Cryo-EM structures of intact V-ATPase from bovine brain

Principle role of the (pro)renin receptor system in cardiovascular and metabolic diseases: An update

(Pro)renin receptor (PRR), along with its soluble form, sPRR, functions not only as a crucial activator of the local renin-angiotensin system but also engages with and activates various angiotensin II-independent signaling pathways, thus playing complex and significant roles in numerous physiological and pathophysiological processes, including cardiovascular and metabolic disorders. This article reviews current knowledge on the intracellular partners of the PRR system and explores its physiological and pathophysiological impacts on cardiovascular diseases as well as conditions related to glucose and lipid metabolism, such as hypertension, heart disease, liver disease, diabetes, and diabetic complications. Targeting the PRR system could emerge as a promising therapeutic strategy for treating these conditions. Elevated levels of circulating sPRR might indicate the severity of these diseases, potentially serving as a biomarker for diagnosis and prognosis in clinical settings. A comprehensive understanding of the functions and regulatory mechanisms of the PRR system could facilitate the development of novel therapeutic approaches for the prevention and management of cardiovascular and metabolic diseases.

A nanobody against the V-ATPase c subunit inhibits metastasis of 4T1-12B breast tumor cells to lung in mice

The vacuolar H+-ATPase (V-ATPase) is an ATP-dependent proton pump that functions to control the pH of intracellular compartments as well as to transport protons across the plasma membrane of various cell types, including cancer cells. We have previously shown that selective inhibition of plasma membrane V-ATPases in breast tumor cells inhibits the invasion of these cells in vitro. We have now developed a nanobody directed against an extracellular epitope of the mouse V-ATPase c subunit. We show that treatment of 4T1-12B mouse breast cancer cells with this nanobody inhibits V-ATPase-dependent acidification of the media and invasion of these cells in vitro. We further find that injection of this nanobody into mice implanted with 4T1-12B cells orthotopically in the mammary fat pad inhibits metastasis of tumor cells to lung. These results suggest that plasma membrane V-ATPases represent a novel therapeutic target to limit breast cancer metastasis.

High-resolution electron cryomicroscopy of V-ATPase in native synaptic vesicles

Intercellular communication in the nervous system occurs through the release of neurotransmitters into the synaptic cleft between neurons. In the presynaptic neuron, the proton pumping vesicular- or vacuolar-type ATPase (V-ATPase) powers neurotransmitter loading into synaptic vesicles (SVs), with the V1 complex dissociating from the membrane region of the enzyme before exocytosis. We isolated SVs from rat brain using SidK, a V-ATPase-binding bacterial effector protein. Single-particle electron cryomicroscopy allowed high-resolution structure determination of V-ATPase within the native SV membrane. In the structure, regularly spaced cholesterol molecules decorate the enzyme's rotor and the abundant SV protein synaptophysin binds the complex stoichiometrically. ATP hydrolysis during vesicle loading results in a loss of the V1 region of V-ATPase from the SV membrane, suggesting that loading is sufficient to induce dissociation of the enzyme.

Structure and topography of the synaptic V-ATPase-synaptophysin complex

Synaptic vesicles are organelles with a precisely defined protein and lipid composition1,2, yet the molecular mechanisms for the biogenesis of synaptic vesicles are mainly unknown. Here we discovered a well-defined interface between the synaptic vesicle V-ATPase and synaptophysin by in situ cryo-electron tomography and single-particle cryo-electron microscopy of functional synaptic vesicles isolated from mouse brains3. The synaptic vesicle V-ATPase is an ATP-dependent proton pump that establishes the proton gradient across the synaptic vesicle, which in turn drives the uptake of neurotransmitters4,5. Synaptophysin6 and its paralogues synaptoporin7 and synaptogyrin8 belong to a family of abundant synaptic vesicle proteins whose function is still unclear. We performed structural and functional studies of synaptophysin-knockout mice, confirming the identity of synaptophysin as an interaction partner with the V-ATPase. Although there is little change in the conformation of the V-ATPase upon interaction with synaptophysin, the presence of synaptophysin in synaptic vesicles profoundly affects the copy number of V-ATPases. This effect on the topography of synaptic vesicles suggests that synaptophysin assists in their biogenesis. In support of this model, we observed that synaptophysin-knockout mice exhibit severe seizure susceptibility, suggesting an imbalance of neurotransmitter release as a physiological consequence of the absence of synaptophysin.

Eukaryotic yeast V1-ATPase rotary mechanism insights revealed by high-resolution single-molecule studies

Vacuolar ATP-dependent proton pumps (V-ATPases) belong to a super-family of rotary ATPases and ATP synthases. The V1 complex consumes ATP to drive rotation of a central rotor that pumps protons across membranes via the Vo complex. Eukaryotic V-ATPases are regulated by reversible disassembly of subunit C, V1 without C, and VO. ATP hydrolysis is thought to generate an unknown rotary state that initiates regulated disassembly. Dissociated V1 is inhibited by subunit H that traps it in a specific rotational position. Here, we report the first single-molecule studies with high resolution of time and rotational position of Saccharomyces cerevisiae V1-ATPase lacking subunits H and C (V1ΔHC), which resolves previously elusive dwells and angular velocity changes. Rotation occurred in 120° power strokes separated by dwells comparable to catalytic dwells observed in other rotary ATPases. However, unique V1ΔHC rotational features included: 1) faltering power stroke rotation during the first 60°; 2) a dwell often occurring ∼45° after the catalytic dwell, which did not increase in duration at limiting MgATP; 3) a second dwell, ∼2-fold longer occurring 112° that increased in duration and occurrence at limiting MgATP; 4) limiting MgATP-dependent decreases in power stroke angular velocity where dwells were not observed. The results presented here are consistent with MgATP binding to the empty catalytic site at 112° and MgADP released at ∼45°, and provide important new insight concerning the molecular basis for the differences in rotary positions of substrate binding and product release between V-type and F-type ATPases.

Human V-ATPase a-subunit isoforms bind specifically to distinct phosphoinositide phospholipids

Vacuolar H+-ATPases (V-ATPases) are highly conserved multisubunit enzymes that maintain the distinct pH of eukaryotic organelles. The integral membrane a-subunit is encoded by tissue- and organelle-specific isoforms, and its cytosolic N-terminal domain (aNT) modulates organelle-specific regulation and targeting of V-ATPases. Organelle membranes have specific phosphatidylinositol phosphate (PIP) lipid enrichment linked to maintenance of organelle pH. In yeast, the aNT domains of the two a-subunit isoforms bind PIP lipids enriched in the organelle membranes where they reside; these interactions affect activity and regulatory properties of the V-ATPases containing each isoform. Humans have four a-subunit isoforms, and we hypothesize that the aNT domains of these isoforms will also bind to specific PIP lipids. The a1 and a2 isoforms of human V-ATPase a-subunits are localized to endolysosomes and Golgi, respectively. We determined that bacterially expressed Hua1NT and Hua2NT bind specifically to endolysosomal PIP lipids PI(3)P and PI(3,5)P2 and Golgi enriched PI(4)P, respectively. Despite the lack of canonical PIP-binding sites, we identified potential binding sites in the HuaNT domains by sequence comparisons and existing subunit structures and models. We found that mutations at a similar location in the distal loops of both HuaNT isoforms compromise binding to their cognate PIP lipids, suggesting that these loops encode PIP specificity of the a-subunit isoforms. These data suggest a mechanism through which PIP lipid binding could stabilize and activate V-ATPases in distinct organelles.

Lysosomes in senescence and aging

Dysfunction of lysosomes, the primary hydrolytic organelles in animal cells, is frequently associated with aging and age-related diseases. At the cellular level, lysosomal dysfunction is strongly linked to cellular senescence or the induction of cell death pathways. However, the precise mechanisms by which lysosomal dysfunction participates in these various cellular or organismal phenotypes have remained elusive. The ability of lysosomes to degrade diverse macromolecules including damaged proteins and organelles puts lysosomes at the center of multiple cellular stress responses. Lysosomal activity is tightly regulated by many coordinated cellular processes including pathways that function inside and outside of the organelle. Here, we collectively classify these coordinated pathways as the lysosomal processing and adaptation system (LYPAS). We review evidence that the LYPAS is upregulated by diverse cellular stresses, its adaptability regulates senescence and cell death decisions, and it can form the basis for therapeutic manipulation for a wide range of age-related diseases and potentially for aging itself.

Six states of Enterococcus hirae V-type ATPase reveals non-uniform rotor rotation during turnover

The vacuolar-type ATPase from Enterococcus hirae (EhV-ATPase) is a thus-far unique adaptation of V-ATPases, as it performs Na⁺ transport and demonstrates an off-axis rotor assembly. Recent single molecule studies of the isolated V₁ domain have indicated that there are subpauses within the three major states of the pseudo three-fold symmetric rotary enzyme. However, there was no structural evidence for these. Herein we activate the EhV-ATPase complex with ATP and identified multiple structures consisting of a total of six states of this complex by using cryo-electron microscopy. The orientations of the rotor complex during turnover, especially in the intermediates, are not as perfectly uniform as expected. The densities in the nucleotide binding pockets in the V₁ domain indicate the different catalytic conditions for the six conformations. The off-axis rotor and its' interactions with the stator a-subunit during rotation suggests that this non-uniform rotor rotation is performed through the entire complex.

Structural and functional understanding of disease-associated mutations in V-ATPase subunit a1 and other isoforms

The vacuolar-type ATPase (V-ATPase) is a multisubunit protein composed of the cytosolic adenosine triphosphate (ATP) hydrolysis catalyzing V1 complex, and the integral membrane complex, Vo, responsible for proton translocation. The largest subunit of the Vo complex, subunit a, enables proton translocation upon ATP hydrolysis, mediated by the cytosolic V1 complex. Four known subunit a isoforms (a1-a4) are expressed in different cellular locations. Subunit a1 (also known as Voa1), the neural isoform, is strongly expressed in neurons and is encoded by the ATP6V0A1 gene. Global knockout of this gene in mice causes embryonic lethality, whereas pyramidal neuron-specific knockout resulted in neuronal cell death with impaired spatial and learning memory. Recently reported, de novo and biallelic mutations of the human ATP6V0A1 impair autophagic and lysosomal activities, contributing to neuronal cell death in developmental and epileptic encephalopathies (DEE) and early onset progressive myoclonus epilepsy (PME). The de novo heterozygous R740Q mutation is the most recurrent variant reported in cases of DEE. Homology studies suggest R740 deprotonates protons from specific glutamic acid residues in subunit c, highlighting its importance to the overall V-ATPase function. In this paper, we discuss the structure and mechanism of the V-ATPase, emphasizing how mutations in subunit a1 can lead to lysosomal and autophagic dysfunction in neurodevelopmental disorders, and how mutations to the non-neural isoforms, a2-a4, can also lead to various genetic diseases. Given the growing discovery of disease-causing variants of V-ATPase subunit a and its function as a pump-based regulator of intracellular organelle pH, this multiprotein complex warrants further investigation.

Tender love and disassembly: How a TLDc domain protein breaks the V-ATPase

Vacuolar ATPases (V-ATPases, V1 Vo -ATPases) are rotary motor proton pumps that acidify intracellular compartments, and, when localized to the plasma membrane, the extracellular space. V-ATPase is regulated by a unique process referred to as reversible disassembly, wherein V1 -ATPase disengages from Vo proton channel in response to diverse environmental signals. Whereas the disassembly step of this process is ATP dependent, the (re)assembly step is not, but requires the action of a heterotrimeric chaperone referred to as the RAVE complex. Recently, an alternative pathway of holoenzyme disassembly was discovered that involves binding of Oxidation Resistance 1 (Oxr1p), a poorly characterized protein implicated in oxidative stress response. Unlike conventional reversible disassembly, which depends on enzyme activity, Oxr1p induced dissociation can occur in absence of ATP. Yeast Oxr1p belongs to the family of TLDc domain containing proteins that are conserved from yeast to mammals, and have been implicated in V-ATPase function in a variety of tissues. This brief perspective summarizes what we know about the molecular mechanisms governing both reversible (ATP dependent) and Oxr1p driven (ATP independent) V-ATPase dissociation into autoinhibited V1 and Vo subcomplexes.

The cytosolic N-terminal domain of V-ATPase a-subunits is a regulatory hub targeted by multiple signals

Vacuolar H+-ATPases (V-ATPases) acidify several organelles in all eukaryotic cells and export protons across the plasma membrane in a subset of cell types. V-ATPases are multisubunit enzymes consisting of a peripheral subcomplex, V1, that is exposed to the cytosol and an integral membrane subcomplex, Vo, that contains the proton pore. The Vo a-subunit is the largest membrane subunit and consists of two domains. The N-terminal domain of the a-subunit (aNT) interacts with several V1 and Vo subunits and serves to bridge the V1 and Vo subcomplexes, while the C-terminal domain contains eight transmembrane helices, two of which are directly involved in proton transport. Although there can be multiple isoforms of several V-ATPase subunits, the a-subunit is encoded by the largest number of isoforms in most organisms. For example, the human genome encodes four a-subunit isoforms that exhibit a tissue- and organelle-specific distribution. In the yeast S. cerevisiae, the two a-subunit isoforms, Golgi-enriched Stv1 and vacuolar Vph1, are the only V-ATPase subunit isoforms. Current structural information indicates that a-subunit isoforms adopt a similar backbone structure but sequence variations allow for specific interactions during trafficking and in response to cellular signals. V-ATPases are subject to several types of environmental regulation that serve to tune their activity to their cellular location and environmental demands. The position of the aNT domain in the complex makes it an ideal target for modulating V1-Vo interactions and regulating enzyme activity. The yeast a-subunit isoforms have served as a paradigm for dissecting interactions of regulatory inputs with subunit isoforms. Importantly, structures of yeast V-ATPases containing each a-subunit isoform are available. Chimeric a-subunits combining elements of Stv1NT and Vph1NT have provided insights into how regulatory inputs can be integrated to allow V-ATPases to support cell growth under different stress conditions. Although the function and distribution of the four mammalian a-subunit isoforms present additional complexity, it is clear that the aNT domains of these isoforms are also subject to multiple regulatory interactions. Regulatory mechanisms that target mammalian a-subunit isoforms, and specifically the aNT domains, will be described. Altered V-ATPase function is associated with multiple diseases in humans. The possibility of regulating V-ATPase subpopulations via their isoform-specific regulatory interactions are discussed.

CryoEM of V-ATPases: Assembly, disassembly, and inhibition

Vacuolar-type ATPases (V-ATPases) are responsible for the acidification of intracellular compartments in almost all eukaryotic cells, while in some specialized cells they acidify the extracellular environment. As ubiquitous proton pumps, these large membrane-embedded enzymes are involved in many fundamental cellular processes that require tight control of pH. Consequently, V-ATPase malfunction or aberrant activity has been linked to numerous diseases. In the past ten years, electron cryomicroscopy (cryoEM) of yeast V-ATPases has revealed the architecture and rotary catalytic mechanism of these macromolecular machines. More recently, studies have revealed the structures of V-ATPases in animals and plants, uncovered aspects of how V-ATPases are assembled and regulated by reversible dissociation, and shown how V-ATPase activity can be modulated by proteins and small molecule inhibitors. In this review, we highlight these recent developments.

Human V-ATPase a-subunit isoforms bind specifically to distinct phosphoinositide phospholipids

V-ATPases are highly conserved multi-subunit enzymes that maintain the distinct pH of eukaryotic organelles. The integral membrane a-subunit is encoded by tissue and organelle specific isoforms, and its cytosolic N-terminal domain (aNT) modulates organelle specific regulation and targeting of V-ATPases. Organelle membranes have specific phosphatidylinositol phosphate (PIP) lipid enrichment linked to maintenance of organelle pH. In yeast, the aNT domains of the two a-subunit isoforms bind PIP lipids enriched in the organelle membranes where they reside; these interactions affect activity and regulatory properties of the V-ATPases containing each isoform. Humans have four a-subunit isoforms. We hypothesize that the aNT domains of the human isoforms will also bind to specific PIP lipids. The a1 and a2 isoforms of human V-ATPase a-subunits are localized to endolysosomes and Golgi, respectively. Bacterially expressed Hua1NT and Hua2NT bind specifically to endolysosomal PIP lipids PI(3)P and PI(3,5)P2 and Golgi enriched PI(4)P, respectively. Despite the lack of canonical PIP binding sites, potential binding sites in the HuaNT domains were identified by sequence comparisons and existing subunit structures and models. Mutations at a similar location in the distal loops of both HuaNT isoforms compromise binding to their cognate PIP lipids, suggesting that these loops encode PIP specificity of the a-subunit isoforms. These data also suggest a mechanism through which PIP lipid binding could stabilize and activate V-ATPases in distinct organelles.

A Role for the V0 Sector of the V-ATPase in Neuroexocytosis: Exogenous V0d Blocks Complexin and SNARE Interactions with V0c

V-ATPase is an important factor in synaptic vesicle acidification and is implicated in synaptic transmission. Rotation in the extra-membranous V1 sector drives proton transfer through the membrane-embedded multi-subunit V0 sector of the V-ATPase. Intra-vesicular protons are then used to drive neurotransmitter uptake by synaptic vesicles. V0a and V0c, two membrane subunits of the V0 sector, have been shown to interact with SNARE proteins, and their photo-inactivation rapidly impairs synaptic transmission. V0d, a soluble subunit of the V0 sector strongly interacts with its membrane-embedded subunits and is crucial for the canonic proton transfer activity of the V-ATPase. Our investigations show that the loop 1.2 of V0c interacts with complexin, a major partner of the SNARE machinery and that V0d1 binding to V0c inhibits this interaction, as well as V0c association with SNARE complex. The injection of recombinant V0d1 in rat superior cervical ganglion neurons rapidly reduced neurotransmission. In chromaffin cells, V0d1 overexpression and V0c silencing modified in a comparable manner several parameters of unitary exocytotic events. Our data suggest that V0c subunit promotes exocytosis via interactions with complexin and SNAREs and that this activity can be antagonized by exogenous V0d.

Structural and Functional Diversity of Two ATP-Driven Plant Proton Pumps

Two ATP-dependent proton pumps function in plant cells. Plasma membrane H⁺-ATPase (PM H⁺-ATPase) transfers protons from the cytoplasm to the apoplast, while vacuolar H⁺-ATPase (V-ATPase), located in tonoplasts and other endomembranes, is responsible for proton pumping into the organelle lumen. Both enzymes belong to two different families of proteins and, therefore, differ significantly in their structure and mechanism of action. The plasma membrane H⁺-ATPase is a member of the P-ATPases that undergo conformational changes, associated with two distinct E1 and E2 states, and autophosphorylation during the catalytic cycle. The vacuolar H⁺-ATPase represents rotary enzymes functioning as a molecular motor. The plant V-ATPase consists of thirteen different subunits organized into two subcomplexes, the peripheral V₁ and the membrane-embedded V₀, in which the stator and rotor parts have been distinguished. In contrast, the plant plasma membrane proton pump is a functional single polypeptide chain. However, when the enzyme is active, it transforms into a large twelve-protein complex of six H⁺-ATPase molecules and six 14-3-3 proteins. Despite these differences, both proton pumps can be regulated by the same mechanisms (such as reversible phosphorylation) and, in some processes, such as cytosolic pH regulation, may act in a coordinated way.

Mutations in V-ATPase in follicular lymphoma activate autophagic flux creating a targetable dependency

The recent discovery of recurrent gene mutations in chaperones or components of the vacuolar-type H+-translocating ATPase (V-ATPase) in follicular lymphoma (FL) was an unexpected finding. The application of whole exome sequencing and targeted gene re-sequencing has resulted in the identification of mutations in ATP6AP1, ATP6V1B2 and VMA21 in a combined 30% of FL, together constituting a major novel mutated pathway in this disease. Interestingly, no other human hematological malignancy carries these mutations at more than sporadic occurrences, implicating unique aspects of FL biology requiring these mutations. The mutations in ATP6V1B2 and VMA21 through separate mechanisms impair lysosomal V-ATPase activity resulting in an elevated lysosomal pH. The elevated lysosomal pH impairs protein and peptide hydrolysis and associates with reduced cytoplasmic amino acid concentrations resulting in compensatory activation of autophagic flux. The elevated autophagic flux constitutes a survival dependency for FL cells and can be targeted with inhibitors to ULK1 and multiple recently identified cyclin-dependent kinase inhibitors. Targeting autophagy alone or in combination with other targeted therapies constitutes a novel therapeutic opportunity for FL patients.

The (Pro)renin Receptor - A Regulatory Nodal Point in Disease Networks

Experimental inhibition of the (pro)renin receptor [(P)RR] is a promising therapeutic strategy in different disease models ranging from cardiorenal to oncological entities. Here, we briefly review the direct protein-protein interaction partners of the (P)RR and the plethora of distinct diseases in which the (P)RR is involved. The first structural work on the (P)RR using AlphaFold, which was recently published by Ebihara et al., is the center of this mini-review since it can mechanistically link the protein-protein interaction level with the pathophysiological level. More detailed insights into the 3D structure of the (P)RR and its interaction domains might guide drug discovery on this novel target. Finally, antibody- and small molecule-based approaches to inhibit the (P)RR are shortly discussed.

CryoEM of endogenous mammalian V-ATPase interacting with the TLDc protein mEAK-7

V-ATPases are rotary proton pumps that serve as signaling hubs with numerous protein binding partners. CryoEM with exhaustive focused classification allowed detection of endogenous proteins associated with porcine kidney V-ATPase. An extra C subunit was found in ∼3% of complexes, whereas ∼1.6% of complexes bound mEAK-7, a protein with proposed roles in dauer formation in nematodes and mTOR signaling in mammals. High-resolution cryoEM of porcine kidney V-ATPase with recombinant mEAK-7 showed that mEAK-7's TLDc domain interacts with V-ATPase's stator, whereas its C-terminal α helix binds V-ATPase's rotor. This crosslink would be expected to inhibit rotary catalysis. However, unlike the yeast TLDc protein Oxr1p, exogenous mEAK-7 does not inhibit V-ATPase and mEAK-7 overexpression in cells does not alter lysosomal or phagosomal pH. Instead, cryoEM suggests that the mEAK-7:V-ATPase interaction is disrupted by ATP-induced rotation of the rotor. Comparison of Oxr1p and mEAK-7 binding explains this difference. These results show that V-ATPase binding by TLDc domain proteins can lead to effects ranging from strong inhibition to formation of labile interactions that are sensitive to the enzyme's activity.

Identification of mEAK-7 as a human V-ATPase regulator via cryo-EM data mining

Vacuolar-type adenosine triphosphatases (V-ATPases) not only function as rotary proton pumps in cellular organelles but also serve as signaling hubs. To identify the endogenous binding partners of V-ATPase, we collected a large dataset of human V-ATPases and did extensive classification and focused refinement of human V-ATPases. Unexpectedly, about 17% of particles in state 2 of human V-ATPases display additional density with an overall resolution of 3.3 Å. Structural analysis combined with artificial intelligence modeling enables us to identify this additional density as mEAK-7, a protein involved in mechanistic target of rapamycin (mTOR) signaling in mammals. Our structure shows that mEAK-7 interacts with subunits A, B, D, and E of V-ATPases in state 2. Thus, we propose that mEAK-7 may regulate V-ATPase function through binding to V-ATPases in state 2 as well as mediate mTOR signaling.

The emerging role of furin in neurodegenerative and neuropsychiatric diseases

Furin is an important mammalian proprotein convertase that catalyzes the proteolytic maturation of a variety of prohormones and proproteins in the secretory pathway. In the brain, the substrates of furin include the proproteins of growth factors, receptors and enzymes. Emerging evidence, such as reduced FURIN mRNA expression in the brains of Alzheimer's disease patients or schizophrenia patients, has implicated a crucial role of furin in the pathophysiology of neurodegenerative and neuropsychiatric diseases. Currently, compared to cancer and infectious diseases, the aberrant expression of furin and its pharmaceutical potentials in neurological diseases remain poorly understood. In this article, we provide an overview on the physiological roles of furin and its substrates in the brain, summarize the deregulation of furin expression and its effects in neurodegenerative and neuropsychiatric disorders, and discuss the implications and current approaches that target furin for therapeutic interventions. This review may expedite future studies to clarify the molecular mechanisms of furin deregulation and involvement in the pathogenesis of neurodegenerative and neuropsychiatric diseases, and to develop new diagnosis and treatment strategies for these diseases.

Structure of V-ATPase from citrus fruit

We used the Legionella pneumophila effector SidK to affinity purify the endogenous vacuolar-type ATPases (V-ATPases) from lemon fruit. The preparation was sufficient for cryoelectron microscopy, allowing structure determination of the enzyme in two rotational states. The structure defines the ATP:H⁺ ratio of the enzyme, demonstrating that it can establish a maximum ΔpH of ∼3, which is insufficient to maintain the low pH observed in the vacuoles of juice sac cells in lemons and other citrus fruit. Compared with yeast and mammalian enzymes, the membrane region of the plant V-ATPase lacks subunit f and possesses an unusual configuration of transmembrane α helices. Subunit H, which inhibits ATP hydrolysis in the isolated catalytic region of V-ATPase, adopts two different conformations in the intact complex, hinting at a role in modulating activity in the intact enzyme.

Follicular lymphoma-associated mutations in the V-ATPase chaperone VMA21 activate autophagy creating a targetable dependency

The discovery of recurrent mutations in subunits and regulators of the vacuolar-type H+-translocating ATPase (V-ATPase) in follicular lymphoma (FL) highlights a role for macroautophagy/autophagy, amino-acid, and nutrient-sensing pathways in the pathogenesis of this disease. Here, we report on novel mutations in the ER-resident chaperone VMA21, which is involved in V-ATPase assembly in 12% of FL. Mutations in a novel VMA21 hotspot (p.93X) result in the removal of a C-terminal non-canonical ER retrieval signal thus causing VMA21 mislocalization to lysosomes. The resulting impairment in V-ATPase activity prevents full lysosomal acidification and function, including impaired pH-dependent protein degradation as shown via lysosomal metabolomics and ultimately causes a degree of amino acid depletion in the cytoplasm. These deficiencies result in compensatory autophagy activation, as measured using multiple complementary assays in human and yeast cells. Of translational significance, the compensatory activation of autophagy creates a dependency for survival for VMA21-mutated primary human FL as shown using inhibitors to ULK1, the proximal autophagy-regulating kinase. Using high-throughput microscopy-based screening assays for autophagy-inhibiting compounds, we identify multiple clinical grade cyclin-dependent kinase inhibitors as promising drugs and thus provide new rationale for innovative clinical trials in FL harboring aberrant V-ATPase.Abbreviations: ALs: autolysosomes; APs: autophagosomes; ER: endoplasmic reticulum; FL: follicular lymphoma; GFP: green fluorescent protein; IP: immunoprecipitation; LE/LY: late endosomes/lysosomes; Lyso-IP: lysosomal immunoprecipitation; OST: oligosaccharide transferase; prApe1: precursor aminopeptidase I; SEP: super ecliptic pHluorin; V-ATPase: vacuolar-type H+-translocating ATPase.

Structures of Multisubunit Membrane Complexes With the CRYO ARM 200

Progress in structural membrane biology has been significantly accelerated by the ongoing ‘Resolution Revolution’ in cryo-electron microscopy (cryo-EM). In particular, structure determination by single-particle analysis has evolved into the most powerful method for atomic model building of multisubunit membrane protein complexes. This has created an ever-increasing demand in cryo-EM machine time, which to satisfy is in need of new and affordable cryo-electron microscopes. Here, we review our experience in using the JEOL CRYO ARM 200 prototype for the structure determination by single-particle analysis of three different multisubunit membrane complexes: the Thermus thermophilus V-type ATPase V_O complex, the Thermosynechococcus elongatus photosystem I monomer and the flagellar motor lipopolysaccharide peptidoglycan ring (LP ring) from Salmonella enterica.

Molecular basis of mEAK7-mediated human V-ATPase regulation

The activity of V-ATPase is well-known to be regulated by reversible dissociation of its V1 and Vo domains in response to growth factor stimulation, nutrient sensing, and cellular differentiation. The molecular basis of its regulation by an endogenous modulator without affecting V-ATPase assembly remains unclear. Here, we discover that a lysosome-anchored protein termed (mammalian Enhancer-of-Akt-1-7 (mEAK7)) binds to intact V-ATPase. We determine cryo-EM structure of human mEAK7 in complex with human V-ATPase in native lipid-containing nanodiscs. The structure reveals that the TLDc domain of mEAK7 engages with subunits A, B, and E, while its C-terminal domain binds to subunit D, presumably blocking V1-Vo torque transmission. Our functional studies suggest that mEAK7, which may act as a V-ATPase inhibitor, does not affect the activity of V-ATPase in vitro. However, overexpression of mEAK7 in HCT116 cells that stably express subunit a4 of V-ATPase represses the phosphorylation of ribosomal protein S6. Thus, this finding suggests that mEAK7 potentially links mTOR signaling with V-ATPase activity.

V-ATPase is a universal regulator of LC3-associated phagocytosis and non-canonical autophagy

Non-canonical autophagy is a key cellular pathway in immunity, cancer, and neurodegeneration, characterized by conjugation of ATG8 to endolysosomal single membranes (CASM). CASM is activated by engulfment (endocytosis, phagocytosis), agonists (STING, TRPML1), and infection (influenza), dependent on K490 in the ATG16L1 WD40-domain. However, factors associated with non-canonical ATG16L1 recruitment and CASM induction remain unknown. Here, using pharmacological inhibitors, we investigate a role for V-ATPase during non-canonical autophagy. We report that increased V0–V1 engagement is associated with, and sufficient for, CASM activation. Upon V0–V1 binding, V-ATPase recruits ATG16L1, via K490, during LC3-associated phagocytosis (LAP), STING- and drug-induced CASM, indicating a common mechanism. Furthermore, during LAP, key molecular players, including NADPH oxidase/ROS, converge on V-ATPase. Finally, we show that LAP is sensitive to Salmonella SopF, which disrupts the V-ATPase–ATG16L1 axis and provide evidence that CASM contributes to the Salmonella host response. Together, these data identify V-ATPase as a universal regulator of CASM and indicate that SopF evolved in part to evade non-canonical autophagy.

Coordinated conformational changes in the V1 complex during V-ATPase reversible dissociation

Vacuolar-type ATPases (V-ATPases) are rotary enzymes that acidify intracellular compartments in eukaryotic cells. These multi-subunit complexes consist of a cytoplasmic V₁ region that hydrolyzes ATP and a membrane-embedded V_O region that transports protons. V-ATPase activity is regulated by reversible dissociation of the two regions, with the isolated V₁ and V_O complexes becoming autoinhibited on disassembly and subunit C subsequently detaching from V₁. In yeast, assembly of the V₁ and V_O regions is mediated by the regulator of the ATPase of vacuoles and endosomes (RAVE) complex through an unknown mechanism. We used cryogenic-electron microscopy of yeast V-ATPase to determine structures of the intact enzyme, the dissociated but complete V₁ complex and the V₁ complex lacking subunit C. On separation, V₁ undergoes a dramatic conformational rearrangement, with its rotational state becoming incompatible for reassembly with V_O. Loss of subunit C allows V₁ to match the rotational state of V_O, suggesting how RAVE could reassemble V₁ and V_O by recruiting subunit C.

Oxidative stress protein Oxr1 promotes V-ATPase holoenzyme disassembly in catalytic activity-independent manner

The vacuolar ATPase (V-ATPase) is a rotary motor proton pump that is regulated by an assembly equilibrium between active holoenzyme and autoinhibited V1 -ATPase and Vo proton channel subcomplexes. Here, we report cryo-EM structures of yeast V-ATPase assembled in vitro from lipid nanodisc reconstituted Vo and mutant V1 . Our analysis identified holoenzymes in three active rotary states, indicating that binding of V1 to Vo provides sufficient free energy to overcome Vo autoinhibition. Moreover, the structures suggest that the unequal spacing of Vo 's proton-carrying glutamic acid residues serves to alleviate the symmetry mismatch between V1 and Vo motors, a notion that is supported by mutagenesis experiments. We also uncover a structure of free V1 bound to Oxr1, a conserved but poorly characterized factor involved in the oxidative stress response. Biochemical experiments show that Oxr1 inhibits V1 -ATPase and causes disassembly of the holoenzyme, suggesting that Oxr1 plays a direct role in V-ATPase regulation.

Current progress in plant V-ATPase: From biochemical properties to physiological functions

Vacuolar-type adenosine triphosphatase (V-ATPase, VHA) is a highly conserved, ATP-driven multisubunit proton pump that is widely distributed in all eukaryotic cells. V-ATPase consists of two domains formed by at least 13 different subunits, the membrane peripheral V₁ domain responsible for ATP hydrolysis, and the membrane-integral V₀ domain responsible for proton translocation. V-ATPase plays an essential role in energizing secondary active transport and is indispensable to plants. In addition to multiple stress responses, plant V-ATPase is also implicated in physiological processes such as growth, development, and morphogenesis. Based on the identification of distinct V-ATPase mutants and advances in luminal pH measurements in vivo, it has been revealed that this holoenzyme complex plays a pivotal role in pH homeostasis of the plant endomembrane system and endocytic and secretory trafficking. Here, we review recent progress in comprehending the biochemical properties and physiological functions of plant V-ATPase and explore the topics that require further elucidation.

Variants in ATP6V0A1 cause progressive myoclonus epilepsy and developmental and epileptic encephalopathy

The vacuolar H+-ATPase is a large multi-subunit proton pump, composed of an integral membrane V0 domain, involved in proton translocation, and a peripheral V1 domain, catalysing ATP hydrolysis. This complex is widely distributed on the membrane of various subcellular organelles, such as endosomes and lysosomes, and plays a critical role in cellular processes ranging from autophagy to protein trafficking and endocytosis. Variants in ATP6V0A1, the brain-enriched isoform in the V0 domain, have been recently associated with developmental delay and epilepsy in four individuals. Here, we identified 17 individuals from 14 unrelated families with both with new and previously characterized variants in this gene, representing the largest cohort to date. Five affected subjects with biallelic variants in this gene presented with a phenotype of early-onset progressive myoclonus epilepsy with ataxia, while 12 individuals carried de novo missense variants and showed severe developmental and epileptic encephalopathy. The R740Q mutation, which alone accounts for almost 50% of the mutations identified among our cases, leads to failure of lysosomal hydrolysis by directly impairing acidification of the endolysosomal compartment, causing autophagic dysfunction and severe developmental defect in Caenorhabditis elegans. Altogether, our findings further expand the neurological phenotype associated with variants in this gene and provide a direct link with endolysosomal acidification in the pathophysiology of ATP6V0A1-related conditions.

Vacuolar-type proton ATPase is required for maintenance of apicobasal polarity of embryonic visceral endoderm

The endocytic compartments keep their interior acidic through the inward flow of protons and anions from the cytosol. Acidification is mediated by a proton pump known as vacuolar-type ATPase (V-ATPase) and transporters conferring anion conductance to the organellar membrane. In this study, we analysed the phenotype of mouse embryos lacking the V-ATPase c-subunit. The mutant embryos differentiated embryonic epithelial tissues, primitive endoderm, epiblast, and extraembryonic ectoderm; however, the organisation of these epithelia was severely affected. The apical-basal polarity in the visceral endoderm layer was not properly established in the mutant embryos, resulting in abnormal epithelial morphology. Thus, the function of V-ATPase is imperative for the establishment and/or maintenance of epithelial cell polarity, which is required for early embryogenesis.

Plasma Membrane Receptors Involved in the Binding and Response of Osteoclasts to Noncellular Components of the Bone

Osteoclasts differentiate from hematopoietic cells and resorb the bone in response to various signals, some of which are received directly from noncellular elements of the bone. In vitro, adherence to the bone triggers the reduction of cell–cell fusion events between osteoclasts and the activation of osteoclasts to form unusual dynamic cytoskeletal and membrane structures that are required for degrading the bone. Integrins on the surface of osteoclasts are known to receive regulatory signals from the bone matrix. Regulation of the availability of these signals is accomplished by enzymatic alterations of the bone matrix by protease activity and phosphorylation/dephosphorylation events. Other membrane receptors are present in osteoclasts and may interact with as yet unidentified signals in the bone. Bone mineral has been shown to have regulatory effects on osteoclasts, and osteoclast activity is also directly modulated by mechanical stress. As understanding of how osteoclasts and other bone cells interact with the bone has emerged, increasingly sophisticated efforts have been made to create bone biomimetics that reproduce both the structural properties of the bone and the bone’s ability to regulate osteoclasts and other bone cells. A more complete understanding of the interactions between osteoclasts and the bone may lead to new strategies for the treatment of bone diseases and the production of bone biomimetics to repair defects.

Purification of active human vacuolar H+-ATPase in native lipid-containing nanodiscs

Vacuolar H+-ATPases (V-ATPases) are large, multisubunit proton pumps that acidify the lumen of organelles in virtually every eukaryotic cell and in specialized acid-secreting animal cells, the enzyme pumps protons into the extracellular space. In higher organisms, most of the subunits are expressed as multiple isoforms, with some enriched in specific compartments or tissues and others expressed ubiquitously. In mammals, subunit a is expressed as four isoforms (a1-4) that target the enzyme to distinct biological membranes. Mutations in a isoforms are known to give rise to tissue-specific disease, and some a isoforms are upregulated and mislocalized to the plasma membrane in invasive cancers. However, isoform complexity and low abundance greatly complicate purification of active human V-ATPase, a prerequisite for developing isoform-specific therapeutics. Here, we report the purification of an active human V-ATPase in native lipid nanodiscs from a cell line stably expressing affinity-tagged a isoform 4 (a4). We find that exogenous expression of this single subunit in HEK293F cells permits assembly of a functional V-ATPase by incorporation of endogenous subunits. The ATPase activity of the preparation is >95% sensitive to concanamycin A, indicating that the lipid nanodisc-reconstituted enzyme is functionally coupled. Moreover, this strategy permits purification of the enzyme's isolated membrane subcomplex together with biosynthetic assembly factors coiled-coil domain-containing protein 115, transmembrane protein 199, and vacuolar H+-ATPase assembly integral membrane protein 21. Our work thus lays the groundwork for biochemical characterization of active human V-ATPase in an a subunit isoform-specific manner and establishes a platform for the study of the assembly and regulation of the human holoenzyme.

RAVE and Rabconnectin-3 Complexes as Signal Dependent Regulators of Organelle Acidification

The yeast RAVE (Regulator of H⁺-ATPase of Vacuolar and Endosomal membranes) complex and Rabconnectin-3 complexes of higher eukaryotes regulate acidification of organelles such as lysosomes and endosomes by catalyzing V-ATPase assembly. V-ATPases are highly conserved proton pumps consisting of a peripheral V₁ subcomplex that contains the sites of ATP hydrolysis, attached to an integral membrane V_o subcomplex that forms the transmembrane proton pore. Reversible disassembly of the V-ATPase is a conserved regulatory mechanism that occurs in response to multiple signals, serving to tune ATPase activity and compartment acidification to changing extracellular conditions. Signals such as glucose deprivation can induce release of V₁ from V_o, which inhibits both ATPase activity and proton transport. Reassembly of V₁ with V_o restores ATP-driven proton transport, but requires assistance of the RAVE or Rabconnectin-3 complexes. Glucose deprivation triggers V-ATPase disassembly in yeast and is accompanied by binding of RAVE to V₁ subcomplexes. Upon glucose readdition, RAVE catalyzes both recruitment of V₁ to the vacuolar membrane and its reassembly with V_o. The RAVE complex can be recruited to the vacuolar membrane by glucose in the absence of V₁ subunits, indicating that the interaction between RAVE and the V_o membrane domain is glucose-sensitive. Yeast RAVE complexes also distinguish between organelle-specific isoforms of the V_o a-subunit and thus regulate distinct V-ATPase subpopulations. Rabconnectin-3 complexes in higher eukaryotes appear to be functionally equivalent to yeast RAVE. Originally isolated as a two-subunit complex from rat brain, the Rabconnectin-3 complex has regions of homology with yeast RAVE and was shown to interact with V-ATPase subunits and promote endosomal acidification. Current understanding of the structure and function of RAVE and Rabconnectin-3 complexes, their interactions with the V-ATPase, their role in signal-dependent modulation of organelle acidification, and their impact on downstream pathways will be discussed.

Role of Biomolecules in Osteoclasts and Their Therapeutic Potential for Osteoporosis

Osteoclasts (OCs) are important cells that are involved in the regulation of bone metabolism and are mainly responsible for coordinating bone resorption with bone formation to regulate bone remodeling. The imbalance between bone resorption and formation significantly affects bone metabolism. When the activity of osteoclasts exceeds the osteoblasts, it results in a condition called osteoporosis, which is characterized by reduced bone microarchitecture, decreased bone mass, and increased occurrences of fracture. Molecules, including transcription factors, proteins, hormones, nucleic acids, such as non-coding RNAs, play an important role in osteoclast proliferation, differentiation, and function. In this review, we have highlighted the role of these molecules in osteoclasts regulation and osteoporosis. The developed therapeutics targeting these molecules for the treatment of osteoporosis in recent years have also been discussed with challenges faced in clinical application.

Novel vertebrate- and brain-specific driver of neuronal outgrowth

During the process of neuronal outgrowth, developing neurons produce new projections, neurites, that are essential for brain wiring. Here, we discover a relatively late-evolved protein that we denote Ac45-related protein (Ac45RP) and that, surprisingly, drives neuronal outgrowth. Ac45RP is a paralog of the Ac45 protein that is a component of the vacuolar proton ATPase (V-ATPase), the main pH regulator in eukaryotic cells. Ac45RP mRNA expression is brain specific and coincides with the peak of neurogenesis and the onset of synaptogenesis. Furthermore, Ac45RP physically interacts with the V-ATPase V₀-sector and colocalizes with V₀ in unconventional, but not synaptic, secretory vesicles of extending neurites. Excess Ac45RP enhances the expression of V₀-subunits, causes a more elaborate Golgi, and increases the number of cytoplasmic vesicular structures, plasma membrane formation and outgrowth of actin-containing neurites devoid of synaptic markers. CRISPR-cas9n-mediated Ac45RP knockdown reduces neurite outgrowth. We conclude that the novel vertebrate- and brain-specific Ac45RP is a V₀-interacting constituent of unconventional vesicular structures that drives membrane expansion during neurite outgrowth and as such may furnish a tool for future neuroregenerative treatment strategies.

Activation of (pro)renin by (pro)renin receptor in extracellular vesicles from osteoclasts

The (pro)renin receptor (PRR) is a multifunctional integral membrane protein that serves as a component of the vacuolar H+-ATPase (V-ATPase) and also activates (pro)renin. We recently showed that full-length PRR, found as part of a V-ATPase sub-complex, is abundant in extracellular vesicles shed by osteoclasts. Here, we tested whether these extracellular vesicles stimulate (pro)renin. Extracellular vesicles isolated from the conditioned media of RAW 264.7 osteoclast-like cells or primary osteoclasts were characterized and counted by nanoparticle tracking. Immunoblotting confirmed that full-length PRR was present. Extracellular vesicles from osteoclasts dose-dependently stimulated (pro)renin activity, while extracellular vesicles from 4T1 cancer cells, in which we did not detect PRR, did not activate (pro)renin. To confirm that the ability of extracellular vesicles from osteoclasts to stimulate (pro)renin activity was due to the PRR, the "handle region peptide" from the PRR, a competitive inhibitor of PRR activity, was tested. It dose-dependently blocked the ability of extracellular vesicles to stimulate the enzymatic activity of (pro)renin. In summary, the PRR, an abundant component of extracellular vesicles shed by osteoclasts, stimulates (pro)renin activity. This represents a novel mechanism by which extracellular vesicles can function in intercellular regulation, with direct implications for bone biology.

Molecular basis of V-ATPase inhibition by bafilomycin A1

Pharmacological inhibition of vacuolar-type H+-ATPase (V-ATPase) by its specific inhibitor can abrogate tumor metastasis, prevent autophagy, and reduce cellular signaling responses. Bafilomycin A1, a member of macrolide antibiotics and an autophagy inhibitor, serves as a specific and potent V-ATPases inhibitor. Although there are many V-ATPase structures reported, the molecular basis of specific inhibitors on V-ATPase remains unknown. Here, we report the cryo-EM structure of bafilomycin A1 bound intact bovine V-ATPase at an overall resolution of 3.6-Å. The structure reveals six bafilomycin A1 molecules bound to the c-ring. One bafilomycin A1 molecule engages with two c subunits and disrupts the interactions between the c-ring and subunit a, thereby preventing proton translocation. Structural and sequence analyses demonstrate that the bafilomycin A1-binding residues are conserved in yeast and mammalian species and the 7'-hydroxyl group of bafilomycin A1 acts as a unique feature recognized by subunit c.

Loss of Furin in β-Cells Induces an mTORC1-ATF4 Anabolic Pathway That Leads to β-Cell Dysfunction

FURIN is a proprotein convertase (PC) responsible for proteolytic activation of a wide array of precursor proteins within the secretory pathway. It maps to the PRC1 locus, a type 2 diabetes susceptibility locus, but its specific role in pancreatic β-cells is largely unknown. The aim of this study was to determine the role of FURIN in glucose homeostasis. We show that FURIN is highly expressed in human islets, whereas PCs that potentially could provide redundancy are expressed at considerably lower levels. β-cell-specific Furin knockout (βFurKO) mice are glucose intolerant as a result of smaller islets with lower insulin content and abnormal dense-core secretory granule morphology. mRNA expression analysis and differential proteomics on βFurKO islets revealed activation of activating transcription factor 4 (ATF4), which was mediated by mammalian target of rapamycin C1 (mTORC1). βFurKO cells show impaired cleavage or shedding of vacuolar-type ATPase (V-ATPase) subunits Ac45 and prorenin receptor, respectively, and impaired lysosomal acidification. Blocking V-ATPase pharmacologically in β-cells increased mTORC1 activity, suggesting involvement of the V-ATPase proton pump in the phenotype. Taken together, these results suggest a model of mTORC1-ATF4 hyperactivation and impaired lysosomal acidification in β-cells lacking Furin, causing β-cell dysfunction.

The H+-ATPase (V-ATPase): from proton pump to signaling complex in health and disease

A primary function of the H⁺-ATPase (or V-ATPase) is to create an electrochemical proton gradient across eukaryotic cell membranes, which energizes fundamental cellular processes. Its activity allows for the acidification of intracellular vesicles and organelles, which is necessary for many essential cell biological events to occur. In addition, many specialized cell types in various organ systems such as the kidney, bone, male reproductive tract, inner ear, olfactory mucosa, and more, use plasma membrane V-ATPases to perform specific activities that depend on extracellular acidification. It is, however, increasingly apparent that V-ATPases are central players in many normal and pathophysiological processes that directly influence human health in many different and sometimes unexpected ways. These include cancer, neurodegenerative diseases, diabetes, and sensory perception, as well as energy and nutrient-sensing functions within cells. This review first covers the well-established role of the V-ATPase as a transmembrane proton pump in the plasma membrane and intracellular vesicles and outlines factors contributing to its physiological regulation in different cell types. This is followed by a discussion of the more recently emerging unconventional roles for the V-ATPase, such as its role as a protein interaction hub involved in cell signaling, and the (patho)physiological implications of these interactions. Finally, the central importance of endosomal acidification and V-ATPase activity on viral infection will be discussed in the context of the current COVID-19 pandemic.

A "Sugar-Coated" Proton Pump Comes into Focus: High-Resolution Structure of a Human V-ATPase

In this issue of Molecular Cell, Wang et al. (2020a) present near-atomic resolution cryoEM structures of a proton-pumping vacuolar ATPase from human cells, illuminating the glycosylation of integral subunits and identifying a novel and conserved glycolipid ligand.

Structures of a Complete Human V-ATPase Reveal Mechanisms of Its Assembly

Vesicular- or vacuolar-type adenosine triphosphatases (V-ATPases) are ATP-driven proton pumps comprised of a cytoplasmic V₁ complex for ATP hydrolysis and a membrane-embedded V_o complex for proton transfer. They play important roles in acidification of intracellular vesicles, organelles, and the extracellular milieu in eukaryotes. Here, we report cryoelectron microscopy structures of human V-ATPase in three rotational states at up to 2.9-Å resolution. Aided by mass spectrometry, we build all known protein subunits with associated N-linked glycans and identify glycolipids and phospholipids in the V_o complex. We define ATP6AP1 as a structural hub for V_o complex assembly because it connects to multiple V_o subunits and phospholipids in the c-ring. The glycolipids and the glycosylated V_o subunits form a luminal glycan coat critical for V-ATPase folding, localization, and stability. This study identifies mechanisms of V-ATPase assembly and biogenesis that rely on the integrated roles of ATP6AP1, glycans, and lipids.

The interaction partners of (pro)renin receptor in the distal nephron

The (pro)renin receptor (PRR), a key regulator of intrarenal renin-angiotensin system (RAS), is predominantly presented in podocytes, proximal tubules, distal convoluted tubules, and the apical membrane of collecting duct A-type intercalated cells, and plays a crucial role in hypertension, cardiovascular disease, kidney disease, and fluid homeostasis. In addition to its well-known renin-regulatory function, increasing evidence suggests PRR can also act in a variety of intracellular signaling cascades independently of RAS in the renal medulla, including Wnt/β-catenin signaling, cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂ ) signaling, and the apelinergic system, and work as a component of the vacuolar H⁺ -ATPase. PRR and these pathways regulate the expression/activity of each other that controlling blood pressure and renal functions. In this review, we highlight recent findings regarding the antagonistic interaction between PRR and ELABELA/apelin, the mutually stimulatory relationship between PRR and COX-2/PGE₂ or Wnt/β-catenin signaling in the renal medulla, and their involvement in the regulation of intrarenal RAS thereby control blood pressure, renal injury, and urine concentrating ability in health and patho-physiological conditions. We also highlight the latest progress in the involvement of PRR for the vacuolar H⁺ -ATPase activity.