Galectin-8 Promotes Cytoskeletal Rearrangement in Trabecular Meshwork Cells through Activation of Rho Signaling

Purpose

The trabecular meshwork (TM) cell-matrix interactions and factors that influence Rho signaling in TM cells are thought to play a pivotal role in the regulation of aqueous outflow. The current study was designed to evaluate the role of a carbohydrate-binding protein, galectin-8 (Gal8), in TM cell adhesion and Rho signaling.

Methods

Normal human TM cells were assayed for Gal8 expression by immunohistochemistry and Western blot analysis. To assess the role of Gal8 in TM cell adhesion and Rho signaling, the cell adhesion and spreading assays were performed on Gal8-coated culture plates in the presence and the absence of anti-β₁ integrin antibody and Rho and Rho-kinase inhibitors. In addition, the effect of Gal8-mediated cell-matrix interactions on TM cell cytoskeleton arrangement and myosin light chain 2 (MLC2) phosphorylation was examined.

Principal Findings

We demonstrate here that Gal8 is expressed in the TM and a function-blocking anti-β₁ integrin antibody inhibits the adhesion and spreading of TM cells to Gal8-coated wells. Cell spreading on Gal8 substratum was associated with the accumulation of phosphorylated myosin light chain and the formation of stress fibers that was inhibited by the Rho inhibitor, C3 transferase, as well as by the Rho-kinase inhibitor, Y27632.

Conclusions/Significance

The above findings present a novel function for Gal8 in activating Rho signaling in TM cells. This function may allow Gal8 to participate in the regulation of aqueous outflow.     

Microtubules Regulate Localization and Availability of Insulin Granules in Pancreatic Beta Cells

Two key prerequisites for glucose-stimulated insulin secretion (GSIS) in β cells are the proximity of insulin granules to the plasma membrane and their anchoring or docking to the plasma membrane (PM). Although recent evidence has indicated that both of these factors are altered in the context of diabetes, it is unclear what regulates localization of insulin granules and their interactions with the PM within single cells. Here, we demonstrate that microtubule (MT)-motor-mediated transport dynamics have a critical role in regulating both factors. Super-resolution imaging shows that whereas the MT cytoskeleton resembles a random meshwork in the cells’ interior, MTs near the cell surface are preferentially aligned with the PM. Computational modeling suggests two consequences of this alignment. First, this structured MT network preferentially withdraws granules from the PM. Second, the binding and transport of insulin granules by MT motors prevents their stable anchoring to the PM. These findings suggest the MT cytoskeleton may negatively regulate GSIS by both limiting the amount of insulin proximal to the PM and preventing or breaking interactions between the PM and the remaining nearby insulin granules. These results predict that altering MT network structure in β cells can be used to tune GSIS. Thus, our study points to the potential of an alternative therapeutic strategy for diabetes by targeting specific MT regulators.     

MiR-124 Promote Neurogenic Transdifferentiation of Adipose Derived Mesenchymal Stromal Cells Partly through RhoA/ROCK1, but Not ROCK2 Signaling Pathway

Objective

Some recent studies suggest that multiple miRNAs might regulate neurogenic transdifferentiation of mesenchymal stromal cells (MSCs). In the present study, we hypothesized that the miR-124 can repress the expression of RhoA upon the neurogenesis of adipose derived MSCs (ADMSCs).

Methods

MiRNA expression dynamics during neurogenic transdifferentiation of ADMSCs were measured. The expression of neuron-specific enolase (NSE), Tuj-1 (Neuron-specific class III beta-tubulin) and glial fibrillary acidic protein (GFAP), as well as electrophysiological properties, were detected after neurogenic transdifferentiation. The targeting of miR-124 over RhoA was verified by dual luciferase assay, qRT-PCR and western blot. The functions of miR-124 and the RhoA/ROCK signaling pathway were studied using gain and loss of function experiments in vitro.

Results

MiR-124 is significantly upregulated during neurogenic transdifferentiation of ADMSCs. Knockdown of endogenous miR-124 hampered neurogenic transdifferentiation and the acquired electrophysiological properties. MiR-124 could directly target RHOA mRNA and repress its expression, through which it increased the proportion of transdifferentiated (transdiff.) cells with positive NSE, Tuj-1 and GFAP. RhoA/ROCK1, but not ROCK2 is a downstream signaling pathway of miR-124 in the process of transdifferentiation.

Conclusion

MiR-124 is an important miRNA modulating neurogenic transdifferentiation of ADMSCs at least partly via the miR-124/RhoA/ROCK1 signaling pathway. These findings provided some fundamental information for future use of ADMSCs as an agent for regenerative medicine and cell therapy for neurological diseases.     

Signaling Pathways in Cell Polarity

A key function of signal transduction during cell polarization is the creation of spatially segregated regions of the cell cortex that possess different lipid and protein compositions and have distinct functions. Polarity can be initiated spontaneously or in response to signaling inputs from adjacent cells or soluble factors and is stabilized by positive-feedback loops. A conserved group of proteins, the Par proteins, plays a central role in polarity establishment and maintenance in many contexts. These proteins generate and maintain their distinct locations in cells by actively excluding one another from specific regions of the plasma membrane. The Par signaling pathway intersects with multiple other pathways that control cell growth, death, and organization.     

Rho/ROCK信号通路与神经可塑性

在神经网络中,神经可塑性是大脑响应内在和外在刺激的重要特征。越来越多的研究已经阐明了神经可塑性与神经损伤性疾病之间的相关性。Rho/Rho相关卷曲螺旋形成蛋白激酶(Rho/Rho associ-ated coiledcoil forming protein kinase, Rho/ROCK)通路是生物体广泛存在的经典信号通路,参与细胞迁移、树突发育和轴突延伸,并且与帕金森、精神发育迟滞和阿尔茨海默症等多种神经退行性或损伤性疾病有关。本文对Rho/ROCK信号通路与神经可塑性的研究进展予以综述,讨论了ROCK抑制剂对各种神经疾病的潜在治疗前景。     

雄激素通过雄激素受体途径调控垂体肿瘤转化基因(PTTG1)的表达

雄激素能上调大鼠前列腺中垂体肿瘤转化基因1(PTTG1)的表达,在前列腺癌标本中,发现PTTG1的表达明显高于正常组织.因此,用雄激素依赖的前列腺癌细胞LNCaP来研究雄激素调控PTTG1表达的分子机制.在LNCaP细胞中,通过雄激素刺激后,PTTG1的表达明显升高.根据序列分析以及5-缺失体实验(deletion)和突变实验(mutation),发现PTTG1的启动子上游-950到-933的序列上有1个雄激素受体反应元件(ARE),染色体免疫共沉淀实验(CHIP)也证实了雄激素能促进雄激素受体与PTTG1启动子上ARE结合,从而在转录水平调控PTTG1的表达.     

Brassinosteroids Regulate Plant Growth through Distinct Signaling Pathways in Selaginella and Arabidopsis

Brassinosteroids (BRs) are growth-promoting steroid hormones that regulate diverse physiological processes in plants. Most BR biosynthetic enzymes belong to the cytochrome P450 (CYP) family. The gene encoding the ultimate step of BR biosynthesis in Arabidopsis likely evolved by gene duplication followed by functional specialization in a dicotyledonous plant-specific manner. To gain insight into the evolution of BRs, we performed a genomic reconstitution of Arabidopsis BR biosynthetic genes in an ancestral vascular plant, the lycophyte Selaginella moellendorffii. Selaginella contains four members of the CYP90 family that cluster together in the CYP85 clan. Similar to known BR biosynthetic genes, the Selaginella CYP90s exhibit eight or ten exons and Selaginella produces a putative BR biosynthetic intermediate. Therefore, we hypothesized that Selaginella CYP90 genes encode BR biosynthetic enzymes. In contrast to typical CYPs in Arabidopsis, Selaginella CYP90E2 and CYP90F1 do not possess amino-terminal signal peptides, suggesting that they do not localize to the endoplasmic reticulum. In addition, one of the three putative CYP reductases (CPRs) that is required for CYP enzyme function co-localized with CYP90E2 and CYP90F1. Treatments with a BR biosynthetic inhibitor, propiconazole, and epi-brassinolide resulted in greatly retarded and increased growth, respectively. This suggests that BRs promote growth in Selaginella, as they do in Arabidopsis. However, BR signaling occurs through different pathways than in Arabidopsis. A sequence homologous to the Arabidopsis BR receptor BRI1 was absent in Selaginella, but downstream components, including BIN2, BSU1, and BZR1, were present. Thus, the mechanism that initiates BR signaling in Selaginella seems to differ from that in Arabidopsis. Our findings suggest that the basic physiological roles of BRs as growth-promoting hormones are conserved in both lycophytes and Arabidopsis; however, different BR molecules and BRI1-based membrane receptor complexes evolved in these plants.     

Reduced Expression of Galectin-9 Contributes to a Poor Outcome in Colon Cancer by Inhibiting NK Cell Chemotaxis Partially through the Rho/ROCK1 Signaling Pathway

Galectin-9 is a widely expressed protein that is involved in immune regulation and tumorpathogenesis and serves as a marker of a poor prognosis in various types of cancers. However, the clinical impact and the precise mechanism by which this protein contributes to colon tumor progression are unclear. In the present study, we detected the expression of galectin-9 and CD56 cells using immunohistochemistry. Spearman''s rank correlation was used to clarify the association between galectin-9 expression and natural killer (NK) cell infiltration. The influence of galectin-9 on NK-92 cell migration was evaluated in vitro using transwell chemotaxis assays. The role of rh-galectin-9 in F-actin polarization in NK-92 cells was investigated using laser scanning confocal microscopy. We showed that galectin-9 was expressed in 101 (78.91%) colon tumor tissues and that was expressed at lower levels in these tissues than in para-tumor tissues. Low levels of galectin-9 expression were positively correlated with a poor histological grade and lymph node metastasis (P<0.05). A Kaplan-Meier method and Cox proportional hazards regression analysis showed that overall survival was longer in patients with high galectin-9 expression in an 8-year follow-up (P<0.05). Spearman''s rank correlation indicated that there was a linear correlation between galectin-9 expression and CD56⁺ NK cell infiltration (R² = 0.658; P<0.0001). Galectin-9 stimulated migration in human NK-92 cells by affecting F-actin polarization through the Rho/ROCK1 signaling pathway. These results suggest that galectin-9 expression potentially represents a novel mechanism for tumors to escape immune surveillance in colon tumors.     

Tetramethylpyrazine Protects Against Oxygen-Glucose Deprivation-Induced Brain Microvascular Endothelial Cells Injury via Rho/Rho-kinase Signaling Pathway

Tetramethylpyrazine (TMP, also known as Ligustrazine), which is isolated from Chinese Herb Medicine Ligustium wollichii Franchat (Chuan Xiong), has been widely used in China for the treatment of ischemic stroke by Chinese herbalists. Brain microvascular endothelial cells (BMECs) are the integral parts of the blood–brain barrier (BBB), protecting BMECs against oxygen-glucose deprivation (OGD) which is important for the treatment of ischemic stroke. Here, we investigated the protective mechanisms of TMP, focusing on OGD-injured BMECs and the Rho/Rho-kinase (Rho-associated kinases, ROCK) signaling pathway. The model of OGD-injured BMECs was established in this study. BMECs were identified by von Willebrand factor III staining and exposed to fasudil, or TMP at different concentrations (14.3, 28.6, 57.3 µM) for 2 h before 24 h of OGD injury. The effect of each treatment was examined by cell viability assays, measurement of intracellular reactive oxygen species (ROS), and transendothelial electric resistance and western blot analysis (caspase-3, endothelial nitric oxide synthase (eNOS), RhoA, Rac1). Our results show that TMP significantly attenuated apoptosis and the permeability of BMECs induced by OGD. In addition, TMP could notably down-regulate the characteristic proteins in Rho/ROCK signaling pathway such as RhoA and Rac1, which triggered abnormal changes of eNOS and ROS, respectively. Altogether, our results show that TMP has a strong protective effect against OGD-induced BMECs injury and suggest that the mechanism might be related to the inhibition of the Rho/ROCK signaling pathway.     

Enhanced Neurite Outgrowth of Human Model (NT2) Neurons by Small-Molecule Inhibitors of Rho/ROCK Signaling

Axonal injury in the adult human central nervous system often results in loss of sensation and motor functions. Promoting regeneration of severed axons requires the inactivation of growth inhibitory influences from the tissue environment and stimulation of the neuron intrinsic growth potential. Especially glial cell derived factors, such as chondroitin sulfate proteoglycans, Nogo-A, myelin-associated glycoprotein, and myelin in general, prevent axon regeneration. Most of the glial growth inhibiting factors converge onto the Rho/ROCK signaling pathway in neurons. Although conditions in the injured nervous system are clearly different from those during neurite outgrowth in vitro, here we use a chemical approach to manipulate Rho/ROCK signalling with small-molecule agents to encourage neurite outgrowth in cell culture. The development of therapeutic treatments requires drug testing not only on neurons of experimental animals, but also on human neurons. Using human NT2 model neurons, we demonstrate that the pain reliever Ibuprofen decreases RhoA (Ras homolog gene family, member A GTPase) activation and promotes neurite growth. Inhibition of the downstream effector Rho kinase by the drug Y-27632 results in a strong increase in neurite outgrowth. Conversely, activation of the Rho pathway by lysophosphatidic acid results in growth cone collapse and eventually to neurite retraction. Finally, we show that blocking of Rho kinase, but not RhoA results in an increase in neurons bearing neurites. Due to its anti-inflammatory and neurite growth promoting action, the use of a pharmacological treatment of damaged neural tissue with Ibuprofen should be explored.     

Wnt-signaling mediates the anti-adipogenic action of lysophosphatidic acid through cross talking with the Rho/Rho associated kinase (ROCK) pathway

Lysophosphatidic acid (LPA) is a bioactive phospholipid with a diverse range of biological activities including the modulation of adipogenesis. Treatment of 3T3-L1 cells and 3T3F44A cells with LPA inhibits adipogenesis and reduces expression of PPARγ through activation of RhoGTPase and its downstream Rho associated kinase (ROCK). The mechanism of suppression of PPARγ expression by Rho/ROCK is poorly understood. By treating the differentiating 3T3-L1 cells with various combinations of LPA and ROCK inhibitors, Y-27632 and fasudil, we observed that LPA treatment resulted in attenuation of adipogenesis and a significant reduction in PPARγ mRNA as early as 3?d post-induction. LPA treatment also resulted in significant but delayed upregulation of components of the canonical Wnt signaling, namely Wnt10b mRNA, β-catenin protein, and mRNA expression of β-catenin target genes, detectable at day 7, but not day 3. Treatment of the 3T3-L1 cells with ROCK inhibitors Y-27632 and fasudil revealed a tonic activation of β-catenin/target genes by ROCK. This study identified the existence of a novel cross talk between the Rho/ROCK pathway and the Wnt-signaling pathway. The LPA/Rho/ROCK pathway inhibits expression of PPARγ and adipogenesis in part through a delayed activation of the canonical Wnt-signaling pathway based on increased Wnt10b expression and β-catenin induction.     

Involvement of Rho/ROCK signalling in small cell lung cancer migration through human brain microvascular endothelial cells

Small cell lung cancer (SCLC) cells migration across human brain microvascular endothelial cells (HBMECs) is an essential step of brain metastases. Here we investigated signalling pathways in HBMECs contributing to the process. Inhibition of endothelial Rho kinase (ROCK) with Y27632 and overexpression of ROCK dominant-negative mutant prevented SCLC cells, NCI-H209, transendothelial migration and the concomitant changes of tight junction. Conversely, inhibition of phosphatidylinositol 3-kinase (PI3K) and protein kinase C (PKC) had no effects. Furthermore, endothelial RhoA protein was activated during NCI-H209 cells transendothelial migration. Rho/ROCK participated in NCI-H209 cells transendothelial migration through regulating actin cytoskeleton reorganization. These results suggested that Rho/ROCK was required for SCLC cells transendothelial migration.     

Roles for Rho/ROCK and vinculin in parietal endoderm migration

The first cell migration event in the mouse embryo is the movement of parietal endoderm cells from the surface of the inner cell mass facing the blastocoel cavity to line the inner surface of the trophectoderm. F9 embryoid bodies provide an in vitro model for this event. They have an inner core of undifferentiated stem cells surrounded by an outer visceral endoderm layer. When plated on a laminin coated substrate, visceral endoderm transitions to parietal endoderm and migrates onto the dish, away from the attached embryoid body. We now show that this outgrowth contains abundant focal complexes and focal adhesions, as well as lamellipodia and filopodia. Treatment with the ROCK inhibitor Y-27632 promotes a 2-fold increase in outgrowth, and a transition from focal adhesions and associated stress fibers, to focal complexes and a decrease in stress fibers. ROCK inhibition also leads to an increase in lamellipodia. Inhibition of RhoA by transfection of a vector encoding C3 transferase, direct administration of the C3 enzyme, or transfection of a vector encoding p190 Rho GTPase Activating Protein also promotes outgrowth and an apparent transition from focal adhesions to focal complexes. Parietal endoderm outgrowth generated using vinculin-deficient F9 stem cells migrates 2-fold further than wild type cultures, but this outgrowth retains the morphology of wild type parietal endoderm, including focal adhesions and stress fibers. Addition of Y-27632 to vinculin-null outgrowth cultures further stimulates migration an additional 2-fold, supporting the conclusion that Rho/ROCK and vinculin regulate parietal endoderm outgrowth by distinct pathways.     

Roles for Rho/ROCK and Vinculin in Parietal Endoderm Migration

The first cell migration event in the mouse embryo is the movement of parietal endoderm cells from the surface of the inner cell mass facing the blastocoel cavity to line the inner surface of the trophectoderm. F9 embryoid bodies provide an in vitro model for this event. They have an inner core of undifferentiated stem cells surrounded by an outer visceral endoderm layer. When plated on a laminin coated substrate, visceral endoderm transitions to parietal endoderm and migrates onto the dish, away from the attached embryoid body. We now show that this outgrowth contains abundant focal complexes and focal adhesions, as well as lamellipodia and filopodia. Treatment with the ROCK inhibitor Y-27632 promotes a 2-fold increase in outgrowth, and a transition from focal adhesions and associated stress fibers, to focal complexes and a decrease in stress fibers. ROCK inhibition also leads to an increase in lamellipodia. Inhibition of RhoA by transfection of a vector encoding C3 transferase, direct administration of the C3 enzyme, or transfection of a vector encoding p190 Rho GTPase Activating Protein also promotes outgrowth and an apparent transition from focal adhesions to focal complexes. Parietal endoderm outgrowth generated using vinculin-deficient F9 stem cells migrates 2-fold further than wild type cultures, but this outgrowth retains the morphology of wild type parietal endoderm, including focal adhesions and stress fibers. Addition of Y-27632 to vinculin-null outgrowth cultures further stimulates migration an additional 2-fold, supporting the conclusion that Rho/ROCK and vinculin regulate parietal endoderm outgrowth by distinct pathways.     

Post-translational Glycoprotein Modifications Regulate Colon Cancer Stem Cells and Colon Adenoma Progression in Apcmin/+ Mice through Altered Wnt Receptor Signaling

Deletion of GnT-V (MGAT5), which synthesizes N-glycans with β(1,6)-branched glycans, reduced the compartment of cancer stem cells (CSC) in the her-2 mouse model of breast cancer, leading to delay of tumor onset. Because GnT-V levels are also commonly up-regulated in colon cancer, we investigated their regulation of colon CSC and adenoma development. Anchorage-independent cell growth and tumor formation induced by injection of colon tumor cells into NOD/SCID mice were positively associated with GnT-V levels, indicating regulation of proliferation and tumorigenicity. Using Apc^min/+ mice with different GnT-V backgrounds, knock-out of GnT-V had no significant effect on the number of adenoma/mouse, but adenoma size was significantly reduced and accompanied increased survival of Apc^min/+ mice with GnT-V deletion (p < 0.01), suggesting an inhibition in the progression of colon adenoma caused by deletion of GnT-V. Decreased expression levels of GnT-V down-regulated the population of colon (intestine) CSC, affecting their ability for self-renewal and tumorigenicity in NOD/SCID mice. Furthermore, altered nuclear translocation of β-catenin and expression of Wnt target genes were positively associated with expression levels of GnT-V, indicating the regulation of canonical Wnt/β-catenin signaling. By overexpressing the Wnt receptor, FZD-7, in colon cancer cells, we found that FZD-7 receptors expressed N-linked β(1,6) branching, indicating that FZD-7 can be modified by GnT-V. The aberrant Wnt signaling observed after modulating GnT-V levels is likely to result from altered N-linked β(1,6) branching on FZD-7, thereby affecting Wnt signaling, the compartment of CSC, and tumor progression.