Mitogen-activated protein (MAP) kinase, extracellular-signal-regulated kinases (ERKs) play an important role in activating AP-1-dependent transcription. Studies using the JB6 mouse epidermal model and a transgenic mouse model have established a requirement for AP-1-dependent transcription in tumor promotion. Tumor promoters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and epidermal growth factor induce activator protein 1 (AP-1) activity and neoplastic transformation in JB6 transformation-sensitive (P ؉ ) cells, but not in transformation-resistant (P ؊ ) variants. The resistance in one of the P ؊ variants can be attributed to the low levels of the MAP kinases, ERKs 1 and 2, and consequent nonresponsiveness to AP-1 activation. The resistant variant is not deficient in c-fos transcription. The purpose of these studies was to define the targets of activated ERK that lead to AP-1 transactivation. The results establish that the transactivation domain of Fra-1 can be activated, that activation of Fra-1 is ERK dependent, and that a putative ERK phosphorylation site must be intact for activation to occur. Fra-1 was activated by TPA in ERK-sufficient P ؉ cells but not in ERK-deficient P ؊ cells. A similar activation pattern was seen for c-Fos but not for Fra-2. Gel shift analysis identified Fra-1 as distinguishing mitogen-activated (P ؉ ) from nonactivated (P ؊ ) AP-1 complexes. A second AP-1-nonresponsive P ؊ variant that underexpresses Fra-1 gained AP-1 response upon introduction of a Fra-1 expression construct. These observations suggest that ERK-dependent activation of Fra-1 is required for AP-1 transactivation in JB6 cells.

Fanconi anemia (FA) 1 is a genetic disease of cancer susceptibility marked by congenital defects, bone marrow failure, and myeloid leukemia (1-4). To date at least 11 complementation groups have been defined (5-7). Eight genes have been cloned (8 -17). However, the gene products resemble no known proteins and have few identifiable functional protein motifs. One exception is the recently cloned FANCL gene, which contains the ubiquitin ligase motif. In addition, the FANCD1 gene has been identified as BRCA2, one of the familial breast cancer genes.Cells derived from patients with the FA exhibit characteristic hypersensitivity caused by DNA cross-linking agents and generalized decreased survival (18 -22). However, no defined biochemical mechanism for this hypersensitivity has been elucidated, although studies have implicated cytokine dysregulation, excessive, oxidative damage, defects in DNA repair, and lack of cell cycle control (23-27). Patient and cellular phenotypes across all the complementation groups are similar, suggesting an inter-relatedness or cooperativity between the FA proteins.This cooperativity has been borne out by work we have done in showing binding of FANCA and FANCC in a protein complex in both nucleus and cytoplasm (28 -30). Recent work has found the FANCE, FANCF, FANCG, and FANCL proteins in the complex as well (31-34). A large complex is suggested by our recent work (35), and binding does not occur in any of the complementation groups except the FA-D1, D2, I, and J groups (7).One clue to FA function lies in the study of the FANCA protein, which contains a classic bipartite nuclear localization signal and is phosphorylated. Generally, FANCA nuclear localization, phosphorylation, and binding to FANCC are abolished in all complementation groups except the FA-D1 and D2 groups (28 -30, 33). This suggests that a nuclear event is critical to the normal function of the FA proteins, and the aberrant proteins in the FA-D groups may have a role downstream of the FA complex in the nucleus. However, some have found FANCA point mutants that are expressed, translocated to the nucleus, and are phosphorylated to some extent. Some of these mutants are of intermediate MMC sensitivity (36).Over the years, little information has been found that addresses the regulation of the FA proteins. mRNA or protein levels change little in response to DNA damage or the cell cycle. Our recent work has revealed that at least a subset of the FA proteins resides in the nucleus bound to chromatin, where increased protein binding occurs in response to DNA damage (37). One of the non-core complex FA proteins, FANCD2, becomes monoubiquitinated in response to DNA damage (38).In addition, we have shown during the cell cycle that the FA proteins detach from chromatin during mitosis, and FANCG becomes phosphorylated while remaining part of the complex (37). One group has demonstrated that FANCG has a isoform seen in asynchronous cells that is phosphatase sensitive (39).In this paper we report the identification of a phosphopeptide from ...