LIM Domain Kinase Research Articles

Abstract 5399: Anti-cancer activity of a new LIM-Kinases inhibitor: “LIM-Pyr1”

Abstract Breast cancer is the second cause of death in Europe with an incidence of 464.00 new cases in 2012. Chemotherapy is frequently used to treat severe breast cancer. Current drugs like taxanes and anthracycline used alone or in combination are efficient. Moreover the use of biomarkers, like HER2 and BRCA status is now helping in the choice of the most adapted chemotherapy to the patient. De novo or acquired resistance limits, however, the clinical usefulness of drugs used in current chemotherapy. The development of new therapeutics effective against drug-resistant cancers thus still represents an important challenge. Our team has discovered a new LIM Kinases (LIMK1/2) inhibitor, “LIM-Pyr1”. LIMK1/2 are situated at a crossroads of several signaling pathways mainly activated by tyrosine kinase receptors and regulate both actin and microtubules dynamics. LIMK1/2 regulate actin dynamics through cofilin phosphorylation. Cofilin is an actin-depolymerizing factor and its phosphorylation inactivates its actin severing activity. LIMK1/2 also regulate microtubule dynamics through a mechanism unknown yet. LIMK1/2 inhibition induce microtubules stabilization (1). Moreover, LIMK1/2 are overexpressed in many invasive cancers and appear to be a relevant target for anticancer therapy (2, 3). We have shown that LIM-Pyr1 is toxic on cell lines resistant to conventional chemotherapy (4) and tested LIM-Pyr1 therapeutic activity on different breast cancer models (xenografts in mice). We found that LIM-Pyr1 shows a potent antitumor activity both on primary and secondary tumors, with no detectable undesirable side effects. The antitumor effect is effective on paclitaxel resistant xenografts. Finally, intravital microscopy analysis indicates that a LIM-Pyr1 treatment induces a strong morphological change of tumor cells inside the tumors and reduces their migration. LIM-Pyr1 and its derivatives could thus represent a pharmacological alternative to overcome resistances often observed when tumors are treated with microtubule targeting agents. (1) O. Bernard, LIM Kinases, regulators of actin dynamics, Int. Journals of Biochemistry and cell biology (2007) 1071-1076 (2) F. Manetti, Recent finding confirm LIM Domain Kinases as emerging target candidates for cancer therapy, Curr. Cancer Drug Targets (2012) 12,543-560 (3) W. Wang, R. Eddy, J. Condeelis, The cofilin pathway in breast cancer invasion and metastasis, Nat. Cancer Reviews (2007) (4) R. Prudent, E. Vassal-Stermann, C-H Nguyen et al., Pharmacological inhibition of LIM Kinases stabilizes microtubules, Cancer Research (2012) Citation Format: Chloé Prunier, Julien Vollaire, Véronique Josserand, Anoek Zomer, Amandine Hurbin, Renaud Prudent, Pascale Cohen, Jacco van Rheenen, Jean-Luc Coll, Marc Billaud, Laurence Lafanechère. Anti-cancer activity of a new LIM-Kinases inhibitor: “LIM-Pyr1”. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5399. doi:10.1158/1538-7445.AM2015-5399

The Rho-GTPase effector ROCK regulates meiotic maturation of the bovine oocyte via myosin light chain phosphorylation and cofilin phosphorylation.

Oocyte meiosis involves a unique asymmetric division involving spindle movement from the central cytoplasm to the cortex, followed by polar body extrusion. ROCK is a Rho-GTPase effector involved in various cellular functions in somatic cells as well as oocyte meiosis. ROCK was previously shown to promote actin organization by phosphorylating several downstream targets, including LIM domain kinase (LIMK), phosphorylated cofilin (p-cofilin), and myosin light chain (MLC). In this study, we investigated the roles of ROCK and MLC during bovine oocyte meiosis. We found that ROCK was localized around the nucleus at the oocyte's germinal-vesicle (GV) stage, but spreads to the rest of the cytoplasm in later developmental stages. On the other hand, phosphorylated MLC (p-MLC) localized at the cortex, and its abundance decreased by the metaphase-II stage. Disrupting ROCK activity, via RNAi or the chemical inhibitor Y-27632, blocked both cell cycle progression and polar body extrusion. ROCK inhibition also resulted in decreased cortical actin, p-cofilin, and p-MLC levels. Similar to the phenotype associated with inhibition of ROCK activity, inhibition of MLC kinase by the chemical inhibitor ML-7 caused defects in polar body extrusion. Collectively, our results suggest that the ROCK/MLC/actomyosin as well as ROCK/LIMK/cofilin pathways regulate meiotic spindle migration and cytokinesis during bovine oocyte maturation.

Inhibiting actin depolymerization enhances osteoblast differentiation and bone formation in human stromal stem cells

Remodeling of the actin cytoskeleton through actin dynamics is involved in a number of biological processes, but its role in human stromal (skeletal) stem cells (hMSCs) differentiation is poorly understood. In the present study, we demonstrated that stabilizing actin filaments by inhibiting gene expression of the two main actin depolymerizing factors (ADFs): Cofilin 1 (CFL1) and Destrin (DSTN) in hMSCs, enhanced cell viability and differentiation into osteoblastic cells (OB) in vitro, as well as heterotopic bone formation in vivo. Similarly, treating hMSC with Phalloidin, which is known to stabilize polymerized actin filaments, increased hMSCs viability and OB differentiation. Conversely, Cytocholasin D, an inhibitor of actin polymerization, reduced cell viability and inhibited OB differentiation of hMSC. At a molecular level, preventing Cofilin phosphorylation through inhibition of LIM domain kinase 1 (LIMK1) decreased cell viability and impaired OB differentiation of hMSCs. Moreover, depolymerizing actin reduced FAK, p38 and JNK activation during OB differentiation of hMSCs, while polymerizing actin enhanced these signaling pathways. Our results demonstrate that the actin dynamic reassembly and Cofilin phosphorylation loop is involved in the control of hMSC proliferation and osteoblasts differentiation.

Depletion of histone deacetylase 1 inhibits metastatic abilities of gastric cancer cells by regulating the miR-34a/CD44 pathway.

Overexpression of histone deacetylases (HDACs) is associated with higher metastatic rates and a poor prognosis in gastric cancer. However, the underlying mechanisms involved remain unclear. The present study aimed to investigate the molecular pathways that are involved in HDAC1-mediated metastatic activities in gastric cancer cells. First we used a microRNA (miRNA or miR) microarray to screen potential miRNAs whose expression can be altered by HDAC1 depletion. Of these miRNAs, miR-34a is important as it is often inactivated in cancer cells and acts as a tumor suppressor for various types of cancer. The reverse transcription-quantitative polymerase chain reaction (RT‑qPCR) results confirmed that miR-34a was upregulated by HDAC1 knockdown. Cells depleted of HDAC1 had lower abilities to migrate, invade and adhere, which were restored by a miR-34a antagomiR. Depletion of HDAC1 also resulted in impaired microfilaments and microtubules, while co-transfection of the miR-34a antagomiR attenuated these changes in the cellular cytoskeleton. The HDAC1/miR-34a axis regulated the expression and activation of CD44 and its downstream factors including Bcl-2, Ras homolog family member A (RhoA), LIM domain kinase 1 (LIMK-1) and matrix metalloproteinase (MMP)-2. The latter three proteins were responsible for the organization of tubulin and actin cytoskeleton and the formation of cellular pseudopodia. In conclusion, results of the present study indicated that HDAC1 depletion inhibits the metastatic abilities of gastric cancer cells by regulating the miRNA-34a/CD44 pathway, which may be a potential target for the treatment of gastric cancer.

Pak2 restrains endomitosis during megakaryopoiesis and alters cytoskeleton organization

AbstractMegakaryocyte maturation and polyploidization are critical for platelet production; abnormalities in these processes are associated with myeloproliferative disorders, including thrombocytopenia. Megakaryocyte maturation signals through cascades that involve p21-activated kinase (Pak) function; however, the specific role for Pak kinases in megakaryocyte biology remains elusive. Here, we identify Pak2 as an essential effector of megakaryocyte maturation, polyploidization, and proplatelet formation. Genetic deletion of Pak2 in murine bone marrow is associated with macrothrombocytopenia, altered megakaryocyte ultrastructure, increased bone marrow megakaryocyte precursors, and an elevation of mature CD41+ megakaryocytes, as well as an increased number of polyploid cells. In Pak2−/− mice, platelet clearance rate was increased, as was production of newly synthesized, reticulated platelets. In vitro, Pak2−/− megakaryocytes demonstrate increased polyploidization associated with alterations in β1-tubulin expression and organization, decreased proplatelet extensions, and reduced phosphorylation of the endomitosis regulators LIM domain kinase 1, cofilin, and Aurora A/B/C. Together, these data establish a novel role for Pak2 as an important regulator of megakaryopoiesis, polyploidization, and cytoskeletal dynamics in developing megakaryocytes.

Rho Kinase Pathway Alterations in the Brain and Leukocytes in Huntington's Disease.

Huntington’s disease (HD) is a fatal neurodegenerative disease caused by an expanded polyglutamine tract in the huntingtin gene. Therapeutic approaches targeting mutant huntingtin (mtHtt) or its downstream toxic consequences are under development, including Rho kinase pathway inhibition. We investigated the messenger RNA (mRNA) expression of Rho kinase pathway genes, including RhoA (Ras homolog family member A), ROCK1 (Rho-associated kinase1), PRK2 (protein kinase C-related protein kinase 2), Profilin1, cofilin1, MYPT1 (myosin phosphatase target subunit 1), and LIMK1 (LIM domain kinase 1) in HD human blood leukocytes, postmortem brain, and in R6/2 HD mouse brain tissue using qPCR. RhoA, ROCK1, PRK2, Profilin1, cofilin1, and MYPT1 were significantly increased in HD blood compared to controls. In frontal cortex of HD postmortem brain tissue, the expression of RhoA, ROCK1, PRK2, Profilin1, and MYPT1 were also significantly increased. In the brain from 4-week-old R6/2 mice, the expression of Rock1, Prk2, Cofilin1, and MYPT1 was significantly increased while RhoA, Rock1, Profilin1, Cofilin1, and Mypt1 were increased and Limk1 mRNA decreased in 13-week-old R6/2 mice. Western blot analysis using human postmortem tissues for ROCK1 and Profilin1 demonstrated significantly increased protein levels, which correlated with the mRNA increases. Collectively, we have shown the panel of Rho kinase pathway genes to be highly altered in human HD blood, postmortem brain tissue, and in R6/2 mice. These studies confirm that HD upregulates the Rho kinase pathway and identifies mRNAs that could serve as peripheral markers in HD patients and translational markers in HD mouse models.

Distribution of LIM domain kinase 1 in the olfactory bulb, cerebral cortex, hippocampus, and cerebellum of the App/PS+/- mice.

LIM domain kinase 1 (LIMK1), an actin-binding kinase, can phosphorylate and inactivate its substrates, and can regulate long-term memory and synaptic plasticity. Both β-amyloid precursor protein (App) and presenilin (PS) are functional degeneration factors during early neuronal development, and are considered as potential factors that contribute to the development of Alzheimer's disease (AD). However, hardly any information is available about the distribution and expression of LIMK1. Thus, using the App and PS deficient mice, the role of LIMK1 was demonstrated in the absence of App and PS. Our results showed that LIMK1 was present in the nerve fiber layer and external plexiform layer of the olfactory bulb, as well as in the mitral cells and Purkinje cells of the cerebellum in App and PS deficient mice. Additionally, LIMK1 was concentrated in the granule cell layer of the olfactory bulb and cerebellum and LIMK1 positive cells were located in the CA1 region of the hippocampus. Our study indicates that there is a connection between LIMK1 and AD in the mouse model of AD. This might explain neurological problems such as cerebellar ataxia, impaired long-term memory, and impaired synaptic plasticity observed in AD.

CXCL12/CXCR4 signaling counteracts docetaxel-induced microtubule stabilization via p21-activated kinase 4-dependent activation of LIM domain kinase 1.

Emerging data highlight the significance of chemokine (C-X-C motif) ligand 12/chemokine (C-X-C motif) receptor 4 (CXCL12/CXCR4) signaling axis in the chemoresistance of several malignancies, including prostate cancer (PCa); however, underlying mechanisms remain largely elusive. Here, we demonstrate that CXCL12 treatment rescues the PCa cells from docetaxel (DTX)-induced toxicity by overriding its effect on cell cycle (G2/M phase arrest). We further demonstrate that the chemoprotective effect of CXCL12 is abolished upon pharmacological inhibition or RNA interference-mediated silencing of CXCR4. Moreover, microtubule stabilization caused by DTX is suppressed in CXCL12-stimulated PCa cells as revealed by immunofluorescence and immunoblot analyses. The effect of CXCL12 on microtubule stabilization is abrogated when PCa cells are pre-treated with a CXCR4 antagonist. In additional studies, we show that the chemoprotective action of CXCL12/CXCR4 signaling is mediated by p21-activated kinase 4 (PAK4)-dependent activation of Lim domain kinase 1 (LIMK1), and inhibition of either PAK4 or LIMK1 leads to re-sensitization of PCa cells to DTX-induced tubulin polymerization and cellular toxicity even in the presence of CXCL12. Altogether, our findings uncover a novel mechanism underlying CXCL12/CXCR4 signaling-induced PCa chemoresistance and suggest that targeting of this signaling axis or its downstream effector pathway could lead to therapeutic enhancement of DTX.

LIMK1 Regulates Human Trophoblast Invasion/Differentiation and Is Down-Regulated in Preeclampsia

Successful human pregnancy requires extensive invasion of maternal uterine tissues by the placenta. Invasive extravillous trophoblasts derived from cytotrophoblast progenitors remodel maternal arterioles to promote blood flow to the placenta. In the pregnancy complication preeclampsia, extravillous trophoblasts invasion and vessel remodeling are frequently impaired, likely contributing to fetal underperfusion and maternal hypertension. We recently demonstrated in mouse trophoblast stem cells that hypoxia-inducible factor-2 (HIF-2)-dependent Lim domain kinase 1 (LIMK1) expression regulates invasive trophoblast differentiation by modulating the trophoblast cytoskeleton. Interestingly, in humans, LIMK1 activity promotes tumor cell invasion by modulating actin and microtubule integrity, as well as by modulating matrix metalloprotease processing. Here, we tested whether HIF-2α and LIMK1 expression patterns suggested similar roles in the human placenta. We found that LIMK1 immunoreactivity mirrored HIF-2α in the human placenta in utero and that LIMK1 activity regulated human cytotrophoblast cytoskeletal integrity, matrix metallopeptidase-9 secretion, invasion, and differentiation in vitro. Importantly, we also found that LIMK1 levels are frequently diminished in the preeclampsia setting in vivo. Our results therefore validate the use of mouse trophoblast stem cells as a discovery platform for human placentation disorders and suggest that LIMK1 activity helps promote human placental development in utero.

AAV.shRNA-mediated downregulation of ROCK2 attenuates degeneration of dopaminergic neurons in toxin-induced models of Parkinson's disease in vitro and in vivo

Parkinson's disease (PD) is a neurodegenerative disorder with prominent neuronal cell death in the substantia nigra (SN) and other parts of the brain. Previous studies in models of traumatic and neurodegenerative CNS disease showed that pharmacological inhibition of Rho-associated kinase (ROCK), a molecule involved in inhibitory signaling in the CNS, by small-molecule inhibitors improves neuronal survival and increases regeneration. Most small-molecule inhibitors, however, offer only limited target specificity and also inhibit other kinases, including both ROCK isoforms. To establish the role of the predominantly brain-expressed ROCK2 isoform in models of regeneration and PD, we used adeno-associated viral vectors (AAV) to specifically knockdown ROCK2 in neurons.Rat primary midbrain neurons (PMN) were transduced with AAV expressing short-hairpin-RNA (shRNA) against ROCK2 and LIM-domain kinase 1 (LIMK1), one of the downstream targets of ROCK2. While knock-down of ROCK2 and LIMK1 both enhanced neurite regeneration in a traumatic scratch lesion model, only ROCK2-shRNA protected PMN against 1-methyl-4-phenylpyridinium (MPP+) toxicity. Moreover, AAV.ROCK2-shRNA increased levels of the pro-survival markers Bcl-2 and phospho-Erk1.In vivo, AAV.ROCK2-shRNA vectors were injected into the ipsilateral SN and a unilateral 6-OHDA striatal lesion was performed. After four weeks, behavioral, immunohistochemical and biochemical alterations were investigated. Downregulation of ROCK2 protected dopaminergic neurons in the SN from 6-OHDA-induced degeneration and resulted in significantly increased TH-positive neuron numbers. This effect, however, was confined to nigral neuronal somata as striatal terminal density, dopamine and metabolite levels were not significantly preserved. Interestingly, motor behavior was improved in the ROCK2-shRNA treated animals compared to control after four weeks.Our studies thus confirm ROCK2 as a promising therapeutic target in models of PD and demonstrate that neuron-specific inhibition of ROCK2 promotes survival of lesioned dopaminergic neurons.

Transcriptional profiling of GBM invasion genes identifies effective inhibitors of the LIM kinase-Cofilin pathway.

Malignant gliomas are highly proliferative and invasive neoplasms where total surgical resection is often impossible and effective local radiation therapy difficult. Consequently, there is a need to develop a greater understanding of the molecular events driving invasion and to identify novel treatment targets. Using microarray analysis comparing normal brain samples and mesenchymal glioblastoma multiforme (GBM), we identified over 140 significant genes involved in cell migration and invasion. The cofilin (CFL) pathway, which disassembles actin filaments, was highly up-regulated compared to normal brain. Up-regulation of LIM domain kinase 1 and 2 (LIMK1/2), that phosphorylates and inactivates cofilin, was confirmed in an additional independent data set comparing normal brain to GBM. We identified and utilized two small molecule inhibitors BMS-5 and Cucurbitacin I directed against the cofilin regulating kinases, LIMK1 and LIMK2, to target this pathway. Significant decreases in cell viability were observed in glioma cells treated with BMS-5 and Cucurbitacin I, while no cytotoxic effects were seen in normal astrocytes that lack LIMK. BMS-5 and Cucurbitacin I promoted increased adhesion in GBM cells, and decreased migration and invasion. Collectively, these data suggest that use of LIMK inhibitors may provide a novel way to target the invasive machinery in GBM.

Interleukin-1β-induced Wnt5a enhances human corneal endothelial cell migration through regulation of Cdc42 and RhoA.

Wnt5a can activate β-catenin-independent pathways for regulation of various cellular functions, such as migration, that play critical roles in wound repair. Investigation of Wnt5a signaling may help identify therapeutic targets for enhancing corneal endothelial wound healing that could provide an alternative to corneal transplantation in patients with blindness from endothelial dysfunction. However, Wnt5a signaling in corneal endothelial cells (CECs) has not been well characterized. In this study, we show transient induction of Wnt5a by interleukin-1β (IL-1β) stimulation proceeds through NF-κB in human CECs. This leads to binding of Fzd5 to Ror2, resulting in activation of disheveled protein (Dvl) and subsequently disheveled-associated activator of morphogenesis 1 (DAAM1). This leads to activation of Cdc42 and subsequent inhibition of RhoA. Inhibition of RhoA leads to parallel dephosphorylation and inactivation of LIM domain kinase 2 along with dephosphorylation and activation of slingshot 1, resulting in dephosphorylation and activation of cofilin and leading to enhanced cell migration. These findings suggest that Wnt5a enhances cell migration through activation of Cdc42 and inactivation of RhoA in human CECs.

MiR-143 inhibits NSCLC cell growth and metastasis by targeting Limk1.

MicroRNAs (miRNAs) have essential roles in carcinogenesis and tumor progression. Here, we investigated the roles and mechanisms of miR-143 in non-small cell lung cancer (NSCLC). miR-143 was significantly decreased in NSCLC tissues and cell lines. Overexpression of miR-143 suppressed NSCLC cell proliferation, induced apoptosis, and inhibited migration and invasion in vitro. Integrated analysis identified LIM domain kinase 1 (Limk1) as a direct and functional target of miR-143. Overexpression of Limk1 attenuated the tumor suppressive effects of miR-143 in NSCLC cells. Moreover, miR-143 was inversely correlated with Limk1 expression in NSCLC tissues. Together, our results highlight the significance of miR-143 and Limk1 in the development and progression of NSCLC.

TRANSCRIPTIONAL PROFILING OF GBM INVASIVE GENES IDENTIFIES EFFECTIVE INHIBITORS OF THE LIM KINASE-COFILIN PATHWAY

BACKGROUND: The malignant astrocytoma is a highly proliferative and invasive neoplasm that infiltrates diffusely into regions of normal brain rendering total surgical resection impossible and effective local radiation therapy difficult. For truly significant advances to be made in the treatment of patients with malignant astrocytoma, we must develop a greater understanding of the molecular machinery driving invasion and identify novel treatment targets. METHODS: We recently compared gene-expression data of 400 invasion/migration genes by performing microarray analysis comparing 10 normal brain samples versus 51 mesenchymal GBM, which are highly invasive, and of poor prognosis. RESULTS: We identified over 141 significant genes with a 1.5 fold change (p-value <0.05, and a false discovery rate (q < 0.05) compared to normal brain. Of the 141 genes, the cofilin pathway, which disassembles actin filaments (namely LIMK1, LIMK2, CFL, CAP1) was highly up-regulated compared to normal brain. Furthermore we identified up-regulation of LIM domain kinase 1 and 2 (LIMK1/2) that phosphorylates and inactivates cofilin (CFL) in an additional data set comparing normal brain to GBM. Using a well-characterized tissue microarray of 20 GBM patients for which a central and a matched periphery sample was available we undertook immunohistochemical (IHC) analysis of LIMK1 and pCFL. We observed significant expression of LIMK1 in the periphery of the GBM compared to the center (11/20 in the periphery versus 2/20 in the center). Previously, we established that pCFL plays an integral role in GBM invasion. Consequently we explored how to target this pathway using small molecule inhibitors. We tested the LIMK1 and LIMK2 inhibitors BMS-5 and Cucurbitacin I. Both BMS-5 and Cucurbitacin I inhibited p-CFL at the protein level at 10uM and 100nM respectively in U87 cells. Using the MTT cell viability assay, we observed significant decrease in cell viability in U87 and T98G cells using doses of 10-20uM BMS-5 and 100nM-10uM Cucurbitacin I while no cytotoxic effect was seen in normal human astrocytes that lack LIMK expression. Both BMS-5 (10uM) and Cucurbitacin I (100nM) promoted increased adhesion in U87 and T98G cells. Interestingly, BMS-5 and Cucurbitacin I reduced migration and invasion of both U87 and T98G cells. CONCLUSIONS: Taken together, the use of LIMK inhibitors to target the invasive machinery in GBM are attractive candidates to move forward with in preclinical trials. SECONDARY CATEGORY: Tumor Biology.

Matrilin-3 as a putative effector of C-type natriuretic peptide signaling during TGF-β induced chondrogenic differentiation of mesenchymal stem cells.

C-type natriuretic peptide (CNP) signaling has been implicated as an important regulator of chondrogenic differentiation during endochondral bone development. This preliminary study further investigated the putative effectors and/or targets of CNP signaling in transforming growth factor (TGF)-β induced in vitro chondrogenic differentiation of mesenchymal stem cells (MSCs). Previously characterized human trabecular bone derived MSCs were induced either with only TGF-β1 or with a combination of TGF-β1 and CNP in micromass culture for 10 or 20 days. Genome wide gene expression profile changes in between these two groups were analyzed on day-10 or day-20 of culture. Results revealed that there were only 7 genes, whose expression change was fourfolds or higher in TGF-β1 and CNP fed group in comparison to only TGF-β1 fed group. The up-regulated genes included matrilin-3 (MATN3), engulfment and cell motility 1 (ELMO1), CD24, and DCN1, defective in cullin neddylation 1, domain containing 1 (DCUN1D1). The down-regulated genes, on the other hand, included LIM domain kinase 2 (LIMK2), Ewing sarcoma breakpoint region 1, and guanine nucleotide binding protein (G protein), gamma 12 (GNG12). The up-regulation of MATN3 was confirmed on the basis of RT-PCR. The known literature on both CNP signaling and MATN3 function in chondrogenesis match with each other and suggest MATN3 as a putative effector and/or target of CNP signaling during this process.

ROCK2 is a major regulator of axonal degeneration, neuronal death and axonal regeneration in the CNS.

The Rho/ROCK/LIMK pathway is central for the mediation of repulsive environmental signals in the central nervous system. Several studies using pharmacological Rho-associated protein kinase (ROCK) inhibitors have shown positive effects on neurite regeneration and suggest additional pro-survival effects in neurons. However, as none of these drugs is completely target specific, it remains unclear how these effects are mediated and whether ROCK is really the most relevant target of the pathway. To answer these questions, we generated adeno-associated viral vectors to specifically downregulate ROCK2 and LIM domain kinase (LIMK)-1 in rat retinal ganglion cells (RGCs) in vitro and in vivo. We show here that specific knockdown of ROCK2 and LIMK1 equally enhanced neurite outgrowth of RGCs on inhibitory substrates and both induced substantial neuronal regeneration over distances of more than 5 mm after rat optic nerve crush (ONC) in vivo. However, only knockdown of ROCK2 but not LIMK1 increased survival of RGCs after optic nerve axotomy. Moreover, knockdown of ROCK2 attenuated axonal degeneration of the proximal axon after ONC assessed by in vivo live imaging. Mechanistically, we demonstrate here that knockdown of ROCK2 resulted in decreased intraneuronal activity of calpain and caspase 3, whereas levels of pAkt and collapsin response mediator protein 2 and autophagic flux were increased. Taken together, our data characterize ROCK2 as a specific therapeutic target in neurodegenerative diseases and demonstrate new downstream effects of ROCK2 including axonal degeneration, apoptosis and autophagy.

Dendritic Cell Motility and T Cell Activation Requires Regulation of Rho-Cofilin Signaling by the Rho-GTPase Activating Protein Myosin IXb

Directed migration of stimulated dendritic cells (DCs) to secondary lymphoid organs and their interaction with Ag-specific T cells is a prerequisite for the induction of primary immune responses. In this article, we show that murine DCs that lack myosin IXB (Myo9b), a motorized negative regulator of RhoA signaling, exhibit increased Rho signaling activity and downstream acto-myosin contractility, and inactivation of the Rho target protein cofilin, an actin-depolymerizing factor. On a functional level, Myo9b(-/-) DCs showed impaired directed migratory activity both in vitro and in vivo. Moreover, despite unaltered Ag presentation and costimulatory capabilities, Myo9b(-/-) DCs were poor T cell stimulators in vitro in a three-dimensional collagen matrix and in vivo, associated with altered DC-T cell contact dynamics and T cell polarization. Accordingly, Myo9b(-/-) mice showed an attenuated ear-swelling response in a model of contact hypersensitivity. The impaired migratory and T cell stimulatory capacity of Myo9b(-/-) DCs was restored in large part by pharmacological activation of cofilin. Taken together, these results identify Myo9b as a negative key regulator of the Rho/RhoA effector Rho-kinase [Rho-associated coiled-coil-forming kinase (ROCK)]/LIM domain kinase signaling pathway in DCs, which controls cofilin inactivation and myosin II activation and, therefore may control, in part, the induction of adaptive immune responses.

Loss of SMAD4 Alters BMP Signaling to Promote Colorectal Cancer Cell Metastasis via Activation of Rho and ROCK

SMAD4 frequently is lost from colorectal cancers (CRCs), which is associated with the development of metastases and a poor prognosis. SMAD4 loss is believed to alter transforming growth factor β signaling to promote tumor progression. However, SMAD4 is also a central component of the bone morphogenetic protein (BMP) signaling pathway, implicated in CRC pathogenesis by human genetic studies. We investigated the effects of alterations in BMP signaling on the invasive and metastatic abilities of CRC cells and changes in members in this pathway in human tumor samples. We activated BMP signaling in SMAD4-positive and SMAD4-negative CRC cells (HCT116, HT-29, SW480, and LS174T); SMAD4 was stably expressed or knocked down using lentiviral vectors. We investigated the effects on markers of epithelial-mesenchymal transition and on cell migration, invasion, and formation of invadopodia. We performed kinase activity assays to characterize SMAD4-independent BMP signaling and used an inhibitor screen to identify pathways that regulate CRC cell migration. We investigated the effects of the ROCK inhibitor Y-27632 in immunocompromised (CD-1 Nu) mice with orthotopic metastatic tumors. Immunohistochemistry was used to detect BMPR1a, BMPR1b, BMPR2, and SMAD4 in human colorectal tumors; these were related to patient survival times. Activation of BMP signaling in SMAD4-negative cells altered proteinand messenger RNA levels of markers of epithelial-mesenchymal transition and increased cell migration, invasion, and formation of invadopodia. Knockdown of the BMP receptor in SMAD4-negative cells reduced their invasive activity invitro. SMAD4-independent BMP signaling activated Rho signaling via ROCK and LIM domain kinase (LIMK). Pharmacologic inhibition of ROCK reduced metastasis of colorectal xenograft tumors in mice. Loss of SMAD4 from colorectal tumors has been associated with reduced survival time; we found that this association is dependent on the expression of BMP receptors but not transforming growth factor β receptors. Loss of SMAD4 from colorectal cancer cells causes BMP signaling to switch from tumor suppressive to metastasis promoting. Concurrent loss of SMAD4 and normal expression of BMP receptors in colorectal tumors was associated with reduced survival times of patients. Reagents that interfere with SMAD4-independent BMP signaling, such as ROCK inhibitors, might be developed as therapeutics for CRC.

Retrograde BMP Signaling Modulates Rapid Activity-Dependent Synaptic Growth via Presynaptic LIM Kinase Regulation of Cofilin

The Drosophila neuromuscular junction (NMJ) is capable of rapidly budding new presynaptic varicosities over the course of minutes in response to elevated neuronal activity. Using live imaging of synaptic growth, we characterized this dynamic process and demonstrated that rapid bouton budding requires retrograde bone morphogenic protein (BMP) signaling and local alteration in the presynaptic actin cytoskeleton. BMP acts during development to provide competence for rapid synaptic growth by regulating the levels of the Rho-type guanine nucleotide exchange factor Trio, a transcriptional output of BMP-Smad signaling. In a parallel pathway, we find that the BMP type II receptor Wit signals through the effector protein LIM domain kinase 1 (Limk) to regulate bouton budding. Limk interfaces with structural plasticity by controlling the activity of the actin depolymerizing protein Cofilin. Expression of constitutively active or inactive Cofilin in motor neurons demonstrates that increased Cofilin activity promotes rapid bouton formation in response to elevated synaptic activity. Correspondingly, the overexpression of Limk, which inhibits Cofilin, inhibits bouton budding. Live imaging of the presynaptic F-actin cytoskeleton reveals that activity-dependent bouton addition is accompanied by the formation of new F-actin puncta at sites of synaptic growth. Pharmacological disruption of actin turnover inhibits bouton budding, indicating that local changes in the actin cytoskeleton at pre-existing boutons precede new budding events. We propose that developmental BMP signaling potentiates NMJs for rapid activity-dependent structural plasticity that is achieved by muscle release of retrograde signals that regulate local presynaptic actin cytoskeletal dynamics.

Select G-Protein-Coupled Receptors Modulate Agonist-Induced Signaling via a ROCK, LIMK, and β-Arrestin 1 Pathway

G-protein-coupled receptors (GPCRs) are typically present in a basal, inactive state but, when bound to an agonist, activate downstream signaling cascades. In studying arrestin regulation of opioid receptors in dorsal root ganglia (DRG) neurons, we find that agonists of delta opioid receptors (δORs) activate cofilin through Rho-associated coiled-coil-containing protein kinase (ROCK), LIM domain kinase (LIMK), and β-arrestin 1 (β-arr1) to regulate actin polymerization. This controls receptor function, as assessed by agonist-induced inhibition of voltage-dependent Ca(2+) channels in DRGs. Agonists of opioid-receptor-like receptors (ORL1) similarly influence the function of this receptor through ROCK, LIMK, and β-arr1. Functional evidence of this cascade was demonstrated in vivo, where the behavioral effects of δOR or ORL1 agonists were enhanced in the absence of β-arr1 or prevented by inhibiting ROCK. This pathway allows δOR and ORL1 agonists to rapidly regulate receptor function.