PPP2R1A Regulates Migration Persistence through the WAVE Shell Complex

Abstract

The RAC1-WAVE-Arp2/3 signaling pathway generates branched actin networks that power lamellipodium protrusion of migrating cells. Feedback is thought to control protrusion lifetime and migration persistence, but its molecular circuitry remains elusive. Using proteomics, we identified PPP2R1A among proteins differentially associated with the WAVE complex subunit ABI1 when RAC1 was activated and downstream generation of branched actin was blocked. PPP2R1A was found to associate at the lamellipodial edge with a novel form of WAVE complex, the WAVE Shell Complex (WSC), that contains NHSL1 instead of the Arp2/3 activating subunit WAVE as in the canonical WAVE Regulatory Complex (WRC). PPP2R1A was required for persistence in random and directed migration assays and for RAC1-dependent actin polymerization in cell extracts. PPP2R1A requirement was abolished by NHSL1 depletion. PPP2R1A mutations found in tumors impaired WSC binding and migration regulation, suggesting that this novel function of PPP2R1A is critical for its tumor suppressor activity.

Nance-Horan-Syndrome-like 1b controls mesodermal cell migration by regulating protrusion and actin dynamics during zebrafish gastrulation

“…Our in vivo analysis of Nhls1b function is overall very consistent with in vitro observations. We observed that Nhsl1b localises to cell-cell contacts, and, as seen in vitro 20,21 , to the tip of actin-rich protrusions, which are the in vivo functional equivalents of lamellipodia. As in vitro , our results clearly establish a role of Nhsl1b in controlling cell migration speed and persistence, likely through modulation of actin dynamics.…”

“…Knockdown and overexpression experiments revealed a role for nhsl1b in controlling migration speed and persistence. For cells migrating in vitro , on a 2D substrate, both speed and persistence are largely determined by the dynamics of the lamellipodium 19 , and NHSL1 has been shown to localise to the very edge of the lamellipodium in cultured cells 20,21 . In vivo , in complex 3D environments, migrating cells such as the lateral mesoderm do not form characteristic lamellipodia, but rely on functionally equivalent actin-rich protrusions 16 .…”

“…First, while two studies have reported that NHSL1 knockdown increases migration persistence, suggesting that it acts as a negative regulator of cell migration 20,21 , its in vitro function may not be as clear cut. Indeed, Law et al reported that while NHSL1 inhibits Arp2/3, NHSL1 knockdown reduces actin assembly in the lamellipodium 20 .…”

“…Modulating this Rac1-WAVE-Arp2/3 pathway directly affects the length and lifetime of protrusions, thereby determining the speed and persistence of migration 19 . Very recently, NHSL1, has been identified as a novel regulator of protrusion dynamics and cell migration in vitro 20,21 . NHSL1 is a member of the Nance-Horan syndrome (NHS) family, which in mammals also includes NHS and NHSL2 22,23 .…”

“…Consistently, NHSL1 colocalises with WAVE complex subunits at the very edge of lamellipodia 20 , where both studies proposed that it negatively regulates cell migration, since its knockdown induces an increase in migration persistence of randomly moving cells. However, its precise function may be more complex, as overexpression induced similar defects as the knockdown 20 , and NHSL1 appears required to mediate the effect of PPP2R1A, another new interactor of the WAVE Shell Complex, which positively regulates migration persistence 21 . Its effect on the persistence of cells migrating in more physiological contexts has not yet been tested.…”