Julie Spielman

Structural and functional aspects of tumor cell sialomucins

Sialomucins are abundant on the surfaces of certain ascites tumor cells and have been implicated in the escape of tumors from immune destruction and metastasis. They are large, highly glycosylated glycoproteins which are rich in serine and threonine and have a variety of 0-linked oligosaccharides. The sialomucin (ASGP-1) or 13762 rat mammary adenocarcinoma ascites cells represents more than 0.5% of the total cell protein and can be isolated from cell membranes by centrifugation in 4 M guanidine hydrochloride-cesium chloride. ASGP-1 can also be isolated from membranes or cells by nonionic detergent extraction as a 1:1 complex with a second glycoprotein ASGP-2. Studies with the fluorescent lectins peanut agglutinin, which binds ASGP-1, and Concanavalin A, which binds ASGP-2, indicate that the glycoproteins are present at the cell surface as a complex. ASGP-1 is shed into cell culture medium or ascites fluid, apparently by a proteolytic cleavage mechanism. 13762 ascites cells grown in culture or as solid tumors lose their ASGP-1. The sialomucin reappears with extensive passage of the tumor cells in ascites form. Studies on the biosynthesis of ASGP-1 indicate that carbohydrate is being added over nearly the entire period of transit of ASGP-1 from the site of polypeptide synthesis to the plasma membrane. The negatively charged, rod-like structure of the sialomucins suggests that they may play a role in inhibiting recognition or binding processes necessary for the immune destruction of these tumor cells.

Consequences of Fas-Ligand and Perforin Expression by Colon T Cells in a Mouse Model of Inflammatory Bowel Disease

BACKGROUND & AIMS We describe a type of colitis that develops after transplantation of nonallogeneic wt bone marrow cells into T cell- and natural killer cell-deficient Tg26 mice (BM-->Tg26). In these animals, severe wasting and inflammation of the colon correlates with the expansion of mucosal T lymphocytes that displays cytotoxic activity. The aims of this study were to determine the relative contribution of perforin and Fas ligand (Fas-L) expression to the cytotoxic action of these T cells and to examine the influence of each pathway in this model of colitis. METHODS Colonic T cells were tested for their ability to mediate Fas- and perforin-dependent killing in redirected cytotoxicity assays. Bone marrow cells from donor mice lacking either Fas-L (gld mice) or perforin (PFPnull mice) or both molecules were used to reconstitute Tg26 mice. RESULTS Colon cytotoxic T lymphocyte displayed both Fas- and perforin-dependent killing. Deficiency in perforin, but not Fas-L, resulted in reduced incidence of wasting and, to a lesser extent, severe colitis in BM-->Tg26 animals. CONCLUSIONS Colon T cells from BM-->Tg26 mice express both perforin and Fas-L. Although neither pathway is critical in the development of colitis, perforin does have a measurable influence on disease in the BM-->Tg26 colitis model.

Biosynthesis of the Cell Surface Sialomucin from Ascites 13762 Rat Mammary Adenocarcinoma Cells: Intracellular Maturation

Considerable attention has been directed in recent years toward tumor cell surface sialomucins (Carraway and Spielman, 1986). The presence of these O-glycosylated glycoproteins has been correlated with metastasis in the 13762NF rat mammary adenocarcinoma (Steck and Nicolson, 1983), and they are proposed to protect carcinomas from immune destruction by “masking” cell surface antigens, including histocompatibility antigens (Codington, 1981). Monoclonal antibodies prepared against whole tumor cells (Lan et al., 1985), tumor cell membranes (Kufe et al., 1984) or human milk fat globule membranes (Taylor-Papadimitriou, 1981) in many cases react specifically with carcinoma cell sialomucins and are being investigated for their potential in diagnosis and therapy (Schlom, 1986). Why should these mucin-like molecules, which are also products of normal tissues (Ceriani et al., 1983), be recognized as “carcinoma-associated antigens”? One possibility is that changes in the glycosylation of these glycoproteins in carcinomas yields epitopes which are absent or uncommon in normal tissues or other tumors (Hull and Carraway, 1988).