1 Departments of Medicine and Physiology, University of Maryland School of Medicine, and Medical Service, Department of Veterans Affairs Medical Center, Baltimore, Maryland 21201; and 2 Department of Pharmacology and Cancer Biology, Duke University School of Medicine, Durham, North Carolina 27710
![]() |
ABSTRACT |
---|
The activity of the sodium/hydrogen exchanger 3 (NHE3) isoform of the sodium/hydrogen exchanger in the brush-border membrane of the renal proximal tubule is tightly regulated. Recent biochemical and cellular experiments have established the essential requirement for a new class of regulatory factors, sodium/hydrogen exchanger regulatory factor (NHERF) and NHERF-like proteins, in cAMP-mediated inhibition of NHE3 activity. NHERF is the first PSD-95/Dlg/ZO-1 (PDZ) motif-containing protein localized to apical membranes and appears to facilitate cAMP-dependent protein kinase A (PKA) phosphorylation of NHE3 by interacting with the cytoskeleton to target a multiprotein complex to the brush-border membrane. Other recent experiments have indicated that NHERF also regulates the activity of other renal transport proteins, suggesting that the signal complex model of signal transduction in the kidney may be more common than presently appreciated. This article reviews studies on the regulation of NHE3 by NHERF, PKA, and ezrin and introduces the concept of regulation of renal transporters by signal complexes. Although not the primary focus of this review, recent studies have indicated a role for NHERF in membrane targeting, trafficking, and sorting of transporters, receptors, and signaling proteins. Thus NHERF and related PDZ-containing proteins appear to be essential adapters for regulation of renal transporters in the mammalian kidney that maintain salt and water balance.
ezrin; sodium/hydrogen exchanger regulatory factor; sodium/hydrogen exchanger 3; signal transduction; protein kinase A
![]() |
INTRODUCTION |
---|
THE SHORT- AND LONG-TERM
REGULATION of transport proteins including the apical membrane
renal and intestinal Na+/H exchanger 3 (NHE3) involves
multiple processes including phosphorylation/dephosphorylation of the
transporter, transcriptional regulation, regulated exocytotic and
endocytotic events, and, perhaps, regulated mechanisms for partitioning
between an inactive subapical pool and an active pool located in the
plasma membrane (3, 8, 15,
28). In the course of study of the inhibition of
Na+/H+ exchange transport in the brush-border
membrane of the proximal tubule of the kidney by cAMP-dependent protein
kinase A (PKA), we demonstrated that an additional cofactor was
required. These experiments ultimately led to the identification of a
new family of PSD-95/Dlg/ZO-1 (PDZ) motif proteins called the
Na+/H+ exchanger regulatory factor family
(NHERF and NHERF2) (46, 48,
51).1 Subsequent
experiments defined an expanding role for the NHERF family of proteins
in systems other than the kidney, including the effect of estrogen in
estrogen receptor- positive breast cancer cell lines and testicular
differentiation (9, 29). An expanding role
for NHERF in the function of epithelial cells has also been elucidated,
and at least three interrelated but unique areas of interaction between
NHERF and the regulation of electrolyte transport have been suggested.
First, NHERF appears to function in PKA regulation of NHE3 by
facilitating the formation of a multiprotein complex, a "signal
complex," that is necessary to permit phosphorylation of NHE3 and,
thereby, inhibit its activity. Second, there is intriguing new
evidence that implicates NHERF in membrane targeting, trafficking, and
sorting of not only epithelial transporters but also receptors and
signaling proteins (4, 22, 23,
37). NHERF appears to target the cystic fibrosis
transmembrane regulator (CFTR) to the plasma membrane. In addition,
NHERF regulates the endocytic retrieval of the
2-adrenergic receptor and, possibly, the PY2 purinergic
receptor, and regulates the fate of the retrieved proteins by sorting
them to either recycling endosomes for reinsertion into the plasma
membrane or to lysosomal degratory pathways. Third, new evidence
indicates an important role of the NHERF family of protein in the
regulation of certain membrane receptors such as the platelet-derived
growth factor receptor. NHERF and NHERF2 function to permit
dimerization of subunits of the receptor with the consequent activation
of tyrosine kinase activity and downstream signaling events. The
present review focuses on PKA regulation of NHE3 and the evidence that
this form of regulation involves participation of a preformed complex
of proteins including the transporter itself, ezrin, PKA, and NHERF
(45, 54). At the present time, PKA regulation
of NHE3 is the only well-studied example of regulation by a signal
complex in the kidney although it is suspected that this form of signal
transduction may be common and that other examples will be elucidated
shortly. The role of NHERF in processes related to targeting,
trafficking, and sorting of epithelial transporters, receptors, and
signaling proteins, as well of the role of this family of protein in
receptor signaling pathways, will be reviewed in a later communication.
![]() |
EVOLUTION OF THE SIGNAL COMPLEX MODEL OF CELL REGULATION |
---|
Physiological processes are determined by the interaction of many
proteins and are often represented as biochemical cascades, whereby a
single protein is activated by an external stimulus. This activated
protein then acts as a catalyst to convert a second protein from an
inactive to an active state, and the sequential activation process is
continued until the final effect is expressed. Sequential activation
cascades were defined for extracellular processes, and when it became
possible to measure intracellular biochemical reactions the cascade
paradigm was incorporated into the cell context. A growing number of
experimental observations, however, are difficult to explain or
rationalize by using a sequential linear activation model. For example,
the protein concentration in areas immediately adjacent to cell
membranes might be high enough to restrict the free movement of
proteins required by the cascade model. Moreover, a number of processes
such as perception of light and dark, involving the opening and closing
of multiple channels, are mediated by specific protein kinases and
protein phosphatases (38). Despite the complexity,
these processes occur with remarkable rapidity, at rates too rapid to
be explained by mere sequential activation and deactivation of
individual proteins. Finally, there has been a perplexing issue related
to the observations that individual cells may contain multiple hormone
receptors that use the same signal pathways. Nonetheless, the cells are
able to respond to each hormone in a specific manner. For example, proximal tubule cells contain receptors for dopamine, parathyroid hormone, and 2-adrenergic agonists. Despite the fact
that all three of these receptors use cAMP as a second messenger, the
cellular response to each hormone is unique. From such considerations, it was suggested that some phenomena were better explained by postulating that there were complexes of proteins preassembled in
discrete locations within the cell (27, 33).
Moreover, under some circumstances, the reactive proteins were required concurrently rather than sequentially as in the cascade model. Although
other names have been used, the term signal complex encompasses the
basic elements of this alternate model. The presence of preassembled multiprotein signal complexes within cells provides a reasonable model
to explain rapid cellular responses to stimuli and to explain cell
specificity in response to hormones and neurotransmitters.
Signal complexes require a mechanism for the individual proteins to bind to one another to maintain the complex. It was soon recognized that members of the ezrin-moesin-radixin family of proteins, and the more distantly related merlin protein, might provide a "scaffold" for signal complexes by virtue of their ability to bind to both the actin core of cells as well as to proteins in the plasma membrane. Soon thereafter, a number of adaptor proteins were recognized that contained protein-protein binding motifs. Within the category of adaptor proteins, identification of members of the PDZ class of proteins has grown rapidly (17, 28).
![]() |
IDENTIFICATION OF THE REQUIREMENT FOR REGULATORY PROTEINS FOR PKA REGULATION OF NHE3 |
---|
Experiments from a number of laboratories have indicated that cAMP inhibits sodium and water transport in the renal proximal tubule (1, 6, 40). The inhibition of sodium transport by cAMP required the presence of bicarbonate in the luminal perfusate and was associated with inhibition of bicarbonate reabsorption (5, 21). Collectively, these experiments suggested that cAMP inhibited the apical brush-border membrane Na+/H+ exchanger. Using isolated rabbit renal brush-border membranes, we demonstrated that activation of membrane-bound PKA or provision of exogenous PKA inhibited Na+/H+ exchange activity in an ATP-dependent manner and that this inhibition was blocked by a specific inhibitor of the protein kinase (16, 44). We reasoned, therefore, that the Na+/H+ exchange transporter, the structure of which was unknown at the time, was phosphorylated and that identification of the membrane proteins phosphorylated by PKA might provide an approach to isolating the exchanger. In later experiments, however, particularly those involving assay of Na+/H+ exchange activity in artificial lipid vesicles, we observed that freezing and thawing, or trypsin treatment of solubilized renal brush-border membrane proteins, resulted in normal or increased Na+/H+ exchange transport activity but loss of regulation of the transporter by PKA (41-44). We subsequently isolated a brush-border membrane protein that, when coreconstituted with trypsinized brush-border membrane proteins, restored the inhibitory response to PKA (46). This protein did not express Na+/H+ exchange activity, and it became clear that it was not the brush-border membrane Na+/H+ exchanger that we had sought but rather a regulatory cofactor required for PKA regulation of the transporter. While our studies were in progress, Sardet et al. (32) reported cloning of cDNA for a housekeeping form of a Na+/H+ exchanger, now called NHE1, and Tse et al. (36) and Orlowski et al. (25) reported cloning of other members of this family of proteins, including NHE3, the epithelial isoform. In 1995, after isolating enough of the regulatory protein for partial amino acid sequencing, we cloned the factor and named it the NHERF (48). PS120 cells are a human fibroblast cell line that has been negatively selected to contain no Na+/H+ exchangers, and they do not express native NHERF. cAMP did not affect Na+/H+ exchange activity in PS120 cells expressing NHE3, but if NHERF was coexpressed with NHE3, cAMP inhibited the activity of the transporter (52). Thus these studies provided in vivo confirmation of the role of NHERF in PKA regulation of NHE3.
![]() |
RECOGNITION OF NHERF AS PART OF A SIGNAL COMPLEX OF PROTEINS |
---|
It was appreciated immediately that NHERF contained an
~100-amino acid internal repeat that we postulated to be protein
binding domains (48). This was a reasonable conclusion
given that NHERF did not contain putative lipid membrane-spanning
domains but was, nonetheless, isolated from a brush-border membrane
fraction of renal proximal tubule cells. Shortly thereafter, these
regions of NHERF were identified as PDZ domains (52).
After the demonstration that NHERF bound ezrin, models were developed
that hypothesized that NHERF, ezrin, and PKA formed a signal complex
that mediated the acute regulation of NHE3 activity (30).
An example of such a model is shown in Fig.
1. The predictions of the model proved to
be accurate, and the remaining discussion focuses on the biochemical properties of NHERF as they pertain to its physiological role as a
regulator of the action of PKA on NHE3 activity.
|
NHERF Binds to NHE3 and Mediates Its Phosphorylation
The model predicts a physical association between NHERF and NHE3. The relationship among NHE3, NHERF, and ezrin was studied by using PS120 cells. As summarized in Table 1, in PS120 cells that are cotransfected and express NHE3 and NHERF, immunoprecipitation of NHERF resulted in the coimmunoprecipitation of NHE3 (54). Immunoprecipitation of NHE3 resulted in the coimmunoprecipitation of NHERF. Of interest, the binding of these two proteins was not affected by cAMP, suggesting a continuing association even in the absence of stimulation by PKA and that PKA-mediated phosphorylation of either NHE3 or NHERF was not required for binding. The interaction between NHE3 and NHERF differs from the relationship between NHERF and the
|
NHERF Binding to Ezrin is Required for PKA-Mediated Inhibition of NHE3
Using a pull-down assay, ezrin was demonstrated to bind with high affinity to a previously unknown protein that was ultimately demonstrated to be the human homolog of NHERF (30). At the same time, another group identified a binding ligand of merlin, which was also identified as human NHERF (24). Ezrin binding to the COOH terminus of NHERF involves a region of NHERF distinct from the PDZ domains (31). To study the in vivo relationship between NHERF binding to ezrin as it relates to PKA regulation of NHE3, PS120 cells expressing NHE3 were cotransfected with either wild-type NHERF or a truncated form of NHERF lacking the ezrin binding domain. In contrast to wild-type, truncated NHERF did not coimmunoprecipitate ezrin, did not result in cAMP-associated phosphorylation of NHE3, and, most importantly, did not support cAMP-mediated inhibition of NHE3 activity (45). Thus NHERF binding to ezrin is critical to its function in mediating PKA inhibition of NHE3 activity.The above evidence demonstrates the in vivo interaction between NHERF and NHE3 and the requirement for NHERF binding to ezrin. Lamprecht et al. (20) and others (7) demonstrated that NHERF was not an A kinase anchoring protein (AKAP), but earlier studies indicated that ezrin itself could function as an AKAP (7, 20). Accordingly, the model proposed PKA binding to ezrin although the possible role of another AKAP linked to the complex is not excluded. It would appear that NHERF functions in this complex to facilitate the physical approximation of PKA to NHE3 and the subsequent phosphorylation of the tail of the transporter. In turn, the phosphorylation of serine 605 results in decreased NHE3 activity.
![]() |
THE SIGNIFICANCE OF THE PHOSPHORYLATION OF NHERF |
---|
NHERF was demonstrated to be an in vitro substrate for PKA when it was isolated initially by using sequential column chromatography (41). This finding was confirmed when recombinant NHERF proteins became available (47). By using site-directed mutagenesis, phosphorylation was localized to an array of serine residues at positions 287, 289, and 290 of the NHERF protein (47). Mutation of these three residues resulted in a loss of activity of the protein when assayed in vitro. Accordingly, we believed that PKA phosphorylated not only NHE3 but also NHERF. However, when NHERF was expressed in metabolically labeled HEK-293 cells, we found that NHERF was phosphorylated in unstimulated cells and that cAMP had little effect on its phosphorylation (47). This observation was confirmed subsequently when NHERF was expressed in opossum kidney cells and in PS120 cells (20, 54). Lamprecht et al. (20) ruled out the possibility that the apparent lack of effect of cAMP on the phosphorylation of NHERF was the result of increased phosphorylation of one residue of the protein and a decrease in the phosphorylation of another by phosphopeptide mapping of NHERF immunoprecipitated from [32P]ATP-labeled cells (20). These studies suggested that NHERF was phosphorylated on a single residue; findings were consistent with preliminary in vitro data suggesting a 1:1 molar ratio of phosphate to NHERF protein. Recently, it was demonstrated that serine 289 of NHERF is phosphorylated in vivo and that the endogenous "NHERF kinase" is G protein receptor kinase (GRK) 6A (13). This finding is striking given that this is only the second example of this class of protein kinases showing preference for a substrate other than a seven-membrane-spanning receptor. The physiological significance of this observation is as yet unknown, but it may provide an explanation of why cAMP did not appreciably increase the in vivo phosphorylation of NHERF given that the basal phosphorylation of serine 289 of NHERF by GRK 6A would have blocked the site from subsequent phosphorylation by PKA (20, 47, 54).
In the above studies, NHERF was overexpressed, and it remained possible that there was a small pool of NHERF within the NHE3 signal complex that was specifically phosphorylated by PKA but that this phosphorylation was obscured by the large amount of noncomplexed NHERF phosphorylated by GRK 6A. To test this possibility, NHERF containing serine-to-alanine mutations of residues 287, 289, and 290 was transfected in PS120 cells expressing NHE3 (54). The mutant NHERF was not phosphorylated in vivo in the basal state or after cAMP but did coimmunoprecipitate NHE3, did mediate the phosphorylation of NHE3, and was effective as wild-type NHERF in mediating cAMP inhibition of NHE3 activity. These results indicate that the phosphorylation of NHERF is not required for it to function in PKA regulation of NHE3. In this regard, NHERF is like a closely related PDZ protein, NHERF2, which also supports cAMP inhibition of NHE3 but is not a phosphoprotein in the basal state or after stimulation with cAMP (51, 52).
![]() |
THE NATURE OF THE BINDING OF NHERF TO NHE3 |
---|
To determine the biologically relevant portion of NHERF that interacts with NHE3, recombinant proteins representing full-length rabbit NHERF, PDZ I, or PDZ II (including the COOH terminus) were assayed by using a reconstitution assay of renal brush-border membrane proteins (47). Full-length NHERF and PDZ II supported PKA-associated inhibition of Na+/H+ exchange activity, but PDZ I did not. In recent experiments, we expressed rabbit NHE3 and either full-length mouse NHERF, PDZ I, or PDZ II (including the COOH terminus) in PS120 cells (45, see Table 1). We found that full-length NHERF and the PDZ II domain of NHERF coimmunoprecipitated with NHE3, were associated with cAMP-mediated phosphorylation of NHE3 and cAMP-mediated inhibition of Na+/H+ exchange activity. PDZ I did not coimmunoprecipitate with NHE3, did not support the phosphorylation of the transporter, and was not effective in mediating inhibition of transporter activity by cAMP. Moreover, the efficacy of full-length NHERF and PDZ II was approximately equal in both the in vitro and in vivo experiments. These results suggested that NHE3 binds to NHERF in the PDZ II region of the protein and that some portion of the COOH terminus of NHERF is required for interaction with NHE3. In a similar fashion, NHERF2 binds NHE3 using PDZ II and also requires the COOH terminus of the protein to demonstrate binding, at least in vitro (51).
As initially defined, PDZ domains bind to the COOH terminus four amino acids of their respective ligands, and the amino acid sequences that bind to a specific PDZ class are narrowly defined (17, 28). Using a peptide display library, Wang et al. (39) determined the optimal amino acid sequence for binding to each of the two PDZ domains of NHERF. Although PDZ I and PDZ II share >80% identity with one another, the predicted substrates for each domain are unique. Nonetheless, the preferred binding sequences for either of the PDZ domains of NHERF are not present in the COOH terminus of NHE3, indicating that NHERF-NHE3 binding must involve a different paradigm. There is precedent for nonclassic interactions between PDZ domains and other proteins, and PDZ-mimetic sequences located in internal portions of proteins have been described (10, 14, 26, 34). It is worth noting that it has not been established that NHE3 binding to NHERF involves the PDZ domain per se. NHERF has been demonstrated to interact with several substrates by using sequences in the NHERF protein distinct from the PDZ domains. The best-studied example of such an interaction is NHERF binding to ezrin (31). It is possible that NHERF binding to NHE3 does not involve the PDZ domains directly. Indeed, if neither ezrin nor NHE3 utilizes PDZ regions for binding, the NHERF protein could potentially recruit additional proteins by using its PDZ protein-protein interactive domains. These possibilities remain to be explored.
![]() |
NHERF AND THE REGULATION OF OTHER RENAL TRANSPORTERS AND CHANNELS |
---|
The potential role of NHERF and NHERF-like proteins to organize
signal complexes to facilitate the regulation of other renal transporters and channels is just beginning to be explored. On the
basis of sequence specificity of the terminal four amino acids, it was
predicted that the CFTR would bind to NHERF. Several recent papers have
provided in vitro confirmation of the high affinity of NHERF for CFTR
(11, 35, 39). To date, however,
no direct physiological correlate of the in vitro binding has been
defined although a recent report indicates that NHERF targets CFTR to the plasma membrane (23). There appears to be an
interaction between the renal outer medullary potassium channel (ROMK)
and NHERF. Of considerable interest is the suggestion that NHERF may function to link and/or to assemble an ion channel complex consisting of CFTR and ROMK (50). The significance of these
observations is also under active investigation. Finally, both in vitro
and in vivo experiments by Bernardo et al. (2) have
indicated that the renal Na+-HCO3
cotransporter (NBC) is regulated by PKA and that this regulation has an
absolute requirement for NHERF in a manner analogous to the
relationship between NHERF and NHE3 (2). By using a
reconstitution assay to determine the activity of NBC, it was found
that PKA did not inhibit the transporter unless recombinant NHERF was
present. In addition, PKA did not inhibit native NBC activity in type 1 bumetanide-sensitive cotransporter cells that lack endogenous NHERF.
When these cells were transfected with NHERF, however, activation of
PKA inhibited NBC activity. The relationship between PKA inhibition of
NHE3 and PKA inhibition of NBC, and the requirement for NHERF in both
these processes, raises the possibility that NHERF is part of a signal
complex that regulates NBC activity. This question is under
investigation. It is also of interest that, in the renal proximal
tubule, there is coordinated regulation of NHE3 in the apical membrane
and NBC in the basolateral membrane. It remains possible that NHERF is
involved in the parallel regulation of these two transporters.
![]() |
CONCLUDING REMARKS |
---|
Adaptor proteins, including those proteins containing PDZ domains,
were initially ascribed a scaffold function that facilitated the
function of other regulatory proteins such as protein kinases and
protein phosphatases. It is our present view that NHERF functions in
the PKA regulation of NHE3 in such a manner. Recent studies suggest,
however, the possibility that NHERF plays a more dynamic role in the
physiology of some cells. For example, treatment of estrogen
receptor-positive cells with estrogen rapidly increases NHERF mRNA and
protein concentrations whereas treatment of serum-starved opossum
kidney cells with serum decreases NHERF mRNA and protein (9, 49). The specificity and physiological
relevance of these observations are under study. Nonetheless, it is
curious that some cells express mechanisms for rapid regulation of
cellular NHERF, a property not usually ascribed to adaptor proteins.
Hall et al. (12) demonstrated that agonist occupation of
the 2-adrenergic receptor resulted in the movement of
NHERF from a submembrane location to the plasma membrane where it
colocalized with the receptor. Such a dynamic response is not typical
of this class of proteins. Moreover, the shift of NHERF from other
sites in the cell to the
2-adrenergic receptor is
associated with a functional change in the behavior of the response of
NHE3 to activation of PKA. The model that ensues these observations
suggests an internal competition between proteins with affinity for
either of the PDZ domains of NHERF. It is far too early to generalize,
but the implications of such experiments are far reaching for
understanding the potential involvement of NHERF and NHERF-like
proteins in cellular processes and signal transduction.
![]() |
ACKNOWLEDGEMENTS |
---|
These studies were supported by National Institute of Diabetes and Digestive and Kidney Diseases Grants DK-37319 and DK-55881 (to E. J. Weinman and S. Shenolikar) and the Research Service, Department of Veterans Affairs (E. J. Weinman).
![]() |
FOOTNOTES |
---|
1 The nomenclature regarding the NHERF family of proteins has become confused. Rabbit Na+/H+ NHERF was partially sequenced in 1993 and cloned in 1995. In 1997, the Na+/H+ exchanger 3 protein kinase A regulatory protein (E3KARP) was cloned. E3KARP is identical to a protein named tyrosine kinase activator 1 (TKA1). In 1998, two groups cloned the human homolog of NHERF, one group calling the protein hNHERF, the other ezrin binding protein 50 (EBP50). It has recently been suggested that NHERF be used for the originally described protein and NHERF2 to designate E3KARP/TKA1. When identified, other members of this family of protein would be numbered sequentially and single lower case prefixes used to distinguish homologs. This convention will be used in this review.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: E. J. Weinman, Div. of Nephrology, Rm. N3W143, Univ. of Maryland Hospital, 22 S. Greene St., Baltimore, MD 21201 (E-mail: eweinman1440{at}yahoo.com).
![]() |
REFERENCES |
---|
1.
Agus, ZS,
Puschett JB,
Senesky D,
and
Goldberg M.
Mode of action of parathyroid hormone and cyclic adenosine 3'-5' monophosphate on renal tubular phosphate reabsorption in the dog.
J Clin Invest
50:
617-626,
1971[ISI][Medline].
2.
Bernardo, AA,
Kear FT,
Santos AV,
Ma J,
Steplock D,
Robey RB,
and
Weinman EJ.
Basolateral Na+/HCO3 cotransport activity is regulated by the dissociable Na+/H+ exchanger regulatory factor.
J Clin Invest
104:
195-201,
1999
3.
Biemesderfer, D,
Nagy T,
DeGray B,
and
Aronson PS.
Specific association of megalin and the Na+/H+ exchanger isoform NHE3 in the proximal tubule.
J Biol Chem
274:
17518-17524,
1999
4.
Cao, TT,
Deacon HW,
Reczek D,
Bretscher A,
and
von Zastrow M.
A kinase-regulated PDZ-domain interaction controls endocytic sorting of the beta2-adrenergic receptor.
Nature
40:
286-290,
1999.
5.
Dennis, V.
Influence of bicarbonate on parathyroid hormone induced changes in fluid reabsorption by the proximal tubule.
Kidney Int
10:
373-380,
1976[ISI][Medline].
6.
Dolson, GM,
Hise MK,
and
Weinman EJ.
Relationship among parathyroid hormone, cAMP, and calcium on proximal tubule sodium transport.
Am J Physiol Renal Fluid Electrolyte Physiol
249:
F409-F416,
1985[ISI][Medline].
7.
Dransfield, DT,
Bradford AJ,
Smith J,
Martin M,
Roy C,
Mangeat PH,
and
Goldring JR.
Ezrin is a cyclic AMP-dependent protein kinase anchoring protein.
EMBO J
2:
35-43,
1997.
8.
D'Souza, S,
Garcia-Cabado A,
Yu F,
Teter K,
Lukacs G,
Skorecki K,
Moore HP,
Orlowski J,
and
Grinstein S.
The epithelial sodium-hydrogen antiporter Na+/H+ exchanger 3 accumulates and is functional in recycling endosomes.
J Biol Chem
273:
2035-2043,
1998
9.
Ediger, TR,
Kraus WL,
Weinman EJ,
and
Katzenellenbogen BS.
Estrogen receptor regulation of the Na+/H+ exchanger regulatory factor.
Endocrinology
40:
2976-2982,
1999.
10.
Gee, SH,
Sekely SA,
Lombardo C,
Kurakin A,
Froehner SC,
and
Kay BK.
Cyclic peptides as non-carboxyl-terminal ligands of syntrophin PDZ domains.
J Biol Chem
273:
21980-21987,
1998
11.
Hall, RA,
Ostedgaard LS,
Premont RT,
Blitzer JT,
Rahman N,
Welsh MJ,
and
Lefkowitz RJ.
A C-terminal motif found in the beta2-adrenergic receptor, P2Y1 receptor and cystic fibrosis transmembrane conductance regulator determines binding to the Na+/H+ exchanger regulatory factor family of PDZ proteins.
Proc Natl Acad Sci USA
95:
8496-501,
1998
12.
Hall, RA,
Premont RT,
Chow CW,
Blitzer JT,
Pitcher JA,
Claing A,
Stoffel RH,
Barak LS,
Shenolikar S,
Weinman EJ,
Grinstein S,
and
Lefkowitz R.
The 2-adrenergic receptor interacts with the Na+/H+-exchanger regulatory factor to control Na+/H+exchange.
Nature
392:
626-30,
1998[ISI][Medline].
13.
Hall, RA,
Spurney RF,
Premont RT,
Rahman N,
Blitzer JT,
Pitcher JA,
and
Lefkowitz RJ.
G protein-coupled receptor kinase 6A phosphorylates the Na+/H+ exchange regulatory factor (NHERF) via a PDZ domain-mediated interaction.
J Biol Chem
274:
24328-24334,
1999
14.
Hillier, BJ,
Christopherson KS,
Prehoda KE,
Bredt DS,
and
Lim WA.
Unexpected modes of PDZ domain scaffolding revealed by structure of nNOS-syntrophin complex.
Science
284:
812-815,
1999
15.
Janecki, AJ,
Montrose MH,
Zimniak P,
Zweibaum A,
Tse CM,
Khurana S,
and
Donowitz M.
Subcellular redistribution is involved in acute regulation of the brush border Na+/H+ exchanger isoform 3 in human colon adenocarcinoma cell line Caco-2. Protein kinase C-mediated inhibition of the exchanger.
J Biol Chem
273:
8790-8798,
1998
16.
Kahn, AM,
Dolson GM,
Hise MK,
Bennett SC,
and
Weinman EJ.
Parathyroid hormone and dibutyryl cyclic AMP inhibit Na+/H+ countertransport in brush border membrane vesicles isolated from a suspension of rabbit proximal tubules.
Am J Physiol Renal Fluid Electrolyte Physiol
248:
F212-F218,
1985
17.
Kim, E,
Niethammer M,
Rothchild A,
Jan YN,
and
Sheng S.
Clustering of the Shaker-type K+ channels by direct interaction with the PSD-95/SAP90 family of membrane-associated guanylate kinases.
Nature
378:
85-88,
1995[ISI][Medline].
18.
Kurashima, K,
D'Souza S,
Szaszi K,
Ramjeesingh R,
Orlowski J,
and
Grinstein S.
The apical Na(+)/H(+) exchanger isoform NHE3 is regulated by the actin cytoskeleton.
J Biol Chem
274:
29843-29849,
1999
19.
Kurashima, K,
Yu FH,
Cabado AG,
Szabo EZ,
Grinstein S,
and
Orlowski J.
Identification of sites required for down-regulation of Na+/H+ exchanger NHE3 activity by cAMP-dependent protein kinase. Phosphorylation-dependent and -independent mechanisms.
J Biol Chem
272:
28672-28679,
1997
20.
Lamprecht, G,
Weinman EJ,
and
Yun CH.
The role of NHERF and E3KARP in the cAMP-mediated inhibition of NHE3 cAMP-mediated inhibition of NHE3.
J Biol Chem
273:
29972-29978,
1998
21.
McKinney, TD,
and
Meyers P.
Bicarbonate transport by proximal tubules: effect of parathyroid hormone and dibutyryl cyclic AMP.
Am J Physiol Renal Fluid Electrolyte Physiol
238:
F166-F179,
1980
22.
Mohler, PJ,
Kreda SM,
Boucher RC,
Sudol M,
Stutts MJ,
and
Milgram SL.
Yes-associated protein 65 localizes p62(c-Yes) to the apical compartment of airway epithelia by association with EBP50.
J Cell Biol
147:
879-890,
1999
23.
Moyer, BD,
Denton J,
Karlson KH,
Reynolds D,
Wang S,
Mickle JE,
Milewski M,
Cutting GR,
Guggino WB,
Li M,
and
Stanton BA.
A PDZ-interacting domain in CFTR is an apical membrane polarization signal.
J Clin Invest
104:
1353-1361,
1999
24.
Murthy, A,
Gonzales-Agosti C,
Cordero E,
Pinney D,
Candia C,
Solomon F,
Gusella J,
and
Ramesh V.
NHE-RF, a regulatory cofactor for Na+-H+ exchange, is a common interactor for Merlin and ERM (MERM) proteins.
J Biol Chem
27:
1273-1276,
1998.
25.
Orlowski, J,
Kandassmy RA,
and
Shull GE.
Molecular cloning of putative members of the Na/H exchanger gene family.
J Biol Chem
267:
9331-9339,
1992
26.
Oschkinat, H.
A new type of PDZ domain recognition.
Nat Struct Biol
5:
408-410,
1999.
27.
Pawson, T,
and
Scott JD.
Signaling through scaffold, anchoring, and adaptor proteins.
Science
278:
2075-2080,
1997
28.
Ponting, CP,
Phillips C,
Davies KE,
and
Blake DJ.
PDZ domains: targeting signaling molecules to sub-membranous sites.
Bioessays
19:
469-479,
1997[ISI][Medline].
29.
Poulat, F,
Barbara PS,
Desclozeaux M,
Soullier S,
Moniot B,
Bonneaud N,
Boizet B,
and
Berta P.
The human testis determining factor SRY binds a nuclear factor containing PDZ protein interaction domains.
J Biol Chem
272:
7167-7172,
1997
30.
Reczek, D,
Berryman M,
and
Bretscher A.
Identification of EBP50: a PDZ-containing phosphoprotein that associates with members of the ERM family.
Cell Biol
139:
169-179,
1997.
31.
Reczek, D,
and
Bretscher A.
The carboxyl-terminal region of EBP50 binds to a site in the amino-terminal domain of ezrin that is masked in the dormant molecule.
J Biol Chem
273:
18452-18458,
1998
32.
Sardet, C,
Franchi A,
and
Pouyssegur J.
Molecular cloning, primary structure and expression of human growth factor-activatable Na+-H+ antiporter.
Cell
56:
271-280,
1989[ISI][Medline].
33.
Schillace, RV,
and
Scott JD.
Organization of kinases, phosphatases, and receptor signaling complexes.
J Clin Invest
103:
761-765,
1999
34.
Shieh, B-H,
and
Zhu M-Y.
Regulation of the TRP Ca2+ channel by INAD in Drosophila photoreceptors.
Neuron
16:
991-998,
1996[ISI][Medline].
35.
Short, DB,
Trotter KW,
Reczek D,
Kreda SM,
Bretscher A,
Boucher RC,
Stutts MJ,
and
Milgram SL.
An apical PDZ protein anchors the cystic fibrosis transmembrane conductance regulator to the cytoskeleton.
J Biol Chem
273:
19797-19801,
1998
36.
Tse, CM,
Brant SR,
Walker MS,
Pouyssegur J,
and
Donowitz M.
Cloning and sequencing of a rabbit cDNA encoding an intestional and kidney specific N+/H+ exchanger isoform (NHE-3).
J Biol Chem
267:
9340-9346,
1992
37.
Tsukita, A,
and
Yonemura S.
Cortical actin organization: lessons from ERM (ezrin/radizin/moesin) proteins.
J Biol Chem
274:
34507-34510,
1999
38.
Tunoda, S,
Sierralta J,
Bodner R,
Suzuki E,
Becker A,
Socolich M,
and
Zucker CA.
A multivalent PDZ-domain protein assembles signalling complexes in a G-protein-coupled cascade.
Nature
388:
243-249,
1997[ISI][Medline].
39.
Wang, S,
Raab RW,
Schatz PJ,
Guggino WB,
and
Li M.
Peptide binding consensus of the NHE-RF-PDZ1 domain matches the C-terminal sequence of cystic fibrosis transmembrane conductance regulator (CFTR).
FEBS Lett
427:
103-108,
1998[ISI][Medline].
40.
Weinman, EJ,
Bennett SC,
Brady RC,
Harper JF,
Hise MK,
and
Kahn AM.
Effect of cAMP and calmodulin inhibitors on water absorption in rat proximal tubule.
Proc Soc Exp Biol Med
176:
322-326,
1984[Abstract].
41.
Weinman, EJ,
Dubinsky WP,
Dinh Q,
Steplock D,
and
Shenolikar S.
The effect of limited trypsin digestion on the renal Na+-H+ exchanger and its regulation by CAMP dependent protein kinase.
J Membr Biol
109:
233-241,
1989[ISI][Medline].
42.
Weinman, EJ,
Dubinsky WP,
and
Shenolikar S.
Reconstitution of cAMP-dependent protein kinase regulated renal Na+-H+ exchanger.
J Membr Biol
101:
11-18,
1988[ISI][Medline].
43.
Weinman, EJ,
Shenolikar S,
Cragoe EJ, Jr,
and
Dubinsky WP.
Solubilization and reconstitution of renal brush border Na+-H+ exchanger.
J Membr Biol
101:
1-9,
1988[ISI][Medline].
44.
Weinman, EJ,
Shenolikar S,
and
Kahn AM.
cAMP-associated inhibition of Na+-H+ exchanger in rabbit kidney brush-border membranes.
Am J Physiol Renal Fluid Electrolyte Physiol
252:
F19-F25,
1987
45.
Weinman, EJ,
Steplock D,
Donowitz M,
and
Shenolikar S.
NHERF associations with sodium-hydrogen exchanger isoform 3 (NHE3) and ezrin are essential for cAMP-mediated phosphorylation and inhibition of NHE3.
Biochemistry
23:
6123-6129,
2000.
46.
Weinman, EJ,
Steplock D,
and
Shenolikar S.
CAMP mediated inhibition of the renal BBM Na+-H+ exchanger requires a dissociable phosphoprotein co-factor.
J Clin Invest
92:
1781-1786,
1993[ISI][Medline].
47.
Weinman, EJ,
Steplock D,
Tate K,
Hall RA,
Spurney RF,
and
Shenolikar S.
Structure-function of the Na/H exchanger regulatory factor (NHE-RF).
J Clin Invest
101:
2199-2206,
1998
48.
Weinman, EJ,
Steplock D,
Wang Y,
and
Shenolikar S.
Characterization of a protein cofactor that mediates protein kinase A regulation of the renal brush border membrane Na+-H+ exchanger.
J Clin Invest
95:
2143-2149,
1995[ISI][Medline].
49.
Weinman, EJ,
Steplock D,
Yun CH,
Lamprecht G,
and
Shenolikar S.
Regulation of the Na/H exchanger regulatory factor (NHE-RF) in OK cells.
Miner Electrolyte Metab
25:
135-142,
1999[ISI][Medline].
50.
Welling, PA,
Flagg TP,
Olsen O,
Ramesh K,
Foskett K,
Merot R,
and
Raghuram R.
Assembly of a multiprotein KATP channel complex in the kidney by PDZ interactions (Abstract).
J Am Soc Nephrol
10:
49a,
1999.
51.
Yun, CH,
Lamprecht G,
Forster DV,
and
Sidor A.
NHE3 kinase A regulatory protein E3KARP binds the epithelial brush border Na+/H+ exchanger NHE3 and the cytoskeletal protein ezrin.
J Biol Chem
273:
25856-25863,
1998
52.
Yun, CH,
Oh S,
Zizak M,
Steplock D,
Tsao S,
Tse C,
Weinman EJ,
and
Donowitz M.
cAMP-mediated inhibition of the epithelial brush border Na+/H+ exchanger, NHE3, requires an associated regulatory protein.
Proc Natl Acad Sci USA
94:
3010-3015,
1997
53.
Zhao, H,
Wiederkehr MR,
Fan L,
Collazo RL,
Crowder LA,
and
Moe OW.
Acute inhibition of Na/H exchanger NHE-3 by cAMP. Role of protein kinase a and NHE-3 phosphoserines 552 and 605.
J Biol Chem
274:
3978-3987,
1999
54.
Zizak, M,
Lamprecht G,
Steplock D,
Tariq N,
Shenolikar S,
Donowitz M,
Yun C,
and
Weinman EJ.
cAMP-induced phosphorylation and inhibition of Na+/H+ exchanger 3 (NHE3) is dependent on the presence but not the phosphorylation of NHERF.
J Biol Chem
274:
24753-24758,
1999