Podosomes

Podosome
Podosomes (yellow) in melanoma cells, along with cell nuclei (blue), actin (red), and an actin regulator (green).
Details
Latin	Podosoma
TH	H1.00.01.1.02034
Anatomical terminology []

Podosomes are conical, actin-rich structures found on the outer surface of the plasma membrane of animal cells. Their size ranges from approximately 0.5 um to 2.0 µm in diameter. While usually situated on the periphery of the cellular membrane, these unique structures display a polarized pattern of distribution in migrating cells, situating at the front border between the lamellipodium and lamellum. Their primary purpose is connected to cellular motility and invasion; therefore, they serve as both sites of attachment and degradation along the extracellular matrix. Many different specialized cells exhibit these dynamic structures such as invasive cancer cells, osteoclasts, vascular smooth muscle cells, endothelial cells, and certain immune cells like macrophages and dendritic cells.

In the early 1980s, chicken embryo fibroblasts were transformed using the Rous sarcoma virus (RSV) containing the oncogene v-src. This transformation elicited the relocalization of vinculin and α-actin in the cytoskeleton from focal adhesions forming circular clusters. Later in 1985, it was shown using the same cells that these protein clusters were localized to protrusions in the ventral plasma membrane, were substratum adhesion sites; therefore, these structures were termed podosomes indicating their foot-like character in cells. In 1989, it was demonstrated that these podosomes played a role in matrix degradation. To reflect this newly discovered destructive nature the name invadopodia was given to these dynamic structures.