MST3 is involved in ENaC-mediated hypertension

Abstract

Liddle syndrome is an inherited form of human hypertension caused by increasing epithelial Na+ channel (ENaC) expression. Increased Na+ retention through ENaC with subsequent volume expansion causes hypertension. In addition to ENaC, the Na+-K+-Cl− cotransporter (NKCC) and Na+-Cl− symporter (NCC) are responsible for Na+ reabsorption in the kidneys. Several Na+ transporters are evolutionarily regulated by the Ste20 kinase family. Ste20-related proline/alanine-rich kinase and oxidative stress-responsive kinase-1 phosphorylate downstream NKCC2 and NCC to maintain Na+ and blood pressure (BP) homeostasis. Mammalian Ste20 kinase 3 (MST3) is another member of the Ste20 family. We previously reported that reduced MST3 levels were found in the kidneys in spontaneously hypertensive rats and that MST3 was involved in Na+ regulation. To determine whether MST3 is involved in BP stability through Na+ regulation, we generated a MST3 hypomorphic mutation and designated MST3+/− and MST3−/− mice to examine BP and serum Na+ and K+ concentrations. MST3−/− mice exhibited hypernatremia, hypokalemia, and hypertension. The increased ENaC in the kidney played roles in hypernatremia. The reabsorption of more Na+ promoted more K+ secretion in the kidney and caused hypokalemia. The hypernatremia and hypokalemia in MST3−/− mice were significantly reversed by the ENaC inhibitor amiloride, indicating that MST3−/− mice reabsorbed more Na+ through ENaC. Furthermore, Madin-Darby canine kidney cells stably expressing kinase-dead MST3 displayed elevated ENaC currents. Both the in vivo and in vitro results indicated that MST3 maintained Na+ homeostasis through ENaC regulation. We are the first to report that MST3 maintains BP stability through ENaC regulation.

Epithelial polarization in the 3D matrix requires MST3 signaling to regulate ZO-1 position

“…Coordination of fluid accumulation, membrane delivery, cell proliferation and apoptosis is required for epithelial polarization and cyst and tubule formation. Among the diverse roles of MST3, we have defined its roles in the regulation of renal ion channels to maintain stable blood pressure [ 18 , 19 , 28 ], cell apoptosis [ 16 ] and cell migration [ 17 ]. These functions of MST3 are all involved in cell polarity and cyst formation.…”

“…In the kidney, our study showed that MST3 localized at the subapical site and cytosol of the renal tubules [ 18 , 19 ]. Although the MST3 knockdown mice exhibited normal renal tubule morphology, more ENaC was present at apical sites than in WT mice, indicating that MST3 inhibited ENaC expression at apical sites in the kidney [ 18 ]. Here, we found that overexpressed MST3 localized close to the basal membrane instead of the subapical membrane of cysts.…”

“…Membranes were incubated with primary antibodies and secondary antibodies ( Table 1 ). The MST3 antibody against MST3, a kind gift from Dr. Ming-Derg Lai, was validated in our previous publications [ 17 , 18 ]. Bands were detected by Western Lightning Plus (Perkin Elmer) using LAS2000.…”

“…In contrast, suppression of MST3 by siRNA enhanced cellular migration in MCF7 cells with reduced expression of E-cad at the edge of migrating cells [ 17 ]. In an in vivo study, MST3 knockout mice exhibited higher ENaC apical expression in renal tubules [ 18 ]. We also found that spontaneous hypertensive mice with higher ENaC expression had lower MST3 expression than control mice [ 19 ].…”

Lessons learned about epithelial sodium channels from transgenic mouse models

“…Mammalian Ste20-like protein kinase 3 (MST3/STK24) is mainly expressed in the thick ascending tubule, and at lower levels in the distal convoluted tubules. Hypomorphic mice for this protein kinase exhibited higher ENaC activity causing hypernatremia and hypertension [49]. In response to K þ loading, these maintained Na þ /K þ homeostasis by regulation of WNK4 expression thereby enhancing Na þ retention through increased NKCC2 and ENaC activity [50].…”