Regulation of trans-activating capacity of CRE-BPa by phorbol ester tumor promoter TPA

CRE-BPa, here designated as CRE-BPaα, is a novel member of the CRE (cAMP response element)-binding protein CRE-BP1 family. CRE-BPaα has four regions highly homologous to CRE-BP1, including a putative metal finger structure and a DNA-binding domain consisting of a basic amino acid cluster and a leucine zipper. CRE-BPa specifically binds to CRE as a homodimer or heterodimer with c-Jun or CRE-BP1. Here we report three alternative splicing forms of CRE-BPaa: two of them, CRE-BPaβ and CRE-BPaγ, lack the N-terminal 7 and 33 amino acids of CRE-BPaα, and the third one CRE-BPaδ, has 16 additional amino acids in the N-terminus and amino acids 156-508 of CRE-BPaα. In CAT cotransfection experiments using CV-1 cells, transient expression of each of four CRE-BPa proteins caused a 1.6- to 3.4-fold increase of CRE-dependent transcription, respectively. Interestingly, these weak frans-activating capacities of CRE-BPa proteins were enhanced 2.7- to 3.6-fold by treatment of cells with 12-O-tetradecanoyl-phorbol 13-acetate (TPA). However, CRE-BPa did not affect the TPA-induced and TRE (TPA response element)-dependent transcription. These results indicate that CRE-BPa is a CRE-dependent trans-activator, and that CRE-BPa can confer TPA inducibility on CRE. Thus, CRE-BPa has an unique characteristic of cross-talk between cAMP pathway and TPA pathway.