Cancer cell invasion in three-dimensional collagen is regulated differentially by Gα₁₃ protein and discoidin domain receptor 1-Par3 protein signaling

Cancer cells can invade in three-dimensional collagen as single cells or as a cohesive group of cells that require coordination of cell-cell junctions and the actin cytoskeleton. To examine the role of Gα₁₃, a G₁₂ family heterotrimeric G protein, in regulating cellular invasion in three-dimensional collagen, we established a novel method to track cell invasion by membrane type 1 matrix metalloproteinase-expressing cancer cells. We show that knockdown of Gα₁₃ decreased membrane type 1 matrix metalloproteinase-driven proteolytic invasion in three-dimensional collagen and enhanced E-cadherin-mediated cell-cell adhesion. E-cadherin knockdown reversed Gα₁₃ siRNA-induced cell-cell adhesion but failed to reverse the effect of Gα₁₃ siRNA on proteolytic invasion. Instead, concurrent knockdown of E-cadherin and Gα₁₃ led to an increased number of single cells rather than groups of cells. Significantly, knockdown of discoidin domain receptor 1 (DDR1), a collagen-binding protein that also co-localizes to cell-cell junctions, reversed the effects of Gα₁₃ knockdown on cell-cell adhesion and proteolytic invasion in three-dimensional collagen. Knockdown of the polarity protein Par3, which can function downstream of DDR1, also reversed the effects of Gα₁₃ knockdown on cell-cell adhesion and proteolytic invasion in three-dimensional collagen. Overall, we show that Gα₁₃ and DDR1-Par3 differentially regulate cellcell junctions and the actin cytoskeleton to mediate invasion in three-dimensional collagen.