Polarization of Na+/H+ and Cl−/Hco 3− Exchangers in Migrating Renal Epithelial Cells

Abstract

Cell migration is crucial for processes such as immune defense, wound healing, or the formation of tumor metastases. Typically, migrating cells are polarized within the plane of movement with lamellipodium and cell body representing the front and rear of the cell, respectively. Here, we address the question of whether this polarization also extends to the distribution of ion transporters such as Na+/H+ exchanger (NHE) and anion exchanger in the plasma membrane of migrating cells. Both transporters are required for locomotion of renal epithelial (Madin-Darby canine kidney, MDCK-F) cells and human melanoma cells since their blockade reduces the rate of migration in a dose-dependent manner. Inhibition of migration of MDCK-F cells by NHE blockers is accompanied by a decrease of pHi. However, when cells are acidified with weak organic acids, migration of MDCK-F cells is normal despite an even more pronounced decrease of pHi. Under these conditions, NHE activity is increased so that cells are swelling due to the accumulation of organic anions and Na+. When exclusively applied to the lamellipodium, blockers of NHE or anion exchange inhibit migration of MDCK-F cells as effectively as when applied to the entire cell surface. When they are directed to the cell body, migration is not affected. These data are confirmed immunocytochemically in that the anion exchanger AE2 is concentrated at the front of MDCK-F cells. Our findings show that NHE and anion exchanger are distributed in a polarized way in migrating cells. They are consistent with important contributions of both transporters to protrusion of the lamellipodium via solute uptake and consequent volume increase at the front of migrating cells.

The chemistry, physiology and pathology of pH in cancer

“…The pH sensors involved in cancer disease progression have proved to be more challenging to identify, possibly because of difficulties in distinguishing bona fide pH sensors from the plethora of proteins that bind H þ ions [2]. Cells sensing an alkaline pH i have been shown to proliferate [61], enter the cell cycle [62,63], differentiate [64], migrate [65,66], reduce apoptosis [67] and clastogenesis [68], and undergo malignant transformation [69,70]-events that are critical in cancer formation and metastasis. Considering the complexity of these processes, the observed pH i sensitivity may involve a number of H þ -binding molecular switches.…”

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

“…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.…”

BAX inhibitor-1 enhances cancer metastasis by altering glucose metabolism and activating the sodium-hydrogen exchanger: the alteration of mitochondrial function

“…It is required for the migration of keratinocytes (Bereiter-Hahn and Voth, 1988), neutrophil granulocytes (Rosengren et al, 1994), fibroblasts and renal epithelial cells (Klein et al, 2000). NHE inhibition reduces the migration rate of MDCK-F cells (Klein et al, 2000), whereas NHE activation augments the motility and the invasiveness of human breast carcinoma cells (Reshkin et al 2000). Interestingly, the NHE and integrin receptor molecules are often colocalized at the focal adhesion sites of the leading edges of lamellipodia (Grinstein et al, 1993;Plopper et al, 1995).…”

“…NHE could be strongly inhibited by 5-(Nethyl-N-isopropyl) amiloride (EIPA, an inhibitor of NHE1) in BI-1 cells ( Figure 5c). NHE extrudes H þ through intrusion of Na þ to regulate intracellular pH (Plopper et al, 1995;Klein et al, 2000). To understand the physiological meaning of NHE1 in BI-1 cells, intraand extracellular pH were measured in Neo, BI-1 and CDBI-1 cells with or without EIPA.…”

“…Alterations of glucose metabolism regulate cancer metastasis by high glucose uptake, high lactate formation, low extracellular pH (pH e ) and reduction of intratumoral pH (Bhujwalla et al, 2002;Schornack and Gillies, 2003;Gatenby and Gillies, 2004;Gatenby et al, 2006). The acidic environment is produced by the activity of ion channels and transporters such as Na þ /H þ or Cl/HCO 3 exchangers (Klein et al, 2000;Saadoun et al, 2005). The ubiquitously expressed Na þ /H þ exchanger isoform, sodium hydrogen exchanger (NHE1), also contributes to this acidic environment (Plopper et al, 1995).…”