THE CAMP-RESPONSE-ELEMENT-BINDING PROTEIN INTERACTS, BUT FOS PROTEIN DOES NOT INTERACT, WITH THE PROENKEPHALIN ENHANCER IN RAT STRIATUM

The proenkephalin gene is a well-studied model of transcription factor -target gene interaction in the nervous system and has been proposed a s a regulatory target of the protein product of the immediate-early ge ne c-fos. This regulatory mechanism has been proposed, in part, becaus e the cAMP response element 2 (CRE-2) site, the key DNA regulatory ele ment within the proenkephalin second-messenger-inducible enhancer, avi dly binds AP-1 proteins, including Fos, in vitro. However, we observe a dissociation in the time course of activation of c-fos and proenkeph alin mRNA in rat striatum after administration of the dopamine D2 rece ptor antagonist haloperidol. This result prompted us to investigate th e composition of protein complexes in striatal nuclear extracts that b ind to the CRE-2 site. Even though our striatal nuclear extracts had s ubstantial basal and haloperidol-inducible AP-1-binding activities tha t contained Fos, we could not detect Fos in complexes bound to the CRE -2 element. Instead, as determined by antibody supershift analysis, we detect CRE-binding protein (CREB)-like proteins binding to CRE-2 in b oth basal and haloperidol-stimulated conditions. Finally, we show that haloperidol induces CREB protein phosphorylation in striatum.