A role for CBFß in maintaining the metastatic phenotype of breast cancer cells.

Epithelial to mesenchymal transition (EMT) is a dynamic process that drives cancer cell plasticity and is thought to play a major role in metastasis. Here we show, using MDA-MB-231 cells as a model, that the plasticity of at least some metastatic breast cancer cells is dependent on the transcriptional co-regulator CBFß. We demonstrate that CBFß is essential to maintain the mesenchymal phenotype of triple-negative breast cancer cells and that CBFß-depleted cells undergo a mesenchymal to epithelial transition (MET) and re-organise into acini-like structures, reminiscent of those formed by epithelial breast cells. We subsequently show, using an inducible CBFß system, that the MET can be reversed, thus demonstrating the plasticity of CBFß-mediated EMT. Moreover, the MET can be reversed by expression of the EMT transcription factor Slug whose expression is dependent on CBFß. Finally, we demonstrate that loss of CBFß inhibits the ability of metastatic breast cancer cells to invade bone cell cultures and suppresses their ability to form bone metastases in vivo. Together our findings demonstrate that CBFß can determine the plasticity of the metastatic cancer cell phenotype, suggesting that its regulation in different micro-environments may play a key role in the establishment of metastatic tumours.

Fas stimulation of T lymphocytes promotes rapid intercellular exchange of death signals via membrane nanotubes.

The Fas/CD95 surface receptor mediates rapid death of various cell types, including autoreactive T cells with the potential for triggering autoimmunity. Here, we present novel aspects of Fas signalling that define a 'social' dimension to receptor-induced apoptosis. Fas stimulation rapidly induces extensive membrane nanotube formation between neighbouring T cells. This is critically dependent on Rho GTPases but not on caspase activation. Bidirectional transfer of membrane and cytosolic elements including active caspases can be observed to occur via these nanotubes. Nanotube formation and intercellular exchanges of death signals are defective in T lymphocytes from patients with autoimmune lymphoproliferative syndrome harbouring mutations in the Fas receptor. We conclude that nanotube-mediated exchanges constitute a novel form of intercellular communication that augments the propagation of death signalling between neighbouring T cells.