Molecular cloning and functional characterization of a type-I neurotensin receptor (NTR) and a novel NTR from the bullfrog brain

Abstract

Neurotensin (NT) is a tridecapeptide that functions as a neurotransmitter and neuromodulator in the nervous system. To date, three different types of NT receptor (NTR), NTR1, NTR2 and NTR3, have been identified only in mammalian species. In the present study we isolated the cDNAs for an NTR1 and a novel NTR in the bullfrog brain, designated bfNTR1 and bfNTR4 respectively. bfNTR1 and bfNTR4 encode 422-and 399-amino acid residue proteins respectively. bfNTR1 has a 64% amino acid identity with mammalian NTR1, and 34-37% identity with mammalian NTR2. bfNTR4 exhibits 43% and 45-47% identity with mammalian NTR1 and NTR2 respectively. Both receptors are mainly expressed in the brain and pituitary. bfNTR1 triggers both CRE-luc, a protein kinase A (PKA)-specific reporter, and c-fos-luc, a PKC-specific reporter, activities, indicating that bfNTR1 can activate PKA-and PKC-linked signaling pathways. However, bfNTR4 appears to be preferentially coupled to the PKA-linked pathway as it induces a higher CRE-luc activity than c-fos-luc activity. bfNTRs exhibit different pharmacological properties as compared with mammalian NTRs. Mammalian NTR1 but not NTR2 responds to NT, whereas both bfNTR1 and bfNTR4 show a high sensitivity to NT. SR 48692 and SR 142948A, antagonists for mammalian NTR1 but agonists for mammalian NTR2, function as antagonists for both bfNTR1 and bfNTR4. In conclusion, this report provides the first molecular, pharmacological and functional characterization of two NTRs in a non-mammalian vertebrate. These data should help to elucidate the phylogenetic history of the G protein-coupled NTRs in the vertebrate lineage as well as the structural features that determine their pharmacological properties.

Sensorimotor gating in neurotensin-1 receptor null mice

“…There are three NT receptor subtypes, NT1, NT2 and NT3 that have been identified to date and evidence suggests that additional subtypes exist (Li et al, 2005; Mazella and Vincent, 2006). It is not known which receptors mediate the effects of NT on PPI but converging evidence most strongly implicates NT1 receptors.…”

Molecular characterization of structure and tissue distribution of chicken neurotensin receptor

“…Recently, NTR2 cDNA together with NTR1 cDNA have been cloned in bullfrog [27]. NTR2 has also been identified in Xenopus tropicalis by a BLAST search [20].…”

“…Studies have shown intracellular signaling pathways of mammalian NTR1 and NTR2 to be associated with intracellular Ca 2+ mobilization [10,19,27]. Chicken NT also induces Ca 2+ release from internal store, which is responsible for the contractile activity in the longitudinal smooth muscle of the rectum [24].…”

“…In non-mammalian species, two G protein-coupled NTRs, designated as bfNTR1 and bfNTR4, have been identified in bullfrog [27]. Currently, bfNTR4 is designated as bfNTR2 because this receptor is interpreted as the mammalian NTR2 homolog by genome synteny analysis [20].…”

Effects of neurotensin-2 receptor deletion on sensorimotor gating and locomotor activity

“…Three NT receptor subtypes, NT1, NT2 and NT3 have been identified and there is evidence that additional subtypes exist [14,15]. NT1 and NT2 are high and low affinity G-protein coupled receptors (GPCRs), respectively.…”