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EB1, p150Glued, and Clasp1 control endothelial tubulogenesis through microtubule assembly, acetylation, and apical polarization.

ABSTRACT: Vascular tube morphogenesis requires the establishment of endothelial cell (EC) apical-basal polarity in three-dimensional (3D) extracellular matrices. To date, there is little understanding of how EC polarity is controlled during these highly dynamic and rapid morphogenic events. We show that the microtubule tip complex proteins, end binding 1 (EB1), p150(Glued), and Clasp1, control human EC tube formation by (1) inducing microtubule assembly and asymmetric cytoskeletal polarization, whereby acetylated and detyrosinated tubulins distribute in a subapical membrane location and filamentous actin distributes basally; (2) increasing tubulin posttranslational modifications, including required acetylation events; and (3) regulating an EC lumen signaling cascade that involves membrane type 1 matrix metallopatrinase (MT1-MMP)-dependent proteolysis as well as Pak, Raf, and Erk kinases. Another regulator of this process is the microtubule stabilizing protein, tau, which binds p150(Glued) and similarly affects EC lumen formation by controlling the levels of acetylated and detyrosinated tubulins. Increased expression of the tubulin deacetylases, sirtuin 2, and histone deacetylase 6 (HDAC6), blocks EC tube formation and cytoskeletal polarization, while siRNA suppression of these deacetylases stimulates these events. Overall, this work reveals a fundamental role for microtubule tip complex proteins in coordinating microtubule assembly, posttranslational modifications including acetylation, and apical-basal cytoskeletal polarization to control the developing apical membrane surface during blood vessel tubulogenesis in 3D matrix environments.

SUBMITTER: Kim DJ

PROVIDER: S-EPMC3637019 | biostudies-literature | 2013 Apr

REPOSITORIES: biostudies-literature

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EB1, p150Glued, and Clasp1 control endothelial tubulogenesis through microtubule assembly, acetylation, and apical polarization.

Kim Dae Joong DJ Martinez-Lemus Luis A LA Davis George E GE

Blood 20130226 17

Vascular tube morphogenesis requires the establishment of endothelial cell (EC) apical-basal polarity in three-dimensional (3D) extracellular matrices. To date, there is little understanding of how EC polarity is controlled during these highly dynamic and rapid morphogenic events. We show that the microtubule tip complex proteins, end binding 1 (EB1), p150(Glued), and Clasp1, control human EC tube formation by (1) inducing microtubule assembly and asymmetric cytoskeletal polarization, whereby ac ...[more]

PMID: 23444400

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Project description:Tubulin-binding TOG domains are found arrayed in a number of proteins that regulate microtubule dynamics. While much is known about the structure and function of TOG domains from the XMAP215 microtubule polymerase family, less in known about the TOG domain array found in animal CLASP family members. The animal CLASP TOG array promotes microtubule pause, potentiates rescue, and limits catastrophe. How structurally distinct the TOG domains of animal CLASP are from one another, from XMAP215 family TOG domains, and whether a specific order of structurally distinct TOG domains in the TOG array is conserved across animal CLASP family members is poorly understood. We present the x-ray crystal structures of Homo sapiens (H.s.) CLASP1 TOG1 and TOG2. The structures of H.s. CLASP1 TOG1 and TOG2 are distinct from each other and from the previously determined structure of Mus musculus (M.m.) CLASP2 TOG3. Comparative analyses of CLASP family TOG domain structures determined to date across species and paralogs supports a conserved CLASP TOG array paradigm in which structurally distinct TOG domains are arrayed in a specific order. H.s. CLASP1 TOG1 bears structural similarity to the free-tubulin binding TOG domains of the XMAP215 family but lacks many of the key tubulin-binding determinants found in XMAP215 family TOG domains. This aligns with studies that report that animal CLASP family TOG1 domains cannot bind free tubulin or microtubules. In contrast, animal CLASP family TOG2 and TOG3 domains have reported microtubule-binding activity but are structurally distinct from the free-tubulin binding TOG domains of the XMAP215 family. H.s. CLASP1 TOG2 has a convex architecture, predicted to engage a hyper-curved tubulin state that may underlie its ability to limit microtubule catastrophe and promote rescue. M.m. CLASP2 TOG3 has unique structural elements in the C-terminal half of its α-solenoid domain that our modeling studies implicate in binding to laterally-associated tubulin subunits in the microtubule lattice in a mode similar to, yet distinct from those predicted for the XMAP215 family TOG4 domain. The potential ability of the animal CLASP family TOG3 domain to engage lateral tubulin subunits may underlie the microtubule rescue activity ascribed to the domain. These findings highlight the structural diversity of TOG domains within the CLASP family TOG array and provide a molecular foundation for understanding CLASP-dependent effects on microtubule dynamics.

Project description:A critical and understudied property of endothelial cells is their ability to form lumens and tube networks. Although considerable information has been obtained concerning these issues, including the role of Cdc42 and Rac1 and their effectors such as Pak2, Pak4, Par6b, and co-regulators such as integrins, MT1-MMP and Par3; many key questions remain that are necessary to elucidate molecular and signaling requirements for this fundamental process. In this work, we identify new small GTPase regulators of EC tubulogenesis including k-Ras, Rac2 and Rap1b that act in conjunction with Cdc42 as well as the key downstream effectors, IQGAP1, MRCKβ, beta-Pix, GIT1, and Rasip1 (which can assemble into multiprotein complexes with key regulators including α2β1 integrin and MT1-MMP). In addition, we identify the negative regulators, Arhgap31 (by inactivating Cdc42 and Rac) and Rasa1 (by inactivating k-Ras) and the positive regulator, Arhgap29 (by inactivating RhoA) which play a major functional role during the EC tubulogenic process. Human EC siRNA suppression or mouse knockout of Rasip1 leads to identical phenotypes where ECs form extensive cord networks, but cannot generate lumens or tubes. Essential roles for these molecules during EC tubulogenesis include; i) establishment of asymmetric EC cytoskeletal polarization (subapical distribution of acetylated tubulin and basal membrane distribution of F-actin); and ii) directed membrane trafficking of pinocytic vacuoles or other intracellular vesicles along acetylated tubulin tracks to the developing apical membrane surface. Cdc42 co-localizes subapically with acetylated tubulin, while Rac1 and k-Ras strongly label vacuole/ vesicle membranes which accumulate and fuse together in a polarized, perinuclear manner. We observe polarized apical membrane and subapical accumulation of key GTPases and effectors regulating EC lumen formation including Cdc42, Rac1, Rac2, k-Ras, Rap1b, activated c-Raf and Rasip1 to control EC tube network assembly. Overall, this work defines novel key regulators and their functional roles during human EC tubulogenesis.

Dataset Information

EB1, p150Glued, and Clasp1 control endothelial tubulogenesis through microtubule assembly, acetylation, and apical polarization.

Publications

EB1, p150Glued, and Clasp1 control endothelial tubulogenesis through microtubule assembly, acetylation, and apical polarization.

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