Transcription Factor ATF2 Cooperates with v-Jun To Promote Growth Factor-Independent Proliferation In Vitro and Tumor Formation In Vivo

Abstract

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-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.

Artificial oncoproteins: modified versions of the yeast bZip protein GCN4 induce cellular transformation

“…Chimeras in which the zipper domain of Jun is replaced with that of GCN4 form only homodimers. The transforming activity of these constructs suggests that heterodimerization between Jun and other bZip proteins is not required for transformation (Bos et al, 1990;Huguier et al, 1998). In order to eliminate possible interactions with partner proteins that bind to Jun outside the zipper sequence, we have replaced all Jun sequences in our constructs.…”

Distinct roles of Jun : Fos and Jun : ATF dimers in oncogenesis

“…In multiple cell lines (Hela, F9, NIH3T3 and CEF), Jun-m1 only e ciently transactivates promoters via Jun : ATF(-like) sites, which can be enhanced by co-addition of ATF2, but not of c-Fos. In contrast, Jun-m0 only can activate transcription via Jun : Fos(-like) sites, which is further enhanced by co-transfection of c-Fos, but not of ATF2 Huguier et al, 1998). These mutants are, therefore, powerful tools for the analysis of Jun : Fos-and Jun : ATF2-speci®c functions.…”

“…(The levels of JunD are low in CEFs and appear also to be down-regulated upon transformation by v-Jun; M Hartl, personal communication) Co-immunoprecipitation assays con®rmed that the endogenous avian Fra2 and ATF2 proteins indeed speci®cally interact with the exogenous wild-type or mutant Jun molecules. Fra2 and ATF2 are the only Fos and ATF family members known so far to be constitutively present in the Jun-transformed CEFs (Nishina et al, 1990;Huguier et al, 1998).…”

Hepatocyte growth factor/scatter factor activates proliferation in melanoma cells through p38 MAPK, ATF-2 and cyclin D1

“…The transcription factor ATF-2 controls gene expression via CRE/ATF-2 binding motifs either as a homodimer or heterodimer (Landshultz et al, 1988;Maekawa et al, 1989;Hai et al, 1989). ATF-2 has never been directly implicated in oncogenesis; however, it enhances resistance to UV irradiation-induced apoptosis of late stage melanoma cells (Ronai et al, 1998), and cooperates with v-Jun in promoting proliferation and tumor formation (Huguier et al, 1998). ATF-2 is activated both by JNK/SAPK and p38 stress kinases, and is involved in the transcriptional regulation of a number of oncogenes (i.e.…”