Interfering with the ERC1-LL5β interaction disrupts plasma membrane-Associated platforms and affects tumor cell motility.

Cell migration requires a complex array of molecular events to promote protrusion at the front of motile cells. The scaffold protein LL5β interacts with the scaffold ERC1, and recruits it at plasma membrane-associated platforms that form at the front of migrating tumor cells. LL5 and ERC1 proteins support protrusion during migration as shown by the finding that depletion of either endogenous protein impairs tumor cell motility and invasion.

A functional interaction between liprin-α1 and B56γ regulatory subunit of protein phosphatase 2A supports tumor cell motility.

Scaffold liprin-α1 is required to assemble dynamic plasma membrane-associated platforms (PMAPs) at the front of migrating breast cancer cells, to promote protrusion and invasion. We show that the N-terminal region of liprin-α1 contains an LxxIxE motif interacting with B56 regulatory subunits of serine/threonine protein phosphatase 2A (PP2A). The specific interaction of B56γ with liprin-α1 requires an intact motif, since two point mutations strongly reduce the interaction.

Paxillin: A Hub for Mechano-Transduction from the β3 Integrin-Talin-Kindlin Axis.

Focal adhesions are specialized integrin-dependent adhesion complexes, which ensure cell anchoring to the extracellular matrix. Focal adhesions also function as mechano-signaling platforms by perceiving and integrating diverse physical and (bio)chemical cues of their microenvironment, and by transducing them into intracellular signaling for the control of cell behavior. The fundamental biological mechanism of creating intracellular signaling in response to changes in tensional forces appears to be tightly linked to paxillin recruitment and binding to focal adhesions.

Liprins in oncogenic signaling and cancer cell adhesion.

Liprins are a multifunctional family of scaffold proteins, identified by their involvement in several important neuronal functions related to signaling and organization of synaptic structures. More recently, the knowledge on the liprin family has expanded from neuronal functions to processes relevant to cancer progression, including cell adhesion, cell motility, cancer cell invasion, and signaling. These proteins consist of regions, which by prediction are intrinsically disordered, and may be involved in the assembly of supramolecular structures relevant for their functions.

Liquid-Liquid Phase Separation at the Plasma Membrane-Cytosol Interface: Common Players in Adhesion, Motility, and Synaptic Function.

Networks of scaffold proteins and enzymes assemble at the interface between the cytosol and specific sites of the plasma membrane, where these networks guide distinct cellular functions. Some of these plasma membrane-associated platforms (PMAPs) include shared core components that are able to establish specific protein-protein interactions, to produce distinct supramolecular assemblies regulating dynamic processes as diverse as cell adhesion and motility, or the formation and function of neuronal synapses. How cells organize such dynamic networks is still an open question.

Rac1 and Rac3 have opposite functions in Schwann cells during developmental myelination.

Small Rho GTPases such as Cdc42 and Rac1 regulate peripheral myelination during development. Deletion of Rac1 in Schwann cell conditional knockout mice causes a delay in the process of radial sorting, followed by hypomyelination as well as defective PAK1 activation and high number of immature Oct6 Schwann cells. Rac3 has been shown to have redundant, specific and even opposite functions to Rac1 depending on the cell type, age and other factors.

Dysregulation of myelin synthesis and actomyosin function underlies aberrant myelin in CMT4B1 neuropathy.

Charcot-Marie-Tooth type 4B1 (CMT4B1) is a severe autosomal recessive demyelinating neuropathy with childhood onset, caused by loss-of-function mutations in the myotubularin-related 2 () gene. MTMR2 is a ubiquitously expressed catalytically active 3-phosphatase, which in vitro dephosphorylates the 3-phosphoinositides PtdIns3 and PtdIns(3,5), with a preference for PtdIns(3,5) A hallmark of CMT4B1 neuropathy are redundant loops of myelin in the nerve termed myelin outfoldings, which can be considered the consequence of altered growth of myelinated fibers during postnatal development. How MTMR2 loss and the resulting imbalance of 3'-phosphoinositides cause CMT4B1 is unknown.

Biomolecular Condensates at the Front: Cell Migration Meets Phase Separation.

Liquid-liquid phase separation drives the formation of biomolecular condensates (BCs) for the spatiotemporal organization of several cellular processes. Recent evidences indicate that components of plasma-membrane-associated platforms form biomolecular condensates near focal adhesions (FAs), and suggest that phase separation regulates dynamic processes occurring at the front of migrating cells.

The Rac3 GTPase in Neuronal Development, Neurodevelopmental Disorders, and Cancer.

Rho family small guanosine triphosphatases (GTPases) are important regulators of the cytoskeleton, and are critical in many aspects of cellular and developmental biology, as well as in pathological processes such as intellectual disability and cancer. Of the three members of the family, Rac3 has a more restricted expression in normal tissues compared to the ubiquitous member of the family, Rac1. The Rac3 polypeptide is highly similar to Rac1, and orthologues of the gene for Rac3 have been found only in vertebrates, indicating the late appearance of this gene during evolution.

Rac1 and Rac3 GTPases differently influence the morphological maturation of dendritic spines in hippocampal neurons.

The Rac1 and Rac3 GTPases are co-expressed in the developing nervous system, where they are involved in different aspects of neuronal development, including the formation of synapses. The deletion of both Rac genes determines a stronger reduction of dendritic spines in vitro compared to the knockout of either gene, indicating that Rac1 and Rac3 play a synergistic role in the formation of these structures. Here, we have addressed the role of each GTPase in the formation of dendritic spines by overexpressing either Rac1 or Rac3 in wildtype neurons, or by re-expressing either GTPase in double knockout hippocampal cultures.

A Method to Culture GABAergic Interneurons Derived from the Medial Ganglionic Eminence.

Understanding the mechanisms guiding interneuron development is a central aspect of the current research on cortical/hippocampal interneurons, which is highly relevant to brain function and pathology. In this methodological study we have addressed the setup of protocols for the reproducible culture of dissociated cells from murine medial ganglionic eminences (MGEs), to provide a culture system for the analysis of interneurons . This study includes the detailed protocols for the preparation of the dissociated cells, and for their culture on optimal substrates for cell migration or differentiation.

Identification of a membrane-less compartment regulating invadosome function and motility.

Depletion of liprin-α1, ERC1 or LL5 scaffolds inhibits extracellular matrix degradation by invasive cells. These proteins co-accumulate near invadosomes in NIH-Src cells, identifying a novel invadosome-associated compartment distinct from the core and adhesion ring of invadosomes. Depletion of either protein perturbs the organization of invadosomes without influencing the recruitment of MT1-MMP metalloprotease.

Novel role of Rac-Mid1 signaling in medial cerebellar development.

Rac signaling impacts a relatively large number of downstream targets; however, few studies have established an association between Rac pathways and pathological conditions. In the present study, we generated mice with double knockout of and ( ) in cerebellar granule neurons (CGNs). We observed impaired tangential migration at E16.

Identification of a Protein Network Driving Neuritogenesis of MGE-Derived GABAergic Interneurons.

Interneurons are essential modulators of brain activity and their abnormal maturation may lead to neural and intellectual disabilities. Here we show that cultures derived from murine medial ganglionic eminences (MGEs) produce virtually pure, polarized γ-aminobutyric acid (GABA)-ergic interneurons that can form morphologically identifiable inhibitory synapses. We show that Rac GTPases and a protein complex including the GIT family scaffold proteins are expressed during maturation , and are required for the normal development of neurites.

Disruption of ArhGAP15 results in hyperactive Rac1, affects the architecture and function of hippocampal inhibitory neurons and causes cognitive deficits.

During brain development, the small GTPases Rac1/Rac3 play key roles in neuronal migration, neuritogenesis, synaptic formation and plasticity, via control of actin cytoskeleton dynamic. Their activity is positively and negatively regulated by GEFs and GAPs molecules, respectively. However their in vivo roles are poorly known.

Liprin-α1 and ERC1 control cell edge dynamics by promoting focal adhesion turnover.

Liprin-α1 and ERC1 are interacting scaffold proteins regulating the motility of normal and tumor cells. They act as part of plasma membrane-associated platforms at the edge of motile cells to promote protrusion by largely unknown mechanisms. Here we identify an amino-terminal region of the liprin-α1 protein (liprin-N) that is sufficient and necessary for the interaction with other liprin-α1 molecules.

Role of Liprins in the Regulation of Tumor Cell Motility and Invasion.

Invasion leading to the formation of metastasis is one of the hallmarks of cancer. Analysis of different human cancers has led to the identification of the PPFIA1 gene encoding the protein liprin-α1, a possible player in cancer. The PPFIA1 gene is amplified in malignant tumors, including about 20% of breast cancers.

Effects of the scaffold proteins liprin-α1, β1 and β2 on invasion by breast cancer cells.

Background Information: The expression of the scaffold protein liprin-α1 is upregulated in human breast cancer. This protein is part of a molecular network that is important for tumour cell invasion in vitro. Liprin-α1 promotes invasion by supporting the protrusive activity at the leading edge of the migrating tumour cell and the degradation of the extracellular matrix by invadopodia.

Loss of Either Rac1 or Rac3 GTPase Differentially Affects the Behavior of Mutant Mice and the Development of Functional GABAergic Networks.

Rac GTPases regulate the development of cortical/hippocampal GABAergic interneurons by affecting the early development and migration of GABAergic precursors. We have addressed the function of Rac1 and Rac3 proteins during the late maturation of hippocampal interneurons. We observed specific phenotypic differences between conditional Rac1 and full Rac3 knockout mice.

Plasma membrane-associated platforms: dynamic scaffolds that organize membrane-associated events.

Specialized regions of the plasma membrane dedicated to diverse cellular processes, such as vesicle exocytosis, extracellular matrix remodeling, and cell migration, share a few cytosolic scaffold proteins that associate to form large plasma membrane-associated platforms (PMAPs). PMAPs organize signaling events and trafficking of membranes and molecules at specific membrane domains. On the basis of the intrinsic disorder of the proteins constituting the core of these PMAPs and of the dynamics of these structures at the periphery of motile cells, we propose a working model for the assembly and turnover of these platforms.

Roles of Rac1 and Rac3 GTPases during the development of cortical and hippocampal GABAergic interneurons.

Rac GTPases are regulators of the cytoskeleton that play an important role in several aspects of neuronal and brain development. Two distinct Rac GTPases are expressed in the developing nervous system, the widely expressed Rac1 and the neural-specific Rac3 proteins. Recent experimental evidence supports a central role of these two Rac proteins in the development of inhibitory GABAergic interneurons, important modulatory elements of the brain circuitry.

Liprin-α1, ERC1 and LL5 define polarized and dynamic structures that are implicated in cell migration.

Cell migration during development and metastatic invasion requires the coordination of actin and adhesion dynamics to promote protrusive activity at the front of the cell. The knowledge of the molecular mechanisms required to achieve such coordination is fragmentary. Here, we identify a new functional complex that drives cell motility.

Reduction in parvalbumin-positive interneurons and inhibitory input in the cortex of mice with experimental autoimmune encephalomyelitis.

In multiple sclerosis (MS), inflammation leads to damage of central nervous system myelin and axons. Previous studies have postulated impaired GABA transmission in MS, and recent postmortem analysis has shown that GABAergic parvalbumin (PV)-positive interneurons are decreased in the primary motor cortex (M1) of patients with MS. In this report, we present evidence for the loss of a specific population of GABAergic interneurons in the experimental autoimmune encephalomyelitis mouse model of MS.