Disease relevance of SLC9A1

• The low-serum component of this microenvironment confers increased motility and invasion in breast cancer cells by activating the Na+/H+ exchanger isoform 1 (NHE1) [1].
• The NHE1 to NHE3 and NHE5 loci did not demonstrate evidence for linkage to ESRD [2].
• APNH is a plausible candidate gene for human essential hypertension; the APNH polymorphism combined with a knowledge of its genetic map location allow this candidate to be tested in hypertensive kindreds and sib-pairs [3].
• In situ hybridization revealed that NHE1 mRNA in the turbinate mucosa and nasal polyp was localized in the epithelial layer and submucosal glands [4].
• For this study, age-matched type 2 diabetic (n=8) and normal (n=8) pregnant women were recruited to investigate the effects of controlled hyperglycemia on the expression of placental NHE-1 at term delivery [5].

High impact information on SLC9A1

• Through its effects on pHi homeostasis, cell volume, and the actin cortical network, NHE1 regulates a number of cell behaviors, including adhesion, shape determination, migration, and proliferation [6].
• Recently, it was determined that NHE1 also functions as a membrane anchor for the actin-based cytoskeleton, independently of its role in ion translocation [6].
• Here, we show that the plasma membrane ion exchanger NHE1 acts as an anchor for actin filaments to control the integrity of the cortical cytoskeleton [7].
• Fibroblasts expressing NHE1 with mutations that disrupt ERM binding, but not ion translocation, have impaired organization of focal adhesions and actin stress fibers, and an irregular cell shape [7].
• NHE1 and ERM proteins associate directly and colocalize in lamellipodia [7].

Chemical compound and disease context of SLC9A1

• It was hypothesized that the increase in intracellular Na(+) ([Na(+)](i)) mediated by NHE-1 activity may induce the reverse mode of Na(+)/Ca(2+) exchanger (NCX(rev)) increasing intracellular Ca(2+) ([Ca(2+)](i)) which in turn will induce hypertrophy [8].
• Taken together, our results suggest that CD44 interaction with a ROK-activated NHE1 (a Na(+)-H(+) exchanger) in cholesterol/ganglioside-containing lipid rafts plays a pivotal role in promoting intracellular/extracellular acidification required for Hyal-2 and cysteine proteinase-mediated matrix degradation and breast cancer progression [9].
• RESULTS: Human ventricular myocytes exhibited readily detectable sarcolemmal NHE activity after the induction of intracellular acidosis, and this activity was suppressed by the NHE1-selective inhibitor HOE-642 (cariporide) at 1 micromol/L [10].
• Selective insulin resistance and hyperinsulinism estimulates the tubular sodium-hydrogen exchanger and facilitates the active reabsorption of urate [11].
• During ischemia, there is a metabolic mismatch between glycolysis and glucose oxidation that results in accumulation of hydrogen ions, which, in turn, activates the Na+/H+ exchange system (NHE-1), leading to Na+ and Ca2+ overload and cell death [12].

Biological context of SLC9A1

• Direct binding of the Na--H exchanger NHE1 to ERM proteins regulates the cortical cytoskeleton and cell shape independently of H(+) translocation [7].
• The phosphorylation state of CHP may therefore be an important signal controlling mitogenic regulation of NHE1 [13].
• We conclude that NHE1 promotes cell survival by dual mechanisms: by defending cell volume and pH(i) through Na(+)/H(+) exchange and by functioning as a scaffold for recruitment of a signalplex that includes ERM, phosphoinositide 3-kinase, and Akt [14].
• Apoptosis results in cell shrinkage and intracellular acidification, processes opposed by the ubiquitously expressed NHE1 Na(+)/H(+) exchanger [14].
• We propose that serum-independent activation of NHE1 by bound CHP2 is one of the key mechanisms for the maintenance of high pH(i) and the resistance to serum deprivation-induced cell death in malignantly transformed cells [15].

Anatomical context of SLC9A1

• We propose a structural role for NHE1 in regulating the cortical cytoskeleton that is independent of its function as an ion exchanger [7].
• Protein kinase A gating of a pseudopodial-located RhoA/ROCK/p38/NHE1 signal module regulates invasion in breast cancer cell lines [1].
• However, we have found that the Na+/H+ exchanger (NHE), NHE1, is functionally active in these cells, and like AC8 (and AC6) it resides in lipid rafts or caveolae, which may create cellular microdomains where pH(i) is tightly regulated [16].
• Long-term exposure (24 h) of HT-29 cells to IFN-gamma resulted in a concentration-dependent decrease in NHE1 activity [17].
• Caco-2 cells express endogenous NHE1, NHE2 and NHE3 proteins, as detected by immunoblotting [18].

Associations of SLC9A1 with chemical compounds

• Ectopic NHE1, but not NHE3, expression rescued NHE1-null cells from apoptosis induced by staurosporine or N-ethylmaleimide-stimulated KCl efflux [14].
• Co-precipitation experiments demonstrated the interaction of human TSC with NHE1 in vitro and in vivo, and 45Ca(2+) overlay assay revealed that TSC binds Ca(2+) [19].
• Furthermore, we found that a novel synthetic aminoguanidine derivative, T-162559 ((5E,7S)-[7-(5-fluoro-2-methylphenyl)-4-methyl-7,8-dihydro-5(6H)-quinolinylideneamino] guanidine dimethanesulfonate), causes a selective inhibition of hNHE1 with more potent activity than cariporide and eniporide (IC50 value of 0.96 nM) [20].
• Potent and selective inhibition of the human Na+/H+ exchanger isoform NHE1 by a novel aminoguanidine derivative T-162559 [20].
• Each residue was mutated to cysteine in cysteine-less NHE1 [21].

Physical interactions of SLC9A1

• A novel carbonic anhydrase II binding site regulates NHE1 activity [22].
• Crystallization and preliminary crystallographic analysis of the human calcineurin homologous protein CHP2 bound to the cytoplasmic region of the Na+/H+ exchanger NHE1 [23].
• ERM protein binding and actin anchoring by NHE1 are necessary to retain the localization of NHE1 in specialized plasma membrane domains and to promote cytoskeleton-dependent processes, including actin filament bundling and cell-substrate adhesions [24].
• In a genetic screen, NHE1 interacted with NIK at a site N-terminal (amino acids 407-502) to the Nck-binding domain, and this site is critical for its association with NHE1 in vivo [25].

Enzymatic interactions of SLC9A1

• These findings indicate that NIK acts downstream of platelet-derived growth factor receptors to phosphorylate and activate NHE1 divergently of its activation of JNK [25].

Regulatory relationships of SLC9A1

• Transient overexpression of CHP inhibits serum- and GTP-ase-stimulated NHE1 activity [13].
• Serum (10%) induced a significant cytoplasmic alkalinization (0.1-0.2 pH unit) in cells co-expressing CHP1 and NHE1 but not in cells co-expressing CHP2 and NHE1 [15].
• Rac1 and RhoA were antagonistic regulators of both basal and stimulated tumour cell NHE1 activity [26].
• Rapid (<10 min) stimulation of NHE1 with a Ga13/Gaz chimera also was inhibited by a kinase-inactive MEKK [27].
• In most tissues, it is proposed that the NHE-1 could compensate for an inhibited MCT to prevent acidification, but in melanoma cells this did not occur [28].

Other interactions of SLC9A1

• These properties of CHP2/NHE1 cells are similar to those of malignantly transformed cells [15].
• CAII did not bind to acidic sequences in NHE1 that were similar to the CAII binding site of bicarbonate transporters [22].
• The activity of RhoA and Rac1 was modified using their dominant negative and constitutively active mutants and the activity of NHE1, cell motility/invasion, F-actin content and cell shape were measured [26].
• We conclude that AE2 operates in parallel with NHE1 to regulate pH(i) during RVD of human cervical cancer cells [29].
• To date, 5 isoforms of NHE have been cloned in mammals (NHE1 to NHE5) [2].

Analytical, diagnostic and therapeutic context of SLC9A1

• Immunofluorescence studies indicated that TSC is prominent in cellular lamellipodia where it colocalizes with NHE1 [19].
• Western blot analysis was performed for NHE1, -2, and -3 in NHMEE cells [30].
• Using isoform-specific primers, mRNA transcripts of Na(+)/H(+) exchanger isoform 1 (NHE1) and isoform 3 were identified by reverse transcriptase polymerase chain reaction (RT-PCR) and the results confirmed by Western immunoblotting [29].
• Northern blot analysis and reverse transcriptase polymerase chain reaction confirmed the presence of the 5 kb NHE-1 message in primary cultures of isolated myocytes [31].
• Using immunofluorescence and 3-dimensional confocal microscopy techniques, the present study was designed to verify if NHE-1 is present at the level of the nuclear membrane in cells that are known to express this type of exchanger [32].

References