Abstract
The dominant negative c‐jun TAM‐67 has been shown to inhibit tumor promotion induced by 12‐O‐tetradecanoylphorbol‐13‐acetate and okadaic acid (OA). To better understand this phenomenon, we investigated the mechanism of action of TAM‐67 in response to OA. To identify the mechanism of action, we used a 6xHis‐tagged TAM‐67 as well as chimeric constructs of TAM‐67 that either cannot bind DNA or cannot heterodimerize with wild‐type transcription factors. The results of these studies indicated that TAM‐67 acts by blocking or squelching. The results of elecrophoretic mobility‐shift assays showed that TAM‐67 must act by squelching in response to OA, as TAM‐67 cannot be found in DNA‐binding complexes. We then identified some of the proteins with which TAM‐67 interacts. They include all members of the jun and fos families as well as the cAMP response element binding protein, activating transcription factor‐1, activating transcription factor‐2, and RelA (p65). Thus, we have shown that TAM‐67 squelches the induction of activating transcription factor‐1 transactivation in response to OA and that TAM‐67 is capable of interacting with proteins that control transactivation by binding to the 12‐O‐tetradecanoylphorbol‐13‐acetate response element, cAMP response element and nuclear factor‐κB sites. © 2002 Wiley‐Liss, Inc.