Screening of enzymatic synthesis and expression of Lewis determinants in human colorectal carcinoma

Resumo

Background: Although colorectal carcinogenesis has been intensively studied, the published investigations do not provide a consistent description of how different carbohydrate determinants of colorectal epithelium are modified in colorectal cancer (CRC). Objective: This study is an attempt to characterize the terminal fucosylation steps responsible for the synthesis of mono- (Lea /Lex ) and difucosylated (Leb /Ley ) Lewis antigens in healthy and tumour CRC tissue. Methods: An immunohistochemical study of Lewis antigens’ expression was undertaken, along with screening of the fucosyltransferase (FT) activities involved in their synthesis, on healthy and tumour samples from 18 patients undergoing CRC. Results: Analysis of a(1,2/3/4)FT activities involved in the sequential fucosylation of cores 1 and 2 showed significant increases in tumour tissue. Expressed as mU/mg and control vs. tumour activity (p from Wilcoxon’s test), the FT activities for Lea / Leb synthesis were: lacto-N-biose a(1,2)/a(1,4)FT, 65.4 ± 19.0 vs. 186 ± 35.1 (p < 0.005); lacto-N-fucopentaose 1 a(1,4)FT, 64.9 ± 11.9 vs. 125.4 ± 20.7 (p < 0.005); Lea a(1,2)FT, 56.2 ± 7.2 vs. 130.5 ± 15.6 (p < 0.001). Similarly, for Lex /Ley synthesis were: N-acetyllactosamine a(1,2)-/a(1,3)FT, 53.4 ± 12.2 vs. 108.1 ± 18.9 (p < 0.001); 2’-Fucosyl-N-acetyllactosamine a(1,3)FT, 61.3 ± 10.7 vs. 126.4 ± 22.9 (p < 0.001); 2’-Fucosyllactose a(1,3)FT, 38.9 ± 10.9 vs. 143.6 ± 28.9 (p < 0.001); 2’-Methyllactose a(1,3) FT, 30.9 ± 4.8 vs. 66.1 ± 8.1 (p < 0.005); and Lex a(1,2)FT, 54.3 ± 11.9 vs. 88.2 ± 14.4 (p < 0.001). Immunohistochemical Ley expression was increased (p < 0.01 according to Wilcoxon’s test) in tumour tissue, with 84.6% of specimens being positive: 7.7% weak, 15.4% moderate and 61.5% high intensity. Conclusions: Results suggest the activation of the biosynthesis pathways of mono- and difucosylated Lewis histo-blood antigens in tumour tissue from CRC patients, leading to the overexpression of Ley , probably at the expense of Lex .