BREVICAN, A CHONDROITIN SULFATE PROTEOGLYCAN OF RAT-BRAIN, OCCURS AS SECRETED AND CELL-SURFACE GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED ISOFORMS

cDNA clones encoding proteins related to the aggrecan/versican family of proteoglycan core proteins have been isolated with antisera against rat brain synaptic junctions, Two sets of overlapping cDNAs have been characterized that differ in their 3'-terminal regions. Northern analyses with probes derived from unique regions of each set were found to hybridize with two brain-specific transcripts of 3.3 and 3.6 kilobases (kb), The 3.6-kb transcript encodes a polypeptide that exhibits 82% sequence identity with bovine brevican and is thought to be the rat ortholog of brevican, Interestingly, the polypeptide deduced from the open reading frame of the 3.3-kb transcript is truncated just carboxyl-terminal of the central domain of brevican and instead contains a putative glypiation signal, Antibodies raised against a bacterially expressed glutathione S-transferase-brevi can fusion protein have been used to show that both soluble:and membrane-bound brevican isoforms exist, Treatment of the crude membrane fraction and purified synaptic plasma membranes with phosphatidylinositol-specific phospholipase C revealed that isoforms of brevican are indeed glycosylphosphatidylinositol-anchored to the plasma membrane, Moreover, digestions with chondroitinase ABC have indicated that rat brevican, like its bovine ortholog, is a conditional chondroitin sulfate proteoglycan. Immunohistochemical studies have shown that brevican is widely distributed in the brain and is localized extracellularly, During postnatal development, amounts of both soluble and phosphatidylinositol:specific phospholipase C-sensitive isoforms increase, suggesting a role for brevican in the terminally differentiating and the adult nervous system.