Laminins are major constituents of basement membranes and are essential for tissue homeostasis. Laminin-511 is highly expressed in the intestine and its absence causes severe malformation of the ...intestine and embryonic lethality. To understand the mechanistic role of laminin-511 in tissue homeostasis, we used RNA profiling of embryonic intestinal tissue of lama5 knockout mice and identified a lama5 specific gene expression signature. By combining cell culture experiments with mediated knockdown approaches, we provide a mechanistic link between laminin α5 gene deficiency and the physiological phenotype. We show that laminin α5 plays a crucial role in both epithelial and mesenchymal cell behavior by inhibiting Wnt and activating PI3K signaling. We conclude that conflicting signals are elicited in the absence of lama5, which alter cell adhesion, migration as well as epithelial and muscle differentiation. Conversely, adhesion to laminin-511 may serve as a potent regulator of known interconnected PI3K/Akt and Wnt signaling pathways. Thus deregulated adhesion to laminin-511 may be instrumental in diseases such as human pathologies of the gut where laminin-511 is abnormally expressed as it is shown here.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
During development, neuronal growth cones navigate over long distances to reach their target and establish appropriate connections. This process is usually described as a step-by-step mechanism of ...growth recruiting several guidance cues with attractive and repulsive properties. Among these signals, the semaphorins define a large family of more than 20 members divided into eight classes according to their phylogenic relationship and the existence of differential structural domains or sequence motifs 1 Fig. 1). Classes I and II are found in invertebrates and classes III, IV and VII in vertebrates while class V contains members from both vertebrates and invertebrates. The class VIII corresponds to viral semaphorins. Semaphorins can be soluble proteins (classes II and III), transmembrane proteins (classes I, IV, V and VI) or membrane-bound through a glycosylphosphatidylinositol anchor (class VII). Together with plexins and scatter factor receptors, semaphorins belong to the semaphorin superfamily whose defining feature is the existence of a conserved domain: the semaphorin domain. This domain of more than 500 amino acids located at the mature protein N-terminus was first identified by Kolodkin and collaborators in 1993 2. All semaphorins also contain N-glycosylation sites and their C-terminal part is differing from one class to another. Indeed, class V contains seven copies of thrombospondin repeats, classes II–V and VII contain an immunoglobulin-like domain while class III has an N-terminus basic motif. Semaphorins are widely expressed in the developing nervous system. Initially described as guidance cues ensuring axon targeting, further studies showed that they are also key regulators of cell migration, cell death or synapse formation during nervous system development. Like other guidance cues, semaphorins are also clearly implicated in various aspects of organogenesis 3 (including lung and kidney formation or angiogenesis) and during tumor progression 4. Here, we review the major functions of semaphorins in the nervous system together with the signaling mechanisms involved both at the level of receptor complex formation and recruitment of selective intracellular pathways.
Sialidases, or neuraminidases, are involved in several human disorders such as neurodegenerative, infectious and cardiovascular diseases, and cancers. Accumulative data have shown that inhibition of ...neuraminidases, such as NEU1 sialidase, may be a promising pharmacological target, and selective inhibitors of NEU1 are therefore needed to better understand the biological functions of this sialidase. In the present study, we designed interfering peptides (IntPep) that target a transmembrane dimerization interface previously identified in human NEU1 that controls its membrane dimerization and sialidase activity. Two complementary strategies were used to deliver the IntPep into cells, either flanked to a TAT sequence or non-tagged for solubilization in detergent micelles. Combined with molecular dynamics simulations and heteronuclear nuclear magnetic resonance (NMR) studies in membrane-mimicking environments, our results show that these IntPep are able to interact with the dimerization interface of human NEU1, to disrupt membrane NEU1 dimerization and to strongly decrease its sialidase activity at the plasma membrane. In conclusion, we report here new selective inhibitors of human NEU1 of strong interest to elucidate the biological functions of this sialidase.
There is increasing evidence for a crucial role of proteases and metalloproteinases during axon growth and guidance. In this context, we recently described a functional link between the ...chemoattractive Sema3C and Matrix metalloproteinase 3 (MMP3). Here, we provide data demonstrating the involvement of MMP-2 to trigger the growth-promoting effect of Sema3A in cortical dendrites. The in situ analysis of MMP-2 expression and activity is consistent with a functional growth assay demonstrating in vitro that the pharmacological inhibition of MMP-2 reduces the growth of cortical dendrites in response to Sema3A. Hence, our results suggest that the selective recruitment and activation of MMP-2 in response to Sema3A requires a PKC alpha dependent mechanism. Altogether, we provide a second set of data supporting MMPs as effectors of the growth-promoting effects of semaphorins, and we identify the potential signalling pathway involved.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Amyloid precursor protein (APP), commonly associated with Alzheimer disease, is upregulated and distributes evenly along the injured axons, and therefore, also known as a marker of demyelinating ...axonal injury and axonal degeneration. However, the physiological distribution and function of APP along myelinated axons was unknown. We report that APP aggregates at nodes of Ranvier (NOR) in the myelinated central nervous system (CNS) axons but not in the peripheral nervous system (PNS). At CNS NORs, APP expression co-localizes with tenascin-R and is flanked by juxtaparanodal potassium channel expression demonstrating that APP localized to NOR. In APP-knockout (KO) mice, nodal length is significantly increased, while sodium channels are still clustered at NORs. Moreover, APP KO and APP-overexpressing transgenic (APP TG) mice exhibited a decreased and an increased thickness of myelin in spinal cords, respectively, although the changes are limited in comparison to their littermate WT mice. The thickness of myelin in APP KO sciatic nerve also increased in comparison to that in WT mice. Our observations indicate that APP acts as a novel component at CNS NORs, modulating nodal formation and has minor effects in promoting myelination.
Previously, we demonstrated that loss of SEMA3F, a secreted semaphorin encoded in 3p21.3, is associated with higher stages in lung cancer and primary tumor cells studied with anti-vascular ...endothelial growth factor (VEGF) and SEMA3F antibodies. In vitro, SEMA3F inhibits cell spreading; this activity is opposed by VEGF. These results suggest that VEGF and SEMA3F compete for binding to their common neuropilin receptor. In the present report, we investigated the attractive/repulsive effects of SEMA3F on cell migration when cells were grown in a threedimensional system and exposed to a SEMA3F gradient. In addition, we adapted the neurobiologic stripe assay to analyze the migration of tumor cells in response to SEMA3F. In the motile breast cancer cell line C100, which expresses both neuropilin-1 (NRPi) and neuropilin-2 (NRP2) receptors, SEMA3F had a repulsive effect, which was blocked by anti-NRP2 antibody. In less motile MCF7 cells, which express only NRPi, SEMA3F inhibited cell contacts with loss of membrane-associated E-cadherin and β-catenin without motility induction. Cell spreading and proliferation were reduced. These results support the concept that in a first step during tumorigenesis, normal tissues expressing SEMA3F would try to prevent tumor cells from spreading and attaching to the stroma for further implantation.
The dynamic and coordinated interaction between cells and their microenvironment controls cell migration, proliferation, and apoptosis, mediated by different cell surface molecules. We have studied ...the response of a neuroectodermal progenitor cell line, Dev, to a guidance molecule, semaphorin 3A (Sema3A), described previously as a repellent-collapsing signal for axons, and we have shown that Sema3A acts as a repellent guidance cue for migrating progenitor cells and, on prolonged application, induces apoptosis. Both repulsion and induction of cell death are mediated by neuropilin-1, the ligand-binding component of the Sema3A receptor. The vascular endothelial growth factor, VEGF165, antagonizes Sema3A-induced apoptosis and promotes cell survival, migration, and proliferation. Surprisingly, repulsion by Sema3A also depends on expression of VEGFR1, a VEGF165 receptor, expressed in Dev cells. Moreover, we found that these repulsive effects of Sema3A require tyrosine kinase activity, which can be attributed to VEGFR1. These results indicate that the balance between guidance molecules and angiogenic factors can modulate the migration, apoptosis (or survival), and proliferation of neural progenitor cells through shared receptors.
Our understanding of the molecular and cellular mechanisms controlling cell adhesion and migration has never been so high. The era of "molecular interactions" requires an appropriate tool for ...exchanging views, presenting outstanding results and discussing new concepts in the field. This is why we decided to launch Cell Adhesion and Migration (CAM), a multi-disciplinary journal publishing original research articles and reviews covering the latest aspects of cellular and molecular mechanisms and their regulation both during physiological and pathological processes.
Human death receptors control apoptotic events during cell differentiation, cell homeostasis and the elimination of damaged or infected cells. Receptor activation involves ligand-induced structural ...reorganizations of preformed receptor trimers. Here we show that the death receptor transmembrane domains only have a weak intrinsic tendency to homo-oligomerize within a membrane, and thus these domains potentially do not significantly contribute to receptor trimerization. However, mutation of Pro183 in the human CD95/Fas receptor transmembrane helix results in a dramatically increased interaction propensity, as shown by genetic assays. The increased interaction of the transmembrane domain is coupled with a decreased ligand-sensitivity of cells expressing the Fas receptor, and thus in a decreased number of apoptotic events. Mutation of Pro183 likely results in a substantial rearrangement of the self-associated Fas receptor transmembrane trimer, which likely abolishes further signaling of the apoptotic signal but may activate other signaling pathways. Our study shows that formation of a stable Fas receptor transmembrane helix oligomer does not per se result in receptor activation.
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•Human death cell receptor transmembrane domains oligomerize within membranes•Pro183 in the transmembrane helix abolished oligomerization of the Fas receptor•A Pro183→Ala mutated Fas receptor has an increased oligomerization propensity.•A Pro183→Ala mutated Fas receptor has a decreased ligand-sensitivity.•Mutation of Pro183 results in a decreased number of apoptotic events
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