The Src Homology 2 Domain Protein Shep1 Plays an Important Role in the Penetration of Olfactory Sensory Axons into the Forebrain
Shep1 is a multidomain signaling protein that forms a complex with Cas, a key scaffolding component of integrin signaling pathways, to promote the migration of non-neuronal cells. However, the physiological function of Shep1 in the nervous system remains unknown. Interestingly, we found that Shep1 and Cas are both concentrated in the axons of developing olfactory sensory neurons (OSNs). These neurons extend their axons from the olfactory epithelium to the olfactory bulb located at the anterior tip of the forebrain. However, in developing Shep1 knock-out mice, we did not detect penetration of OSN axons across the pial basement membrane surrounding the olfactory bulb, suggesting that Shep1 function is important for the establishment of OSN connections with the olfactory bulb. Interestingly, we observed reduced levels of Cas tyrosine phosphorylation in OSN axons of Shep1 knock-out mice, suggesting compromised Cas signaling function. Indeed, when embedded in a three-dimensional gel of basement membrane proteins, explants from Shep1 knock-out olfactory epithelium extend neuronal processes less efficiently than explants from control epithelium. Furthermore, ectopic expression of Shep1 in non-neuronal cells promotes cell migration through a collagen gel. Later in development, loss of Shep1 function also causes a marked reduction in olfactory bulb size and disruption of bulb lamination, which may be primarily attributable to the defective innervation. The greatly reduced OSN connections and hypoplasia of the olfactory bulb, likely resulting in anosmia, are reminiscent of the symptoms of Kallmann syndrome, a human developmental disease that can be caused by mutations in a growing number of genes.
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ABSTRACT: Members of the novel SH2-containing protein (NSP) and Crk-associated substrate (Cas) protein families form multidomain signaling platforms that mediate cell migration and invasion through a collection of distinct signaling motifs. Members of each family interact via their respective C-terminal domains, but the mechanism of this association has remained enigmatic. Here we present the crystal structures of the C-terminal domain from the NSP protein BCAR3 and the complex of NSP3 with p130Cas. BCAR3 adopts the Cdc25-homology fold of Ras GTPase exchange factors, but it has a 'closed' conformation incapable of enzymatic activity. The structure of the NSP3-p130Cas complex reveals that this closed conformation is instrumental for interaction of NSP proteins with a focal adhesion-targeting domain present in Cas proteins. This enzyme-to-adaptor conversion enables high-affinity, yet promiscuous, interactions between NSP and Cas proteins and represents an unprecedented mechanistic paradigm linking cellular signaling networks.
Nature Structural & Molecular Biology 11/2011; 18(12):1381-7. DOI:10.1038/nsmb.2152 · 13.31 Impact Factor
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ABSTRACT: The CAS (CRK-associated substrate) family of adaptor proteins comprises 4 members, which share a conserved modular domain structure that enables multiple protein-protein interactions, leading to the assembly of intracellular signaling platforms. Besides their physiological role in signal transduction downstream of a variety of cell surface receptors, CAS proteins are also critical for oncogenic transformation and cancer cell malignancy through associations with a variety of regulatory proteins and downstream effectors. Among the regulatory partners, the 3 recently identified adaptor proteins constituting the NSP (novel SH2-containing protein) family avidly bind to the conserved carboxy-terminal focal adhesion-targeting (FAT) domain of CAS proteins. NSP proteins use an anomalous nucleotide exchange factor domain that lacks catalytic activity to form NSP-CAS signaling modules. Additionally, the NSP SH2 domain can link NSP-CAS signaling assemblies to tyrosine-phosphorylated cell surface receptors. NSP proteins can potentiate CAS function by affecting key CAS attributes such as expression levels, phosphorylation state, and subcellular localization, leading to effects on cell adhesion, migration, and invasion as well as cell growth. The consequences of these activities are well exemplified by the role that members of both families play in promoting breast cancer cell invasiveness and resistance to antiestrogens. In this review, we discuss the intriguing interplay between the NSP and CAS families, with a particular focus on cancer signaling networks.
Genes & cancer 05/2012; 3(5-6):382-93. DOI:10.1177/1947601912460050
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ABSTRACT: The CD200/CD200R inhibitory immune ligand-receptor system regulates microglial activation/quiescence in adult brain. Here, we investigated CD200/CD200R at different stages of postnatal development, when microglial maturation takes place. We characterized the spatiotemporal, cellular, and quantitative expression pattern of CD200 and CD200R in the developing and adult C57/BL6 mice brain by immunofluorescent labeling and Western blotting. CD200 expression increased from postnatal day 1 (P1) to P5-P7, when maximum levels were found, and decreased to adulthood. CD200 was located surrounding neuronal bodies, and very prominently in cortical layer I, where CD200(+) structures included glial fibrillary acidic protein (GFAP)(+) astrocytes until P7. In the hippocampus, CD200 was mainly observed in the hippocampal fissure, where GFAP(+) /CD200(+) astrocytes were also found until P7. CD200(+) endothelium was seen in the hippocampal fissure and cortical blood vessels, notably from P14, showing maximum vascular CD200 in adults. CD200R(+) cells were a population of ameboid/pseudopodic Iba1(+) microglia/macrophages observed at all ages, but significantly decreasing with increasing age. CD200R(+) /Iba1(+) macrophages were prominent in the pial meninges and ventricle lining, mainly at P1-P5. CD200R(+) /Iba1(+) perivascular macrophages were observed in cortical and hippocampal fissure blood vessels, showing maximum density at P7, but being prominent until adulthood. CD200R(+) /Iba1(+) ameboid microglia in the cingulum at P1-P5 were the only CD200R(+) cells in the nervous tissue. In conclusion, the main sites of CD200/CD200R interaction seem to include the molecular layer and pial surface in neonates and blood vessels from P7 until adulthood, highlighting the possible role of the CD200/CD200R system in microglial development and renewal.
The Journal of Comparative Neurology 08/2012; 520(12):2657-75. DOI:10.1002/cne.23062 · 3.23 Impact Factor
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