Activation of the cloned human NK3 receptor in Chinese Hamster Ovary cells characterized by the cellular acidification response using the Cytosensor microphysiometer

An artificial peptide with corticotropin-releasing factor receptor-2 (CRF-R2) selective properties: the role of primary structure in the induction of signal transduction pathways

Considerable plasticity can occur within the amino acid sequence of amphiphilic peptide hormones. This is particularly evident within the corticotropin-releasing factor (CRF) family of peptides where, despite less than 15% sequence similarity among the four paralogous lineages, all are capable of acting as high affinity ligands to members of the CRF receptor family. This suggests that these peptides could undergo many mutational changes and remain as high affinity ligands to their receptors as long as the functional motifs do not change radically. Because paralogous peptide lineages are a product of genome duplications, additional genes encoding peptide-like sequences, which through mutation have lost their functional integrity, may exist. Function to these sequences may be restored if the appropriate motifs are reinserted into the primary structure. We screened rat genomic DNA with highly degenerate polymerase chain reaction (PCR) primers targeted to hybridize with the termini of CRF-related sequences. One set of sauvagine-based primers hybridized with a 120-bp sequence. The theoretical peptide sequence (SV4) showed similarity to the CRF family of peptides at the primary structure level. The encoded sequence was prepared by solid-phase synthesis and its activity assayed against mouse R1 and human R1/R2 receptors. SV4 did not bind to either mouse or human variants of the R1 receptor, but did bind to the R2 receptor with an affinity comparable to human CRF. SV4 exhibited a similar efficacy of cellular activation as CRF in trials quantifying the acidification rate of human R2alpha-transfected Chinese hamster ovary (CHO) cells, but not R1-transfected cells. SV4 utilizes adenylate cyclase as the principal secondary messenger of R2 signal transduction but, unlike urocortin or sauvagine, does not activate guanylate cyclase-, calcium- or mitogen-activated protein (MAP) kinase-mediated pathways. These data suggest that this artificial peptide may be useful to understand the cyclic adenosine monophosphate (cAMP)-dependent component of the CRF-R2 signal transduction cascade, and that additional sequences in the genome may be used to engineer bioactive peptides.

Continuous measurement of glucose utilization in heart myoblasts

Understanding quantitative aspects of cell energy metabolism and how it is influenced by environment is central to biology, medicine, and biotechnology. Most methods used for measuring metabolic fluxes associated with energy metabolism require considerable personnel effort or high maintenance instrumentation. The microphysiometer is a commercially available instrument that measures acid extrusion rates, which are commonly used for drug screening. With the addition of oxygen sensors, the instrument can also be used to measure cell oxygen consumption rates and thereby calculate glycolytic fluxes. In the work described here, oxygen consumption and acid extrusion rates were used to measure glucose utilization by the H9c2 rat heart myoblast cell line and these results are compared with fluxes measured with a radiometric assay. Both assays were used to investigate changes in H9c2 energy metabolism due to cell stimulation with carbachol and insulin. The results demonstrate the utility of the microphysiometer method for measuring both transient and sustained changes in partitioning of glucose utilization between glycolysis and oxidation in live cells.

Role of the conserved DRY motif on G protein activation of rat angiotensin II receptor type 1A

To delineate the functional importance of the highly conserved triplet amino acid sequence, Asp-Arg-Tyr (DRY) among G protein-coupled receptors in the second intracellular loop, these residues of rat angiotensin II (Ang II) receptor type 1A (AT(1A)) were changed by alanine or glycine by site-directed mutagenesis. These mutant receptors were stably expressed in CHO-K1 cells, and the binding of Ang II, GTP effect, InsP(3) production, and the acidification of the medium in response to Ang II were determined. The effects of GTPgammaS on Ang II binding in the mutant receptors D125A and D125G were markedly reduced. InsP(3) production of the mutant D125A, D125G, R126A, and R126G was markedly reduced. Extracellular acidification of D125A was not distinguishable from untransfected CHO-K1 cells. Mutant Y127A was able to produce InsP(3) and acidify medium comparable with wild type AT(1A). These results indicate as follows; Asp(125) is essential for intracellular signal transduction involving G protein coupling, Arg(126) is essential for coupling of G(q) protein but not other G proteins, and Tyr(127) is not important for G protein coupling.

Differentiation of bipolar CG-4 line oligodendrocytes is associated with regulation of CREB, MAP kinase and PKC signalling pathways

Undifferentiated bipolar CG-4 cell line oligodendrocytes provide a model system for the O-2A progenitor cell from which oligodendrocytes are derived both in vivo and in vitro. The exchange of neuroblastoma conditioned basal media for basal media causes differentiation of undifferentiated bipolar CG-4 cells into multipolar oligodendrocyte-like cells whilst replacement with basal media containing 20% foetal bovine serum favours the formation of type-2 astrocyte-like cells. Here, we demonstrate that activation of these differentiation pathways correlates with distinct changes both in cell metabolism and in signal transduction. Exchange of neuroblastoma conditioned media for basal media correlates with stimulation of basal metabolic activity, reduced phosphorylation of p44/42 MAP kinase and reduced phosphorylation of the transcription factor CREB. In contrast, differentiation with basal medium containing 20% foetal bovine serum (FBS), into type 2 astrocyte-like cells, correlates with reduction in basal metabolic activity, increased phosphorylation of p44/42 MAP kinase and increased phosphorylation of the transcription factor CREB. Inhibition of protein kinase C blocked both the metabolic and morphological changes associated with differentiation towards mature multipolar oligodendrocyte-like cells. Inhibition of PKA and MEK did not effect metabolic activity. The rapid return of neuroblastoma conditioned basal media to cells treated with basal media, increased phosphorylation of CREB and MAP kinase. These results demonstrate that protein kinase C and p44/42 MAP kinase signalling pathways are modulated during bipolar CG-4 cell differentiation and demonstrate that the transcription factor CREB may play a pivotal role in differentiation along oligodendrocyte-or astrocyte-lineages.

Biphasic response to human galanin of extracellular acidification in human Bowes melanoma cells

The metabolic response of galanin GAL1 receptor subtype, endogenously expressed in human Bowes melanoma (HBM) cells, was investigated. Cytosensor microphysiometry was used to determine the extracellular acidification rate. A biphasic response, consisting of a rapid increase in the extracellular acidification rate followed by a decrease below the basal level, was observed after perfusion with human galanin. The magnitude and the rate of onset of both phases were dependent on the galanin concentration. The increase in the extracellular acidification rate (maximum of 25% of basal level; -log(EC(50))=7.23+/-0.14) was transient, whereas the following decrease (maximum of 40% of basal level; -log(EC(50))=7.77+/-0.23) was sustained. The EC(50) values for the increase and decrease were in a similar range. After consecutive galanin administration, the magnitude of the response was the same as for the unexposed cells, indicating the absence of galanin receptor desensitization or internalization in HBM cells. Responses were blocked by pretreatment with pertussis toxin and phorbol-12-myristate-13-acetate (PMA), indicating a G-protein/protein kinase C signalling pathway. Our microphysiometry results show a biphasic response of the extracellular acidification rate mediated by the galanin receptor expressed in HBM cells which has not been described previously for any other endogenously expressed neuropeptide receptor.

Cytosensor techniques for examining signal transduction of neurohormones

This review describes the principles of microphysiometry and how they can be applied, using the Cytosensor, to the investigation of the signal transduction mechanisms activated by both G-protein and non-G-protein coupled hormone and neuropeptide receptors. The use of the Cytosensor to study desensitisation and cross-talk is also discussed, as are the benefits and limitations of this technique.Key words: Cytosensor, microphysiometry, signal transduction, neuropeptides, hormones.

Novel action of pituitary adenylate cyclase-activating polypeptide. Stimulation of extracellular acidification in rat pituitary GH4C1 cells

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the vasoactive intestinal peptide/secretin family. Using microphysiometry, we have found that PACAP acutely (1 min) increased the extracellular acidification rate (ECAR) in GH4C1 cells approximately 40% above basal in a concentration-dependent manner. ECAR, maximally induced by PACAP, can be increased further by thyrotropin-releasing hormone (TRH), indicating that the signalling pathways for these two neuropeptides are not identical. In studies on the mechanism of PACAP-enhanced ECAR, we found that maximum stimulation of the cAMP/PKA pathway by treatment with FSK, or the PKC pathway with PMA, did not inhibit the ECAR response to PACAP. The PKC inhibitor calphostin C and the MAP kinase inhibitor PD98059 had no effect on the ECAR response to PACAP. Furthermore, PACAP induced little or no change in cytosolic Ca(2+) ([Ca(2+)](i)), while TRH induced a large increase in [Ca(2+)](i). However, the tyrosine kinase inhibitor genistein completely blocked PACAP-induced ECAR, suggesting involvement of tyrosine kinase(s). We conclude that PACAP causes an increase in ECAR in GH4C1 rat pituitary cells, which is not dependent on the PKA, PKC, MAP kinase or Ca(2+) signalling pathways, but does require tyrosine kinase activity.

Molecular and pharmacological characterization of a functional tachykinin NK3 receptor cloned from the rabbit iris sphincter muscle

1. A functional tachykinin NK3 receptor was cloned from the rabbit iris sphincter muscle and its distribution investigated in ocular tissues. 2. Standard polymerase chain reaction (PCR) techniques were used to clone a full length rabbit NK3 receptor cDNA consisting of 1404 nucleotides. This cDNA encoded a protein of 467 amino acids with 91 and 87% homology to the human and rat NK3 receptors respectively. 3. In CHO-K1 cells transiently expressing the recombinant rabbit NK3 receptor, the relative order of potency of NKB>>NKA>/=SP to displace [125I]-[MePhe7]-NKB binding and to increase intracellular calcium, together with the high affinity of NK3 selective agonists (e.g. senktide, [MePhe7]-NKB) and antagonists (e.g. SR 142801, SB 223412) in both assays was consistent with NK3 receptor pharmacology. In binding and functional experiments, agonist concentration response curves were shallow (0.7 - 0.8), suggesting the possibility of multiple affinity states of the receptor. 4. Quantitative real time PCR analysis revealed highest expression of rabbit NK3 receptor mRNA in iris sphincter muscle, lower expression in retina and iris dilator muscle, and no expression in lens and cornea. In situ hybridization histochemistry revealed discrete specific localization of NK3 receptor mRNA in the iris muscle and associated ciliary processes. Discrete specific labelling of NK3 receptors with the selective NK3 receptor agonist [125I]-[MePhe7]-NKB was also observed in the ciliary processes using autoradiography. 5. Our study reveals a high molecular similarity between rabbit and human NK3 receptor mRNAs, as predicted from previous pharmacological studies, and provide the first evidence that NK3 receptors are precisely located on ciliary processes in the rabbit eye. In addition, there could be two affinity states of the receptor which may correspond to the typical and 'atypical' NK3 receptor subtypes previously reported.

The interleukin-1 type I receptor is expressed in human hypothalamus

Several lines of evidence suggest that interleukin-1 (IL-1) acts directly on the central nervous system, probably within the hypothalamus, causing effects such as fever, activation of the immune response and sickness behaviour. IL-1 has also been shown to be involved in the aetiology of several neuronal diseases, including neurodegeneration, stroke and Alzheimer's disease. However, the question as to whether the full-length type I IL-1 receptor (IL-1RI) is expressed in the human hypothalamus has yet to be addressed. Using the polymerase chain reaction, we cloned a full-length cDNA encoding the human hypothalamic IL-1RI from human hypothalamic cDNA. The DNA sequence of the human hypothalamic receptor was identical to that of the human fibroblast IL-1RI. The IL-1RI receptor protein was detected in astrocytes of normal human hypothalamic brain sections using immunocytochemical techniques. To ascertain that the cloned receptor was functional, Chinese hamster ovary (CHO) cells were transfected with a plasmid vector containing the IL-1RI coding region. IL-1RI-mediated-signal transduction was assessed by microphysiometry and activation of p38 MAP (mitogen-activated protein) kinase. We report the first demonstration that both the type I IL-1 transcript and the protein are expressed in the human hypothalamus. The receptor was expressed in a stable CHO cell line, providing a tool with which to embark on a thorough analysis of the signalling mechanisms mediated by IL-1 via this receptor.

Characterisation using microphysiometry of CRF receptor pharmacology

We have assessed the utility of the Cytosensor microphysiometer for studying the pharmacology of recombinant CRF receptors. Chinese hamster ovary cells stably expressing the human CRF1 or CRF2 receptor were perfused in the Cytosensor with bicarbonate-free Hams F12 (pH 7.4) containing 0.2% bovine serum albumin. The rank order of potencies of agonist peptides were CRF = sauvagine = urocortin = urotensin at CRF1 (pEC50 values 11.16 +/- 0.17, 11.37 +/- 0.14, 11.43 +/- 0.09 and 11.46 +/- 0.13; n = 4), and urocortin = sauvagine > urotensin > CRF at CRF2 (pEC50 values 10.88 +/- 0.12, 10.44 +/- 0.05, 9.36 +/- 0.12 and 8.53 +/- 0.07; n = 7-9). alpha-Helical CRF (9-41) was a competitive antagonist at the CRF2 receptor (pK(B) = 6.99 +/- 0.08, n = 4), but was a partial agonist at the CRF1 receptor (pEC50 = 6.85 +/- 0.08, Emax = 33%, n = 3). CP 154,526 was a competitive antagonist at the CRF1 receptor (pK(B) = 8.17 +/- 0.05, n = 6), but was inactive at the CRF2 receptor. These data are consistent with established CRF receptor pharmacology and show that the Cytosensor is a viable method for assessing the functional activity of CRF-receptor agonists and antagonists.

Rainbow trout (Oncorhynchus mykiss) urotensin-I: structural differences between urotensins-I and urocortins

In bony fishes, both corticotropin-releasing factor (CRF) and urotensin-I play a role in the regulation of interrenal glucocorticoid release. The rainbow trout, Oncorhynchus mykiss, is a useful model for understanding the mechanisms of stress and the hypothalamo-pituitary-interrenal axis because of its phylogenetic position at the base of the euteleostei and its popularity as a food fish. Urotensin-I may act as a glucocorticoid releaser in a mechanism phylogenetically older than that of CRF. The structural and functional relationships of trout urotensin-I have been investigated. The transcript was cloned from a trout brain hypothalamic cDNA library. A single positive clone was isolated and sequenced. It possesses 3218 bases and has the longest 3' untranslated region of all urotensins-I and CRF transcripts found to date. In comparison to the other fish orthologues, it has the closest sequence identity to the mammalian urocortins. The transcript appears to be differentially processed in brain and urophysis as determined by Northern blot analysis and the presence of polyadenylation signals in the 3' untranslated region. Synthetic trout urotensin-I activated both human CRF-R1 and -R2 receptor-transfected CHO cells with a potency similar to that of white sucker (Catostomus commersoni) urotensin-I. Both fish neuropeptides possessed an order of magnitude less potency than human urocortin in CRF-R2 transfected cells.

Cloning and characterization of corticotropin-releasing factor and urocortin in Syrian hamster (Mesocricetus auratus)

Corticotropin-releasing factor and urocortin belong to a superfamily of neuropeptides that includes the urotensins-I in fishes and the insect diuretic peptides. Sequence analysis suggests that urocortin is the mammalian ortholog of urotensin-I, although the physiological role for this peptide in mammals is not known. Within the Rodentia, hamsters belong to a phylogenetically older lineage than that of mice and rats and possess significant differences in hypothalamic organization. We have, therefore, cloned the coding region of the Syrian hamster (Mesocricetus auratus) corticotropin-releasing factor and urocortin mature peptide by polymerase chain reaction. Hamster urocortin was prepared by solid-phase synthesis, and its pharmacological actions on human corticotropin-releasing factor R1 and R2 receptors were investigated. The deduced hamster corticotropin-releasing factor amino acid sequence and cleavage site is identical to that in rat, whereas the urocortin sequence is unique among the urocortin/urotensin-I/sauvagine family in possessing asparagine and alanine in positions 38 and 39, respectively. The hamster urocortin carboxy terminus sequence bears greater structural similarity to the insect diuretic peptide family, suggesting either retrogressive mutational changes within the mature peptide or convergent sequence evolution. Despite these changes, human and hamster urocortin are generally equipotent at cAMP activation, neuronal acidification rate, and R1/R2 receptor affinities.