Upregulation of NHE1 protein expression enables glioblastoma cells to escape TMZ-mediated toxicity via increased H⁺extrusion, cell migration and survival

Abstract

Sodium-hydrogen exchanger isoform 1 (NHE1) plays a role in survival and migration/invasion of several cancers and is an emerging new therapeutic target. However, the role of NHE1 in glioblastoma and the interaction of NHE1 expression and function in glioblastoma cells with cytotoxic temozolomide (TMZ) therapy remain unknown. In this study, we detected high levels of NHE1 protein only in primary human glioma cells (GC), glioma xenografts and glioblastoma, but not in human neural stem cells or astrocytes. GC exhibited an alkaline resting pH i (7.46 ± 0.04) maintained by robust NHE1-mediated H + extrusion. GC treatment with TMZ for 2-24 h triggered a transient decrease in pH i , which recovered by 48 h and correlated with concurrent upregulation of NHE1 protein expression. NHE1 protein was colocalized with ezrin at lamellipodia and probably involved in GC migration. The TMZ-treated GC exhibited increased migration and invasion, which was attenuated by addition of NHE1 inhibitor HOE-642. Most importantly, NHE1 inhibition prevented prosurvival extracellular signal-regulated kinase activation and accelerated TMZ-induced apoptosis. Taken together, our study provides the first evidence that GC upregulate NHE1 protein to maintain alkaline pH i . Combining TMZ therapy with NHE1 inhibition suppresses GC migration and invasion, and also augments TMZ-induced apoptosis. These findings strongly suggest that NHE1 is an important cytoprotective mechanism in GC and presents a new therapeutic strategy of combining NHE1 inhibition and TMZ chemotherapy.

Cancer cell behaviors mediated by dysregulated pH dynamics at a glance

“…Evidence suggests that NHE1 is a significant contributor to matrix degradation through local extracellular acidification or effects on MMP expression and localization (Lin et al, 2012;Putney and Barber, 2004). Increased pH i resulting from ion transporter activity has been shown to enable cancer cell migration in oncogene-transformed mammary cells (Lauritzen et al, 2012), in patient-derived glioma cell lines (Cong et al, 2014) and in cervical cancer cell lines that do not exhibit hallmarks of metabolic adaptation (De Saedeleer et al, 2014). Furthermore, increased pH i due to higher ion transporter activity has been linked to cell invasion phenotypes (Lin et al, 2012;Grillo-Hill et al, 2015).…”

“…Importantly, decreasing pH i or increasing pH e inhibits cell migration (Parks and Pouyssegur, 2015;Cong et al, 2014;Frantz et al, 2008;Denker and Barber, 2002). We recently described how protonation and deprotonation regulate selective pH sensors involved in cell migration (Schönichen et al, 2013).…”

“…This reversed pH gradient in cancer cells is an early event in cancer development (Reshkin et al, 2000) and increases during neoplastic progression (Cardone et al, 2005). The higher pH i in cancer cells is paradoxical, considering that metabolic acids are generated through increased metabolism and proliferation; however, an increased pH i is maintained in cancer cells through the increased expression or activity of plasma membrane ion transporters and pH i regulators, including the Na + -H + exchanger 1 (NHE1) (Cong et al, 2014;Reshkin et al, 2014), carbonic anhydrases (CAs) (Zheng et al, 2015;Gallagher et al, 2015), monocarboxylate transporter 1 and 4 (MCT1 and MCT4, respectively) (Counillon et al, 2016), and Na + -driven HCO 3 − exchangers (Parks and Pouyssegur, 2015;Lee et al, 2016;Gorbatenko et al, 2014). The dysregulated pH of cancer cells enables cellular processes that are sensitive to small changes in pH i , including cell proliferation, migration and metabolism.…”

The Ser/Thr Kinase MAP4K4 Controls Pro-Metastatic Cell Functions

“…MAP4K4 binds to and phosphorylates the C-terminus of NHE1 and causes its activation, which increases the intracellular pH in proximity of the plasma membrane [13]. NHE1 is involved in cell migration control [70][71][72] and associated with metastatic functions in cancer cells [73][74][75]. GF control of this central regulator of cortical cell functions through MAP4K4 may contribute to local remodeling of the cytoskeleton [76,77] and enable the formation of invasive membrane protrusions.…”

NHE1 has a notable role in metastasis and drug resistance of T-cell acute lymphoblastic leukemia

“…The ERM family is established to be important molecules in cytoskeletal activity as they link actin to the plasma membrane proteins. ERMs are frequently identified to be highly expressed in numerous cancer types and are important mediators of cell survival signaling (10)(11)(12). Previous studies have suggested that high ezrin expression may be associated with cellular motility, therefore having a role in metastasis and invasion (13)(14)(15) in T-ALL drug resistance with ezrin, an important molecule in C-C-motif chemokine ligand 25 (CCL25)-induced T-ALL metastasis (12,16).…”