Cell migration requires both ion translocation and cytoskeletal anchoring by the Na-H exchanger NHE1

Abstract

Directed cell movement is a multi-step process requiring an initial spatial polarization that is established by asymmetric stimulation of Rho GTPases, phosphoinositides (PIs), and actin polymerization. We report that the Na-H exchanger isoform 1 (NHE1), a ubiquitously expressed plasma membrane ion exchanger, is necessary for establishing polarity in migrating fibroblasts. In fibroblasts, NHE1 is predominantly localized in lamellipodia, where it functions as a plasma membrane anchor for actin filaments by its direct binding of ezrin/radixin/moesin (ERM) proteins. Migration in a wounding assay was impaired in fibroblasts expressing NHE1 with mutations that independently disrupt ERM binding and cytoskeletal anchoring or ion transport. Disrupting either function of NHE1 impaired polarity, as indicated by loss of directionality, mislocalization of the Golgi apparatus away from the orientation of the wound edge, and inhibition of PI signaling. Both functions of NHE1 were also required for remodeling of focal adhesions. Most notably, lack of ion transport inhibited de-adhesion, resulting in trailing edges that failed to retract. These findings indicate that by regulating asymmetric signals that establish polarity and by coordinating focal adhesion remodeling at the cell front and rear, cytoskeletal anchoring by NHE1 and its localized activity in lamellipodia act cooperatively to integrate cues for directed migration.

Actin filaments are involved in the maintenance of Golgi cisternae morphology and intra‐Golgi pH

“…Ion exchangers and (V)H þ -ATPases can be both Golgi-resident and en route to the plasma membrane [Kellokumpu et al, 1988;Kopito, 1990;Moriyama and Nelson, 1998;Nishi and Forgac, 2002;Vitavska et al, 2003;Chen et al, 2004b]. By analogy to NHEs isoforms localized to the plasma membrane (NHE1) and endocytic compartments (NHE3 and NHE5) [Szaszi et al, 2000;Denker and Barber, 2002], Golgi-associated NHEs isoforms (NHE7 and NHE8) [Nakamura et al, 2005] might be regulated by the state of F-actin in the Golgi complex. In the plasma membrane of red blood cells, an ankyrin/spectrin meshwork associates with anion exchanger 1 (AE1 or Band 3).…”

Ratiometric Imaging of pH Probes

“…For example, increased cytosolic pH and decreased extracellular pH at the leading edge of migrating cells are evolutionarily conserved signals necessary for directed cell migration. Experiments using BCECF and SNARF demonstrate that increased pHi promotes de novo actin polymerization in a variety of organisms including sea urchin eggs (Begg & Rebhun, 1979), the slime mold Dictyostelium discoideum (Patel & Barber, 2005;Plant et al, 1999;Van Duijn & Inouye, 1991), and mammalian cells (Denker & Barber, 2002). More recently, the use of TIRF microscopy using BCECF (Brett et al, 2005;Ludwig, Schwab, & Stock, 2013) and paxillin-mCherry-pHluorin ( Fig.…”

Traditional and emerging roles for the SLC9 Na+/H+ exchangers

“…In contrast, in migrating fibroblasts, NHE1 concentrates at the leading edge of the cell along the border of lamellipodia [41,40]. NHE1 abundance at the plasma membrane was recently shown to be regulated by direct ubiquitylation of the exchanger [154].…”

“…NHE1 also participates in cell migration [82,40,41,150,79]. Inhibition or genetic ablation of NHE1 from fibroblasts significantly reduces migration speed and inhibits chemotaxis.…”