Arf6 arbitrates fibrinogen endocytosis.

In this issue of Blood, in a departure from studies of classic platelet function, Huang et al turn their attention to endocytosis and show that adenosine 5′-diphosphate-ribosylation factor 6 (Arf6) plays a key role in fibrinogen engulfment. Although platelets are known to bind, absorb, and load their granules with plasma proteins, this report is one of the first to explore mechanisms that control endocytosis in this anucleate cell. Huang et al demonstrate that Arf6-dependent endocytosis is restricted to fibrinogen, implying that Arf6 also modulates trafficking of αIIbβ3 integrins in platelets. Consistent with this notion, deletion of Arf6 in platelets enhances spreading on fibrinogen and accelerates clot retraction (see figure). However, activation of surface αIIbβ3 is unaffected, and Arf6 deficiency does not alter thrombosis in vivo. These incongruous results point toward the complexity of anucleate platelets and the need for more detailed studies to understand intracellular trafficking, recycling, and endocytosis in platelets and their precurs