Activated ezrin-radixin-moesin (ERM) proteins link the plasma membrane to the actin cytoskeleton to generate apical structures, including microvilli. Among many kinases implicated in ERM activation are the homologues LOK and SLK. CRISPR/Cas9 was used to knock out all ERM proteins or LOK/SLK in human cells. LOK/SLK knockout eliminates all ERM-activating phosphorylation. The apical domains of cells lacking LOK/SLK or ERMs are strikingly similar and selectively altered, with loss of microvilli and with junctional actin replaced by ectopic myosin-II–containing apical contractile structures. Constitutively active ezrin can reverse the phenotypes of either ERM or LOK/SLK knockouts, indicating that a central function of LOK/SLK is to activate ERMs. Both knockout lines have elevated active RhoA with concomitant enhanced myosin light chain phosphorylation, revealing that active ERMs are negative regulators of RhoA. As RhoA-GTP activates LOK/SLK to activate ERM proteins, the ability of active ERMs to negatively regulate RhoA-GTP represents a novel local feedback loop necessary for the proper apical morphology of epithelial cells.
Effector-mediated ERM activation locally inhibits RhoA activity to shape the apical cell domain
C. Sauvanet’s present address is Unit of Structural Studies of Macromolecular Machines in Cellula, Department of Structural Biology and Chemistry, Institut Pasteur, Centre national de la recherche scientifique, Unité mixte de recherche 3528, Paris, France.
R. Viswanatha’s present address is Blavatnik Institute of Genetics, Harvard Medical School, Boston, MA.
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Riasat Zaman, Andrew Lombardo, Cécile Sauvanet, Raghuvir Viswanatha, Valerie Awad, Locke Ezra-Ros Bonomo, David McDermitt, Anthony Bretscher; Effector-mediated ERM activation locally inhibits RhoA activity to shape the apical cell domain. J Cell Biol 7 June 2021; 220 (6): e202007146. doi: https://doi.org/10.1083/jcb.202007146
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