Neuropeptide TLQP-21, a VGF Internal Fragment, Modulates Hormonal Gene Expression and Secretion in GH3 Cell Line
ABSTRACT 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.
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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 report describes the use of a series of studies that show G protein-coupled receptor (GPCR)-mediated biological activity of TLQP-21 signalling in CHO-K1 cells. Unbiased genome wide sequencing of the transcriptome from responsive CHO-K1 cells identified a prioritized list of possible GPCRs bringing about this activity. Further experiments using a series of defined receptor antagonists as well as siRNAs led to the identification of the complement receptor 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 signalling to pertussis toxin is consistent with the known signalling pathway of the C3AR1 receptor. The binding of TLQP-21 to the C3AR1 not only has effects on signalling but it also modulates cellular functions as TLQP-21 was shown to have a role in directing migration of RAW264.7 mouse cells.Journal of Biological Chemistry 08/2013; DOI:10.1074/jbc.M113.497214 · 4.60 Impact Factor