The essential role of the mitogen-activated protein kinase pathway and c-Jun induction in epidermal growth factor (EGF)-induced gene expression of human 12(S)-lipoxygenase was studied. Transfection of cells with Ras, ERK2, Rac and JNK dominant negative mutants all inhibited the EGF-induced promoter activation of the 12(S)-lipoxygenase gene. The EGF induced the expression of c-Jun, and overexpression of c-Jun induced the expression of 12(S)-lipoxygenase mRNA. The Sp1-binding sites in the promoter region of the 12(S)-lipoxygenase gene were requisite for the c-Jun response, which was similar to that observed in the EGF response. Furthermore, the EGF stimulated the interaction between c-Jun and Sp1. The co-expression of the c-Jun dominant negative mutant inhibited the interaction between c-Jun and Sp1, and the promoter activation of the 12(S)-lipoxygenase gene, which was induced by c-Jun overexpression in cells. The EGF activated the chimeric promoter consisting of 10 tandem GAL4-binding sites, which replaced the three Sp1-binding sites in the 12(S)-lipoxygenase promoter only when co-expressed with GAL4-c-Jun (1–223) fusion proteins. These results indicate that the direct interaction between c-Jun and Sp1 induced by the EGF cooperatively activated expression of the 12(S)-lipoxygenase gene, and that Sp1 may function at least in part as a carrier to bring c-Jun to the promoter.
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