Mechanotransduction of strain regulates an invasive phenotype in newly transformed epithelial cells

Abstract

Carcinoma, the most common type of cancer, develops in the sheets of cells forming the epithelium and lining our organs and cavities. It usually begins with the transformation of a single cell via the activation of oncogenes such as Ras. The capacity of epithelia to eliminate newly transformed cells via apical extrusion is believed to be a critical defense mechanism to eradicate initial stages of carcinoma. Our organs and tissues are in constant motion, exposing epithelial cells to mechanical stretch. How these external forces impact the onset and progression of tumor growth is thus of primary interest, but little is known currently. Here we show that mechanical strains jeopardize the epithelial defense mechanisms against Ras V12 -transformed MDCK cells by impeding their apical extrusion. Concurrently, they prevent the formation of strong circumferential belts of actin in Ras V12 cells, previously established as a primary step of apical extrusion under static conditions. Cyclic stretching also changes the metastatic phenotype of newly transformed cells by greatly promoting the formation of Ras V12 protrusions. We show that Ras V12 and wild type MDCK cells possess distinct sensitivity to strain. External forces remodel their actin cytoskeletons and adhesion complexes differently, resulting in a more invasive system dynamic. Our work also shows that the Rho-ROCK mechanotransduction pathway is involved in regulating the mechanically-induced switch to a more aggressive phenotype. Such insight may lead to the targeting of mechanotransduction pathways in innovative future therapies. Significance statement:Cancer progression is increasingly viewed as a complex journey in which the mechanical properties of the microenvironment play a key role. The entire human body is in constant motion, yet the initial stage of cancer development at the cellular level is commonly studied in static petri dishes. Here we demonstrate that in a mechanically dynamic microenvironment, oncogenic Ras-transformed cells exhibit drastically different cellular dynamics and movements when compared to static conditions. They grow larger invasive protrusions, and they are much less likely to be eliminated from the healthy tissues. A deeper understanding of how external physical cues regulate early stage microtumor growth can reveal potentially new and unexplored avenues for cancer therapies.

OncogenicRASinstructs morphological transformation of human epithelia via differential tissue mechanics

“…At the tissue scale, RAS disrupts epithelial homeostasis, resulting in loss of tissue polarity (13) and barrier function (14). Normal epithelia act as a barrier against single RAS cells or RAS cell clusters through their extrusion or delamination (15)(16)(17)(18)(19)(20)(21). The extrusion of RAS cells has been shown to be driven by actomyosin-dependent forces acting at the interface between normal and transformed cells (18,20) and can be affected by tissue-level mechanical forces (17).…”

“…Normal epithelia act as a barrier against single RAS cells or RAS cell clusters through their extrusion or delamination (15)(16)(17)(18)(19)(20)(21). The extrusion of RAS cells has been shown to be driven by actomyosin-dependent forces acting at the interface between normal and transformed cells (18,20) and can be affected by tissue-level mechanical forces (17). Larger clusters of RAS cells can separate from normal neighbors (22,23) to form cysts (19), outgrowths, or invaginations (24).…”

The role of RAS oncogenes in controlling epithelial mechanics

“…It is clear, however, that this is not a fail-safe mechanism, because epithelia are able to accumulate cells with somatic mutations [ 75 ], and retention of activated RAS cells throughout an epithelial monolayer can lead to whole-tissue morphogenesis and hyperplasia [ 20 ]. This may be due to the role of mechanics in the extrusion process, because experimental work has shown that the extrusion of transformed RAS cells from monolayers is reduced by the application of external strain, which instead promotes basal invasion, partially through activation of the Rho-ROCK pathway and FAK [ 76 ]. Extrusion is also weakened by matrix stiffening.…”

Oncogenic RAS instructs morphological transformation of human epithelia via differential tissue mechanics

“…In addition, more than 50% of cancers involve the hyperactivation of the RAS/RAF/MEK/ERK pathway (10,11), with more than 30% of all cancers being associated with specific activating mutations in RAS genes [8][9][10] . RASoncogenes disrupt epithelial homeostasis both in cell culture (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) (mostly studied by using clones) and in animal tissues (17,18,(23)(24)(25)(26)(27). These studies show how RAS-transformed cells scattered within an epithelium may be segregated and expelled from the monolayer via extrusion or delamination (12,14,19,20,22,23), through the mechanical engagement of the cellular interface with surrounding normal cells.…”

“…RASoncogenes disrupt epithelial homeostasis both in cell culture (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) (mostly studied by using clones) and in animal tissues (17,18,(23)(24)(25)(26)(27). These studies show how RAS-transformed cells scattered within an epithelium may be segregated and expelled from the monolayer via extrusion or delamination (12,14,19,20,22,23), through the mechanical engagement of the cellular interface with surrounding normal cells. Also, clusters of cells expressing oncogenic RAS or SRC (an upstream regulator of RAS (28)) can induce local dysplasia (23,24,26,27), segregation (16,24) or morphing (23,24,26,27) of the affected area of the tissue as a consequence of differential mechanics along the extended interface between the non-transformed and transformed domains of the epithelial tissue.…”