Adaptation to volumetric compression drives hepatoblastoma cells to an apoptosis-resistant and invasive phenotype.

Liver cancer involves tumor cells rapidly growing within a packed tissue environment. Patient tumor tissues reveal densely packed and deformed cells, especially at tumor boundaries, indicative of physical crowding and compression. It is not well understood how these physical signals modulate tumor evolution and therapeutic susceptibility. Here we investigate the impact of volumetric compression on liver cancer (HepG2) behavior. We find that conditioning cells under a highly compressed state leads to major transcriptional reprogramming, notably the loss of hepatic markers, the epithelial-to-mesenchymal transition (EMT)-like changes, and altered calcium signaling-related gene expression, over the course of several days. Biophysically, compressed cells exhibit increased Rac1-mediated cell spreading and cell-extracellular matrix interactions, cytoskeletal reorganization, increased YAP and β-catenin nuclear translocation, and dysfunction in cytoplasmic and mitochondrial calcium signaling. Furthermore, compressed cells are resistant to chemotherapeutics and desensitized to apoptosis signaling. Apoptosis sensitivity can be rescued by stimulated calcium signaling. Our study demonstrates that volumetric compression is a key microenvironmental factor that drives tumor evolution in multiple pathological directions and highlights potential countermeasures to re-sensitize therapy-resistant cells. Significance statement: Compression can arise as cancer cells grow and navigate within the dense solid tumor microenvironment. It is unclear how compression mediates critical programs that drive tumor progression and therapeutic complications. Here, we take an integrative approach in investigating the impact of compression on liver cancer. We identify and characterize compressed subdomains within patient tumor tissues. Furthermore, using in vitro systems, we induce volumetric compression (primarily via osmotic pressure but also via mechanical force) on liver cancer cells and demonstrate significant molecular and biophysical changes in cell states, including in function, cytoskeletal signaling, proliferation, invasion, and chemoresistance. Importantly, our results show that compressed cells have impaired calcium signaling and acquire resistance to apoptosis, which can be countered via calcium mobilization.