RhoA prevents apoptosis during zebrafish embryogenesis through activation of Mek/Erk pathway

The role of angiotensin II activation of yes-associated protein/PDZ-binding motif signaling in hypertensive cardiac and vascular remodeling

Vascular remodeling is the pathogenic basis of hypertension and end organ injury, and the proliferation of vascular smooth muscle cells (VSMCs) is central to vascular remodeling. Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) are key effectors of the Hippo pathway and crucial for controlling cell proliferation, apoptosis and differentiation. The present study investigated the role of YAP/TAZ in cardiac and vascular remodeling of angiotensin II-induced hypertension. Ang II induced YAP/TAZ activation in the heart and aorta, which was prevented by YAP/TAZ inhibitor verteporfin. Treatment with verteporfin significantly reduced Ang II-induced cardiac and vascular hypertrophy with a mild reduction in systolic blood pressure (SBP), verteporfin attenuated Ang II-induced cardiac and aortic fibrosis with the inhibition of transform growth factor (TGF)β/Smad2/3 fibrotic signaling and extracellular matrix collagen I deposition. Ang II induced Rho A, extracellular signal-regulated kinase 1/2 (ERK1/2) and YAP/TAZ activation in VSMCs, either Rho kinase inhibitor fasudil or ERK inhibitor PD98059 suppressed Ang II-induced YAP/TAZ activation, cell proliferation and fibrosis of VSMCs. Verteporfin also inhibited Ang II-induced VSMC proliferation and fibrotic TGFβ1/Smad2/3 pathway. These results demonstrate that Ang II activates YAP/TAZ via Rho kinase/ERK1/2 pathway in VSMCs, which may contribute to cardiac and vascular remodeling in hypertension. Our results suggest that YAP/TAZ plays a critical role in the pathogenesis of hypertension and end organ damage, and targeting the YAP/TAZ pathway may be a new strategy for the prevention and treatment of hypertension and cardiovascular diseases.

Mechanism of RhoA regulating benign prostatic hyperplasia: RhoA-ROCK-β-catenin signaling axis and static & dynamic dual roles

BACKGROUND

The pathogenesis of benign prostatic hyperplasia (BPH) has not been fully elucidated. Ras homology family member A (RhoA) plays an important role in regulating cell cytoskeleton, growth and fibrosis. The role of RhoA in BPH remains unclear.

METHODS

This study aimed to clarify the expression, functional activity and mechanism of RhoA in BPH. Human prostate tissues, human prostate cell lines, BPH rat model were used. Cell models of RhoA knockdown and overexpression were generated. Immunofluorescence staining, quantitative real time PCR (qRT-PCR), Western blotting, cell counting kit-8 (CCK-8), flow cytometry, phalloidine staining, organ bath study, gel contraction assay, protein stability analysis, isolation and extraction of nuclear protein and cytoplasmic protein were performed.

RESULTS

In this study we found that RhoA was localized in prostate stroma and epithelial compartments and was up-regulated in both BPH patients and BPH rats. Functionally, RhoA knockdown induced cell apoptosis and inhibited cell proliferation, fibrosis, epithelial-mesenchymal transformation (EMT) and contraction. Consistently, overexpression of RhoA reversed all aforementioned processes. More importantly, we found that β-catenin and the downstream of Wnt/β-catenin signaling, including C-MYC, Survivin and Snail were up-regulated in BPH rats. Downregulation of RhoA significantly reduced the expression of these proteins. Rho kinase inhibitor Y-27632 also down-regulated β-catenin protein in a concentration-dependent manner. However, overexpression of β-catenin did not affect RhoA-ROCK levels, suggesting that β-catenin was the downstream of RhoA-ROCK regulation. Further data suggested that RhoA increased nuclear translocation of β-catenin and up-regulated β-catenin expression by inhibiting its proteasomal degradation, thereby activating Wnt/β-catenin signaling. Overexpression of β-catenin partially reversed the changes in cell growth, fibrosis and EMT except cell contraction caused by RhoA downregulation. Finally, Y-27632 partially reversed prostatic hyperplasia in vivo, further suggesting the potential of RhoA-ROCK signaling in BPH treatment.

CONCLUSION

Our novel data demonstrated that RhoA regulated both static and dynamic factors of BPH, RhoA-ROCK-β-catenin signaling axis played an important role in the development of BPH and might provide more possibilities for the formulation of subsequent clinical treatment strategies.

Small GTPases and Their Regulators: A Leading Road toward Blood Vessel Development in Zebrafish

Members of the Ras superfamily have been found to perform several functions leading to the development of eukaryotes. These small GTPases are divided into five major subfamilies, and their regulators can “turn on” and “turn off” signals. Recent studies have shown that this superfamily of proteins has various roles in the process of vascular development, such as vasculogenesis and angiogenesis. Here, we discuss the role of these subfamilies in the development of the vascular system in zebrafish.

Use of melatonin as an inhibitor of apoptotic process for cryopreservation of zebrafish (Danio rerio) embryos

This study investigated the use of melatonin to arrest the effects of apoptosis in vitrified zebrafish (D. rerio) embryos. Dechorionated embryos at 22-24 somite-stage were divided (n = 60/treatment) into a non-vitrified (Control Group, 0 M melatonin) and vitrified treatments with 0 M (T1), 1 µM (T2) and 1 mM of melatonin (T3). For vitrified treatments, a solution methanol/propylene glycol based was used and the embryos stored in -196 °C for a week. After thaw, survival rate, scanning electron microscopy, expression of anti (bcl-2) and pro-apoptotic (bax/caspase-3) genes, reactive oxygen species (ROS) formation and DNA fragmentation analyses were performed. No live embryos were obtained from vitrified treatments, observing a rapid degeneration immediately after thawing, with the vitelline layer rupture and leakage of its content, followed by breakdown of epithelial cells and melanisation of the tissue. Regarding the apoptotic process, T3 had the highest relative gene expression, for the three genes (P < 0.05) furthermore, T2 had similar expression of pro-apoptotic genes to CG (P < 0.05). ROS formation revealed that CG presented lower percentage of embryo surface area affected (3.80 ± 0.40%) (P < 0.05), in contrast, no differences were found among the other groups. T1 was most significantly (P < 0.05) damaged by DNA fragmentation. The vitrified groups with melatonin had similar damage levels of CG (P > 0.05). The inclusion of 1 µM of melatonin in the vitrifying solution, countered the effects of apoptotic process in post-thaw embryos, suggesting its utility in cryopreserving fish embryos.

Rho GTPases Signaling in Zebrafish Development and Disease

Cells encounter countless external cues and the specificity of their responses is translated through a myriad of tightly regulated intracellular signals. For this, Rho GTPases play a central role and transduce signals that contribute to fundamental cell dynamic and survival events. Here, we review our knowledge on how zebrafish helped us understand the role of some of these proteins in a multitude of in vivo cellular behaviors. Zebrafish studies offer a unique opportunity to explore the role and more specifically the spatial and temporal dynamic of Rho GTPases activities within a complex environment at a level of details unachievable in any other vertebrate organism.

Influence of ARHGAP29 on the Invasion of Mesenchymal-Transformed Breast Cancer Cells

Aggressive and mesenchymal-transformed breast cancer cells show high expression levels of Rho GTPase activating protein 29 (ARHGAP29), a negative regulator of RhoA. ARHGAP29 was the only one of 32 GTPase-activating enzymes whose expression significantly increased after the induction of mesenchymal transformation in breast cancer cells. Therefore, we investigated the influence of ARHGAP29 on the invasiveness of aggressive and mesenchymal-transformed breast cancer cells. After knock-down of ARHGAP29 using siRNA, invasion of HCC1806, MCF-7-EMT, and T-47D-EMT breast cancer cells was significantly reduced. This could be explained by reduced inhibition of RhoA and a consequent increase in stress fiber formation. Proliferation of the breast cancer cell line T-47D-EMT was slightly increased by reduced expression of ARHGAP29, whereas that of HCC1806 and MCF-7-EMT significantly increased. Using interaction analyses we found that AKT1 is a possible interaction partner of ARHGAP29. Therefore, the expression of AKT1 after siRNA knock-down of ARHGAP29 was tested. Reduced ARHGAP29 expression was accompanied by significantly reduced AKT1 expression. However, the ratio of active pAKT1 to total AKT1 remained unchanged or was significantly increased after ARHGAP29 knock-down. Our results show that ARHGAP29 could be an important factor in the invasion of aggressive and mesenchymal-transformed breast cancer cells. Further research is required to fully understand the underlying mechanisms.

Sphingosine 1-phosphate but not Fingolimod protects neurons against excitotoxic cell death by inducing neurotrophic gene expression in astrocytes

Sphingosine 1-phosphate (S1P) is an essential lipid metabolite that signals through a family of five G protein-coupled receptors, S1PR1-S1PR5, to regulate cell physiology. The multiple sclerosis drug Fingolimod (FTY720) is a potent S1P receptor agonist that causes peripheral lymphopenia. Recent research has demonstrated direct neuroprotective properties of FTY720 in several neurodegenerative paradigms; however, neuroprotective properties of the native ligand S1P have not been established. We aimed to establish the significance of neurotrophic factor up-regulation by S1P for neuroprotection, comparing S1P with FTY720. S1P induced brain-derived neurotrophic factor (BDNF), leukemia inhibitory factor (LIF), platelet-derived growth factor B (PDGFB), and heparin-binding EGF-like growth factor (HBEGF) gene expression in primary human and murine astrocytes, but not in neurons, and to a much greater extent than FTY720. Accordingly, S1P but not FTY720 protected cultured neurons against excitotoxic cell death in a primary murine neuron-glia coculture model, and a neutralizing antibody to LIF blocked this S1P-mediated neuroprotection. Antagonists of S1PR1 and S1PR2 both inhibited S1P-mediated neurotrophic gene induction in human astrocytes, indicating that simultaneous activation of both receptors is required. S1PR2 signaling was transduced through Gα₁₃ and the small GTPase Rho, and was necessary for the up-regulation and activation of the transcription factors FOS and JUN, which regulate LIF, BDNF, and HBEGF transcription. In summary, we show that S1P protects hippocampal neurons against excitotoxic cell death through up-regulation of neurotrophic gene expression, particularly LIF, in astrocytes. This up-regulation requires both S1PR1 and S1PR2 signaling. FTY720 does not activate S1PR2, explaining its relative inefficacy compared to S1P.

Pseudomonas aeruginosa ExoS Induces Intrinsic Apoptosis in Target Host Cells in a Manner That is Dependent on its GAP Domain Activity

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes serious infections in immunocompromised individuals and cystic fibrosis patients. ExoS and ExoT are two homologous bifunctional Type III Secretion System (T3SS) virulence factors that induce apoptosis in target host cells. They possess a GTPase Activating Protein (GAP) domain at their N-termini, which share ~76% homology, and an ADP-ribosyltransferase (ADPRT) domain at their C-termini, which target non-overlapping substrates. Both the GAP and the ADPRT domains contribute to ExoT's cytotoxicity in target epithelial cells, whereas, ExoS-induced apoptosis is reported to be primarily due to its ADPRT domain. In this report, we demonstrate that ExoS/GAP domain is both necessary and sufficient to induce mitochondrial apoptosis. Our data demonstrate that intoxication with ExoS/GAP domain leads to enrichment of Bax and Bim into the mitochondrial outer-membrane, disruption of mitochondrial membrane and release of and cytochrome c into the cytosol, which activates initiator caspase-9 and effector caspase-3, that executes cellular death. We posit that the contribution of the GAP domain in ExoS-induced apoptosis was overlooked in prior studies due to its slower kinetics of cytotoxicity as compared to ADPRT. Our data clarify the field and reveal a novel virulence function for ExoS/GAP as an inducer of apoptosis.

TNF-stimulated gene 6 promotes formation of hyaluronan-inter-α-inhibitor heavy chain complexes necessary for ozone-induced airway hyperresponsiveness

Exposure to pollutants, such as ozone, exacerbates airway inflammation and hyperresponsiveness (AHR). TNF-stimulated gene 6 (TSG-6) is required to transfer inter-α-inhibitor heavy chains (HC) to hyaluronan (HA), facilitating HA receptor binding. TSG-6 is necessary for AHR in allergic asthma, because it facilitates the development of a pathological HA-HC matrix. However, the role of TSG-6 in acute airway inflammation is not well understood. Here, we hypothesized that TSG-6 is essential for the development of HA- and ozone-induced AHR. TSG-6^-/- and TSG-6^+/+ mice were exposed to ozone or short-fragment HA (sHA), and AHR was assayed via flexiVent. The AHR response to sHA was evaluated in the isolated tracheal ring assay in tracheal rings from TSG-6^-/- or TSG-6^+/+, with or without the addition of exogenous TSG-6, and with or without inhibitors of Rho-associated, coiled-coil-containing protein kinase (ROCK), ERK, or PI3K. Smooth-muscle cells from mouse tracheas were assayed in vitro for signaling pathways. We found that TSG-6 deficiency protects against AHR after ozone (in vivo) or sHA (in vitro and in vivo) exposure. Moreover, TSG-6^-/- tracheal ring non-responsiveness to sHA was reversed by exogenous TSG-6 addition. sHA rapidly activated RhoA, ERK, and Akt in airway smooth-muscle cells, but only in the presence of TSG-6. Inhibition of ROCK, ERK, or PI3K/Akt blocked sHA/TSG-6-mediated AHR. In conclusion, TSG-6 is necessary for AHR in response to ozone or sHA, in part because it facilitates rapid formation of HA-HC complexes. The sHA/TSG-6 effect is mediated by RhoA, ERK, and PI3K/Akt signaling.

Genetic variants in RhoA and ROCK1 genes are associated with the development, progression and prognosis of prostate cancer

The contribution of genetic variants in RhoA and ROCK1 genes towards prostate cancer risk has not been reported before. We genotyped six potentially functional genetic variants in a case-control study of 1699 subjects. Overall, we found rs2410 mutant allele and rs2269736 wild allele were risk factors for prostate cancer. Individuals carrying more than two risk alleles were exposed to hazard of prostate cancer. In addition, we demonstrated that the risk of biochemical recurrence might be linked with clinico-pathological characteristics and also genetic factors. Unfortunately, no associations were observed between all polymorphisms and clinico-pathological characteristics. Moreover, no genotype was found as significant independent prognostic predictor for biochemical recurrence survival in Multivariate Cox regression analysis after Bonferroni correction. Our study is the first to clarify the relations of genetic variants of RhoA and ROCK1 genes with development, progression and prognosis of prostate cancer. These variants may be promising novel biomarkers to facilitate clinical treatment decision-making.

Integrin α8 and Pcdh15 act as a complex to regulate cilia biogenesis in sensory cells

The way an organism perceives its surroundings depends on sensory systems and the highly specialized cilia present in the neurosensory cells. Here, we describe the existence of an integrin α8 (Itga8) and protocadherin-15a (Pcdh15a) ciliary complex in neuromast hair cells in a zebrafish model. Depletion of the complex via downregulation or loss-of-function mutation leads to a dysregulation of cilia biogenesis and endocytosis. At the molecular level, removal of the complex blocks the access of Rab8a into the cilia as well as normal recruitment of ciliary cargo by centriolar satellites. These defects can be reversed by the introduction of a constitutively active form of Rhoa, suggesting that Itga8-Pcdh15a complex mediates its effect through the activation of this small GTPase and probably by the regulation of actin cytoskeleton dynamics. Our data points to a novel mechanism involved in the regulation of sensory cilia development, with the corresponding implications for normal sensory function.

A GAL4-inducible transgenic tool kit for the in vivo modulation of Rho GTPase activity in zebrafish

BACKGROUND

Rho GTPases are small monomeric G-proteins that play key roles in many cellular processes. Due to Rho GTPases' widespread expression and broad functions, analyses of their function during late development require tissue-specific modulation of activity. The GAL4/UAS system provides an excellent tool for investigating the function of Rho GTPases in vivo. With this in mind, we created a transgenic tool kit enabling spatial and temporal modulation of Rho GTPase activity in zebrafish.

RESULTS

Transgenic constructs were assembled driving dominant-negative, constitutively active, and wild-type versions of Cdc42, RhoA, and Rac1 under 10XUAS control. The self-cleaving viral peptide F2A was utilized to allow bicistronic expression of a fluorescent reporter and Rho GTPase. Global heat shock of hsp70l:gal4(+) transgenic embryos confirmed GAL4-specific construct expression. Western blot analysis indicated myc-tagged Rho GTPases were expressed only in the presence of GAL4. Construct expression was confined to proper cells when combined with pou4f3:gal4 or ptf1a:gal4. Finally, transgene expression resulted in reproducible defects in lens formation, indicating that the transgenes are functional in vivo.

CONCLUSIONS

We generated and validated 10 transgenic lines, creating a versatile tool kit for the temporal-spatial modulation of Cdc42, RhoA, and Rac1 activity in vivo. These lines will enable systematic analysis of Rho GTPase function in any tissue of interest. Developmental Dynamics 245:844-853, 2016. © 2016 Wiley Periodicals, Inc.

Pseudomonas aeruginosa ExoT Induces Mitochondrial Apoptosis in Target Host Cells in a Manner That Depends on Its GTPase-activating Protein (GAP) Domain Activity

Pseudomonas aeruginosa is the most common cause of hospital-acquired pneumonia and a killer of immunocompromised patients. We and others have demonstrated that the type III secretion system (T3SS) effector protein ExoT plays a pivotal role in facilitating P. aeruginosa pathogenesis. ExoT possesses an N-terminal GTPase-activating protein (GAP) domain and a C-terminal ADP-ribosyltransferase (ADPRT) domain. Because it targets multiple non-overlapping cellular targets, ExoT performs several distinct virulence functions for P. aeruginosa, including induction of apoptosis in a variety of target host cells. Both the ADPRT and the GAP domain activities contribute to ExoT-induced apoptosis. The ADPRT domain of ExoT induces atypical anoikis by transforming an innocuous cellular protein, Crk, into a cytotoxin, which interferes with integrin survival signaling. However, the mechanism underlying the GAP-induced apoptosis remains unknown. In this study, we demonstrate that the GAP domain activity is both necessary and sufficient to induce mitochondrial (intrinsic) apoptosis. We show that intoxication with GAP domain results in: (i) JNK1/2 activation; (ii) substantial increases in the mitochondrial levels of activated pro-apoptotic proteins Bax and Bid, and to a lesser extent Bim; (iii) loss of mitochondrial membrane potential and cytochrome c release; and (iv) activation of initiator caspase-9 and executioner caspase-3. Further, GAP-induced apoptosis is partially mediated by JNK1/2, but it is completely dependent on caspase-9 activity. Together, the ADPRT and the GAP domains make ExoT into a highly versatile and potent cytotoxin, capable of inducing multiple forms of apoptosis in target host cells.

Spatiotemporal 16p11.2 protein network implicates cortical late mid-fetal brain development and KCTD13-Cul3-RhoA pathway in psychiatric diseases

The psychiatric disorders autism and schizophrenia have a strong genetic component, and copy number variants (CNVs) are firmly implicated. Recurrent deletions and duplications of chromosome 16p11.2 confer a high risk for both diseases, but the pathways disrupted by this CNV are poorly defined. Here we investigate the dynamics of the 16p11.2 network by integrating physical interactions of 16p11.2 proteins with spatiotemporal gene expression from the developing human brain. We observe profound changes in protein interaction networks throughout different stages of brain development and/or in different brain regions. We identify the late mid-fetal period of cortical development as most critical for establishing the connectivity of 16p11.2 proteins with their co-expressed partners. Furthermore, our results suggest that the regulation of the KCTD13-Cul3-RhoA pathway in layer 4 of the inner cortical plate is crucial for controlling brain size and connectivity and that its dysregulation by de novo mutations may be a potential determinant of 16p11.2 CNV deletion and duplication phenotypes.

Pseudomonas aeruginosa exotoxin T induces potent cytotoxicity against a variety of murine and human cancer cell lines

In patients with malignancy, the major barrier to achieving complete response is emergence of resistance to current chemotherapeutic agents. One of the major mechanisms by which tumour cells become resistant to therapies is by altering cellular drug targets through mutations and/or deletions. Resistance by this mechanism is achieved more easily if the drug has limited cellular targets and/or processes. We hypothesized that as Pseudomonas aeruginosa exotoxin T (ExoT) targets six proteins that are required for cancer cell survival and proliferation, it is highly unlikely for cancer cells to develop resistance to this toxin. We assessed ExoT's cytotoxicity against multiple invasive and highly resistant tumour cell lines in order to evaluate its potential as a chemotherapeutic agent. Our data demonstrated that ExoT induced potent cytotoxicity in all tumour cell lines that we examined. Collectively, our data highlighted the potential of ExoT as a possible chemotherapeutic candidate for the treatment of cancer.

DEPDC1B coordinates de-adhesion events and cell-cycle progression at mitosis

Cells entering mitosis become rounded, lose attachment to the substrate, and increase their cortical rigidity. Pivotal to these events is the dismantling of focal adhesions (FAs). How mitotic reshaping is linked to commitment to divide is unclear. Here, we show that DEPDC1B, a protein that accumulates in G2, coordinates de-adhesion events and cell-cycle progression at mitosis. DEPDC1B functions as an inhibitor of a RhoA-based signaling complex, which assembles on the FA-associated protein tyrosine phosphatase, receptor type, F (PTPRF) and mediates the integrity of FAs. By competing with RhoA for the interaction with PTPRF, DEPDC1B promotes the dismantling of FAs, which is necessary for the morphological changes preceding mitosis. The circuitry is relevant in whole organisms, as shown by the control exerted by the DEPDC1B/RhoA/PTPRF axis on mitotic dynamics during zebrafish development. Our results uncover an adhesion-dependent signaling mechanism that coordinates adhesion events with the control of cell-cycle progression.

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DEPDC1B is a cell-cycle gene involved in the transition from G2 phase to mitosis

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Persistent adhesion at G2 phase delays CycB/CDK1 activation and G2/M transition

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DEPDC1B controls RhoA/ROCK-dependent adhesion dynamics at G2 phase

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DEPDC1B inhibits RhoA activation by displacing it from the PTPRF/GEF-H1 complex

Human Kidney Disease-causing INF2 Mutations Perturb Rho/Dia Signaling in the Glomerulus

Mutations in Inverted Formin 2 (INF2), a diaphanous formin family protein that regulates actin cytoskeleton dynamics, cause focal segmental glomerulosclerosis (FSGS) and Charcot-Marie-Tooth Disease (CMT) in humans. In addition to directly remodeling actin filaments in vitro, we have shown that INF2 regulates intracellular actin dynamics and actin dependent cellular behavior by opposing Rhoa/Dia signaling. As a step towards a better understanding of the human kidney disease, we wanted to explore the relevance of these findings to the in vivo situation. We used dose dependent knockdown of INF2 to first define an in vivo model and establish an overt glomerular phenotype in zebrafish. This simple assay was validated by rescue with wild type INF2 confirming the specificity of the findings. The edema, podocyte dysfunction, and an altered glomerular filtration barrier observed in the zebrafish pronephros correlate with mistrafficking of glomerular slit diaphragm proteins, defective slit-diaphragm signaling, and disinhibited diaphanous formin (mDia) activity. In contrast to wild-type human INF2, INF2 mutants associated with kidney disease fail to rescue the zINF2 morphant phenotype. Of particular interest, this INF2 knockdown phenotype is also rescued by loss of either RhoA or Dia2. This simple assay allows the demonstration that INF2 functions, at least in part, to modulate Dia-mediated Rho signaling, and that disease causing mutations specifically impair this regulatory function. These data support a model in which disease-associated diaphanous inhibitory domain (DID) mutants in INF2 interfere with its binding to and inhibition of Dia, leading to uncontrolled Rho/Dia signaling and perturbed actin dynamics. Methods to fine tune Rho signaling in the glomerulus may lead to new approaches to therapy in humans.

Developmental processes regulated by the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) pathway: highlights from animal studies

The 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) is the rate-limiting enzyme in the biosynthesis of cholesterol and isoprenoids, which are substrates required for post-translational modification of signalling proteins that can potentially regulate various aspects of embryonic development. The HMGCR transcripts are detectable during early embryogenesis in both invertebrates and vertebrates, which suggests a conserved developmental requirement for mevalonate derivatives. Consistently, recent animal and in vitro studies have yielded valuable insights into potential morphogenic parameters that are modulated by HMGCR activity. These developmental end-points include brain and craniofacial morphogenesis, PGC migration and survival, myocardial epithelial migration and fusion, EC migration and survival, and vascular stabilization. By providing a synthesis of these studies, we hope that this review will highlight the need to comprehensively examine the entire suite of developmental processes regulated by HMGCR.

Increased cytoplasmic localization of p27(kip1) and its modulation of RhoA activity during progression of chronic myeloid leukemia

The role of p27^kip1 in Chronic Myeloid Leukemia (CML) has been well studied in relation to its function as a cell cycle inhibitor. However, its cytoplasmic function especially in CML remains to be seen. We studied the localization of p27^kip1 and its function during the progression of CML from chronic to blast phase. Our investigations revealed an increased localization of p27^kip1 in the cytoplasm of CD34⁺ cells in the blast phase compared to chronic phase. Cytoplasmic p27^kip1 was found to modulate RhoA activity in CD34⁺ stem and progenitor cells. Further, RhoA activity was shown to be dependent on cytoplasmic p27^kip1 which in turn was dependent on p210^Bcr-Abl kinase activity. Interestingly, RhoA activity was observed to affect cell survival in the presence of imatinib through the SAPK/JNK pathway. Accordingly, inhibition of SAPK/JNK pathway using SP600125 increased apoptosis of K562 cells in presence of imatinib. Our results, for the first time, thus reveal a crucial link between cytoplasmic p27^kip1, RhoA activity and SAPK/JNK signalling. To this effect we observed a correlation between increased cytoplasmic p27^kip1, increased RhoA protein levels, decreased RhoA-GTP levels and increased SAPK/JNK phosphorylation in blast phase CD34⁺ cells compared to chronic phase CD34⁺ cells.

Crosstalk of Ras and Rho: activation of RhoA abates Kras-induced liver tumorigenesis in transgenic zebrafish models

RAS and Rho small GTPases are key molecular switches that control cell dynamics, cell growth and tissue development through their distinct signaling pathways. Although much has been learnt about their individual functions in both cell and animal models, the physiological and pathophysiological consequences of their signaling crosstalk in multi-cellular context in vivo remain largely unknown, especially in liver development and liver tumorigenesis. Furthermore, the roles of RhoA in RAS-mediated transformation and their crosstalk in vitro remain highly controversial. When challenged with carcinogens, zebrafish developed liver cancer that resembles the human liver cancer both molecularly and histopathologically. Capitalizing on the growing importance and relevance of zebrafish (Danio rerio) as an alternate cancer model, we have generated liver-specific, Tet-on-inducible transgenic lines expressing oncogenic Kras(G12V), RhoA, constitutively active RhoA(G14V) or dominant-negative RhoA(T19N). Double-transgenic lines expressing Kras(G12V) with one of the three RhoA genes were also generated. Based on quantitative bioimaging and molecular markers for genetic and signaling aberrations, we showed that the induced expression of oncogenic Kras during early development led to liver enlargement and hepatocyte proliferation, associated with elevated Erk phosphorylation, activation of Akt2 and modulation of its two downstream targets, p21Cip and S6 kinase. Such an increase in liver size and Akt2 expression was augmented by dominant-negative RhoA(T19N), but was abrogated by the constitutive-active RhoA(G14V). Consequently, induced expression of the oncogenic Kras in adult transgenic fish led to the development of hepatocellular carcinomas. Survival studies further revealed that the co-expression of dominant-negative RhoA(T19N) with oncogenic Kras increased the mortality rate compared with the other single or double-transgenic lines. This study provides evidence of the previously unappreciated signaling crosstalk between Kras and RhoA in regulating liver overgrowth and liver tumorigenesis. Our results also implicate that activating Rho could be beneficial to suppress the Kras-induced liver malignancies.

Human height genes and cancer

Body development requires the ability to control cell proliferation and metabolism, together with selective 'invasive' cell migration for organogenesis. These requirements are shared with cancer. Human height-associated loci have been recently identified by genome-wide SNP-association studies. Strikingly, most of the more than 100 genes found associated to height appear linked to neoplastic growth, and impose a higher risk for cancer. Height-associated genes drive the HH/PTCH and BMP/TGFβ pathways, with p53, c-Myc, ERα, HNF4A and SMADs as central network nodes. Genetic analysis of body-size-affecting diseases and evidence from genetically-modified animals support this model. The finding that cancer is deeply linked to normal, body-plan master genes may profoundly affect current paradigms on tumor development.

Contributions of the RhoGEF activity of p210 BCR/ABL to disease progression

We have previously identified a tyrosine kinase-independent, guanine nucleotide exchange factor (GEF) activity that is contained within the region of p210 BCR/ABL that distinguishes it from p190 BCR/ABL. In the current study we have compared the transforming activity of p190 BCR/ABL, p210 BCR/ABL, and a mutant that lacks GEF activity (p210 BCR/ABL(S509A)). In cell-based, ex vivo, and murine bone marrow transplantation assays (BMT) the transforming activity of p210 BCR/ABL(S509A) mimics p190 BCR/ABL, and is distinct from p210 BCR/ABL. Thus, in the BMT assay, the p190 BCR/ABL and p210 BCR/ABL(S509A) transplanted mice exhibit a more rapid onset of disease than mice transplanted with p210 BCR/ABL. The reduced disease latency is associated with erythroid hyperplasia in the absence of anemia, and expansion of the MEP, CMP and GMP populations, producing a phenotype that is similar to acute myeloid leukemia (AML-M6). The disease phenotype is readily transplantable into secondary recipients. This is consistent with ex vivo clonogenicity assays where p210 BCR/ABL preferentially supports the growth of CFU-GM, while p190 BCR/ABL and the mutant preferentially support the growth of BFU-E. These results suggest that the GEF activity that distinguishes p210 BCR/ABL from p190 BCR/ABL actively regulates disease progression.

Involvement of cyclin K posttranscriptional regulation in the formation of Artemia diapause cysts

Background

Artemia eggs tend to develop ovoviviparously to yield nauplius larvae in good rearing conditions; while under adverse situations, they tend to develop oviparously and encysted diapause embryos are formed instead. However, the intrinsic mechanisms regulating this process are not well understood.

Principal Finding

This study has characterized the function of cyclin K, a regulatory subunit of the positive transcription elongation factor b (P-TEFb) in the two different developmental pathways of Artemia. In the diapause-destined embryo, Western blots showed that the cyclin K protein was down-regulated as the embryo entered dormancy and reverted to relatively high levels of expression once development resumed, consistent with the fluctuations in phosphorylation of position 2 serines (Ser2) in the C-terminal domain (CTD) of the largest subunit (Rpb1) of RNA polymerase II (RNAP II). Interestingly, the cyclin K transcript levels remained constant during this process. In vitro translation data indicated that the template activity of cyclin K mRNA stored in the postdiapause cyst was repressed. In addition, in vivo knockdown of cyclin K in developing embryos by RNA interference eliminated phosphorylation of the CTD Ser2 of RNAP II and induced apoptosis by inhibiting the extracellular signal-regulated kinase (ERK) survival signaling pathway.

Conclusions/Significance

Taken together, these findings reveal a role for cyclin K in regulating RNAP II activity during diapause embryo development, which involves the post-transcriptional regulation of cyclin K. In addition, a further role was identified for cyclin K in regulating the control of cell survival during embryogenesis through ERK signaling pathways.

Using zebrafish for studying Rho GTPases signaling in vivo

Rho small GTPases play pivotal roles in a variety of dynamic cellular processes including cytoskeleton rearrangement, cell migration, cell proliferation, cell survival, and gene regulation. However, their functions in vivo are much less understood. Recently, the zebrafish, Danio rerio has emerged as a powerful model organism for developmental and genetic studies. Zebrafish embryos have many unique characteristics, such as optical transparency, external fertilization and development, and amenability for various molecular manipulations including morpholino oligo-mediated gene knockdown, mRNA or DNA overexpression-induced gain of function or rescue, in situ hybridization (ISH) with riboprobes for gene expression, western blot for protein analysis, small-molecule inhibition on signaling pathways, and bioimaging for tracking of molecular events. Taking many of such advantages, we have demonstrated the role of rhoA small GTPase in the control of gastrulation cell movements and cell survival during early zebrafish embryogenesis, linking RhoA functions to at least the noncanonical Wnt, Mek/Erk, and Bcl2 signaling nodes in vivo. Here, we describe the use of such techniques, including gene knockdown by morpholino oligo, functional rescue by mRNA overexpression, microinjection, ISH, western blot analysis and pharmacological inhibition of signaling pathways by small molecule inhibitors, with special considerations on their merits, potential drawbacks, and adaptation which could pave the way to our better understanding of the roles of various classes of small GTPases in regulating cell dynamics and development in vivo.

Proteomic modification in gills and brains of medaka fish (Oryzias melastigma) after exposure to a sodium channel activator neurotoxin, brevetoxin-1

Although brevetoxins (PbTxs) produced by the marine dinoflagellate Karenia brevis are known to be absorbed across gill membranes and exert their acute toxic effects through an ion-channel mediated pathway in neural tissue, the exact biochemical mechanism concerning PbTxs neurotoxicity in neural tissue and gas-exchange organs has not been well elucidated. In this study, we calculated the LC(50) value of PbTx-1 using the medaka fish model, and presented the molecular responses of sub-acute exposure to PbTx-1 with proteomic method. By adopting two-dimensional electrophoresis, the abundances of 14 and 24 proteins were found to be remarkably altered in the gills and brains, respectively, in response to toxin exposure. Thirteen gill and twenty brain proteins were identified using matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry analysis. These proteins could be categorized into diverse functional classes such as cell structure, macromolecule metabolism, signal transduction and neurotransmitter release. These findings can help to elucidate the possible pathways by which aquatic toxins affect marine organisms within target organs.

Inhibition of MLC phosphorylation restricts replication of influenza virus--a mechanism of action for anti-influenza agents

Influenza A viruses are a severe threat worldwide, causing large epidemics that kill thousands every year. Prevention of influenza infection is complicated by continuous viral antigenic changes. Newer anti-influenza agents include MEK/ERK and protein kinase C inhibitors; however, the downstream effectors of these pathways have not been determined. In this study, we identified a common mechanism for the inhibitory effects of a significant group of anti-influenza agents. Our studies showed that influenza infection activates a series of signaling pathways that converge to induce myosin light chain (MLC) phosphorylation and remodeling of the actin cytoskeleton. Inhibiting MLC phosphorylation by blocking RhoA/Rho kinase, phospholipase C/protein kinase C, and HRas/Raf/MEK/ERK pathways with the use of genetic or chemical manipulation leads to the inhibition of influenza proliferation. In contrast, the induction of MLC phosphorylation enhances influenza proliferation, as does activation of the HRas/Raf/MEK/ERK signaling pathway. This effect is attenuated by inhibiting MLC phosphorylation. Additionally, in intracellular trafficking studies, we found that the nuclear export of influenza ribonucleoprotein depends on MLC phosphorylation. Our studies provide evidence that modulation of MLC phosphorylation is an underlying mechanism for the inhibitory effects of many anti-influenza compounds.

Proteome profiles in medaka (Oryzias melastigma) liver and brain experimentally exposed to acute inorganic mercury

Mercury is a widespread and persistent pollutant occurring in a variety of forms in freshwater and marine ecosystems. Using the proteomic approach, this study examined the protein profiles of the medaka (Oryzias melastigma) liver and brain exposed to an acute mercuric chloride (HgCl(2)) concentration (1000μg/L) for 8h. The results showed that acute exposure of medaka to inorganic mercury enhanced metal accumulation in both the liver and brain, and a higher content of mercury was detected in the latter. Comparison of the two-dimensional electrophoresis protein profiles of HgCl(2)-exposed and non-exposed group revealed that altered protein expression was quantitatively detected in 20 spots in the brain and 27 in the liver. The altered protein spots were subjected to matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry analysis, with the resultant identification of 46 proteins. The proteins identified were involved in oxidative stress, cytoskeletonal assembly, signal transduction, protein modification, metabolism and other related functions (e.g. immune response, ionoregulation and transporting), highlighting the fact that inorganic mercury toxicity in fish seems to be complex and diverse. This study provided basic information to aid our understanding of the possible molecular mechanisms of acute inorganic mercury toxicity in aquatic organisms, as well as potential protein biomarker candidates for aquatic environmental monitoring.

Structure based design of a Ca2+-sensitive RhoA protein that controls cell morphology

The Rho proteins are important regulators of cell morphology, and the prototypical protein RhoA is known to regulate contraction, blebbing and bleb retraction. We have identified and experimentally confirmed that RhoA has a binding site for calmodulin, a ubiquitous transducer of the Ca(2+) second messenger. Using structural modeling, a fusion protein was designed wherein RhoA activity was controlled by Ca(2+) via calmodulin. Living cells transfected with this synthetic protein underwent Ca(2+) sensitive and calmodulin-dependent bleb retraction within minutes. Further, the modularity of Ca(2+) signaling was exploited to induce bleb retraction in response to blue light (using channelrhodopsin-2) or exogenous chemicals (with acetylcholine receptor), showing input signal versatility. The widespread use of Ca(2+) signaling in nature suggests that fully exploring its signaling potential may allow powerful applications to other synthetic biological systems.

Inhibition of cGMP phosphodiesterase 5 suppresses matrix metalloproteinase-2 production in pulmonary artery smooth muscles cells

1. It has been shown that the beneficial effects of phosphodiesterase (PDE) 5 inhibition on pulmonary hypertension (PH) are associated with the induction of vascular relaxation and suppression of the proliferation of pulmonary artery smooth muscle cells (PASMC). In the present study, we investigated whether PDE5 inhibition affects the production and/or secretion of matrix metalloproteinases (MMPs) in PASMC, resulting in extracellular matrix remodelling in the pulmonary vasculature and, thus, the development of PH. 2. Primary cultured PASMC were stimulated with endothelin (ET)-1 and MMP-2 production and RhoA activation were then determinded using gelatin zymography and a GTP-bound RhoA assay, respectively. The effects of the selective PDE5 inhibitor sildenafil and subsequent protein kinase G-specific inhibitor Rp-8Br-cGMPs on MMP-2 production and RhoA activation were further exmamined. 3. Endothelin-1 (1-1000 nmol/L) concentration-dependently stimulated MMP-2 production and/or secretion in primary cultured PASMC, with 100 nmol/L ET-1 causing a 2.41-fold increase in MMP-2 production compared with control (P < 0.01). This increase in MMP-2 production was accompanied by RhoA activation, which was abolished by preincubation of cells with 10 micromol/L Y27632, an inhibitor of Rho-associated kinase (ROCK). Furthermore, 10 micromol/L Y27632 abolished the ET-1-induced production of MMP-2. 4. The selective PDE5 inhibitor sildenafil (0.1-1 micromol/L) concentration-dependently reduced the increased MMP-2 production induced by 100 nmol/L ET-1. Specifically, in the presence of 1 micromol/L sildenafil, the 100 nmol/L ET-1-induced increase in MMP-2 production was only increased 1.3-fold over that of the control (P < 0.01 vs 100 nmol/L ET-1-stimulated cells). 5. Suppression of RhoA activation was found to mediate the inhibitory effect of sildenafil on ET-1-induced increases in MMP-2 production. Furthermore, the protein kinase G-specific inhibitor Rp-8Br-cGMPs reversed the inhibitory effects of sildenafil on RhoA activation and MMP-2 production. 6. The results of the present study indicate that PDE5 inhibition suppresses RhoA/ROCK-mediated MMP-2 production by PASMC, which may contribute to the regulation of pulmonary vascular remodelling. Thus, PDE5 inhibition may benefit patients with PH through multiple mechanisms of action.

Ethanol-modulated camouflage response screen in zebrafish uncovers a novel role for cAMP and extracellular signal-regulated kinase signaling in behavioral sensitivity to ethanol

Ethanol, a widely abused substance, elicits evolutionarily conserved behavioral responses in a concentration-dependent manner in vivo. The molecular mechanisms underlying such behavioral sensitivity to ethanol are poorly understood. While locomotor-based behavioral genetic screening is successful in identifying genes in invertebrate models, such complex behavior-based screening has proven difficult for recovering genes in vertebrates. Here we report a novel and tractable ethanol response in zebrafish. Using this ethanol-modulated camouflage response as a screening assay, we have identified a zebrafish mutant named fantasma (fan), which displays reduced behavioral sensitivity to ethanol. Positional cloning reveals that fan encodes type 5 adenylyl cyclase (AC5). fan/ac5 is required to maintain the phosphorylation of extracellular signal-regulated kinase (ERK) in the forebrain structures, including the telencephalon and hypothalamus. Partial inhibition of phosphorylation of ERK in wild-type zebrafish mimics the reduction in sensitivity to stimulatory effects of ethanol observed in the fan mutant, whereas, strikingly, strong inhibition of phosphorylation of ERK renders a stimulatory dose of ethanol sedating. Since previous studies in Drosophila and mice show a role of cAMP signaling in suppressing behavioral sensitivity to ethanol, our findings reveal a novel, isoform-specific role of AC signaling in promoting ethanol sensitivity, and suggest that the phosphorylation level of the downstream effector ERK is a critical "gatekeeper" of behavioral sensitivity to ethanol.

The small GTPase RhoA is crucial for MC3T3-E1 osteoblastic cell survival

Prolongation of cell survival through prevention of apoptosis is considered to be a significant factor leading to anabolic responses in bone. The current studies were carried out to determine the role of the small GTPase, RhoA, in osteoblast apoptosis, since RhoA has been found to be critical for cell survival in other tissues. We investigated the effects of inhibitors and activators of RhoA signaling on osteoblast apoptosis. In addition, we assessed the relationship of this pathway to parathyroid hormone (PTH) effects on apoptotic signaling and cell survival. RhoA is activated by geranylgeranylation, which promotes its membrane anchoring. In serum-starved MC3T3-E1 osteoblastic cells, inhibition of geranylgeranylation with geranylgeranyl transferase I inhibitors increased activity of caspase-3, a component step in the apoptosis cascade, and increased cell death. Dominant negative RhoA and Y27632, an inhibitor of the RhoA effector Rho kinase, also increased caspase-3 activity. A geranylgeranyl group donor, geranylgeraniol, antagonized the effect of the geranylgeranyl transferase I inhibitor GGTI-2166, but could not overcome the effect of the Rho kinase inhibitor. PTH 1-34, a potent anti-apoptotic agent, completely antagonized the stimulatory effects of GGTI-2166, dominant negative RhoA, and Y27632, on caspase-3 activity. The results suggest that RhoA signaling is essential for osteoblastic cell survival but that the survival effects of PTH 1-34 are independent of this pathway.

PHR regulates growth cone pausing at intermediate targets through microtubule disassembly

Axonal growth cones use intermediate targets to navigate in the developing nervous system. Encountering these sites is correlated with growth cone pausing. PHR (Phr1, Esrom, Highwire, RPM-1) is a large neuronal ubiquitin ligase that interacts with multiple signaling pathways. Mouse and zebrafish phr mutants have highly penetrant axon pathfinding defects at intermediate targets. Mouse phr mutants contain excessive microtubules in the growth cone, which has been attributed to upregulation of DLK/p38 signaling. Here, we ask whether this pathway and microtubule misregulation are indeed linked to guidance errors in the vertebrate brain, using the zebrafish. By live imaging, we show that loops form when microtubules retract without depolymerizing. JNK, but not p38, phosphorylation is increased in mutant growth cones. However microtubule looping cannot be suppressed by inhibiting JNK. The phr microtubule defect can be phenocopied by taxol, while microtubule destabilization in vitro using nocodazole prevents loop formation. Acute disruption in vivo with nocodazole suppresses the intermediate target guidance defect. Given that microtubule looping is associated with growth cone pausing, we propose that microtubule disassembly, mediated by PHR, is essential for exiting the paused state at intermediate targets.

Muscarinic receptors prevent oxidative stress-mediated apoptosis induced by domoic acid in mouse cerebellar granule cells

In mouse cerebellar granule neurons (CGNs) low concentrations of domoic acid (DomA) induce apoptotic cell death, which is mediated by oxidative stress; apoptosis is more pronounced in CGNs from Gclm (-/-) mice, which lack the modifier subunit of glutamate cysteine ligase (GCL) and have very low GSH levels. By activating M(3) muscarinic receptors, the cholinergic agonist carbachol inhibits DomA-induced apoptosis, and the anti-apoptotic action of carbachol is more pronounced in CGNs from Gclm (+/+) mice. Carbachol does not prevent DomA-induced increase in reactive oxygen species, suggesting that its anti-apoptotic effect is downstream of reactive oxygen species production. Carbachol inhibits DomA-induced activation of Jun N-terminal (JNK) and p38 kinases, increased translocation to mitochondria of the pro-apoptotic protein Bax, and activation of caspase-3. Carbachol activates extracellular signal-regulated kinases 1/2 (ERK1/2) MAPK and phospahtidylinositol-3 kinase (PI3K) in CGNs from both genotypes. However, while the protective effect of carbachol is mediated by ERK1/2 MAPK in CGNs from both mouse genotypes, inhibitors of PI3K are only effective at antagonizing the action of carbachol in CGNs from Gclm (+/+) mice. In CGNs from both Gclm (+/+) and (-/-) mice, carbachol induces a MAPK-dependent increase in the level of the anti-apoptotic protein Bcl-2. In contrast, carbachol causes a PI3K-dependent increase in GCL activity and of GSH levels only in CGNs from Gclm (+/+) mice. Such increase in GCL is not because of a transcriptionally-mediated increase in glutamate cysteine ligase catalytic subunit or glutamate cysteine ligase modifier subunit, but rather to an increase in the formation of the GCL holoenzyme. The results indicate that multiple pathways may contribute to the protective action of carbachol toward DomA-induced apoptosis. Compromised GCLM expression, which is also found in a common genetic polymorphism in humans, leads to lower GSH levels, which can exacerbate the neurotoxicity of DomA, and decreases the anti-apoptotic effectiveness of muscarinic agonists.

Rho GTPase function in tumorigenesis

Malignant tumor cells display uncontrolled proliferation, loss of epithelial cell polarity, altered interactions with neighboring cells and the surrounding extracellular matrix, and enhanced migratory properties. Proteins of the Rho GTPase family regulate all these processes in cell culture and, for that reason, Rho GTPases, their regulators, and their effectors have been suggested to control tumor formation and progression in humans. However, while the tumor-relevant functions of Rho GTPases are very well documented in vitro, we are only now beginning to assess their contribution to cancer in human patients and in animal models. This review will give a very brief overview of Rho GTPase function in general and then focus on in vivo evidence for a role of Rho GTPases in malignant tumors, both in human patients and in genetically modified mice.

Small molecule modifier screen for kit-dependent functions in zebrafish embryonic melanocytes

Zebrafish is gaining popularity as a vertebrate model for screening small molecules that affect specific phenotypes or genetic pathways. In this study, we present a targeted drug screen to identify drug modifiers of the melanocyte migration defect of a temperature-sensitive allele of the Kit receptor tyrosine kinase, kit(ts). We first test two candidate drugs, the phosphatidylinositol-3-kinase kinase inhibitor (LY294002) and the Erk/MAP kinase inhibitor (PD98059), for their effect on melanocyte migration and survival. We find that LY294002 enhances the migration defect of kit(ts), implicating the phosphatidylinositol-3-kinase kinase pathway in promoting kit-dependent melanocyte migration, but not survival. We then used the kit(ts)-sensitized genetic background to screen a panel of 1280 pharmacologically active drugs to identify drug enhancers and suppressors of the kit(ts) melanocyte migration defect. We identified three drug enhancers of migration, two of which, Papaverine and Isoliquiritigenin, specifically enhance the kit(ts) migration defect, while 8-DPAT affected both melanocyte migration and survival. These drugs now provide additional experimental tools for investigating the mechanisms of kit-promoted melanocyte migration and survival in the zebrafish embryo.

Simulation of crosstalk between small GTPase RhoA and EGFR-ERK signaling pathway via MEKK1

MOTIVATION

Small GTPase RhoA regulates cell-cycle progression via several mechanisms. Apart from its actions via ROCK, RhoA has recently been found to activate a scaffold protein MEKK1 known to promote ERK activation. We examined whether RhoA can substantially affect ERK activity via this MEKK1-mediated crosstalk between RhoA and EGFR-ERK pathway. By extending the published EGFR-ERK simulation models represented by ordinary differential equations, we developed a simulation model that includes this crosstalk, which was validated with a number of experimental findings and published simulation results.

RESULTS

Our simulation suggested that, via this crosstalk, RhoA elevation substantially prolonged duration of ERK activation at both normal and reduced Ras levels. Our model suggests ERK may be activated in the absence of Ras. When Ras is overexpressed, RhoA elevation significantly prolongs duration of ERK activation but reduces the amount of active ERK partly due to competitive binding between ERK and RhoA to MEKK1. Our results indicated possible roles of RhoA in affecting ERK activities via MEKK1-mediated crosstalk, which seems to be supported by indications from several experimental studies that may also implicate the collective regulation of cell fate and progression of cancer and other diseases.