Ras activates the epithelial Na(+) channel through phosphoinositide 3-OH kinase signaling.
Aldosterone induces expression and activation of the GTP-dependent signaling switch K-Ras. This small monomeric G protein is both necessary and sufficient for activation of the epithelial Na(+) channel (ENaC). The mechanism by which K-Ras enhances ENaC activity, however, is uncertain. We demonstrate here that K-Ras activates human ENaC reconstituted in Chinese hamster ovary cells in a GTP-dependent manner. K-Ras influences ENaC activity most likely by affecting open probability. Inhibition of phosphoinositide 3-OH kinase (PI3K) abolished K-Ras actions on ENaC. In contrast, inhibition of other K-Ras effector cascades, including the MAPK and Ral/Rac/Rho cascades, did not affect K-Ras actions on ENaC. Activation of ENaC by K-Ras, moreover, was sensitive to co-expression of dominant negative p85(PI3K). The G12:C40 effector-specific double mutant of Ras, which preferentially activates PI3K, enhanced ENaC activity in a manner sensitive to inhibition of PI3K. Other effector-specific mutants preferentially activating MAPK and RalGDS signaling had no effect. Constitutively active PI3K activated ENaC independent of K-Ras with the effects of PI3K and K-Ras on ENaC not being additive. We conclude that K-Ras activates ENaC via the PI3K cascade.
Staruschenko
Alexander
A
University of Texas Health Science Center at San Antonio, Department of Physiology, San Antonio, Texas 78229-3900, USA.
Patel
Pravina
P
Tong
Qiusheng
Q
Medina
Jorge L
JL
Stockand
James D
JD
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D053503:Epithelial Sodium Channels; D006160:Guanosine Triphosphate / Q000378:metabolism; D008856:Microscopy, Fluorescence; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D015398:Signal Transduction; D015222:Sodium Channels / Q000378:metabolism*
D053503:Epithelial Sodium Channels; D015222:Sodium Channels; D006160:Guanosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D016283:Proto-Oncogene Proteins p21(ras)