Tissues of the body are constantly subjected to external forces throughout development and in adulthood. External forces are transduced to cells via the extracellular matrix, and initiate mechanotransduction signalling pathways that generate dynamic intracellular forces that counteract external mechanical forces. This reciprocity is fundamental to the maintenance of tissue integrity. In disease states such as cancer, enhanced extracellular matrix density and rapid growth within a constrained space enhance signalling through mechanotransduction pathways, many of which have been shown to be tumour-promoting. We therefore wondered whether external forces could themselves be tumour-promoting.
We have found that acute compressive force, applied to isolated murine mammary cancer cells embedded in 3D matrices or to intact mammary tumour tissue, can activate the Rho-ROCK mechanotransduction pathway, elevating RhoA-GTP levels and increasing actomyosin contractility and tension. We have discovered that this is mediated by the mechanosensitive ion channel Piezo1 and downstream calcium signalling. Compression induces calcium ion influx and activation of calmodulin-dependent protein kinase II (CaMKII), leading to Rho-ROCK pathway activation. This can be suppressed by silencing Piezo1, calcium chelation, or pharmacologically inhibiting or silencing CaMKII. Consequently, mammary tumours or cells that had been subjected to compressive force grew more rapidly when orthotopically engrafted into mice than those that had not been subjected to compressive force.
We show that acute compressive forces transduced via the induction of this Piezo1-CaMKII-Rho-ROCK cascade engender mechanical memory to promote tumour progression. This is evidenced by Piezo1-CaMKII-Rho-ROCK pathway-dependent histone modifications associated with open chromatin that regulate the expression of key cancer-related genes across cell, explant, and in vivo tumour models. Our results therefore strongly suggest that Rho-ROCK-mediated mechanotransduction in cancer, induced by compressive stress from mammary tumour growth within a constricted space, may play a role in cancer progression via persistent tumour-promoting epigenetic changes, in a context-dependent manner.