serum growth correlates with the activity of a
Jun-ATF2-dependent model promoter in stably transformed CEFs. Analysis
of ATF2 and Jun dimerization mutants showed that the growth-stimulatory
effect of ATF2 is likely to be mediated by v-Jun-ATF2 heterodimers
since (i) v-Jun-m1, a mutant with enhanced affinity for ATF2, induces
growth in low-serum medium much more efficiently than v-Jun, when
expressed alone or in combination with ATF2; and (ii) ATF2/fos, a
mutant that efficiently binds to v-Jun but is unable to form stable
homodimers, shows enhanced oncogenic cooperation with v-Jun. In
addition, we examined the role of ATF2 in tumor formation by
subcutaneous injection of CEFs into chickens. In contrast to v-Jun,
v-Jun-m1 gave rise to numerous fibrosarcomas while coexpression of ATF2
and v-Jun-m1 led to a dramatic development of fibrosarcomas visible
within 1 week. Together these data demonstrate that overexpressed ATF2
potentiates the ability of v-Jun-transformed CEFs to grow in low-serum
medium in vitro and contributes to the formation of tumors in vivo.
*
Corresponding author. Mailing address: INSERM-U412, 46 Allée d'Italie, 69364 Lyon Cedex 07, France. Phone:
33-(0)4-7272-8165. Fax: 33-(0)4-7272-8696. E-mail:
marc.castellazzi{at}ens-lyon.fr.
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