Glycosyltransferase expression in human colonic tissue examined by oligonucleotide arrays

For an understanding of tumor-related alterations of the complex carbohydrate pattern of carcinomas, it is indispensable to monitor the expression profile of the various glycosyltransferases. The objective of this contribution was to perform an evaluation of the usefulness and the limits of the microarray approach for the identification of enzymes responsible for carbohydrate synthesis with differential expression in carcinomas. Expression profiles of colonic carcinomas were studied by oligonucleotide arrays using a novel strategy: colonic tissue of healthy individuals was compared with early staged colonic carcinomas; 'pure' cell populations were obtained by laser microdissection; RNA samples for hybridization with the oligonucleotide arrays were prepared by in vitro transcription without additional amplification. Expression of 39 glycosyltransferases and of 10 sulfotransferases in colonic tissues was analyzed by Affymetrix GeneChip technology. GeneChip analysis proved the high expression level of ST6Gal-I, beta4Gal-TI, II and III, GalNacT-1, FT-III and showed that ST3Gal-IV was the most abundantly expressed enzyme in healthy tissue. The strong overexpression of FT-VI in healthy tissue has not been described so far, as well as the upregulation of FT-VIII and downregulation of GnT-I in carcinoma tissue. Quantitative RT-PCR confirmed that FT-VI expression was significantly enhanced in healthy tissue. On the other hand, GeneChip analysis failed to detect any expression of GnT-III and GnT-V as well as of ST3Gal-I and ST3Gal-II, although these sequences could be amplified from the samples used for microarray analysis. According to our restricted analysis of only those 39 glycosyltransferases present on the GeneChip U95A, alterations of sialyltransferases ST6Gal-I, ST3Gal-IV, of fucosyltransferases FT-VI, FT-III, and probably FT-VIII, of GalNacT-I, and of beta4GalT-II seem to be of relevance for the aberrant biosynthesis of membrane-bound carbohydrates during colonic carcinogenesis and metastasis.