A Novel Membrane-associated Glycovariant of BEHAB/Brevican Is Up-regulated during Rat Brain Development and in a Rat Model of Invasive Glioma

Abstract

The ECM 1 of the central nervous system is composed of a hyaluronic acid scaffold invested with proteoglycans and nonfibrous glycoproteins (1), but it lacks the typical fibrous proteins found in other tissues (2, 3). Proteins that interact with this HA-based matrix organize the central nervous system ECM and regulate many of the developmental processes in the central nervous system, including cell motility, neurite extension, synaptogenesis, and synaptic stabilization (for reviews see Refs. 4 -6). The lecticans, a family of chondroitin sulfate proteoglycans (7) including aggrecan, versican, neurocan, and BEHAB (brain-enriched HA-binding protein)/brevican, interact with HA in the central nervous system. Each lectican is expressed in the central nervous system in a temporally and spatially regulated manner (8). Two of the lecticans, neurocan and BEHAB/brevican, are expressed exclusively in the central nervous system, the latter being the most prominent chondroitin sulfate proteoglycan in the adult rat brain (9).Like all of the lecticans, the structure of BEHAB/brevican includes an N-terminal HA-binding domain, a middle chondroitin sulfate attachment region and a C-terminal selectinlike domain consisting of an epidermal growth factor-like, a C-type lectin, and a complement regulatory protein-like domains (10). Apart from HA, bound by the N-terminal domain of BEHAB/brevican, two other binding partners have been described. BEHAB/brevican binds the ECM glycoprotein tenascin-R and a subset of membrane sulfated glycolipids via its C-type lectin domain, both through calcium-dependent mechanisms (11,12).BEHAB/brevican mRNA expression increases over the course of rat brain development, reaching a plateau in adulthood (13). The roles proposed for BEHAB/brevican in normal developing brain include regulation of cell adhesion and neurite outgrowth and a role in synaptic plasticity (14, 15). Our studies, demonstrating a spike in BEHAB/brevican expression early in development in the ventricular zone coincident with gliogenesis (16) and an increase in BEHAB/brevican expression during reactive gliosis after a stab injury (17), have suggested a role for BEHAB/brevican in glial cell proliferation and motility. Consistent with these results, BEHAB/brevican expression is also dramatically up-regulated in surgical samples of glioma, notoriously invasive primary tumors of the central nervous system, as well as in a rodent glioma model (18). We have further shown that BEHAB/brevican up-regulation and its subsequent proteolytic processing contribute to the invasive phenotype of glioma (19,20). An understanding of the molecular interactions and mechanisms through which these many functions are mediated is still incomplete.One of the difficulties in characterizing the functions of BEHAB/brevican is the molecular complexity of this protein. Two isoforms of BEHAB/brevican are generated by alternative splicing, a full-length, secreted protein and a C-terminally truncated splice variant (21). The latter lacks the entire Cterminal domain, which ...

BEHAB/brevican requires ADAMTS-mediated proteolytic cleavage to promote glioma invasion

“…These results are in agreement with our previous observations in vivo and in several cell lines [34,36,38,39], and indicate that cleavage of B/b by proteases other than ADAMTS, while possible, may not contribute appreciably to glioma invasion.…”

“…It is important to remark that intracranial grafts of CNS-1 cells express and cleave B/b endogenously ( Figure 4A), as previously reported [33,38]. The absence of any inhibitory effects by B NVY on cell invasion indicates that this construct did not affect the expression or cleavage of endogenous B/b, a lack of effect that we verified by co-expression of B/b and B NVY in culture ( Figure 1D).…”

“…Three rabbit polyclonal anti-B/b antibodies were employed in this study: B6, against the chondroitin sulfate-attachment region (aa506-529) of rat B/b; B5, against the NH 2 terminus (AA 60-73) of rat B/b; and B50, against the neoepitope QEAVESE (AA 389-395) that is exposed in the NH 2 -terminal fragment of B/b after cleavage by ADAMTS proteases (see Figure 1A). These antibodies have been extensively characterized for the detection of rat and human B/b [38,39].…”

“…However, experimental overexpression of B/b dramatically enhances glioma growth and invasion in vitro and in vivo [33][34][35]. B/b is not cleaved by MMPs in vivo, but is processed at a single site by metalloproteases of the Disintegrin and Metalloprotease with Thrombospondin Motifs (ADAMTS) family, both during normal CNS development and in malignant gliomas [36][37][38][39]. Upregulation of B/b cleavage products has been observed in human gliomas [39] and overexpression of these fragments increases glioma cell motility in vitro as well as tumor dispersion in vivo [34,35].…”

The Extracellular Matrix Protein Brevican Limits Time-Dependent Enhancement of Cocaine Conditioned Place Preference

“…Acute antibodymediated disruption of LTP maintenance points to a yetunidentified brevican-regulated cellular signal transduction process, which may also be (partially) affected in Bcan +/ − mice. Our biochemical approach allowed detection of the 145 kDa secreted brevican core protein, a 130 kDa membraneassociated isoform that lacks glycosaminoglycan side chains (Viapiano et al, 2003) and an 80 kDa terminally truncated fragment (Seidenbecher et al, 1995). The 130 kDa brevican variant was substantially increased in Bcan +/ − mice that received AAV-Bcan, supporting the possibility of a change in a signal transduction process by this membrane-associated form.…”