Synergy between the RE-1 silencer of transcription and NFκB in the repression of the neurotransmitter gene TAC1 in human mesenchymal stem cells

The RE-1 silencer of transcription ( REST) is a transcriptional regulator that represses neuron-specific genes in non-neuronal tissues by remodeling chromatin structure. We have utilized human mesenchymal stem cells (MSCs) as a research tool to understand the molecular mechanisms that regulate a neurogenic program of differentiation in non-neuronal tissue. MSCs are mesoderm-derived cells that generate specialized cells such as stroma, fat, bone, and cartilage. We have reported previously the transdifferentiation of MSCs into functional neuronal cells (Cho, K. J., Trzaska, K. A., Greco, S. J., McArdle, J., Wang, F. S., Ye, J.-H., and Rameshwar, P. ( 2005) Stem Cells 23, 383-391). Expression of the neurotransmitter gene TAC1 was detected only in neuronal cells and thus served as a model to study transcriptional regulation of neuron-specific genes in undifferentiated MSCs. Bone marrow stromal cells are known to transiently express TAC1 following stimulation with the microenvironmental factor interleukin-1 alpha. We thus compared the effects of interleukin-1 alpha stimulation and neuronal induction of MSCs on TAC1 regulation. Transcription factor mapping of the 5'-flanking region of the TAC1 promoter predicted two REST-binding sites adjacent to one NF kappa B site within exon 1. Chromatin immunoprecipitation, mutagenesis, and loss-of-function studies showed that both transcription factors synergistically mediated repression of TAC1 in the neurogenic and microenvironmental models. Together, the results support the novel finding of synergism between REST and NF kappa B in the suppression of TAC1 in non-neuronal cells.