Podosome

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.

A podosome consists of a core rich in actin surrounded by adhesion and scaffolding proteins. The actin filaments within these structures are highly regulated by many actin nucleators, polymerization activators, actin binding and crosslinking proteins, kinases, small GTPases, and scaffold proteins; therefore, total actin turnover occurs within seconds. To distinguish podosomes from others types of cellular adhesions, the protein Tks5 and WASP (Wiskott-Aldrich Syndrome protein) are used as markers alongside actin, cortactin and the Arp2/3 complex to localize and isolate these protrusions because Tks5 and WASP are unique to the podosome when compared with other actin-based cellular structures.