P2X and P2X receptor expression in human bladder urothelium and changes in interstitial cystitis.

OBJECTIVE: To investigate whether the expression of P2X(3) receptors (implicated in the pathophysiology of pain) is altered in human bladder urothelium from patients with interstitial cystitis (IC, a major symptom of which is pain), and as P2X(2) receptors can be co-expressed with P2X(3) receptors, to assess their expression also. PATIENTS AND METHODS: Bladder tissue samples were collected from patients undergoing cystectomy or radical prostatectomy. Patients with IC were diagnosed using the international criteria. RNA protein expression levels of both receptors were evaluated using reverse transcription-polymerase chain reaction (PCR), real-time quantitative PCR and Western blot analysis. RESULTS: P2X(2) was expressed in the human urothelium, in a glycosylated form. There was less gene expression of P2X(3) in IC urothelium, whereas P2X(2) gene expression was unchanged. This contrasted with the protein expression, which was increased for both P2X(2) and P2X(3). CONCLUSION: This is the first report of the expression of the P2X(2) receptor in human bladder urothelium. There was greater protein expression of both P2X(2) and P2X(3) in IC bladder urothelium which did not directly correlate with the gene expression. Changes in expression of P2X(2) and P2X(3) receptors may contribute to the pain that patients with IC have, and might provide novel drug targets.

Titrating the expression of a Gi protein-coupled receptor using an ecdysone-inducible system in CHO-K1 cells.

Changes in receptor density are often associated with pathological conditions. For example, high levels of the G protein-coupled somatostatin receptor, sst2, have been detected in a number of malignant cell types, a characteristic feature that is routinely utilised as a diagnostic tool. However, how the increased receptor expression affects cellular function through alterations in G protein-coupling or changes in the intensity or duration of activated signalling pathways is poorly understood. The current report details the use of an ecdysone-inducible expression system in CHO-K1 cells, whereby the consequence of modulating the level of human sst2 receptor expression on specific transduction events can be examined. A time- and concentration-dependent induction of sst2 receptor expression was attained by exposure of cells to the ecdysteroid-inducing agent, muristerone A (MuA). Increases in sst2 receptor expression were determined by immunoassay, immunoblotting and immunocytochemical analysis. Maximal sst2 receptor expression was obtained after treatment of cells with 7 microM MuA for 24 h. Functionality of the sst2 receptor was assessed by immunoblot analysis of phosphorylated forms of MAP kinase. Following receptor activation, time-dependent increases in the level of MAP kinase phosphorylation were shown to correlate with the degree of sst2 receptor induction. Confirmation of receptor activation was determined by visualisation of ligand-induced redistribution of sst2 receptors from the plasma membrane to discrete intracellular compartments. However, in a series of further studies, both immunocytochemical and fluorescence-activated cell sorting (FACS) analyses demonstrated that over a prolonged period, stable receptor expression could not be maintained in CHO-K1 cells using this expression system. Thus, routine analysis of the sst2 receptor expressing cell population is required to derive comparable results between assays, especially when some assays provide information from the whole cell population whilst others are based at the single cell level. On the basis of these observations we conclude that, providing such quality control measurements are taken, the ecdysone inducible expression system is a useful tool to modulate functional sst2 receptor expression in an in vitro environment over short time periods.

Adenosine A(1) receptor-mediated inhibition of protein kinase A-induced calcitonin gene-related peptide release from rat trigeminal neurons.

Calcitonin gene-related peptide (CGRP), a potent vasodilator, has been implicated in the pathogenesis of migraine. Its release from adult rat trigeminal neurons in culture was shown to be markedly increased by the activation of adenylate cyclase with forskolin. Modulation of this secretion was investigated by a number of agents with known inhibitory effects on cAMP generation mediated via receptor coupling to G(i/o) proteins. Significantly, forskolin-stimulated CGRP release could be closely correlated with the phosphorylation of the protein kinase A (PKA) substrate cyclic AMP response element-binding protein (CREB). Forskolin-stimulated CGRP release could be potently and effectively inhibited by the adenosine A(1) receptor-selective agonist GR79236X (pIC(50) = 7.7 +/- 0.1, maximal inhibition 65 +/- 2.5% at 300 nM), whereas the A(2A) (CGS21680) and the A(3) (2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide) receptor-selective agonists were without effect. GR79236X-mediated inhibition was abolished by the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. Immunocytochemical studies and Western analysis revealed the presence of adenosine A(1) receptors on trigeminal neurons. However, despite the additional detection of 5-hydroxytryptamine (5-HT)(1B) receptors on these cells, the clinically effective antimigraine 5-HT(1B/1D) agonist sumatriptan did not inhibit forskolin-stimulated CGRP release nor did it show any effect on the concomitant CREB phosphorylation. In contrast, the mu-opioid agonist fentanyl elicited a 74 +/- 4% reduction in CGRP levels. Forskolin-stimulated CGRP release and CREB phosphorylation could be mimicked by incubation of the cells with chlorophenylthio-cAMP and blocked by pretreatment with the PKA inhibitor myrPKI(14-22). Taken together, the present data confirm the PKA-dependence of forskolin-stimulated CGRP release and suggest that A(1) adenosine agonists may warrant further investigation in models of migraine and neurogenic inflammation.

High-intensity p38 kinase activity is critical for p21(cip1) induction and the antiproliferative function of G(i) protein-coupled receptors.

G protein-coupled receptors can stimulate the p38 kinase cascade, but the effect this has on cell growth remains poorly characterized. Here we show human somatostatin sst(2) and sst(4) receptors inhibit basic fibroblast growth factor (bFGF)-induced proliferation, via a mechanism that was blocked by the p38 inhibitor PD 169316. The sst(4) receptor could also induce a proliferative activity in the absence of bFGF, which was unaffected by PD 169316. In contrast, the sst(3) receptor had no effect on basal cell growth or on the proliferation evoked by bFGF. The extracellular signal-regulated kinase activity stimulated by the sst(3) receptor was transient in duration compared with a sustained activity induced by the sst(2) and sst(4) receptors and which was critical for the proliferative response of the latter receptor. In addition, activated sst(2) and sst(4) but not sst(3) receptors evoked a prolonged phosphorylation of p38 that was amplified by bFGF. The accumulation of the cell cycle inhibitor p21(cip1) was only apparent after sst(2) and sst(4) receptor activation in the presence of bFGF, which was sensitive to PD 169316 or pertussis toxin. Thus, the contrasting antiproliferative effects evoked by the human sst(2), sst(3), and sst(4) receptors can be accounted for by their differential abilities to activate p38. This activity is critical for p21(cip1) induction, blockade of entry into S phase, as indicated by the lack of retinoblastoma protein phosphorylation, and the associated antiproliferative activity of somatostatin. Furthermore, by changing the intracellular signaling threshold of p38 through cooperative effects of somatostatin and bFGF, the sst(4) receptor can mediate opposing effects on cell proliferation.

Somatostatin activates two types of inwardly rectifying K+ channels in MIN-6 cells.

Western blotting revealed the presence of five somatostatin receptor types, sst1, sst2, sst3, sst4 and sst5, in the mouse pancreatic -cell line MIN-6. In MIN-6 cells, glucose-induced electrical activity was potently (pEC50 = 12.7) and irreversibly reduced by somatostatin (SRIF-14); this was associated with hyperpolarization of the membrane potential (pEC50 = 11.2) and a decrease in the input resistance (pEC50 = 12.7). The effects of SRIF-14 were mimicked by 100 nM L-362,855 (a partial agonist at sst5 receptors), but not BIM-23027 or NNC-26,9100 (selective agonists at sst2 and sst4 receptors, respectively). CH-275 at 100 nM (a selective agonist at sst1 receptors) partially inhibited electrical activity but without membrane potential hyperpolarization. One hundred nanomolar SRIF-28 activated an inwardly rectifying K+ current (ISRIF) ISRIF was activated neither by 1 M BIM-23056 nor CYN-154806 (antagonists at sst5 and sst2 receptors, respectively). The activation of ISRIF by 100 nM SRIF-28 was, however, inhibited 93 % by BIM-23056; CYN-154806 had no effect. Both 100 nM glibenclamide and 200 M tolbutamide, blockers of the -cell ATP-sensitive K+ channel (K-ATP), reduced ISRIF by ~44 %, whereas 1 mM Ba2+ abolished ISRIF. In cell-attached patches, 100 nM SRIF-14 activated two types of single-channel currents whose properties were consistent with those of K-ATP and GIRK channels. In conclusion, somatostatin can inhibit glucose-induced electrical activity in MIN-6 cells by the combined activation of K-ATP and GIRK channels. Studies with selective agonists and antagonists are consistent with this effect being mediated by the sst5 receptor.

Adenosine nucleotides acting at the human P2Y1 receptor stimulate mitogen-activated protein kinases and induce apoptosis.

For the widely distributed P2Y receptors for nucleotides, the transductional and functional responses downstream of their coupling to G proteins are poorly characterized. Here we describe apoptotic induction and the associated differential stimulation of mitogen-activated protein (MAP) kinase family members by the human P2Y(1) receptor. The potent P2Y(1) receptor agonist, 2-methylthio-ADP (2-MeSADP), stimulated the extracellular-signal regulated kinases (ERK1/2) (EC(50) approximately 5 nm) as well as several, but not all isoforms detected, of the stress-activated protein kinase (SAPK) family. Phospho-isoforms of p38 were unaffected. The induced kinase activity was blocked by the P2Y(1) receptor-selective antagonist, adenosine-2'-phosphate-5'-phosphate, but unaffected by pertussis toxin. In addition, the endogenous ligand ADP, and significantly also 2-MeSATP, induced concentration-dependent phosphorylation changes in the same MAP kinase family members. The sustained activation of ERK1/2 was associated with Elk-1 phosphorylation that was abolished by the MEK1 inhibitor, PD 98059. However, the concomitant transient activation of the SAPKs was not sufficient to induce c-Jun or ATF-2 phosphorylation. The transient phase of the ERK activity was partially inhibited either by the phosphatidylinositol 3-kinase inhibitor, LY 294002, or the PKC inhibitor, Gö 6976. In addition, the Src inhibitor, PP1, or expression of dominant negative Ras also attenuated the transient phase of ERK phosphorylation. In contrast, inhibition of Ras or Src had no effect on the sustained ERK activity, which was critically dependent on phosphatidylinositol 3-kinase. The transient SAPK activity was suppressed by expression of a dominant negative form of MKK4. Furthermore, this kinase-deficient mutant inhibited 2-MeSADP-induced caspase-3 stimulation and the associated decrease in cell number. In conclusion, adenosine di- and triphosphate stimulation of the human P2Y(1) receptor can transiently activate the Ras-ERK cascade via the cooperative effects of phosphatidylinositol 3-kinase, Src and PKC. The sustained ERK stimulation, via a Ras-insensitive pathway, culminates in Elk-1 activation without inducing a proliferation effect. The transient SAPK activity did not evoke transcription factor phosphorylation but was required for the P2Y(1) receptor-mediated apoptotic function.

Receptor isoforms mediate opposing proliferative effects through gbetagamma-activated p38 or Akt pathways.

The opposing effects on proliferation mediated by G-protein-coupled receptor isoforms differing in their COOH termini could be correlated with the abilities of the receptors to differentially activate p38, implicated in apoptotic events, or phosphatidylinositol 3-kinase (PI 3-K), which provides a source of survival signals. These contrasting growth responses of the somatostatin sst(2) receptor isoforms, which couple to identical Galpha subunit pools (Galpha(i3) > Galpha(i2) >> Galpha(0)), were both inhibited following betagamma sequestration. The sst(2(a)) receptor-mediated ATF-2 activation and inhibition of proliferation induced by basic fibroblast growth factor (bFGF) were dependent on prolonged phosphorylation of p38. In contrast, cell proliferation and the associated transient phosphorylation of Akt and p70(rsk) induced by sst(2(b)) receptors were blocked by the PI 3-K inhibitor LY 294002. Stimulation with bFGF alone had no effect on the activity of either p38 or Akt but markedly enhanced p38 phosphorylation mediated by sst(2(a)) receptors, suggesting that a complex interplay exists between the transduction cascades activated by these distinct receptor types. In addition, although all receptors mediated a sustained activation of extracellular signal-regulated kinases (ERK1 and ERK2), induction of the tumor suppressor p21(cip1) was detected only following amplification of ERK and p38 phosphorylation by concomitant bFGF and sst(2(a)) receptor activation. Expression of constitutively active Akt in the presence of a p38 inhibitor enabled a proliferative response to be detected in sst(2(a)) receptor-expressing cells. These findings demonstrate that the duration of activation and a critical balance between the mitogen-activated protein kinase and PI 3-K pathways are important for controlling cell proliferation and that the COOH termini of the sst(2) receptor isoforms may determine the selection of appropriate betagamma-pairings necessary for interaction with distinct kinase cascades.

The pivotal role of phosphoinositide-3 kinase in the human somatostatin sst(4) receptor-mediated stimulation of p44/p42 mitogen-activated protein kinase and extracellular acidification.

We have previously demonstrated in CHO-K1 cells expressing recombinant human sst(4) receptors that somatostatin-induced increases in extracellular acidification are susceptible to a marked desensitisation after pretreatment with somatostatin, but not the somatostatin analogue, L-362855. In the present study, we have examined the human sst(4) receptor-mediated stimulation of p44/p42 mitogen-activated protein (MAP) kinase to determine whether this response is susceptible to a similar agonist-specific desensitisation. Western analysis using phosphospecific antibodies revealed that both somatostatin and L-362855 induced a transient stimulation of MAP kinase which could be desensitised by pretreatment with somatostatin, but not L-362855. The selective phosphoinositide (PI) 3-kinase inhibitor, LY 249002, blocked both the somatostatin-induced increase in MAP kinase phosphorylation and extracellular acidification. However, the MEK1 inhibitor, PD 98059, blocked only the sst(4) receptor-mediated stimulation of MAP kinase and not the extracellular acidification response. In summary, the human sst(4) receptor is selectively desensitised by somatostatin and not by L-362855 and signals through two different PI 3-kinase linked pathways.

Prolonged activation of extracellular signal-regulated kinase by a protein kinase C-dependent and N17Ras-insensitive mechanism mediates the proliferative response of G(i/o)-coupled somatostatin sst(4) receptors.

The human sst(4) receptor, recombinantly expressed in Chinese hamster ovary cells, mediates proliferative activity of the peptide hormone somatostatin. This effect was shown to involve activation of pertussis toxin-sensitive G proteins and was inhibited by overexpression of the betagamma-sequestrant, transducin. Somatostatin-induced proliferation was abolished by the MEK1 inhibitor, PD 98059, whereas the Src inhibitor, PP1, had no effect. A marked increase was observed in the phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1 and ERK2) 10 min after sst(4) receptor activation, which was blocked by pertussis toxin, decreased by PP1 and the betagamma-sequestrant, but unaffected by PD 98059. In contrast, the somatostatin-induced phosphorylation of ERK obtained at 4 h, although sensitive to both pertussis toxin and transducin, was unaffected by PP1 but ablated by PD 98059. Protein kinase C inhibition also abolished this somatostatin-induced sustained phosphorylation of ERK, together with the associated increase in cell proliferation. Expression of dominant negative Ras (N17) failed to significantly reduce the proliferative effect mediated by the sst(4) receptor but markedly attenuated the acute phase of the somatostatin-induced phosphorylation of ERK obtained at 10 min. In contrast, the phosphorylation induced at 4 h was unaffected. We conclude that ERK activation by G(i/o)-coupled sst(4) receptors involves a Src and Ras-dependent acute phase, but the proliferative response is dependent upon the prolonged ERK-induced activity, mediated by protein kinase C.

Activated G protein-coupled receptor induces tyrosine phosphorylation of STAT3 and agonist-selective serine phosphorylation via sustained stimulation of mitogen-activated protein kinase. Resultant effects on cell proliferation.

The peptide hormone somatostatin exhibits antiproliferative activity by interacting with the G protein-coupled sst2 or sst5 receptor types. We show here that somatostatin at the human recombinant sst4 receptor induced a concentration-dependent increase in proliferation (EC50 20 nM) with a maximal response 5-fold greater than that produced by its synthetic analog, L-362,855. Analysis of the phosphorylation status of extracellular signal-regulated kinase (ERK)1 and ERK2 showed temporal differences in the changes evoked by the agonists. Phosphorylation induced by somatostatin (100 nM) peaked 10 min after the application and produced a response that continued for at least 4 h. In contrast, L-362,855 (1 microM) showed transient phosphorylation that had declined to basal levels by 1 h. However, both agonists induced rapid and sustained tyrosine phosphorylation of signal transducer and activator of transcription 3 (STAT3) which was pertussis toxin-insensitive. Serine phosphorylation of STAT3 was only apparent after somatostatin treatment and was abolished by pertussis toxin or PD 98059, together with the associated increases in proliferation. Mitogen-activated protein/ERK kinase-1 inhibition also decreased the time interval over which somatostatin-induced ERK phosphorylation was observed (<2 h). We conclude that the difference in the magnitude of the proliferative response evoked by the two agonists at the sst4 receptor can be accounted for by their differential ability to phosphorylate STAT3 on serine residues and supports the concept that selective signaling can be achieved through pharmacological diversity.

Molecular cloning and functional characterization of a rat somatostatin sst2(b) receptor splice variant.

1. The mouse somatostatin (SRIF) sst2 receptor exists in two splice variants, sst2(a) and sst2(b), which differ in their intracellular carboxy-termini only. The murine sst2(b) receptor was reported to be less prone to agonist-induced desensitization as compared with the sst2(a) receptor. To determine whether a sst2(b) splice variant with similar functional characteristics exists in the rat, we have isolated a cDNA fragment from rat gastric mucosa encoding a sst2(b) receptor and expressed the full-length protein in CHO-K1 cells for functional characterization. 2. This study provides the first evidence for the occurrence in the rat of the sst2(b) receptor, which has a 15 amino acid carboxy-terminus differing in composition to the 38 amino acid C-terminus of the rat sst2(a) receptor. 3. In CHO-K1 cells expressing rat recombinant sst2(a) or sst2(b) receptors, SRIF caused concentration-dependent increases in extracellular acidification rates (EAR) with pEC50 values of 9.0 and 9.9, respectively. Pre-treatment with pertussis toxin (Ptx) caused a rightward displacement of the SRIF concentration-effect curves with pEC50 values of 8.3 (sst2(a) and 8.4 (sst2(b)). 4. SRIF (3 pM-3 nM) also caused concentration-dependent inhibition of forskolin-stimulated cyclic AMP formation in CHO-sst2(a) cells (pIC50 10.5) and CHO-sst2(b) cells (pIC50 10.4). The degree of inhibition was less with higher concentrations of SRIF resulting in bell-shaped concentration-effect curves. Following pre-treatment with Ptx, the inhibitory effect of SRIF was abolished and SRIF caused only increases in cyclic AMP formation. 5. Both the SRIF-induced increases in EAR and inhibition of cyclic AMP formation were susceptible to agonist-induced desensitization, but this was less apparent following pre-treatment with Ptx. 6. This demonstrates that the operational characteristics of the recombinant rat sst2(a) and sst2(b) receptors are broadly similar. Both isoforms couple to Ptx-sensitive as well as -insensitive G proteins and are equally prone to agonist-induced desensitization.

Immunohistochemical localization of the somatostatin SST2(A) receptor in the rat brain and spinal cord.

The neuropeptide somatostatin is widely distributed in the CNS and is believed to play a role as a neurotransmitter or a neuromodulator. Somatostatin mediates its actions by the binding of the peptide to high affinity membrane receptors. The genes for five somatostatin receptor types have been cloned recently and Northern blotting and in situ hybridization studies have shown that the transcripts of all five types are expressed in the CNS. Here we report the cellular distribution of somatostatin sst2(a) receptor protein in the adult rat CNS, using a polyclonal anti-peptide antibody directed against a portion of the C-terminal domain of the receptor. The specificity of the affinity-purified antibody was demonstrated by Western blotting and immunolabelling of cells transfected with a hemagglutinin epitope-tagged version of the sst2(a) receptor. Immunohistochemistry showed a distinct distribution of the receptor protein in the rat brain. Cells and processes were labelled in a number of areas, including the basolateral amygdala, the locus coeruleus, the endopiriform nucleus, the deep layers of the cerebral cortex, the subiculum, the claustrum, the habenula, the interpenduncular nucleus, the hippocampus and the central grey. In the spinal cord, the substantia gelatinosa showed strongly-labelled cell bodies and their processes. This study provides an improved understanding of the distribution of the sst2(a) receptor in rat brain.

Somatostatin sst5 inhibition of receptor mediated regeneration of rat aortic vascular smooth muscle cells.

1. The aim of the present study was to determine the effect of somatostatin (SRIF) on mitogen-induced regeneration of rat aortic vascular smooth muscle cells (VSMC) and for comparison Chinese hamster ovary (CHO)-K1 cells expressing human recombinant sst5 receptors (CHOsst5), following partial denudation of a confluent cell monolayer. Regeneration was assessed by measuring areas of recovery into the denuded area and by counting total cell numbers. 2. In VSMC, SRIF (0.1 nM - 1 microM) had no effect on the basal levels of regeneration but caused a concentration-dependent inhibition (pIC50 8.0-8.6) of the stimulated regeneration induced by submaximal concentrations of basic fibroblast growth factor (bFGF, 10 ng ml[-1]), platelet-derived growth factor-BB (PDGF, 5 ng ml[-1]) or endothelin-1 (ET-1, 100 nM). SRIF (pIC50 8.8) also inhibited bFGF-induced regeneration of CHOsst5 cells. 3. In VSMC, the inhibitory action of SRIF on the regeneration induced by bFGF (10 ng ml[-1]) was due to an anti-proliferative effect, rather than an effect on cell migration, as SRIF (0.1 nM - 1 microM) abolished bFGF-induced increases in total cell numbers. The bFGF-induced increase in cell numbers was also abolished by actinomycin D (0.1 microg ml[-1]). 4. The sst5 receptor-selective agonist, L-362,855 (pIC50 10.5), was about 100 times more potent than SRIF at inhibiting bFGF-induced regeneration of both VSMC and CHOsst5 cells whilst the sst2 receptor-selective agonist, BIM-23027 (pIC50 6.8), was approximately 20 times weaker than SRIF. 5. The sst5 receptor antagonist, BIM-23056 (100 nM), antagonized SRIF-induced inhibition of bFGF-induced regeneration in both VSMC and CHOsst5 cells (estimated pKB values 8.8 and 8.3, respectively). 6. SRIF-induced inhibition of bFGF-induced regeneration of VSMC and CHOsst5 cells was abolished by pretreating cells with pertussis toxin (100 ng ml[-1]) for 20 h. 7. These findings suggest that SRIF-induced inhibition of the proliferation of rat aortic VSMC is mediated via activation of receptors which are similar to human sst5 receptors. Furthermore this inhibitory effect is transduced via pertussis toxin-sensitive Gi/Go proteins.

Potent antagonism by BIM-23056 at the human recombinant somatostatin sst5 receptor.

We have investigated the effects of somatostatin (SRIF) and the linear octapeptide BIM-23056 on changes in intracellular calcium ion concentration ([Ca2+]i) and on the formation of inositol-1,4,5-trisphosphate (Ins(1,4,5)P3) in CHO-K1 cells transfected with the human recombinant SRIF sst5 receptor. SRIF elicited concentration-dependent increases in [Ca2+]i, with a pEC50 of 7.02 +/- 0.06, while BIM-23056 (1 x 10(-7) M) behaved not as an agonist but as a potent, surmountable antagonist of these increases in [Ca2+]i. The SRIF concentration-effect curve for increases in [Ca2+]i was shifted rightward producing an estimated pKB for the antagonist of 8.0. BIM-23056 (1 x 10(-7) M) also significantly attenuated Ins(1,4,5)P3 increases due to SRIF, but had no effect on either basal or uridine 5'-triphosphate (UTP) (1 x 10(-4) M) stimulated increases in the levels of [Ca2+]i or Ins(1,4,5)P3.

Cloning and characterization of the epsilon and zeta isoforms of the 14-3-3 proteins.

Two prominent proteins (30 and 33 kD) in a purified preparation of the sheep pineal gland were studied. Amino acid analysis of tryptic peptides indicated that the 33-kD protein was the epsilon isoform of the 14-3-3 family of proteins, and that the 30-kD protein was the zeta isoform. The sheep pineal gland was found to have six other 14-3-3 isoforms in addition to the epsilon and zeta, suggesting that copurification of the epsilon and zeta forms may reflect the existence of homo- or heterodimers comprised of these isoforms. To characterize 14-3-3 proteins further in the pineal gland, the full sequence of the epsilon isoform and a partial sequence of the zeta isoform were cloned from a rat pineal cDNA library and are reported here. Tissue distribution studies using Western blot analysis revealed that rat pineal and retina have levels of 14-3-3 protein similar to those found in brain, and that relatively low levels occur in other tissues. This investigation also revealed the epsilon isoform was present at high levels in the rat pineal gland early in development and decreased steadily thereafter and that 30-kD isoforms exhibited the inverse developmental pattern.

Multiple isoforms of a protein kinase C inhibitor (KCIP-1/14-3-3) from sheep brain. Amino acid sequence of phosphorylated forms.

A potent inhibitor of protein kinase C (PKC), inhibitor protein-1 (KCIP-1), isolated from sheep brain has been shown to consist of eight isoforms by reverse-phase HPLC. Direct protein sequence analysis has revealed these to be the same as those of 14-3-3 protein, described as an activator of tyrosine and tryptophan hydroxylases involved in neurotransmitter biosynthesis. The N-termini of KCIP-1 isoforms were shown to be acetylated, and secondary structure predictions revealed a high degree of alpha-helix with an amphipathic nature. KCIP-1 showed no inhibitory activity towards protein kinase M (the catalytic fragment of PKC) and had no effect on the activities of three other protein kinases, cAMP-dependent protein kinase, Ca2+/calmodulin-dependent protein kinase II and casein kinase 2. Four forms of KCIP-1 were shown to be substrates for PKC in vitro, but none were phosphorylated by the other protein kinases mentioned above.

The rheology of pig small intestinal and colonic mucus: weakening of gel structure by non-mucin components.

Mechanical spectroscopy has been used to study the structure and properties of pig small intestinal and colonic adherent mucus gel. Both mucus secretions had properties of viscoelastic gels, but that from the small intestine was substantially weaker in quality. Small intestinal mucus gel was disrupted by acid (pH 1), detergents (bile) and protein denaturants while that from the colon remained stable following these treatments. Concentration of purified colonic mucin produced a gel with the same rheological properties as the native secretion. Purified small intestinal mucin when concentrated produced a stronger gel than the native secretion and, in contrast to the latter, one which was not disrupted by acid or denaturants. The instability of native small intestinal mucus was shown not to be a function of the mucin components (which alone could account for the gel-forming properties), but to arise from the presence of insoluble material largely from sloughed mucosal cells. These studies show (1) that mucus gels from the colon and small intestine have similar mechanical behaviour and properties to those from the stomach and duodenum, and (2) emphasise the caution that should be exercised when interpreting the rheological properties of mucus preparations, particularly with respect to their content of mucosal cellular material.

Protein kinase C inhibitor proteins. Purification from sheep brain and sequence similarity to lipocortins and 14-3-3 protein.

Potent inhibitors of protein kinase C have been isolated from sheep brain by DEAE-cellulose, phenyl-Sepharose CL-4B and Mono Q anion-exchange chromatography. Analysis by one- and two-dimensional SDS/polyacrylamide gel electrophoresis showed the purified preparation to contain three bands ranging over 29-33 kDa in molecular mass, each consisting of several charge isomers with similar pI values (5.4-5.7). Peptide mapping, amino acid analysis and sequencing suggested that the proteins are related, with the possibility that some species are distinct gene products. The concentration of inhibitor proteins required for half-maximal inhibition of protein kinase C activity is 1.7 microM. Inhibitory activity could not be affected by increasing the substrate, cofactor or ATP concentration in the standard protein kinase C assay, but was abolished by heat treatment. The inhibitor preparation did not affect the binding of phorbol dibutyrate to protein kinase C and could inhibit phosphorylation over a wide range of calcium concentrations. Inhibitory activity could be removed by immunoprecipitation of the purified inhibitor proteins with polyclonal antibodies raised against synthetic peptides, the sequences corresponding to those of peptide fragments obtained from protein digests. Amino acid sequence analysis of the inhibitors confirms they are novel proteins although similarities exist with a neuronal specific protein termed 14-3-3 and the carboxy terminus of the calcium-lipid binding series (endonexin/calpactin/lipocortin).