Uroguanylin modulates (Na++K+)ATPase in a proximal tubule cell line: Interactions among the cGMP/protein kinase G, cAMP/protein kinase A, and mTOR pathways.
BACKGROUND
The natriuretic effect of uroguanylin (UGN) involves reduction of proximal tubule (PT) sodium reabsorption. However, the target sodium transporters as well as the molecular mechanisms involved in these processes remain poorly understood.


METHODS
To address the effects of UGN on PT (Na(+)+K(+))ATPase and the signal transduction pathways involved in this effect, we used LLC-PK1 cells. The effects of UGN were determined through ouabain-sensitive ATP hydrolysis and immunoblotting assays during different experimental conditions.


RESULTS
We observed that UGN triggers cGMP/PKG and cAMP/PKA pathways in a sequential way. The activation of PKA leads to the inhibition of mTORC2 activity, PKB phosphorylation at S473, PKB activity and, consequently, a decrease in the mTORC1/S6K pathway. The final effects are decreased expression of the α1 subunit of (Na(+)+K(+))ATPase and inhibition of enzyme activity.


CONCLUSIONS
These results suggest that the molecular mechanism of action of UGN on sodium reabsorption in PT cells is more complex than previously thought. We propose that PKG-dependent activation of PKA leads to the inhibition of the mTORC2/PKB/mTORC1/S6K pathway, an important signaling pathway involved in the maintenance of the PT sodium pump expression and activity.


CONCLUSIONS
The current results expand our understanding of the signal transduction pathways involved in the overall effect of UGN on renal sodium excretion.
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Avenida Carlos Chagas Filho, 373, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21941-902, Brazil; Instituto Superior de Ciências Biomédicas, Universidade Estadual do Ceará, Avenida Dr. Silas Munguba, 1700, Campus do Itaperi, Fortaleza, Ceará 60714-903, Brazil.
Francisco J
FJ
Arnaud-Batista
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Avenida Carlos Chagas Filho, 373, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21941-902, Brazil.
Diogo B
DB
Peruchetti
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Avenida Carlos Chagas Filho, 373, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21941-902, Brazil.
Thiago P
TP
Abreu
Instituto Superior de Ciências Biomédicas, Universidade Estadual do Ceará, Avenida Dr. Silas Munguba, 1700, Campus do Itaperi, Fortaleza, Ceará 60714-903, Brazil.
Nilberto R F
NR
do Nascimento
Instituto de Ciências Biomédicas, Universidade de São Paulo, Avenida Prof. Lineu Prestes, 1524, Cidade Universitária "Armando Salles Oliveira", São Paulo, São Paulo 05508-900, Brazil.
Gerhard
G
Malnic
Instituto Superior de Ciências Biomédicas, Universidade Estadual do Ceará, Avenida Dr. Silas Munguba, 1700, Campus do Itaperi, Fortaleza, Ceará 60714-903, Brazil.
Manasses C
MC
Fonteles
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Avenida Carlos Chagas Filho, 373, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21941-902, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia e Bioimagem, Avenida Carlos Chagas Filho, 373, Cidade Universitária, Rio de Janeiro, Rio de Janeiro 21941-902, Brazil. Electronic address: caruso@biof.ufrj.br.
Celso
C
Caruso-Neves
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006868:Hydrolysis; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000201:enzymology; D018374:LLC-PK1 Cells; D009318:Natriuresis / Q000187:drug effects; D045283:Natriuretic Agents / Q000494:pharmacology*; D045265:Natriuretic Peptides / Q000494:pharmacology*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D065667:Renal Elimination / Q000187:drug effects; D065608:Renal Reabsorption / Q000187:drug effects; D015290:Second Messenger Systems / Q000187:drug effects*; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D045283:Natriuretic Agents; D045265:Natriuretic Peptides; D047428:Protein Kinase Inhibitors; C084362:uroguanylin; D000255:Adenosine Triphosphate; D012964:Sodium; D000242:Cyclic AMP; D058570:TOR Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D000254:Sodium-Potassium-Exchanging ATPase; D006152:Cyclic GMP
Cell signaling; Kidney; Proximal tubule; Sodium pump; Sodium reabsorption; Uroguanylin