Neurotrophin-3 and a CREB-mediated signaling pathway regulate Bcl-2 expression in oligodendrocyte progenitor cells.

Our previous results suggested that the transcription factor CREB mediates the actions of neuroligands and growth factor signals that coupled to different signaling pathways may play different roles along oligodendrocyte (OLG) development. We showed before that CREB phosphorylation in OLG progenitors is up-regulated by neurotrophin-3 (NT-3); and moreover CREB is required for NT-3 to stimulate the proliferation of these cells. We now show that treatment of OLG progenitors with NT-3 is also accompanied by an increase in the levels of the anti-apoptotic protein Bcl-2. Interestingly, the presence of a putative CREB binding site (CRE) in the Bcl-2 gene raised the possibility that CREB could also be involved in regulating Bcl-2 expression in the OLGs. Supporting this hypothesis, the NT-3 dependent increase in Bcl-2 levels is abolished by inhibition of CREB expression. In addition, transient transfection experiments using various regions of the Bcl-2 promoter and mutation of the CRE site indicate a direct role of CREB in regulating Bcl-2 gene activity in response to NT-3. Furthermore, protein-DNA binding assays show that the CREB protein from freshly isolated OLGs indeed binds to the Bcl-2 promoter CRE. Together with our previous results, these observations suggest that CREB may play an important role in linking proliferation and survival pathways in the OLG progenitors.