Dysregulation of Rac or Rho elicits death of motor neurons and activation of these GTPases is altered in the G93A mutant hSOD1 mouse model of amyotrophic lateral sclerosis

Current development in sulfonamide derivatives to enable CNS-drug discovery

The encouraging therapeutic potential of sulfonamide-based derivatives has been unraveled by breakthrough discovery of Paul Ehrlich, who pointed out the possibility of fighting microbes with chemicals. Over the decades, the utility of sulfonamides has expanded beyond antimicrobial agents, revealing their usefulness in many areas of pharmacotherapy, including the treatment of central nervous system (CNS) diseases. Through a detailed analysis of preclinical and clinical data, we identify key sulfonamide-based compounds that have demonstrated significant CNS activity. We also discuss the challenges in the development of sulfonamide derivatives as enzyme/ion channel inhibitors or receptor ligands for CNS applications, describing their mode of action and therapeutic significance. This is followed by the characteristics of pharmacological targets, structure-activity relationships, ADMET properties, efficacy in experimental animal models, and outcomes from clinical trials. Overall, the versatile nature of arylsulfonamides makes them a valuable motif in drug discovery, offering diverse opportunities for the development of novel agents for treating CNS disorders.

Ras, RhoA, and vascular pharmacology in neurodevelopment and aging

Small GTPases Ras, Rac, and RhoA are crucial regulators of cellular functions. They also act in dysregulated cell proliferation and transformation. Multiple publications have focused on illuminating their roles and mechanisms, including in immune system pathologies. Their functions in neurology-related diseases, neurodegeneration and neurodevelopment, are also emerging, as well as their potential as pharmacological targets in both pathologies. Observations increasingly suggest that these pathologies may relate to activation (or suppression) of signaling by members of the Ras superfamily, especially Ras, Rho, and Rac isoforms, and components of their signaling pathways. Germline (or embryonic) mutations that they harbor are responsible for neurodevelopmental disorders, such as RASopathies, autism spectrum disorder, and dilated cardiomyopathy. In aging, they promote neurodegenerative diseases, with Rho GTPase featuring in their pharmacology, as in the case of Alzheimer's disease (AD). Significantly, drugs with observed anti-AD activity, particularly those involved in cardiovascular systems, are associated with the RhoA signaling, as well as cerebral vasculature in brain development and aging. This leads us to suggest that anti-AD drugs could inform neurodevelopmental disorders, including pediatric low-grade gliomas pharmacology. Neurodevelopmental disorders associated with RhoA, like autism, are also connected with vascular systems, thus could be targets of vascular system-connected drugs.

Role of Rho-associated kinases and their inhibitor fasudil in neurodegenerative diseases

Neurodegenerative diseases (NDDs) are prevalent in the elderly. The pathogenesis of NDDs is complex, and currently, there is no cure available. With the increase in aging population, over 20 million people are affected by common NDDs alone (Alzheimer's disease and Parkinson's disease). Therefore, NDDs have profound negative impacts on patients, their families, and society, making them a major global health concern. Rho-associated kinases (ROCKs) belong to the serine/threonine protein kinases family, which modulate diverse cellular processes (e.g., apoptosis). ROCKs may elevate the risk of various NDDs (including Huntington's disease, Parkinson's disease, and Alzheimer's disease) by disrupting synaptic plasticity and promoting inflammatory responses. Therefore, ROCK inhibitors have been regarded as ideal therapies for NDDs in recent years. Fasudil, one of the classic ROCK inhibitor, is a potential drug for treating NDDs, as it repairs nerve damage and promotes axonal regeneration. Thus, the current review summarizes the relationship between ROCKs and NDDs and the mechanism by which fasudil inhibits ROCKs to provide new ideas for the treatment of NDDs.

RBM5 induces motor neuron apoptosis in hSOD1G93A-related amyotrophic lateral sclerosis by inhibiting Rac1/AKT pathways

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder distinguished by gradual depletion of motor neurons. RNA binding motif protein 5 (RBM5), an abundantly expressed RNA-binding protein, plays a critical role in the process of cellular death. However, little is known about the role of RBM5 in the pathogenesis of ALS. Here, we found that RBM5 was upregulated in ALS hSOD1G93A-NSC34 cell models and hSOD1G93A mice due to a reduction of miR-141-5p. The upregulation of RBM5 increased the apoptosis of motor neurons by inhibiting Rac1-mediated neuroprotection. In contrast, genetic knockdown of RBM5 rescued motor neurons from hSOD1G93A-induced degeneration by activating Rac1 signaling. The neuroprotective effect of RBM5-knockdown was significantly inhibited by the Rac1 inhibitor, NSC23766. These findings suggest that RBM5 could potentially serve as a therapeutic target in ALS by activating the Rac1 signalling.

Novel insights into RAGE signaling pathways during the progression of amyotrophic lateral sclerosis in RAGE-deficient SOD1 G93A mice

Amyotrophic lateral sclerosis (ALS) is neurodegenerative disease characterized by a progressive loss of motor neurons resulting in paralysis and muscle atrophy. One of the most prospective hypothesis on the ALS pathogenesis suggests that excessive inflammation and advanced glycation end-products (AGEs) accumulation play a crucial role in the development of ALS in patients and SOD1 G93A mice. Hence, we may speculate that RAGE, receptor for advanced glycation end-products and its proinflammatory ligands such as: HMGB1, S100B and CML contribute to ALS pathogenesis. The aim of our studies was to decipher the role of RAGE as well as provide insight into RAGE signaling pathways during the progression of ALS in SOD1 G93A and RAGE-deficient SOD1 G93A mice. In our study, we observed alternations in molecular pattern of proinflammatory RAGE ligands during progression of disease in RAGE KO SOD1 G93A mice compared to SOD1 G93A mice. Moreover, we observed that the amount of beta actin (ACTB) as well as Glial fibrillary acidic protein (GFAP) was elevated in SOD1 G93A mice when compared to mice with deletion of RAGE. These data contributes to our understanding of implications of RAGE and its ligands in pathogenesis of ALS and highlight potential targeted therapeutic interventions at the early stage of this devastating disease. Moreover, inhibition of the molecular cross-talk between RAGE and its proinflammatory ligands may abolish neuroinflammation, gliosis and motor neuron damage in SOD1 G93A mice. Hence, we hypothesize that attenuated interaction of RAGE with its proinflammatory ligands may improve well-being and health status during ALS in SOD1 G93A mice. Therefore, we emphasize that the inhibition of RAGE signaling pathway may be a therapeutic target for neurodegenerative diseases.

A novel anti-apoptotic role for Cdc42/ACK-1 signaling in neurons

Neurodegenerative diseases such as amyotrophic lateral sclerosis, Alzheimer's and Parkinson's disease are caused by a progressive and aberrant destruction of neurons in the brain and spinal cord. These disorders lack effective long-term treatments that impact the underlying mechanisms of pathogenesis and as a result, existing options focus primarily on alleviating symptomology. Dysregulated programmed cell death (i.e., apoptosis) is a significant contributor to neurodegeneration, and is controlled by a number of different factors. Rho family GTPases are molecular switches with recognized importance in proper neuronal development and migration that have more recently emerged as central regulators of apoptosis and neuronal survival. Here, we investigated a role for the Rho GTPase family member, Cdc42, and its downstream effectors, in neuronal survival and apoptosis. We initially induced apoptosis in primary cultures of rat cerebellar granule neurons (CGNs) by removing both growth factor-containing serum and depolarizing potassium from the cell medium. We then utilized both chemical inhibitors and adenoviral shRNA targeted to Cdc42 to block the function of Cdc42 or its downstream effectors under either control or apoptotic conditions. Our in vitro studies demonstrate that functional inhibition of Cdc42 or its downstream effector, activated Cdc42-associated tyrosine kinase-1 (ACK-1), had no adverse effects on CGN survival under control conditions, but significantly sensitized neurons to cell death under apoptotic conditions. In conclusion, our results suggest a key pro-survival role for Cdc42/ACK-1 signaling in neurons, particularly in regulating neuronal susceptibility to pro-apoptotic stress such as that observed in neurodegenerative disorders.

Tiam1 coordinates synaptic structural and functional plasticity underpinning the pathophysiology of neuropathic pain

Neuropathic pain is a common, debilitating chronic pain condition caused by damage or a disease affecting the somatosensory nervous system. Understanding the pathophysiological mechanisms underlying neuropathic pain is critical for developing new therapeutic strategies to treat chronic pain effectively. Tiam1 is a Rac1 guanine nucleotide exchange factor (GEF) that promotes dendritic and synaptic growth during hippocampal development by inducing actin cytoskeletal remodeling. Here, using multiple neuropathic pain animal models, we show that Tiam1 coordinates synaptic structural and functional plasticity in the spinal dorsal horn via actin cytoskeleton reorganization and synaptic NMDAR stabilization and that these actions are essential for the initiation, transition, and maintenance of neuropathic pain. Furthermore, an antisense oligonucleotides (ASO) targeting spinal Tiam1 persistently alleviate neuropathic pain sensitivity. Our findings suggest that Tiam1-coordinated synaptic functional and structural plasticity underlies the pathophysiology of neuropathic pain and that intervention of Tiam1-mediated maladaptive synaptic plasticity has long-lasting consequences in neuropathic pain management.

An Initial miRNA Profile of Persons With Persisting Neurobehavioral Impairments and States of Disordered Consciousness After Severe Traumatic Brain Injury

OBJECTIVE

To examine the merits of using microRNAs (miRNAs) as biomarkers of disorders of consciousness (DoC) due to traumatic brain injury (TBI).

SETTINGS

Acute and subacute beds.

PARTICIPANTS

Patients remaining in vegetative and minimally conscious states (VS, MCS), an average of 1.5 years after TBI, and enrolled in a randomized clinical trial ( n = 6). Persons without a diagnosed central nervous system disorder, neurotypical controls ( n = 5).

DESIGN

Comparison of whole blood miRNA profiles between patients and age/gender-matched controls. For patients, correlational analyses between miRNA profiles and measures of neurobehavioral function.

MAIN MEASURES

Baseline measures of whole blood miRNAs isolated from the cellular and fluid components of blood and measured using miRNA-seq and real-time polymerase chain reaction (RT-PCR). Baseline neurobehavioral measures derived from 7 tests.

RESULTS

For patients, relative to controls, 48 miRNA were significantly ( P < .05)/differentially expressed. Cluster analysis showed that neurotypical controls were most similar to each other and with 2 patients (VS: n = 1; and MCS: n = 1). Three patients, all in MCS, clustered separately. The only female in the sample, also in MCS, formed an independent group. For the 48 miRNAs, the enriched pathways identified are implicated in secondary brain damage and 26 miRNAs were significantly ( P < .05) correlated with measures of neurobehavioral function.

CONCLUSIONS

Patients remaining in states of DoC an average of 1.5 years after TBI showed a different and reproducible pattern of miRNA expression relative to age/gender-matched neurotypical controls. The phenotypes, defined by miRNA profiles relative to persisting neurobehavioral impairments, provide the basis for future research to determine the miRNA profiles differentiating states of DoC and the basis for future research using miRNA to detect treatment effects, predict treatment responsiveness, and developing targeted interventions. If future research confirms and advances reported findings, then miRNA profiles will provide the foundation for patient-centric DoC neurorehabilitation.

Rac is required for the survival of cortical neurons

Rac1, a member of small Rho GTPases, is involved in diverse cellular processes in neuronal cells. Rac1 plays especially important roles during development, and its roles have been extensively studied using Rac1-deficient mice. Rac3, a close homolog of Rac1, is ubiquitously expressed in the nervous system and may therefore compensate for Rac1 in Rac1-deficient cells. Exploration of the roles of Rac in neurons may therefore be difficult. We thus deleted both Rac1 and Rac3 in cortical neurons. Rac-deficient cerebral cortices formed slightly hypoplastic but almost normally layered structures at birth, but cortical neurons underwent apoptosis soon after birth. Rac-deficient cortical neurons had poor survivability and there was reduction in the length and the number of neurites in vitro. Activation of Pak1, a downstream effector of Rac, in Rac-deficient cortical neurons rescued the survivability in vitro. Pak1-activated Rac-deficient neurons had numerous dendrites, but no axons. Restoration of p35, a regulator of Cdk5, partly rescued the survivability of Rac-deficient neurons both in vitro and in vivo. Expression of p35 also partly rescued the length and the number of neurites in Rac-deficient neurons in vitro. Rac was shown to be indispensable for the survival of cortical neurons, and Pak1 and Cdk5/p35 work as downstream effectors of Rac to promote neuronal survival.

Crosstalk between the Rho and Rab family of small GTPases in neurodegenerative disorders

Neurodegeneration is associated with defects in cytoskeletal dynamics and dysfunctions of the vesicular trafficking and sorting systems. In the last few decades, studies have demonstrated that the key regulators of cytoskeletal dynamics are proteins from the Rho family GTPases, meanwhile, the central hub for vesicle sorting and transport between target membranes is the Rab family of GTPases. In this regard, the role of Rho and Rab GTPases in the induction and maintenance of distinct functional and morphological neuronal domains (such as dendrites and axons) has been extensively studied. Several members belonging to these two families of proteins have been associated with many neurodegenerative disorders ranging from dementia to motor neuron degeneration. In this analysis, we attempt to present a brief review of the potential crosstalk between the Rab and Rho family members in neurodegenerative pathologies such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington disease, and amyotrophic lateral sclerosis (ALS).

RhoA-LIMK Signaling Axis Reveals Rostral-Caudal Plane and Spatial Dysregulation in the Brain of Alzheimer's Disease Mouse Models

BACKGROUND

RhoA signaling is widely reported to be dysregulated in Alzheimer's disease (AD), but its therapeutic targeting demonstrated mixed outcomes. We hypothesize that the activation and inactivation states of RhoA and LIMK are different in the cortex and in subregions of hippocampus along the rostral-caudal dimensions.

OBJECTIVE

We intended to elucidate the plane and spatial dependent RhoA signaling in association with AD.

METHODS

We applied antibody pRhoA that recognizes an inactive state of RhoA (S188 phosphorylation) and antibody pLIMK against an active state of LIMK (T508 phosphorylation) to investigate RhoA signaling in wildtype (WT) and triple transgenic AD (3xTg-AD) mouse model. We prepared serial sections from the rostral to caudal coronal planes of the entire mouse brain followed by immunofluorescence staining with pRhoA and pLIMK antibodies.

RESULTS

Both pRhoA and pLIMK elicited a shift of expression pattern from rostral to caudal planes. Additionally, pRhoA demonstrated dynamic redistribution between the nucleus and cytoplasm. pLIMK did not show such nucleus and cytoplasm redistribution but the expression level was changed from rostral to caudal planes. At some planes, pRhoA showed an increasing trend in expression in the cortex but a decreasing trend in the dentate gyrus of the 3xTg-AD mouse hippocampus. pLIMK tends to decrease in the cortex but increase in the dentate gyrus of 3xTg-AD mouse hippocampus.

CONCLUSIONS

RhoA activation is dysregulated in both human and mouse AD brains, and the RhoA-LIMK signaling axis reveals spatial dysregulation along the rostral-caudal plane dimensions.

Dermcidin Enhances the Migration, Invasion, and Metastasis of Hepatocellular Carcinoma Cells In Vitro and In Vivo

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is a common primary liver neoplasm with high mortality. Dermcidin (DCD), an antimicrobial peptide, has been reported to participate in oncogenesis. This study assessed the effects and underlying molecular events of DCD overexpression and knockdown on the regulation of HCC progression in vitro and in vivo.

METHODS

The serum DCD level was detected using enzyme-linked immunosorbent assay. DCD overexpression, knockdown, and Ras-related C3 botulinum toxin substrate 1 (Rac1) rescue were performed in SK-HEP-1 cells using plasmids. Immunofluorescence staining, quantitative PCR, and Western blotting were used to detect the expression of different genes and proteins. Differences in HCC cell migration and invasion were detected by Transwell migration and invasion assays. A nude mouse HCC cell orthotopic model was employed to verify the in vitro data.

RESULTS

The level of serum DCD was higher in patients with HCC and in SK-HEP-1 cells. DCD overexpression caused upregulation of DCD, fibronectin, Rac1, and cell division control protein 42 homologue (Cdc42) mRNA and proteins as well as actin-related protein 2/3 (Arp2/3) protein (but reduced Arp2/3 mRNA levels) and activated Rac1 and Cdc42. Phenotypically, DCD overexpression induced HCC cell migration and invasion in vitro, whereas knockout of DCD expression had the opposite effects. A Rac1 rescue experiment in DCD-knockdown HCC cells increased HCC cell migration and invasion and increased the levels of active Rac1/total Rac1, Wiskott-Aldrich syndrome family protein (WASP), Arp2/3, and fibronectin. DCD overexpression induced HCC cell metastasis to the abdomen and liver in vivo.

CONCLUSIONS

DCD promotes HCC cell migration, invasion, and metastasis through upregulation of noncatalytic region of tyrosine kinase adaptor protein 1 (Nck1), Rac1, Cdc42, WASP, and Arp2/3, which induce actin cytoskeletal remodeling and fibronectin-mediated cell adhesion in HCC cells.

Multitarget Hybrid Fasudil Derivatives as a New Approach to the Potential Treatment of Amyotrophic Lateral Sclerosis

Hybrid compounds containing structural fragments of the Rho kinase inhibitor fasudil and the NRF2 inducers caffeic and ferulic acids were designed with the aid of docking and molecular mechanics studies. Following the synthesis of the compounds using a peptide-coupling methodology, they were characterized for their ROCK2 inhibition, radical scavenging, effects on cell viability (MTT assay), and NRF2 induction (luciferase assay). One of the compounds (1d) was selected in view of its good multitarget profile and good tolerability. It was able to induce the NRF2 signature, promoting the expression of the antioxidant response enzymes HO-1 and NQO1, via a KEAP1-dependent mechanism. Analysis of mRNA and protein levels of the NRF2 pathway showed that 1d induced the NRF2 signature in control and SOD1-ALS lymphoblasts but not in sALS, where it was already increased in the basal state. These results show the therapeutic potential of this compound, especially for ALS patients with a SOD1 mutation.

Rac-maninoff and Rho-vel: The symphony of Rho-GTPase signaling at excitatory synapses

Synaptic connections between neurons are essential for every facet of human cognition and are thus regulated with extreme precision. Rho-family GTPases, molecular switches that cycle between an active GTP-bound state and an inactive GDP-bound state, comprise a critical feature of synaptic regulation. Rho-GTPases are exquisitely controlled by an extensive suite of activators (GEFs) and inhibitors (GAPs and GDIs) and interact with many different signalling pathways to fulfill their roles in orchestrating the development, maintenance, and plasticity of excitatory synapses of the central nervous system. Among the mechanisms that control Rho-GTPase activity and signalling are cell surface receptors, GEF/GAP complexes that tightly regulate single Rho-GTPase dynamics, GEF/GAP and GEF/GEF functional complexes that coordinate multiple Rho-family GTPase activities, effector positive feedback loops, and mutual antagonism of opposing Rho-GTPase pathways. These complex regulatory mechanisms are employed by the cells of the nervous system in almost every step of development, and prominently figure into the processes of synaptic plasticity that underlie learning and memory. Finally, misregulation of Rho-GTPases plays critical roles in responses to neuronal injury, such as traumatic brain injury and neuropathic pain, and in neurodevelopmental and neurodegenerative disorders, including intellectual disability, autism spectrum disorder, schizophrenia, and Alzheimer's Disease. Thus, decoding the mechanisms of Rho-GTPase regulation and function at excitatory synapses has great potential for combatting many of the biggest current challenges in mental health.

Immune Signaling Kinases in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD)

Amyotrophic lateral sclerosis (ALS) is the most common neurodegenerative disorder of motor neurons in adults, with a median survival of 3-5 years after appearance of symptoms, and with no curative treatment currently available. Frontotemporal dementia (FTD) is also an adult-onset neurodegenerative disease, displaying not only clinical overlap with ALS, but also significant similarities at genetic and pathologic levels. Apart from the progressive loss of neurons and the accumulation of protein inclusions in certain cells and tissues, both disorders are characterized by chronic inflammation mediated by activated microglia and astrocytes, with an early and critical impact of neurodegeneration along the disease course. Despite the progress made in the last two decades in our knowledge around these disorders, the underlying molecular mechanisms of such non-cell autonomous neuronal loss still need to be clarified. In particular, immune signaling kinases are currently thought to have a key role in determining the neuroprotective or neurodegenerative nature of the central and peripheral immune states in health and disease. This review provides a comprehensive and updated view of the proposed mechanisms, therapeutic potential, and ongoing clinical trials of immune-related kinases that have been linked to ALS and/or FTD, by covering the more established TBK1, RIPK1/3, RACK I, and EPHA4 kinases, as well as other emerging players in ALS and FTD immune signaling.

UNC-45A Is Highly Expressed in the Proliferative Cells of the Mouse Genital Tract and in the Microtubule-Rich Areas of the Mouse Nervous System

UNC-45A (Protein unc-45 homolog A) is a cytoskeletal-associated protein with a dual and non-mutually exclusive role as a regulator of the actomyosin system and a Microtubule (MT)-destabilizing protein, which is overexpressed in human cancers including in ovarian cancer patients resistant to the MT-stabilizing drug paclitaxel. Mapping of UNC-45A in the mouse upper genital tract and central nervous system reveals its enrichment not only in highly proliferating and prone to remodeling cells, but also in microtubule-rich areas, of the ovaries and the nervous system, respectively. In both apparatuses, UNC-45A is also abundantly expressed in the ciliated epithelium. As regulators of actomyosin contractility and MT stability are essential for the physiopathology of the female reproductive tract and of neuronal development, our findings suggest that UNC-45A may have a role in ovarian cancer initiation and development as well as in neurodegeneration.

Pharmacological Modulators of Small GTPases of Rho Family in Neurodegenerative Diseases

Classical Rho GTPases, including RhoA, Rac1, and Cdc42, are members of the Ras small GTPase superfamily and play essential roles in a variety of cellular functions. Rho GTPase signaling can be turned on and off by specific GEFs and GAPs, respectively. These features empower Rho GTPases and their upstream and downstream modulators as targets for scientific research and therapeutic intervention. Specifically, significant therapeutic potential exists for targeting Rho GTPases in neurodegenerative diseases due to their widespread cellular activity and alterations in neural tissues. This study will explore the roles of Rho GTPases in neurodegenerative diseases with focus on the applications of pharmacological modulators in recent discoveries. There have been exciting developments of small molecules, nonsteroidal anti-inflammatory drugs (NSAIDs), and natural products and toxins for each classical Rho GTPase category. A brief overview of each category followed by examples in their applications will be provided. The literature on their roles in various diseases [e.g., Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Frontotemporal dementia (FTD), and Multiple sclerosis (MS)] highlights the unique and broad implications targeting Rho GTPases for potential therapeutic intervention. Clearly, there is increasing knowledge of therapeutic promise from the discovery of pharmacological modulators of Rho GTPases for managing and treating these conditions. The progress is also accompanied by the recognition of complex Rho GTPase modulation where targeting its signaling can improve some aspects of pathogenesis while exacerbating others in the same disease model. Future directions should emphasize the importance of elucidating how different Rho GTPases work in concert and how they produce such widespread yet different cellular responses during neurodegenerative disease progression.

Roles of palmitoylation in structural long-term synaptic plasticity

Long-term potentiation (LTP) and long-term depression (LTD) are important cellular mechanisms underlying learning and memory processes. N-Methyl-d-aspartate receptor (NMDAR)-dependent LTP and LTD play especially crucial roles in these functions, and their expression depends on changes in the number and single channel conductance of the major ionotropic glutamate receptor α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) located on the postsynaptic membrane. Structural changes in dendritic spines comprise the morphological platform and support for molecular changes in the execution of synaptic plasticity and memory storage. At the molecular level, spine morphology is directly determined by actin cytoskeleton organization within the spine and indirectly stabilized and consolidated by scaffold proteins at the spine head. Palmitoylation, as a uniquely reversible lipid modification with the ability to regulate protein membrane localization and trafficking, plays significant roles in the structural and functional regulation of LTP and LTD. Altered structural plasticity of dendritic spines is also considered a hallmark of neurodevelopmental disorders, while genetic evidence strongly links abnormal brain function to impaired palmitoylation. Numerous studies have indicated that palmitoylation contributes to morphological spine modifications. In this review, we have gathered data showing that the regulatory proteins that modulate the actin network and scaffold proteins related to AMPAR-mediated neurotransmission also undergo palmitoylation and play roles in modifying spine architecture during structural plasticity.

Mechanisms and consequences of dysregulation of the Tiam family of Rac activators in disease

The Tiam family proteins - Tiam1 and Tiam2/STEF - are Rac1-specific Guanine Nucleotide Exchange Factors (GEFs) with important functions in epithelial, neuronal, immune and other cell types. Tiam GEFs regulate cellular migration, proliferation and survival, mainly through activating and directing Rac1 signalling. Dysregulation of the Tiam GEFs is significantly associated with human diseases including cancer, immunological and neurological disorders. Uncovering the mechanisms and consequences of dysregulation is therefore imperative to improving the diagnosis and treatment of diseases. Here we compare and contrast the subcellular localisation and function of Tiam1 and Tiam2/STEF, and review the evidence for their dysregulation in disease.

Evaluation of active Rac1 levels in cancer cells: A case of misleading conclusions from immunofluorescence analysis

A large number of aggressive cancer cell lines display elevated levels of activated Rac1, a small GTPase widely implicated in cytoskeleton reorganization, cell motility, and metastatic dissemination. A commonly accepted methodological approach for detecting Rac1 activation in cancer cells involves the use of a conformation-sensitive antibody that detects the active (GTP-bound) Rac1 without interacting with the GDP-bound inactive form. This antibody has been extensively used in fixed cell immunofluorescence and immunohistochemistry. Taking advantage of prostate and pancreatic cancer cell models known to have high basal Rac1-GTP levels, here we have established that this antibody does not recognize Rac1 but rather detects the intermediate filament protein vimentin. Indeed, Rac1-null PC3 prostate cancer cells or cancer models with low levels of Rac1 activation still show a high signal with the anti-Rac1-GTP antibody, which is lost upon silencing of vimentin expression. Moreover, this antibody was unable to detect activated Rac1 in membrane ruffles induced by epidermal growth factor stimulation. These results have profound implications for the study of this key GTPase in cancer, particularly because a large number of cancer cell lines with characteristic mesenchymal features show simultaneous up-regulation of vimentin and high basal Rac1-GTP levels when measured biochemically. This misleading correlation can lead to assumptions about the validity of this antibody and inaccurate conclusions that may affect the development of appropriate therapeutic approaches for targeting the Rac1 pathway.