Regulation of Na(+) reabsorption by the aldosterone-induced small G protein K-Ras2A.
Xenopus laevis A6 cells were used as model epithelia to test the hypothesis that K-Ras2A is an aldosterone-induced protein necessary for steroid-regulated Na(+) transport. The possibility that increased K-Ras2A alone is sufficient to mimic aldosterone action on Na(+) transport also was tested. Aldosterone treatment increased K-Ras2A protein expression 2.8-fold within 4 h. Active Ras is membrane associated. After aldosterone treatment, 75% of K-Ras was localized to the plasma membrane compared with 25% in the absence of steroid. Aldosterone also increased the amount of active (phosphorylated) mitogen-activated protein kinase kinase likely through K-Ras2A signaling. Steroid-induced K-Ras2A protein levels and Na(+) transport were decreased with antisense K-ras2A oligonucleotides, showing that K-Ras2A is necessary for the natriferic actions of aldosterone. Aldosterone-induced Na(+) channel activity, was decreased from 0.40 to 0.09 by pretreatment with antisense ras oligonucleotide, implicating the luminal Na(+) channel as one final effector of Ras signaling. Overexpression of K-Ras2A increased Na(+) transport approximately 2.2-fold in the absence of aldosterone. These results suggest that aldosterone signals to the luminal Na(+) channel via multiple pathways and that K-Ras2A levels are limiting for a portion of the aldosterone-sensitive Na(+) transport.
Stockand
J D
JD
Center for Cell and Molecular Signaling, Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA. jstocka2emory.edu
Spier
B J
BJ
Worrell
R T
RT
Yue
G
G
Al-Baldawi
N
N
Eaton
D C
DC
D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004847:Epithelial Cells / Q000502:physiology; D053503:Epithelial Sodium Channels; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D007700:Kinetics; D008954:Models, Biological; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology*; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism; D014982:Xenopus laevis
D053503:Epithelial Sodium Channels; D020319:Oligodeoxyribonucleotides, Antisense; D015222:Sodium Channels; D000450:Aldosterone; D012964:Sodium; D019204:GTP-Binding Proteins