c-Jun NH2-terminal Kinases Target the Ubiquitination of Their Associated Transcription Factors

Abstract

Regulatory proteins are often ubiquitinated, depending on their phosphorylation status as well as on their association with ancillary proteins that serve as adapters of the ubiquitination machinery. We previously demonstrated that c-Jun is targeted for ubiquitination by its association with inactive c-Jun NH 2 -terminal kinase (JNK). Phosphorylation by activated JNK protects cJun from ubiquitination, thus by prolonging its half-life. In the study reported here, we determined the ability of JNK to target ubiquitination of its other substrates (Elk1 and activating transcription factor 2 (ATF2)) and associated proteins (ATF2 and JunB). We demonstrate that phosphorylation by JNK protects ATF2, but not Elk1, from JNK-targeted ubiquitination. We also show that association of inactive JNK with JunB or ATF2 is necessary to target them for ubiquitination. Unlike its targeting of c-Jun, JNK requires additional cellular components, yet to be identified, to target the ubiquitination of ATF2. Elk1 is phosphorylated by JNK, but JNK neither associates with nor targets Elk1 for ubiquitination. The implications for the dual role of JNK in the regulation of ubiquitination and stability of c-Jun, ATF2, and JunB in normally growing versus stressed cells are discussed.

Role of the ATFa/JNK2 complex in Jun activation

“…It has indeed been shown that phosphorylation by JNK protects substrates from JNK-targeted ubiquitinylation and subsequent proteolytic degradation (Fuchs et al, 1996(Fuchs et al, , 1997Musti et al, 1997). Interestingly, we recently identi®ed UBC9, a ubiquitin conjugating enzyme (Kovalenko et al, 1996), as a potential partner of ATFa, using a two-hybrid screen in yeast (unpublished results).…”

“…The JNKs were initially identi®ed by their ability to bind the N-terminus of the c-Jun protein, on a site (now de®ned as the docking site) encompassing amino acids 33 ± 47, and to subsequently phosphorylate the Ser63 and Ser73 residues (Whitmarsh and Davis, 1996;Minden and Karin, 1997). Phosphorylation of these sites stimulates the ability of c-Jun to activate transcription of speci®c target genes by a mechanism which remains largely unknown: it has been proposed, for example, that this phosphorylation may indirectly protect c-Jun from ubiquitinylation, thereby prolonging its half-life (Fuchs et al, 1996(Fuchs et al, , 1997; alternatively, this phosphorylation may induce the dephosphorylation of Thr231, Ser243 and Ser249 residues and, as a consequence, increase cJun DNA-binding activity (Papavassiliou et al, 1995).…”

Proteomic identification of C/EBP-DBD multiprotein complex: JNK1 activates stem cell regulator C/EBPα by inhibiting its ubiquitination

“…C/EBPa physically interacts with JNK1 in vitro and in vivo c-Jun N-terminal kinase (JNK) is an important member of mitogen-activated protein kinase (MAPK) family and regulates the activity of its physically associated substrates (Fuchs et al, 1997). Therefore, we chose JNK to study the biological relevance of its interaction with C/EBPa.…”

MAPK signaling in neurodegeneration: influences of flavonoids and of nitric oxide

“…In addition to c-Jun, JNKs also phosphorylate other AP-1 proteins, including JunB and JunD [25,95]. The regulatory effect of JNKs on AP-1 transcription might not only be due to phosphorylation of Jun but may also involve JNKregulated ubiquitin-mediated degradation of AP-1 proteins [66,67]. JNKs appear to be essential in cytokine and stressinduced activation of AP-1 but are not required for AP-1 activation in response to other stimuli.…”