Bicarbonate-regulated Adenylyl Cyclase (sAC) Is a Sensor That Regulates pH-dependent V-ATPase Recycling

Cornell University, Итак, New York, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 01/2004; 278(49):49523-9. DOI: 10.1074/jbc.M309543200
Source: PubMed


Modulation of environmental pH is critical for the function of many biological systems. However, the molecular identity of the pH sensor and its interaction with downstream effector proteins remain poorly understood. Using the male reproductive tract as a model system in which luminal acidification is critical for sperm maturation and storage, we now report a novel pathway for pH regulation linking the bicarbonate activated soluble adenylyl cyclase (sAC) to the vacuolar H+ATPase (V-ATPase). Clear cells of the epididymis and vas deferens contain abundant V-ATPase in their apical pole and are responsible for acidifying the lumen. Proton secretion is regulated via active recycling of V-ATPase. Here we demonstrate that this recycling is regulated by luminal pH and bicarbonate. sAC is highly expressed in clear cells, and apical membrane accumulation of V-ATPase is triggered by a sAC-dependent rise in cAMP in response to alkaline luminal pH. As sAC is expressed in other acid/base transporting epithelia, including kidney and choroid plexus, this cAMP-dependent signal transduction pathway may be a widespread mechanism that allows cells to sense and modulate extracellular pH.

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    • "Also, the initial studies on sAC were impaired by the lack of pharmacological inhibitors specific for sAC. However, KH7 and derivatives of catechol estrogen are now proving to be effective against sACs from cyanobacteria (Steegborn et al., 2005a), coral (Barott et al., 2013), sea urchin (Beltrán et al., 2007), shark (Tresguerres et al., 2010c) and mammals (Hess et al., 2005; Pastor-Soler et al., 2003). "
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    ABSTRACT: Soluble adenylyl cyclase (sAC) is a recently recognized source of the signaling molecule cyclic AMP (cAMP) that is genetically and biochemically distinct from the classic G-protein-regulated transmembrane adenylyl cyclases (tmACs). Mammalian sAC is distributed throughout the cytoplasm and it may be present in the nucleus and inside mitochondria. sAC activity is directly stimulated by HCO3(-), and sAC has been confirmed to be a HCO3(-) sensor in a variety of mammalian cell types. In addition, sAC can functionally associate with carbonic anhydrases to act as a de facto sensor of pH and CO2. The two catalytic domains of sAC are related to HCO3(-)-regulated adenylyl cyclases from cyanobacteria, suggesting the cAMP pathway is an evolutionarily conserved mechanism for sensing CO2 levels and/or acid/base conditions. Reports of sAC in aquatic animals are still limited but are rapidly accumulating. In shark gills, sAC senses blood alkalosis and triggers compensatory H(+) absorption. In the intestine of bony fishes, sAC modulates NaCl and water absorption. And in sea urchin sperm, sAC may participate in the initiation of flagellar movement and in the acrosome reaction. Bioinformatics and RT-PCR results reveal that sAC orthologs are present in most animal phyla. This review summarizes the current knowledge on the physiological roles of sAC in aquatic animals and suggests additional functions in which sAC may be involved.
    Journal of Experimental Biology 03/2014; 217(Pt 5):663-72. DOI:10.1242/jeb.086157 · 2.90 Impact Factor
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    • "In such cases, different isoforms need to be trafficked to the endosomes or their activity modulated in order to establish and maintain the proper pH. sAC has already been shown to modulate the pH-dependent translocation of the V-ATPase to plasma membranes (Pastor-Soler et al., 2003; Tresguerres et al., 2010b); might sAC-generated cAMP play a role in trafficking V-ATPases or other chloride channels to endosomal/lysosomal membranes and hence establishing intra-vesicular pH? "
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    ABSTRACT: Soluble adenylyl cyclase (sAC) is a source of the second messenger cyclic adenosine 3', 5' monophosphate (cAMP). sAC is directly regulated by bicarbonate (HCO(-) 3) ions. In living cells, HCO(-) 3 ions are in nearly instantaneous equilibrium with carbon dioxide (CO2) and pH due to the ubiquitous presence of carbonic anhydrases. Numerous biological processes are regulated by CO2, HCO(-) 3, and/or pH, and in a number of these, sAC has been shown to function as a physiological CO2/HCO3/pH sensor. In this review, we detail the known pH sensing functions of sAC, and we discuss two highly-studied, pH-dependent pathways in which sAC might play a role.
    Frontiers in Physiology 11/2013; 4:343. DOI:10.3389/fphys.2013.00343 · 3.53 Impact Factor
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    • "In clear cells an alkaline pH in the epididymal lumen is sensed by a bicarbonate-sensitive adenylate cyclase, which increases the cellular level of cAMP. This increase activates PKA, finally leading to the fusion of V-ATPase-containing vesicles with the apical membrane (Pastor-Soler et al., 2003). Little is known about the activity and regulation of the V-ATPase in Malpighian tubules. "
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    ABSTRACT: Transepithelial ion transport in insect Malpighian tubules is energized by an apical V-ATPase. In hematophagous insects, a blood meal during which the animal ingests huge amounts of salt and water stimulates transepithelial transport processes linked to V-ATPase activation, but how this is accomplished is still unclear. Here we report that membrane-permeant derivatives of cAMP increase the bafilomycin-sensitive ATPase activity in Malpighian tubules of Aedes aegypti twofold and activate ATP-dependent transport processes. In parallel, membraneassociation of the V1 subunits C and D increases, consistent with the assembly of the holoenzyme. The protein kinase A inhibitor H-89 abolishes all cAMP-induced effects, consistent with PKA being involved in V-ATPase activation. Metabolic inhibition induced by KCN, azide and 2,4-dinitrophenol, respectively, also induces assembly of functional V-ATPases at the membrane without protein kinase A involvement, indicating a phosphorylation independent activation mechanism.
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