MgcRacGAP regulates cortical activity through RhoA during cytokinesis

Although Rho GTPases regulate multiple cellular events, their role in cell division is still obscure. Here we show that expression of a GTPase-activating protein (GAP)-deficient mutant (R386A) of the Rho regulator MgcRacGAP induces abnormal cortical activity during cytokinesis in U2OS cells. Multiple large blebs were observed in cells expressing MgcRacGAP R386A from the onset of anaphase to the late stage of cell division. When mitotic blebbing was excessive, cytokinesis was inhibited, and cells with micronuclei were generated. It has been reported that blebbing is caused by abnormal cortical activity. The MgcRacGAP R386A-induced abnormal cortical activity was inhibited by the dominant negative form of RhoA, but not Rac1 or Cdc42. Moreover, expression of constitutively active RhoA also induced drastic cortical activity during cytokinesis. Unlike apoptotic blebbing, MgcRacGAP R386A-induced blebbing was not inhibited by the ROCK inhibitor Y-27632, suggesting that MgcRacGAP regulates cortical activity during cytokinesis through a novel signaling pathway. We propose that MgcRacGAP plays a pivotal role in cytokinesis by regulating cortical movement through RhoA.     

FAP和Rho家族蛋白在卵巢癌侵袭迁移中的作用

目的：明确FAP是否通过RhoA／ROCK、Racl-GTP通路发挥促增殖、侵袭和迁移作用。方法：用MTT实验,Transwell实验和迁移实验检测FAP、RhoA／ROCK、Racl-GTP对卵巢癌细胞系HO-8910PM的增殖,侵袭和迁移的影响。结果：1、MTT法,迁移和侵袭实验证实用Y-27632抑制RhoA／ROCK途径能够促进卵巢癌细胞的增殖、迁移和侵袭,与FAP联合作用时促进作用增强。2、MTT法,迁移和侵袭实验证实NSC23766抑制Racl途径能够抑制卵巢癌细胞的增殖、迁移和侵袭,与FAP联合作用使FAP的促进作用减弱。结论：l、RhoA／ROCK通路抑制HO一8910PM细胞增殖、迁移和侵袭;Racl-GTP促进H0—8910PM细胞增殖、迁移和侵袭。2、FAP不是通过RhoA／ROCK而是通过Racl—GTP信号通路在HO．8910PM细胞发挥促增殖、迁移和侵袭作用的。     

FAP和Rho 家族蛋白在卵巢癌侵袭迁移中的作用

目的：明确FAP 是否通过RhoA/ROCK、Rac1-GTP 通路发挥促增殖、侵袭和迁移作用。方法：用MTT 实验,Transwell 实验 和迁移实验检测FAP、RhoA/ROCK、Rac1-GTP 对卵巢癌细胞系HO-8910PM 的增殖,侵袭和迁移的影响。结果：1、MTT 法,迁移和 侵袭实验证实用Y-27632 抑制RhoA/ROCK 途径能够促进卵巢癌细胞的增殖、迁移和侵袭,与FAP 联合作用时促进作用增强。 2、MTT 法, 迁移和侵袭实验证实NSC23766 抑制Rac1 途径能够抑制卵巢癌细胞的增殖、迁移和侵袭,与FAP 联合作用使FAP 的 促进作用减弱。结论：1、RhoA/ROCK 通路抑制HO-8910PM 细胞增殖、迁移和侵袭;Rac1-GTP 促进HO-8910PM 细胞增殖、迁移 和侵袭。2、FAP不是通过RhoA/ROCK而是通过Rac1-GTP 信号通路在HO-8910PM细胞发挥促增殖、迁移和侵袭作用的。     

Identification and comparative expression analyses of Daam genes in mouse and Xenopus

During vertebrate embryogenesis, secreted Wnt molecules regulate cell fates by signaling through the canonical pathway mediated by beta-catenin, and regulate planar cell polarity (PCP) and convergent extension movements through alternative pathways. The phosphoprotein Dishevelled (Dsh/Dvl) is a Wnt signal transducer thought to function in all Wnt signaling pathways. A recently identified member of the Formin family, Daam (Dishevelled--associated activator of morphogenesis), regulates the morphogenetic movements of vertebrate gastrulation in a Wnt-dependent manner through direct interactions with Dsh/Dvl and RhoA. We describe two mouse Daam cDNAs, mDaam1 and mDaam2, which encode proteins characterized by highly conserved formin homology domains and which are expressed in complementary patterns during mouse development. Cross-species comparisons indicate that the expression domains of Xenopus Daam1 (XDaam1) mirror mDaam1 expression. Our results demonstrate that Daams are expressed in tissues known to require Wnts and are consistent with Daams being effectors of Wnt signaling during vertebrate development.     

RhoA and ROCK promote migration by limiting membrane protrusions

Previously, we and others have shown that RhoA and ROCK signaling are required for negatively regulating integrin-mediated adhesion and for tail retraction of migrating leukocytes. This study continues our investigation into the molecular mechanisms underlying RhoA/ROCK-regulated integrin adhesion. We show that inhibition of ROCK up-regulates integrin-mediated adhesion, which is accompanied by both increased phosphotyrosine signaling through Pyk-2 and paxillin and inappropriate membrane protrusions. We provide evidence that inhibition of ROCK induces integrin adhesion by promoting remodeling of the actin cytoskeleton. Furthermore, we find that ROCK regulates membrane activity through a pathway involving cofilin. Inhibition of RhoA signaling allows the formation of multiple competing lamellipodia that disrupt productive migration of monocytes. Together, our results show that RhoA/ROCK signaling promotes migration by restricting integrin activity and membrane protrusions to the leading edge.     

Rho guanine nucleotide exchange factor xNET1 implicated in gastrulation movements during Xenopus development

During Xenopus development, embryonic cells dramatically change their shape and position. Rho family small GTPases, such as RhoA, Rac, and Cdc42, play important roles in this process. These GTPases are generally activated by guanine nucleotide exchange factors (GEFs); however, the roles of RhoGEFs in Xenopus development have not yet been elucidated. We therefore searched for RhoGEF genes in our Xenopus EST database, and we identified several genes expressed during embryogenesis. Among them, we focused on one gene, designated xNET1. It is similar to mammalian NET1, a RhoA-specific GEF. An in vitro binding assay revealed that xNET1 bound to RhoA, but not to Rac or Cdc42. In addition, transient expression of xNET1 activated endogenous RhoA. These results indicated that xNET1 is a GEF for RhoA. Epitope-tagged xNET1 was localized mainly to the nucleus, and the localization was regulated by nuclear localization signals in the N-terminal region of xNET1. Overexpression of either wild-type or a mutant form of xNET1 severely inhibited gastrulation movements. We demonstrated that xNET1 was co-immunoprecipitated with the Dishevelled protein, which is an essential signaling component in the non-canonical Wnt pathway. This pathway has been shown to activate RhoA and regulate gastrulation movements. We propose that xNET1 or a similar RhoGEF may mediate Dishevelled signaling to RhoA in the Wnt pathway.     

Fibroblast Growth Factor Receptor-induced Phosphorylation of EphrinB1 Modulates Its Interaction with Dishevelled

The Eph family of receptor tyrosine kinases and their membrane-bound ligands, the ephrins, have been implicated in regulating cell adhesion and migration during development by mediating cell-to-cell signaling events. The transmembrane ephrinB1 protein is a bidirectional signaling molecule that signals through its cytoplasmic domain to promote cellular movements into the eye field, whereas activation of the fibroblast growth factor receptor (FGFR) represses these movements and retinal fate. In Xenopus embryos, ephrinB1 plays a role in retinal progenitor cell movement into the eye field through an interaction with the scaffold protein Dishevelled (Dsh). However, the mechanism by which the FGFR may regulate this cell movement is unknown. Here, we present evidence that FGFR-induced repression of retinal fate is dependent upon phosphorylation within the intracellular domain of ephrinB1. We demonstrate that phosphorylation of tyrosines 324 and 325 disrupts the ephrinB1/Dsh interaction, thus modulating retinal progenitor movement that is dependent on the planar cell polarity pathway. These results provide mechanistic insight into how fibroblast growth factor signaling modulates ephrinB1 control of retinal progenitor movement within the eye field.     

ROCK Is Involved in Vasculogenic Mimicry Formation in Hepatocellular Carcinoma Cell Line

Ras homolog family member A (RhoA) and Rho-associated coiled coil-containing protein kinases 1 and 2 (ROCK1 and 2) are key regulators of focal adhesion, actomyosin contraction and cell motility. RhoA/ROCK signaling has emerged as an attractive target for the development of new cancer therapeutics. Whether RhoA/ROCK is involved in regulating the formation of tumor cell vasculogenic mimicry (VM) is largely unknown. To confirm this hypothesis, we performed in vitro experiments using hepatocellular carcinoma (HCC) cell lines. Firstly, we demonstrated that HCC cells with higher active RhoA/ROCK expression were prone to form VM channels, as compared with RhoA/ROCK low-expressing cells. Furthermore, Y27632 (a specific inhibitor of ROCK) rather than exoenzyme C3 (a specific inhibitor of RhoA) effectively inhibited the formation of tubular network structures in a dose-dependent manner. To elucidate the possible mechanism of ROCK on VM formation, real-time qPCR, western blot and immunofluorescence were used to detect changes of the key VM-related factors, including VE-cadherin, erythropoietin-producing hepatocellular carcinoma-A2 (EphA2), phosphoinositide 3-kinase (PI3K), matrix metalloproteinase (MMP)14, MMP2, MMP9 and laminin 5γ2-chain (LAMC2), and epithelial-mesenchymal-transition (EMT) markers: E-cadherin and Vimentin. The results showed that all the expression profiles were attenuated by blockage of ROCK. In addition, in vitro cell migration and invasion assays showed that Y27632 inhibited the migration and invasion capacity of HCC cell lines in a dose-dependent manner markedly. These data indicate that ROCK is an important mediator in the formation of tumor cell VM, and suggest that ROCK inhibition may prove useful in the treatment of VM in HCC.     

RhoA/ROCK pathway mediates the effect of oestrogen on regulating epithelial‐mesenchymal transition and proliferation in endometriosis

Endometriosis is a benign gynaecological disease appearing with pelvic pain, rising dysmenorrhoea and infertility seriously impacting on 10% of reproductive‐age females. This research attempts to demonstrate the function and molecular mechanism of RhoA/ROCK pathway on epithelial‐mesenchymal transition (EMT) and proliferation in endometriosis. The expression of Rho family was abnormally changed in endometriotic lesions; in particular, RhoA and ROCK1/2 were significantly elevated. Overexpression of RhoA in human eutopic endometrial epithelial cells (eutopic EECs) enhanced the cell mobility, epithelial‐mesenchymal transition (EMT) and proliferation, and RhoA knockdown exhibited the opposite function. Oestrogen up‐regulated the RhoA activity and expression of RhoA and ROCK1/2. RhoA overexpression reinforced the effect of oestrogen on promoting EMT and proliferation, and RhoA knockdown impaired the effect of oestrogen. oestrogen receptor α (ERα) was involved with the regulation of oestrogen on EMT and proliferation and up‐regulated RhoA activity and expression of RhoA and ROCK1/2. The function of ERα was modulated by the change in RhoA expression. Furthermore, phosphorylated ERK that was enhanced by oestrogen and ERα promoted the protein expression of RhoA/ROCK pathway. Endometriosis mouse model revealed that oestrogen enhanced the size and weight of endometriotic lesions. The expression of RhoA and phosphorylated ERK in mouse endometriotic lesions was significantly elevated by oestrogen. We conclude that abnormal activated RhoA/ROCK pathway in endometriosis is responsible for the function of oestrogen/ERα/ERK signalling, which promoted EMT and proliferation and resulted in the development of endometriosis.     

Role of RhoA/ROCK-dependent actin contractility in the induction of tenascin-C by cyclic tensile strain

In chick embryo fibroblasts, the mRNA for extracellular matrix protein tenascin-C is induced 2-fold by cyclic strain (10%, 0.3 Hz, 6 h). This response is attenuated by inhibiting Rho-dependent kinase (ROCK). The RhoA/ROCK signaling pathway is primarily involved in actin dynamics. Here, we demonstrate its crucial importance in regulating tenascin-C expression. Cyclic strain stimulated RhoA activation and induced fibroblast contraction. Chemical activators of RhoA synergistically enhanced the effects of cyclic strain on cell contractility. Interestingly, tenascin-C mRNA levels perfectly matched the extent of RhoA/ROCK-mediated actin contraction. First, RhoA activation by thrombin, lysophosphatidic acid, or colchicine induced tenascin-C mRNA to a similar extent as strain. Second, RhoA activating drugs in combination with cyclic strain caused a super-induction (4- to 5-fold) of tenascin-C mRNA, which was again suppressed by ROCK inhibition. Third, disruption of the actin cytoskeleton with latrunculin A abolished induction of tenascin-C mRNA by chemical RhoA activators in combination with cyclic strain. Lastly, we found that myosin II activity is required for tenascin-C induction by cyclic strain. We conclude that RhoA/ROCK-controlled actin contractility has a mechanosensory function in fibroblasts that correlates directly with tenascin-C gene expression. Previous RhoA/ROCK activation, either by chemical or mechanical signals, might render fibroblasts more sensitive to external tensile stress, e.g., during wound healing.     

Role of glypican 4 in the regulation of convergent extension movements during gastrulation in Xenopus laevis

Coordinated morphogenetic cell movements during gastrulation are crucial for establishing embryonic axes in animals. Most recently, the non-canonical Wnt signaling cascade (PCP pathway) has been shown to regulate convergent extension movements in Xenopus and zebrafish. Heparan sulfate proteoglycans (HSPGs) are known as modulators of intercellular signaling, and are required for gastrulation movements in vertebrates. However, the function of HSPGs is poorly understood. We analyze the function of Xenopus glypican 4 (Xgly4), which is a member of membrane-associated HSPG family. In situ hybridization revealed that Xgly4 is expressed in the dorsal mesoderm and ectoderm during gastrulation. Reducing the levels of Xgly4 inhibits cell-membrane accumulation of Dishevelled (Dsh), which is a transducer of the Wnt signaling cascade, and thereby disturbs cell movements during gastrulation. Rescue analysis with different Dsh mutants and Wnt11 demonstrated that Xgly4 functions in the non-canonical Wnt/PCP pathway, but not in the canonical Wnt/beta-catenin pathway, to regulate gastrulation movements. We also provide evidence that the Xgly4 protein physically binds Wnt ligands. Therefore, our results suggest that Xgly4 functions as positive regulator in non-canonical Wnt/PCP signaling during gastrulation.     

Nitric oxide-induced inhibition of smooth muscle cell proliferation involves S-nitrosation and inactivation of RhoA

Nitric oxide (NO) acts as a vasoregulatory molecule that inhibits vascular smooth muscle cell (SMC) proliferation. Studies have illustrated that NO inhibits SMC proliferation via the extracellular signal-regulated kinase (ERK) pathway, leading to increased protein levels of the cyclin-dependent kinase inhibitor p21^Waf1/Cip1. The ERK pathway can be pro- or antiproliferative, and it has been demonstrated that the activation status of the small GTPase RhoA determines the proliferative fate of ERK signaling, whereby inactivation of RhoA influences ERK signaling to increase p21^Waf1/Cip1 and inhibit proliferation. The purpose of these investigations was to examine the effect of NO on RhoA activation/S-nitrosation and to test the hypothesis that inhibition of SMC proliferation by NO is dependent on inactivation of RhoA. NO decreases activation of RhoA, as demonstrated by RhoA GTP-binding assays, affinity precipitation, and phalloidin staining of the actin cytoskeleton. Additionally, these effects are independent of cGMP. NO decreases SMC proliferation, and gene transfer of constitutively active RhoA (RhoA^63L) diminished the antiproliferative effects of NO, as determined by thymidine incorporation. Western blots of p21^Waf1/Cip1 correlated with changes in proliferation. S-nitrosation of recombinant RhoA protein and immunoprecipitated RhoA was demonstrated by Western blotting for nitrosocysteine and by measurement of NO release. Furthermore, NO decreases GTP loading of recombinant RhoA protein. These findings indicate that inactivation of RhoA plays a role in NO-mediated SMC antiproliferation and that S-nitrosation is associated with decreased GTP binding of RhoA. Nitrosation of RhoA and other proteins likely contributes to cGMP-independent effects of NO. cell signaling; posttranslational modification; vascular disease     

RhoA modulates Smad signaling during transforming growth factor-beta-induced smooth muscle differentiation

We recently reported that transforming growth factor (TGF)-beta induced the neural crest stem cell line Monc-1 to differentiate into a spindle-like contractile smooth muscle cell (SMC) phenotype and that Smad signaling played an important role in this phenomenon. In addition to Smad signaling, other pathways such as mitogen-activated protein kinase (MAPK), phosphoinositol-3 kinase, and RhoA have also been shown to mediate TGF-beta actions. The objectives of this study were to examine whether these signaling pathways contribute to TGF-beta-induced SMC development and to test whether Smad signaling cross-talks with other pathway(s) during SMC differentiation induced by TGF-beta. We demonstrate here that RhoA signaling is critical to TGF-beta-induced SMC differentiation. RhoA kinase (ROCK) inhibitor Y27632 significantly blocks the expression of multiple SMC markers such as smooth muscle alpha-actin, SM22alpha, and calponin in TGF-beta-treated Monc-1 cells. In addition, Y27632 reversed the cell morphology and abolished the contractility of TGF-beta-treated cells. RhoA signaling was activated as early as 5 min following TGF-beta addition. Dominant negative RhoA blocked nuclear translocation of Smad2 and Smad3 because of the inhibition of phosphorylation of both Smads and inhibited Smad-dependent SBE promoter activity, whereas constitutively active RhoA significantly enhanced SBE promoter activity. Consistent with these results, C3 exotoxin, an inhibitor of RhoA activation, significantly attenuated SBE promoter activity and inhibited Smad nuclear translocation. Taken together, these data point to a new role for RhoA as a modulator of Smad activation while regulating TGF-beta-induced SMC differentiation.     

Small GTPase RhoA regulates cytoskeleton dynamics during porcine oocyte maturation and early embryo development

Mammalian oocyte maturation is distinguished by asymmetric division that is regulated primarily by cytoskeleton, including microtubules and microfilaments. Small Rho GTPase RhoA is a key regulator of cytoskeletal organization which regulates cell polarity, migration, and division. In this study, we investigated the roles of RhoA in mammalian oocyte meiosis and early embryo cleavage. (1) Disrupting RhoA activity or knock down the expression of RhoA caused the failure of polar body emission. This may have been due to decreased actin assembly and subsequent spindle migration defects. The involvement of RhoA in this process may have been though its regulation of actin nucleators ROCK, p-Cofilin, and ARP2 expression. (2) In addition, spindle morphology was also disrupted and p-MAPK expression decreased in RhoA inhibited or RhoA KD oocytes, which indicated that RhoA also regulated MAPK phosphorylation for spindle formation. (3) Porcine embryo development was also suppressed by inhibiting RhoA activity. Two nuclei were observed in one blastomere, and actin expression was reduced, which indicated that RhoA regulated actin-based cytokinesis of porcine embryo. Thus, our results demonstrated indispensable roles for RhoA in regulating porcine oocyte meiosis and cleavage during early embryo development.