N-terminal nesprin-2 variants regulate ß-catenin signalling.

The spatial compartmentalisation of biochemical signalling pathways is essential for cell function. Nesprins are a multi-isomeric family of proteins that have emerged as signalling scaffolds, herein, we investigate the localisation and function of novel nesprin-2 N-terminal variants. We show that these nesprin-2 variants display cell specific distribution and reside in both the cytoplasm and nucleus. Immunofluorescence microscopy revealed that nesprin-2 N-terminal variants colocalised with ß-catenin at cell-cell junctions in U2OS cells. Calcium switch assays demonstrated that nesprin-2 and ß-catenin are lost from cell-cell junctions in low calcium conditions whereas emerin localisation at the NE remained unaltered, furthermore, an N-terminal fragment of nesprin-2 was sufficient for cell-cell junction localisation and interacted with ß-catenin. Disruption of these N-terminal nesprin-2 variants, using siRNA depletion resulted in loss of ß-catenin from cell-cell junctions, nuclear accumulation of active ß-catenin and augmented ß-catenin transcriptional activity. Importantly, we show that U2OS cells lack nesprin-2 giant, suggesting that the N-terminal nesprin-2 variants regulate ß-catenin signalling independently of the NE. Together, these data identify N-terminal nesprin-2 variants as novel regulators of ß-catenin signalling that tether ß-catenin to cell-cell contacts to inhibit ß-catenin transcriptional activity.