Rho in podosomes

Berdeaux, Díaz, and colleagues report that active Rho (Rho[GTP]) is localized to podosomes in oncogenically transformed cells (page 317). These matrix-digesting, actin-rich, short-lived protrusions help osteoclasts to eat bone and migratory and cancer cells to chew their way through matrix. Their function in Src-transformed cells is now found to rely on Rho activity.

Rho is known to promote the formation of focal adhesions and actin stress fibers, so the disappearance of stress fibers after transformation with oncogenic Src was presumed to reflect down-regulation of Rho. But Berdeaux et al. report that levels of Rho[GTP] are not decreased in Src-transformed cells. Instead, focal adhesions and stress fibers may be lost because Src induces a block in signaling downstream of Rho and a loss in cell–matrix adhesion.

Active Rho is, however, found in Src- induced podosomes....