A decrease in proteasome activity induces an activation of the myelin basic protein promoter

CA CALATAYUD, CI GARCÍA, PM PAEZ, EF SOTO, JM PASQUINI AND LA PASQUINI

Madison, Wisconsin

Congreso; thirty-Sixth Annual Meeting; 2005

American Society of Neurochemistry

The Ub-proteasome system (UbPS) participates in the oligodendroglial cell (OLGc) differentiation. The addition of a proteasome inhibitor, lactacystin (Lc), to a primary OLGc culture, produces arrest of the cell cycle and cell differentiation. The regulation of the mbp gene takes place particularly at the beginning of transcription. The mbp promoter contains numerous binding sites to different transcription factors, among them Sp1. The level of expression of some of these factors is regulated through the UbPS. To elucidate the mechanism and the signal transduction pathways participating in the accelerated maturation of OLGcs induced by a decrease in proteasome activity, we used an OLGc line (N20.1), transiently transfected with the mbp promoter bound to a reporter gene (b-galactosidase) and different inhibitors of signal transduction pathways. Proteasome inhibitors (Lc and MG132) were able to significantly increase the expression of the mbp promoter. Regarding the signaling pathways participation, our results seem to indicate thattyrosine kinase and PI3K-Akt participate positively in the effect of Lc and MG132. PKA, Ras-Ras-MAPK-MEK/ERK1 and Ca-CaM seem to contribute negatively to such effect. When a PKC inhibitor and an Sp1-DNAbinding inhibitor were tested, the expression of the mbp promoter was markedly decreased and it was reverted by Lc or MG132. The decrease in proteasome activity also produced a significant increase in p27 and Sp1 levels and an increased binding of Sp1 to DNA. These results indicate that the increased activation of the mbp promoter by partial inhibition of the proteasome could be due in part to the stabilization  of p27 and Sp1.