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

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.

A strategy to reveal potential glycan markers from serum glycoproteins associated with breast cancer progression

Aberrant glycosylation on glycoproteins that are either presented on the surface or secreted by cancer cells is a potential source of disease biomarkers and provides insights into disease pathogenesis. N-Glycans of the total serum glycoproteins from advanced breast cancer patients and healthy individuals were sequenced by HPLC with fluorescence detection coupled with exoglycosidase digestions and mass spectrometry. We observed a significant increase in a trisialylated triantennary glycan containing alpha1,3-linked fucose which forms part of the sialyl Lewis x epitope. Following digestion of the total glycan pool with a combination of sialidase and beta-galactosidase, we segregated and quantified a digestion product, a monogalactosylated triantennary structure containing alpha1,3-linked fucose. We compared breast cancer patients and controls and detected a 2-fold increase in this glycan marker in patients. In 10 patients monitored longitudinally, we showed a positive correlation between this glycan marker and disease progression and also demonstrated its potential as a better indicator of metastasis compared to the currently used biomarkers, CA 15-3 and carcinoembryonic antigen (CEA). A pilot glycoproteomic study of advanced breast cancer serum highlighted acute-phase proteins alpha1-acid glycoprotein, alpha1-antichymotrypsin, and haptoglobin beta-chain as contributors to the increase in the glycan marker which, when quantified from each of these proteins, marked the onset of metastasis in advance of the CA 15-3 marker. These preliminary findings suggest that specific glycans and glycoforms of proteins may be candidates for improved markers in the monitoring of breast cancer progression.

Malignant cell glycoproteins and glycolipids

The cell surface is involved in cell growth and division, cell-cell interaction, communication, differentiation and migration, and other processes likely to be involved in malignant transformation and/or the metastatic spread of cancer. Although there are many alterations of glycoproteins and glycolipids on the malignant cell surface, it is unclear whether these alterations are epiphenomena or an integral part of the malignancy process. This article reviews the recent literature and some earlier studies relevant for understanding emerging concepts and trends with respect to malignant cell glycoconjugates. Emphasis is on structural alterations of the carbohydrate portions of malignant cell glycoproteins and glycolipids and on the enzymes (glycosyltransferases and glycosidases) involved in their metabolism. Practical applications derived from malignant cell glycoconjugate studies are discussed briefly with respect to the diagnosis, staging, monitoring, and treatment of malignant disease. The review concludes by indicating which research areas on malignant cell glycoconjugates are likely to be fruitful in increasing our basic understanding of, and ability to deal effectively with, malignant disease.

Long-term study of serum glycosyl-transferase levels in pregnant women and their newborn infants

1. The authors have studied changes of glucosyl-, galactosyl- and sialyl-transferase activities in the sera of women during pregnancy and the early post-partum period, and in neonates from birth to 1 yr of age. 2. Galactosyl- and glucosyl-transferase activities throughout pregnancy were high in comparison to control values, and increased with advancing gestation. In the early post-partum period, the activities of these enzymes decreased markedly, reaching values similar to those of control subjects. 3. There were no variations, however, in serum sialyl-transferase activity at any stage of pregnancy or the post-partum period. In newborn infants, serum glucosyl- and sialyl-transferase activities were identical to control values. 4. Galactosyl-transferase activity was high at birth, decreased progressively and returned to the normal range only after 1 yr. 5. The physiological significance of these glycosyl-transferases in the sera of pregnant women and newborn infants is discussed.

Biological markers for breast carcinoma

During the last decade, there has been an intense search for biological markers for breast carcinoma. Many different types of materials have been found that may be elevated in the body fluids of patients with this disease. However, no markers specific for breast cancer have been discovered and those currently available lack the sensitivity and specificity for early detection of the disease or for determining when the tumor burden is low. Problems may also occur in the interpretation of marker data due to apparent biological variations in synthesis or secretion. Plasma carcinoembryonic antigen (CEA), elevated in 60%-70% of patients with metastases, has had the most extensive evaluation. For the latter patients with increased plasma CEA, the levels in general are proportional to tumor burden. Changes in level with therapy correlate with measurable clinical parameters of response or progression in the majority of these patients. Specific patterns of serial CEA measurements after mastectomy may be helpful for predicting those patients most likely to develop recurrent disease. More recent attention has focused on trials of combinations of markers and on tissue measurement. The search for a specific marker for breast cancer using monoclonal antibody techniques is a promising area of considerable research interest.