Cyclic AMP inducibility of the myelin basic protein gene promoter requires the NF1 site

In the central nervous system oligodendrocyte differentiation is accompanied by the activation of a specific transcriptional program responsible for the synthesis of myelin genes. One of the signals leading to the expression of myelin components, such as the myelin basic protein (MBP) gene is cyclic AMP (cAMP). Previous work using a cell line in which the endogenous MBP gene can be induced by increased cAMP levels (D6P2T) showed that the region of the MBP gene that was required for induction of the gene by cAMP lay between -248 and -105 in the 5' flanking region. This region contains numerous transcription factor binding sites, including sites for NF1, Sp1, and MEBA. In order to determine if the NF1 site itself was specifically responsible for the cAMP responsiveness of the MBP promoter, stably transfected cells carrying MBP promoter deletion constructs were used. Deletion of just the NF1 site caused loss of responsiveness to cAMP levels. Furthermore, site-specific mutations in the NF1 site that interfere with NF1 protein binding, in the context of the full length promoter, abolished cAMP responsiveness and caused derepression of the promoter. Analysis of protein binding to the NF1 site showed that the mutation resulted in loss of binding to the site and that the proteins binding at the site are modified in the presence of cAMP elevating agents. These results demonstrate that the NF1 site is indispensable for cAMP responsiveness of the MBP promoter and, together with other DNA elements, plays a role in controlling MBP gene expression.