RAB26-dependent autophagy protects adherens junctional integrity in acute lung injury
Creators: name: Dong, Weijie
name: He, Binfeng
name: Qian, Hang
name: Liu, Qian
name: Wang, Dong
name: Li, Jin
name: Wei, Zhenghua
name: Wang, Zi
name: Xu, Zhi
name: Wu, Guangyu
name: Qian, Guisheng
name: Wang, Guansong
Publisher: name: Taylor & Francis
Year: 2018
Subjects: subject: Biochemistry
subject: Medicine
subject: Microbiology
subject: FOS: Biological sciences
subject: Cell Biology
subject: Physiology
subject: Immunology
subject: FOS: Clinical medicine
subject: Plant Biology
subject: Virology

description: Microvascular barrier dysfunction is the central pathophysiological feature of acute lung injury (ALI). RAB26 is a newly identified small GTPase involved in the regulation of endothelial cell (EC) permeability. However, the mechanism behind this protection has not been clearly elucidated. Here we found that RAB26 promoted the integrity of adherens junctions (AJs) in a macroautophagy/autophagy-dependent manner in ALI. RAB26 is frequently downregulated in mouse lungs after LPS treatment. Mice lacking <i>Rab26</i> exhibited phosphorylated SRC expression and increased CDH5/VE-cadherin phosphorylation, leading to AJ destruction. <i>rab26</i>-null mice showed further aggravation of the effects of endotoxin insult on lung vascular permeability and water content. Depletion of <i>RAB26</i> resulted in upregulation of phosphorylated SRC, enhancement of CDH5 phosphorylation, and aggravation of CDH5 internalization, thereby weakening AJ integrity and endothelial barrier function in human pulmonary microvascular endothelial cells (HPMECs). <i>RAB26</i> overexpression caused active interaction between SRC and the autophagy marker LC3-II and promoted degradation of phosphorylated SRC. Furthermore, RAB26 was involved in a direct and activation-dependent manner in autophagy induction through interaction with ATG16L1 in its GTP-bound form. These findings demonstrate that RAB26 exerts a protective effect on endothelial cell (EC) permeability, which is in part dependent on autophagic targeting of active SRC, and the resultant CDH5 dephosphorylation maintains AJ stabilization. Thus, RAB26-mediated autophagic targeting of phosphorylated SRC can maintain barrier integrity when flux through the RAB26-SRC pathway is protected. These findings suggest that activation of RAB26-SRC signaling provides a new therapeutic opportunity to prevent vascular leakage in ALI. <b>Abbreviations:</b> AJs: adherens junctions; ALI: acute lung injury; ARDS: acute respiratory distress syndrome; ATG5: autophagy related 5; ATG12: autophagy related 12; ATG 16L1: autophagy related 16 like; 1 BALF: bronchoalveolar lavage fluidCQ: chloroquine; Ctrl: control; EC: endothelial cell; GFP: green fluorescent protein; HA-tagged; RAB26<sup>WT</sup>: HA-tagged wild-type; RAB26  HA-tagged; RAB26<sup>QL</sup>: HA-tagged; RAB26<sup>Q123L</sup>HA-tagged; RAB26<sup>NI</sup>: HA-tagged; RAB26<sup>N177I</sup>HPMECs: human pulmonary microvascular endothelial cells; H&amp;E: hematoxylin &amp; eosin; IgG: immunoglobulin; GIF: immunofluorescence; IP: immunoprecipitationi;. p.: intraperitoneal; LPS: lipopolysaccharide; PBS: phosphate-buffered salinesi; RNA: small interfering;RNASQSTM1/p62, sequestosome; 1TBS: Tris-buffered saline; VEGF: vascular endothelial growth factor; WB: western blot; WT: wild-type