Contribution of R domain phosphoserines to the function of CFTR studied in Fischer rat thyroid epithelia

2000 ◽  
Vol 279 (5) ◽  
pp. L835-L841 ◽  
Author(s):  
Olafur Baldursson ◽  
Herbert A. Berger ◽  
Michael J. Welsh
Keyword(s):  
Functional Role ◽  
Transmembrane Conductance Regulator ◽  
Regulatory Domain ◽  
Wild Type ◽  
Transmembrane Conductance ◽  
Dependent Protein ◽  
Rat Thyroid ◽  
Cystic Fibrosis Transmembrane

The regulatory domain of cystic fibrosis transmembrane conductance regulator (CFTR) regulates channel activity when several serines are phosphorylated by cAMP-dependent protein kinase. To further define the functional role of individual phosphoserines, we studied CFTR containing previously studied and new serine to alanine mutations. We expressed these constructs in Fischer rat thyroid epithelia and measured transepithelial Cl− current. Mutation of four in vivo phosphorylation sites, Ser660, Ser737, Ser795, and Ser813 (S-Quad-A), substantially decreased cAMP-stimulated current, suggesting that these four sites account for most of the phosphorylation-dependent response. Mutation of either Ser660 or Ser813 alone significantly decreased current, indicating that these residues play a key role in phosphorylation-dependent stimulation. However, neither Ser660 nor Ser813 alone increased current to wild-type levels; both residues were required. Changing Ser737 to alanine increased current above wild-type levels, suggesting that phosphorylation of Ser737 may inhibit current in wild-type CFTR. These data help define the functional role of regulatory domain phosphoserines and suggest interactions between individual phosphoserines.

CFTR chloride channel activation by genistein: the role of serine/threonine protein phosphatases

1996 ◽  
Vol 271 (2) ◽  
pp. C650-C657 ◽  
Author(s):  
W. W. Reenstra ◽  
K. Yurko-Mauro ◽  
A. Dam ◽  
S. Raman ◽  
S. Shorten
Keyword(s):  
Chloride Channel ◽  
Kinase Inhibitor ◽  
Maximal Activity ◽  
Calyculin A ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Nih 3T3 ◽  
Cystic Fibrosis Transmembrane

We have previously shown [B. Illek, H. Fischer, G. F. Santos, J. H. Widdicombe, T. E. Machen, and W. W. Reenstra, Am. J. Physiol. 268 (Cell Physiol. 37): C886-C893, 1995] that genistein, a tyrosine kinase inhibitor, activates the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel in NIH/3T3 cells that have been stably transfected with an expression vector for the CFTR (NIH-CFTR cells). In this study, we present evidence suggesting that both genistein and the serine/threonine protein phosphatase (PPase) inhibitor calyculin A activate the CFTR by inhibiting PPase activity. As measured by 125I efflux, genistein and calyculin A stimulate the CFTR to approximately 50% of the maximal activity with forskolin. Neither agonist increases CFTR activity at saturating forskolin concentrations, but genistein and calyculin A have an additive effect on CFTR activity. Forskolin, but neither genistein nor calyculin A, stimulates protein kinase A(PKA) activity. The PKA inhibitor H-89 inhibits CFTR activation and in vivo phosphorylation by all three agonists. Proteolytic digestion of in vivo phosphorylated CFTR suggests that the CFTR is phosphorylated on the same sites during stimulation with genistein and forskolin but on different sites stimulation with calyculin A. The data suggest that genistein and calyculin A inhibit different PPase activities, allowing CFTR phosphorylation and partial stimulation, by a basal PKA activity.

scholarly journals Defective function of the cystic fibrosis-causing missense mutation G551D is recovered by genistein

1999 ◽  
Vol 277 (4) ◽  
pp. C833-C839 ◽  
Author(s):  
Beate Illek ◽  
Lei Zhang ◽  
Nancy C. Lewis ◽  
Richard B. Moss ◽  
Jian-Yun Dong ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Transmembrane Conductance Regulator ◽  
Wild Type ◽  
Adrenergic Stimulation ◽  
Transmembrane Conductance ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Nasal Potential Difference ◽  
Cystic Fibrosis Transmembrane

The patch-clamp technique was used to investigate the effects of the isoflavone genistein on disease-causing mutations (G551D and ΔF508) of the cystic fibrosis transmembrane conductance regulator (CFTR). In HeLa cells recombinantly expressing the trafficking-competent G551D-CFTR, the forskolin-stimulated Cl currents were small, and average open probability of G551D-CFTR was P o = 0.047 ± 0.019. Addition of genistein activated Cl currents ∼10-fold, and the P o of G551D-CFTR increased to 0.49 ± 0.12, which is a P o similar to wild-type CFTR. In cystic fibrosis (CF) epithelial cells homozygous for the trafficking-impaired ΔF508 mutation, forskolin and genistein activated Cl currents only after 4-phenylbutyrate treatment. These data suggested that genistein activated CFTR mutants that were present in the cell membrane. Therefore, we tested the effects of genistein in CF patients with the G551D mutation in nasal potential difference (PD) measurements in vivo. The perfusion of the nasal mucosa of G551D CF patients with isoproterenol had no effect; however, genistein stimulated Cl-dependent nasal PD by, on average, −2.4 ± 0.6 mV, which corresponds to 16.9% of the responses (to β-adrenergic stimulation) found in healthy subjects.

Genistein activates CFTR Cl- channels via a tyrosine kinase- and protein phosphatase-independent mechanism

1997 ◽  
Vol 273 (2) ◽  
pp. C747-C753 ◽  
Author(s):  
P. J. French ◽  
J. Bijman ◽  
A. G. Bot ◽  
W. E. Boomaars ◽  
B. J. Scholte ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Tyrosine Kinases ◽  
Kinase Inhibitor ◽  
Direct Interaction ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Cl Channels ◽  
Dependent Protein ◽  
Cystic Fibrosis Transmembrane

Previous studies have revealed an adenosine 3',5'-cyclic monophosphate (cAMP)-independent activation of cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels by the tyrosine kinase inhibitor genistein. To further explore its mechanism of action, we have reconstituted genistein activation of CFTR in excised inside-out membrane patches. In the presence or absence of ATP, genistein appeared unable to open silent CFTR Cl- channels. However, on CFTR prephosphorylation by cAMP-dependent protein kinase (cAK), genistein enhanced CFTR activity by twofold, resulting from a prolonged burst duration. Genistein could also hyperactivate partially phosphorylated CFTR in the absence of cAK and therefore is different from 5'-adenylylimidodiphosphate, which required fully phosphorylated CFTR. Phosphatase-resistant thiophosphorylation likewise primed the CFTR Cl- channel for hyperactivation by genistein in the absence of cAK. Replacement of ATP by GTP as a hydrolyzable nucleotide triphosphate for CFTR did not impair the ability of genistein to activate thiophosphorylated CFTR, despite the fact that GTP is a poor substrate for tyrosine kinases. These findings argue against a role of protein phosphatases or tyrosine kinases but suggest a more direct interaction of genistein with CFTR, possibly at the level of the second nucleotide-binding domain.

In vivo activation of CFTR-dependent chloride transport in murine airway epithelium by CNP

1997 ◽  
Vol 273 (5) ◽  
pp. L1065-L1072 ◽  
Author(s):  
Thomas J. Kelley ◽  
Calvin U. Cotton ◽  
Mitchell L. Drumm
Keyword(s):  
Cystic Fibrosis ◽  
Chloride Transport ◽  
Nasal Epithelium ◽  
Transmembrane Conductance Regulator ◽  
Wild Type ◽  
Transmembrane Conductance ◽  
Cyclic Monophosphate ◽  
Δf508 Cftr ◽  
Membrane Bound

Inhibitors of guanosine 3′,5′-cyclic monophosphate (cGMP)-inhibited phosphodiesterases stimulate Cl− transport across the nasal epithelia of cystic fibrosis mice carrying the ΔF508 mutation [cystic fibrosis transmembrane conductance regulator (CFTR) (ΔF/ΔF)], suggesting a role for cGMP in regulation of epithelial ion transport. Here we show that activation of membrane-bound guanylate cyclases by C-type natriuretic peptide (CNP) stimulates hyperpolarization of nasal epithelium in both wild-type and ΔF508 CFTR mice in vivo but not in nasal epithelium of mice lacking CFTR [CFTR(−/−)]. With the use of a nasal transepithelial potential difference (TEPD) assay, CNP was found to hyperpolarize lumen negative TEPD by 6.1 ± 0.6 mV in mice carrying wild-type CFTR. This value is consistent with that obtained with 8-bromoguanosine 3′,5′-cyclic monophosphate (6.2 ± 0.9 mV). A combination of the adenylate cyclase agonist forskolin and CNP demonstrated a synergistic ability to induce Cl− secretion across the nasal epithelium of CFTR(ΔF/ΔF) mice. No effect on TEPD was seen with this combination when used on CFTR(−/−) mice, implying that the CNP-induced change in TEPD in CFTR(ΔF/ΔF) mice is CFTR dependent.

Examining basal chloride transport using the nasal potential difference response in a murine model

2001 ◽  
Vol 281 (5) ◽  
pp. L1173-L1179 ◽  
Author(s):  
Kristine G. Brady ◽  
Thomas J. Kelley ◽  
Mitchell L. Drumm
Keyword(s):  
Cystic Fibrosis ◽  
Chloride Transport ◽  
Inbred Mice ◽  
Inbred Strains ◽  
Potential Difference ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Inbred Strains Of Mice ◽  
Cystic Fibrosis Transmembrane

Epithelia of humans and mice with cystic fibrosis are unable to secrete chloride in response to a chloride gradient or to cAMP-elevating agents. Bioelectrical properties measured using the nasal transepithelial potential difference (TEPD) assay are believed to reflect these cystic fibrosis transmembrane conductance regulator (CFTR)-dependent chloride transport defects. Although the response to forskolin is CFTR mediated, the mechanisms responsible for the response to a chloride gradient are unknown. TEPD measurements performed on inbred mice were used to compare the responses to low chloride and forskolin in vivo. Both responses show little correlation between or within inbred strains of mice, suggesting they are mediated through partially distinct mechanisms. In addition, these responses were assayed in the presence of several chloride channel inhibitors, including DIDS, diphenylamine-2-carboxylate, glibenclamide, and 5-nitro-2-(3-phenylpropylamino)-benzoic acid, and a protein kinase A inhibitor, the Rp diastereomer of adenosine 3′,5′-cyclic monophosphothioate ( Rp-cAMPS). The responses to low chloride and forskolin demonstrate significantly different pharmacological profiles to both DIDS and Rp-cAMPS, indicating that channels in addition to CFTR contribute to the low chloride response.

Actin filament organization is required for proper cAMP-dependent activation of CFTR

1999 ◽  
Vol 277 (6) ◽  
pp. C1160-C1169 ◽  
Author(s):  
Adriana G. Prat ◽  
C. Casey Cunningham ◽  
G. Robert Jackson ◽  
Steven C. Borkan ◽  
Yihan Wang ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Single Channel ◽  
Fold Increase ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Whole Cell ◽  
Excised Patches ◽  
Cystic Fibrosis Transmembrane ◽  
Molecular Nature

Previous studies have indicated a role of the actin cytoskeleton in the regulation of the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel. However, the exact molecular nature of this regulation is still largely unknown. In this report human epithelial CFTR was expressed in human melanoma cells genetically devoid of the filamin homologue actin-cross-linking protein ABP-280 [ABP(−)]. cAMP stimulation of ABP(−) cells or cells genetically rescued with ABP-280 cDNA [ABP(+)] was without effect on whole cell Cl− currents. In ABP(−) cells expressing CFTR, cAMP was also without effect on Cl− conductance. In contrast, cAMP induced a 10-fold increase in the diphenylamine-2-carboxylate (DPC)-sensitive whole cell Cl− currents of ABP(+)/CFTR(+) cells. Further, in cells expressing both CFTR and a truncated form of ABP-280 unable to cross-link actin filaments, cAMP was also without effect on CFTR activation. Dialysis of ABP-280 or filamin through the patch pipette, however, resulted in a DPC-inhibitable increase in the whole cell currents of ABP(−)/CFTR(+) cells. At the single-channel level, protein kinase A plus ATP activated single Cl−channels only in excised patches from ABP(+)/CFTR(+) cells. Furthermore, filamin alone also induced Cl− channel activity in excised patches of ABP(−)/CFTR(+) cells. The present data indicate that an organized actin cytoskeleton is required for cAMP-dependent activation of CFTR.

scholarly journals Carbon monoxide-releasing molecules inhibit the cystic fibrosis transmembrane conductance regulator Cl− channel

2020 ◽  
Vol 319 (6) ◽  
pp. L997-L1009
Author(s):  
Mayuree Rodrat ◽  
Walailak Jantarajit ◽  
Demi R. S. Ng ◽  
Bartholomew S. J. Harvey ◽  
Jia Liu ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Carbon Monoxide ◽  
Current Flow ◽  
Open Channels ◽  
Transmembrane Conductance Regulator ◽  
Channel Activity ◽  
Wild Type ◽  
Transmembrane Conductance ◽  
Flow Through ◽  
Cystic Fibrosis Transmembrane

The gasotransmitter carbon monoxide (CO) regulates fluid and electrolyte movements across epithelial tissues. However, its action on anion channels is incompletely understood. Here, we investigate the direct action of CO on the cystic fibrosis transmembrane conductance regulator (CFTR) by applying CO-releasing molecules (CO-RMs) to the intracellular side of excised inside-out membrane patches from cells heterologously expressing wild-type human CFTR. Addition of increasing concentrations of tricarbonyldichlororuthenium(II) dimer (CORM-2) (1–300 μM) inhibited CFTR channel activity, whereas the control RuCl3 (100 μM) was without effect. CORM-2 predominantly inhibited CFTR by decreasing the frequency of channel openings and, hence, open probability ( Po). But, it also reduced current flow through open channels with very fast kinetics, particularly at elevated concentrations. By contrast, the chemically distinct CO-releasing molecule CORM-3 inhibited CFTR by decreasing Po without altering current flow through open channels. Neither depolarizing the membrane voltage nor raising the ATP concentration on the intracellular side of the membrane affected CFTR inhibition by CORM-2. Interestingly, CFTR inhibition by CORM-2, but not by CFTRinh-172, was prevented by prior enhancement of channel activity by the clinically approved CFTR potentiator ivacaftor. Similarly, when added after CORM-2, ivacaftor completely relieved CFTR inhibition. In conclusion, CORM-2 has complex effects on wild-type human CFTR consistent with allosteric inhibition and open-channel blockade. Inhibition of CFTR by CO-releasing molecules suggests that CO regulates CFTR activity and that the gasotransmitter has tissue-specific effects on epithelial ion transport. The action of ivacaftor on CFTR Cl− channels inhibited by CO potentially expands the drug’s clinical utility.

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