alpha-Adducin mutations increase Na/K pump activity in renal cells by affecting constitutive endocytosis: implications for tubular Na reabsorption.
Genetic variation in alpha-adducin cytoskeletal protein is implicated in the polymerization and bundling of actin and alteration of the Na/K pump, resulting in abnormal renal sodium transport and hypertension in Milan hypertensive rats and humans. To investigate the molecular involvement of alpha-adducin in controlling Na/K pump activity, wild-type or mutated rat and human alpha-adducin forms were, respectively, transfected into several renal cell lines. Through multiple experimental approaches (microscopy, enzymatic assays, coimmunoprecipitation), we showed that rat and human mutated forms increased Na/K pump activity and the number of pump units; moreover, both variants coimmunoprecipitate with Na/K pump. The increased Na/K pump activity was not due to changes in its basolateral localization, but to an alteration of Na/K pump residential time on the plasma membrane. Indeed, both rat and human mutated variants reduced constitutive Na/K pump endocytosis and similarly affected transferrin receptor trafficking and fluid-phase endocytosis. In fact, alpha-adducin was detected in clathrin-coated vesicles and coimmunoprecipitated with clathrin. These results indicate that adducin, besides its modulatory effects on actin cytoskeleton dynamics, might play a direct role in clathrin-dependent endocytosis. The constitutive reduction of the Na/K pump endocytic rate induced by mutated adducin variants may be relevant in Na-dependent hypertension.
Prassis sigma tau Research Institute, Milan, Italy. lucia.torielli@prassis.it
Lucia
L
Torielli
Simona
S
Tivodar
Rosa Chiara
RC
Montella
Roberto
R
Iacone
Gloria
G
Padoani
Paolo
P
Tarsini
Ornella
O
Russo
Daniela
D
Sarnataro
Pasquale
P
Strazzullo
Patrizia
P
Ferrari
Giuseppe
G
Bianchi
Chiara
C
Zurzolo
D000042:Absorption / Q000502:physiology; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D004285:Dogs; D004705:Endocytosis / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D009154:Mutation / Q000235:genetics*; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014162:Transfection; D000099291:Adducins
D002148:Calmodulin-Binding Proteins; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D000099291:Adducins