Leucine Repeats and an Adjacent DNA Binding Domain Mediate the Formation of Functional cFos-cJun Heterodimers

Abstract

The discovery that the AP-1 family of enhancer binding factors includes a complex of the cellular Fos (cFos) and cellular Jun (cJun) proteins established a direct and important link between oncogenesis and transcriptional regulation. Homodimeric cJun protein synthesized in vitro is capable of binding selectively to AP-1 recognition sites, whereas the cFos polypeptide is not. When cotranslated, the cFos and cJun proteins can form a stable, heterodimeric complex with the DNA binding properties of AP-1/cJun. The related proteins Jun B and vJun are also able to form DNA binding complexes with cFos. Directed mutagenesis of the cFos protein reveals that a leucine repeat structure is required for binding to cJun, in a manner consistent with the proposed function of the "leucine zipper." A novel domain adjacent to, but distinct from, the leucine repeat of cFos is required for DNA binding by cFos-cJun heterodimers. Thus experimental evidence is presented that leucine repeats can mediate complex formation between heterologous proteins and that promotes further understanding of the molecular mechanisms underlying the function of two proto-oncogene products.

The protein kinase C-η isoform induces proliferation in glioblastoma cell lines through an ERK/Elk-1 pathway

“…The following expression vectors were obtained from UCSF: c-jun (Turner and Tjian, 1989), Gal-c-jun, Gal-c-jun 63/73 and Gal-Elk-1 (originally from Richard Treisman). Coll73: luciferase, (GAL-RE) 5 : luciferase and actin b-galactosidase reporter constructs have been described (Lopez et al, 1993;Uht et al, 1997;Webb et al, 1999).…”

Inhibition of c-Jun DNA binding by mitogen-activated protein kinase.

“…These findings suggest that phosphorylation of serine 243 prevents c-Jun from binding to the TRE, either by inhibiting dimer formation or by inhibiting interaction of the dimer with the TRE. c-Jun homodimers can be trapped by glutaraldehyde cross-linking and detected as 80-to 90-kDa species on SDS polyacrylamide gels (Turner and Tjian, 1989). cJun phosphorylated in vitro by p42 MAP kinase was found to be capable of forming dimers ( Figure 6B).…”

“…Glutaraldehyde Cross-Linking 32P-labeled c-Jun samples were treated with 0.001% glutaraldehyde at room temperature for 1 h to cross-link Jun-Jun dimers, as described (Turner and Tjian, 1989). Samples were subjected to electrophoresis on 10% polyacrylamide SDS gels.…”

Suppression of ischemia‐induced fos expression and AP‐1 activity by an antisense oligodeoxynucleotide to c‐fos mRNA

“…Glutamate receptor-mediated activation of phospholipases and protein kinases results in the alteration of nuclear regulatory processes, including the expression of immediate early genes such as c-fos, junB, and c-jun [5,12]. The Fos, Jun, and JunB proteins have been shown to form activator protein 1 (AP-1) through a conserved dimerization domain, i.e., the leucine zipper [13]. Transcription regulator AP-1 protein binds a specific DNA motif and is believed to transactivate the expression of a number of late effector genes [14][15][16][17][18][19].…”