Sialyl transferase activity: a serum enzyme marker in the follow-up of cancer patients

Cleavage of ST6Gal I by radiation-induced BACE1 inhibits golgi-anchored ST6Gal I-mediated sialylation of integrin β1 and migration in colon cancer cells

Background

Previously, we found that β-galactoside α2,6-sialyltransferase (ST6Gal I), an enzyme that adds sialic acids to N-linked oligosaccharides of glycoproteins and is frequently overexpressed in cancer cells, is up-regulated by ionizing radiation (IR) and cleaved to a form possessing catalytic activity comparable to that of the Golgi-localized enzyme. Moreover, this soluble form is secreted into the culture media. Induction of ST6Gal I significantly increased the migration of colon cancer cells via sialylation of integrin β1. Here, we further investigated the mechanisms underlying ST6Gal I cleavage, solubilization and release from cells, and addressed its functions, focusing primarily on cancer cell migration.

Methods

We performed immunoblotting and lectin affinity assay to analyze the expression of ST6 Gal I and level of sialylated integrin β1. After ionizing radiation, migration of cells was measured by in vitro migration assay. α2, 6 sialylation level of cell surface was analyzed by flow cytometry. Cell culture media were concentrated and then analyzed for soluble ST6Gal I levels using an α2, 6 sialyltransferase sandwich ELISA.

Result

We found that ST6Gal I was cleaved by BACE1 (β-site amyloid precursor protein-cleaving enzyme), which was specifically overexpressed in response to IR. The soluble form of ST6Gal I, which also has sialyltransferase enzymatic activity, was cleaved from the Golgi membrane and then released into the culture media. Both non-cleaved and cleaved forms of ST6Gal I significantly increased colon cancer cell migration in a sialylation-dependent manner. The pro-migratory effect of the non-cleaved form of ST6Gal I was dependent on integrin β1 sialylation, whereas that of the cleaved form of ST6Gal I was not, suggesting that other intracellular sialylated molecules apart from cell surface molecules such as integrin β1 might be involved in mediating the pro-migratory effects of the soluble form of ST6Gal I. Moreover, production of soluble form ST6Gal I by BACE 1 inhibited integrin β1 sialylation and migration by Golgi-anchored form of ST6Gal I.

Conclusions

Our results suggest that soluble ST6Gal I, possibly in cooperation with the Golgi-bound form, may participate in cancer progression and metastasis prior to being secreted from cancer cells.

Serum sialyl transferase levels in patients with metastatic breast cancer treated by chemotherapy

Serum sialyl transferase (SST) was measured in 49 female patients with advanced breast cancer and 60 female controls. The mean SST level was significantly raised in patients with advanced breast cancer. There was no correlation between specific sites, or numbers of sites of metastatic disease and SST levels. The patients with advanced breast cancer were all treated with chemotherapy; in 13/21 responders there was a significant fall in SST and in 2 responders a significant rise in SST. The 6 patients who died after one course of chemotherapy had a significantly higher mean SST than those surviving longer. SST appears to lack sufficient specificity to be of practical value as a marker of response in patients with breast cancer treated by chemotherapy, though constant measurement of changes in SST may be of use in monitoring drug response. Raised SST at the commencement of chemotherapy may signify poor prognosis.

Usefulness of clinical chemistry measurements in classifying patients with breast cancer

Laboratory measurements can be used to detect, classify, and monitor patients with breast cancer. This review covers in detail the clinical usefulness of carcino embryonic antigen, tissue polypeptide antigen, various glycoproteins, pregnancy-associated proteins, casein, lactalbumin, beta-2-microglobulin, ferritin, immunoglobins, acute phase proteins, placental-like alkaline phosphatase, liver-associated enzymes, glycosyltransferases, human chorionic gonadotropin, calcitonin, polyamines, and collagen breakdown products, in relationship to their diagnostic utility in patients suspected of having or known to have breast cancer. In addition, these authors assess the merits of various multivariate techniques using a number of clinical chemistry quantities in the same regard. Finally, the relative contribution of biochemical tests vs. the information values gained from "surgical pathology" data (number of positive nodes, number of negative nodes, and degree of anaplasia) is discussed.

Serum levels of glycosyltransferases and related glycoproteins as indicators of cancer: biological and clinical implications

Many studies have suggested that malignant transformation is associated with fundamental changes in the cell surface; similar changes have been described for normal stem cells and cells of embryonic or fetal origin. There is now evidence that the tumor cell secretes or sheds glycoproteins and glycosyltransferases into the surrounding medium and into serum. There are claims that some of these serum glycoproteins and glycosyltransferases are associated with, or specifically related to, the extent of tumor growth and may serve as a cancer marker. A cancer-associated galactosyltransferase isoenzyme (GT-II) has been described and purified. Different isoelectric forms of fucosyltransferase have also been described as indicative of malignancy. The articles to be published in CRC Critical Reviews in Clinical Laboratory Sciences will analyze the evidence for the association of these membrane factors with tumor growth. In order to better understand the possible significance of altered glycoproteins and of increased or different forms of glycosyltransferases during tumor growth, recent data on glycoprotein synthesis will be discussed including the new concepts on the control of glycoprotein synthesis through lipid intermediates. The possible mechanisms whereby malignant transformation could alter glycoprotein synthesis will be discussed with particular emphasis on the significance of these alterations to the biology of the malignant cell. Changes in surface membrane glycoproteins have long been implicated in the ability of a cell to metastasize. Secretion and/or shedding of the cell surface may also be important in the process of metastasis and in altering the host immune response. Detection and the study of these "shed" materials in patients appear to be indicating a new approach to cancer biology detection and therapy.