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The Cerebral Cavernous Malformation1 (CCM1) Gene Product, KRIT‐1, is a Rap1 Effector that Regulates Endothelial Cell‐Cell Junctions
Author(s) -
Glading Angela,
Han Jaewon,
Stockton Rebecca,
Ginsberg Mark H.
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a187-a
Subject(s) - rap1 , microbiology and biotechnology , effector , endothelial stem cell , cell junction , biology , cell adhesion , cell , chemistry , signal transduction , biochemistry , in vitro
Cerebral cavernous malformation (CCM), a disease associated with defective endothelial junctions, results from autosomal dominant CCM1 mutations that cause loss of KRIT‐1 protein. Rap1 GTPase is known to regulate cell‐cell junctions, and we demonstrate that KRIT‐1 binds Rap1 in a GTP‐dependent manner, making it an authentic Rap1 effector‐protein. We developed anti‐KRIT‐1 monoclonal antibodies that enabled us to demonstrate that KRIT‐1 protein is expressed in cultured arterial and venous endothelial cells and is present in both the nucleus and cell‐cell junctions. Furthermore, using novel, conformation‐specific, anti‐KRIT antibodies we find that the KRIT‐1 FERM domain is masked through an interaction with the KRIT‐1 N‐terminus and that Rap1 binding disrupts this interaction, unmasking the FERM domain. In addition, we find that the FERM domain mediates the junctional localization of KRIT‐1; and that activation of Rap1 enhances this localization and association with junction proteins. Finally, depletion of KRIT‐1 disrupted endothelial junctional integrity and abolished the stabilization of endothelial junctions by Rap1 activation. Thus, these studies establish that KRIT‐1 is a Rap1 effector that regulates endothelial junctional integrity and provide a molecular explanation for aspects of the CCM phenotype.