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

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Spatial organization of biochemical signaling is crucial for cellular functions.
• Nesprins are a family of proteins acting as signaling scaffolds.
• Understanding nesprin functions, particularly novel variants, is key to cell biology.

Purpose of the Study:

• To investigate the localization and function of novel nesprin-2 N-terminal variants.
• To determine the role of these nesprin-2 variants in beta-catenin signaling.
• To elucidate the relationship between nesprin-2 variants, beta-catenin, and cell-cell junctions.

Main Methods:

• Immunofluorescence microscopy to observe protein colocalization.
• Calcium switch assays to study protein dynamics under varying calcium conditions.
• siRNA depletion to assess the functional impact of nesprin-2 variants.
• Analysis of beta-catenin transcriptional activity.

Main Results:

• Nesprin-2 N-terminal variants localize to both cytoplasm and nucleus, with cell-specific distribution.
• These variants colocalize with beta-catenin at cell-cell junctions in U2OS cells.
• Nesprin-2 and beta-catenin are lost from cell-cell junctions in low calcium, while emerin at the nuclear envelope remains unaffected.
• An N-terminal nesprin-2 fragment interacts with beta-catenin and is sufficient for localization to cell-cell junctions.
• siRNA-mediated depletion of N-terminal nesprin-2 variants leads to beta-catenin loss from junctions, nuclear accumulation of active beta-catenin, and increased transcriptional activity.
• U2OS cells lack nesprin-2 giant, indicating regulation of beta-catenin signaling independent of the nuclear envelope.

Conclusions:

• N-terminal nesprin-2 variants act as novel regulators of beta-catenin signaling.
• These variants tether beta-catenin to cell-cell contacts, inhibiting its transcriptional activity.
• The findings highlight a mechanism for controlling beta-catenin activity independent of the nuclear envelope in specific cellular contexts.