A mechanical memory of pancreatic cancer cells

Cells sense and respond to mechanical stimuli in healthy and pathological conditions. Although the major mechanisms un-derlying cellular mechanotransduction have been described, it remains largely unclear how cells store information on past mechanical cues over time. Such mechanical memory is extremely relevant in the onset of metastasis in which cancer cells migrate through tissues of different stiffness, e.g. from a stiffer tumor microenvironment to softer metastatic sites as commonly occurs for pancreatic cancer. Here, we used micropillar-based traction force microscopy to show that Suit-2.28 pancreatic cancer cells mechanically primed on a stiff matrix exerted higher traction forces even when transferred to a soft secondary matrix, as compared to soft-primed cells. This mechanical memory effect was mediated by the Yes-associated protein (YAP) and the microRNA-21 (miR-21) that are two mechanosensors initially identified as long-term memory keepers in mesenchymal stem cells. Soft-primed cells showed (i) a lower YAP nuclear translocation when transferred to a stiff secondary matrix and (ii) a loss of rigidity sensing through YAP, as compared to stiff-primed cells. The mechanical adaptation resulted in a differential expression of miR-21, inversely proportional to the priming rigidity. The long-term mechanical memory retained by miR-21 unveiled a previously unidentified mechanical modulation of drug resistance by past matrix stiffness. The higher expression of miR-21 in soft-primed cells correlated with the increased resistance to gemcitabine, as compared to stiff-primed and non-primed pancreatic cancer cells.