A signaling loop of REST, TSC2 and β-catenin governs proliferation and function of PC12 neural cells

Abstract

The RE-1-specific silencing transcription factor (REST or NRSF) is a transcription repressor that orchestrates differentiation and also operates in differentiated neurons and neurosecretory cells (neural cells). Its role in proliferation has been investigated so far only in rapidly growing tumors, with conflicting results: suppression in non-neural tumors, stimulation in medulloblastomas. Working with two clones of chromaffin-neuronal PC12 cells, which express different levels of REST, and using genetic complementation and knockdown approaches, we show that REST also promotes proliferation in differentiated neural cells. Mechanistically, this occurs by a signaling pathway involving REST, the GTPase-activating protein tuberin (TSC2) and the transcription co-factor β-catenin. In PC12 cells, raised expression of REST correlates with reduced TSC2 levels, nuclear accumulation and co-transcriptional activation of β-catenin, and increased expression of its target oncogenes Myc and Ccnd1, which might account for the proliferation advantage and the distinct morphology. Rest transcription is also increased, unveiling the existence of a self-sustaining, feed-forward REST-TSC2-β-catenin signaling loop that is also operative in another neural cell model, NT2/D1 cells. Transfection of REST, knockdown of TSC2 or forced expression of active β-catenin recapitulated the biochemical, functional and morphological properties of the high-expressing REST clone in wild-type PC12 cells. Upregulation of REST promoted proliferation and phenotypic changes, thus hindering neurosecretion. The new REST-TSC2-β-catenin signaling paradigm might have an important role in various aspects of neural cell physiology and pathology, including the regulation of proliferation and neurosecretion.