HYPOSMOLARITY INCREASES THE EXPRESSION OF P75NTR THROUGH CHANGES IN ACTIVITY OF SP1 TRANSCRIPTION FACTOR

RAMOS AJ; FORTE S; BOUTILIER J; BARKER PA

Pinamar, Argentina

Congreso; 10th Congress of Panamerican Association for Biochemistry and Molecular Biology -20va Reunion de la Sociedad Argentina de Neuroquimica; 2005

PABMB-SAIB-SAN

The p75NTR is involved in neuronal functions that range from induction of apoptosis and growth inhibition to the promotion of survival. p75NTR expression is induced in central nervous system by a wide range of pathological conditions (stroke, seizures, traumatic brain injury), but the cellular mechanisms regulating this response are unknown. Hyposmolarity increases p75NTR levels in several cell lines, raising the possibility that post-traumatic edema may contribute to injury-induced p75NTR expression. We studied the hyposmolarity-induced p75NTR expression to identify the elements controlling p75NTR expression. Our results showed that hyposmolarity robustly induces p75NTR expression in cell lines and in primary mouse cortical neurons. The hyposmolarity-exposed neurons were susceptible to the killing induced by Pro-NGF (a known p75NTR ligand) demonstrating the biological activity of the newly synthesized p75NTR. We performed reporter assays that demonstrated that a highly conserved Sp1-rich area in the proximal p75NTR promoter and a potential silencer element were involved in the increased transcriptional activity. Chromatin IP assays demonstrated that Sp1 was bound to the proximal p75NTR promoter after the hyposmolar exposure. Transfection of DN-Sp1 or siRNA for Sp1 dramatically reduced the hyposmolarity-induced p75NTR response. These results indicate that Sp1 transcription factor is an essential component for the induction of p75NTR expression after hyposmolarity and a novel silencer element may collaborate to regulate p75NTR transcription. Supported by the CIHR and Killam Foundation.