MLL regulates the actin cytoskeleton and cell migration by stabilising Rho GTPases via the expression of RhoGDI1.

Attainment of proper cell shape and the regulation of cell migration are essential processes in the development of an organism. The mixed lineage leukemia (MLL or KMT2A) protein, a histone 3 lysine 4 (H3K4) methyltransferase, plays a critical role in cell-fate decisions during skeletal development and haematopoiesis in higher vertebrates. Rho GTPases - RhoA, Rac1 and CDC42 - are small G proteins that regulate various key cellular processes, such as actin cytoskeleton formation, the maintenance of cell shape and cell migration. Here, we report that MLL regulates the homeostasis of these small Rho GTPases. Loss of MLL resulted in an abnormal cell shape and a disrupted actin cytoskeleton, which lead to diminished cell spreading and migration. MLL depletion affected the stability and activity of Rho GTPases in a SET domain-dependent manner, but these Rho GTPases were not direct transcriptional targets of MLL. Instead, MLL regulated the transcript levels of their chaperone protein RhoGDI1 (also known as ARHGDIA). Using MDA-MB-231, a triple-negative breast cancer cell line with high RhoGDI1 expression, we show that MLL depletion or inhibition by small molecules reduces tumour progression in nude mice. Our studies highlight the central regulatory role of MLL in Rho/Rac/CDC42 signalling pathways. This article has an associated First Person interview with the first author of the paper.

The lipid phosphatase-like protein PLPPR1 associates with RhoGDI1 to modulate RhoA activation in response to axon growth inhibitory molecules.

Phospholipid Phosphatase-Related Protein Type 1 (PLPPR1) is a member of a family of lipid phosphatase related proteins, integral membrane proteins characterized by six transmembrane domains. This family of proteins is enriched in the brain and recent data indicate potential pleiotropic functions in several different contexts. An inherent ability of this family of proteins is to induce morphological changes, and we have previously reported that members of this family interact with each other and may function co-operatively. However, the function of PLPPR1 is not yet understood. Here we show that the expression of PLPPR1 reduces the inhibition of neurite outgrowth of cultured mouse hippocampal neurons by chondroitin sulfate proteoglycans and the retraction of neurites of Neuro-2a cells by lysophosphatidic acid (LPA). Further, we show that PLPPR1 reduces the activation of Ras homolog family member A (RhoA) by LPA in Neuro-2a cells, and that this is because of an association of PLPPR1with the Rho-specific guanine nucleotide dissociation inhibitor (RhoGDI1). These results establish a novel signaling pathway for the PLPPR1 protein.

Baculovirus-mediated miRNA regulation to suppress hepatocellular carcinoma tumorigenicity and metastasis.

MicroRNA 122 (miR-122) is a tumor suppressor for hepatocellular carcinoma (HCC) but is lowly expressed in HCC cells. MiR-151 is aberrantly overexpressed in HCC cells and promotes HCC metastasis yet its roles on HCC tumorigenicity are unknown. To combat HCC tumorigenicity/metastasis, we developed Sleeping Beauty (SB)-based hybrid baculovirus (BV) vectors that expressed (i) miR-122 precursors (pre-miR-122), (ii) miR-151 sponges, or (iii) pre-miR-122 and miR-151 sponges. Transduction of aggressive HCC cells (Mahlavu) with the pre-miR-122-expressing BV tremendously enhanced miR-122 levels for >6 weeks, suppressed the levels of downstream effectors (e.g., ADAM10 and Bcl-w), proliferation, anchorage-independent growth, motility and migration/invasion in vitro. Intratumoral injection of the pre-miR-122-expressing BV attenuated the HCC growth/metastasis. The miR-151 sponges-expressing BV diminished the miR-151 levels for 6 weeks, enhanced RhoGDIA expression, suppressed RhoGTPases, as well as motility and migration/invasion of Mahlavu cells. Intratumoral injection of the miR-151 sponge-expressing BV impeded not only HCC metastasis but also cell proliferation, MMP expression and tumor growth in vivo. The BV co-expressing pre-miR-122 and miR-151 sponges also simultaneously enhanced miR-122 expression and inhibited miR-151, and conferred antitumor/anti-metastasis effects albeit lack of synergism. These data implicate the potentials of the SB-based hybrid BV for persistently modulating miRNA and suppressing HCC tumorigenicity/metastasis.

Role of Rho GDP dissociation inhibitor α in control of epithelial sodium channel (ENaC)-mediated sodium reabsorption.

The epithelial sodium channel (ENaC) is expressed in the aldosterone-sensitive distal nephron where it performs sodium reabsorption from the lumen. We have recently shown that ENaC activity contributes to the development of salt-induced hypertension as a result of deficiency of EGF level. Previous studies revealed that Rho GDP-dissociation inhibitor α (RhoGDIα) is involved in the control of salt-sensitive hypertension and renal injury via Rac1, which is one of the small GTPases activating ENaC. Here we investigated the intracellular mechanism mediating the involvement of the RhoGDIα/Rac1 axis in the control of ENaC and the effect of EGF on ENaC in this pathway. We demonstrated that RhoGDIα is highly expressed in the cortical collecting ducts of mice and rats, and its expression is down-regulated in Dahl salt-sensitive rats fed a high salt diet. Knockdown of RhoGDIα in cultured cortical collecting duct principal cells increased ENaC subunits expression and ENaC-mediated sodium reabsorption. Furthermore, RhoGDIα deficiency causes enhanced response to EGF treatment. Patch clamp analysis reveals that RhoGDIα significantly decreases ENaC current density and prevents its up-regulation by RhoA and Rac1. Inhibition of Rho kinase with Y27632 had no effects on ENaC response to EGF either in control or RhoGDIα knocked down cells. However, EGF treatment increased levels of active Rac1, which was further enhanced in RhoGDIα-deficient cells. We conclude that changes in the RhoGDIα-dependent pathway have a permissive role in the Rac1-mediated enhancement of ENaC activity observed in salt-induced hypertension.

Loss of Rho-GDIα sensitizes podocytes to lipopolysaccharide-mediated injury.

Nephrotic syndrome is a disease of glomerular permselectivity that can arise as a consequence of heritable or acquired changes to the integrity of the glomerular filtration barrier. We recently reported two siblings with heritable nephrotic syndrome caused by a loss of function mutation in the gene ARHGDIA, which encodes for Rho guanine nucleotide dissociation inhibitor-α (GDIα). GDIs are known to negatively regulate Rho-GTPase signaling. We hypothesized that loss of GDIα sensitizes podocytes to external injury via hyperactivation of Rho-GTPases and p38 MAPK. We examined the response of cultured podocytes with and without knockdown of GDIα to LPS injury by assessing the levels of phospho-p38 as well as the degree of synaptopodin loss. GDIα knockdown podocytes showed more pronounced and sustained p38 phosphorylation in response to LPS compared with control podocytes, and this was blunted significantly by the Rac1 inhibitor. In LPS-treated control podocytes, synaptopodin degradation occurred, and this was dependent on p38, the proteasome, and cathepsin L. In GDIα knockdown podocytes, the same events were triggered, but the levels of synaptopodin after LPS treatment were significantly lower than in control podocytes. These experiments reveal a common pathway by which heritable and environmental risk factors converge to injure podocytes, from Rac1 hyperactivation to p38 phosphorylation and synaptopodin degradation via the ubiquitin-proteasome pathway and cathepsin L.

TROY interacts with Rho guanine nucleotide dissociation inhibitor α (RhoGDIα) to mediate Nogo-induced inhibition of neurite outgrowth.

TROY can functionally substitute p75 to comprise the Nogo receptor complex, which transduces the inhibitory signal of myelin-associated inhibitory factors on axon regeneration following CNS injury. The inhibition of neurite extension relies on TROY-dependent RhoA activation, but how TROY activates RhoA remains unclear. Here, we firstly identified Rho guanine nucleotide dissociation inhibitor α (RhoGDIα) as a binding partner of TROY using GST pull-down combined with two-dimensional gel electrophoresis and mass spectra analysis. The interaction was further confirmed by coimmunoprecipitation in vitro and in vivo. Deletion mutagenesis revealed that two regions of the TROY intracellular domain (amino acids 234-256 and 321-350) were essential for the interaction with RhoGDIα. Secondly, TROY and RhoGDIα were coexpressed in postnatal dorsal root ganglion neurons, cortex neurons, and cerebellar granule neurons (CGNs). Thirdly, TROY/RhoGDIα association was potentiated by Nogo-66 and was independent of p75/RhoGDIα interaction. Fourthly, TROY/RhoGDIα interaction was still able to activate RhoA when p75 was deficient. Furthermore, RhoA activation was decreased dramatically when TROY was knocked down in p75-deficient CGNs cells. Finally, RhoGDIα overexpression abolished RhoA activation and following neurite outgrowth inhibition by Nogo-66 in both wild-type and p75-deficient CGNs. These results showed that the association of RhoGDIα with TROY contributed to TROY-dependent RhoA activation and neurite outgrowth inhibition after Nogo-66 stimulation.

ARHGDIA: a novel gene implicated in nephrotic syndrome.

BACKGROUND: Congenital nephrotic syndrome arises from a defect in the glomerular filtration barrier that permits the unrestricted passage of protein across the barrier, resulting in proteinuria, hypoalbuminaemia, and severe oedema. While most cases are due to mutations in one of five genes, in up to 15% of cases, a genetic cause is not identified. We investigated two sisters with a presumed recessive form of congenital nephrotic syndrome. METHODS AND RESULTS: Whole exome sequencing identified five genes with diallelic mutations that were shared by the sisters, and Sanger sequencing revealed that ARHGDIA that encodes Rho GDP (guanosine diphosphate) dissociation inhibitor α (RhoGDIα, OMIM 601925) was the most likely candidate. Mice with targeted inactivation of ARHGDIA are known to develop severe proteinuria and nephrotic syndrome, therefore this gene was pursued in functional studies. The sisters harbour a homozygous in-frame deletion that is predicted to remove a highly conserved aspartic acid residue within the interface where the protein, RhoGDIα, interacts with the Rho family of small GTPases (c.553_555del(p.Asp185del)). Rho-GTPases are critical regulators of the actin cytoskeleton and when bound to RhoGDIα, they are sequestered in an inactive, cytosolic pool. In the mouse kidney, RhoGDIα was highly expressed in podocytes, a critical cell within the glomerular filtration barrier. When transfected in HEK293T cells, the mutant RhoGDIα was unable to bind to the Rho-GTPases, RhoA, Rac1, and Cdc42, unlike the wild-type construct. When RhoGDIα was knocked down in podocytes, RhoA, Rac1, and Cdc42 were hyperactivated and podocyte motility was impaired. The proband's fibroblasts demonstrated mislocalisation of RhoGDIα to the nucleus, hyperactivation of the three Rho-GTPases, and impaired cell motility, suggesting that the in-frame deletion leads to a loss of function. CONCLUSIONS: Mutations in ARHGDIA need to be considered in the aetiology of heritable forms of nephrotic syndrome.

RhoGDIα downregulates androgen receptor signaling in prostate cancer cells.

INTRODUCTION: Treatment of primary prostate cancer (CaP) is the withdrawal of androgens. However, CaP eventually progresses to grow in a castration-resistant state due to aberrant activation of androgen receptor (AR). Understanding the mechanisms leading to the aberrant activation of AR is critical to develop effective therapy. We have previously identified Rho GDP Dissociation Inhibitor alpha (GDIα) as a novel suppressor in prostate cancer. In this study, we examine the effect of GDIα on AR signaling in prostate cancer cells. METHODS: GDIα was transiently or stably transfected into several prostate cancer cell lines including LNCaP, C4-2, CWR22Rv1, and DU145. The regulation of AR expression by GDIα was analyzed by qRT-PCR and Western blot. AR activity was measured by luciferase reporter assays and electrophoretic mobility shift analysis (EMSA). Immunofluorescence assay was performed to study AR nuclear translocation. The interaction between GDIα and AR was examined by co-immunoprecipitation assays. RESULTS: In this study, we have identified GDIα as a negative regulator of AR signaling pathway. Overexpression of GDIα downregulates AR expression at both mRNA and protein levels. Overexpression of GDIα is able to prevent AR nuclear translocation and inhibit transactivation of AR target genes. Co-immunoprecipitation assays showed that GDIα physically interacts with the N-terminal domain of AR. CONCLUSIONS: GDIα suppresses AR signaling through inhibition of AR expression, nuclear translocation, and recruitment to androgen-responsive genes. GDIα regulatory pathway may play a critical role in regulating AR signaling and prostate cancer growth and progression.

CPK3-phosphorylated RhoGDI1 is essential in the development of Arabidopsis seedlings and leaf epidermal cells.

The regulation of Rho of plants (ROP) in morphogenesis of leaf epidermal cells has been well studied, but the roles concerning regulators of ROPs such as RhoGDIs are poorly understood. This study reports that AtRhoGDI1 (GDI1) acts as a versatile regulator to modulate development of seedlings and leaf pavement cells. In mutant gdi1, leaf pavement cells showed shorter lobes in comparison with those in wild type. In GDI1-14 seedlings (GDI1-overexpression line) the growth of lobes in pavement cells was severely suppressed and the development of seedlings was altered. These results indicate that GDI1 plays an essential role in morphogenesis of epidermal pavement cells through modulating the ROP signalling pathways. The interaction between GDI1 and ROP2 or ROP6 was detected in the leaf pavement cells using FRET analysis. Dominant negative, not constitutively active, DN-rop6 could weaken the effect caused by overexpression of GDI1; because the pleiotropic phenotype of GDI1-14 plants was eliminated in the hybrid line GDI1-14 DN-rop6. GDI1 could be phosphorylated by CPK3. Three conserved Ser/Thr residues in GDI1 were determined as targeted amino acids for CPK3. Overexpression of GDI1(3D), not GDI1(3A), could rescue the abnormal growth phenotypes of gdi1-1 seedlings, demonstrating the impact of GDI1 phosphorylation in the development of Arabidopsis. In summary, these results suggest that GDI1 regulation in morphogenesis of seedlings and leaf pavement cells could be undergone through modulating the ROP signalling pathways and the phosphorylation of GDI1 by CPK3 was required for the developmental modulation in Arabidopsis.

Synthetic glycolipids for glioma growth inhibition developed from neurostatin and NF115 compound.

Neurostatin, a natural glycosphingolipid, and NF115, a synthetic glycolipid, are inhibitors of glioma growth. While neurostatin shows high inhibitory activity on gliomas its abundance is low in mammalian brain. On the contrary NF115 exhibits less inhibitory activity on gliomas, but could be prepared by chemical synthesis. In this study we describe synthetic compounds, structurally related to NF115, capable of inhibiting glioma growth at low micromolar range. We used DNA microarray technology to compare the genes inhibited in U373-MG human glioma cells after treatment with the natural or synthetic inhibitor. New synthetic compounds were developed to interact with the product of Rho GDP dissociation inhibitor alpha gene, which was repressed in both treatments. Compounds that were inhibitors of glioma cell growth in assays for [3H]-thymidine incorporation were then injected in C6 tumor bearing rats and the tumor size in each animal group were measured. The GC-17, GC-4 and IG-5 are new compounds derived from NF115 and showed high antiproliferative activity on tumor cell lines. The GC-17 compound inhibited U373-MG glioblastoma cells (3.2 µM), the effects was fifty times more potent than NF115, and caused a significant reduction of tumor volume (P<0.05) when tested in Wistar rats allotransplanted with C6 glioma cells.

RhoGDIα regulates spermatogenesis through Rac1/cofilin/F-actin signaling.

Spermatogenesis is an extremely complex process, and any obstruction can cause male infertility. RhoGDIα has been identified as a risk of male sterility. In this study, we generate RhoGDIα knockout mice, and find that the males have severely low fertility. The testes from RhoGDIα-/- mice are smaller than that in WT mice. The numbers of spermatogonia and spermatocytes are decreased in RhoGDIα-/- testis. Spermatogenesis is compromised, and spermatocyte meiosis is arrested at zygotene stage in RhoGDIα-/- mice. Acrosome dysplasia is also observed in sperms of the mutant mice. At the molecular level, RhoGDIα deficiency activate the LIMK/cofilin signaling pathway, inhibiting F-actin depolymerization, impairing testis and inducing low fertility in mouse. In addition, the treatment of RhoGDIα-/- mice with Rac1 inhibitor NSC23766 alleviate testis injury and improve sperm quality by inhibiting the LIMK/cofilin/F-actin pathway during spermatogenesis. Together, these findings reveal a previously unrecognized RhoGDIα/Rac1/F-actin-dependent mechanism involved in spermatogenesis and male fertility.

RhoGDI1 interacts with PHLDA2, suppresses the proliferation, migration, and invasion of trophoblast cells, and participates in the pathogenesis of preeclampsia.

Preeclampsia (PE) is a pregnancy-associated disease, which is the major cause of mortality on maternity and perinatal infants. It is hypothesized that PE is a consequence of the dysfunction of the trophoblast cells. Pleckstrin homology-like domain, family A, member 2 (PHLDA2) was shown to inhibit the proliferation, migration, and invasion of trophoblast cells in our previous studies. However, the mechanism by which PHLDA2 affects trophoblast cell function has not been clarified. In the current study, co-immunoprecipitation (Co-IP) with mass spectroscopy analysis was used to explore the proteins that interacted with PHLDA2. A total of 291 candidate proteins were found to be associated with PHLDA2. The interaction between PHLDA2 and Rho guanine nucleotide dissociation inhibitor (RhoGDI) 1 was identified by Co-IP and immunofluorescence staining. Western blot analysis indicated that overexpression of PHLDA2 resulted in upregulation of the RhoGDI1 protein levels, which were stabilized in the presence of cycloheximide. Similarly, overexpression of RhoGDI1 promoted PHLDA2 expression and its stability. Furthermore, pull-down and Co-IP results indicated that PHLDA2 repressed the activity of Rho guanosine triphosphate hydrolase family proteins by regulating RhoGDI1 expression. In addition, RhoGDI1 expression was upregulated in the placental tissues of patients with PE. The effects of the suppression of PHLDA2 expression on proliferation, migration, and invasion of trophoblast cells were partly abrogated following knockdown of RhoGDI1. Taken together, the data indicated that RhoGDI1 mediated regulation of PHLDA2 on the biological behavior of trophoblast cells and may participate in the pathophysiology of PE.

miR-497 promotes the migration and invasion of human medulloblast Daoy cell line through targeted regulation of ARHGDIA in vitro.

OBJECTIVES: To further investigate the effects of miR-497 on the biological behavior of human medulloblastoma cell line in vitro. METHODS: Human medulloblastoma cell lines, Daoy and D341, were used in this study, and the miR-497 expression in the cells was measured by Quantitative PCR with fluorescence. The Daoy cells were divided into the mimics group (Daoy cells treated with mimics), inhibitor group (Daoy cells treated with inhibitor), normal Daoy cells, ARHGDIA siRNA group (Daoy cells transfected with ARHGDIA siRNA), ARHGDIA control group (Daoy cells did not receive any treatment), and negative control group (normal cells transfected with ARHGDIA siRNA). The expression of miR-497 and ARHGDIA mRNA was measured by Quantitative PCR with fluorescence, while the level of ARHGDIA protein was measured by Western blot. The binding capability of ARHGDIA and miR-497 was assessed by luciferase assay, the migration of cells was assessed by wound healing assay, and the invasion of cells was assessed by Transwell assay. RESULTS: Compared to D341 cells, the miR-497 level was significantly higher in the Daoy cells (P < 0.01). The dual-luciferase reporter assay showed that miR-497 targets ARHGDIA. Transfecting the normal Daoy cells with miR-497 mimics significantly reduced the expression of ARHGDIA protein (P < 0.05), while transfecting normal Daoy cells with miR-497 inhibitor significantly increased the expression of ARHGDIA protein (P < 0.05). Consequently, the migration and invasion capability of cells increased significantly after transfection with miR-497 mimic (P < 0.05), and decreased significantly after transfection with miR-497 inhibitor (P < 0.05). In addition, the migration and invasion capabilities of the cells also increased significantly after transfection with ARHGDIA siRNA (P < 0.05). CONCLUSIONS: miR-497/ARHGDIA axis participates in the in vitro migration and invasion of human medulloblastoma cell lines.

Comprehensive characterization of protein-protein interactions perturbed by disease mutations.

Technological and computational advances in genomics and interactomics have made it possible to identify how disease mutations perturb protein-protein interaction (PPI) networks within human cells. Here, we show that disease-associated germline variants are significantly enriched in sequences encoding PPI interfaces compared to variants identified in healthy participants from the projects 1000 Genomes and ExAC. Somatic missense mutations are also significantly enriched in PPI interfaces compared to noninterfaces in 10,861 tumor exomes. We computationally identified 470 putative oncoPPIs in a pan-cancer analysis and demonstrate that oncoPPIs are highly correlated with patient survival and drug resistance/sensitivity. We experimentally validate the network effects of 13 oncoPPIs using a systematic binary interaction assay, and also demonstrate the functional consequences of two of these on tumor cell growth. In summary, this human interactome network framework provides a powerful tool for prioritization of alleles with PPI-perturbing mutations to inform pathobiological mechanism- and genotype-based therapeutic discovery.

Downregulation of miR­483­5p inhibits TGF­ß1­induced EMT by targeting RhoGDI1 in pulmonary fibrosis.

Transforming growth factor­ß1 (TGF­ß1)­induced epithelial­mesenchymal transition (EMT) serves a significant role in pulmonary fibrosis (PF). Increasing evidence indicates that microRNAs (miRNAs or miRs) contribute to PF pathogenesis via EMT regulation. However, the role of miR­483­5p in PF remains unclear. Therefore, the present study investigated the potential effect of miR­483­5p on TGF­ß1­induced EMT in PF. It was found that the expression of miR­483­5p was upregulated in both PF tissue and A549 cells treated with TGF­ß1, whereas expression of Rho GDP dissociation inhibitor 1 (RhoGDI1) was downregulated. miR­483­5p mimic transfection promoted TGF­ß1­induced EMT; by contrast, miR­483­5p inhibitor inhibited TGF­ß1­induced EMT. Also, miR­483­5p mimic decreased RhoGDI1 expression, whereas miR­483­5p inhibitor increased RhoGDI1 expression. Furthermore, dual­luciferase reporter gene assay indicated that miR­483­5p directly regulated RhoGDI1. Moreover, RhoGDI1 knockdown eliminated the inhibitory effect of the miR­483­5p inhibitor on TGF­ß1­induced EMT via the Rac family small GTPase (Rac)1/PI3K/AKT pathway. In conclusion, these data indicated that miR­483­5p inhibition ameliorated TGF­ß1­induced EMT by targeting RhoGDI1 via the Rac1/PI3K/Akt signaling pathway in PF, suggesting a potential role of miR­483­5p in the prevention and treatment of PF.

The RHO Family GTPases: Mechanisms of Regulation and Signaling.

Much progress has been made toward deciphering RHO GTPase functions, and many studies have convincingly demonstrated that altered signal transduction through RHO GTPases is a recurring theme in the progression of human malignancies. It seems that 20 canonical RHO GTPases are likely regulated by three GDIs, 85 GEFs, and 66 GAPs, and eventually interact with >70 downstream effectors. A recurring theme is the challenge in understanding the molecular determinants of the specificity of these four classes of interacting proteins that, irrespective of their functions, bind to common sites on the surface of RHO GTPases. Identified and structurally verified hotspots as functional determinants specific to RHO GTPase regulation by GDIs, GEFs, and GAPs as well as signaling through effectors are presented, and challenges and future perspectives are discussed.

Cullin 3/KCTD5 Promotes the Ubiqutination of Rho Guanine Nucleotide Dissociation Inhibitor 1 and Regulates Its Stability.

Rho guanine nucleotide dissociation inhibitor 1 (RhoGDI1) plays important roles in numerous cellular processes, including cell motility, adhesion, and proliferation, by regulating the activity of Rho GTPases. Its expression is altered in various human cancers and is associated with malignant progression. Here, we show that RhoGDI1 interacts with Cullin 3 (CUL3), a scaffold protein for E3 ubiquitin ligase complexes. Ectopic expression of CUL3 increases the ubiquitination of RhoGDI1. Furthermore, potassium channel tetramerization domain containing 5 (KCTD5) also binds to RhoGDI1 and increases its interaction with CUL3. Ectopic expression of KCTD5 increases the ubiquitination of RhoGDI1, whereas its knockdown by RNA interference has the opposite effect. Depletion of KCTD5 or expression of dominant-negative CUL3 (DN-CUL3) enhances the stability of RhoGDI1. Our findings reveal a previously unknown mechanism for controlling RhoGDI1 degradation that involves a CUL3/KCTD5 ubiquitin ligase complex.

Mir20a/106a-WTX axis regulates RhoGDIa/CDC42 signaling and colon cancer progression.

Wilms tumor gene on the X chromosome (WTX) is a putative tumor suppressor gene in Wilms tumor, but its expression and functions in other tumors are unclear. Colorectal cancer (CRC) is the third leading cause of cancer-related deaths in women and the second leading cause in men in the United States. We demonstrated that WTX frequently lost in CRC which was highly correlated with cell proliferation, tumor invasion and metastasis. Mechanistically, WTX loss disrupts the interaction between RhoGDIα and CDC42 by losing of the binding with RhoGDIα and triggers the activation of CDC42 and its downstream cascades, which promotes CRC development and liver metastasis. The aberrant upregulation of miR-20a/miR-106a were identified as the reason of WTX loss in CRC both in vivo and in vitro. These study defined the mechanism how miR-20a/miR-106a-mediated WTX loss regulates CRC progression and metastasis, and provided a potential therapeutic target for preventing CRC progression.

RhoGDI stability is regulated by SUMOylation and ubiquitination via the AT1 receptor and participates in Ang II-induced smooth muscle proliferation and vascular remodeling.

BACKGROUND AND AIMS: The physiological role of Rho-specific guanine nucleotide dissociation inhibitor (RhoGDI) in vascular remodeling remains unknown. We investigated the function of RhoGDI in angiotensin II (Ang II)-induced vascular remodeling in cultured human aortic vascular smooth muscle cells (HA-VSMCs) and in an Ang II-infusion vascular remodeling mouse model. METHODS: For in vitro assays of HA-VSMCs, proliferation was assessed by BrdU and EdU assays and immunofluorescence analysis of ki-67 expression. RhoGDI1 and RhoGDI2 function and expression were assessed by RNAi, Western blotting and real-time RT-PCR. RhoGDI ubiquitination and SUMOylation levels were evaluated by co-immunoprecipitation and Western blotting. The functions of proteosomal-mediated degradation, ubiquitination, SUMOylation and Ang II receptors were assessed using specific inhibitors. To evaluate the in vivo effects of Ang II and RhoGDI, H & E staining, Masson's trichrome staining, and immunostaining were employed. RESULTS: Ang II treatment of HA-VSMCs for 6 or 48 h promoted RhoGDI1 and RhoGDI2 protein degradation and reduced cell proliferation, which was reversed by proteosome inhibition. In contrast, treatment with Ang II for 12 or 24 h induced dose-dependent cell proliferation without affecting RhoGDI expression. RNA interference of either RhoGDI1 or RhoGDI2 blocked proliferation induced by 12 or 24 h treatment of Ang II. Moreover, Ang II-dependent degradation at 6 and 48 h correlated with RhoGDI ubiquitination and inversely correlated with RhoGDI SUMOylation and cell proliferation. Treatment with specific inhibitors suggests that ubiquitin and SUMO competitively bind to RhoGDI1 and RhoGDI2 to reciprocally regulate RhoGDI stability and HA-VSMC proliferation. Furthermore, inhibition of the Ang II receptor 1 (AT1 receptor), but not the Ang II receptor 2, blocked Ang II-dependent RhoGDI stabilization and proliferation at 12 and 24 h. In mice, Ang II infusion increased the intima-media thickness, collagen and myofiber production and VSMC proliferation, and these effects were shown to be dependent on RhoGDI1, RhoGDI2 and AT1 receptor. Ang II infusion exerted no significant effect on RhoGDI1 and RhoGDI2 protein levels, which were decreased after AT1 receptor inhibition. CONCLUSIONS: Together, the results of this study reveal a novel mechanism by which Ang II regulates RhoGDI stability by SUMOylation and ubiquitination via AT1 receptor activation and thus affects VSMC proliferation and vascular remodeling.

EphrinB1 promotes cancer cell migration and invasion through the interaction with RhoGDI1.

Eph receptors and their corresponding ephrin ligands have been associated with regulating cell-cell adhesion and motility, and thus have a critical role in various biological processes including tissue morphogenesis and homeostasis, as well as pathogenesis of several diseases. Aberrant regulation of Eph/ephrin signaling pathways is implicated in tumor progression of various human cancers. Here, we show that a Rho family GTPase regulator, Rho guanine nucleotide dissociation inhibitor 1 (RhoGDI1), can interact with ephrinB1, and this interaction is enhanced upon binding the extracellular domain of the cognate EphB2 receptor. Deletion mutagenesis revealed that amino acids 327-334 of the ephrinB1 intracellular domain are critical for the interaction with RhoGDI1. Stimulation with an EphB2 extracellular domain-Fc fusion protein (EphB2-Fc) induces RhoA activation and enhances the motility as well as invasiveness of wild-type ephrinB1-expressing cells. These Eph-Fc-induced effects were markedly diminished in cells expressing the mutant ephrinB1 construct (Δ327-334) that is ineffective at interacting with RhoGDI1. Furthermore, ephrinB1 depletion by siRNA suppresses EphB2-Fc-induced RhoA activation, and reduces motility and invasiveness of the SW480 and Hs578T human cancer cell lines. Our study connects the interaction between RhoGDI1 and ephrinB1 to the promotion of cancer cell behavior associated with tumor progression. This interaction may represent a therapeutic target in cancers that express ephrinB1.