Dorsoventral Polarity Guides Confined Migration of Cancer Cells

By Emily Wisniewski and Gina Wadas Metastasis is a complex process that requires cancer cells to adapt to diverse environments in the body. After they escape from the primary tumor, the cells embark on a long journey to colonize distant organs by migrating through a maze of three-dimensional tracks created by various anatomical structures. The tracks, or channels, form between adjacent extracellular matrix fibers (collagen), or between

nerves, muscles and their connective tissue. Once the channels are established, the cancerous cells use them to move efficiently to different parts of the body like a highway system.

During metastasis, important motor proteins and signaling molecules organize themselves asymmetrically along the front-to-rear cell axis in a phenomenon called cell polarity. This polarity establishes directionality and is essential for persistent cell migration. Although the importance of front-to-rear cell polarity is well understood, it is not known whether metastasizing cancer cells also exhibit dorsoventral polarity, or polarity along their top-tobottom cell axis. Dorsoventral polarity orients cells to the geometry of their environment. Once cells sense the geometry around them, they respond by altering their signaling and mode of migration. Emily Wisniewski and Panagiotis Mistriotis, under the direction of Konstantinos Konstantopoulos, along with other colleagues, sought to understand the role that dorsoventral polarity plays in cancer cell migration.

“Previous work has only examined top to bottom cellular asymmetry in non-cancerous, epithelial tissues,” Mistriotis said. “Our studies, performed both in vitro and in vivo, are the first to identify and characterize the important role of dorsoventral polarity during cancer cell migration.” Wisniewski is a PhD candidate in the Department of Chemical and Biomolecular Engineering at Johns Hopkins, and Mistriotis, is a former postdoctoral fellow at Johns Hopkins and currently an Assistant Professor at Auburn University. Konstantopoulos is a professor and core faculty member at the INBT and William H. Schwarz Professor of Chemical and Biomolecular Engineering.

The team discovered that cells’ dorsoventral polarity allows them to distinguish between and respond to different geometries of migration tracks by changing the speed, the mode, and/or the mechanism of their locomotion.

The team compared cancer cell migration in two different geometric environments: channels that were tall and narrow (lateral channels) and channels that were short and wide (vertical channels). The channels had the same cross-sectional area, but distinct aspect ratios and had dimensions similar to confining tracks that cells would normally encounter in the body.

They observed that cells moved faster in lateral channels than in vertical channels. In the lateral channels, cells migrated with mesenchymal, or protrusion-based mode, which is classically associated with cell movement on two-dimensional surfaces. In the vertical channels, cells migrated with a bleb-based mode, which look like high pressure bulges or blebs at the cell’s leading and trailing edges.

The team was also curious about the involvement of the cell’s nucleus and the RhoA pathways. The nucleus, which is the largest and stiffest cell organelle, sends out important signals to regulate cell migration, and the RhoA pathway plays many functions in cell locomotion. They found that dorsoventrally polarized cells regulate their migration mode and efficiency in response to these different channel geometries by tuning their nuclear stiffness and RhoA activity.

“We demonstrated for the first time that physical confinement stiffens the cell nucleus, which has direct implications on the mechanisms of cell migration,” said Wisniewski.

(Left) Cells moving through lateral channels use a mesenchymal, or protrusion-based method. Cell moving through vertical channels migrated with a bleb-based method, which look like high pressure bulges (right).

“This work provides a novel perspective on how the physical cues regulate distinct mechanisms of cell movement necessary for tumor cell spreading and metastasis,” Konstantopoulos said. “The physical microenvironment contributes to cell plasticity, which may explain why combating cancer metastasis is not an easy feat.”