Thyroid sialyltransferase mRNA level and activity are increased in Graves' disease

Role of ST6GAL1 in Thyroid Cancers: Insights from Tissue Analysis and Genomic Datasets

Thyroid cancer is the predominant endocrine-related malignancy. ST6 β-galactoside α2,6-sialyltransferase 1 (ST6GAL1) has been studied in various types of cancers; however, the expression and function of ST6GAL1 in thyroid cancer has not been investigated so far. Previously, we conducted two genome-wide association studies and have identified the association of the ST6GAL1 gene with plasma thyroglobulin (Tg) levels. Since Tg levels are altered in thyroid pathologies, in the current study, we wanted to evaluate the expression of ST6GAL1 in thyroid cancer tissues. We performed an immunohistochemical analysis using human thyroid tissue from 89 patients and analyzed ST6GAL1 protein expression in papillary thyroid cancer (including follicular variant and microcarcinoma) and follicular thyroid cancer in comparison to normal thyroid tissue. Additionally, ST6GAL1 mRNA levels from The Cancer Genome Atlas (TCGA, n = 572) and the Genotype-Tissue Expression (GTEx) project (n = 279) were examined. The immunohistochemical analysis revealed higher ST6GAL1 protein expression in all thyroid tumors compared to normal thyroid tissue. TCGA data revealed increased ST6GAL1 mRNA levels in both primary and metastatic tumors versus controls. Notably, the follicular variant of papillary thyroid cancer exhibited significantly higher ST6GAL1 mRNA levels than classic papillary thyroid cancer. High ST6GAL1 mRNA levels significantly correlated with lymph node metastasis status, clinical stage, and reduced survival rate. ST6GAL1 emerges as a potential cancer-associated glycosyltransferase in thyroid malignancies, offering valuable insights into its diagnostic and prognostic significance.

Genome-Wide Association Analysis and Genomic Prediction of Thyroglobulin Plasma Levels

Thyroglobulin (Tg) is an iodoglycoprotein produced by thyroid follicular cells which acts as an essential substrate for thyroid hormone synthesis. To date, only one genome-wide association study (GWAS) of plasma Tg levels has been performed by our research group. Utilizing recent advancements in computation and modeling, we apply a Bayesian approach to the probabilistic inference of the genetic architecture of Tg. We fitted a Bayesian sparse linear mixed model (BSLMM) and a frequentist linear mixed model (LMM) of 7,289,083 variants in 1096 healthy European-ancestry participants of the Croatian Biobank. Meta-analysis with two independent cohorts (total n = 2109) identified 83 genome-wide significant single nucleotide polymorphisms (SNPs) within the ST6GAL1 gene (p<5×10-8). BSLMM revealed additional association signals on chromosomes 1, 8, 10, and 14. For ST6GAL1 and the newly uncovered genes, we provide physiological and pathophysiological explanations of how their expression could be associated with variations in plasma Tg levels. We found that the SNP-heritability of Tg is 17% and that 52% of this variation is due to a small number of 16 variants that have a major effect on Tg levels. Our results suggest that the genetic architecture of plasma Tg is not polygenic, but influenced by a few genes with major effects.

Genetic Variants in the ST6GAL1 Gene Are Associated with Thyroglobulin Plasma Level in Healthy Individuals

Background: Thyroglobulin (Tg) is a 660 kDa iodoglycoprotein that serves as a scaffold for thyroid hormone synthesis. Although a twin study showed that variability of serum Tg levels has a substantial genetic basis, no genome-wide association study (GWAS) of serum/plasma Tg levels has been performed to date. The aim of this study was to identify genetic variants associated with plasma Tg levels among healthy individuals. Methods: A GWAS was conducted on two Croatian cohorts, and a combined analysis was performed. The analyses included 1094 individuals. A total of 7,597,379 variants, imputed using the 1000 Genomes reference panel, were analyzed for association. GWAS was performed under an additive model, controlling for age, sex, and relatedness within each data set. Combined analysis was conducted using the inverse-variance fixed-effects method. Results: Sixteen variants located on chromosome 3, within the ST6GAL1 gene, reached genome-wide significance. The lead SNP was rs4012172 ( \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\usepackage{upgreek}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$p = 1.29 \times {10^{ - 10}}$$ \end{document} ), which explained 3.19% of the variance in Tg levels. ST6GAL1 belongs to the sialyltransferase protein family, which has a fundamental role in the synthesis of specific sialylated structures on various glycoproteins, including Tg. It is known that only immature Tg (poorly sialylated or desialylated) can be transferred to the bloodstream. Conclusions: A highly biologically plausible locus was identified that could have a role in the regulation of plasma Tg levels in healthy individuals.

Glycosylation in the Thyroid Gland: Vital Aspects of Glycoprotein Function in Thyrocyte Physiology and Thyroid Disorders

The key proteins responsible for hormone synthesis in the thyroid are glycosylated. Oligosaccharides strongly affect the function of glycosylated proteins. Both thyroid-stimulating hormone (TSH) secreted by the pituitary gland and TSH receptors on the surface of thyrocytes contain N-glycans, which are crucial to their proper activity. Thyroglobulin (Tg), the protein backbone for synthesis of thyroid hormones, is a heavily N-glycosylated protein, containing 20 putative N-glycosylated sites. N-oligosaccharides play a role in Tg transport into the follicular lumen, where thyroid hormones are produced, and into thyrocytes, where hyposialylated Tg is degraded. N-glycans of the cell membrane transporters sodium/iodide symporter and pendrin are necessary for iodide transport. Some changes in glycosylation result in abnormal activity of the thyroid and alteration of the metabolic clearance rate of hormones. Alteration of glycan structures is a pathological process related to the progression of chronic diseases such as thyroid cancers and autoimmunity. Thyroid carcinogenesis is accompanied by changes in sialylation and fucosylation, β1,6-branching of glycans, the content and structure of poly-LacNAc chains, as well as O-GlcNAcylation, while in thyroid autoimmunity the main processes affected are sialylation and fucosylation. The glycobiology of the thyroid gland is an intensively studied field of research, providing new data helpful in understanding the role of the sugar component in thyroid protein biology and disorders.

Sialic acids: biomarkers in endocrinal cancers

Sialylations are post translational modification of proteins and lipids that play important role in recognition, signaling, immunological response and cell-cell interaction. Improper sialylations due to altered sialyl transferases, sialidases, gene structure and expression, sialic acid metabolism however lead to diseases and thus sialic acids form an important biomarker in disease. In the endocrinal biology such improper sialylations including altered expression of sialylated moieties have been shown to be associated with disorders. Cancer still remains to be the major cause of global death and the cancer of the endocrine organs suffer from the dearth of appropriate markers for disease prediction at the early stage and monitoring. This review is aimed at evaluating the role of sialic acids as markers in endocrinal disorders with special reference to cancer of the endocrine organs. The current study is summarized under the following headings of altered sialylations in endocrinal cancer of the (i) ovary (ii) pancreas (iii) thyroid (iv) adrenal and (v) pituitary gland. Studies in expression of sialic acid in testis cancer are limited. The future scope of this review remains in the targeting of endocrinal cancer by targeting altered sialylation which is a common expression associated with endocrinal cancer.

Sialic acid and sialyltransferase activity in serum and tissues of dogs with mammary tumors

In humans, the glycosylation pattern of serum and of membrane glycoproteins is associated with invasiveness of tumors: specifically, α2,6-sialylation and α2,3-sialylation are associated with metastasizing and nonmetastasizing tumors, respectively. In turn, the type of sialylation depends on the activity of α2,6 or α2,3 sialyltransferase (ST) enzymes. Because of the high prevalence of metastasizing tumors with biological behavior similar to the human counterpart, female dogs with metastasizing neoplasms could provide a good animal model for investigating the potential roles of sialic acid (Sia) and ST enzymes in the pathogenesis of metastatic tumors. The aims of this study were (1) to validate a solid-phase method based on lectin staining of serum and tissue homogenates to investigate sialylation and ST activity and (2) to compare the results obtained with this method and with lectin staining and to collect preliminary information on sialylation and ST activity in dogs with (n = 8) and without (n = 8) mammary tumors. The data recorded in healthy dogs revealed that serum and tissue glycoproteins are prevalently characterized by a α2,6 sialylation, but ST-α2,3 seems to be the most active enzyme in both samples. Sia-α2,3 and ST-α2,3 activity decreases in serum and tissues of dogs with tumors, especially in a dog with metastasis, suggesting that the equilibrium between ST-α2,6 and ST-α2,3 activity shifts toward the former, as reported in humans.

Assessment of total sialic acid and lipid-bound sialic acid in management of brain tumors

BACKGROUND

Glycoconjugate molecules expressed at the plasma membrane of mammalian cells have been reported to be associated with tumor progression. The measurement of total sialic acid (TSA) and lipid-bound sialic acid (LBSA) in the cerebrospinal fluid (CSF) is suggested to be useful for the diagnosis of brain tumors. But there are very few reports available on the serum glycoconjugate levels in patients with brain tumors.

OBJECTIVE

The objective of this study is to check the feasibility of using serum glycoconjugates such as TSA and LBSA as tumor markers in brain tumor patients.

MATERIALS AND METHODS

Colorimetric estimation of TSA using diphenylamine was done on 100 patients with intracranial tumors; follow-up study was carried out in 24 cases. The LBSA fraction was isolated from the serum of 68 brain tumor patients and evaluated using phosphotungstic acid and resorcinol; follow-up study was done on 23 patients. The various types of brain tumors included in this study were glioma, meningioma, and acoustic neurinoma as well as some other types such as medulloblastoma, secondary tumors, and craniopharyngioma.

RESULTS

There was no significant difference between the TSA and LBSA concentrations seen in pretreatment or post-treatment cases and that seen in control subjects.

DISCUSSION

TSA and LBSA do not have the ability to discriminate between benign and malignant brain tumors. TSA and LBSA appear to be tumor markers of very limited value in patients with brain tumors.

A case of thyrotropin-producing pituitary adenoma, accompanied by an increase in anti-thyrotropin receptor antibody after tumor resection

We describe a rare, but interesting, case of TSH-producing adenoma (TSHoma), accompanied by increases in both anti-TSH receptor antibody (TRAb) and thyroid-stimulating antibody (TSAb) after tumor resection. A 21-yr-old woman was referred to our department for further evaluation of pituitary tumor. In a nearby hospital, she had been diagnosed as having pituitary tumor. Her serum free T4, free T3, and TSH levels were all elevated concomitantly. On the basis of a diagnosis of pituitary adenoma with TSH production, transsphenoidal resection of the pituitary adenoma was performed. Two weeks after the operation, the blood concentrations of TSH were undetectable, whereas both TRAb and TSAb levels were elevated. TSAb levels gradually increased further from 2 weeks to 3 months after the operation, accompanied by an increase in TSH and free T4 levels. TSH is an important hormone in maintaining physiology and regulating immunomodulators in thyrocytes, as it can influence a variety of immune-regulating cytokine-like activities and inhibit expressions of Fas antigen, intracellular adhesion molecule-1, and class II trans-activator. Changes in TSH would modulate the immune circumstances in the thyroid, and then induce TRAb and TSAb. Autoimmune parameters with thyroid function should be observed carefully when managing patients with TSHoma.