A NOVEL CYCLIC-AMP RESPONSE ELEMENT, CACTTGATC, MEDIATES FORSKOLIN INDUCTION OF THE MYELIN BASIC-PROTEIN PROMOTER IN THE RAT SCHWANNOMA LINE, D6P2T

The rat Schwannoma cell line D6P2T constitutively expresses the mRNA e ncoding the major myelin protein, P-0, but only expresses the mRNA enc oding myelin basic protein (MBP) after exposure to forskolin or other substances that raise the levels of intracellular cyclic AMP. In this study we have investigated the molecular basis for forskolin induction of MBP transcription in D6P2T cells. We have found that a 9-bp sequen ce element, CACTTGATC, located between nucleotides -85 and -77 in the MBP promoter, is necessary for forskolin induction of chloramphenicol acetyltransferase (CAT) expression after transient transfection of MBP promoter-CAT fusion constructs into D6P2T cells. Although similar DNa se I footprints, one of which is located within the above 9-bp sequenc e element, are produced by nuclear extracts prepared from both forskol in-treated and untreated cells, this same sequence can be shown to int eract with a forskolin-inducible protein complex using an electrophore tic mobility shift assay. In addition, mutation of this 9-bp sequence abolishes both formation of this new protein-DNA complex and forskolin -inducible CAT expression from the heterologous SV40 promoter. Finally , we have shown that the appearance of this forskolin-inducible protei n-DNA complex precedes that of MBP mRNA. Taken together, these data st rongly support the notion that the induction of MBP transcription by f orskolin in D6P2T cells is mediated by the binding of a forskolin-indu cible protein complex to the MBP promoter sequence CACTTGATC.