FIGURE 7:

Model depicting macropinosome formation and transport. Sequential events in the macropinosome lifecycle are represented from PM ruffling, macropinosome formation, movement through the lamella, and into the cell interior (top to bottom of figure). Myosin IIA is present at the ruffling cell edge and myosin IIB is on the actin arc at the base of the lamella. Newly formed macropinosomes are coated in F-actin and myosin IIA and are often seen to compress as they move through the myosin IIB-associated actin arc prior to actin uncoating and release into the cell interior. Microtubules extend outward into the lamella (dashed lines), providing a tract for the incoming macropinosome through the lamellar actin mesh. Active Arf6 is present at the PM and recruits JIP3/4 to the forming macropinosome to engage a dynein motor for completion of macropinocytosis and transport into the cell interior. Two types of CIE cargo are illustrated (MHCI/CD59 and CD98/CD147).