Hyposmolarity regulates p75NTR expression in central neurons through changes in SP1 activity

RAMOS AJ; BARKER PA

Washington DC, USA

Congreso; 34th Annual Meeting of the Society for Neuroscience; 2005

Society for Neuroscience

The p75NTR is involved in neuronal functions that range from induction of apoptosis and inhibition of growth to the promotion of survival. p75NTR expression is induced in central neurons by a wide range of pathological conditions, including stroke, epilepsy and traumatic brain injury, but the cellular mechanisms regulating this response are unknown. Peterson and Bogenman (2003) recently reported that hypo-osmolarity can increase p75NTR levels in several cell lines, raising the possibility that post-traumatic edema may contribute to injury-induced p75NTR expression.  We have studied the hyposmolarity-induced p75NTR expression to identify elements controlling p75NTR expression. We found that hyposmolarity robustly induces p75NTR expression in cell lines and in primary mouse cortical neurons and established that this effect did not require translation of new proteins.  To begin to identify elements in the p75NTR promoter that respond to this effect, we compared 25 kB of genomic sequence lying upstream of the p75NTR transcriptional start site and identified 8 conserved clusters. Each of these clusters was cloned into luciferase reporters and hyposmolarity responsiveness was assessed. 6 of 8 were induced by hyposmolarity and we focused on the most proximal of these for further analysis. We identified a potential silencer element to which binding of trans factors was reduced by hyposmolarity and also noted that the proximal fragment was rich in SP1 binding sites. We found that cells exposed to hyposmolarity have increased SP1 DNA binding activity and found that transfection with dominant-negative SP1 construct (DN-Sp1) reduced hyposmolarity-induced 75NTR expression. These data indicate that hyposmolarity is a potent inducer of p75NTR expression in central neurons and suggest that a novel silencer element and SP1 binding sites may function together to regulate p75NTR transcription. This work was supported by the Canadian Institutes of Health Research and by the Killam Foundation