Transcription factor PEA3 participates in the induction of urokinase plasminogen activator transcription in murine keratinocytes stimulated with epidermal growth factor or phorbol-ester.

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Keratinocytes in culture represent cells which exhibit continued and controlled growth in the organism. We have investigated the synthesis of urokinase plasminogen activator mRNA in exponentially growing cultures of primary murine keratinocytes and the keratinocyte cell line BALB/MK. The tumor promotor 12-O-tetradecanoyl phorbol-13-acetate (TPA) and epidermal growth factor (EGF) induced urokinase mRNA synthesis. We made a series of progressive 5' deletions as well as internal deletions in the region upstream of the murine uPA gene. These were joined to the cat reporter gene, and used to map the TPA and EGF responsive regions of the promoter. We found both responsive sequences within a 90 base pair Hae III fragment, located 2.4 kb. upstream of the mRNA cap site. This DNA fragment conferred TPA inducibility on reporter gene expression independent of its distance and orientation to the transcription initiation site. Footprinting and gel retardation studies identified the responsible sequence to be a binding site for PEA3 juxtaposed to an octameric TRE-element. Transfections with point mutants showed that these target sequences were necessary for TPA and EGF induction of transcription.

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