Isolation and sequence of a cDNA encoding the precursor of a bombesinlike peptide from brain and early embryos of Xenopus laevis

Ranatensin-HL: A Bombesin-Related Tridecapeptide from the Skin Secretion of the Broad-Folded Frog, Hylarana latouchii

Bombesin-related peptides are a family of peptides whose prototype was discovered in amphibian skin and which exhibit a wide range of biological activities. Since the initial isolation of bombesin from Bombina bombina skin, diverse forms of bombesin-related peptides have been found in the skins across Anura. In this study, a novel bombesin-related peptide of the ranatensin subfamily, named ranatensin-HL, was structurally-characterised from the skin secretion of the broad-folded frog, Hylarana latouchii, through combination of molecular cloning and mass spectrometric methodologies. It is composed of 13 amino acid residues, pGlu-RAGNQWAIGHFM-NH₂, and resembles an N-terminally extended form of Xenopus neuromedin B. Ranatensin-HL and its C-terminal decapeptide (ranatensin-HL-10) were chemically synthesised and subjected to in vitro smooth muscle assays in which they were found to display moderate stimulatory effects on rat urinary bladder and uterus smooth muscles with EC₅₀ values in the range of 1–10 nM. The prepro-ranatensin-HL was highly homological to a bombesin-like peptide from Rana catesbeiana at both nucleotide and amino acid levels, which might provide a clue for the taxonomic classification of ranid frogs in the future.

A novel bombesin-like peptide from skin of Rana shuchinae

Bombesin and its receptors have been demonstrated to be involved in a larger array of physiological and pathophysiological conditions including memory and fear behavior, lung development and injury, and tumor growth. A bombesin-like peptide named bombesin-RS was purified and characterized from the skin secretions of the frog, Rana shuchinae. Its amino acid sequence (pETSFMAPSWALGHLM-NH2) was determined by auto Edman degradation and mass spectrometry. The cDNA encoding bombesin-RS precursor was cloned from skin cDNA library of this frog. The precursor is composed of 67 amino acid residues including a copy of mature bombesin-RS. Two predicted enzymatic processing sites (-Lys-Lys- and -Lys-Arg-) are flanked at the mature bombesin-RS sequence. In the in vitro myotropic contraction experiment, the synthesized bombesin-RS displayed stimulating effect toward rat stomach strips, suggesting that bombesin-RS acts as agonist as most other bombesin-related peptides do.

A bombesin-like peptide from skin of Sanguirana varians

Bombesin-like peptides (BLPs) are a family of neuro-endocrinic peptides that mediates a variety of biological activities. A BLP named bombesin-SV from the skin secretions of the frog, Sanguirana varians, was purified and characterized. Its amino acid sequence is pEMIFGAPMWALGHLM-NH2 determined by Edman degradation and mass spectrometry. The cDNA encoding bombesin-SV precursor was cloned from skin cDNA library of S. varians. The precursor is composed of 67 amino acid residues including a copy of mature bombesin-SV. Two predicted enzymatic processing sites (-Lys-Arg-) are flanked at the mature bombesin-SV sequence. In the in vitro myotropic contraction experiment, the synthesized bombesin-SV displayed the stimulating effect toward rat stomach strips, suggesting that bombesin-SV acts as agonist as most other BLPs do.

Multiple bombesin-like peptides with opposite functions from skin of Odorrana grahami

Bombesin-like peptides (BLPs) are a family of neuroendocrinic peptides that mediate a variety of biological activities. Three mature BLPs from the skin secretions of the frog Odorrana grahami were purified. Several bombesin-like peptide cDNA sequences encoding precursors of BLPs were identified from the skin cDNA library of O. grahami. This is the maximal diversity of BLPs ever found in animals. Five mature BLPs (B1-B5) based on the amino acid sequences derived from the cDNA cloning were synthesized. In the in vitro myotropic contraction experiment, all synthesized BLPs displayed a stimulating effect toward rat stomach strips, except B4 and B5 which showed the opposite effect, suggesting that certain BLPs may act as antagonists of bombesin receptors while most other BLPs act as agonists. This finding will facilitate the finding of novel bombesin receptors and novel ligands of bombesin receptors. The diversity of amphibian BLPs and their precursors were also analyzed and results suggest that amphibian BLPs and corresponding precursors of various sizes and processing patterns can be used as markers of taxonomic and molecular phylogenetics. The remarkable similarity of preproregions gives rise to very different BLPs and 3'-terminal regions in distantly related frog species, suggesting that the corresponding genes form a multigene family originating from a common ancestor. The diversification of BLP loci could thus be part of an evolutionary strategy developed by amphibian species as a result of shifts to novel ecological niches when environmental factors change rapidly.

Human Cripto-1 overexpression in the mouse mammary gland results in the development of hyperplasia and adenocarcinoma

Human Cripto-1 (CR-1) is overexpressed in approximately 80% of human breast, colon and lung carcinomas. Mouse Cr-1 upregulation is also observed in a number of transgenic (Tg) mouse mammary tumors. To determine whether CR-1 can alter mammary gland development and/or may contribute to tumorigenesis in vivo, we have generated Tg mouse lines that express human CR-1 under the transcriptional control of the mouse mammary tumor virus (MMTV). Stable Tg MMTV/CR-1 FVB/N lines expressing different levels of CR-1 were analysed. Virgin female MMTV/CR-1 Tg mice exhibited enhanced ductal branching, dilated ducts, intraductal hyperplasia, hyperplastic alveolar nodules and condensation of the mammary stroma. Virgin aged MMTV/CR-1 Tg mice also possessed persistent end buds. In aged multiparous MMTV/CR-1 mice, the hyperplastic phenotype was most pronounced with multifocal hyperplasias. In the highest CR-1-expressing subline, G4, 38% (12/31) of the multiparous animals aged 12-20 months developed hyperplasias and approximately 33% (11/31) developed papillary adenocarcinomas. The long latency period suggests that additional genetic alterations are required to facilitate mammary tumor formation in conjunction with CR-1. This is the first in vivo study that shows hyperplasia and tumor growth in CR-1-overexpressing animals.

Brix from xenopus laevis and brx1p from yeast define a new family of proteins involved in the biogenesis of large ribosomal subunits

A clone was isolated from a cDNA library from early embryos of Xenopus laevis that codes for a highly charged protein containing 339 amino acids. Two putative nuclear localization signals could be identified in its sequence, but no other known motifs or domains. Closely related ORFs are present in the genomes of man, C. elegans, yeast and Arabidopsis. A fusion protein with GFP expressed in HeLa cells or Xenopus oocytes was found to be localized in the nucleolus and coiled (Cajal) bodies. Moreover, immunoprecipitation experiments demonstrated that the new Xenopus protein interacts with 5S, 5.8S and 28S RNAs of large ribosomal subunits. The name Brix (biogenesis of ribosomes in Xenopus) is proposed for this protein and the corresponding gene. In Saccharomyces cerevisiae, the essential gene YOL077c, now named BRX1, codes for the Brix homolog, which is also localized in the nucleolus. Depletion of Brx1 p in a conditional yeast mutant leads to defects in rRNA processing, and a block in the assembly of large ribosomal subunits.

Cripto-1 enhances migration and branching morphogenesis of mouse mammary epithelial cells

Cripto-1 is an EGF-CFC protein that performs an important role during early vertebrate development and is overexpressed in several types of human cancer. In the present study mouse EpH4, NMuMG, and TAC-2 mammary epithelial cells that are negative for endogenous cripto-1 expression were transfected with the murine cripto-1 cDNA. Cripto-1-transfected cell lines exhibited functional and physiological differences from the original cell lines including enhanced anchorage-independent growth in soft agar (EpH4 cells), growth in serum-free medium, increased proliferation, and formation of branching, duct-like structures when grown in a three-dimensional collagen type I matrix. Furthermore, cripto-1-expressing cell lines showed elevated migration in vitro in Boyden chamber and wound-healing assays. These results indicate that cripto-1 can function through an autocrine pathway that enables mammary epithelial cells to undergo an epithelial to mesenchymal transition.

Molecular cloning and expression of cDNA encoding a brain bombesin/gastrin-releasing peptide-like peptide in goldfish

A complementary DNA (cDNA) of 928 bp encoding a bombesin (BBS)/gastrin-releasing peptide (GRP) precursor was identified from goldfish brain. Goldfish BBS/GRP messenger RNA (mRNA) encodes a 157 amino acid precursor, which contains a signal peptide sequence, the 22 amino acid putative BBS/GRP-like peptide, and a carboxy-terminal extension peptide. Reverse transcription-polymerase chain reaction (PCR) (RT-PCR) demonstrated that the mRNA for this precursor has a widespread distribution in goldfish brain, and is also present in skin, gastrointestinal tract, gonad, and gill. Phylogenetic analysis of BBS/GRP-like peptide precursors in vertebrates shows that goldfish BBS/GRP is more closely related to the known GRP precursors than to BBS precursors.

Bv8, a small protein from frog skin and its homologue from snake venom induce hyperalgesia in rats

From skin secretions of Bombina variegata and Bombina bombina, we isolated a small protein termed Bv8. The sequence of its 77 amino acids was established by peptide analysis and by cDNA cloning of the Bv8 precursor. Bv8 stimulates the contraction of the guinea-pig ileum at nanomolar concentrations. The contraction is not inhibited by a variety of antagonists. Injection of a few micrograms of Bv8 into the brain of rats elicits, as assessed by the tail-flick test and paw pressure threshold, a marked hyperalgesia which lasts for about 1 h. Bv8 is related to protein A, a component of the venom of the black mamba. After i.c.v. injection, protein A is even more active than Bv8 in inducing hyperalgesia.

Cloning of cDNAs encoding new peptides of the dermaseptin-family

Dermaseptins are a group of basic (lysine-rich) peptides, 27-34 amino acids in length and involved in the defense of frog skin against microbial invasion. By using a degenerated oligonucleotide primer binding to the 5'-untranslated region of previously characterized cDNAs of these peptides, it was possible to identify new members of the dermaseptin family in the South American frogs Agalychnis annae and Pachymedusa dacnicolor. Amino acid alignment and secondary structure prediction reveals, that only five of the deduced peptides can be supposed to be also functional homologs to the known dermaseptins from Phyllomedusa bicolor and Phyllomedusa sauvagei. The remaining six peptides described in this paper have not been isolated and characterized yet.

Discovery of a high affinity radioligand for the human orphan receptor, bombesin receptor subtype 3, which demonstrates that it has a unique pharmacology compared with other mammalian bombesin receptors

An orphan receptor discovered in 1993 was called bombesin receptor subtype 3 (BRS-3) because of 47-51% amino acid identity with bombesin (Bn) receptors. Its pharmacology is unknown, because no naturally occurring tissues have sufficient receptors to allow studies. We made two cell lines stably expressing the human BRS-3 (hBRS-3). hBRS-3 was overexpressed in the human non-small cell lung cancer cells, NCI-H1299, and the other was made in Balb 3T3 cells, which lack endogenous BRS-3. [D-Phe6,beta-Ala11,Phe13, Nle14]Bn-(6-14) (where Nle represents norleucine) was discovered to have high potency for stimulating inositol phosphate formation in both cell lines. [125I-D-Tyr6,beta-Ala11,Phe13, Nle14]Bn-(6-14) bound to both cell lines with high affinity. Neither Bn nor 14 other naturally occurring Bn peptides bound to hBRS-3 with a Kd <1000 nM. Twenty-six synthetic peptides that are high affinity agonists or antagonists at other bombesin receptors had an affinity >1000 nM. Guanosine 5'-(beta,gamma-imido)triphosphate inhibited binding to both cells due to a change in receptor affinity. These results demonstrate hBRS-3 has a unique pharmacology. It does not interact with high affinity with any known natural agonist or high affinity antagonist of the Bn receptor family, suggesting the natural ligand is either an undiscovered member of the Bn peptide family or an unrelated peptide. The availability of these cell lines and the hBRS-3 ligand should facilitate identification of the natural ligand for BRS-3, its pharmacology, and cell biology.

There are three distinct forms of bombesin. Identification of [Leu13]bombesin, [Phe13]bombesin, and [Ser3,Arg10,Phe13]bombesin in the frog Bombina orientalis

Amphibian bombesin is the prototypic peptide that defines the bombesin-like peptide family. In this paper we show that in the frog Bombina orientalis, there are actually 3 distinct forms of bombesin, and each of these peptides is an agonist with differing affinities for the known bombesin receptors. Oligonucleotides complementary to the 5'- and 3'-untranslated regions of the bombesin mRNA were used to amplify bombesin-related cDNAs from the skin, brain, and gut of B. orientalis. Three classes of cDNAs were found. One class encoded the previously characterized form of bombesin which has a Leu at position 13 ([Leu13]bombesin). The other two classes, respectively, encoded new bombesin-like peptides which we have designated as [Phe13]bombesin and [Ser3,Arg10,Phe13]bombesin ([SAP]bombesin). The existence of [SAP]bombesin in skin was confirmed by tandem mass spectrometry. Polymerase chain reaction analysis of genomic DNA showed the mRNAs for [Leu13]bombesin, [Phe13]bombesin, and [SAP]bombesin most likely arise from separate genes. Polymerase chain reaction analysis showed different patterns of tissue-specific expression for each form. [Leu13]Bombesin and [SAP]bombesin were predominantly expressed in skin, brain, and gut; [Phe13]bombesin was expressed only in brain, and [Leu13]bombesin predominated in oocytes. [SAP]Bombesin contained a cleavage site between residues 4 and 5, which if used would yield the peptide [SAP]bombesin(5-14) which has the sequence [Gln3,Arg6]neuromedin B. Thus a frog homolog of NMB could derive from the [SAP]bombesin prohormone. [Phe13]Bombesin, [SAP]bombesin, and [SAP]bombesin(5-14) were synthesized and their affinities for the mammalian bombesin-like peptide (GRP and NMB) receptors determined. These peptides acted as agonists for the GRP and NMB receptors, with relative potencies for the GRP receptor of [Leu13]bombesin > [Phe13]bombesin > [SAP]bombesin(5-14) > [SAP]bombesin and for the NMB receptor of [Phe13]bombesin > [SAP]bombesin(5-14) > [Leu13]bombesin > [SAP]bombesin. None of these peptides demonstrated high affinity binding for the BRS-3 receptor. The different receptor affinities and tissue distribution of these peptides suggests distinct physiologic roles and raises the possibility of as yet uncharacterized mammalian homologs of these new amphibian peptides.

BSTI, a trypsin inhibitor from skin secretions of Bombina bombina related to protease inhibitors of nematodes

From skin secretions of the European frog Bombina bombina, a new peptide has been isolated that contains 60 amino acids, including 10 cysteine residues. Its sequence was determined by automated Edman degradation and confirmed by analysis of the cDNA encoding the precursor. A search in the databanks demonstrated that the pattern of cysteine residues in this skin peptide is similar to the ones found in protease inhibitors from Ascaris and in a segment of human von Willebrand factor. The 3D structure of the trypsin inhibitor from Ascaris suum could be used as a template to build a model of the amphibian peptide. In addition, we have demonstrated that this constituent of skin secretion is indeed an inhibitor of trypsin and thrombin, with K(i) values in the range of 0.1 to 1 microM. The new peptide was thus named BSTI for Bombina skin trypsin/thrombin inhibitor.

Cloning of a receptor for amphibian [Phe13]bombesin distinct from the receptor for gastrin-releasing peptide: identification of a fourth bombesin receptor subtype (BB4)

Bombesin is a tetradecapeptide originally isolated from frog skin and demonstrated to have a wide range of actions in mammals. Based on structural homology and similar biological activities, gastrin-releasing peptide (GRP) has been considered the mammalian equivalent of bombesin. We previously reported that frogs have both GRP and bombesin, which therefore are distinct peptides. We now report the cloning of a bombesin receptor subtype (BB4) that has higher affinity for bombesin than GRP. PCR was used to amplify cDNAs related to the known bombesin receptors from frog brain. Sequence analysis of the amplified cDNAs revealed 3 classes of receptor subtypes. Based on amino acid homology, two classes were clearly the amphibian homologs of the GRP and neuromedin B receptors. The third class was unusual and a full-length clone was isolated from a Bombina orientalis brain cDNA library. Expression of the receptor in Xenopus oocytes demonstrated that the receptor responded to picomolar concentrations of [Phe13]-bombesin, the form of bombesin most prevalent in frog brain. The relative rank potency of bombesin-like peptides for this receptor was [Phe13]bombesin > [Leu13]bombesin > GRP > neuromedin B. In contrast, the rank potency for the GRP receptor is GRP > [Leu13]bombesin > [Phe13]bombesin > neuromedin B. Transient expression in CHOP cells gave a Ki for [Phe13]bombesin of 0.2 nM versus a Ki of 2.1 nM for GRP. Distribution analysis showed that this receptor was expressed only in brain, consistent with the distribution of [Phe13]-bombesin. Thus, based on distribution and affinity, this bombesin receptor is the receptor for [Phe13]bombesin. Phylogenetic analysis suggests that this receptor separated prior to separation of the GRP and neuromedin B receptors; thus, BB4 receptors and their cognate ligands may also exist in mammals.