(314c) Mechanical Tropism in Metastatic Cancer Cells Determined through Cytoskeletal Tension

The ability of a cell to sense and interact with its local environment is important in both normal tissue development such as directing cell lineage during stem cell differentiation as well as progression of diseases like arteriosclerosis, muscular dystrophies, osteoporosis, and cancer (1). Despite a large body of work documenting the role of matrix stiffness in the progression of breast and other cancers, the literature is still unclear if this matrix-stiffness induced cancer progression is conserved throughout all cancers and what determines how a cell responds to matrix stiffness. Moreover, though the stiffness of metastatic site tissue in vivo has been shown to correlate with growth on rigidity-matched substrates in vitro (2), the mechanisms underlying this mechanical tropism remain unknown. We recently demonstrated that ovarian cancer cells that preferentially metastasize to the soft omentum fat pad also become more malignant on soft matrices (3). Thus, we sought to compare these cells with metastatic breast cancer cells which become more malignant on hard matrices in order to understand the drivers of this mechanical tropism. To do so, we cultured cells on soft (2.83 kPa) and hard (34.88 kPa) polyacrylamide substrates and found that these differences appeared within two hours of culture and resulted in altered proliferation, chemoresistance, and motility on substrates of preferred rigidity. Microarray analysis revealed breast cancer cells have significantly higher expression of genes associated with contractility such as myosin light chain, myosin heavy chain, RhoA, and myosin light chain kinase (MLCK). Chemical blockade of these molecules produced rigidity-independent behavior. To probe how this inhibition was altering physical interactions with the underlying substrate, we performed traction force microscopy. Though inhibiting ROCK and MLCK produced equivalent functional outcomes this was accomplished through divergent changes in force profiles. Finally, analysis of matrix displacements suggests that cells with high expression of contractile markers and enhanced malignancy on hard substrates may utilize a stress-sensing mechanism whereas contractile cells with lower contractile gene expression that prefer soft matrices utilize a strain-sensing mechanism when probing their local microenvironment. By contrasting two cancers with inverse response to matrix rigidity, this work helped elucidate potential mechanisms for mechanical tropism in metastatic cancer cells. Molecular analysis revealed large differences in genes associated with actomyosin contractility. Inhibition of these gene products was sufficient to abrogate the observed differences and suggested that matrix preference was based on which mechanosensing regime (stress sensing or strain sensing) was being utilized by the cells.

 

References:
1. Jaalouk DE. Nat. Rev. Mol. Cell Biol. 2009. 10: 63–73.
2. Kostic, A. PLoS One. 2009. 4: e6361
3. McGrail, DJ. J. Cell Sci. 2014. jcs.144378