Abstract
Tachykinin 4 (TAC4) is the latest member of the tachykinin family involved in several physiological functions in mammals. However, little information is available about TAC4 in teleost. In the present study, we firstly isolated TAC4 and six neurokinin receptors (NKRs) from grass carp brain and pituitary. Sequence analysis showed that grass carp TAC4 could encode two mature peptides (namely hemokinin 1 (HK1) and hemokinin 2 (HK2)), in which HK2 retained the typical FXGLM motif in C-terminal of tachyinin, while HK1 contained a mutant VFGLM motif. The ligand-receptor selectivity showed that HK2 could activate all 6 NKRs but with the highest activity for the neurokinin receptor 2 (NK2R). Interestingly, HK1 displayed a very weak activation for each NKR isoform. In grass carp pituitary cells, HK2 could induce prolactin (PRL), somatolactin α (SLα), urotensin 1 (UTS1), neuromedin-B 1 (NMB1), cocaine- and amphetamine-regulated transcript 2 (CART2) mRNA expression mediated by NK2R and neurokinin receptor 3 (NK3R) via activation cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), phospholipase C (PLC)/inositol 1,4,5-triphosphate (IP3)/protein kinase C (PKC) and calcium2+ (Ca2+)/calmodulin (CaM)/calmodulin kinase-II (CaMK II) cascades. However, the corresponding stimulatory effects triggered by HK1 were found to be notably weaker. Furthermore, based on the structural base for HK1, our data suggested that a phenylalanine (F) to valine (V) substitution in the signature motif of HK1 might have contributed to its weak agonistic actions on NKRs and pituitary genes regulation.
Highlights
In mammals, the tachykinin (TAC) family includes three members, namely tachykinin1 (TAC1), tachykinin 3 (TAC3) (tachykinin 2 (TAC2) in rodents), and Tachykinin 4 (TAC4), respectively.Among them, TAC1 gene encodes substance P (SP) and neurokinin A (NKA)
In the present study, only one TAC4 isoform was isolated in teleost, which might be the result of the non-functionalization by forming pseudogenes or deletion/mutations leading to the loss of redundant genes [24] (Supplement Figure S14)
TAC4 gene products were various in different species
Summary
The tachykinin (TAC) family includes three members, namely tachykinin. 1 (TAC1), tachykinin 3 (TAC3) (tachykinin 2 (TAC2) in rodents), and TAC4, respectively. Teleost TAC1 encodes two mature peptides, namely SP and NKA, respectively [5]. TAC3 encodes neurokinin B (NKB), is known to be involved in the regulation of smooth muscles of the gastrointestinal tract, secretion of intestinal epithelial fluid, vasodilation, and stimulating sperm motility [6,7,8]. Our previous studies have shown that both NKB and NKBRP can promote PRL and SLα secretion and mRNA synthesis in grass carp pituitary cells [11]. In the present study, using grass carp (Ctenopharyngodon idellus) as a model, we try to examine the pituitary actions of TAC4 gene product in teleost. The grass carp TAC4 were cloned, which encoded two mature peptides, namely HK-1 and HK-2, respectively. We try to clarify the mechanism of functional differences between HK-1 and HK-2 in teleost
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