Dynamic behavior of invadosome rosettes with ventral lamellipodia

Invadosomes are actin-based cellular protrusions that can locally degrade the extracellular matrix. Invadosomes can arrange into higher order structures, such as clusters and circular rosettes in which individual invadosomes show coordinated behavior. We have previously reported that stimulation of Src-transformed melanoma cells with lysophosphatidic acid (LPA) causes invadosomes to rapidly transform into dynamic invadosome rosettes. Here we combine a new tool, caged LPA, with advanced microscopy techniques to characterize the architecture and dynamic movements of LPA-induced invadosome rosettes in detail. Using automated image analysis, we show that LPA induces rosettes at nanomolar concentrations in a dose-dependent manner. Furthermore, local photolysis of caged LPA demonstrates that activation of LPA receptors in a small region of the cell suffices to locally evoke rosettes, and that cells present in a gradient of LPA form rosettes in a highly polarized manner. We find that rosettes are often accompanied by a dynamic ventral lamellipodium that appears to lead the dynamic behavior of the invadosomes rosettes, providing a candidate-mechanism to start explaining the coordinates movement of invadosomes within the rosette.