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ATF-2 is preferentially activated by stress-activated protein kinases to mediate c-jun induction in response to
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.
Insights
The study reveals distinct signaling pathways regulate the c-jun promoter via ATF-2 and c-Jun. Stress signals activate ATF-2, while TPA activates c-Jun, demonstrating fine-tuned gene expression control.
Area of Science:
- Molecular Biology
- Cellular Signaling
- Gene Regulation
Background:
- The c-jun promoter is regulated by ATF-2 and c-Jun transcription factors, which form pre-bound heterodimers.
- These factors are differentially activated by various extracellular signals, including DNA damage and phorbol esters.
- Understanding these distinct regulatory pathways is crucial for comprehending cellular responses to stress and stimuli.
Purpose of the Study:
- To elucidate the specific roles of ATF-2 and c-Jun in c-jun promoter regulation.
- To investigate the distinct signaling pathways that modulate the transactivating potential of ATF-2 and c-Jun.
- To determine how different extracellular signals converge on these transcription factors.
Main Methods:
- Utilized F9 cells lacking c-Jun but expressing ATF-2 to study ATF-2 specific responses.
- Investigated the effects of genotoxic agents (UV, MNNG, MMS) and phorbol ester (TPA) on c-jun transcription.
- Examined the role of specific threonine residues (69 and 71) in ATF-2 and the involvement of stress-activated protein kinases (SAPKs).
Main Results:
- Genotoxic agents like UV and MMS preferentially stimulate ATF-2 transactivation, while TPA enhances c-Jun transactivation.
- UV and MMS induce c-jun transcription in F9 cells, highlighting ATF-2's role in stress-induced expression.
- SAPKs (p54 and p46) phosphorylate ATF-2, but their activity is not increased by TPA, suggesting a distinct kinase for c-Jun activation by TPA.
Conclusions:
- Distinct signal transduction pathways converge on the c-Jun/ATF-2 complex.
- Each subunit (ATF-2 and c-Jun) is individually regulated by specific protein kinases.
- This differential regulation allows for fine-tuned modulation of c-jun gene expression in response to diverse extracellular signals.