The involvement of SP1 in myelin basic protein gene transcription

sheath. The level of its expression is parallel to oligodendrocyte differentiation and serves as a good marker of oligodendrocyte differentiation. Understanding oligodendrocyte differentiation can give clues to the causes and development of demyelination and how to direct oligodendrocyte progenitor cell's remyelination. Previous studies suggest that p85 can increase MBP transcription independent of the Phosphatidylinositol 3-kinase (PI3K) activity. Here we found that p85 can interact with Fyn in oligodendrocytes, raising the possibility that p85 cooperates with Fyn signaling to activate the MBP promoter.;The transcription factor Sp1 has also been reported to increase MBP promoter activity. The mechanism is unknown. We found that Sp1 phosphorylation is increased during oligodendrocyte differentiation. Using inhibitors of different pathways, we found that the protein kinase C (PKC) modulator phorbol 12-myristate 13-acetate (PMA) can increase Sp1 phosphorylation when the cells are treated for 1 hour and can decrease Sp1 phosphorylation with a longer treatment (12 hours). The increased phosphorylation of Sp1 induced by PMA in short treatments could be abolished by an Extracellular Signal-Regulated Kinase (ERK) pathway inhibitor. This indicates that PKC phosphorylates Sp1 through the ERK pathway. Mutation of Sp1 threonines 453 and 739, which are phosphorylated by ERK, decreased MBP transcriptional activity. ERK pathway activity was found to gradually increase during oligodendrocyte differentiation. Sp1 regulation by the PKC/ERK pathway is stage specific. Furthermore, the binding of Sp1 on the native MBP promoter was found to increase in differentiating oligodendrocytes. The binding of Sp1 and the levels of acetylated histone H3 on the MBP promoter increased in parallel. Inhibition of Sp1 activity by Sp1 inhibitor Mithramycin A decreased RNA polymerase II recruitment to the MBP promoter. In summary, we provide some mechanisms for how Sp1 increases MBP promoter transcription in oligodendrocytes when the cells undergo differentiation.