Durotaxis is a type of directed cell migration in which cells respond to a gradient of extracellular stiffness. Using automated tracking of positional data for large sample sizes of single migrating cells, we investigated 1) whether cancer cells can undergo durotaxis; 2) whether cell durotactic efficiency varies depending on the regional compliance of stiffness gradients; 3) whether a specific cell migration parameter such as speed or time of migration correlates with durotaxis; and 4) whether Arp2/3, previously implicated in leading edge dynamics and migration, contributes to cancer cell durotaxis. Although durotaxis has been characterized primarily in nonmalignant mesenchymal cells, little is known about its role in cancer cell migration. Diffusible factors are known to affect cancer cell migration and metastasis. However, because many tumor microenvironments gradually stiffen, we hypothesized that durotaxis might also govern migration of cancer cells. We evaluated the durotactic potential of multiple cancer cell lines by employing substrate stiffness gradients mirroring the physiological stiffness encountered by cells in a variety of tissues. Automated cell tracking permitted rapid acquisition of positional data and robust statistical analyses for migrating cells. These durotaxis assays demonstrated that all cancer cell lines tested (two glioblastoma, metastatic breast cancer, and fibrosarcoma) migrated directionally in response to changes in extracellular stiffness. Unexpectedly, all cancer cell lines tested, as well as noninvasive human fibroblasts, displayed the strongest durotactic migratory response when migrating on the softest regions of stiffness gradients (2-7 kPa), with decreased responsiveness on stiff regions of gradients. Focusing on glioblastoma cells, durotactic forward migration index and displacement rates were relatively stable over time. Correlation analyses showed the expected correlation with displacement along the gradient but much less with persistence and none with cell speed. Finally, we found that inhibition of Arp2/3, an actin-nucleating protein necessary for lamellipodial protrusion, impaired durotactic migration.For all live-cell fluorescence experiments, DMEM without phenol red or FluoroBrite DMEM (GIBCO) were used, with each supplemented with a 1:100 ratio of Oxyfluor (Oxyrase, Mansfield, OH) and 10 mM DL-lactate (Sigma, St. Louis, MO) to reduce photobleaching and phototoxicity, Durotaxis by Human Cancer Cells

Branching morphogenesis of developing organs requires coordinated but poorly understood changes in epithelial cell-cell adhesion and cell motility. We report that Btbd7 is a crucial regulator of branching morphogenesis in vivo. Btbd7 levels are elevated in peripheral cells of branching epithelial end buds, where it enhances cell motility and cellcell adhesion dynamics. Genetic ablation of Btbd7 in mice disrupts branching morphogenesis of salivary gland, lung and kidney. Btbd7 knockout results in more tightly packed outer bud cells, which display stronger E-cadherin localization, reduced cell motility and decreased dynamics of transient cell separations associated with cleft formation; inner bud cells remain unaffected. Mechanistic analyses using in vitro MDCK cells to mimic outer bud cell behavior establish that Btbd7 promotes loss of E-cadherin from cell-cell adhesions with enhanced migration and transient cell separation. Btbd7 can enhance E-cadherin ubiquitination, internalization, and degradation in MDCK and peripheral bud cells for regulating cell dynamics. These studies show how a specific regulatory molecule, Btbd7, can function at a local region of developing organs to regulate dynamics of cell adhesion and motility during epithelial branching morphogenesis.

Cell migration is essential for many biological processes including development, wound healing and metastasis. However, studying cell migration often requires the time-consuming and labor-intensive task of manually tracking cells. To accelerate the task of obtaining coordinate positions of migrating cells, we have developed a graphical user interface (GUI) capable of automating the tracking of fluorescently labeled nuclei. This GUI provides an intuitive user interface that makes automated tracking accessible to researchers with no image processing experience or familiarity with particle-tracking approaches. Using this GUI, users can interactively determine a minimum of four parameters to identify fluorescently labeled cells and automate acquisition of cell trajectories. Additional features allow for batch processing of numerous time-lapse images, curation of unwanted tracks, and subsequent statistical analysis of tracked cells. Statistical outputs allow users to evaluate migratory phenotypes, including cell speed, distance, displacement and persistence as well as measures of directional movement, such as forward migration index (FMI) and angular displacement.

Background: Sorting Nexin 27 (SNX27) is a 62-kDa protein localized to early endosomes and known to regulate the intracellular trafficking of ion channels and receptors. In addition to a PX domain common among all of the sorting nexin family, SNX27 is the only sorting family member that contains a PDZ domain. To identify novel SNX27–PDZ binding partners, we performed a proteomic screen in mouse principal kidney cortical collecting duct cells (mpkCCD) using a GST-SNX27 fusion construct as bait. We found that the C-terminal type I PDZ binding motif (DTDL) of β-catenin, an adherens junction scaffolding protein and transcriptional co-activator, interacts directly with SNX27. Using biochemical and immunofluorescent techniques, β-catenin was identified in endosomal compartments where co-localization with SNX27 was observed. Furthermore, E-cadherin, but not Axin, GSK3 or Lef-1 was located in SNX27 protein complexes. While overexpression of wild-type β-catenin protein increased TCF-LEF dependent transcriptional activity, an enhanced transcriptional activity was not observed in cells expressing β-Catenin ΔFDTDL or diminished SNX27 expression.These results imply importance of the C-terminal PDZ binding motif for the transcriptional activity of β-catenin and propose that SNX27 might be involved in the assembly of β-catenin complexes in the endosome.

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Sorting Nexin 27 (SNX27) is a 62‐kDa protein localized to early endosomes and known to regulate the intracellular trafficking of ion channels and receptors. In addition to a PX domain, SNX27 is the only sorting family member that contains a PDZ domain. To identify novel SNX27‐PDZ binding partners, we performed a proteomic screen in mouse principal kidney cortical collecting duct cells (mpkCCD) using a GST‐SNX27 fusion construct as bait. We found that the C‐terminal type I PDZ binding motif (DTDL) of β‐Catenin, an adherens junction scaffolding protein and transcriptional co‐activator, interacts directly with SNX27. Using biochemical and immunofluorescent techniques, β‐Catenin was identified in endosomal compartments where co‐localization with SNX27 was observed. As expected, over‐expressed β‐Catenin wild‐type protein was identified in nuclear regions and increased TCF‐LEF dependent transcriptional activity was observed. In contrast, over‐expressed β‐Catenin ΔDTDL was found at sites of cell‐cell contact with transcriptional activity at control levels. These results imply importance of the C‐terminal PDZ binding motif in localization and transcriptional activity of β‐Catenin.

Durotaxis is a mechanism of directional migration in which cells respond to a stiffness gradient in their local microenvironment. While durotaxis has been characterized primarily in cells of mesenchymal origin, its role in cancer biology has not been clearly defined. At a cellular and molecular level, evidence suggests cancer cells sense and respond to the stiffening tumor microenvironment in a manner that promotes malignant and invasive characteristics. Given the gradual stiffening of tumors, it is interesting to speculate how durotaxis might contribute to cell flux to and from primary tumors and metastatic sites. We hypothesize that a durotactic mechanism may, in part, contribute to the dissemination of cancer cells into the stiffened microenvironment associated with primary tumors and also possibly with pre-metastatic sites. To directly characterize the impact of local stiffness on directional migration, cancer cells were cultured on a hydrogel possessing a stiffness gradient, then imaged by time-lapse microscopy and tracked using custom automated tracking software. Automated cell tracking allows for unbiased, accurate, and high-speed generation of large migratory datasets not feasible with conventional manual tracking and enables more robust analysis of cell populations. Preliminary data reveal that multiple cancer cell lines respond to a stiffness gradient with directed migration towards the stiffer part of the gel. The strength of the directional migratory response to stiffness gradients was found to depend on the magnitude of stiffness a cell encounters. By manipulating stiffness gradients to accurately reflect stiffness encountered by cancer subtypes, we will better understand if a durotactic mechanism has a global or cancer-specific impact on disease progression. Citation Format: Brian J. DuChez, Kenneth M. Yamada. Evaluating the role of durotactic migration in the tumor microenvironment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5061.