(158w) The Interplay of Ion Transporters and Cytoskeleton in Breast Cancer Migration and Metastasis

Authors: 
Zhang, Y., Johns Hopkins University
Wang, Y., Johns Hopkins University
Zhao, R., Johns Hopkins University
Mistriotis, P., Johns Hopkins University
Konstantopoulos, K., Johns Hopkins University
The primary cause of death among cancer patients is tumor metastasis. Cell migration is a key step in the metastatic cascade of events, as it enables tumor cells dissociating from a primary tumor to navigate through interstitial tissues and ultimately colonize distant organs. Cell motility is generally governed by cell-ECM interactions and the actomyosin cytoskeleton as well as cell volume regulation. Cell migration in confinement can persist even when F-actin is completely disrupted; a process that can be explained by the Osmotic Engine Model (OEM). According to OEM, cell locomotion is mediated by highly coordinated cycles of local isosmotic swelling at the cell leading edge and shrinkage at the trailing edge, driven by the polarization of select ion transporters and aquaporins (AQPs). We determined that the Na+/H+ exchanger 1 (NHE1), which is polarized at the leading edge of migrating cells in the confinement, mediates regulatory volume increase, which is consistent with its role in cell protrusion. Interestingly, AQP5 is also enriched at the cell front. To date, it is unknown which ion channels and aquaporins regulate cell shrinkage at the cell trailing edge. Using a multidisciplinary approach involving state-of-the-art bioengineering, imaging tools and quantitative analysis, we have discovered that a distinct aquaporin, AQP4 polarizes at the cell rear of metastatic breast cancer cells in confinement, thereby facilitating the local volume decrease by creating an outflow of water. We have also identified a novel ion channel (called X, due to a pending patent) which is preferentially localized at the cell trailing edge of confined breast cancer cells, and works together with AQP4 to mediate cell shrinkage. Dual knockdown of NHE1 and X does not alter cell volume in confinement which is in line with their individual counteracting effect of their role in cell volume regulation. Furthermore, we demonstrate cooperative and pronounced inhibition of motility in narrow channels upon dual NHE1 and X depletion. Taken together, our data support the model by which the repeated and coordinated cycle of swelling and shrinkage at the cell poles mediated by these distinct ion transporters, regulates cell motility in confinement. This presentation will also discuss the interplay between ion transporters and cell cytoskeleton in regulating efficient cell migration in confinement. Overall, our findings extend the Osmotic Engine Model by introducing AQP4 and a novel ion transporter for confined cell migration. These findings may provide the basis for identification of novel therapeutic target to combat breast cancer metastasis.