Cancer adhesion and invasion

Cell dissemination by invasion into neighboring tissues, and the subsequent formation of metastases, are the most devastating properties of malignant cancers. These properties are commonly attributed to the increased migratory activity of cancer cells. To identify specific genes whose expression is associated with cell migration, we have developed specific assays (e.g., a phagokinetic assay; Figure 1)

Figure 1

Cell migration studied using phagokinetic tracks. While phase contrast images (top) provide instantaneous snapshots of shape and location for a number of cells, phagokinetic tracks (PKT) (bottom), display the entire migration history of all cells in the assay. This is clearly demonstrated for PKCf knockdown (right), which impedes directed cell migration.

for assessing the migratory capacity of individual cells. Using multiparametric analyses, we collected rich information enabling us to associate different migratory features with specific genes. We then conducted siRNA migration screens, using cells that migrate individually, as well as those undergoing collective migration. These screens revealed specific genes such as PKCζ and SRPK1 (van Roosmalen et al., under review) whose knockdown drastically suppressed cell migration. A particular recent study focused on the structure and assembly of invadopodia, specialized protrusions that invade the matrix (Figure 2).

Figure 2

The actin core and adhesion ring of invadopodia: A375 cells were cultured on gelatin coated glass bottomed dishes for 2h. Cells were fixed and stained for TKS5, an invadopodia core marker, and vinculin, a marker for integrin adhesions. The adhesion ring (shown enlarged in the upper-right corner) is associated with the invadopodia core at early stages (within minutes) of invadopodia formation, and often disappears at later stages (hours). Stable focal adhesions (FAs), located mainly at the cell’s periphery, are also formed in these cells.

Working on these “invasive organelles,” we examine the interplay between the adhesive domains of these structures, their mechanical-protrusive activity, which drives cellular penetration into the matrix, and the proteolytic domain, which “softens” the matrix, and prepares it for cellular invasion.