Regulation of neurotrophin-3 gene transcription by Sp3 and Sp4 in neurons

Neurotrophin-3 (NT-3), a neurotrophin member, plays crucial roles in neuronal development, function and plasticity. Previous studies have demonstrated that NT-3 gene transcription is driven by alternative promoters A and B, located upstream of exons 1A (EIA) and 1B (EIB), respectively. However, the transcription factors and DNA elements that drive NT-3 gene transcription remain to be identified. Here, we analysed the promoter region of the NT-3 gene and found that an NT-3 transcript containing EIB is predominantly expressed in cortical neurons which preferentially utilize promoter B, and two tandemly repeated GC-boxes, located between -100 and -60 base pairs within promoter B, are required for the transcription. Electrophoretic mobility shift and chromatin immunoprecipitation assays revealed that both specificity protein (Sp)3 and Sp4 were able to bind to the Sp1 binding sequences within the GC boxes. Expression of dominant-negative Sp3 and Sp4 small interfering RNA in cortical neurons reduced the activity of the NT-3 gene promoter. Over-expression of Sp1 family members, especially Sp4, resulted in an increase of the NT-3 gene promoter. These findings indicate that the NT-3 gene is a target gene for Sp4 that is abundantly expressed in the brain.