Elevated hydrostatic pressure enhances the motility and enlarges the size of the lung cancer cells through aquaporin upregulation mediated by caveolin-1 and ERK1/2 signaling

The mechanical characteristics presented in cancer microenvironment are known to have pivotal roles in cancer metastasis, which accounts for the leading cause of death from malignant tumors. However, while a uniformly distributed high interstitial fluid pressure (IFP) is a common feature in solid tumors, the effects of high IFP on the motility and invasiveness of cancer cells remain obscure. Using cell-culture devices that simulated increased IFP conditions by applying hydrostatic pressure (HP) ranging from 0 to 20 mm Hg to the cells, we found that the elevated HPs increased the migration speeds, invasiveness, cell volume, filopodial number and aquaporin-1 (AQP1), Snail and vinculin expression levels, as well as phosphorylation of caveolin-1 and extracellular signal–regulated kinase1/2 (ERK1/2), in the lung cancer cells CL1-5 and A549. The increases of migration speed and cell volume correlated temporally with the increase of AQP1 expression. The elevated HP-induced migration acceleration was hindered by AQP1 knockdown using small interfering RNA (siRNA) transfection. Inhibition of ERK1/2 phosphorylation using the mitogen-activated protein kinase kinase inhibitor PD98059 abrogated the elevated HP-induced AQP1 upregulation and migration acceleration in the cancer cells. Caveolin-1 knockdown by siRNA transfection attenuated the HP-induced, ERK1/2-depedent AQP1 upregulation and migration acceleration. Further biochemical studies revealed that the caveolin-1 activation-driven ERK1/2 signaling is mediated by Akt1/2 phosphorylation. By contrast, the elevated HPs had negligible effects on the migration speed and volume of normal bronchial epithelial cells. These results disclose a novel mechanism relating high IFP to the invasiveness of cancer cells and highlight potential targets to impede cancer spreading.