The proteoglycan lectin domain binds sulfated cell surface glycolipids and promotes cell adhesion.
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The lecticans are a group of chondroitin sulfate proteoglycans characterized by the presence of C-type lectin domains. Despite the suggestion that their lectin domains interact with carbohydrate ligands, the identity of such ligands has not been elucidated. We previously showed that brevican, a nervous system-specific lectican, binds the surface of B28 glial cells (Yamada, H., Fredette, B., Shitara, K., Hagihara, K., Miura, R., Ranscht, B., Stallcup, W. B., and Yamaguchi, Y. (1997) J. Neurosci. 17, 7784-7795). In this paper, we demonstrate that two classes of sulfated glycolipids, sulfatides and HNK-1-reactive sulfoglucuronylglycolipids (SGGLs), act as cell surface receptors for brevican. The lectin domain of brevican binds sulfatides and SGGLs in a calcium-dependent manner as expected of a C-type lectin domain. Intact, full-length brevican also binds both sulfatides and SGGLs. The lectin domain immobilized as a substrate supports adhesion of cells expressing SGGLs or sulfatides, which was inhibited by monoclonal antibodies against these glycolipids or by treatment of the substrate with SGGLs or sulfatides. Our findings demonstrate that the interaction between the lectin domains of lecticans and sulfated glycolipids comprises a novel cell substrate recognition system, and suggest that lecticans in extracellular matrices serve as substrate for adhesion and migration of cells expressing these glycolipids in vivo. (+info)
The absence of fiber regrowth in the injured mammalian CNS is influenced by several different factors and mechanisms. Besides the nonconducive properties of the glial scar tissue that forms around the lesion site, individual molecules present in CNS myelin and expressed by oligodendrocytes, such as NI-35/NI-250, bNI-220, and myelin-associated glycoprotein (MAG), have been isolated and shown to inhibit axonal growth. Here, we report an additional neurite growth-inhibitory activity purified from bovine spinal cord myelin that is not related to bNI-220 or MAG. This activity can be ascribed to the presence of two chondroitin sulfate proteoglycans (CSPGs), brevican and the brain-specific versican V2 splice variant. Neurite outgrowth of neonatal cerebellar granule cells and of dorsal root ganglion neurons in vitro was strongly inhibited by this myelin fraction enriched in CSPGs. Immunohistochemical staining revealed that brevican and versican V2 are present on the surfaces of differentiated oligodendrocytes. We provide evidence that treatment of oligodendrocytes with the proteoglycan synthesis inhibitors beta-xylosides can strongly influence the growth permissiveness of oligodendrocytes. beta-Xylosides abolished cell surface presentation of brevican and versican V2 and reversed growth cone collapse in encounters with oligodendrocytes as demonstrated by time-lapse video microscopy. Instead, growth cones were able to grow along or even into the processes of oligodendrocytes. Our results strongly suggest that brevican and versican V2 are additional components of CNS myelin that contribute to its nonpermissive substrate properties for axonal growth. Expression of these CSPGs on oligodendrocytes may indicate that they participate in the restriction of structural plasticity and regeneration in the adult CNS. (+info)
The chondroitin sulfate proteoglycans neurocan and phosphacan are expressed by reactive astrocytes in the chronic CNS glial scar.
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Chondroitin sulfate proteoglycans (CS-PGs) expressed by reactive astrocytes may contribute to the axon growth-inhibitory environment of the injured CNS. The specific potentially inhibitory CS-PGs present in areas of reactive gliosis, however, have yet to be thoroughly examined. In this study, we used immunohistochemistry, combined immunohistochemistry-in situ hybridization, immunoblot analysis, and reverse transcription-PCR to examine the expression of specific CS-PGs by reactive astrocytes in an in vivo model of reactive gliosis: that is, the glial scar, after cortical injury. Neurocan and phosphacan can be localized to reactive astrocytes 30 d after CNS injury, whereas brevican and versican are not expressed in the chronic glial scar. Neurocan is also expressed by astrocytes in primary cell culture. Relative to the amount present in cultured astrocytes or uninjured cortex, neurocan expression increases significantly in the glial scar resulting from cortical injury, including the re-expression of the neonatal isoform of neurocan. In contrast, phosphacan protein levels are decreased in the glial scar compared with the uninjured brain. Because these CS-PGs are capable of inhibiting neurite outgrowth in vitro, our data suggest that phosphacan and neurocan in areas of reactive gliosis may contribute to axonal regenerative failure after CNS injury. (+info)
A peptide mimic of E-selectin ligand inhibits sialyl Lewis X-dependent lung colonization of tumor cells.
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Selectins bind to carbohydrate ligands in a calcium-dependent manner and play critical roles in host defense and possibly in tumor metastasis. To isolate peptides that mimic E-selectin ligands, we screened a phage peptide library using E-selectin as a target molecule. This attempt unexpectedly failed, probably because the binding affinity of E-selectin to its ligand is low. We then took an approach that is analogous to the isolation of anti-idiotype antibodies and were able to isolate peptides that bound to anticarbohydrate antibodies recognizing E-selectin ligands. These peptides, enriched for their binding to anti-Lewis A antibody, were found to bind to E-, P- and L-selectins in a calcium-dependent manner. Phage harboring the identified peptide IELLQAR and synthetic peptides having the same sequence inhibited the binding of sialyl Lewis X or sialyl Lewis A oligosaccharides to E-selectin. The adhesion of HL-60 and B16 melanoma cells expressing sialyl Lewis X to E-selectin was also inhibited by the phage-displaying IELLQAR peptide. Moreover, i.v. injected IELLQAR peptide inhibited the lung colonization of mouse B16 melanoma and human lung tumor cells expressing sialyl Lewis X. These results demonstrate that it is possible to isolate peptides mimicking carbohydrate ligands by screening the peptides for binding to anticarbohydrate antibodies and then using them to inhibit carbohydrate-dependent experimental tumor metastasis. (+info)
Brain-enriched hyaluronan binding (BEHAB)/brevican cleavage in a glioma cell line is mediated by a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) family member.
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Brain-enriched hyaluronan binding (BEHAB)/brevican is a brain-specific extracellular matrix protein containing a cleavage site between Glu(395)-Ser(396), which bears remarkable homology to the "aggrecanase" site in the cartilage proteoglycan aggrecan. Expression of BEHAB/brevican is dramatically increased in human gliomas, notoriously invasive tumors. Recently, we showed that the rat 9L gliosarcoma cell line, which does not express BEHAB/brevican and forms non-invasive tumors when grown as intracranial grafts, can form invasive tumors when transfected with a 5' cDNA fragment of BEHAB/brevican, but not when transfected with the full-length cDNA. In marked contrast, the highly invasive CNS-1 glioma cell line expresses and cleaves BEHAB/brevican protein when grown as an intracranial graft. These results suggest that both synthesis and cleavage of BEHAB/brevican protein may play a role in the invasiveness of gliomas. We report here, using an antibody developed to the neoepitope created by BEHAB/brevican cleavage at the Glu(395)-Ser(396) site, that the CNS-1 cells are able to cleave the protein in vitro. We characterized the CNS-1-derived cleavage activity by assaying its ability to cleave BEHAB/brevican proteoglycan, and determined that the enzyme is a constitutively expressed, secreted activity. Using a variety of protease inhibitors, reverse transcriptase-polymerase chain reaction, and specific antibodies, we determined that this activity is likely to be a member of the ADAMTS family of metalloproteinases, specifically ADAMTS4. These results suggest a novel function for ADAMTS family members in BEHAB/brevican cleavage and glioma and indicate that inhibition of ADAMTS in glioma may provide a novel therapeutic strategy. (+info)
Brevican is degraded by matrix metalloproteinases and aggrecanase-1 (ADAMTS4) at different sites.
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Brevican is a member of the lectican family of chondroitin sulfate proteoglycans that is predominantly expressed in the central nervous system. The susceptibility of brevican to digestion by matrix metalloproteinases (MMP-1, -2, -3, -7, -8, -9, -10, and -13 and membrane type 1 and 3 MMPs) and aggrecanase-1 (ADAMTS4) was examined. MMP-1, -2, -3, -7, -8, -10, and -13 degraded brevican into a few fragments with similar molecular masses, whereas the degradation products of aggrecanase-1 had apparently different sizes. NH(2)-terminal sequence analyses of the digestion fragments revealed that cleavages of the brevican core protein by these metalloproteinases occurred commonly within the central non-homologous domain. MMP-1, -2, -3, -7, -8, -10, and -13 preferentially attacked the Ala(360)-Phe(361) bond, whereas aggrecanase-1 cleaved the Glu(395)-Ser(396) bond, which are similar to the cleavage sites observed with cartilage proteoglycan (aggrecan) for the MMPs and aggrecanase-1, respectively. These data demonstrate that MMP-1, -2, -3, -7, -8, -10, and -13 and aggrecanase-1 digest brevican in a similar pattern to aggrecan and suggest that they may be responsible for the physiological turnover and pathological degradation of brevican. (+info)
Xenopus brevican is expressed in the notochord and the brain during early embryogenesis.
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A complete cDNA encoding the Xenopus laevis homologue of the aggrecan/versican family member, brevican (Xbcan) was cloned from an embryonic stage 42 cDNA library. In the deduced amino acid sequence, 1152 in length, similarity to the hyaluronan-binding (link) domains of brevicans from other species were present in the N-terminal region as well as EGF-, lectin- and complement regulatory protein-like domains in the C-terminal part, the latter three being characteristic for brevican found within the extracellular matrix (J. Biol. Chem. 269 (1994) 10119). Indeed, Xbcan was secreted into the extracellular space as a soluble protein when expressed in oocytes. No cDNAs encoding a GPI-anchored bcan variant could be isolated from that cDNA library. During embryonic development, the expression of this gene was first observed in the notochord of neurula stage embryos. In addition to this, in tailbuds, Xbcan was also found to be expressed within the fifth and sixth rhombomere of the hindbrain. In tadpole stage embryos, expression was furthermore observed in periventricular regions of the developing brain and the rostral part of the spinal cord. (+info)
Intact aggrecan and fragments generated by both aggrecanse and metalloproteinase-like activities are present in the developing and adult rat spinal cord and their relative abundance is altered by injury.
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Aggrecan is a large proteoglycan (PG) that has been grouped with different PG families on the basis of its physical characteristics. These families include the chondroitin sulfate PGs, which appear to inhibit the migration of cells and axons during development. Although aggrecan has been studied primarily in cartilage, in the present study, tissue samples from developing, mature, and injured-adult rat spinal cords were used to determine whether aggrecan is present in the mammalian spinal cord. By the use of Western blot analysis, tissues were probed with aggrecan-specific antibodies (ATEGQV, TYKHRL, and LEC-7) and aggrecan-specific neoepitope antibodies (NITEGE, FVDIPEN, and TFKEEE) to identify full-length aggrecan and several fragments. Unlike many other aggrecan gene family members, aggrecan species were similar in embryonic day 14, postnatal day 1, and adult spinal cords. Spinal cord injury caused significant decreases in aggrecan. Partial recovery in some aggrecan species was evident by 2 weeks after injury. The presence of specific aggrecan neoepitopes suggested that aggrecan is cleaved in the spinal cord by both a disintegrin and metalloproteinase thrombospondin (also known as aggrecanase) and metalloproteinase-like activities. Many aggrecan species found in the spinal cord were similar to species in cartilage. Additional antibodies were used to identify two other aggrecan gene family members, neurocan and brevican, in the adult spinal cord. These studies present novel information on the aggrecan core protein species and enzymes involved in aggrecan cleavage in vivo in the rat spinal cord throughout development and after injury. They also provide the basis for investigating the function of aggrecan in the spinal cord. (+info)