PI(3,5)P2 controls endosomal branched actin dynamics by regulating cortactin-actin interactions.
Bottom Line: These findings suggest that PI(3,5)P2 formation on endosomes may remove cortactin from endosome-associated branched actin.Conversely, inhibition of Arp2/3 complex activity greatly reduced cortactin localization to late endosomes.These data suggest a model in which PI(3,5)P2 binding removes cortactin from late endosomal branched actin networks and thereby promotes net actin turnover.
Affiliation: Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, TN 37232.Show MeSH
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Mentions: The enzyme complex that synthesizes PI(3,5)P2 localizes to both early and late endosomes and consists of the scaffold protein Vac14, the lipid kinase PIKfyve (which converts PI(3)P to PI(3,5)P2), and the counteracting lipid phosphatase Fig4 (Rudge et al., 2004; Ikonomov et al., 2006; Nicot et al., 2006; Rusten et al., 2006; Rutherford et al., 2006). To determine whether cortactin and the PI(3,5)P2-synthesizing enzyme complex are likely to be present in the same compartment, we immunolocalized cortactin with Vac14. Immunostaining of SCC61 and HeLa cells transiently expressing hVac14-EGFP (Jin et al., 2008) with antibodies against cortactin revealed that cortactin is indeed present on Vac14+ vesicular structures (Fig. 2 A). To further determine whether cortactin is present at PI(3,5)P2-containing endosomes, we localized cortactin with a specific probe for PI(3,5)P2, mCherry-ML1N*2 (Li et al., 2013), and with the late endosomal marker Rab7. As expected, mCherry-ML1N*2 and Rab7 were present together in the same endosomal populations with virtually all ML1N*7+ endosomes containing Rab7+ puncta or rings (Fig. 2, B and C). Consistent with the role of PI(3,5)P2 in late endosomal maturation (de Lartigue et al., 2009; Dove et al., 2009), individual endosomes had different proportions of Rab7 or ML1N*2 positivity (Fig. 2 C). Cortactin localized to some of these Rab7-ML1N*2+ endosomes (Fig. 2 B).
Affiliation: Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, TN 37232.