Podosome

Podosomes are the primary sites of integrin stimulated actin polymerization in leukocytes of the monocytic lineage. B cells have also been reported to form podosomes. Podosomes are similar in composition and structure to the invadopodia found in fibroblasts transformed with the v-Src oncogene which are matrix-degrading and whose formation is associated with increased tumor cell invasiveness.

In myeloid cells, podosomes are necessary for directional movement and trans-cellular diapedesis at sites of inflammation. In osteoclasts, podosomes are thought to aid in the creation of sealing rings associated with the area of bone resorption.

Unlike focal contacts in fibroblasts and epithelial cells, the formation of podosomes does not require protein synthesis.