Migration of human melanoma cells depends on extracellular pH and Na⁺/H⁺ exchange

Abstract

Their glycolytic metabolism imposes an increased acid load upon tumour cells. The surplus protons are extruded by the Na + /H + exchanger (NHE) which causes an extracellular acidification. It is not yet known by what mechanism extracellular pH (pH e ) and NHE activity affect tumour cell migration and thus metastasis. We studied the impact of pH e and NHE activity on the motility of human melanoma (MV3) cells. Cells were seeded on/in collagen I matrices. Migration was monitored employing time lapse video microscopy and then quantified as the movement of the cell centre. Intracellular pH (pH i ) was measured fluorometrically. Cell-matrix interactions were tested in cell adhesion assays and by the displacement of microbeads inside a collagen matrix. Migration depended on the integrin α2β1. Cells reached their maximum motility at pH e ∼7.0. They hardly migrated at pH e 6.6 or 7.5, when NHE was inhibited, or when NHE activity was stimulated by loading cells with propionic acid. These procedures also caused characteristic changes in cell morphology and pH i . The changes in pH i , however, did not account for the changes in morphology and migratory behaviour. Migration and morphology more likely correlate with the strength of cell-matrix interactions. Adhesion was the strongest at pH e 6.6. It weakened at basic pH e , upon NHE inhibition, or upon blockage of the integrin α2β1. We propose that pH e and NHE activity affect migration of human melanoma cells by modulating cell-matrix interactions. Migration is hindered when the interaction is too strong (acidic pH e ) or too weak (alkaline pH e or NHE inhibition).

Structural model and functional significance of pH-dependent talin–actin binding for focal adhesion remodeling

“…Increased pH i was previously suggested to promote FA remodeling (12,13), and we now show that talin acts as a pH sensor in regulating the stability of FAs. Through a combination of computational simulations, NMR, and functional studies, we demonstrate that talin His-2418 plays a key role in pH sensing and pH-dependent actin binding.…”

“…For protein expression, transformed BL21 cells were grown in minimal medium [Na2HPO4, KH2PO4, NaCl, MgSO4, CaCl2, MEM vitamin mix (Gibco), 15 NH4Cl, 13 C glucose, Isogrow 15 N 13 C, biotin, and FeCl2] with ampicillin. GST fusion proteins with an intervening PreScission protease recognition site were expressed and purified as described (24), cleaved on-column with PreScission protease, eluted, and concentrated to 1 mM.…”

“…In motile cells, an increase in intracellular pH (pH i ) promotes FA remodeling (11)(12)(13) and velocity (12,14). We speculated that increased pH i in motile cells might promote dynamic turnover of FAs by lowering the affinity of actin binding by talin.…”

The acidic microenvironment as a possible niche of dormant tumor cells

“…Stock et al using a model of directional cell migration in an extracellular pH gradient showed that melanoma cells hardly migrate at pHe 6.6 when adhesion was found particularly elevated [72]. Indeed, through computational molecular dynamic simulations, Paradise et al found that acidic extracellular pH (pH 6.0 for 8 h) promotes opening of the αvβ3 headpiece [73], a conformational change supporting a stable interaction between integrin αvβ3 and its ECM biological ligands.…”

Cancer metabolism in space and time: Beyond the Warburg effect

“…This re sults from the ab nor mal meta bolic ac tiv ity of can cer cells, in clud ing in creased gly colytic flux and lac tic acid re lease [150]; car bon diox ide pro duc tion by the TCA cy cle and the pen tose phos phate path way (PPP) [151][152][153][154]; over ex pres sion or up reg u lated ac tiv ity of car bonic an hy drases [155,156] and pro ton trans porters [156]; and de creased pro ton clear ance in the tu mor en vi ron ment [157]. Pro ton ex tru sion and ex tra cel lu lar acid i fi ca tion make ad her ent junc tions lose [158], stim u late mi gra tion and cy toskele ton re or ga ni za tion [159][160][161][162][163], and pro mote the ex pres sion [164,165], re lease [166,167] and ac tiv ity [167,168] of pro teases that de grade the ex tra cel lu lar ma trix. Hence, acidic prim ing was shown to be suf fi cient to in crease lung col o niza tion fol low ing sar coma and melanoma tu mor cell in jec tion in the tail vein of mice [163,167,169,170].…”