Project description:During development, multicellular rosettes serve as important cellular intermediates in the formation of diverse organ systems. Multicellular rosettes are transient epithelial structures that are defined by the apical constriction of cells towards the rosette center. Due to the important role these structures play during development, understanding the molecular mechanisms by which rosettes are formed and maintained is of high interest. Utilizing the zebrafish posterior lateral line primordium (pLLP) as a model system, we identify the RhoA GEF Mcf2lb as a regulator of rosette integrity. The pLLP is a group of ~150 cells that migrates along the zebrafish trunk and is organized into epithelial rosettes; these are deposited along the trunk and will differentiate into sensory organs called neuromasts (NMs). Using single-cell RNA sequencing and whole-mount in situ hybridization, we showed that mcf2lb is expressed in the pLLP during migration. Given the known role of RhoA in rosette formation, we asked whether Mcf2lb plays a role in regulating apical constriction of cells within rosettes. Live imaging and subsequent 3D analysis of mcf2lb mutant pLLP cells showed disrupted apical constriction and subsequent rosette organization. This in turn resulted in a unique posterior Lateral Line phenotype: an excess number of deposited NMs along the trunk of the zebrafish. Cell polarity markers ZO-1 and Par-3 were apically localized, indicating that pLLP cells are normally polarized. In contrast, signaling components that mediate apical constriction downstream of RhoA, Rock-2a and non-muscle Myosin II were diminished apically. Altogether our results suggest a model whereby Mcf2lb activates RhoA, which in turn activates downstream signaling machinery to induce and maintain apical constriction in cells incorporated into rosettes.
Project description:During development, multicellular rosettes serve as important cellular intermediates in the formation of diverse organ systems. Multicellular rosettes are transient epithelial structures that are defined by the apical constriction of cells towards the rosette center. Due to the important role these structures play during development, understanding the molecular mechanisms by which rosettes are formed and maintained is of high interest. Utilizing the zebrafish posterior lateral line primordium (pLLP) as a model system, we identify the RhoA GEF Mcf2lb as a regulator of rosette integrity. The pLLP is a group of ~150 cells that migrates along the zebrafish trunk and is organized into epithelial rosettes; these are deposited along the trunk and will differentiate into sensory organs called neuromasts (NMs). Using single-cell RNA sequencing and whole-mount in situ hybridization, we showed that mcf2lb is expressed in the pLLP during migration. Given the known role of RhoA in rosette formation, we asked whether Mcf2lb plays a role in regulating apical constriction of cells within rosettes. Live imaging and subsequent 3D analysis of mcf2lb mutant pLLP cells showed disrupted apical constriction and subsequent rosette organization. This in turn resulted in a unique posterior Lateral Line phenotype: an excess number of deposited NMs along the trunk of the zebrafish. Cell polarity markers ZO-1 and Par-3 were apically localized, indicating that pLLP cells are normally polarized. In contrast, signaling components that mediate apical constriction downstream of RhoA, Rock-2a and non-muscle Myosin II were diminished apically. Altogether our results suggest a model whereby Mcf2lb activates RhoA, which in turn activates downstream signaling machinery to induce and maintain apical constriction in cells incorporated into rosettes.
Project description:Fibronectin (FN)-binding integrins control a variety of cellular responses through Rho GTPases. The FN-binding integrins, αvβ3 and α5β1, are known to induce different effects on cell morphology and motility. Here we report that FN-bound αvβ3 integrin, but not FN-bound α5β1 integrin, triggers the dissociation of the RhoA GEF Lfc (GEF-H1 in humans) from microtubules (MT), leading to the activation of RhoA, formation of stress fibres and maturation of focal adhesions (FAs). Conversely, loss of Lfc expression decreases RhoA activity, stress fibre formation and FA size, suggesting that Lfc is the major GEF downstream of FN-bound αvβ3 that controls RhoA activity. Mechanistically, FN-engaged αvβ3 integrin activates a kinase cascade involving MARK2/3, which in turn leads to phosphorylation of several phospho-sites on Lfc. In particular, S151 was identified as the main site involved in the regulation of Lfc localization and activity. Our findings indicate that activation of Lfc/RhoA is orchestrated in FN-adherent cells in an integrin-specific manner.
Project description:Hypoxia regulates epithelial to mesenchymal transition (EMT) of cancer cells. However, the mechanism underlying hypoxia-mediated EMT remains largely unknow. Here, utilizing colorectal cell carcinoma (CRC) as a model, we find that HUNK inhibits EMT and suppresses metastasis of CRC cells via its substrate GEF-H1 in a kinase-dependent manner. Mechanistically, HUNK directly phosphorylates GEF-H1 at ser645 site, which activates RhoA and consequently leads to a cascade of phosphorylation of LIMK1/CFL-1, thereby stabilizing F-actin and inhibiting EMT. Moreover, hypoxia suppresses HUNK activity and dephosphorylates GEF-H1 to promote EMT. Clinically, the expression levels of both HUNK and phosphorylation of GEH-H1 ser645 are not only downregulated in CRC tissues with metastasis compared to that without metastasis, but also positively correlated among these tissues. Our findings highlight the importance of hypoxia-regulated HUNK kinase activity and phosphorylation of GEF-H1 in regulation of EMT and metastasis of CRC.
Project description:FoxM1 activates genes that regulate S-G2-M cell-cycle progression and, when overexpressed, is associated with poor clinical outcome in multiple cancers. Here we identify FoxM1 as a tumor suppressor in mice that, through its N-terminal domain, binds to and inhibits Ect2 to limit the activity of RhoA GTPase and its effector mDia1, a catalyst of cortical actin nucleation. FoxM1 insufficiency impedes centrosome movement through excessive cortical actin polymerization, thereby causing the formation of non-perpendicular mitotic spindles that missegregate chromosomes and drive tumorigenesis in mice. Importantly, low FOXM1 expression correlates with RhoA GTPase hyperactivity in multiple human cancer types, indicating that suppression of the newly discovered Ect2-RhoA-mDia1 oncogenic axis by FoxM1 is clinically relevant. Furthermore, by dissecting the domain requirements through which FoxM1 inhibits Ect2 GEF activity, we provide mechanistic insight for the development of pharmacological approaches that target protumorigenic RhoA activity.
Project description:Stable knockdown of NET1, a RhoGEF, was achieved in AGS Gastric Cancer cells. This gene is known to be overexpressed in the disease. Knockdown was achieved using lentiviral shRNA particles. Gene expression was compared between knockdown and scrambled shRNA treated control cells. Cells were treated with and without LPA, a known activator of RhoA.
Project description:Stable knockdown of NET1, a RhoGEF, was achieved in AGS Gastric Cancer cells. This gene is known to be overexpressed in the disease. Knockdown was achieved using lentiviral shRNA particles. Gene expression was compared between knockdown and scrambled shRNA treated control cells. Cells were treated with and without LPA, a known activator of RhoA. Three distinct cell lines were used in this study (all AGS cells); (i) Non Target cell (NT) stably expressing non targetting shRNA (ii) 63 and (iii) 65; the latter two are stable NET1 knockdown cells and are seperatly transduced with separate NET1 targetting shRNA particles. Cells were treated with and without 10microM LPA for 4 hr. Experimental replicates were performed for each treatment (A & B), RNA was prepared from each and seperatly hybridised to U133A arrays.
Project description:In acute critical illness the capillary barrier may break down resulting in hypovolemia, extracellular edema, tissue dysoxia and even death. Restoration of the tight junction dependent capillary barrier is regulated by small GTPases, the specific regulatory molecules most active in this setting are not well described. Transcriptional profiling of tight junction forming human dermal microvascular ECs (HDMECs) and adherens junctions forming human umbilical vein EC (HUVECs) demonstrate ARHGEF12 is significantly differentially regulated in HDMECs before and after stimulation with tumor necrosis factor (TNF). HDMEC depleted of ArhGEF12 demonstrate significantly exacerbated TNF-induced decrease in trans-endothelial electrical resistance and disruption of tight junction proteins claudin-5 and ZO-1. ArhGEF12 is a RhoA-GEF, an established finding which is inconsistent with our observed results. Pulldown activation assays from of HDMECs depleted of ArhGEF12 and treated with TNF show decreased Rap1A activity after four hours and paradoxically increased RhoA activity after 12 hours. In cell-free pulldown assays, immunoprecipitated ArhGEF12 effectively activates Rap1A and RhoA and not Rap2A-C, RhoB-C or even Rap1B which shares 95% sequence identity with Rap1A. We conclude that in tight junction forming EC, ArhGEF12 selectively activates Rap1A to promote capillary barrier restoration in a mechanism independent of traditionally described cAMP-mediated Epac1 activation. The unique dual in vitro specificity of ArhGEF12 for RhoA, Rap1A and not Rap1B cannot be explained by sequence identity and requires additional investigation.
Project description:The Arabidopsis rosette core can display full resistance against Botrytis cinerea. To reveal potential players in this resistance, the transcriptome of the Arabidopsis rosette core was determined.