ATF-2 is preferentially activated by stress-activated protein kinases to mediate c-jun induction in response to genotoxic agents.

Abstract

The major regulators of the c‐jun promoter are ATF‐2 and c‐Jun. They act as pre‐bound heterodimers on two ‘AP‐1‐like’ sites, and are preferentially addressed by different types of extracellular signals. The transactivating potential of ATF‐2 is stimulated to a higher extent than that of c‐Jun by a broad group of agents causing DNA damage and other types of cellular stress, such as short‐wavelength UV, or the alkylating compounds N‐methyl‐N’‐nitro‐N‐nitroso‐guanidine (MNNG) or methylmethanesulphonate (MMS). In contrast, treatment with the phorbol ester TPA preferentially enhances c‐Jun‐dependent transactivation but does not affect ATF‐2. Accordingly, UV and MMS but not TPA induce c‐jun transcription in F9 cells, which express ATF‐2, but not c‐Jun. Stimulation of ATF‐2‐dependent transactivation by genotoxic agents requires the presence of threonines 69 and 71 located in the N‐terminal transactivation domain. These sites are the target of p54 and p46 stress‐activated protein kinases (SAPKs) which bind to, and phosphorylate ATF‐2 in vitro. However, p46 and p54 kinase activity is not increased by phorbol ester, which strongly suggests that the protein kinase phosphorylating c‐Jun in response to TPA is distinct from SAPKs and does not act on ATF‐2. Our data demonstrate that distinct signal transduction pathways converge at c‐Jun/ATF‐2, whereby each subunit is individually addressed by a specific class of protein kinases. This allows fine tuned modulation of c‐jun expression by a large spectrum of extracellular signals.

Role of the ATFa/JNK2 complex in Jun activation

“…To complete the picture, the following sequence of events may be inferred from our present ®ndings: after cell treatment with stressinducing agents, activated JNK2 is recruited by ATFa into ATFa/JunD heterodimers where it may phosphorylate and thereby activate JunD; eventually, this may result in c-Jun promoter stimulation and increased cJun expression. Following c-Jun accumulation, ATFa/cJun heterodimers (or c-Jun homodimers) would in turn replace ATFa/JunD heterodimers and ultimately lead to the induction of cell proliferation (van Dam et al, 1995;Wang et al, 1996).…”

“…The JNKs have recently been found to phosphorylate and activate other transcription factors like Elk1 (Cavigelli et al, 1995) or ATF2 (Gupta et al, 1995;Livingstone et al, 1995;van Dam et al, 1995). ATF2 forms homodimers but can also readily heterodimerize with other members of the ATF and Jun/Fos families (Benbrook and Jones, 1990;Hai and Curran, 1991;Lee, 1992), thus yielding factors with extended regulatory potentials.…”

“…ATF2 forms homodimers but can also readily heterodimerize with other members of the ATF and Jun/Fos families (Benbrook and Jones, 1990;Hai and Curran, 1991;Lee, 1992), thus yielding factors with extended regulatory potentials. ATF2 has indeed been found to mediate transcriptional activation of speci®c target genes by adenovirus E1a (Maekawa et al, 1991;Flint and Jones, 1991;Green, 1990, 1993) or by stress-inducing agents (van Dam et al, 1995). While residues 20 ± 60 of ATF2 are required for binding of JNK1, phosphorylation occurs on two closely spaced residues (Thr69 and Thr71) located within the Nterminal activation domain of ATF2 (Gupta et al, 1995;Livingstone et al, 1995).…”

Diverse functions of JNK signaling and c-Jun in stress response and apoptosis

“…Their expression is subject to regulation by a large number of stimuli and signaling pathways (Whitmarsh and Davis, 1996). Other AP-1 codinggenes, such as junD and ATF-2, are expressed at fairly constant levels (de Groot et al, 1991;Gupta et al, 1995;Hirai et al, 1989;Van Dam et al, 1995).…”

The N-terminal transactivation domain of ATF2 is a target for the co-operative activation of the c-jun promoter by p300 and 12S E1A

“…Expression of c-jun is induced in response to various stimuli, including growth factors (Ryseck et al, 1988;Quantin and Breathnach, 1988), cytokines (Brenner et al, 1989), transforming oncogenes such as v-src, Ha-ras and E1A (van Dam et al, , 1993Angel and Karin, 1991), tumor promoters (like 12-O-tetradecanoylphorbol-13-acetate (TPA); Angel et al, 1988) and DNA-damaging agents (Devary et al, 1991;Stein et al, 1992;van Dam et al, 1995). Activation of c-jun transcription by most of these agents has been shown to be mediated by two AP1/ ATF-like binding elements, designated jun1 and jun2 elements (Devary et al, 1991;Stein et al, 1992;van Dam et al, , 1993van Dam et al, , 1995. In vitro binding studies using extracts from various primary and transformed cell lines have shown that these elements can bind cJun/ATF2 and cJun/ATF3 heterodimers and heterodimers composed of cJun and a protein sharing homology with ATF2 (van Dam et al, 1993;Hagmeyer et al, 1996).…”