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PI(3,5)P2 controls endosomal branched actin dynamics by regulating cortactin-actin interactions.

Hong NH, Qi A, Weaver AM - J. Cell Biol. (2015)

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.

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Affiliation: Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, TN 37232.

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PI(3,5)P2 regulates the interaction of cortactin with actin filaments. (A) Schematic of WT and mutant cortactin constructs. (B, left) Representative Western blot from n = 3 Arp2/3 binding experiments, probed with an antibody to Arp2. (right) Coomassie-stained gel of GST-tagged proteins immobilized on glutathione beads used in Arp2/3 binding experiment. The same amount of beads was loaded in each lane and used in the experiment. (C and D) Representative Western blots from (C) GST-N-term and (D) GST-Δ4RP cortactin–pull-down experiments. Cortactin proteins bound to PI(3,5)P2-liposomes were identified with an anti-GST antibody. Relative binding affinity was quantified by densitometric analysis of Western blot data from three independent experiments. Mean ± SE. *, P < 0.05; ****, P < 0.0001. (E and F) F-actin competes with PI(3,5)P2 for binding to cortactin. (E) Increasing concentrations of actin filaments were incubated with 70 nM cortactin and 250 nM PI(3,5)P2-containing liposomes. In the presence of F-actin, cortactin binding to liposomes was significantly reduced. (F) Data points show mean binding from four independent experiments. Fit to hyperbolic decay model yields a Ki value of 0.461 µM.
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fig5: PI(3,5)P2 regulates the interaction of cortactin with actin filaments. (A) Schematic of WT and mutant cortactin constructs. (B, left) Representative Western blot from n = 3 Arp2/3 binding experiments, probed with an antibody to Arp2. (right) Coomassie-stained gel of GST-tagged proteins immobilized on glutathione beads used in Arp2/3 binding experiment. The same amount of beads was loaded in each lane and used in the experiment. (C and D) Representative Western blots from (C) GST-N-term and (D) GST-Δ4RP cortactin–pull-down experiments. Cortactin proteins bound to PI(3,5)P2-liposomes were identified with an anti-GST antibody. Relative binding affinity was quantified by densitometric analysis of Western blot data from three independent experiments. Mean ± SE. *, P < 0.05; ****, P < 0.0001. (E and F) F-actin competes with PI(3,5)P2 for binding to cortactin. (E) Increasing concentrations of actin filaments were incubated with 70 nM cortactin and 250 nM PI(3,5)P2-containing liposomes. In the presence of F-actin, cortactin binding to liposomes was significantly reduced. (F) Data points show mean binding from four independent experiments. Fit to hyperbolic decay model yields a Ki value of 0.461 µM.

Mentions: To map the PI(3,5)P2 binding site of cortactin, we tested the ability of the purified cortactin N terminus and fourth repeat deletion mutant to bind PI(3,5)P2-containing liposomes (Fig. 5 A). The cortactin repeat domains each contain 37 aa (Wu et al., 1991) and are not likely to be involved in large scale folding of cortactin because common splice variants of cortactin have lost either the sixth or fifth + sixth repeats (van Rossum et al., 2003) and purified cortactin has been shown to have an extended structure (Weaver et al., 2002). Furthermore, deletion of the fourth repeat domain from either end of N- or C-terminal cortactin fragments leads to loss of binding of those fragments to actin filaments (Weed et al., 2000), suggesting a specific activity of that domain and not whole-scale unfolding of the molecule. Finally, we find that cortactin lacking the fourth repeat can still bind to Arp2/3 complex (Fig. 5 B), further suggesting that loss of the fourth repeat domain does not affect cortactin activities located in other parts of the N terminus. Consistent with our hypothesis that the PI(3,5)P2 binding activity might be located in the fourth repeat domain in the N terminus, we found that the N terminus of cortactin is sufficient to bind PI(3,5)P2 (Fig. 5 C), whereas the fourth repeat deletion mutant of cortactin cannot bind PI(3,5)P2-liposomes (Fig. 5 D).


PI(3,5)P2 controls endosomal branched actin dynamics by regulating cortactin-actin interactions.

Hong NH, Qi A, Weaver AM - J. Cell Biol. (2015)

PI(3,5)P2 regulates the interaction of cortactin with actin filaments. (A) Schematic of WT and mutant cortactin constructs. (B, left) Representative Western blot from n = 3 Arp2/3 binding experiments, probed with an antibody to Arp2. (right) Coomassie-stained gel of GST-tagged proteins immobilized on glutathione beads used in Arp2/3 binding experiment. The same amount of beads was loaded in each lane and used in the experiment. (C and D) Representative Western blots from (C) GST-N-term and (D) GST-Δ4RP cortactin–pull-down experiments. Cortactin proteins bound to PI(3,5)P2-liposomes were identified with an anti-GST antibody. Relative binding affinity was quantified by densitometric analysis of Western blot data from three independent experiments. Mean ± SE. *, P < 0.05; ****, P < 0.0001. (E and F) F-actin competes with PI(3,5)P2 for binding to cortactin. (E) Increasing concentrations of actin filaments were incubated with 70 nM cortactin and 250 nM PI(3,5)P2-containing liposomes. In the presence of F-actin, cortactin binding to liposomes was significantly reduced. (F) Data points show mean binding from four independent experiments. Fit to hyperbolic decay model yields a Ki value of 0.461 µM.
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fig5: PI(3,5)P2 regulates the interaction of cortactin with actin filaments. (A) Schematic of WT and mutant cortactin constructs. (B, left) Representative Western blot from n = 3 Arp2/3 binding experiments, probed with an antibody to Arp2. (right) Coomassie-stained gel of GST-tagged proteins immobilized on glutathione beads used in Arp2/3 binding experiment. The same amount of beads was loaded in each lane and used in the experiment. (C and D) Representative Western blots from (C) GST-N-term and (D) GST-Δ4RP cortactin–pull-down experiments. Cortactin proteins bound to PI(3,5)P2-liposomes were identified with an anti-GST antibody. Relative binding affinity was quantified by densitometric analysis of Western blot data from three independent experiments. Mean ± SE. *, P < 0.05; ****, P < 0.0001. (E and F) F-actin competes with PI(3,5)P2 for binding to cortactin. (E) Increasing concentrations of actin filaments were incubated with 70 nM cortactin and 250 nM PI(3,5)P2-containing liposomes. In the presence of F-actin, cortactin binding to liposomes was significantly reduced. (F) Data points show mean binding from four independent experiments. Fit to hyperbolic decay model yields a Ki value of 0.461 µM.
Mentions: To map the PI(3,5)P2 binding site of cortactin, we tested the ability of the purified cortactin N terminus and fourth repeat deletion mutant to bind PI(3,5)P2-containing liposomes (Fig. 5 A). The cortactin repeat domains each contain 37 aa (Wu et al., 1991) and are not likely to be involved in large scale folding of cortactin because common splice variants of cortactin have lost either the sixth or fifth + sixth repeats (van Rossum et al., 2003) and purified cortactin has been shown to have an extended structure (Weaver et al., 2002). Furthermore, deletion of the fourth repeat domain from either end of N- or C-terminal cortactin fragments leads to loss of binding of those fragments to actin filaments (Weed et al., 2000), suggesting a specific activity of that domain and not whole-scale unfolding of the molecule. Finally, we find that cortactin lacking the fourth repeat can still bind to Arp2/3 complex (Fig. 5 B), further suggesting that loss of the fourth repeat domain does not affect cortactin activities located in other parts of the N terminus. Consistent with our hypothesis that the PI(3,5)P2 binding activity might be located in the fourth repeat domain in the N terminus, we found that the N terminus of cortactin is sufficient to bind PI(3,5)P2 (Fig. 5 C), whereas the fourth repeat deletion mutant of cortactin cannot bind PI(3,5)P2-liposomes (Fig. 5 D).

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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, TN 37232.

Show MeSH
Related in: MedlinePlus