High viscosity microenvironment induces chemoresistance of cancer cells through upregulating P-gp.

Chemoresistance remains a major obstacle to the efficacy of cancer chemotherapy. The tumor mechanical microenvironment such as substrate stiffness, fluid shear stress, and solid stress can considerably influence drug resistance. Compared with normal tissues (∼0.7 cP), high extracellular fluid viscosity (∼8 cP) is another typical mechanical feature of tumors. However, whether cancer cells can sense this mechanical stimulus and engage mechanosensitive signaling to influence chemoresistance remains unclear. We found that high-viscosity treatment promotes P-gp (ABCB1) expression, enhancing doxorubicin (DOX) chemoresistance. The elevated viscosity increased the density of the F-actin-vinculin cytoskeleton and promoted Na+/H+ exchanger 1 (NHE1)/aquaporin 1 (AQP1)-dependent water influx, increasing cell membrane tension, as suggested by atomic force microscopy (AFM) and fluorescence lifetime measurements. This high tension may enhance the activity of the mechanosensitive channel transient receptor potential vanilloid 4 (TRPV4), which promotes Yes-associated protein (YAP) nuclear translocation, as evidenced by increased intracellular Ca2+ fluorescence and nuclear YAP fluorescence intensity. The elevated expression of the YAP target genes CTGF and CYR61 indicates the enhanced transcriptional activity of nuclear-localized YAP. The inhibition of YAP transcriptional activity suppressed the high viscosity-induced increases of P-gp mRNA and protein levels, supporting the YAP dependence of P-gp upregulation. Reducing tumor viscosity may provide new insights for overcoming drug resistance in clinical settings.