Cell and molecular Biological Study of 60Da mucin molecules.

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Abstract : We have previously studied the biosynthesis and secretion of mucin in the normal human stomach and reported that the tetramer of the 60-kDa subunit of mucin core protein was synthesized and highly glycosylated, and that only high molecular weight mucin was secreted. In this study, we investigated the mucin-related products of a gastric cancer cell line (Hs746T). Analysis of intracellular and extracellular products immunoprecipitated with an anti-apomucin monoclonal antibody revealed that a ll0-kDa protein, the dimer of the 55-kDa subunit, was synthesized and secreted. Tunicamycin treatment inhibited the secretion of the ll0-kDa protein. These findings suggest that N-glycosylation may be involved in the secretory mechanism of the mucin-related product.charides, and some of these antigens have been used as tumor markers.^<3-7> Low molecular weight mucin-related products, as well as high molecular weight ones, can be detected in the serum of cancer patients.^<H-11> However, very little is known about the intracellular transport and secretory mechanisms of mucin-related products. In the present study. we examined this mechanism in a human gastric carcinoma cell line (Hs746T) and compared it to that in the normal gastric mucosa. After pulse-labeling with [^<35>S] methionine and chase incubation, we analyzed the intracellular and extracellular products with an anti-carboxyl terminal of the apomucin monoclonal anti-body.