Increasing the intra-Golgi pH of cultured LS174T goblet-differentiated cells mimics the decreased mucin sulfation and increased Thomsen-Friedenreich antigen (Gal 1-3GalNac -) expression seen in colon cancer

Abstract

Mucins in ulcerative colitis and colon cancer share common properties of reduced sulfation and increased oncofetal carbohydrate antigen expression. It has previously been shown that there is no simple correlation between these changes and the activity of the relevant glycosyl-, sialyl-, and sulfo-transferases. We examined mucin sulfation and expression of oncofetal Thomsen-Friedenreich (TF) antigen (galactosylβ1-3N-acetylgalactosamineα-) in the goblet cell–differentiated human colon cancer cell line LS174T following treatment with bafilomycin A_1, which raises intra-Golgi pH, or monensin, which disrupts medial-trans Golgi transport. Cells were dual-labeled with sodium [³⁵S]-sulfate andD-[6-³H(N)]-glucosamine hydrochloride, or labeled with L-[U-¹⁴C]-threonine alone. Mucin was purified using Sepharose CL-4B gel filtration. Mucin sulfo-Lewis^a and TF antigen expression were assessed using the F2 anti-sulfo-Lewis^a monoclonal antibody and peanut agglutinin binding respectively. Bafilomycin (0.01 µM; 48 h) reduced total mucin sulfation, expressed relative to incorporation of glucosamine, to 0.50 ± 0.04 d.p.m. [³⁵S]-sulfate per d.p.m. [³H]-glucosamine compared to control, 0.84 ± 0.05 (p< 0.001, n = 16). This was accompanied by 50.3 ± 8.0% increased expression of TF antigen (p < 0.01) and 50.1 ± 5.5% decreased expression of sulfo-Lewis^a (p < 0.01). The reduced sulfate:glucosamine ratio was largely due to increased incorporation of glucosamine into newly synthesized mucin rather than reduction in total sulfate incorporation. In contrast, monensin only reduced total mucin glycosylation at concentrations > 0.1µM and had no significant effect on mucin sulfation or TF expression. Intra-Golgi alkalinization affects mucin glycosylation, resulting in decreased mucin sulfation and increased expression of TF antigen, changes that mimic those seen in cancerous and premalignant human colonic epithelium.