Neuropeptide TLQP-21, a VGF Internal Fragment, Modulates Hormonal Gene Expression and Secretion in GH3 Cell Line
Institute of Cell Biology and Neurobiology and Institute of Translational Pharmacology, CNR Rome, Rome, Italy. Neuroendocrinology
(Impact Factor: 4.37).
06/2012; 97(3). DOI: 10.1159/000339855
In the present study we demonstrated that TLQP-21, a biologically active peptide derived from the processing of the larger pro-VGF granin, plays a role in mammotrophic cell differentiation. We used an established in vitro model, the GH3 cell line, which upon treatment with epidermal growth factor develops a mammotrophic phenotype consisting of induction of prolactin expression and secretion, and inhibition of growth hormone. Here we determined for the first time that during mammotrophic differentiation, epidermal growth factor also induces Vgf gene expression and increases VGF protein precursor processing and peptide secretion. After this initial observation we set out to determine the specific role of the VGF encoded TLQP-21 peptide on this model. TLQP-21 induced a trophic effect on GH3 cells and increased prolactin expression and its own gene transcription without affecting growth hormone expression. TLQP-21 was also able to induce a significant rise of cytoplasmic calcium, as measured by Fura2AM, due to the release from a thapsigargin-sensitive store. TLQP-21-dependent rise in cytoplasmic calcium was, at least in part, dependent on the activation of phospholipase followed by phosphorylation of PKC and ERK. Taken together, the present results demonstrate that TLQP-21 contributes to differentiation of the GH3 cell line toward a mammotrophic phenotype and suggest that it may exert a neuroendocrine role in vivo on lactotroph cells in the pituitary gland.
Available from: jbc.org
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ABSTRACT: TLQP-21, a peptide derived from VGF (non-acronymic) by proteolytic processing, has been shown to modulate energy metabolism,
differentiation, and cellular response to stress. Although extensively investigated, the receptor for this endogenous peptide
has not previously been described. This study describes the use of a series of studies that show G protein-coupled receptor-mediated
biological activity of TLQP-21 signaling in CHO-K1 cells. Unbiased genome-wide sequencing of the transcriptome from responsive
CHO-K1 cells identified a prioritized list of possible G protein-coupled receptors bringing about this activity. Further experiments
using a series of defined receptor antagonists and siRNAs led to the identification of complement C3a receptor-1 (C3AR1) as
a target for TLQP-21 in rodents. We have not been able to demonstrate so far that this finding is translatable to the human
receptor. Our results are in line with a large number of physiological observations in rodent models of food intake and metabolic
control, where TLQP-21 shows activity. In addition, the sensitivity of TLQP-21 signaling to pertussis toxin is consistent
with the known signaling pathway of C3AR1. The binding of TLQP-21 to C3AR1 not only has effects on signaling but also modulates
cellular functions, as TLQP-21 was shown to have a role in directing migration of mouse RAW264.7 cells.
Available from: Ricardo Borges
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ABSTRACT: Catecholamines (CAs) and granin peptides are costored in dense-core vesicles within the chromaffin cells of the adrenal medulla and in other endocrine organs and neurons. Granins play a major functional and structural role in chromaffin cells but are ubiquitous proteins, which are present also in secretory cells of the nervous, endocrine, and immune systems, where they regulate a number of cellular functions. Furthermore, recent studies also demonstrate that granin-derived peptides can functionally interact with CA to modulate key physiological functions such as lipolysis and blood pressure. In this chapter, we will provide a brief update on the interaction between CA and granins at the cellular and organ levels. We will first discuss recent data on the regulation of exocytosis of CA and peptides from the chromaffin cells by the sympathetic nervous system with a specific reference to the prominent role played by splanchnic nerve-derived pituitary adenylate cyclase-activating peptide (PACAP). Secondly, we will discuss the role of granins in the storage and regulation of exocytosis in large dense-core vesicles. Finally, we will provide an up-to-date review of the roles played by two granin-derived peptides, the chromogranin A-derived peptide catestatin and the VGF-derived peptide TLQP-21, on lipolysis and obesity. In conclusion, the knowledge gathered from recent findings on the role played by proteins/peptides in the sympathetic/target cell synapses, discussed in this chapter, would contribute to and provide novel mechanistic support for an increased appreciation of the physiological role of CA in human pathophysiology.
Available from: Roberta Possenti
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ABSTRACT: Insulin secretion control is critical for glucose homeostasis. Paracrine and autocrine molecules secreted by cells of the islet of Langherans, as well as by intramural and autonomic neurons, control release of the different hormones that modulate insulin secretion. In pancreatic islets, the abundant presence of the granin protein VGF (nonacronymic; unrelated to VEGF) suggests that some of its proteolytically derived peptides could modulate hormone release. Thus, for the present study, we screened several VGF-derived peptides for their ability to induce insulin secretion, identifying the VGF C-terminal peptide TLQP-62 as the most effective fragment. TLQP-62 induced a potent increase in basal insulin secretion as well as in glucose-induced insulin release in several insulinoma cell lines. We found that this peptide stimulated insulin release via increased intracellular calcium mobilization and fast expression of the insulin 1 gene. Moreover, peripheral injection of TLQP-62 in mice improved glucose tolerance. Together, our findings suggest that TLQP-62, acting as an endocrine, paracrine, or autocrine factor, can be considered a new, strong insulinotropic peptide that can be targeted for innovative anti-diabetic drug discovery programs.
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