The Na+, K+-ATPase β1 subunit regulates epithelial tight junctions via MRCKα.

Haiqing Bai,Rosemary Norman,Xin Lin,Jennifer L Young,David A Dean,Alan E Friedman,Rui Zhou,Michael Barravecchia,Deborah Yu

doi:10.1172/jci.insight.134881

Abstract

An intact lung epithelial barrier is essential for lung homeostasis. The Na+, K+-ATPase (NKA), primarily serving as an ion transporter, also regulates epithelial barrier function via modulation of tight junctions. However, the underlying mechanism is not well understood. Here, we show that overexpression of the NKA β1 subunit upregulates the expression of tight junction proteins, leading to increased alveolar epithelial barrier function by an ion transport–independent mechanism. Using IP and mass spectrometry, we identified a number of unknown protein interactions of the β1 subunit, including a top candidate, myotonic dystrophy kinase–related cdc42-binding kinase α (MRCKα), which is a protein kinase known to regulate peripheral actin formation. Using a doxycycline-inducible gene expression system, we demonstrated that MRCKα and its downstream activation of myosin light chain is required for the regulation of alveolar barrier function by the NKA β1 subunit. Importantly, MRCKα is expressed in both human airways and alveoli and has reduced expression in patients with acute respiratory distress syndrome (ARDS), a lung illness that can be caused by multiple direct and indirect insults, including the infection of influenza virus and SARS-CoV-2. Our results have elucidated a potentially novel mechanism by which NKA regulates epithelial tight junctions and have identified potential drug targets for treating ARDS and other pulmonary diseases that are caused by barrier dysfunction.

Highlights

An intact alveolar epithelial barrier is essential for normal gas exchange and alveolar liquid reabsorption
Given that tight junctions components are localized to the apical membrane of cells in a mature epithelial layer, we aimed to investigate if the β1 subunit increases tight junctions at cell membranes and enhances alveolar barrier function
We have found that the small, non–catalytic β1 subunit promotes alveolar epithelial barrier integrity through a transport-independent mechanism that involves protein interaction and activation of myotonic dystrophy kinase–related cdc42-binding kinase α (MRCKα) (Figure 6D)

Summary

Introduction

An intact alveolar epithelial barrier is essential for normal gas exchange and alveolar liquid reabsorption. The whole pump is composed of a catalytic α subunit and a noncatalytic β subunit, which facilitates maturation and membrane targeting of the α subunit Both subunits have decreased expression and/or activity in lung illnesses resulting from respiratory viral infection or lung edema [3,4,5,6]. Overexpression of these subunits in ARDS animal models accelerated alveolar fluid clearance, reduced lung edema, and improved disease outcome [7,8,9,10,11,12,13]. Whether the effect is due to pump activity or other signaling pathways remains elusive

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