O-linked β-N-acetylglucosamine transferase is involved in pro-opiomelanocortin gene expression in mouse pituitary corticotroph AtT-20 cells

O-GlcNAcylation in Endocrinology: The Sweet Link

O-GlcNAcylation is a dynamic posttranslational modification that involves the addition of N-acetylglucosamine (GlcNAc) to the serine and threonine residues of proteins. Over the past 4 decades, this modification has become increasingly recognized as having a critical influence in the field of endocrinology. The carefully controlled hormonal input for regulating sleep, mood, response to stress, growth, development, and metabolism are often associated with O-GlcNAc-dependent signaling. As protein O-GlcNAcylation patterns are heavily dependent on environmental glucose concentrations, hormone-secreting cells sense the changes in local environmental glucose concentrations and adjust hormone secretion accordingly. This ability of cells to sense nutritional cues and fine-tune hormonal production is particularly relevant toward maintaining a functional and responsive endocrine system, therefore emphasizing the importance of O-GlcNAc in the scope and application of endocrinology. This review examines how O-GlcNAcylation participates in hormonal homeostasis in different endocrine tissues and systems, from the pineal gland to the placenta, and underscores the significance of O-GlcNAc in the field of endocrinology.

The diverging role of O-GlcNAc transferase in corticotroph and somatotroph adenomas

PURPOSE

Molecular mechanisms involved in the pathogenesis and tumor progression of pituitary adenomas (PA) remain incompletely understood. Corticotroph and somatotroph PA are associated with a high clinical burden, and despite improved surgical outcomes and medical treatment options, they sometimes require multiple surgeries and radiation. Preliminary data suggested a role for O-GlcNAc Transferase (OGT), the enzyme responsible for the O-GlcNAcylation of proteins. O-GlcNAcylation and OGT have been found elevated in other types of tumors.

METHODS

We evaluated 60 functioning and nonfunctioning PA (NFPA) from operated patients and postmortem normal and tumoral pituitary tissue by immunohistochemistry. We performed transcriptomic analyses to explore the relevance of the O-GlcNAc Transferase (OGT) in PAs. We detected OGT in immunobiological analysis and define its level in PA tissue in patients.

RESULTS

OGT was strongly associated with PA hormone secretory capacity in functioning PA and with tumor growth in NFPAs. In NFPAs, OGT was positively associated with tumor size but not with cavernous sinus invasion (Knosp grading). In GH-secreting PA, OGT expression was negatively correlated with circulating Insulin-like Growth Factor 1 level. In adrenocorticotropic hormone (ACTH)-secreting PA, OGT expression was positively associated with circulating ACTH levels. OGT did not correlate with tumor size in secreting PAs. OGT levels were higher in gonadotroph PA compared to normal glands.

CONCLUSION

O-GlcNAcylation can be downregulated in non-cancerous tumors such as GH-secreting adenomas. Future studies are warranted to elucidate the role of OGT in the pathogenesis of PAs.

Molecular Derangements and the Diagnosis of ACTH-Dependent Cushing's Syndrome

Endogenous Cushing's syndrome (CS) is associated with morbidities (diabetes, hypertension, clotting disorders) and shortens life because of infections, pulmonary thromboembolism, and cardiovascular disease. Its clinical presentation is immensely variable, and diagnosis and treatment are often delayed. Thus, there are many opportunities for basic and clinical research leading to better tests, faster diagnosis, and optimized medical treatments. This review focuses on CS caused by excessive adrenocorticotropin (ACTH) production. It describes current concepts of the regulation of ACTH synthesis and secretion by normal corticotropes and mechanisms by which dysregulation occurs in corticotrope (termed "Cushing's disease") and noncorticotrope (so-called ectopic) ACTH-producing tumors. ACTH causes adrenal gland synthesis and pulsatile release of cortisol; the excess ACTH in these forms of CS leads to the hypercortisolism of endogenous CS. Again, the differences between healthy individuals and those with CS are highlighted. The clinical presentations and their use in the interpretation of CS screening tests are described. The tests used for screening and differential diagnosis of CS are presented, along with their relationship to cortisol dynamics, pathophysiology, and negative glucocorticoid feedback regulation in the two forms of ACTH-dependent CS. Finally, several gaps in current understanding are highlighted in the hope of stimulating additional research into this challenging disorder.

The activation of G protein-coupled receptor 30 increases pro-opiomelanocortin gene expression through cAMP/PKA/NR4A pathway in mouse pituitary corticotroph AtT-20 cells

G protein-coupled receptor 30 (GPR30) signaling plays an important role in many regulatory pathways, such as gene expression, cell proliferation and migration. However, whether GPR30 is involved in transcription of the pro-opiomelanocortin (Pomc) gene in pituitary corticotroph cells is currently unknown. Here, we report that GPR30 signaling, activated by the GPR30 specific agonist G-1, increases Pomc expression in the mouse corticotroph cell line AtT-20. G-1 also increased nuclear receptor subfamily 4 group A member 1- and 2-dependent transcription activity and phosphorylation of cyclic adenosine monophosphate response element binding protein. Furthermore, protein kinase A inhibitors strongly attenuated G-1-mediated transactivation. The findings suggest that G-1 stimulates GPR30-mediated mechanisms via cyclic adenosine monophosphate/protein kinase A/nuclear receptor subfamily 4 group A members activity in the regulation of Pomc in corticotroph cells.