Tissue-type transglutaminases (TGases) were recently shown to exert dual enzymatic activities; they catalyze the posttranslational modification of proteins by transamidation, and they also act as guanosine triphosphatase (GTPase). Here we show that a tissue-type TGase is expressed in rat brain astrocytes in vitro, and is induced by the inflammation-associated cytokines interleukin-1␤ and to a lesser extent by tumor necrosis factor-␣. Induction is accompanied by overexpression and appearance of an additional shorter clone, which does not contain the long 3 -untranslated region and encodes for a novel TGase enzyme whose C terminus lacks a site that affects the enzyme's interaction with guanosine triphosphate (GTP). Expression of two clones revealed that the long form is inhibited noncompetitively by GTP, but the short form significantly less so. The different affinities for GTP may account for the difference in physiological function between these two enzymes.

The HNK-1 carbohydrate epitope is expressed on several neural adhesion glycoproteins and as a glycolipid, and is involved in cell interactions. The structural element of the epitope common to glycoproteins and glycolipids has been determined to be sulfate-3-GlcA␤13 3Gal␤134GlcNAc. The glucuronyltransferase and sulfotransferase are considered to be the key enzymes in the biosynthesis of this epitope because the rest of the structure occurs often in glycoconjugates. Here we describe the isolation of the rat sulfotransferase cDNA via an expression cloning strategy. The clone finally isolated predicts a protein of 356 amino acids, with characteristics of a type II transmembrane protein and with no sequence similarity to other known sulfotransferases. Both the enzyme expressed as a soluble fusion protein and homogenates of cells transfected with the fulllength cDNA could transfer sulfate from a sulfate donor to acceptor substrates containing terminal glucuronic acid.The carbohydrate antigen recognized by the monoclonal antibody HNK-1 was originally described as a marker for human natural killer cells (1). Later it was shown to be expressed predominantly on glycolipids and glycoproteins from nervous tissue (2-5). The expression pattern of the HNK-1 carbohydrate in both the central and peripheral nervous system is spatially and developmentally regulated (6 -11). The HNK-1 carbohydrate epitope is carried by many, but not all, neural recognition glycoproteins and is involved in homo-and heterophilic binding of these proteins (for a review, see Ref. 12). Of special interest is the association of the epitope with Schwann cells myelinating motor but not sensory axons (10), where it may be involved in the preferential reinervation of muscle nerves by motor axons after lesion (13,14).Determination of the structure of the glycolipid (15) and glycoprotein (16) forms has shown that both carry sulfate-3-GlcA␤133Gal␤134GlcNAc at the nonreducing end. The minimal requirement for recognition by HNK-1 is unknown, but the antibody only binds to the sulfated form(17). Several other monoclonal antibodies have been isolated that recognize identical or similar structures(4, 18); of these, L2-412 is important for this study, because it also recognizes the non-sulfated form of the carbohydrate(19).The key enzymes in the biosynthesis of HNK-1 carbohydrates are a glucuronyltransferase (20, 21), transferring GlcA in ␤133 linkage to a terminal galactose, and a sulfotransferase (22), responsible for coupling sulfate to the C-3 position of this GlcA residue. A cDNA encoding the glucuronyltransferase involved in the biosynthesis of at least the HNK-1 glycoprotein epitope has recently been cloned (23). We describe here the cloning of a cDNA coding for a sulfotransferase active on terminal glucuronic acid residues and whose expression can render cells immunoreactive with HNK-1 antibody when cotransfected with a glucuronyltransferase cDNA. EXPERIMENTAL PROCEDURESCell Lines, Antibodies, and Plasmids-CHOP2 cells (24) were grown in minimal essential medi...

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It is now widely accepted that injured nerves, like any other injured tissue, need assistance from their extracellular milieu in order to heal. We compared the postinjury activities of thrombin and gelatinases, two types of proteolytic activities known to be critically involved in tissue healing, in nonregenerative (rat optic nerve) and regenerative (fish optic nerve and rat sciatic nerve) neural tissue. Unlike gelatinases, whose induction pattern was comparable in all three nerves, thrombin-like activity differed clearly between regenerating and nonregenerating nervous systems. Postinjury levels of this latter activity seem to dictate whether it will display beneficial or detrimental effects on the capacity of the tissue for repair. The results of this study further highlight the fact that tissue repair and nerve regeneration are closely linked and that substances that are not unique to the nervous system, but participate in wound healing in general, are also crucial for regeneration or its failure in the nervous system.

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