Inhibition of prostasin-induced ENaC activities by PN-1 and regulation of PN-1 expression by TGF-beta1 and aldosterone.
Prostasin has been shown to regulate sodium handling in the kidney. Recently, a serine protease inhibitor, protease nexin-1 (PN-1), was identified as an endogenous inhibitor for prostasin. Therefore, we hypothesized that PN-1 may regulate sodium reabsorption by reducing prostasin activity, and that expression of PN-1 was regulated by transforming growth factor-beta1 (TGF-beta1) or aldosterone, like prostasin. cRNAs for epithelial sodium channel (ENaC), prostasin, and PN-1 were expressed in Xenopus oocytes, and the amiloride-sensitive sodium currents (I(Na)) were measured. The effect of TGF-beta1 and aldosterone on the mRNA and protein abundance of PN-1 and ENaC was detected by real-time polymerase chain reaction and immunoblotting in M-1 cells. Expression of PN-1 substantially decreased prostasin-induced I(Na) by approximately 68% in oocytes. Treatment of M-1 cells with 20 ng/ml TGF-beta1 significantly increased protein expression of PN-1 by 3.8+/-0.5-fold, whereas administration of 10(-6) M aldosterone markedly decreased protein expression of PN-1 to 53.7+/-6.7%. Basolateral, but not apical, application of TGF-beta1 significantly reduced I(eq). To elucidate the involvement of PN-1 in basal ENaC activity, we silenced the expression of PN-1 by using short-interfering RNA. This increased I(eq) by 1.6+/-0.1-fold. Our study indicates that PN-1 could have a natriuretic role by inhibiting prostasin activity and suggests the possibility that aldosterone and TGF-beta reciprocally regulate the expression of PN-1 in renal epithelial cells contributing to salt retention or natriuresis, respectively by an additional mechanism. PN-1 could represent a new factor that contributes to regulation of ENaC activity in the kidney.
Wakida
N
N
Department of Nephrology, Kumamoto University Graduate School of Medical Sciences, Kumamoto, Japan.
Kitamura
K
K
Tuyen
D G
DG
Maekawa
A
A
Miyoshi
T
T
Adachi
M
M
Shiraishi
N
N
Ko
T
T
Ha
V
V
Nonoguchi
H
H
Tomita
K
K
D000450:Aldosterone / Q000502:physiology*; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D004594:Electrophysiology; D053503:Epithelial Sodium Channels; D005260:Female; D005786:Gene Expression Regulation; D020868:Gene Silencing; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism; D051379:Mice; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D058255:Protease Nexins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000502:physiology*; D053773:Transforming Growth Factor beta1; D014981:Xenopus; D000099271:Prostasin
D000450:Aldosterone; D016564:Amyloid beta-Protein Precursor; D053503:Epithelial Sodium Channels; D058255:Protease Nexins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D012697:Serine Endopeptidases; D012964:Sodium; D015222:Sodium Channels; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D000099271:Prostasin; C508961:Tgfb1 protein, mouse