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Effect of Tunicamycin on Sialomucin and Natural Killer Susceptibility of Rat Mammary Tumor Ascites Cells¹

Departments of Biochemistry [S. B., J. M., A. P. S.] and Microbiology [C. E. M.], University of Maine, Orono, Maine 04469

The MAT-B1 and MAT-C1 ascites sublines of the 13762 rat mammary adenocarcinoma contain a dominant cell surface "complex" consisting of two glycoproteins: ascites sialoglycoprotein (ASGP)-1, a M_r 600,000–700,000 peanut agglutinin-binding sialomucin, and ASGP-2, a M_r 120,000 concancavalin A-binding glycoprotein (Sherblom et al., J. Biol. Chem., 255: 783–790, 1980; Sherblom and Carraway, J. Biol. Chem., 255: 12051–12059, 1980). Although both cell lines are resistant to lysis by natural killer cells, treatments which result in loss of cell surface ASGP-1 render the cells susceptible to natural killer cell lysis (Sherblom and Moody, Cancer Res., 46: 4543–4546, 1986). Treatment of the ascites cells with 5 µg/ml tunicamycin for 24 h effectively inhibits glycosylation of ASGP-2 without affecting cell viability or total protein synthesis. Under these conditions, expression of ASGP-1 is depressed by at least 50% in both cell lines, as monitored by [³H]glucosamine incorporation and by binding of peanut agglutinin to intact cells. The size distribution of O-linked oligosaccharides in ASGP-1 from tunicamycin-treated versus control MAT-B1 cells is indistinguishable, as determined by Bio-Gel P-4 chromatography following alkaline-borohydride treatment. Complex isolated from either treated or control cells bands at the same density in a CsCl gradient containing Triton X-100 and contains a diffuse band corresponding to ASGP-2 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Tunicamycin-treated cells, consistent with the reduced expression of ASGP-1, are significantly more susceptible to natural killer cell-mediated lysis, when compared to untreated controls. The results suggest that N-linked glycosylation is a prerequisite for sialomucin synthesis and/or complex formation.

¹ This work was supported by Grant CA33238 from the NIH (A. P. S.) and Projects 8758 and 8407 from the Maine Life Sciences and Agriculture Experiment Station (Publication No. 1472).

² To whom requests for reprints should be addressed.

Received 12/29/89. Revised 3/28/90.

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