The NHERF1 PDZ2 domain regulates PKA-RhoA-p38-mediated NHE1 activation and invasion in breast tumor cells

Translational Results of Zo-NAnTax: A Phase II Trial of Neoadjuvant Zoledronic Acid in HER2-Positive Breast Cancer

Breast cancer is a heterogeneous disease with distinct clinical and molecular characteristics. Scientific advances in molecular subtype differentiation support the understanding of cellular signaling, crosstalk, proliferation, survival, migration, and invasion mechanisms, allowing the development of new molecular drug targets. The breast cancer subtype with super expression and/or amplification of human growth factor receptor 2 (HER2) is clinically aggressive, but prognosis significantly shifted with the advent of anti-HER2 targeted therapy. Zoledronic-acid (ZOL) combined with a neoadjuvant Trastuzumab-containing chemotherapy regimen (Doxorubicin, Cyclophosphamide followed by Docetaxel, Trastuzumab) increased the pCR rate in a RH-positive/ HER2-positive subgroup, according to the phase II Zo-NAnTax trial. To verify genes that could be related to this response, a microarray assay was performed finding 164 differentially expressed genes. Silico analysis of these genes showed signaling pathways related to growth factors, apoptosis, invasion, and metabolism, as well as differentially expressed genes related to estrogen response. In addition, the RAC3 gene was found to interact with the MVD gene, a member of the mevalonate pathway. Taken together, these results indicate that RH-positive/ HER2-positive patients present gene alterations before treatment, and these could be related to the improvement of pCR.

Phosphatidic acid-PKA signaling regulates p38 and ERK1/2 functions in ligand-independent EGFR endocytosis

Ligand-independent epidermal growth factor receptor (EGFR) endocytosis is inducible by a variety of stress conditions converging upon p38 kinase. A less known pathway involves phosphatidic acid (PA) signaling toward the activation of type 4 phosphodiesterases (PDE4) that decrease cAMP levels and protein kinase A (PKA) activity. This PA/PDE4/PKA pathway is triggered with propranolol used to inhibit PA hydrolysis and induces clathrin-dependent and clathrin-independent endocytosis, followed by reversible accumulation of EGFR in recycling endosomes. Here we give further evidence of this signaling pathway using biosensors of PA, cAMP, and PKA in live cells and then show that it activates p38 and ERK1/2 downstream the PKA inhibition. Clathrin-silencing and IN/SUR experiments involved the activity of p38 in the clathrin-dependent route, while ERK1/2 mediates clathrin-independent EGFR endocytosis. The PA/PDE4/PKA pathway selectively increases the EGFR endocytic rate without affecting LDLR and TfR constitute endocytosis. This selectiveness is probably because of EGFR phosphorylation, as detected in Th1046/1047 and Ser669 residues. The EGFR accumulates at perinuclear recycling endosomes colocalizing with TfR, fluorescent transferrin, and Rab11, while a small proportion distributes to Alix-endosomes. A non-selective recycling arrest includes LDLR and TfR in a reversible manner. The PA/PDE4/PKA pathway involving both p38 and ERK1/2 expands the possibilities of EGFR transmodulation and interference in cancer.

Solute carriers as potential oncodrivers or suppressors: their key functions in malignant tumor formation

Solute carrier (SLC) transporters are primarily known for their function in the transportation of various exogenous/endogenous substances via influx/efflux mechanisms. In addition to their diverse role in several tumor-modulating functions, such as proliferation, migration, angiogenesis, epithelial-mesenchymal transition (EMT), epigenetic modification, chemoresistance, immunoregulation, and oncometabolism, influx/efflux-independent contributions of SLCs in the activation of various signaling network cascades that might drive metastatic tumor formation have also been uncovered. Disappointingly, even after two decades and the discovery of >450 SLCs, many of their members remain orphans in terms of cancer pathogenesis. In this review, we summarize the current understanding of the tumor-modulating functions, mechanisms, and complexity of SLCs, as well as their potential as targets for cancer therapy.

NHERF1/EBP50 as a Target for Modulation of MRP Function in HepG2 Cells

As increased expression and activities of efflux transporters (ETs) often cause drug resistance in cancers, we tried modulating ET activity in cancer cells, using scaffold proteins such as ezrin/radixin/moesin (ERM) proteins, and Na⁺/H⁺ exchanger regulatory factor-1 (NHERF1)/ERM-binding phosphoprotein of 50 kDa (EBP50). To see whether EBP50 modulated ET activities in human liver cancer HepG2 cells, we used EBP50 siRNA and a designed TAT-PDZ1 peptide. The EBP50 knockdown (EBP50^KD) cells had significantly higher intracellular accumulations of Rho123 and carboxy-dichlorofluorescein (CDF), but not H33342 (i.e., the respective substrates of P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and breast cancer resistance protein (BCRP)), compared with control HepG2, suggesting that EBP50 knockdown in HepG2 cells decreased activity of P-gp and MRP but not BCRP. Treatment with TAT-PDZ1 peptide (>1 pM) resulted in significantly higher CDF accumulation in HepG2 cells, which persisted for ≥180 min after TAT-PDZ1 peptide treatment. These results imply that EBP50 can modulate ET activities. To our knowledge, this is the first report on using a competitive peptide to modulate interactions between MRP and EBP50.

Integrin-Linked Kinase Links Integrin Activation to Invadopodia Function and Invasion via the p(T567)-Ezrin/NHERF1/NHE1 Pathway

Tumor cell invasion depends largely on degradation of the extracellular matrix (ECM) by protease-rich structures called invadopodia, whose formation and activity requires the convergence of signaling pathways engaged in cell adhesion, actin assembly, membrane regulation and ECM proteolysis. It is known that β1-integrin stimulates invadopodia function through an invadopodial p(T567)-ezrin/NHERF1/NHE1 signal complex that regulates NHE1-driven invadopodia proteolytic activity and invasion. However, the link between β1-integrin and this signaling complex is unknown. In this study, in metastatic breast (MDA-MB-231) and prostate (PC-3) cancer cells, we report that integrin-linked kinase (ILK) integrates β1-integrin with this signaling complex to regulate invadopodia activity and invasion. Proximity ligation assay experiments demonstrate that, in invadopodia, ILK associates with β1-integrin, NHE1 and the scaffold proteins p(T567)-ezrin and NHERF1. Activation of β1-integrin increased both invasion and invadopodia activity, which were specifically blocked by inhibition of either NHE1 or ILK. We conclude that ILK integrates β1-integrin with the ECM proteolytic/invasion signal module to induce NHE1-driven invadopodial ECM proteolysis and cell invasion.

MINDIN Exerts Protumorigenic Actions on Primary Prostate Tumors via Downregulation of the Scaffold Protein NHERF-1

Advanced prostate cancer preferential metastasis to bone is associated with osteomimicry. MINDIN is a secreted matrix protein upregulated in prostate tumors that overexpresses bone-related genes during prostate cancer progression. Na+/H+ exchanger regulatory factor (NHERF-1) is a scaffold protein that has been involved both in tumor regulation and osteogenesis. We hypothesize that NHERF-1 modulation is a mechanism used by MINDIN to promote prostate cancer progression. We analyzed the expression of NHERF-1 and MINDIN in human prostate samples and in a premetastatic prostate cancer mouse model, based on the implantation of prostate adenocarcinoma TRAMP-C1 (transgenic adenocarcinoma of the mouse prostate) cells in immunocompetent C57BL/6 mice. The relationship between NHERF-1 and MINDIN and their effects on cell proliferation, migration, survival and osteomimicry were evaluated. Upregulation of MINDIN and downregulation of NHERF-1 expression were observed both in human prostate cancer samples and in the TRAMP-C1 model. MINDIN silencing restored NHERF-1 expression to control levels in the mouse model. Stimulation with MINDIN reduced NHERF-1 expression and triggered its mobilization from the plasma membrane to the cytoplasm in TRAMP-C1 cells. MINDIN-dependent downregulation of NHERF-1 promoted tumor cell migration and proliferation without affecting osteomimicry and adhesion. We propose that MINDIN downregulates NHERF-1 expression leading to promotion of processes involved in prostate cancer progression.

Noncanonical Sequences Involving NHERF1 Interaction with NPT2A Govern Hormone-Regulated Phosphate Transport: Binding Outside the Box

Na+/H+ exchange factor-1 (NHERF1), a multidomain PDZ scaffolding phosphoprotein, is required for the type II sodium-dependent phosphate cotransporter (NPT2A)-mediated renal phosphate absorption. Both PDZ1 and PDZ2 domains are involved in NPT2A-dependent phosphate uptake. Though harboring identical core-binding motifs, PDZ1 and PDZ2 play entirely different roles in hormone-regulated phosphate transport. PDZ1 is required for the interaction with the C-terminal PDZ-binding sequence of NPT2A (-TRL). Remarkably, phosphocycling at Ser290 distant from PDZ1, the penultimate step for both parathyroid hormone (PTH) and fibroblast growth factor-23 (FGF23) regulation, controls the association between NHERF1 and NPT2A. PDZ2 interacts with the C-terminal PDZ-recognition motif (-TRL) of G Protein-coupled Receptor Kinase 6A (GRK6A), and that promotes phosphorylation of Ser290. The compelling biological puzzle is how PDZ1 and PDZ2 with identical GYGF core-binding motifs specifically recognize distinct binding partners. Binding determinants distinct from the canonical PDZ-ligand interactions and located "outside the box" explain PDZ domain specificity. Phosphorylation of NHERF1 by diverse kinases and associated conformational changes in NHERF1 add more complexity to PDZ-binding diversity.

Sodium Hydrogen Exchanger Regulatory Factor-1 (NHERF1) Regulates Fetal Membrane Inflammation

The fetal inflammatory response, a key contributor of infection-associated preterm birth (PTB), is mediated by nuclear factor kappa B (NF-kB) activation. Na⁺/H⁺ exchanger regulatory factor-1 (NHERF1) is an adapter protein that can regulate intracellular signal transduction and thus influence NF-kB activation. Accordingly, NHERF1 has been reported to enhance proinflammatory cytokine release and amplify inflammation in a NF-kB-dependent fashion in different cell types. The objective of this study was to examine the role of NHERF1 in regulating fetal membrane inflammation during PTB. We evaluated the levels of NHERF1 in human fetal membranes from term labor (TL), term not in labor (TNIL), and PTB and in a CD1 mouse model of PTB induced by lipopolysaccharide (LPS). Additionally, primary cultures of fetal membrane cells were treated with LPS, and NHERF1 expression and cytokine production were evaluated. Gene silencing methods using small interfering RNA targeting NHERF1 were used to determine the functional relevance of NHERF1 in primary cultures. NHERF1 expression was significantly (p < 0.001) higher in TL and PTB membranes compared to TNIL membranes, and this coincided with enhanced (p < 0.01) interleukin (IL)-6 and IL-8 expression levels. LPS-treated animals delivering PTB had increased levels of NHERF1, IL-6, and IL-8 compared to phosphate-buffered saline (PBS; control) animals. Silencing of NHERF1 expression resulted in a significant reduction in NF-kB activation and IL-6 and IL-8 production as well as increased IL-10 production. In conclusion, downregulation of NHERF1 increased anti-inflammatory IL-10, and reducing NHERF1 expression could be a potential therapeutic strategy to reduce the risk of infection/inflammation associated with PTB.

Alteration in the sensitivity to crizotinib by Na+/H+ exchanger regulatory factor 1 is dependent to its subcellular localization in ALK-positive lung cancers

Background

Na⁺/H⁺ exchanger regulatory factor 1 (NHERF1) is an important scaffold protein participates in the modulation of a variety of intracellular signal pathways. NHERF1 was able to enhance the effects of chemo-drugs in breast and cervical cancer cells. Anaplastic lymphoma kinase (ALK) fusion mutations are validated molecules targeted therapy in lung cancers, where crizotinib can be used as the specific inhibitor to suppress tumor progression. However, due to the less frequent occurrence of ALK mutations and the complexity for factors to determine drug responses, the genes that could alter crizotinib sensitivity are unclear.

Methods

Both ALK-translocated and ALK-negative lung adenocarcinoma specimens in tissue sections were collected for immunohistochemistry. The possible mechanisms of NHERF1 and its role in the cell sensitivity to crizotinib were investigated using an ALK-positive and crizotinib-sensitive lung adenocarcinoma cell line H3122. Either a NHERF1 overexpression vector or agents for NHERF1 knockdown was used for crizotinib sensitivity measures, in association with cell viability and apoptosis assays.

Results

The expression level of NHERF1 in ALK-translocated NSCLC was significantly higher than that in other lung cancer tissues. NHERF1 expression in ALK positive lung cancer cells was regulated by ALK activities, and was in return able to alter the sensitivity to crizotinib. The function of NHERF1 to influence crizotinib sensitivity was depending on its subcellular distribution in cytosol instead of its nucleus localized form.

Conclusion

Ectopically overexpressed NHERF1 could be a functional protein for consideration to suppress lung cancers. The determination of NHERF1 levels in ALK positive NSCLC tissues might be useful to predict crizotinib resistance, especially by distinguishing cytosolic or nuclear localized NHERF1 for the overexpressed molecules.

New roles of the Na+/H+ exchange regulatory factor 1 scaffolding protein: a review

Na⁺/H⁺ exchange regulatory factor 1 (NHERF1), a member of a PDZ scaffolding protein family, was first identified as an organizer of membrane-bound protein complexes composed of hormone receptors, signal transduction pathways, and electrolyte and mineral transporters and channels. NHERF1 is involved in the regulation of Na⁺/H⁺ exchanger 3, Na⁺-dependent phosphate transporter 2a, and Na⁺-K⁺-ATPase through its ability to scaffold these transporters to the plasma membrane, allowing regulation of these protein complexes with their associated hormone receptors. Recently, NHERF1 has received increased interest in its involvement in a variety of functions, including cell structure and trafficking, tumorigenesis and tumor behavior, inflammatory responses, and tissue injury. In this review, we highlight the evidence for the expansive role of NHERF1 in cell biology and speculate on the implications for renal physiology and pathophysiology.

Prognostic and therapeutic implications of NHERF1 expression and regulation in colorectal cancer

BACKGROUND

Na⁺ /H⁺ exchanger regulatory factor 1 (NHERF1) has been implicated in the tumorigenesis of several cancer types and is a potential therapeutic target. The current study evaluated the relationship between NHERF1 expression and clinical outcome in colorectal cancer (CRC).

METHODS

NHERF1 expression was evaluated by immunohistochemistry in 167 patients with CRC primary tumors, 37 patients with no disease, and 27 patients with metastatic CRC (mCRC); and in the orthotopically implanted tumors in mice. NHERF1 expression was manipulated in CRC cells using inducible short hairpin RNAs to determine its biological functions.

RESULTS

High expression of NHERF1 correlated with CRC progression and metastasis, as well as significantly worse overall survival, recurrence-free survival, and disease-specific survival. Orthotopic implantation studies demonstrated increased NHERF1 expression in liver metastases. Treatment of CRC xenografts with insulin-like growth factor 1 receptor (IGF1R) inhibitors downregulated NHERF1 expression, indicating NHERF1 is downstream of IGF1R signaling. Knockdown of NHERF1 increased apoptosis and reduced X-linked inhibitor of apoptosis protein (XIAP) and survivin expression, indicating NHERF1 is critical for CRC cell survival.

CONCLUSION

NHERF1 expression levels correlated with worse prognosis in patients with CRC and plays a critical role in CRC cell survival. Together, our findings establish NHERF1 as a novel potential marker for increased risk of CRC-specific mortality and identify NHERF1 as an attractive therapeutic target for mCRC treatment.

Tumor Infiltrating Lymphocytes and NHERF1 Impact on Prognosis of Breast Cancer Patients

BACKGROUND

Breast cancer (BC) is a heterogeneous disease, and patients with apparently similar clinicopathological characteristics in clinical practice show different outcome. This study evaluated in primary BCs and in the subgroup of the triple-negative breast cancers (TNBCs) the level of tumor infiltrating lymphocytes (TILs), Na⁺/H⁺ exchanger regulatory factor 1 (NHERF1) expression, and their association respect to the clinical outcome of patients.

MATERIAL AND METHODS

NHERF1 expression was assessed by immunohistochemistry in 338 BC samples; the analysis of TILs was examined using hematoxylin and eosin stained slides, according to International TILs Working Group 2014.

RESULTS

Multivariate analysis identified TILs as an independent prognostic factor for DFS in the entire cohort and in the TNBC subgroup (HR, 0.32; 95% CI, 0.12-0.87; P = 0.026; and HR, 0.22; 95% CI, 0.06-0.80; P = 0.022, respectively). Univariate and survival analysis by Kaplan-Meier method revealed that patients with cytoplasmic (c) NHERF1^-/TILs⁺ expression had better DFS than other patients (P = 0.049), and this result was also found in the TNBC subgroup (P = 0.031). Moreover, TNBC patients with cNHERF1^-/TILs^- expression had a worse DFS and OS than other patients (P = 0.057 and P = 0.002, respectively).

CONCLUSIONS

In the complex scenario of BC and in the era of tumor immunogenicity and immunotherapy, we found an association of TIL levels and cNHERF1 expression that could be useful to identify BCs and particularly TNBC patients with different prognosis and clinical outcome.

NHERF1 Is Required for Localization of PMCA2 and Suppression of Early Involution in the Female Lactating Mammary Gland

Prior studies have demonstrated that the calcium pump, plasma membrane calcium ATPase 2 (PMCA2), mediates calcium transport into milk and prevents mammary epithelial cell death during lactation. PMCA2 also regulates cell proliferation and cell death in breast cancer cells, in part by maintaining the receptor tyrosine kinase ErbB2/HER2 within specialized plasma membrane domains. Furthermore, the regulation of PMCA2 membrane localization and activity in breast cancer cells requires its interaction with the PDZ domain-containing scaffolding molecule sodium-hydrogen exchanger regulatory factor (NHERF) 1. In this study, we asked whether NHERF1 also interacts with PMCA2 in normal mammary epithelial cells during lactation. Our results demonstrate that NHERF1 expression is upregulated during lactation and that it interacts with PMCA2 at the apical membrane of secretory luminal epithelial cells. Similar to PMCA2, NHERF1 expression is rapidly reduced by milk stasis after weaning. Examining lactating NHERF1 knockout (KO) mice showed that NHERF1 contributes to the proper apical location of PMCA2, for proper apical-basal polarity in luminal epithelial cells, and that it participates in the suppression of Stat3 activation and the prevention of premature mammary gland involution. Additionally, we found that PMCA2 also interacts with the closely related scaffolding molecule, NHERF2, at the apical membrane, which likely maintains PMCA2 at the plasma membrane of mammary epithelial cells in lactating NHERF1KO mice. Based on these data, we conclude that, during lactation, NHERF1 is required for the proper expression and apical localization of PMCA2, which, in turn, contributes to preventing the premature activation of Stat3 and the lysosome-mediated cell death pathway that usually occur only early in mammary involution.

The Role of Sodium Hydrogen Exchanger 1 in Dysregulation of Proton Dynamics and Reprogramming of Cancer Metabolism as a Sequela

Cancer cells have an unusual regulation of hydrogen ion dynamics that are driven by poor vascularity perfusion, regional hypoxia, and increased glycolysis. All these forces synergize/orchestrate together to create extracellular acidity and intracellular alkalinity. Precisely, they lead to extracellular pH (pH_e) values as low as 6.2 and intracellular pH values as high as 8. This unique pH gradient (∆pH_i to ∆pH_e) across the cell membrane increases as the tumor progresses, and is markedly displaced from the electrochemical equilibrium of protons. These unusual pH dynamics influence cancer cell biology, including proliferation, metastasis, and metabolic adaptation. Warburg metabolism with increased glycolysis, even in the presence of Oxygen with the subsequent reduction in Krebs’ cycle, is a common feature of most cancers. This metabolic reprogramming confers evolutionary advantages to cancer cells by enhancing their resistance to hypoxia, to chemotherapy or radiotherapy, allowing rapid production of biological building blocks that support cellular proliferation, and shielding against damaging mitochondrial free radicals. In this article, we highlight the interconnected roles of dysregulated pH dynamics in cancer initiation, progression, adaptation, and in determining the programming and re-programming of tumor cell metabolism.

Independent Negative Prognostic Role of TCF1 Expression within the Wnt/β-Catenin Signaling Pathway in Primary Breast Cancer Patients

The Wnt pathway is involved in the progression of breast cancer (BC). We aimed to evaluate the expression of some components of the Wnt pathway (β-catenin, FZD4 (frizzled receptor 4), LRP5 (low-density lipoprotein receptor-related protein 5), LRP6, and TCF1 (T-cell factor 1)) to detect potential associations with NHERF1 (Na+/H+ exchanger regulatory factor 1) protein. Besides, we assessed their impact on patients’ clinical outcome. We evaluated 220 primary BC samples by immunohistochemistry (IHC) and protein localization by immunofluorescence. We found a significant correlation between NHERF1 and FZD4, LRP5, LRP6, and TCF1. Univariate analysis showed that the overexpression of β-catenin (p < 0.0001), FZD4 (p = 0.0001), LRP5, LRP6, and TCF1 (p < 0.0001 respectively) was related to poor disease-free survival (DFS). A Kaplan-Meier analysis confirmed univariate data and showed a poor DFS for cNHERF1+/FZD4+ (p = 0.0007), cNHERF1+/LRP5+ (p = 0.0002), cNHERF1+/LRP6+ (p < 0.0001), and cNHERF1+/TCF1+ phenotypes (p = 0.0034). In multivariate analysis, the expression of TCF1 and β-catenin was an independent prognostic variable of worse DFS (p = 0.009 and p = 0.027, respectively). In conclusion, we found that the overexpression of β-catenin, FZD4, LRP5, LRP6, and TCF1 was associated with poor prognosis. Furthermore, we first identified TCF1 as an independent prognostic factor of poor outcome, indicating it as a new potential biomarker for the management of BC patients. Also, the expression of Wnt pathway proteins, both alone and in association with NHERF1, suggests original associations of biological significance for new studies.

CAIX Regulates Invadopodia Formation through Both a pH-Dependent Mechanism and Interplay with Actin Regulatory Proteins

Tumor metastasis is tightly linked with invasive membrane protrusions, invadopodia, formed by actively invading tumor cells. Hypoxia and pH modulation play a role in the invadopodia formation and in their matrix degradation ability. Tumor-associated carbonic anhydrase IX (CAIX), induced by hypoxia, is essential for pH regulation and migration, predisposing it as an active component of invadopodia. To investigate this assumption, we employed silencing and inhibition of CA9, invadopodia isolation and matrix degradation assay. Quail chorioallantoic membranes with implanted tumor cells, and lung colonization assay in murine model were used to assess efficiency of in vivo invasion and the impact of CAIX targeting antibodies. We showed that CAIX co-distributes to invadopodia with cortactin, MMP14, NBCe1, and phospho-PKA. Suppression or enzymatic inhibition of CAIX leads to impaired invadopodia formation and matrix degradation. Loss of CAIX attenuated phosphorylation of Y421-cortactin and influenced molecular machinery coordinating actin polymerization essential for invadopodia growth. Treatment of tumor cells by CAIX-specific antibodies against carbonic or proteoglycan domains results in reduced invasion and extravasation in vivo. For the first time, we demonstrated in vivo localization of CAIX within invadopodia. Our findings confirm the key role of CAIX in the metastatic process and gives rationale for its targeting during anti-metastatic therapy.

Structural and Functional Changes in the Na+/H+ Exchanger Isoform 1, Induced by Erk1/2 Phosphorylation

The human Na⁺/H⁺ exchanger isoform 1 (NHE1) is a plasma membrane transport protein that plays an important role in pH regulation in mammalian cells. Because of the generation of protons by intermediary metabolism as well as the negative membrane potential, protons accumulate within the cytosol. Extracellular signal-regulated kinase (ERK)-mediated regulation of NHE1 is important in several human pathologies including in the myocardium in heart disease, as well as in breast cancer as a trigger for growth and metastasis. NHE1 has a N-terminal, a 500 amino acid membrane domain, and a C-terminal 315 amino acid cytosolic domain. The C-terminal domain regulates the membrane domain and its effects on transport are modified by protein binding and phosphorylation. Here, we discuss the physiological regulation of NHE1 by ERK, with an emphasis on the critical effects on structure and function. ERK binds directly to the cytosolic domain at specific binding domains. ERK also phosphorylates NHE1 directly at multiple sites, which enhance NHE1 activity with subsequent downstream physiological effects. The NHE1 cytosolic regulatory tail possesses both ordered and disordered regions, and the disordered regions are stabilized by ERK-mediated phosphorylation at a phosphorylation motif. Overall, ERK pathway mediated phosphorylation modulates the NHE1 tail, and affects the activity, structure, and function of this membrane protein.

HPV16 E6 promotes cervical cancer cell migration and invasion by downregulation of NHERF1

HPV16 is the predominant type of HPV causing invasive cervical cancer. However, the underlying molecular mechanism of the unparalleled carcinogenic power of HPV16 compared to other types of high-risk (HR)-HPV including HPV18 remains elusive. The PDZ binding motif (PBM) of high-risk HPV E6 plays an important role in neoplasia and progression of cervical cancer. HPV16 E6 rather than HPV18 E6, interacted with NHERF1 by its PBM region, and induced degradation of NHERF1. NHERF1 retarded the assembly of cytoskeleton by downregulation of ACTN4, thereby inhibited the migration and invasion of cervical cancer cells in both cell and mouse model. HPV16 E6 was confirmed to enhance actin polymerization with increased ACTN4 level by downregulation of NHERF1, and result in enhanced migration and invasion of cervical cancer cells. GSEA analysis of cervical cancer specimens also showed that HPV16 E6 rather than HPV18 E6, was significantly associated with actin cytoskeleton assembly. That downregulation of NHERF1 by HPV16 E6 promoted cytoskeleton assembly and cell invasion, was an important cause in cervical cancer carcinogenesis. These findings provided the differential mechanism between HPV16 E6 and HPV18 E6 in the development and progression of cervical cancer, which may partially explain the differences of carcinogenic power between these two types of HR-HPVs.

Inhibition of ezrin causes PKCα-mediated internalization of erbb2/HER2 tyrosine kinase in breast cancer cells

Unlike other ErbB family members, HER2 levels are maintained on the cell surface when the receptor is activated, allowing prolonged signaling and contributing to its transforming ability. Interactions between HER2, HSP90, PMCA2, and NHERF1 within specialized plasma membrane domains contribute to the membrane retention of HER2. We hypothesized that the scaffolding protein ezrin, which has been shown to interact with NHERF1, might also help stabilize the HER2-PMCA2-NHERF1 complex at the plasma membrane. Therefore, we examined ezrin expression and its relationship with HER2, NHERF1, and PMCA2 levels in murine and human breast cancers. We also used genetic knockdown and/or pharmacologic inhibition of ezrin, HSP90, NHERF1, PMCA2, and HER2 to examine the functional relationships between these factors and membrane retention of HER2. We found ezrin to be expressed at low levels at the apical surface of normal mammary epithelial cells, but its expression is up-regulated and correlates with HER2 expression in hyperplasia and tumors in murine mammary tumor virus-Neu mice, in human HER2-positive breast cancer cell lines, and in ductal carcinoma in situ and invasive breast cancers from human patients. In breast cancer cells, ezrin co-localizes and interacts with HER2, NHERF1, PMCA2, and HSP90 in specialized membrane domains, and inhibiting ezrin disrupts interactions between HER2, PMCA2, NHERF1, and HSP90, inhibiting HER2 signaling and causing PKCα-mediated internalization and degradation of HER2. Inhibition of ezrin synergizes with lapatinib in a PKCα-dependent fashion to inhibit proliferation and promote apoptosis in HER2-positive breast cancer cells. We conclude that ezrin stabilizes a multiprotein complex that maintains active HER2 at the cell surface.

Phosphorylation of NHERF1 S279 and S301 differentially regulates breast cancer cell phenotype and metastatic organotropism

Metastatic cancer cells are highly plastic for the expression of different tumor phenotype hallmarks and organotropism. This plasticity is highly regulated but the dynamics of the signaling processes orchestrating the shift from one cell phenotype and metastatic organ pattern to another are still largely unknown. The scaffolding protein NHERF1 has been shown to regulate the expression of different neoplastic phenotypes through its PDZ domains, which forms the mechanistic basis for metastatic organotropism. This reprogramming activity was postulated to be dependent on its differential phosphorylation patterns. Here, we show that NHERF1 phosphorylation on S279/S301 dictates several tumor phenotypes such as in vivo invasion, NHE1-mediated matrix digestion, growth and vasculogenic mimicry. Remarkably, injecting mice with cells having differential NHERF1 expression and phosphorylation drove a shift from the predominantly lung colonization (WT NHERF1) to predominately bone colonization (double S279A/S301A mutant), indicating that NHERF1 phosphorylation also acts as a signaling switch in metastatic organotropism.

NHERF1 inhibits beta-catenin-mediated proliferation of cervical cancer cells through suppression of alpha-actinin-4 expression

Cervical cancer is one of the most lethal types of cancer in female. Aberrant activation of Wnt/β-catenin signaling pathway has been found to be involved in cervical cancer development and progression, whereas the underlying molecular mechanisms remain poorly understood. The present study showed that NHERF1 was a novel gene associated with both cell proliferation and Wnt signaling pathway in cervical cancer by analysis of differential gene expression and gene cluster for the cervical cancer specimens from GEO data sets. It was further demonstrated in cellular study that NHERF1 inhibition of cervical cancer cell proliferation through Wnt/β-catenin signaling was dependent on α-actinin-4 (ACTN4) expression. A negative association between NHERF1 expression and levels of ACTN4 and β-catenin was found in mouse xenograft model and cervical cancer specimens. Low levels of NHERF1 in cervical cancer specimens were found to associate with activation of cell proliferation and Wnt/β-catenin signaling by gene set enrichment analysis, and also were an independent predictive factor for worse prognosis of cervical cancer patients by Cox regression analysis. These findings demonstrate that NHERF1 inhibits Wnt signaling-mediated proliferation of cervical cancer via suppression of ACTN4, and NHERF1 downregulation may contribute to the progression of cervical cancer. These findings may also shed some lights for understanding the underlying mechanisms of cisplatin resistance and worse prognosis of HPV-inactive cervical cancer patients.

Ezrin-Radixin-Moesin Binding Phosphoprotein 50: A Potential Novel Biomarker in Human Papilloma Virus-Associated Head and Neck Squamous Cell Carcinomas

High-risk human papilloma virus (HR-HPV) has increasingly been associated with head and neck squamous cell carcinoma (HNSCC), in particular oropharyngeal cancers. Ezrin-Radixin-Moesin Binding Phosphoprotein 50 (EBP50), a putative tumour suppressor, localises to the plasma membrane in suprabasal epithelium and to the cytoplasm in proliferative basal layers, and is a target for degradation by the HR-HPV E6 oncoprotein. The aim of this study was to investigate EBP50 protein expression patterns in HNSCC in a large Scottish cohort to determine if there was a correlation with HPV status and clinical outcomes. EBP50 expression patterns were assessed in 156 HNSCC including oropharyngeal (37.8%), laryngeal (24%), oral (19%) and other sites (18.5%), which were genotyped for presence of HR-HPV. HNSCC were generally negative for membranous EBP50. EBP50 expression was either cytoplasmic/absent, being 'predominantly cytoplasmic' in 76 (49%), 'weak/negligible cytoplasmic' in 44 (28%), 'strongly cytoplasmic' in 5 (3%), 'heterogeneous' in 26 (17%) and 'other' in 5 (3%) samples. Forty tumours (25%) were positive for HPV DNA, predominantly HR-HPV 16, and 44 (28%) were p16 positive. The majority of tumours (71%) with 'weak/negligible cytoplasmic' EBP50 expression originated in the oropharynx were more likely to have positive neck nodes, overexpression of p16 and positive tumour HR-HPV status (P < 0.001). Differences in EBP50 levels between oropharyngeal and non-oropharyngeal tumours may be linked to degradation of EBP50 by HR-HPV, and loss of EBP50 may therefore be a surrogate biomarker for HR-HPV infection in oropharyngeal tumours.

NHERF1 and tumor microenvironment: a new scene in invasive breast carcinoma

BACKGROUND

Tumor microenvironment (TME) includes many factors such as tumor associated inflammatory cells, vessels, and lymphocytes, as well as different signaling molecules and extracellular matrix components. These aspects can be de-regulated and consequently lead to a worsening of cancer progression. In recent years an association between the scaffolding protein Na⁺/H⁺ exchanger regulatory factor 1 (NHERF1) and tumor microenvironment changes in breast cancer (BC) has been reported.

METHODS

Subcellular NHERF1 localization, vascular endothelial growth factor (VEGF), its receptor VEGFR1, hypoxia inducible factor 1 alpha (HIF-1α), TWIST1 expression and microvessel density (MVD) in 183 invasive BCs were evaluated, using immunohistochemistry on tissue microarrays (TMA). Immunofluorescence was employed to explore protein interactions.

RESULTS

Cytoplasmic NHERF1(cNHERF1) expression was directly related to cytoplasmic VEGF and VEGFR1 expression (p = 0.001 and p = 0.027 respectively), and inversely to nuclear HIF-1α (p = 0.021) and TWIST1 (p = 0.001). Further, immunofluorescence revealed an involvement of tumor cells with NHERF1 positive staining in neo-vascular formation, suggesting a "mosaic" structure development of these neo-vessels. Survival analyses showed that loss of nuclear TWIST1 (nTWIST1) expression was related to a decrease of disease free survival (DFS) (p < 0.001), while nTWIST1-/mNHERF1+ presented an increased DFS with respect to nTWIST1+/mNHERF1- phenotype (p < 0.001). Subsequently, the analyses of nTWIST1+/cNHERF1+ phenotype selected a subgroup of patients with a worse DFS compared to nTWIST1-/cNHERF1- patients (p = 0.004).

CONCLUSION

Resulting data suggested a dynamic relation between NHERF1 and TME markers, and confirmed both the oncosuppressor role of membranous NHERF1 expression and the oncogene activity of cytoplasmic NHERF1.

NHERF1 Between Promises and Hopes: Overview on Cancer and Prospective Openings

Na+/H+ exchanger regulatory factor 1 (NHERF1) is a scaffold protein, with two tandem PDZ domains and a carboxyl-terminal ezrin-binding (EB) region. This particular sticky structure is responsible for its interaction with different molecules to form multi-complexes that have a pivotal role in a lot of diseases. In particular, its involvement during carcinogenesis and cancer progression has been deeply analyzed in different tumors. The role of NHERF1 is not unique in cancer; its activity is connected to its subcellular localization. The literature data suggest that NHERF1 could be a new prognostic/predictive biomarker from breast cancer to hematological cancers. Furthermore, the high potential of this molecule as therapeutical target in different carcinomas is a new challenge for precision medicine. These evidences are part of a future view to improving patient clinical management, which should allow different tumor phenotypes to be treated with tailored therapies. This article reviews the biology of NHERF1, its engagement in different signal pathways and its involvement in different cancers, with a specific focus on breast cancer. It also considers NHERF1 potential role during inflammation related to most human cancers, designating new perspectives in the study of this "Janus-like" protein.

β-catenin knockdown promotes NHERF1-mediated survival of colorectal cancer cells: implications for a double-targeted therapy

Nuclear activated β-catenin plays a causative role in colorectal cancers (CRC) but remains an elusive therapeutic target. Using human CRC cells harboring different Wnt/β-catenin pathway mutations in APC/KRAS or β-catenin/KRAS genes, and both genetic and pharmacological knockdown approaches, we show that oncogenic β-catenin signaling negatively regulates the expression of NHERF1 (Na⁺/H⁺ exchanger 3 regulating factor 1), a PDZ-adaptor protein that is usually lost or downregulated in early dysplastic adenomas to exacerbate nuclear β-catenin activity. Chromatin immunoprecipitation (ChIP) assays demonstrated that β-catenin represses NHERF1 via TCF4 directly, while the association between TCF1 and the Nherf1 promoter increased upon β-catenin knockdown. To note, the occurrence of a cytostatic survival response in settings of single β-catenin-depleted CRC cells was abrogated by combining NHERF1 inhibition via small hairpin RNA (shRNA) or RS5517, a novel PDZ1-domain ligand of NHERF1 that prevented its ectopic nuclear entry. Mechanistically, dual NHERF1/β-catenin targeting promoted an autophagy-to-apoptosis switch consistent with the activation of Caspase-3, the cleavage of PARP and reduced levels of phospho-ERK1/2, Beclin-1, and Rab7 autophagic proteins compared with β-catenin knockdown alone. Collectively, our data unveil novel β-catenin/TCF-dependent mechanisms of CRC carcinogenesis, also offering preclinical proof of concept for combining β-catenin and NHERF1 pharmacological inhibitors as a mechanism-based strategy to augment apoptotic death of CRC cells refractory to current Wnt/β-catenin-targeted therapeutics.

NHERF1, a novel GPER associated protein, increases stability and activation of GPER in ER-positive breast cancer

G protein-coupled estrogen receptor (GPER) plays an important role in mediating the effects of estradiol. High levels of GPER have been implicated to associate with the malignant progress of invasive breast cancer (IBC). However, the mechanisms by which GPER protein levels were regulated remain unclear. In this study, PDZ protein Na+/H+ exchanger regulatory factor (NHERF1) was found to interact with GPER in breast cancer cells. This interaction was mediated by the PDZ2 domain of NHERF1 and the carboxyl terminal PDZ binding motif of GPER. NHERF1 was demonstrated to facilitate GPER expression at post-transcriptional level and improve GPER protein stability by inhibiting the receptor degradation via ubiquitin-proteasome pathway in a GPER/NHERF1 interaction-dependent manner. In addition, GPER protein levels are positively associated with NHERF1 protein levels in a panel of estrogen receptor (ER)-positive breast cancer cells. Furthermore, analysis of clinical IBC data from The Cancer Genome Atlas (TCGA) showed no significant difference in GPER mRNA levels between ER-positive IBC and normal breast tissues. However, gene set enrichment analysis (GSEA) showed that GPER signaling is ultra-activated in ER-positive IBC when compared with normal and its activation is positively associated with NHERF1 mRNA levels. Taken together, our findings identify NHERF1 as a new binding partner for GPER and its overexpression promotes protein stability and activation of GPER in ER-positive IBC. Our data indicate that regulation of GPER stability by NHERF1 may contribute to GPER-mediated carcinogenesis in ER-positive IBC.

Hypoxia induces cancer-associated cAMP/PKA signalling through HIF-mediated transcriptional control of adenylyl cyclases VI and VII

Hypoxia is a phenomenon often arising in solid tumours, linked to aggressive malignancy, bad prognosis and resistance to therapy. Hypoxia-inducible factor-1 has been identified as a key mediator of cell and tissue adaptation to hypoxic conditions through transcriptional activation of many genes involved in glucose metabolism and other cancer-related processes, such as angiogenesis, cell survival and cell invasion. Cyclic adenosine 3′5′-monophosphate is one of the most ancient and evolutionarily conserved signalling molecules and the cAMP/PKA signalling pathway plays an important role in cellular adaptation to hypoxia. We have investigated possible new mechanisms behind hypoxic activation of the cAMP/PKA pathway. For the first time, we have shown that hypoxia induces transcriptional up-regulation of the system of adenylyl cyclases, enzymes responsible for cAMP production, in a panel of carcinoma cell lines of various origin. Our data prove functional relevance of the hypoxic increase of adenylyl cyclases VI and VII at least partially mediated by HIF-1 transcription factor. We have identified adenylyl cyclase VI and VII isoforms as mediators of cellular response to hypoxia, which led to the elevation of cAMP levels and enhanced PKA activity, with an impact on cell migration and pH regulation.

NHERF1 together with PARP1 and BRCA1 expression as a new potential biomarker to stratify breast cancer patients

It has been recognized that Na⁺/H⁺ Exchanger Regulatory Factor 1 (NHERF1) in breast cancer (BC) acts as a tumor suppressor or as an oncogenic protein, depending on its subcellular localization. This study aims to correlate NHERF1 expression to BRCA1 and PARP1 proteins, to investigate their relationship, and their biological and clinical significance. Using immunohistochemistry on tissue microarrays, we evaluated subcellular NHERF1, BRCA1 and PARP1 expression in 308 BCs including a subgroup (n=80) of triple negative BCs (TNBCs). Herein, we show that nuclear NHERF1 (nNHERF1) expression was significantly associated with nuclear BRCA1 (nBRCA1) expression (p=0.0008), and an association was also found between nuclear PARP1 (nPARP1) and nBRCA1 (p<0.0001). Cytoplasmic NHERF1 (cNHERF1) was correlated to nPARP1 (p<0.0001). Survival analyses showed that the patients with positive nPARP1 and nNHERF1 tended toward a shorter 5-year overall survival (OS) (p=0.057). In TNBCs, the association between nBRCA1 and nPARP1 was maintained (p<0.0001), and an association between nNHERF1 and nPARP1 was observed (p=0.010). Univariate analysis revealed that TNBCs with positive cNHERF1 and nPARP1 had a shorter 5-year OS (p=0.048).

Our data suggest that NHERF1 could be a new potential biomarker in combination with PARP1 and BRCA1 expression to stratify BC patients. In particular, in TNBCs, cNHERF1 associated with nPARP1 expression identified a patient subgroup with a shorter survival, for whom it may be useful to develop novel therapeutic strategies.

Roles of NHERF Family of PDZ-Binding Proteins in Regulating GPCR Functions

Multicellular organisms are equipped with an array of G-protein-coupled receptors (GPCRs) that mediate cell-cell signaling allowing them to adapt to environmental cues and ultimately survive. This is mechanistically possible through complex intracellular GPCR machinery that encompasses a vast network of proteins. Within this network, there is a group called scaffolding proteins that facilitate proper localization of signaling proteins for a quick and robust GPCR response. One protein family within this scaffolding group is the PSD-95/Dlg/ZO-1 (PDZ) family which is important for GPCR localization, internalization, recycling, and downstream signaling. Although the PDZ family of proteins regulate the functions of several receptors, this chapter focuses on a subfamily within the PDZ protein family called the Na⁺/H⁺ exchanger regulatory factors (NHERFs). Here we extensively review the predominantly characterized roles of NHERFs in renal phosphate absorption, intestinal ion regulation, cancer progression, and immune cell functions. Finally, we discuss the future perspectives and possible clinical application of targeting NHERFs in several disorders.

Dynamic relocalization of NHERF1 mediates chemotactic migration of ovarian cancer cells toward lysophosphatidic acid stimulation

NHERF1/EBP50 (Na⁺/H⁺ exchanger regulating factor 1; Ezrin-binding phosphoprotein of 50 kDa) organizes stable protein complexes beneath the apical membrane of polar epithelial cells. By contrast, in cancer cells without any fixed polarity, NHERF1 often localizes in the cytoplasm. The regulation of cytoplasmic NHERF1 and its role in cancer progression remain unclear. In this study, we found that, upon lysophosphatidic acid (LPA) stimulation, cytoplasmic NHERF1 rapidly translocated to the plasma membrane, and subsequently to cortical protrusion structures, of ovarian cancer cells. This movement depended on direct binding of NHERF1 to C-terminally phosphorylated ERM proteins (cpERMs). Moreover, NHERF1 depletion downregulated cpERMs and further impaired cpERM-dependent remodeling of the cell cortex, suggesting reciprocal regulation between these proteins. The LPA-induced protein complex was highly enriched in migratory pseudopodia, whose formation was impaired by overexpression of NHERF1 truncation mutants. Consistent with this, NHERF1 depletion in various types of cancer cells abolished chemotactic cell migration toward a LPA gradient. Taken together, our findings suggest that the high dynamics of cytosolic NHERF1 provide cancer cells with a means of controlling chemotactic migration. This capacity is likely to be essential for ovarian cancer progression in tumor microenvironments containing LPA.

Quantification of hypoxia-related gene expression as a potential approach for clinical outcome prediction in breast cancer

Breast cancers are solid tumors frequently characterized by regions with low oxygen concentrations. Cellular adaptations to hypoxia are mainly determined by “hypoxia inducible factors” that mediate transcriptional modifications involved in drug resistance and tumor progression leading to metastasis and relapse occurrence. In this study, we investigated the prognostic value of hypoxia-related gene expression in breast cancer. A systematic review was conducted to select a set of 45 genes involved in hypoxia signaling pathways and breast tumor progression. Gene expression was quantified by RT-qPCR in a retrospective series of 32 patients with invasive ductal carcinoma. Data were analyzed in relation to classical clinicopathological criteria and relapse occurrence. Coordinated overexpression of selected genes was observed in high-grade and HER2+ tumors. Hierarchical cluster analysis of gene expression significantly segregated relapsed patients (p = 0.008, Chi² test). All genes (except one) were up-regulated and six markers were significantly expressed in tumors from recurrent patients. The expression of this 6-gene set was used to develop a basic algorithm for identifying recurrent patients according to a risk score of relapse. Analysis of Kaplan-Meier relapse-free survival curves allowed the definition of a threshold score of 2 (p = 0.021, Mantel-Haenszel test). The risk of recurrence was increased by 40% in patients with a high score. In addition to classical prognostic factors, we showed that hypoxic markers have potential prognostic value for outcome and late recurrence prediction, leading to improved treatment decision-making for patients with early-stage invasive breast cancer. It will be necessary to validate the clinical relevance of this prognostic approach through independent studies including larger prospective patient cohorts.

The scaffolding protein NHERF1 regulates the stability and activity of the tyrosine kinase HER2

We examined whether the scaffolding protein sodium-hydrogen exchanger regulatory factor 1 (NHERF1) interacts with the calcium pump PMCA2 and the tyrosine kinase receptor ErbB2/HER2 in normal mammary epithelial cells and breast cancer cells. NHERF1 interacts with the PDZ-binding motif in PMCA2 in both normal and malignant breast cells. NHERF1 expression is increased in HER2-positive breast cancers and correlates with HER2-positive status in human ductal carcinoma in situ (DCIS) lesions and invasive breast cancers as well as with increased mortality in patients. NHERF1 is part of a multiprotein complex that includes PMCA2, HSP90, and HER2 within specific actin-rich and lipid raft-rich membrane signaling domains. Knocking down NHERF1 reduces PMCA2 and HER2 expression, inhibits HER2 signaling, dissociates HER2 from HSP90, and causes the internalization, ubiquitination, and degradation of HER2. These results demonstrate that NHERF1 acts with PMCA2 to regulate HER2 signaling and membrane retention in breast cancers.

Role of the PDZ-scaffold protein NHERF1/EBP50 in cancer biology: from signaling regulation to clinical relevance

The transmission of cellular information requires fine and subtle regulation of proteins that need to interact in a coordinated and specific way to form efficient signaling networks. The spatial and temporal coordination relies on scaffold proteins. Thanks to protein interaction domains such as PDZ domains, scaffold proteins organize multiprotein complexes enabling the proper transmission of cellular information through intracellular networks. NHERF1/EBP50 is a PDZ-scaffold protein that was initially identified as an organizer and regulator of transporters and channels at the apical side of epithelia through actin-binding ezrin-moesin-radixin proteins. Since, NHERF1/EBP50 has emerged as a major regulator of cancer signaling network by assembling cancer-related proteins. The PDZ-scaffold EBP50 carries either anti-tumor or pro-tumor functions, two antinomic functions dictated by EBP50 expression or subcellular localization. The dual function of NHERF1/EBP50 encompasses the regulation of several major signaling pathways engaged in cancer, including the receptor tyrosine kinases PDGFR and EGFR, PI3K/PTEN/AKT and Wnt-β-catenin pathways.

Similar expression pattern of NHERF1 and EZRIN in papillary but not in solid areas of human serous ovarian carcinomas

NHERF1 is an adaptor protein expressed in the apical membrane of polarized epithelia, which interacts with the EZRIN-Radixin-Moesin (ERM) family of proteins connecting signaling pathways to the cell cytoskeleton. NHERF1 and EZRIN cooperate in the maintenance of the apical microvilli in polarized epithelial cells. In several types of cancers, NHERF1 and EZRIN are displaced from the apical compartment to the cytoplasm and nuclei of cancer cells. At the present, the distribution of NHERF1 in ovarian tumors is not well known. In this study, NHERF1 expression was examined by immunohistochemistry in cyst adenofibromas, serous borderline tumors, and serous ovarian carcinomas. We observed a strong staining of NHERF1 and EZRIN at the membrane level of borderline tumors and areas of papillary structures in ovarian carcinomas. In tumors without papillary structures and compact structure, NHERF1 was exclusively expressed in the apical pole of the cells at the edges of the clefts of luminal spaces. In contrast, positive expression of EZRIN was found in the membrane of tumor cells within the solid tumor where NHERF1 was not expressed. In summary, this study shows, for the first time, the distribution of NHERF1 in ovarian cancer and reveals a different regulation of NHERF1 and EZRIN expression in ovarian tumors which represents the complexity of the molecular changes of this disease.

Expression of transmembrane protein 26 (TMEM26) in breast cancer and its association with drug response

We have previously shown that stromal cells desensitize breast cancer cells to the anti-estrogen fulvestrant and, along with it, downregulate the expression of TMEM26 (transmembrane protein 26). In an effort to study the function and regulation of TMEM26 in breast cancer cells, we found that breast cancer cells express non-glycosylated and N-glycosylated isoforms of the TMEM26 protein and demonstrate that N-glycosylation is important for its retention at the plasma membrane. Fulvestrant induced significant changes in expression and in the N-glycosylation status of TMEM26. In primary breast cancer, TMEM26 protein expression was higher in ERα (estrogen receptor α)/PR (progesterone receptor)-positive cancers. These data suggest that ERα is a major regulator of TMEM26. Significant changes in TMEM26 expression and N-glycosylation were also found, when MCF-7 and T47D cells acquired fulvestrant resistance. Furthermore, patients who received aromatase inhibitor treatment tend to have a higher risk of recurrence when tumoral TMEM26 protein expression is low. In addition, TMEM26 negatively regulates the expression of integrin β1, an important factor involved in endocrine resistance. Data obtained by spheroid formation assays confirmed that TMEM26 and integrin β1 can have opposite effects in breast cancer cells. These data are consistent with the hypothesis that, in ERα-positive breast cancer, TMEM26 may function as a tumor suppressor by impeding the acquisition of endocrine resistance. In contrast, in ERα-negative breast cancer, particularly triple-negative cancer, high TMEM26 expression was found to be associated with a higher risk of recurrence. This implies that TMEM26 has different functions in ERα-positive and -negative breast cancer.

PMCA2 regulates HER2 protein kinase localization and signaling and promotes HER2-mediated breast cancer

In the lactating mammary gland, the plasma membrane calcium ATPase2 (PMCA2) transports milk calcium. Its expression is activated in breast cancers, where high tumor levels predict increased mortality. We find that PMCA2 expression correlates with HER2 levels in breast cancers and that PMCA2 interacts with HER2 in specific actin-rich membrane domains. Knocking down PMCA2 increases intracellular calcium, disrupts interactions between HER2 and HSP-90, inhibits HER2 signaling, and results in internalization and degradation of HER2. Manipulating PMCA2 levels regulates the growth of breast cancer cells, and knocking out PMCA2 inhibits the formation of tumors in mouse mammary tumor virus (MMTV)-Neu mice. These data reveal previously unappreciated molecular interactions regulating HER2 localization, membrane retention, and signaling, as well as the ability of HER2 to generate breast tumors, suggesting that interactions between PMCA2 and HER2 may represent therapeutic targets for breast cancer.

A novel NHE1-centered signaling cassette drives epidermal growth factor receptor-dependent pancreatic tumor metastasis and is a target for combination therapy

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers principally because of early invasion and metastasis. The epidermal growth factor receptor (EGFR) is essential for PDAC development even in the presence of Kras, but its inhibition with erlotinib gives only a modest clinical response, making the discovery of novel EGFR targets of critical interest. Here, we revealed by mining a human pancreatic gene expression database that the metastasis promoter Na⁺/H⁺ exchanger (NHE1) associates with the EGFR in PDAC. In human PDAC cell lines, we confirmed that NHE1 drives both basal and EGF-stimulated three-dimensional growth and early invasion via invadopodial extracellular matrix digestion. EGF promoted the complexing of EGFR with NHE1 via the scaffolding protein Na +/H + exchanger regulatory factor 1, engaging EGFR in a negative transregulatory loop that controls the extent and duration of EGFR oncogenic signaling and stimulates NHE1. The specificity of NHE1 for growth or invasion depends on the segregation of the transient EGFR/Na +/H + exchanger regulatory factor 1/NHE1 signaling complex into dimeric subcomplexes in different lipid raftlike membrane domains. This signaling complex was also found in tumors developed in orthotopic mice. Importantly, the specific NHE1 inhibitor cariporide reduced both three-dimensional growth and invasion independently of PDAC subtype and synergistically sensitized these behaviors to low doses of erlotinib.

Expression of Na+/H+ exchanger regulatory factor 1 in autosomal-dominant polycystic kidney disease

OBJECTIVE

To explore the role of Na(+)/H(+) exchanger regulatory factor 1 (NHERF1) in autosomal-dominant polycystic kidney disease (ADPKD).

METHODS

NHERF1 and β-catenin protein were detected by immunohistochemistry and Western blotting of kidney tissue samples from patients with ADPKD and controls (normal kidney tissue [>5 cm from the foci] collected from patients undergoing unilateral nephrectomy for kidney cancer). NHERF1 and β-catenin protein and mRNA were quantified by Western blot and real-time fluorescent quantitative polymerase chain reaction, respectively, in kidney tissue samples from Han:SPRD (+/+) and (cy/+) rats. The effects of human recombinant NHERF1 on proliferation and cell cycle of ADPKD cyst-lining epithelial cells (WT9-12) were evaluated by MTT assay and flow cytometry, respectively.

RESULTS

Levels of NHERF1 protein and mRNA were significantly lower, and β-catenin levels significantly higher, in patients with ADPKD and Han:SPRD (cy/+) rats, compared with control subjects and (+/+) rats, respectively. Exogenous recombinant NHERF1 significantly inhibited proliferation of WT9-12 cells and increased the proportion of cells in G(0)/G(1) phase.

CONCLUSIONS

ADPKD is associated with a decrease in NHERF1 protein and mRNA levels. Supplementing exogenous NHERF1 inhibited the proliferation of WT9-12 cells.

Drug Transporters and Na+/H+ Exchange Regulatory Factor PSD-95/Drosophila Discs Large/ZO-1 Proteins

Drug transporters govern the absorption, distribution, and elimination of pharmacologically active compounds. Members of the solute carrier and ATP binding-cassette drug transporter family mediate cellular drug uptake and efflux processes, thereby coordinating the vectorial movement of drugs across epithelial barriers. To exert their physiologic and pharmacological function in polarized epithelia, drug transporters must be targeted and stabilized to appropriate regions of the cell membrane (i.e., apical versus basolateral). Despite the critical importance of drug transporter membrane targeting, the mechanisms that underlie these processes are largely unknown. Several clinically significant drug transporters possess a recognition sequence that binds to PSD-95/Drosophila discs large/ZO-1 (PDZ) proteins. PDZ proteins, such as the Na(+)/H(+) exchanger regulatory factor (NHERF) family, act to stabilize and organize membrane targeting of multiple transmembrane proteins, including many clinically relevant drug transporters. These PDZ proteins are normally abundant at apical membranes, where they tether membrane-delimited transporters. NHERF expression is particularly high at the apical membrane in polarized tissue such as intestinal, hepatic, and renal epithelia, tissues important to drug disposition. Several recent studies have highlighted NHERF proteins as determinants of drug transporter function secondary to their role in controlling membrane abundance and localization. Mounting evidence strongly suggests that NHERF proteins may have clinically significant roles in pharmacokinetics and pharmacodynamics of several pharmacologically active compounds and may affect drug action in cancer and chronic kidney disease. For these reasons, NHERF proteins represent a novel class of post-translational mediators of drug transport and novel targets for new drug development.

The potential predictive role of nuclear NHERF1 expression in advanced gastric cancer patients treated with epirubicin/oxaliplatin/capecitabine first line chemotherapy

Cellular resistance in advanced gastric cancer (GC) might be related to function of multidrug resistance (MDR) proteins. The adaptor protein NHERF1 (Na(+)/H(+) exchanger regulatory factor) is an important player in cancer progression for a number of solid malignancies, even if its role to develop drug resistance remains uncertain. Herein, we aimed to analyze the potential association between NHERF1 expression and P-gp, sorcin and HIF-1α MDR-related proteins in advanced GC patients treated with epirubicin/oxaliplatin/capecitabine (EOX) chemotherapy regimen, and its relation to response. Total number of 28 untreated patients were included into the study. Expression and subcellular localization of all proteins were assessed by immunohistochemistry on formalin-fixed paraffin embedded tumor samples. We did not found significant association between NHERF1 expression and the MDR-related proteins. A trend was observed between positive cytoplasmic NHERF1 (cNHERF1) expression and negative nuclear HIF-1α (nHIF-1α) expression (68.8% versus 31.3% respectively, P = 0.054). However, cytoplasmic P-gp (cP-gp) expression was positively correlated with both cHIF-1α and sorcin expression (P = 0.011; P = 0.002, respectively). Interestingly, nuclear NHERF1 (nNHERF1) staining was statistically associated with clinical response. In detail, 66.7% of patients with high nNHERF1 expression had a disease control rate, while 84.6% of subjects with negative nuclear expression of the protein showed progressive disease (P = 0.009). Multivariate analysis confirmed a significant correlation between nNHERF1 and clinical response (OR 0.06, P = 0.019). These results suggest that nuclear NHERF1 could be related to resistance to the EOX regimen in advanced GC patients, identifying this marker as a possible independent predictive factor.

Proton channels and exchangers in cancer

Although cancer is characterized by an intratumoral genetic heterogeneity, a totally deranged pH control is a common feature of most cancer histotypes. Major determinants of aberrant pH gradient in cancer are proton exchangers and transporters, including V-ATPase, Na+/H+ exchanger (NHE), monocarboxylate transporters (MCTs) and carbonic anhydrases (CAs). Thanks to the activity of these proton transporters and exchangers, cancer becomes isolated and/or protected not only from the body reaction against the growing tumor, but also from the vast majority of drugs that when protonated into the acidic tumor microenvironment do not enter into cancer cells. Proton transporters and exchangers represent a key feature tumor cells use to survive in the very hostile microenvironmental conditions that they create and maintain. Detoxifying mechanisms may thus represent both a key survival option and a selection outcome for cells that behave as unicellular microorganisms rather than belonging to an organ, compartment or body. It is, in fact, typical of malignant tumors that, after a clinically measurable yet transient initial response to a therapy, resistant tumor clones emerge and proliferate, thus bursting a more malignant behavior and rapid tumor progression. This review critically presents the background of a novel and efficient approach that aims to fight cancer through blocking or inhibiting well characterized proton exchangers and transporters active in human cancer cells. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Role of pHi, and proton transporters in oncogene-driven neoplastic transformation

The change of a normal, healthy cell to a transformed cell is the first step in the evolutionary arc of a cancer. While the role of oncogenes in this 'passage' is well known, the role of ion transporters in this critical step is less known and is fundamental to our understanding the early physiological processes of carcinogenesis. Cancer cells and tissues have an aberrant regulation of hydrogen ion dynamics leading to a reversal of the normal tissue intracellular to extracellular pH gradient (ΔpHi to ΔpHe). When this perturbation in pH dynamics occurs during carcinogenesis is less clear. Very early studies using the introduction of different oncogene proteins into cells observed a concordance between neoplastic transformation and a cytoplasmic alkalinization occurring concomitantly with a shift towards glycolysis in the presence of oxygen, i.e. 'Warburg metabolism'. These processes may instigate a vicious cycle that drives later progression towards fully developed cancer where the reversed pH gradient becomes ever more pronounced. This review presents our understanding of the role of pH and the NHE1 in driving transformation, in determining the first appearance of the cancer 'hallmark' characteristics and how the use of pharmacological approaches targeting pH/NHE1 may open up new avenues for efficient treatments even during the first steps of cancer development.

Carbonic anhydrase IX, a hypoxia-induced catalytic component of the pH regulating machinery in tumors

Acidic tissue microenvironment contributes to tumor progression via multiple effects including the activation of angiogenic factors and proteases, reduced cell-cell adhesion, increased migration and invasion, etc. In addition, intratumoral acidosis can influence the uptake of anticancer drugs and modulate the response of tumors to conventional therapy. Acidification of the tumor microenvironment often develops due to hypoxia-triggered oncogenic metabolism, which leads to the extensive production of lactate, protons, and carbon dioxide. In order to avoid intracellular accumulation of the acidic metabolic products, which is incompatible with the survival and proliferation, tumor cells activate molecular machinery that regulates pH by driving transmembrane inside-out and outside-in ion fluxes. Carbonic anhydrase IX (CA IX) is a hypoxia-induced catalytic component of the bicarbonate import arm of this machinery. Through its catalytic activity, CA IX directly participates in many acidosis-induced features of tumor phenotype as demonstrated by manipulating its expression and/or by in vitro mutagenesis. CA IX can function as a survival factor protecting tumor cells from hypoxia and acidosis, as a pro-migratory factor facilitating cell movement and invasion, as a signaling molecule transducing extracellular signals to intracellular pathways (including major signaling and metabolic cascades) and converting intracellular signals to extracellular effects on adhesion, proteolysis, and other processes. These functional implications of CA IX in cancer are supported by numerous clinical studies demonstrating the association of CA IX with various clinical correlates and markers of aggressive tumor behavior. Although our understanding of the many faces of CA IX is still incomplete, existing knowledge supports the view that CA IX is a biologically and clinically relevant molecule, exploitable in anticancer strategies aimed at targeting adaptive responses to hypoxia and/or acidosis.

Roles of ion transport in control of cell motility

Cell motility is an essential feature of life. It is essential for reproduction, propagation, embryonic development, and healing processes such as wound closure and a successful immune defense. If out of control, cell motility can become life-threatening as, for example, in metastasis or autoimmune diseases. Regardless of whether ciliary/flagellar or amoeboid movement, controlled motility always requires a concerted action of ion channels and transporters, cytoskeletal elements, and signaling cascades. Ion transport across the plasma membrane contributes to cell motility by affecting the membrane potential and voltage-sensitive ion channels, by inducing local volume changes with the help of aquaporins and by modulating cytosolic Ca(2+) and H(+) concentrations. Voltage-sensitive ion channels serve as voltage detectors in electric fields thus enabling galvanotaxis; local swelling facilitates the outgrowth of protrusions at the leading edge while local shrinkage accompanies the retraction of the cell rear; the cytosolic Ca(2+) concentration exerts its main effect on cytoskeletal dynamics via motor proteins such as myosin or dynein; and both, the intracellular and the extracellular H(+) concentration modulate cell migration and adhesion by tuning the activity of enzymes and signaling molecules in the cytosol as well as the activation state of adhesion molecules at the cell surface. In addition to the actual process of ion transport, both, channels and transporters contribute to cell migration by being part of focal adhesion complexes and/or physically interacting with components of the cytoskeleton. The present article provides an overview of how the numerous ion-transport mechanisms contribute to the various modes of cell motility.

Nuclear NHERF1 expression as a prognostic marker in breast cancer

Our purpose was to investigate whether Na⁺/H⁺ exchanger regulatory factor 1 (NHERF1) expression could be linked to prognosis in invasive breast carcinomas. NHERF1, an ezrin-radixin-moesin (ERM) binding phosphoprotein 50, is involved in the linkage of integral membrane proteins to the cytoskeleton. It is therefore believed to have an important role in cell signaling associated with changes in cell cytoarchitecture. NHERF1 expression is observed in various types of cancer and is related to tumor aggressiveness. To date the most extensive analyses of the influence of NHERF1 in cancer development have been performed on breast cancer. However, the underlying mechanism and its prognostic significance are still undefined. NHERF1 expression was studied by immunohistochemistry (IHC) in a cohort of 222 breast carcinoma patients. Association of cytoplasmic and nuclear NHERF1 expression with survival was analyzed. Disease-free survival (DFS) and overall survival (OS) were determined based on the Kaplan–Meier method. Cytoplasmic NHERF1 expression was associated with negative progesterone receptor (PgR) (P=0.017) and positive HER2 expression (P=0.023). NHERF1 also showed a nuclear localization and this correlated with small tumor size (P=0.026) and positive estrogen receptor (ER) expression (P=0.010). Multivariate analysis identified large tumor size (P=0.011) and nuclear NHERF1 expression (P=0.049) to be independent prognostic variables for DFS. Moreover, the nuclear NHERF1(−)/ER(−) immunophenotype (27%) was statistically associated with large tumor size (P=0.0276), high histological grade (P=0.0411), PgR-negative tumors (P<0.0001) and high proliferative activity (P=0.0027). These patients had worse DFS compared with patients with nuclear NHERF1(+)/ER(+) tumors (75.4% versus 92.6% P=0.010). These results show that the loss of nuclear NHERF1 expression is associated with reduced survival, and the link between nuclear NHERF1 and ER expression may serve as a prognostic marker for the routine clinical management of breast cancer patients.

Ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50) and nuclear factor-κB (NF-κB): a feed-forward loop for systemic and vascular inflammation

The interaction between vascular cells and macrophages is critical during vascular remodeling. Here we report that the scaffolding protein, ezrin-binding phosphoprotein 50 (EBP50), is a central regulator of macrophage and vascular smooth muscle cells (VSMC) function. EBP50 is up-regulated in intimal VSMC following endoluminal injury and promotes neointima formation. However, the mechanisms underlying these effects are not fully understood. Because of the fundamental role that inflammation plays in vascular diseases, we hypothesized that EBP50 mediates macrophage activation and the response of vessels to inflammation. Indeed, EBP50 expression increased in primary macrophages and VSMC, and in the aorta of mice, upon treatment with LPS or TNFα. This increase was nuclear factor-κB (NF-κB)-dependent. Conversely, activation of NF-κB was impaired in EBP50-null VSMC and macrophages. We found that inflammatory stimuli promote the formation of an EBP50-PKCζ complex at the cell membrane that induces NF-κB signaling. Macrophage activation and vascular inflammation after acute LPS treatment were reduced in EBP50-null cells and mice as compared with WT. Furthermore, macrophage recruitment to vascular lesions was significantly reduced in EBP50 knock-out mice. Thus, EBP50 and NF-κB participate in a feed-forward loop leading to increased macrophage activation and enhanced response of vascular cells to inflammation.