Novel Functional Role of NK3R Expression in the Potentiating Effects on Somatolactin α Autoregulation in grass carp pituitary cells.

Guangfu Hu,Mulan He,Anderson On Lam Wong

doi:10.1038/srep36102

Guangfu Hu, Mulan He + Show 1 more

Open Access

https://doi.org/10.1038/srep36102

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Abstract

In our previous study, NKB/NK3R system has been shown to act at the pituitary level to up-regulate SLα synthesis and secretion in grass carp. However, whether NK3R expression can serve as a regulatory target at the pituitary level and contribute to NKB interactions with other SLα regulators is still unclear. In current study, using grass carp pituitary cells as a model, we have a novel finding that co-treatment of SLα/SLβ with carp TAC3 gene products, could induce a noticeable enhancement in SLα mRNA expression and these potentiating effects occurred with a parallel rise in NK3R transcript level after SLα/SLβ treatment. Interestingly, the stimulatory effects of SLα/SLβ on NK3R gene expression could be further potentiated by co-treatment with IGF-I/-II and simultaneous exposure of carp pituitary cells to SLα/SLβ and IGF-I/-II in the presence of TAC3 gene products was found to markedly elevated SLα mRNA expression (20 fold increase) and this synergistic stimulation was mediated by cAMP/PKA-, PLC/PKC- and Ca2+ -dependent cascades functionally coupled with NK3R activation. These findings suggest that local release of SLα via functional interactions with IGF-I/-II and TAC3/NK3R system may constitute a potent stimulatory signal for SLα gene expression in the carp pituitary via up-regulation of NK3R expression.

Highlights

Somatolactin (SL), the latest member of growth hormone (GH)/prolactin (PRL) family, is a fish-specific hormone released from the neurointermediate lobe (NIL) of the posterior pituitary[1]
The signal transduction mechanisms involved in SLαand SLβinduction of NK3R mRNA expression were elucidated and the functional role of NK3R expression and the post-receptor signaling pathways coupled with NK3R activation in the potentiating effects on SLαmRNA expression observed with cotreatment of insulin-like growth factors (IGFs)-I/-II and tachykinin 3 (TAC3) gene products was confirmed at the pituitary cell level
Given that (i) two somatolactin isoforms, SLαand SLβ, have been previously shown to trigger SLαsecretion and gene expression at the pituitary level[7], and (ii) TAC3a gene products could stimulate SLαsecretion and gene expression via activation of NK3R in carp pituitary cells[14], we examined the functional interaction between TAC3a gene products and SLs in their stimulatory activity on SLαgene expression

Summary

Introduction

Somatolactin (SL), the latest member of growth hormone (GH)/prolactin (PRL) family, is a fish-specific hormone released from the neurointermediate lobe (NIL) of the posterior pituitary[1]. The investigation on SLαregulation by TAC3 gene products in the carp model have become more exciting with the recent demonstration that IGF-I/-II could act in a synergistic manner with TAC3 gene products, namely NKB and NKBRP, to up-regulate SLαgene expression at the pituitary level and this potentiating effect could be paralleled with the concurrent rise in NK3R expression induced by IGF-I/-II treatment. These new findings demonstrated for the first time that NK3R expression at the pituitary level could serve as a regulatory target for modulation of pituitary hormone gene expression in vertebrate species. Our studies for the first time provide evidence that local release of SLαand SLβcould interact with IGF-I/-II and TAC3 gene products to up-regulate SLαgene expression in the carp pituitary via stimulation of NK3R expression at the pituitary level

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