The Rho-associated protein kinase p160ROCK is required for centrosome positioning

Inhibition of microRNA-34c reduces detrusor ROCK2 expression and urinary bladder inflammation in experimental cystitis

Interstitial cystitis (IC), also called painful bladder syndrome (PBS), is 2 to 5 times more common in women than in men, yet its cause and pathogenesis remain unclear. In our study using the cyclophosphamide (CYP)-induced mouse model of cystitis, histological evaluation of the urinary bladder (UB) lamina propria (LP) showed immune cell infiltrations, indicating moderate to severe inflammation. In this study, we noticed a differential expression of a subset of microRNAs (miRs) in the UB cells (UBs) of CYP-induced cystitis as compared to the control. UB inflammatory scores and inflammatory signaling were also elevated in CYP-induced cystitis as compared to control. We identified eight UBs miRs that exhibited altered expression after CYP induction and are predicted to have a role in inflammation and smooth muscle function (miRs-34c-5p, -34b-3p, -212-3p, -449a-5p, -21a-3p, -376b-3p, -376b-5p and - 409-5p). Further analysis using ELISA for inflammatory markers and real-time PCR (RT-PCR) for differentially enriched miRs identified miR-34c as a potential target for the suppression of UB inflammation in cystitis. Blocking miR-34c by antagomir ex vivo reduced STAT3, TGF-β1, and VEGF expression in the UBs, which was induced during cystitis as compared to control. Interestingly, miR-34c inhibition also downregulated ROCK2 but elevated ROCK1 expression in bladder and detrusor cells. Thus, the present study shows that targeting miR-34c can mitigate the STAT3, TGF-β, and VEGF, inflammatory signaling in UB, and suppress ROCK2 expression in UBs to effectively suppress the inflammatory response in cystitis. This study highlights miR-34c as a potential biomarker and/or serves as the basis for new therapies for the treatment of cystitis.

Inhibitors of Rho kinases (ROCK) induce multiple mitotic defects and synthetic lethality in BRCA2-deficient cells

The trapping of Poly-ADP-ribose polymerase (PARP) on DNA caused by PARP inhibitors (PARPi) triggers acute DNA replication stress and synthetic lethality (SL) in BRCA2-deficient cells. Hence, DNA damage is accepted as a prerequisite for SL in BRCA2-deficient cells. In contrast, here we show that inhibiting ROCK in BRCA2-deficient cells triggers SL independently from acute replication stress. Such SL is preceded by polyploidy and binucleation resulting from cytokinesis failure. Such initial mitosis abnormalities are followed by other M phase defects, including anaphase bridges and abnormal mitotic figures associated with multipolar spindles, supernumerary centrosomes and multinucleation. SL was also triggered by inhibiting Citron Rho-interacting kinase, another enzyme that, similarly to ROCK, regulates cytokinesis. Together, these observations demonstrate that cytokinesis failure triggers mitotic abnormalities and SL in BRCA2-deficient cells. Furthermore, the prevention of mitotic entry by depletion of Early mitotic inhibitor 1 (EMI1) augmented the survival of BRCA2-deficient cells treated with ROCK inhibitors, thus reinforcing the association between M phase and cell death in BRCA2-deficient cells. This novel SL differs from the one triggered by PARPi and uncovers mitosis as an Achilles heel of BRCA2-deficient cells.

Actin network architecture can ensure robust centering or sensitive decentering of the centrosome

The orientation of cell polarity depends on the position of the centrosome, the main microtubule-organizing center (MTOC). Microtubules (MTs) transmit pushing forces to the MTOC as they grow against the cell periphery. How the actin network regulates these forces remains unclear. Here, in a cell-free assay, we used purified proteins to reconstitute the interaction of a microtubule aster with actin networks of various architectures in cell-sized microwells. In the absence of actin filaments, MTOC positioning was highly sensitive to variations in microtubule length. The presence of a bulk actin network limited microtubule displacement, and MTOCs were held in place. In contrast, the assembly of a branched actin network along the well edges centered the MTOCs by maintaining an isotropic balance of pushing forces. An anisotropic peripheral actin network caused the MTOC to decenter by focusing the pushing forces. Overall, our results show that actin networks can limit the sensitivity of MTOC positioning to microtubule length and enforce robust MTOC centering or decentering depending on the isotropy of its architecture.

Belumosudil, ROCK2-Specific Inhibitor, alleviates cardiac fibrosis by inhibiting cardiac fibroblasts activation

Cardiac fibrosis is thought to be the hallmark of pathological hypertrophic remodeling, of which the myofibroblasts transdifferentiation is the key cell biological event. However, there is still no specific and effective therapeutic agent approved for cardiac fibrosis. To investigate the effects of Belumosudil, the first ROCK2-specific inhibitor, on cardiac hypertrophy, fibrosis and dysfunction induced by pressure overload, the transverse aortic constriction (TAC) or sham operation was carried out on wild-type C57BL/6 mice (male, 6-8 week old) under pentobarbital anesthesia. After that, mice were randomly divided into three groups: sham operation + vehicle, TAC + vehicle, TAC + 50 mg·kg^-1·d^-1 Belumosudil. We found that Belumosudil effectively ameliorated cardiac hypertrophy, fibrosis and dysfunction in TAC mice. To elucidate the underlying mechanism, we inhibited the expression of ROCK2 in vitro by either Belumosudil or siRNA. We showed that the inhibition of ROCK2 by either Belumosudil or knockdown suppressed cardiac fibroblasts activation and proliferation significantly induced by Transforming Growth Factor-β1 (TGF-β1). Furthermore, our study confirmed ROCK2 mediates cardiac fibrosis by interacting with Transforming Growth Factor-β1 (TGF-β1)/mothers against decapentaplegic homolog (Smad2) pathway. Taken together, we demonstrated that Belumosudil ameliorates cardiac hypertrophy and fibrosis induced by TAC via inhibiting cardiac fibroblasts activation. In conclusion, Belumosudil may be a promising therapeutic drug for cardiac hypertrophy and fibrosis induced by myocardial pressure overload.

The Outcomes of Small-Molecule Kinase Inhibitors and the Role of ROCK2 as a Molecular Target for the Treatment of Alzheimer's Disease

BACKGROUND

Alzheimer's disease is rapidly becoming a major threat to public health, with an increasing number of individuals affected as the world's population ages. In this sense, studies have been carried out aiming at the identification of new small-molecule kinase inhibitors useful for the treatment of Alzheimer's disease.

OBJECTIVE

In the present study, we investigated the compounds developed as inhibitors of different protein kinases associated with the pathogenesis of Alzheimer's disease.

METHODS

The applied methodology was the use of the Clarivate Analytics Integrity and ClinicalTrials. com databases. Moreover, we highlight ROCK2 as a promising target despite being little studied for this purpose. A careful structure-activity relationship analysis of the ROCK2 inhibitors was performed to identify important structural features and fragments for the interaction with the kinase active site, aiming to rationally design novel potent and selective inhibitors.

RESULTS

We were able to notice some structural characteristics that could serve as the basis to better guide the rational design of new ROCK2 inhibitors as well as some more in-depth characteristics regarding the topology of the active site of both isoforms of these enzymes, thereby identifying differences that could lead to planning more selective compounds.

CONCLUSION

We hope that this work can be useful to update researchers working in this area, enabling the emergence of new ideas and a greater direction of efforts for designing new ROCK2 inhibitors to identify new therapeutic alternatives for Alzheimer's disease.

RhoGTPase Signalling in Cancer Progression and Dissemination

Rho GTPases are a family of small G proteins that regulate a wide array of cellular processes related to their key roles controlling the cytoskeleton. On the other hand, cancer is a multi-step disease caused by the accumulation of genetic mutations and epigenetic alterations, from the initial stages of cancer development when cells in normal tissues undergo transformation, to the acquisition of invasive and metastatic traits, responsible for a large number of cancer related deaths. In this review, we discuss the role of Rho GTPase signalling in cancer in every step of disease progression. Rho GTPases contribute to tumour initiation and progression, by regulating proliferation and apoptosis, but also metabolism, senescence and cell stemness. Rho GTPases play a major role in cell migration, and in the metastatic process. They are also involved in interactions with the tumour microenvironment and regulate inflammation, contributing to cancer progression. After years of intensive research, we highlight the importance of relevant models in the Rho GTPase field, and we reflect on the therapeutic opportunities arising for cancer patients.

Bone fracture healing: perspectives according to molecular basis

Fractures have a great impact on health all around the world and with fracture healing optimization; this problem could be resolved partially. To make a practical contribution to this issue, the knowledge of bone tissue, cellularity, and metabolism is essential, especially cytoskeletal architecture and its transformations according to external pressures. Special physical and chemical characteristics of the extracellular matrix (ECM) allow the transmission of mechanical stimuli from outside the cell to the plasmatic membrane. The osteocyte cytoskeleton is conformed by a complex network of actin and microtubules combined with crosslinker proteins like vinculin and fimbrin, connecting and transmitting outside stimuli through EMC to cytoplasm. Herein, critical signaling pathways like Cx43-depending ones, MAPK/ERK, Wnt, YAP/TAZ, Rho-ROCK, and others are activated due to mechanical stimuli, resulting in osteocyte cytoskeletal changes and ECM remodeling, altering the tissue and, therefore, the bone. In recent years, the osteocyte has gained more interest and value in relation to bone homeostasis as a great coordinator of other cell populations, thanks to its unique functions. By integrating the latest advances in relation to intracellular signaling pathways, mechanotransmission system of the osteocyte and bone tissue engineering, there are promising experimental strategies, while some are ready for clinical trials. This work aims to show clearly and precisely the integration between cytoskeleton and main molecular pathways in relation to mechanotransmission mechanism in osteocytes, and the use of this theoretical knowledge in therapeutic tools for bone fracture healing.

Rocking the Boat: The Decisive Roles of Rho Kinases During Oocyte, Blastocyst, and Stem Cell Development

The rho-associated coiled-coil-containing proteins (ROCKs or rho kinase) are effectors of the small rho-GTPase rhoA, which acts as a signaling molecule to regulate a variety of cellular processes, including cell proliferation, adhesion, polarity, cytokinesis, and survival. Owing to the multifunctionality of these kinases, an increasing number of studies focus on understanding the pleiotropic effects of the ROCK signaling pathway in the coordination and control of growth (proliferation, initiation, and progression), development (morphology and differentiation), and survival in many cell types. There is growing evidence that ROCKs actively phosphorylate several actin-binding proteins and intermediate filament proteins during oocyte cytokinesis, the preimplantation embryos as well as the stem cell development and differentiation. In this review, we focus on the participation of ROCK proteins in oocyte maturation, blastocyst formation, and stem cell development with a special focus on the selective targeting of ROCK isoforms, ROCK1, and ROCK2. The selective switching of cell fate through ROCK inhibition would provide a novel paradigm for in vitro oocyte maturation, experimental embryology, and clinical applications.

Polycystin-1 regulates ARHGAP35-dependent centrosomal RhoA activation and ROCK signaling

Mutations in PKD1 (encoding for polycystin-1 [PC1]) are found in 80%–85% of patients with autosomal dominant polycystic kidney disease (ADPKD). We tested the hypothesis that changes in actin dynamics result from PKD1 mutations through dysregulation of compartmentalized centrosomal RhoA signaling mediated by specific RhoGAP (ARHGAP) proteins resulting in the complex cellular cystic phenotype. Initial studies revealed that the actin cytoskeleton was highly disorganized in cystic cells derived from patients with PKD1 and was associated with an increase in total and centrosomal active RhoA and ROCK signaling. Using cilia length as a phenotypic readout for centrosomal RhoA activity, we identified ARHGAP5, -29, and -35 as essential regulators of ciliation in normal human renal tubular cells. Importantly, a specific decrease in centrosomal ARHGAP35 was observed in PKD1-null cells using a centrosome-targeted proximity ligation assay and by dual immunofluorescence labeling. Finally, the ROCK inhibitor hydroxyfasudil reduced cyst expansion in both human PKD1 3D cyst assays and an inducible Pkd1 mouse model. In summary, we report a potentially novel interaction between PC1 and ARHGAP35 in the regulation of centrosomal RhoA activation and ROCK signaling. Targeting the RhoA/ROCK pathway inhibited cyst formation in vitro and in vivo, indicating its relevance to ADPKD pathogenesis and for developing new therapies to inhibit cyst initiation.

Polycystin-1, the major protein mutated in autosomal dominant polycystic kidney disease, activates centrosomal RhoA activity via interaction with the Rho-GAP protein ARHGAP35, resulting in shorter cilia.

Druggable targets in the Rho pathway and their promise for therapeutic control of blood pressure

The prevalence of high blood pressure (also known as hypertension) has steadily increased over the last few decades. Known as a silent killer, hypertension increases the risk for cardiovascular disease and can lead to stroke, heart attack, kidney failure and associated sequela. While numerous hypertensive therapies are currently available, it is estimated that only half of medicated patients exhibit blood pressure control. This signifies the need for a better understanding of the underlying cause of disease and for more effective therapies. While blood pressure homeostasis is very complex and involves the integrated control of multiple body systems, smooth muscle contractility and arterial resistance are important contributors. Strong evidence from pre-clinical animal models and genome-wide association studies indicate that smooth muscle contraction and BP homeostasis are governed by the small GTPase RhoA and its downstream target, Rho kinase. In this review, we summarize the signaling pathways and regulators that impart tight spatial-temporal control of RhoA activity in smooth muscle cells and discuss current therapeutic strategies to target these RhoA pathway components. We also discuss known allelic variations in the RhoA pathway and consider how these polymorphisms may affect genetic risk for hypertension and its clinical manifestations.

Cell polarity: having and making sense of direction-on the evolutionary significance of the primary cilium/centrosome organ in Metazoa

Cell-autonomous polarity in Metazoans is evolutionarily conserved. I assume that permanent polarity in unicellular eukaryotes is required for cell motion and sensory reception, integration of these two activities being an evolutionarily constrained function. Metazoans are unique in making cohesive multicellular organisms through complete cell divisions. They evolved a primary cilium/centrosome (PC/C) organ, ensuring similar functions to the basal body/flagellum of unicellular eukaryotes, but in different cells, or in the same cell at different moments. The possibility that this innovation contributed to the evolution of individuality, in being instrumental in the early specification of the germ line during development, is further discussed. Then, using the example of highly regenerative organisms like planarians, which have lost PC/C organ in dividing cells, I discuss the possibility that part of the remodelling necessary to reach a new higher-level unit of selection in multi-cellular organisms has been triggered by conflicts among individual cell polarities to reach an organismic polarity. Finally, I briefly consider organisms with a sensorimotor organ like the brain that requires exceedingly elongated polarized cells for its activity. I conclude that beyond critical consequences for embryo development, the conservation of cell-autonomous polarity in Metazoans had far-reaching implications for the evolution of individuality.

A High-Resolution Proteomic Landscaping of Primary Human Dental Stem Cells: Identification of SHED- and PDLSC-Specific Biomarkers

Dental stem cells (DSCs) have emerged as a promising tool for basic research and clinical practice. A variety of adult stem cell (ASC) populations can be isolated from different areas within the dental tissue, which, due to their cellular and molecular characteristics, could give rise to different outcomes when used in potential applications. In this study, we performed a high-throughput molecular comparison of two primary human adult dental stem cell (hADSC) sub-populations: Stem Cells from Human Exfoliated Deciduous Teeth (SHEDs) and Periodontal Ligament Stem Cells (PDLSCs). A detailed proteomic mapping of SHEDs and PDLSCs, via employment of nano-LC tandem-mass spectrometry (MS/MS) revealed 2032 identified proteins in SHEDs and 3235 in PDLSCs. In total, 1516 proteins were expressed in both populations, while 517 were unique for SHEDs and 1721 were exclusively expressed in PDLSCs. Further analysis of the recorded proteins suggested that SHEDs predominantly expressed molecules that are involved in organizing the cytoskeletal network, cellular migration and adhesion, whereas PDLSCs are highly energy-producing cells, vastly expressing proteins that are implicated in various aspects of cell metabolism and proliferation. Applying the Rho-GDI signaling pathway as a paradigm, we propose potential biomarkers for SHEDs and for PDLSCs, reflecting their unique features, properties and engaged molecular pathways.

ROCK as a therapeutic target for ischemic stroke

INTRODUCTION

Stroke is a major cause of disability and the fifth leading cause of death. Currently, the only approved acute medical treatment of ischemic stroke is tissue plasminogen activator (tPA), but its effectiveness is greatly predicated upon early administration of the drug. There is, therefore, an urgent need to find new therapeutic options for acute stroke. Areas covered: In this review, we summarize the role of Rho-associated coiled-coil containing kinase (ROCK) and its potential as a therapeutic target in stroke pathophysiology. ROCK is a major regulator of cell contractility, motility, and proliferation. Many of these ROCK-mediated processes in endothelial cells, vascular smooth muscle cells, pericytes, astrocytes, glia, neurons, leukocytes, and platelets are important in stroke pathophysiology, and the inhibition of such processes could improve stroke outcome. Expert commentary: ROCK is a potential therapeutic target for cardiovascular disease and ROCK inhibitors have already been approved for human use in Japan and China for the treatment of acute stroke. Further studies are needed to determine the role of ROCK isoforms in the pathophysiology of cerebral ischemia and whether there are further therapeutic benefits with selective ROCK inhibitors.

The Centrosome as the Main Integrator of Endothelial Cell Functional Activity

The centrosome is an intracellular structure of the animal cell responsible for organization of cytoplasmic microtubules. According to modern concepts, the centrosome is a very important integral element of the living cell whose functions are not limited to its ability to polymerize microtubules. The centrosome localization in the geometric center of the interphase cell, the high concentration of various regulatory proteins in this area, the centrosome-organized radial system of microtubules for intracellular transport by motor proteins, the centrosome involvement in the perception of external signals and their transmission - all these features make this cellular structure a unique regulation and distribution center managing dynamic morphology of the animal cell. In conjunction with the tissue-specific features of the centrosome structure, this suggests the direct involvement of the centrosome in execution of cell functions. This review discusses the involvement of the centrosome in the vital activity of endothelial cells, as well as its possible participation in the implementation of barrier function, the major function of endothelium.

Advances in pancreatic islet monolayer culture on glass surfaces enable super-resolution microscopy and insights into beta cell ciliogenesis and proliferation

A robust and reproducible method for culturing monolayers of adherent and well-spread primary islet cells on glass coverslips is required for detailed imaging studies by super-resolution and live-cell microscopy. Guided by an observation that dispersed islet cells spread and adhere well on glass surfaces in neuronal co-culture and form a monolayer of connected cells, we demonstrate that in the absence of neurons, well-defined surface coatings combined with components of neuronal culture media collectively support robust attachment and growth of primary human or rat islet cells as monolayers on glass surfaces. The islet cell monolayer cultures on glass stably maintain distinct mono-hormonal insulin+, glucagon+, somatostatin+ and PP+ cells and glucose-responsive synchronized calcium signaling as well as expression of the transcription factors Pdx-1 and NKX-6.1 in beta cells. This technical advance enabled detailed observation of sub-cellular processes in primary human and rat beta cells by super-resolution microscopy. The protocol is envisaged to have broad applicability to sophisticated analyses of pancreatic islet cells that reveal new biological insights, as demonstrated by the identification of an in vitro protocol that markedly increases proliferation of primary beta cells and is associated with a reduction in ciliated, ostensibly proliferation-suppressed beta cells.

Functions of Rho family of small GTPases and Rho-associated coiled-coil kinases in bone cells during differentiation and mineralization

BACKGROUND

Members of Rho-associated coiled-coil kinases (ROCKs) are effectors of Rho family of small GTPases. ROCKs have multiple functions that include regulation of cellular contraction and polarity, adhesion, motility, proliferation, apoptosis, differentiation, maturation and remodeling of the extracellular matrix (ECM).

SCOPE OF THE REVIEW

Here, we focus on the action of RhoA and RhoA effectors, ROCK1 and ROCK2, in cells related to tissue mineralization: mesenchymal stem cells, chondrocytes, preosteoblasts, osteoblasts, osteocytes, lining cells and osteoclasts.

MAJOR CONCLUSIONS

The activation of the RhoA/ROCK pathway promotes stress fiber formation and reduces chondrocyte and osteogenic differentiations, in contrast to that in mesenchymal stem cells which stimulated the osteogenic and the chondrogenic differentiation. The effects of Rac1 and Cdc42 in promoting chondrocyte hypertrophy and of Rac1, Rac2 and Cdc42 in osteoclast are discussed. In addition, members of the Rho family of GTPases such Rac1, Rac2, Rac3 and Cdc42, acting upstream of ROCK and/or other protein effectors, may compensate the actions of RhoA, affecting directly or indirectly the actions of ROCKs as well as other protein effectors.

GENERAL SIGNIFICANCE

ROCK activity can trigger cartilage degradation and affect bone formation, therefore these kinases may represent a possible therapeutic target to treat osteoarthritis and osseous diseases. Inhibition of Rho/ROCK activity in chondrocytes prevents cartilage degradation, stimulate mineralization of osteoblasts and facilitate bone formation around implanted metals. Treatment with osteoprotegerin results in a significant decrease in the expression of Rho GTPases, ROCK1 and ROCK2, reducing bone resorption. Inhibition of ROCK signaling increases osteoblast differentiation in a topography-dependent manner.

Rho Kinases in Health and Disease: From Basic Science to Translational Research

Rho-associated kinases ROCK1 and ROCK2 are key regulators of actin cytoskeleton dynamics downstream of Rho GTPases that participate in the control of important physiologic functions, S including cell contraction, migration, proliferation, adhesion, and inflammation. Several excellent review articles dealing with ROCK function and regulation have been published over the past few years. Although a brief overview of general molecular, biochemical, and functional properties of ROCKs is included, an effort has been made to produce an original work by collecting and synthesizing recent studies aimed at translating basic discoveries from cell and experimental models into knowledge of human physiology, pathophysiological mechanisms, and medical therapeutics. This review points out the specificity and distinct roles of ROCK1 and ROCK2 isoforms highlighted in the last few years. Results obtained from genetically modified mice and genetic analysis in humans are discussed. This review also addresses the involvement of ROCKs in human diseases and the potential use of ROCK activity as a biomarker or a pharmacological target for specific inhibitors.

ROCK2 mediates the proliferation of pulmonary arterial endothelial cells induced by hypoxia in the development of pulmonary arterial hypertension

It has been reported that RhoA activation and Rho-kinase (ROCK) expression are increased in chronic hypoxic lungs, and the long-term inhibition of ROCK markedly improves the survival of patients with pulmonary arterial hypertension (PAH). However, whether Rho-kinase α (ROCK2) participates in regulation of the growth of pulmonary arterial endothelial cells (PAECs) remains unknown. The aim of the present study was to investigate the effect of hypoxia on the proliferation of PAECs and the role of ROCK2 in the underlying mechanism. The results of western blotting and reverse transcription-quantitative polymerase chain reaction analysis showed that hypoxia increased the activity and expression of ROCK2 in PAECs, and the stimulating effects of hypoxia on the proliferation of PAECs were attenuated by either the ROCK inhibitor Y27632 or transfection with ROCK2 small interfering RNA. Moreover, analysis of cyclin A and cyclin D1 mRNA expression indicated that ROCK2 mediates the cell cycle progression promoted by hypoxia. These results indicate that hypoxia promotes the proliferation of pulmonary arterial endothelial cells via activation of the ROCK2 signaling pathway.

The centrosome is an actin-organizing centre

Microtubules and actin filaments are the two main cytoskeleton networks supporting intracellular architecture and cell polarity. The centrosome nucleates and anchors microtubules and is therefore considered to be the main microtubule-organizing centre. However, recurring, yet unexplained, observations have pointed towards a connection between the centrosome and actin filaments. Here we have used isolated centrosomes to demonstrate that the centrosome can directly promote actin-filament assembly. A cloud of centrosome-associated actin filaments could be identified in living cells as well. Actin-filament nucleation at the centrosome was mediated by the nucleation-promoting factor WASH in combination with the Arp2/3 complex. Pericentriolar material 1 (PCM1) seemed to modulate the centrosomal actin network by regulating Arp2/3 complex and WASH recruitment to the centrosome. Hence, our results reveal an additional facet of the centrosome as an intracellular organizer and provide mechanistic insights into how the centrosome can function as an actin-filament-organizing centre.

The Function of Rho-Associated Kinases ROCK1 and ROCK2 in the Pathogenesis of Cardiovascular Disease

Rho-associated kinases ROCK1 and ROCK2 are serine/threonine kinases that are downstream targets of the small GTPases RhoA, RhoB, and RhoC. ROCKs are involved in diverse cellular activities including actin cytoskeleton organization, cell adhesion and motility, proliferation and apoptosis, remodeling of the extracellular matrix and smooth muscle cell contraction. The role of ROCK1 and ROCK2 has long been considered to be similar; however, it is now clear that they do not always have the same functions. Moreover, depending on their subcellular localization, activation, and other environmental factors, ROCK signaling can have different effects on cellular function. With respect to the heart, findings in isoform-specific knockout mice argue for a role of ROCK1 and ROCK2 in the pathogenesis of cardiac fibrosis and cardiac hypertrophy, respectively. Increased ROCK activity could play a pivotal role in processes leading to cardiovascular diseases such as hypertension, pulmonary hypertension, angina pectoris, vasospastic angina, heart failure, and stroke, and thus ROCK activity is a potential new biomarker for heart disease. Pharmacological ROCK inhibition reduces the enhanced ROCK activity in patients, accompanied with a measurable improvement in medical condition. In this review, we focus on recent findings regarding ROCK signaling in the pathogenesis of cardiovascular disease, with a special focus on differences between ROCK1 and ROCK2 function.

The Rho kinases: critical mediators of multiple profibrotic processes and rational targets for new therapies for pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by progressive lung scarring, short median survival, and limited therapeutic options, creating great need for new pharmacologic therapies. IPF is thought to result from repetitive environmental injury to the lung epithelium, in the context of aberrant host wound healing responses. Tissue responses to injury fundamentally involve reorganization of the actin cytoskeleton of participating cells, including epithelial cells, fibroblasts, endothelial cells, and macrophages. Actin filament assembly and actomyosin contraction are directed by the Rho-associated coiled-coil forming protein kinase (ROCK) family of serine/threonine kinases (ROCK1 and ROCK2). As would therefore be expected, lung ROCK activation has been demonstrated in humans with IPF and in animal models of this disease. ROCK inhibitors can prevent fibrosis in these models, and more importantly, induce the regression of already established fibrosis. Here we review ROCK structure and function, upstream activators and downstream targets of ROCKs in pulmonary fibrosis, contributions of ROCKs to profibrotic cellular responses to lung injury, ROCK inhibitors and their efficacy in animal models of pulmonary fibrosis, and potential toxicities of ROCK inhibitors in humans, as well as involvement of ROCKs in fibrosis in other organs. As we discuss, ROCK activation is required for multiple profibrotic responses, in the lung and multiple other organs, suggesting ROCK participation in fundamental pathways that contribute to the pathogenesis of a broad array of fibrotic diseases. Multiple lines of evidence therefore indicate that ROCK inhibition has great potential to be a powerful therapeutic tool in the treatment of fibrosis, both in the lung and beyond.

Revisiting the tubulin folding pathway: new roles in centrosomes and cilia

Centrosomes and cilia are critical eukaryotic organelles which have been in the spotlight in recent years given their implication in a myriad of cellular and developmental processes. Despite their recognized importance and intense study, there are still many open questions about their biogenesis and function. In the present article, we review the existing data concerning members of the tubulin folding pathway and related proteins, which have been identified at centrosomes and cilia and were shown to have unexpected roles in these structures.

Separate to operate: control of centrosome positioning and separation

The centrosome is the main microtubule (MT)-organizing centre of animal cells. It consists of two centrioles and a multi-layered proteinaceous structure that surrounds the centrioles, the so-called pericentriolar material. Centrosomes promote de novo assembly of MTs and thus play important roles in Golgi organization, cell polarity, cell motility and the organization of the mitotic spindle. To execute these functions, centrosomes have to adopt particular cellular positions. Actin and MT networks and the association of the centrosomes to the nuclear envelope define the correct positioning of the centrosomes. Another important feature of centrosomes is the centrosomal linker that connects the two centrosomes. The centrosome linker assembles in late mitosis/G1 simultaneously with centriole disengagement and is dissolved before or at the beginning of mitosis. Linker dissolution is important for mitotic spindle formation, and its cell cycle timing has profound influences on the execution of mitosis and proficiency of chromosome segregation. In this review, we will focus on the mechanisms of centrosome positioning and separation, and describe their functions and mechanisms in the light of recent findings.

Planar cell polarity aligns osteoblast division in response to substrate strain

Exposure of bone to dynamic strain increases the rate of division of osteoblasts and also influences the directional organization of the cellular and molecular structure of the bone tissue that they produce. Here, we report that brief exposure to dynamic substrate strain (sufficient to rapidly stimulate cell division) influences the orientation of osteoblastic cell division. The initial proliferative response to strain involves canonical Wnt signaling and can be blocked by sclerostin. However, the strain-related orientation of cell division is independently influenced through the noncanonical Wnt/planar cell polarity (PCP) pathway. Blockade of Rho-associated coiled kinase (ROCK), a component of the PCP pathway, prevents strain-related orientation of division in osteoblast-like Saos-2 cells. Heterozygous loop-tail mutation of the core PCP component van Gogh-like 2 (Vangl2) in mouse osteoblasts impairs the orientation of division in response to strain. Examination of bones from Vangl2 loop-tail heterozygous mice by µCT and scanning electron microscopy reveals altered bone architecture and disorganized bone-forming surfaces. Hence, in addition to the well-accepted role of PCP involvement in response to developmental cues during skeletal morphogenesis, our data reveal that this pathway also acts postnatally, in parallel with canonical Wnt signaling, to transduce biomechanical cues into skeletal adaptive responses. The simultaneous and independent actions of these two pathways appear to influence both the rate and orientation of osteoblast division, thus fine-tuning bone architecture to meet the structural demands of functional loading.

Rho-associated coiled-coil containing kinases (ROCK): structure, regulation, and functions

Rho-associated coiled-coil containing kinases (ROCK) were originally identified as effectors of the RhoA small GTPase. (1)(-) (5) They belong to the AGC family of serine/threonine kinases (6) and play vital roles in facilitating actomyosin cytoskeleton contractility downstream of RhoA and RhoC activation. Since their discovery, ROCK kinases have been extensively studied, unveiling their manifold functions in processes including cell contraction, migration, apoptosis, survival, and proliferation. Two mammalian ROCK homologs have been identified, ROCK1 (also called ROCK I, ROKβ, Rho-kinase β, or p160ROCK) and ROCK2 (also known as ROCK II, ROKα, or Rho kinase), hereafter collectively referred to as ROCK. In this review, we will focus on the structure, regulation, and functions of ROCK.

Rho kinases in cardiovascular physiology and pathophysiology: the effect of fasudil

Rho kinase (ROCK) is a major downstream effector of the small GTPase RhoA. ROCK family, consisting of ROCK1 and ROCK2, plays central roles in the organization of actin cytoskeleton and is involved in a wide range of fundamental cellular functions, such as contraction, adhesion, migration, proliferation, and apoptosis. Due to the discovery of effective inhibitors, such as fasudil and Y27632, the biological roles of ROCK have been extensively explored with particular attention on the cardiovascular system. In many preclinical models of cardiovascular diseases, including vasospasm, arteriosclerosis, hypertension, pulmonary hypertension, stroke, ischemia-reperfusion injury, and heart failure, ROCK inhibitors have shown a remarkable efficacy in reducing vascular smooth muscle cell hypercontraction, endothelial dysfunction, inflammatory cell recruitment, vascular remodeling, and cardiac remodeling. Moreover, fasudil has been used in the clinical trials of several cardiovascular diseases. The continuing utilization of available pharmacological inhibitors and the development of more potent or isoform-selective inhibitors in ROCK signaling research and in treating human diseases are escalating. In this review, we discuss the recent molecular, cellular, animal, and clinical studies with a focus on the current understanding of ROCK signaling in cardiovascular physiology and diseases. We particularly note that emerging evidence suggests that selective targeting ROCK isoform based on the disease pathophysiology may represent a novel therapeutic approach for the disease treatment including cardiovascular diseases.

Rho GTPases modulate malignant transformation of tumor cells

Rho GTPases are involved in the acquisition of all the hallmarks of cancer, which comprise 6 biological capabilities acquired during the development of human tumors. The hallmarks include proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, and activating invasion and metastasis programs, as defined by Hanahan and Weinberg. (1) Controlling these hallmarks are genome instability and inflammation. Emerging hallmarks are reprogramming of energy metabolism and evading immune destruction. To give a different view to the readers, we will not be focusing on invasion, metastasis, or cytoskeletal remodeling, but we will review here how Rho GTPases contribute to other hallmarks of cancer with a special emphasis on malignant transformation.

Rho/Rho-associated coiled-coil forming kinase pathway as therapeutic targets for statins in atherosclerosis

SIGNIFICANCE

The 3-hydroxy-methylglutaryl coenzyme A reductase inhibitors or statins are important therapeutic agents for lowering serum cholesterol levels. However, recent studies suggest that statins may exert atheroprotective effects beyond cholesterol lowering. These so-called "pleiotropic effects" include effects of statins on vascular and inflammatory cells. Thus, it is important to understand whether other signaling pathways that are involved in atherosclerosis could be targets of statins, and if so, whether individuals with "overactivity" of these pathways could benefit from statin therapy, regardless of serum cholesterol level.

RECENT ADVANCES

Statins inhibit the synthesis of isoprenoids, which are important for the function of the Rho/Rho-associated coiled-coil containing kinase (ROCK) pathway. Indeed, recent studies suggest that inhibition of the Rho/ROCK pathway by statins could lead to improved endothelial function and decreased vascular inflammation and atherosclerosis. Thus, the Rho/ROCK pathway has emerged as an important target of statin therapy for reducing atherosclerosis and possibly cardiovascular disease.

CRITICAL ISSUES

Because atherosclerosis is both a lipid and an inflammatory disease, it is important to understand how inhibition of Rho/ROCK pathway could contribute to statins' antiatherosclerotic effects.

FUTURE DIRECTIONS

The role of ROCKs (ROCK1 and ROCK2) in endothelial, smooth muscle, and inflammatory cells needs to be determined in the context of atherogenesis. This could lead to the development of specific ROCK1 or ROCK2 inhibitors, which could have greater therapeutic benefits with less toxicity. Also, clinical trials will need to be performed to determine whether inhibition of ROCKs, with and without statins, could lead to further reduction in atherosclerosis and cardiovascular disease.

Rho-GTPase effector ROCK phosphorylates cofilin in actin-meditated cytokinesis during mouse oocyte meiosis

During oocyte meiosis, a spindle forms in the central cytoplasm and migrates to the cortex. Subsequently, the oocyte extrudes a small body and forms a highly polarized egg; this process is regulated primarily by actin. ROCK is a Rho-GTPase effector that is involved in various cellular functions, such as stress fiber formation, cell migration, tumor cell invasion, and cell motility. In this study, we investigated possible roles for ROCK in mouse oocyte meiosis. ROCK was localized around spindles after germinal vesicle breakdown and was colocalized with cytoplasmic actin and mitochondria. Disrupting ROCK activity by RNAi or an inhibitor resulted in cell cycle progression and polar body extrusion failure. Time-lapse microscopy showed that this may have been due to spindle migration and cytokinesis defects, as chromosomes segregated but failed to extrude a polar body and then realigned. Actin expression at oocyte membranes and in cytoplasm was significantly decreased after these treatments. Actin caps were also disrupted, which was confirmed by a failure to form cortical granule-free domains. The mitochondrial distribution was also disrupted, which indicated that mitochondria were involved in the ROCK-mediated actin assembly. In addition, the phosphorylation levels of Cofilin, a downstream molecule of ROCK, decreased after disrupting ROCK activity. Thus, our results indicated that a ROCK-Cofilin-actin pathway regulated meiotic spindle migration and cytokinesis during mouse oocyte maturation.

The Drosophila FHOD1-like formin Knittrig acts through Rok to promote stress fiber formation and directed macrophage migration during the cellular immune response

A tight spatiotemporal control of actin polymerization is important for many cellular processes that shape cells into a multicellular organism. The formation of unbranched F-actin is induced by several members of the formin family. Drosophila encodes six formin genes, representing six of the seven known mammalian subclasses. Knittrig, the Drosophila homolog of mammalian FHOD1, is specifically expressed in the developing central nervous system midline glia, the trachea, the wing and in macrophages. knittrig mutants exhibit mild tracheal defects but survive until late pupal stages and mainly die as pharate adult flies. knittrig mutant macrophages are smaller and show reduced cell spreading and cell migration in in vivo wounding experiments. Rescue experiments further demonstrate a cell-autonomous function of Knittrig in regulating actin dynamics and cell migration. Knittrig localizes at the rear of migrating macrophages in vivo, suggesting a cellular requirement of Knittrig in the retraction of the trailing edge. Supporting this notion, we found that Knittrig is a target of the Rho-dependent kinase Rok. Co-expression with Rok or expression of an activated form of Knittrig induces actin stress fibers in macrophages and in epithelial tissues. Thus, we propose a model in which Rok-induced phosphorylation of residues within the basic region mediates the activation of Knittrig in controlling macrophage migration.

Crucial role of ROCK2 in vascular smooth muscle cells for hypoxia-induced pulmonary hypertension in mice

OBJECTIVE

Rho/Rho-kinase (ROCK) pathway in vascular smooth muscle cells (VSMCs) plays an important role in the pathogenesis of cardiovascular diseases, including pulmonary arterial hypertension (PAH). Rho-kinase has 2 isoforms, ROCK1 and ROCK2, with different functions in different cells; ROCK1 for circulating inflammatory cells and ROCK2 for the vasculature. In the present study, we aimed to examine whether ROCK2 in VSMC is involved in the pathogenesis of PAH.

APPROACH AND RESULTS

In patients with PAH, the expression of ROCK2 was increased in pulmonary arterial media and primary pulmonary arterial smooth muscle cells when compared with controls. To investigate the role of ROCK2 in VSMC, we generated VSMC-specific heterozygous ROCK2-deficient (ROCK2(+/-)) mice and VSMC-specific ROCK2-overexpressing transgenic (ROCK2-Tg) mice. The extent of hypoxia-induced pulmonary hypertension was reduced in ROCK2(+/-) mice and was enhanced in ROCK2-Tg mice compared with respective littermates. The protein expression of ROCK activity and phosphorylated extracellular signal-regulated kinase and the number of Ki67-positive proliferating cells in the lung were reduced in ROCK2(+/-) mice and were increased in ROCK2-Tg mice compared with respective littermates. In cultured mouse aortic VSMC, migration and proliferation activities were reduced in ROCK2(+/-) mice, and migration activity was increased in ROCK2-Tg mice compared with respective littermates. In addition, in primary pulmonary arterial smooth muscle cells from a patient with PAH, ROCK2 was required for migration and proliferation through ROCK and extracellular signal-regulated kinase activation.

CONCLUSIONS

ROCK2 in VSMC contributes to the pathogenesis of PAH.

Rho GTPase-independent regulation of mitotic progression by the RhoGEF Net1

Neuroepithelial transforming gene 1 (Net1) is a RhoA-subfamily-specific guanine nucleotide exchange factor that is overexpressed in multiple human cancers and is required for proliferation. Molecular mechanisms underlying its role in cell proliferation are unknown. Here we show that overexpression or knockdown of Net1 causes mitotic defects. Net1 is required for chromosome congression during metaphase and generation of stable kinetochore microtubule attachments. Accordingly, inhibition of Net1 expression results in spindle assembly checkpoint activation. The ability of Net1 to control mitosis is independent of RhoA or RhoB activation, as knockdown of either GTPase does not phenocopy effects of Net1 knockdown on nuclear morphology, and effects of Net1 knockdown are effectively rescued by expression of catalytically inactive Net1. We also observe that Net1 expression is required for centrosomal activation of p21-activated kinase and its downstream kinase Aurora A, which are critical regulators of centrosome maturation and spindle assembly. These results identify Net1 as a novel regulator of mitosis and indicate that altered expression of Net1, as occurs in human cancers, may adversely affect genomic stability.

Rho-associated coiled-coil kinase (ROCK) signaling and disease

The small Rho GTPase family of proteins, encompassing the three major G-protein classes Rho, Rac and cell division control protein 42, are key mitogenic signaling molecules that regulate multiple cancer-associated cellular phenotypes including cell proliferation and motility. These proteins are known for their role in the regulation of actin cytoskeletal dynamics, which is achieved through modulating the activity of their downstream effector molecules. The Rho-associated coiled-coil kinase 1 and 2 (ROCK1 and ROCK2) proteins were the first discovered Rho effectors that were primarily established as players in RhoA-mediated stress fiber formation and focal adhesion assembly. It has since been discovered that the ROCK kinases actively phosphorylate a large cohort of actin-binding proteins and intermediate filament proteins to modulate their functions. It is well established that global cellular morphology, as modulated by the three cytoskeletal networks: actin filaments, intermediate filaments and microtubules, is regulated by a variety of accessory proteins whose activities are dependent on their phosphorylation by the Rho-kinases. As a consequence, they regulate many key cellular functions associated with malignancy, including cell proliferation, motility and viability. In this current review, we focus on the role of the ROCK-signaling pathways in disease including cancer.

Distinct distribution and localization of Rho-kinase in mouse epithelial, muscle and neural tissues

The small GTP-binding protein Rho plays a crucial role in a wide variety of cellular functions through various effector proteins. Rho-kinase is a key effector protein of Rho, which is composed of two isoforms, ROCK1 and ROCK2. To clarify the site of action of ROCK1 and ROCK2, we performed immunofluorescence and immunoelectron microscopic analyses using isoform-specific antibodies in mouse tissues. In the large and small intestines, ROCK1 immunoreactivity was predominantly identified in epithelial cells, and ROCK2 immunoreactivity was negligible. In these epithelial cells, ROCK1 immunoreactivity was distributed on plasma membranes, while ROCK1 immunogold signals were localized at cell-cell contacts and cell adhesion sites, especially at the adherens junctions at the ultrastructural level. In the bladder epithelium, however, ROCK1 and ROCK2 signals were identified at intermediate filaments, and ROCK2 signals were also observed in nuclei. In the three types of muscular cells-smooth, cardiac, and skeletal muscle cells-ROCK1 and ROCK2 also showed differential distribution. ROCK1 signals were localized at actin filaments, plasma membranes, and vesicles near plasma membranes in smooth muscle cells; at the lysosomes in skeletal muscle cells; and were undetectable in cardiac muscle cells. ROCK2 signals were localized at actin filaments and centrosomes in smooth muscle cells, at intercalated discs in cardiac muscle cells, and at Z-discs and sarcoplasmic reticulum in skeletal muscle cells. In the brain, ROCK1 immunoreactivity was distributed in glia, whereas ROCK2 immunoreactivity was observed in neurons. These results indicate that the two isoforms of Rho-kinase distribute differentially to accomplish their specific functions.

ROCKII Ser1366 phosphorylation reflects the activation status

ROCK (Rho-associated protein kinase), a downstream effector of RhoA, plays an important role in many cellular processes. Accumulating evidence has shown the involvement of ROCK activation in the pathogenesis of many diseases. However, a reagent capable of detecting ROCK activation directly is lacking. In the present study, we show autophosphorylation of ROCKII in an in vitro kinase reaction. The phosphorylation sites were identified by MS, and the major phosphorylation site was found to be at the highly conserved residue Ser1366. A phospho-specific antibody was generated that can specifically recognize ROCKII Ser1366 phosphorylation. We found that the extent of Ser1366 phosphorylation of endogenous ROCKII is correlated with that of myosin light chain phosphorylation in cells in response to RhoA stimulation, showing that Ser1366 phosphorylation reflects its kinase activity. In addition, ROCKII Ser1366 phosphorylation could be detected in human breast tumours by immunohistochemical staining. The present study provides a new approach for revealing the ROCKII activation status by probing ROCKII Ser1366 phosphorylation directly in cells or tissues.

Striking crosstalk of ROCK signaling with endothelial function

Rho-associated coiled-coil forming protein kinases (ROCKs), the downstream target proteins of RhoA, are ubiquitously expressed serine-threonine protein kinases. ROCKs have diverse cellular functions, e.g. smooth muscle contraction, actin cytoskeleton organization, cell adhesion, and gene expression. Accumulating evidence has revealed that ROCKs are substantially involved in cardiovascular disorders such as angina, cerebral ischemia, myocardial ischemia, and cardiac hypertrophy. So far, the significant relationship of ROCKs with endothelial function has been reported. ROCKs inhibition by statins or other selective inhibitors leads to the upregulation and activation of endothelial nitric oxide synthase, resulting in the reduction of vascular inflammation and atherosclerosis. Meanwhile, it has been also demonstrated that endogenous nitric oxide could inhibit RhoA/ROCK signaling pathway. Taken together, there might be critical crosstalk of ROCKs with endothelial function. In addition, we further focus on leukocyte ROCK activity as a surrogate marker in patients with atherosclerosis-related diseases. Indeed, leukocyte ROCK activity has been shown to be increased in atherosclerotic patients, indicating the possible usage of leukocyte ROCK activity as a surrogate marker similar to endothelial function evaluated by flow-mediated dilation. Here, we review concerning ROCK signaling pathway, especially focusing on the crosstalk of ROCKs with endothelial function.

Arsenic trioxide induces abnormal mitotic spindles through a PIP4KIIγ/Rho pathway

Arsenite-induced spindle abnormalities result in mitotic cell apoptosis in several cancer cell lines, but how arsenite induces these effects is not known. Evidence to date has revealed that arsenite activates Rho guanosine triphosphatases (GTPases). Because Rho GTPases regulate spindle orientation, chromosome congression, and cytokinesis, we therefore examined the involvement of Rho GTPases and their modulators in arsenite-induced mitotic abnormalities. We demonstrated that arsenic trioxide (ATO) disrupted the positioning of bipolar mitotic spindles and induced centrosome and spindle abnormalities. ATO increased the level of the active guanosine triphosphate-bound form of Rho. Inhibition of Rho-associated protein kinases (ROCKs) by Y-27632 ameliorated ATO-induced spindle defects, mitotic arrest, and cell death. These results indicate that ATO may induce spindle abnormalities and mitotic cell death through a Rho/ROCK pathway. In addition, screening of a human kinase and phosphatase shRNA library to select genes that mediate ATO induction of spindle abnormalities resulted in the identification of phosphatidylinositol-5-phosphate 4-kinase type-2 gamma (PIP4KIIγ), a phosphatidylinositol 4,5-biphosphate (PIP2) synthesis enzyme that belongs to the phosphatidylinositol phosphate kinase (PIPK) family. Sequestration of PIP2 by ectopic overexpression of the pleckstrin homology domain of phospholipase C-δ1 protected cells from ATO-induced cell death. Furthermore, depletion of PIP4KIIγ, but not other isoforms of the PIPK family, not only reduced Rho GTPase activation in ATO-treated cells but also alleviated ATO-induced spindle defects, mitotic arrest, and mitotic cell apoptosis. Thus, our results imply that ATO induces abnormalities in mitotic spindles through a PIP4KIIγ/Rho pathway, leading to apoptosis of mitotic cells.

Human Mob1 proteins are required for cytokinesis by controlling microtubule stability

The completion of cytokinesis requires abscission of the midbody, a microtubule-rich cytoplasmic bridge that connects the daughter cells before their final separation. Although it has been established that both the midbody structure and membrane fusion are essential for abscission, the biochemical machinery and the cellular processes of abscission remain ill-defined. Here we report that human Mob1A and Mob1B proteins are involved in the regulation of abscission of the intercellular bridge. The Mob family is a group of highly conserved proteins in eukaryotes, described as binding partners as well as co-activators of protein kinases of the Ndr family, and as members of the Hippo pathway. We show that depletion of Mob1A and Mob1B by RNAi causes abscission failure as a consequence of hyper-stabilization of microtubules in the midbody region. Interestingly, depleting Mob1 also increases cell motility after cytokinesis, and induces prolonged centriole separation in G1 phase. In contrast, centrosomes fail to split when either Mob1A or Mob1B is overexpressed. Our findings indicate that human Mob1 proteins are involved in the regulation of microtubule stability at the midbody. We conclude that Mob1A and Mob1B are needed for cell abscission and centriole re-joining after telophase and cytokinesis.

Centrioles resist forces applied on centrosomes during G2/M transition

BACKGROUND INFORMATION

Centrosome movements at the onset of mitosis result from a balance between the pulling and pushing forces mediated by microtubules. The structural stability of the centrosome core structure, the centriole pair, is correlated with a heavy polyglutamylation of centriole tubulin.

RESULTS

Using HeLa cells stably expressing centrin-green fluorescent protein as a centriole marker, we monitored the effect of microinjecting an anti-(polyglutamylated tubulin) monoclonal antibody, GT335, in G1/S or G2 cells. In contrast with the slow effect of the monoclonal antibody GT335 during interphase, a dramatic and rapid centrosome fragmentation occurred in cells microinjected in G2 that was both Eg5- and dynein-dependent. Inhibition of either one of these two motors significantly decreased the scattering of centrosome fragments, and inhibition of centrosome segregation by impairing microtubule dynamics abolished centrosome fragmentation.

CONCLUSIONS

Our results demonstrate that the compact structure of the mitotic centrosome is capable of absorbing most of the pulling and pushing forces during G2/M transition and suggest that centrosomes could act as mechanosensors integrating tensions during cell division.

Stages of ciliogenesis and regulation of ciliary length

Cilia and flagella are highly conserved eukaryotic microtubule-based organelles that protrude from the surface of most mammalian cells. These structures require large protein complexes and motors for distal addition of tubulin and extension of the ciliary membrane. In order for ciliogenesis to occur, coordination of many processes must take place. An intricate concert of cell cycle regulation, vesicular trafficking, and ciliary extension must all play out with accurate timing to produce a cilium. Here, we review the stages of ciliogenesis as well as regulation of the length of the assembled cilium. Regulation of ciliogenesis during cell cycle progression centers on centrioles, from which cilia extend upon maturation into basal bodies. Centriole maturation involves a shift from roles in cell division to cilium nucleation via migration to the cell surface and docking at the plasma membrane. Docking is dependent on a variety of proteinaceous structures, termed distal appendages, acquired by the mother centriole. Ciliary elongation by the process of intraflagellar transport (IFT) ensues. Direct modification of ciliary structures, as well as modulation of signal transduction pathways, play a role in maintenance of the cilium. All of these stages are tightly regulated to produce a cilium of the right size at the right time. Finally, we discuss the implications of abnormal ciliogenesis and ciliary length control in human disease as well as some open questions.

A new micropatterning method of soft substrates reveals that different tumorigenic signals can promote or reduce cell contraction levels

In tissues, cell microenvironment geometry and mechanics strongly impact on cell physiology. Surface micropatterning allows the control of geometry while deformable substrates of tunable stiffness are well suited for the control of the mechanics. We developed a new method to micropattern extracellular matrix proteins on poly-acrylamide gels in order to simultaneously control cell geometry and mechanics. Microenvironment geometry and mechanics impinge on cell functions by regulating the development of intra-cellular forces. We measured these forces in micropatterned cells. Micropattern geometry was streamlined to orient forces and place cells in comparable conditions. Thereby force measurement method could be simplified and applied to large-scale experiment on chip. We applied this method to mammary epithelial cells with traction force measurements in various conditions to mimic tumoral transformation. We found that, contrary to the current view, all transformation phenotypes were not always associated to an increased level of cell contractility.

Myosin phosphatase-targeting subunit 1 controls chromatid segregation

Myosin phosphatase is a heterotrimeric holoenzyme consisting of myosin phosphatase-targeting subunit 1 (MYPT1), a catalytic subunit of PP1Cβ, and a 20-kDa subunit of an unknown function. We have previously reported that myosin phosphatase also controls mitosis, apparently by antagonizing polo-like kinase 1 (PLK1). Here we found that depletion of MYPT1 by siRNA led to precocious chromatid segregation when HeLa cells were arrested at metaphase by a proteasome inhibitor, MG132, or by Cdc20 depletion. Consistently, cyclin B1 and securin were not degraded, indicating that the chromatid segregation is independent of the anaphase-promoting complex/cyclosome. Precocious segregation induced by MYPT1 depletion requires PLK1 activity because a PLK1 inhibitor, BI-2536, blocked precocious segregation. Furthermore, the expression of an unphosphorylatable mutant of SA2 (SCC3 homologue 2), a subunit of the cohesin complex, prevented precocious chromatid segregation induced by MYPT1 depletion. It has been shown that SA2 at centromeres is protected from phosphorylation by PP2A phosphatase recruited by Shugoshin (Sgo1), whereas SA2 along chromosome arms is phosphorylated by PLK1, leading to SA2 dissociation at chromosome arms. Taken together, our results suggest that hyperactivation of PLK1 caused by MYPT1 reduction could override the counteracting PP2A phosphatase, resulting in precocious chromatid segregation. We propose that SA2 at the centromeres is protected by two phosphatases. One is PP2A directly dephosphorylating SA2, and the other is myosin phosphatase counteracting PLK1.

Cell shape and contractility regulate ciliogenesis in cell cycle-arrested cells

Adhesive micropatterns show the effect of spatial confinement and actin network architecture on basal body positioning and primary cilium formation.

In most lineages, cell cycle exit is correlated with the growth of a primary cilium. We analyzed cell cycle exit and ciliogenesis in human retinal cells and found that, contrary to the classical view, not all cells exiting the cell division cycle generate a primary cilium. Using adhesive micropatterns to control individual cell spreading, we demonstrate that cell spatial confinement is a major regulator of ciliogenesis. When spatially confined, cells assemble a contractile actin network along their ventral surface and a protrusive network along their dorsal surface. The nucleus–centrosome axis in confined cells is oriented toward the dorsal surface where the primary cilium is formed. In contrast, highly spread cells assemble mostly contractile actin bundles. The nucleus–centrosome axis of spread cells is oriented toward the ventral surface, where contractility prevented primary cilium growth. These results indicate that cell geometrical confinement affects cell polarity via the modulation of actin network architecture and thereby regulates basal body positioning and primary cilium growth.

Rho-associated coiled-coil-forming kinases (ROCKs): potential targets for the treatment of atherosclerosis and vascular disease

ROCKs are important regulators of the actin cytoskeleton. Because changes in the actin cytoskeleton underlie vascular contractility and remodeling, inflammatory cell recruitment, and cell proliferation, it is likely that the Rho/ROCK pathway will play a central role in mediating vascular function. Indeed, increased ROCK activity is observed in cerebral and coronary vasospasm, hypertension, vascular inflammation, arteriosclerosis, and atherosclerosis. Recent experimental and clinical studies suggest that inhibition of ROCK could be a promising target for the treatment of cardiovascular disease. For example, inhibition of ROCK might be the underlying mechanism by which statins or HMG-CoA reductase inhibitors exert their therapeutic benefits beyond cholesterol reduction. In this review we summarize current understanding of the crucial role of RhoA/ROCK pathway in the regulation of vascular function and discuss its therapeutic potential in the treatment of atherosclerosis and vascular disease.