Common target for 12‐O‐tetradecanoylphorbol‐13‐acetate and ras in the transcriptional enhancer of the growth factor—inducible JE gene

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Abstract
JE gene expression in the mouse osteoblast cell line MC3T3‐E1 is activated transiently by the tumor promoter 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). In ras‐transformed MC3T3‐E1 cells the JE gene is constitutively expressed at a high level, whereas in their raf‐transformed counterparts it is not constitutively expressed or inducible by TPA. Using these cells, we investigated a specific sequence recognized by nuclear factors in the 5′‐upstream region of the rat JE gene. By gel‐mobility shift assays, we determined that the amount of nuclear factors that bind to the region ‐ 130 to ‐ 96 bp upstream from the cap site of the rat JE gene (JE‐1 probe) increased after TPA treatment of MC3T3‐E1 cells. However, in the ras transformants it was elevated constitutively, and in the raf transformants it was not detectable. Both unlabeled JE‐1 probe and a probe containing a TPA‐responsive element (TGACTCA) competed with the binding of these nuclear factors. Preincubation of the nuclear extracts with fos‐ or jun‐specific antibodies interfered with the binding of the factors to the JE‐1 probe. The essential sequence in the JE‐1 element for the binding of nuclear factors was found to be TTACTCA. c‐fos and c‐jun proteins synthesized in vitro could bind to the DNA fragment containing this sequence, but the binding was weaker than to the TPA‐responsive element (TGACTCA). These results suggest that the sequence TTACTCA in the JE‐1 element is a common target of TPA and ras and that protein complexes containing fos‐ and jun‐related proteins recognize the sequence.