Interactions between a transcription factor and its target genes clearly require the transcription factor to be expressed in the right place at the right time and the presence of the corresponding recognition elements in the target gene. Just as importantly, we need to know the molecular interactions that direct the actions of these activators and repressors to specific promoters. We are particularly interested in examining the role of REST/NRSF during neuronal differentiation. The original proposed role for REST was that of a factor responsible for restricting neuronal gene expression to the nervous system by silencing expression of these genes in non-neuronal cells. Although it was initially thought to repress neuronal genes in non-neuronal cells, the role of REST is complex and tissue dependent. Moreover, it should be considered that REST may function in different ways at different stages of cell differentiation as a result of changing expression of associated proteins or other signals as it may form complexes with other cellular factors, such as CoREST Sin3A and histone deacetylase which contribute to modulate REST-mediated repression. An N-terminal expression domain of REST interacts with Sin3A whilst the C-terminal recruits a complex that contains CoREST and a component of the chromatin-remodeling complex. We propose that REST is regulated by growth factors, like IGF-I, and PKC activators in a time-dependent manner: it is elevated during early steps of neural induction and could contribute to down-regulate genes not yet required by the differentiation program while it declines later for the acquisition of neural phenotypes, concomitantly with a progressive neurite extension. This later decline is regulated by the proteasome system activation and adds more evidences to the hypothesis that REST down-regulation contributes to differentiation and arrest of proliferation of neuroblastoma cells. The expression pattern of REST could be consistent with the theory that, during early neuronal differentiation induced by IGF-I, it may help to repress the expression of several genes not yet required by the differentiation program and then it declines later. Interestingly, the observation that REST expression is progressively reduced in parallel with cell proliferation seems to indicate that the role of this transcription factor could also be related to cell survival or to counteract apotosis events.

Finally, the glycosylation pattern of the REST protein is analysed, moving from the observation that the molecular weight calculated on REST sequence is about 116 kDa but using western blotting this transcription factor appears to have distinct apparent molecular weight: this difference could be explained by post-translational modifications of the proteins, like glycosylation. In fact recently, several studies underlined the importance of O-glycosylation in modulating transcriptional silencing, protein phosphorylation, protein degradation by proteasome and protein–protein interactions.