Single H2Kb, H2Db and double H2KbDb knockout mice: peripheral CD8+ T cell repertoire and anti-lymphocytic choriomeningitis virus cytolytic responses

Single H2Kb, H2Db and double H2KbDb homozygous knockout (KO) mice were generated and their peripheral CD8+ T cell repertoires compared to that of C57BL/6 (B6) mice. Limited (10-20%, H2Db), substantial (30-50%, H2Kb) and profound (90%, H2KbDb) reduction of peripheral CD8+ T cells was observed in KO mice, without Vbeta diversity alteration. Classical class Ia molecules therefore ensure most but not all of the peripheral CD8+ T cell repertoire education. As expected, H2Kb but also H2Db KO mice developed choriomeningitis following intracranial infection by lymphocytic choriomeningitis virus with the same kinetics, lethality and CD8+ cell implication as wild-type B6 mice. By contrast, H2KbDb (class Ia-Ib+) KO mice survived. Choriomeningitis of H2Db KO mice was linked to the development of a subdominant (in normal B6 mice) H2Kb-restricted cytotoxic T lymphocyte response. Mice expressing a restricted set of histocompatibility class I molecules should represent useful tools to evaluate the immunological potentials of individual MHC class I molecules.

TRPV4 mediates tumor-derived endothelial cell migration via arachidonic acid-activated actin remodeling

Changes in intracellular calcium [Ca(2+)](i) levels control critical cytosolic and nuclear events that are involved in the initiation and progression of tumor angiogenesis in endothelial cells (ECs). Therefore, the mechanism(s) involved in agonist-induced Ca(2+)(i) signaling is a potentially important molecular target for controlling angiogenesis and tumor growth. Several studies have shown that blood vessels in tumors differ from normal vessels in their morphology, blood flow and permeability. We had previously reported a key role for arachidonic acid (AA)-mediated Ca(2+) entry in the initial stages of tumor angiogenesis in vitro. In this study we assessed the mechanism involved in AA-induced EC migration. We report that TRPV4, an AA-activated channel, is differentially expressed in EC derived from human breast carcinomas (BTEC) as compared with 'normal' EC (HMVEC). BTEC display a significant increase in TRPV4 expression, which was correlated with greater Ca(2+) entry, induced by AA or 4αPDD (a selective TRPV4 agonist) in the tumor-derived ECs. Wound-healing assays revealed a key role of TRPV4 in regulating cell migration of BTEC but not HMVEC. Knockdown of TRPV4 expression completely abolished AA-induced BTEC migration, suggesting that TRPV4 mediates the pro-angiogenic effects promoted by AA. Furthermore, pre-incubation of BTEC with AA induced actin remodeling and a subsequent increase in the surface expression of TRPV4. This was consistent with the increased plasma membrane localization of TRPV4 and higher AA-stimulated Ca(2+) entry in the migrating cells. Together, the data presented herein demonstrate that: (1) TRPV4 is differentially expressed in tumor-derived versus 'normal' EC; (2) TRPV4 has a critical role in the migration of tumor-derived but not 'normal' EC migration; and (3) AA induces actin remodeling in BTEC, resulting in a corresponding increase of TRPV4 expression in the plasma membrane. We suggest that the latter is critical for migration of EC and thus in promoting angiogenesis and tumor growth.

Molecularly cloned SHIV-1157ipd3N4: a highly replication- competent, mucosally transmissible R5 simian-human immunodeficiency virus encoding HIV clade C Env

Human immunodeficiency virus type 1 (HIV-1) clade C causes >50% of all HIV infections worldwide, and an estimated 90% of all transmissions occur mucosally with R5 strains. A pathogenic R5 simian-human immunodeficiency virus (SHIV) encoding HIV clade C env is highly desirable to evaluate candidate AIDS vaccines in nonhuman primates. To this end, we generated SHIV-1157i, a molecular clone from a Zambian infant isolate that carries HIV clade C env. SHIV-1157i was adapted by serial passage in five monkeys, three of which developed peripheral CD4(+) T-cell depletion. After the first inoculated monkey developed AIDS at week 137 postinoculation, transfer of its infected blood to a naïve animal induced memory T-cell depletion and thrombocytopenia within 3 months in the recipient. In parallel, genomic DNA from the blood donor was amplified to generate the late proviral clone SHIV-1157ipd3. To increase the replicative capacity of SHIV-1157ipd3, an extra NF-kappaB binding site was engineered into its 3' long terminal repeat, giving rise to SHIV-1157ipd3N4. This virus was exclusively R5 tropic and replicated more potently in rhesus peripheral blood mononuclear cells than SHIV-1157ipd3 in the presence of tumor necrosis factor alpha. Rhesus macaques of Indian and Chinese origin were next inoculated intrarectally with SHIV-1157ipd3N4; this virus replicated vigorously in both sets of monkeys. We conclude that SHIV-1157ipd3N4 is a highly replication-competent, mucosally transmissible R5 SHIV that represents a valuable tool to test candidate AIDS vaccines targeting HIV-1 clade C Env.

Cyclooxygenase-2 in human and experimental ischemic proliferative retinopathy

BACKGROUND

Intravitreal neovascular diseases, as in ischemic retinopathies, are a major cause of blindness. Because inflammatory mechanisms influence vitreal neovascularization and cyclooxygenase (COX)-2 promotes tumor angiogenesis, we investigated the role of COX-2 in ischemic proliferative retinopathy.

METHODS AND RESULTS

We describe here that COX-2 is induced in retinal astrocytes in human diabetic retinopathy, in the murine and rat model of ischemic proliferative retinopathy in vivo, and in hypoxic astrocytes in vitro. Specific COX-2 but not COX-1 inhibitors prevented intravitreal neovascularization, whereas prostaglandin E2, mainly via its prostaglandin E receptor 3 (EP3), exacerbated neovascularization. COX-2 inhibition induced an upregulation of thrombospondin-1 and its CD36 receptor, consistent with the observed antiangiogenic effects of COX-2 inhibition; EP3 stimulation reversed effects of COX-2 inhibitors on thrombospondin-1 and CD36.

CONCLUSIONS

These findings point to an important role for COX-2 in ischemic proliferative retinopathy, as in diabetes.

CD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart

Growth hormone-releasing peptides (GHRPs) are known as potent growth hormone secretagogues whose actions are mediated by the ghrelin receptor, a G protein-coupled receptor cloned from pituitary libraries. Hexarelin, a hexapeptide of the GHRP family, has reported cardiovascular activity. To identify the molecular target mediating this activity, rat cardiac membranes were labeled with a radioactive photoactivatable derivative of hexarelin and purified using lectin affinity chromatography and preparative gel electrophoresis. A binding protein of M(r) 84 000 was identified. The N-terminal sequence determination of the deglycosylated protein was identical to rat CD36, a multifunctional glycoprotein, which was expressed in cardiomyocytes and microvascular endothelial cells. Activation of CD36 in perfused hearts by hexarelin was shown to elicit an increase in coronary perfusion pressure in a dose-dependent manner. This effect was lacking in hearts from CD36-null mice and hearts from spontaneous hypertensive rats genetically deficient in CD36. The coronary vasoconstrictive response correlated with expression of CD36 as assessed by immunoblotting and covalent binding with hexarelin. These data suggest that CD36 may mediate the coronary vasospasm seen in hypercholesterolemia and atherosclerosis.

Atrial natriuretic factor R1 receptor from bovine adrenal zona glomerulosa: purification, characterization, and modulation by amiloride

The atrial natriuretic factor (ANF) R1 receptor from bovine adrenal zona glomerulosa was solubilized with Triton X-100 and purified 13,000-fold, to apparent homogeneity, by sequential affinity chromatography on ANF-agarose and steric exclusion high-performance liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining of the purified receptor preparation in the absence or presence of dithiothreitol revealed a single protein band of Mr 130,000. Affinity cross-linking of 125I-ANF to the purified receptor resulted in the labeling of the Mr 130,000 band. The purified receptor bound ANF with a specific activity of 6.8 nmol/mg of protein, corresponding to a stoichiometry of 0.9 mol of ANF bound/mol of Mr 130,000 polypeptide. Starting with 500 g of adrenal zona glomerulosa tissue, we obtained more than 500 pmol of purified receptor with an overall yield of 9%. The purified receptor showed a typical ANF-R1 pharmacological specificity similar to that of the membrane-bound receptor. The homogeneous Mr 130,000 receptor protein displayed high guanylate cyclase activity [1.4 mumol of cyclic GMP formed min-1 (mg of protein)-1] which was not stimulated by ANF. This finding supports the notion that the ANF binding and the guanylate cyclase activities are intrinsic components of the same polypeptide. Finally, the purified ANF-R1 receptor retained its sensitivity to modulation by amiloride, suggesting the presence of an allosteric binding site for amiloride on the receptor protein.

Radioimmunoassay of atrial natriuretic factor: human plasma levels

A simple and sensitive radioimmunoassay procedure has been developed for the determination of atrial natriuretic factor (ANF) in human plasma. The rabbit antiserum was obtained from a commercial source. ANF was extracted from plasma using an octadecasilyl silica cartridge with a recovery of 78.7%. HPLC of the plasma extract showed the presence of one immunoreactive peak of ANF corresponding to its low molecular weight form. Plasma ANF in humans increased from 8.0 +/- 2.2 in upright position to 20.0 +/- 5.9 fmol/ml (n = 6) in downward position (p less than 0.005).

Specific receptors for synthetic GH secretagogues in the human brain and pituitary gland

In vitro studies have been performed to demonstrate and characterize specific binding sites for synthetic GH secretagogues (sGHS) on membranes from pituitary gland and different human brain regions. A binding assay for sGHS was established using a peptidyl sGHS (Tyr-Ala-hexarelin) which had been radioiodinated to high specific activity at the Tyr residue. Specific binding sites for 125I-labelled Tyr-Ala-hexarelin were detected mainly in membranes isolated from pituitary gland and hypothalamus, but they were also present in other brain areas such as choroid plexus, cerebral cortex, hippocampus and medulla oblongata with no sex-related differences. In contrast, negligible binding was found in the thalamus, striatum, substantia nigra, cerebellum and corpus callosum. The binding of 125I-labelled Tyr-Ala-hexarelin to membrane-binding sites is a saturable and reversible process, depending on incubation time and pH of the buffer. Scatchard analysis of the binding revealed a finite number of binding sites in the hypothalamus and pituitary gland with a dissociation constant (Kd) of (1.5 +/- 0.3) x 10(-9) and (2.1 +/- 0.4) x 10(-9) mol/l respectively. Receptor activity is sensitive to trypsin and phospholipase C digestion, suggesting that protein and phospholipids are essential for the binding of 125I-labelled Tyr-Ala-hexarelin. The binding of 125I-labelled Tyr-Ala-hexarelin to pituitary and hypothalamic membranes was displaced in a dose-dependent manner by different unlabelled synthetic peptidyl (Tyr-Ala-hexarelin, GHRP2, hexarelin, GHRP6) and non-peptidyl (MK 0677) sGHS. An inhibition of the specific binding was also observed when binding was performed in the presence of [D-Arg1-D-Phe5-D-Trp7,9-Leu11]-substance P, a substance P antagonist that has been found to inhibit GH release in response to sGHS. In contrast, no competition was observed in the presence of other neuropeptides (GHRH, somatostatin, galanin or Met-enkephalin) which have a known influence on GH release. In conclusion, the present data demonstrate that sGHS have specific receptors in human brain and pituitary gland and reinforce the hypothesis that these compounds could be the synthetic counterpart of an endogenous GH secretagogue involved in the neuroendocrine control of GH secretion and possibly in other central activities.

Identification and characterization of a new growth hormone-releasing peptide receptor in the heart

Hexarelin, a synthetic hexapeptide of the growth hormone-releasing peptide (GHRP) family with strong growth hormone (GH)-releasing activity, features protecting activity against postischemic ventricular dysfunction in hearts from GH-deficient and senescent rats. To document whether hexarelin action is mediated through specific cardiac receptors, perfusion of Langendorff rat hearts with hexarelin and binding studies were carried out. In the Langendorff rat heart system, hexarelin induced a dose-dependent increase in coronary perfusion pressure. Nifedipine, chelerythrine, and bisindolylmaleimide partially inhibited the vasoconstriction induced by hexarelin, suggesting that this effect was mediated at least in part by L-type Ca(2+) channels and protein kinase C. In contrast, diclofenac and 1-(7-carboxyheptyl)imidazole were without effect, suggesting that prostaglandins and thromboxanes were not involved in the coronary vasoconstriction induced by hexarelin. To characterize the hexarelin binding sites in the rat heart, [(125)I]Tyr-Bpa-Ala-hexarelin was used as photoactivatable radioligand in saturation and competitive binding studies. We specifically labeled a hexarelin receptor with an M(r) of 84 000 in rat cardiac membranes. Saturation binding curves revealed a single class of binding sites with a K(d) of 14.5 nmol/L and a density of 91 fmol/mg of protein. Competition binding studies gave an IC(50) of 2.9 micromol/L for hexarelin; MK-0677 and EP51389, both potent GH secretagogues, did not displace the binding of the photoactivatable derivative from rat cardiac membranes. Interestingly, both compounds were devoid of any vasoconstrictive activity. These results suggest the existence of a new class of hexarelin receptor in the heart, whose role in the regulation of the coronary vascular tone is yet to be determined.

Functional organization of TRPC-Ca2+ channels and regulation of calcium microdomains

TRP family of proteins are components of unique cation channels that are activated in response to diverse stimuli ranging from growth factor and neurotransmitter stimulation of plasma membrane receptors to a variety of chemical and sensory signals. This review will focus on members of the TRPC sub-family (TRPC1-TRPC7) which currently appear to be the strongest candidates for the enigmatic Ca(2+) influx channels that are activated in response to stimulation of plasma membrane receptors which result in phosphatidyl inositol-(4,5)-bisphosphate (PIP(2)) hydrolysis, generation of IP(3) and DAG, and IP(3)-induced Ca(2+) release from the intracellular Ca(2+) store via inositol trisphosphate receptor (IP(3)R). Homomeric or selective heteromeric interactions between TRPC monomers generate distinct channels that contribute to store-operated as well as store-independent Ca(2+) entry mechanisms. The former is regulated by the emptying/refilling of internal Ca(2+) store(s) while the latter depends on PIP(2) hydrolysis (due to changes in PIP(2) per se or an increase in diacylglycerol, DAG). Although the exact physiological function of TRPC channels and how they are regulated has not yet been conclusively established, it is clear that a variety of cellular functions are controlled by Ca(2+) entry via these channels. Thus, it is critical to understand how cells coordinate the regulation of diverse TRPC channels to elicit specific physiological functions. It is now well established that segregation of TRPC channels mediated by interactions with signaling and scaffolding proteins, determines their localization and regulation in functionally distinct cellular domains. Furthermore, both protein and lipid components of intracellular and plasma membranes contribute to the organization of these microdomains. Such organization serves as a platform for the generation of spatially and temporally dictated [Ca(2+)](i) signals which are critical for precise control of downstream cellular functions.

Intracellular Ca(2+) release via the ER translocon activates store-operated calcium entry

Store-operated Ca(2+) entry (SOCE) is activated in response to depletion of intracellular Ca(2+) from the endoplasmic reticulum (ER). A variety of agonists stimulate SOCE via IP(3)-dependent Ca(2+) depletion. SOCE is also activated by thapsigargin, an inhibitor of Ca(2+) reuptake into the ER that induces a net Ca(2+) loss from the ER by unmasking a Ca(2+) "leak" pathway. The molecular identity of this Ca(2+) leak channel and the physiological conditions under which such agonist-independent Ca(2+) depletion might occur remain poorly characterized. In this study, we report that inhibition of the initiation step of protein synthesis (with pactamycin) resulted in detectable Ca(2+) depletion in ER and activation of SOCE. This was completely prevented if the ribosome-nascent chain complexes were first stabilized with an irreversible inhibitor of translational elongation (emetine), suggesting that ER Ca(2+) depletion had occurred through open translocons at the ER. Notably, emetine pretreatment also attenuated thapsigargin-mediated Ca(2+) release and SOCE. Furthermore, both pactamycin and thapsigargin stimulated translocation of STIM1, a protein required for activation of SOCE, to the subplasma membrane region and activated the SOCE-associated current, I (SOC). In aggregate, these data reveal an agonist-independent mechanism for internal Ca(2+) store depletion and activation of SOCE. We suggest that the functional coupling between SOCE and protein synthesis is likely to be critical for maintaining [Ca(2+)](ER) within a range that is required to prevent ER stress during changes in cellular translational activity.

Bovine adrenal chromaffin granules are a site of synthesis of atrial natriuretic factor

We have previously reported the existence of a peptide factor in the adrenal medulla which inhibits aldosterone secretion in cultured bovine zona glomerulosa cells. The acid extracts of chromaffin granules from bovine adrenal medulla were purified by a four step high performance liquid chromatography procedure. Two active fractions exhibited sequence homology with bovine atrial natriuretic factor ANF (Ser99-Tyr126) and its polypeptide precursor (Asn1-Tyr126). The occurrence of both precursor and mature forms of ANF within chromaffin granules indicates the endogenous character of ANF in the adrenal medulla and suggests the potential usefulness of cultured adrenal chromaffin cells for investigating the synthesis, maturation and secretion of atrial peptides.

Quantification of des-Arg9-bradykinin using a chemiluminescence enzyme immunoassay: application to its kinetic profile during plasma activation

There is a renewed interest in the kininase I pathway of kinin metabolism, because des-Arg9-bradykinin (des-Arg9-BK) and des-Arg10-Lys-BK are selective and potent agonists of the B1 receptors, that are apparently upregulated by tissue injury. We have developed a polyclonal rabbit antiserum against des-Arg10-Lys-BK. In a radioimmunoassay for des-Arg10-Lys-BK, this antiserum exhibited high specificity. Notably, native kinins with the C-terminal Arg residue, bradykinin (BK) and Lys-BK, did not cross-react to a significant extent, whereas des-Arg9-BK and digoxigenin (DIG)-des-Arg9-BK exhibited a complete cross-reactivity. The antibodies were used to set up a sensitive chemiluminescence enzyme immunoassay (CLEIA) using the DIG-anti-DIG system as intermediate for the revelation of the immune complexes. The detection limit and the half-maximal saturation concentration for des-Arg9-BK were 27 and 1530 fmol/ml respectively. This assay, as well as another for BK quantification, have been applied in vitro to rabbit plasma activated by kaolin. The conversion of BK into des-Arg9-BK was generally efficient, and the persistence and concentration of both peptides were increased in the presence of enalaprilat an inhibitor of the angiotensin converting enzyme (ACEI). Rabbits treated with bacterial lipopolysaccharide exhibited an increase of plasma immunoreactive des-Arg9-BK that was potentiated in animals also treated with ACEI. This CLEIA for des-Arg9-BK is a new analytical tool applicable to analyze of the kininase I metabolites of kinins in vitro and in vivo. Measurements of des-Arg9-BK may be useful indicators of the kallikrein-kinin system activation.

Increased incidence of sepsis and altered monocyte functions in severely injured type A- glucose-6-phosphate dehydrogenase-deficient African American trauma patients

OBJECTIVE

To determine whether trauma patients with the common, type A- glucose-6-phosphate dehydrogenase (G6PD) deficiency have an aggravated inflammatory response, increased incidence of septic complications, and/or more profound alterations in leukocyte functions compared with nondeficient trauma patients.

SETTINGS

Intensive and surgical care units of a trauma center and flow cytometry and experimental laboratories at a teaching university hospital.

DESIGN

Prospective cohort clinical study with measurements on days 2 and 5 postinjury. Monocyte and neutrophil oxidant content, apoptosis, and CD11b expression and plasma cytokine levels were compared between G6PD-deficient and nondeficient patients.

PATIENTS

A total of 467 male African American trauma patients were screened for the deficiency. Forty-four type A-202/376 G6PD-deficient patients were identified and enrolled in the study; 43 nondeficient patients were also enrolled and were matched by age, clinical criteria of injury severity, and type of trauma.

MAIN RESULTS

After severe injury (Injury Severity Score, > or =16), 50% of the deficient and 6.2% of nondeficient patients developed sepsis with positive bacterial blood cultures. In deficient patients, the frequency of bronchial (75%) and wound infections (25%) was also increased compared with nondeficient patients (32% and 0%). The durations of systemic inflammatory response syndrome, Sepsis Syndrome, and days on antibiotics were three times longer in deficient than in nondeficient individuals. However, adult respiratory distress syndrome occurred in 37% of both groups. Anemia was more severe in the deficient than nondeficient patients from day 10 posttrauma. On day 5, the peroxide content was doubled, apoptosis was decreased, and CD11b expression was increased in monocytes from deficient patients compared with cells from nondeficient patients. On day 5, the plasma interleukin (IL)-10 concentration was significantly lower in deficient than nondeficient patients, whereas tumor necrosis factor-alpha, IL-6, and IL-8 levels were similar. After moderate injuries (Injury Severity Score, 9-16), the deficiency was not associated with adverse clinical effects, and the trauma-induced changes in leukocyte function were similar in deficient and nondeficient patients.

CONCLUSIONS

The common type A- G6PD deficiency predisposes septic complications and anemia in trauma patients after severe injuries as defined by an Injury Severity Score of > or =16. This adverse clinical course is accompanied by altered monocyte functions manifested as augmented oxidative stress, a decreased apoptotic response, increased cell adhesion properties, and a diminished IL-10 response.

Acute cardiovascular and hormonal effects of GH and hexarelin, a synthetic GH-releasing peptide, in humans

Reduced cardiac mass and performances are present in GH deficiency and are counteracted by rhGH replacement. GH and IGF-I possess specific myocardial receptors and have been reported able to exert an acute inotropic effect. Synthetic GH secretagogues (GHS) possess specific pituitary and hypothalamic but even myocardial receptors. In 7 male volunteers, we studied cardiac performance by radionuclide angiocardiography after iv administration of rhGH or hexarelin (HEX), a peptidyl GHS. The administration of rhGH or HEX increased circulating GH levels to the same extent (AUC: 1594.6+/-88.1 vs 1739.3+/-262.2 microg/l/min for 90 min) while aldosterone and catecholamine levels did not change; HEX, but not rhGH, significantly increased cortisol levels. Left ventricular ejection fraction (LVEF), mean blood pressure (MBP) and heart rate (HR) were unaffected by rhGH (62.4+/-2.1 vs 62.1+/-2.3%, 90.6+/-3.4 vs 92.0+/-2.5 mm Hg, 62.3+/-1.8 vs 66.7+/-2.7 bpm). HEX increased LVEF (70.7+/-3.0 vs 64.0+/-1.5%, p<0.03) without significant changes in MBP and HR (92.8+/-4.7 vs 92.4+/-3.2 mm Hg, 63.1+/-2.1 vs 67.0+/-2.9 bpm). LVEF significantly raised at 15 min, peaked at 30 min and lasted up to 60 min after HEX. These findings suggest that in man, the acute administration of Hexarelin exerts a short-lasting, positive inotropic effect. This effect seems GH-independent and might be mediated by specific GHS myocardial receptors.

Testosterone induces expression of transforming growth factor-beta 1 in the murine thymus

Castration of adult male mice results in enlargement of the thymus and diminution of peripheral suppressor T cell function. Replacement therapy with physiologic doses of androgens reverses these phenomena. Although the mediators involved are unknown, these effects of androgens on the thymus and peripheral immune system are reminiscent of those reported for transforming growth factor-beta (TGF-beta 1). We examined expression of TGF-beta 1 mRNA and bioactive protein in thymuses from castrate and androgen-replaced animals. Steady-state levels of thymic TGF-beta 1 mRNA fell slightly after castration, but rose 2.3-fold after testosterone replacement. Bioactive TGF-beta 1 production by cultured thymic explants also fell following castration to approx. 50% of the levels observed in intact animals. Following 1 week of testosterone replacement in castrate animals, TGF-beta 1 bioactivity produced in culture was restored to levels indistinguishable from those observed with explants from intact animals. Reverse transcription/polymerase chain reaction amplification of RNA revealed that thymocytes are a source of the androgen-modulated TGF-beta 1. These results suggest that TGF-beta 1 may mediate effects of androgens on the immune system.

Identification of a pituitary growth hormone-releasing peptide (GHRP) receptor subtype by photoaffinity labeling

Hexarelin, an analogue of GHRP-6, in which D-Tryptophan has been replaced by its 2-methyl derivative, is known to release growth hormone (GH) in vivo and in vitro by direct action on receptors present in anterior pituitary cells. Measurement of second messengers (c-AMP, Ca++, IP3) upon somatotrophs stimulation, suggests the existence of more than one GHRP receptor subtype. In order to document such an hypothesis, we have used a new photoactivatable derivative of Hexarelin, Tyr-Bpa-Ala-Hexarelin. This derivative was shown to be fully active in the release of GH in vivo with neonate rats. Using this photoactivatable ligand, we have specifically labeled a protein with an apparent Mr of 57,000 in human, bovine and porcine anterior pituitary membranes. Hexarelin and the spiroindoline sulfonamide MK-0677 displaced the Mr-57,000 photolabeled band with an apparent ED50 of 6x10(-7) M and 2x10(-5) M respectively. Taking into account the high efficiency (>60%) of covalent incorporation of the Bpa residue, this photoactivatable Hexarelin derivative has allowed the identification of a pituitary GHRP receptor subtype, which is apparently distinct from the recently cloned GH secretagogue receptor.

Allosteric modulation by ATP of the bovine adrenal natriuretic factor R1 receptor functions

Atrial natriuretic factor (ANF-R1) receptor is a 130-kDa protein that contains a cytoplasmic guanylate cyclase domain. We report that ATP interacts in an allosteric manner with the ANF-R1 receptor, resulting in reduced ANF binding and enhanced ANF-stimulated guanylate cyclase activity. The modulatory properties of various nucleotides indicate a preference for the adenine family with a rank order of potency of ATP greater than App(NH)p greater than or equal to ADP greater than or equal to AMP while cyclic and guanine nucleotides except GTP are inactive. The negative modulation by ATP of ANF binding is specific for the ANF-R1 receptor subtype since the amount of ANF bound by the guanylate cyclase uncoupled ANF-R2 subtype is increased in the presence of ATP. Furthermore, the effects of ATP on ANF-R1 receptor binding function are still observed with the affinity-purified ANF-R1 receptor, suggesting an allosteric binding site for ATP on the ANF-R1 receptor. In intact membranes, limited proteolysis of the ANF-R1 receptor with trypsin dose-dependently prevents the ATP-induced decrease in ANF binding concomitantly with the formation of a membrane-associated ANF-binding fragment of 70 kDa. These results confirm the direct modulatory role of ATP on hormone binding activity of ANF-R1 receptor and suggest that the nucleotide regulatory binding site is located in the intracellular domain vicinal to the protease-sensitive region.

Phosphorylation of atrial natriuretic factor R1 receptor by serine/threonine protein kinases: evidences for receptor regulation

The 130 kDa atrial natriuretic factor receptor (ANF-R1) purified from bovine adrenal zona glomerulosa is phosphorylated in vitro by serine/threonine protein kinases such as cAMP-, cGMP-dependent and protein kinase C. This phosphorylation is independent of the presence of ANF (99-126) and there is no detectable intrinsic kinase activity associated with the ANF-R1 receptor or with its activated form. In bovine adrenal zona glomerulosa cells, TPA (phorbol ester) induces a marked inhibition of the ANF-stimulated cGMP accumulation as well as of the membrane ANF-sensitive guanylate cyclase catalytic activity without any change in the binding capacity or affinity for 125I-ANF. However, we have demonstrated a significant 32P incorporation in the ANF-R1 receptor of the TPA-treated cells. The effect of TPA on the zona glomerulosa ANF-R1 receptors was abolished by calphostin C, a specific protein kinase C inhibitor. Altered ANF actions due to blunted response of guanylate cyclase to ANF could be a consequence of the ANF receptor phosphorylation by excessive activity of protein kinase C and might be involved in the pathogenesis of hypertension.

TRPC3 controls agonist-stimulated intracellular Ca2+ release by mediating the interaction between inositol 1,4,5-trisphosphate receptor and RACK1

Activation of TRPC3 channels is concurrent with inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R)-mediated intracellular Ca(2+) release and associated with phosphatidylinositol 4,5-bisphosphate hydrolysis and recruitment to the plasma membrane. Here we report that interaction of TRPC3 with receptor for activated C-kinase-1 (RACK1) not only determines plasma membrane localization of the channel but also the interaction of IP(3)R with RACK1 and IP(3)-dependent intracellular Ca(2+) release. We show that TRPC3 interacts with RACK1 via N-terminal residues Glu-232, Asp-233, Glu-240, and Glu-244. Carbachol (CCh) stimulation of HEK293 cells expressing wild type TRPC3 induced recruitment of a ternary TRPC3-RACK1-IP(3)R complex and increased surface expression of TRPC3 and Ca(2+) entry. Mutation of the putative RACK1 binding sequence in TRPC3 disrupted plasma membrane localization of the channel. CCh-stimulated recruitment of TRPC3-RACK1-IP(3)R complex as well as increased surface expression of TRPC3 and receptor-operated Ca(2+) entry were also attenuated. Importantly, CCh-induced intracellular Ca(2+) release was significantly reduced as was RACK1-IP(3)R association without any change in thapsigargin-stimulated Ca(2+) release and entry. Knockdown of endogenous TRPC3 also decreased RACK1-IP(3)R association and decreased CCh-stimulated Ca(2+) entry. Furthermore, an oscillatory pattern of CCh-stimulated intracellular Ca(2+) release was seen in these cells compared with the more sustained pattern seen in control cells. Similar oscillatory pattern of Ca(2+) release was seen after CCh stimulation of cells expressing the TRPC3 mutant. Together these data demonstrate a novel role for TRPC3 in regulation of IP(3)R function. We suggest TRPC3 controls agonist-stimulated intracellular Ca(2+) release by mediating interaction between IP(3)R and RACK1.

Diffusion of rat atrial natriuretic factor in thermoreversible poloxamer gels

Concentrated poloxamer 407 solutions display a negative thermorheological behaviour, resulting in a higher viscosity at body temperature than below. This could be exploited for various controlled delivery applications including the nasal delivery of peptides. The rheology of the gel and the diffusion of ANF were studied as a function of temperature. A theory is proposed, according to which a temperature rise creates an intermicellar network resulting in a viscosity increase. The diffusion of the drug appears limited only by the presence of micelles which lengthens the diffusion pathways and is not significantly influenced by the formation of this network.

Evidence for the expression of transient receptor potential proteins in guinea pig airway smooth muscle cells

OBJECTIVE

The present study investigates the expression of transient receptor potential (TRPC) proteins in airway smooth muscle (ASM) cells in order to determine whether these proteins may be candidate molecular counterparts of plasma membrane Ca2+-permeable channels involved in the contraction of ASM.

METHODS

Expression of TRPC mRNA was detected using specific primers and RT-PCR. Expression of the TRPC1, TRPC3 and TRPC6 proteins was detected using antibodies in immunoprecipitation and Western blot.

RESULTS

Guinea pig ASM cells exhibited thapsigargin- and acetylcholine-initiated Ca2+ inflow but none by 1-oleoyl-2-acetyl-sn-glycerol. mRNA encoding each of the TRPC1 to TRPC6 proteins was detected in ASM cells. mRNA encoding TRPC1, TRPC3, TRPC4 and TRPC6 was detected in ASM cells at a concentration approximately equivalent to that in guinea pig brain. mRNA encoding TRPC2 and TRPC5 was more abundant in ASM cells than in brain. The TRPC1 protein, but not the TRPC3 or TRPC6 proteins, was detected in extracts of ASM cells, while all three proteins were detected in brain.

CONCLUSION

The results provide evidence for a low level of expression of the TRPC1 to TRPC6 proteins in ASM cells. These proteins may function as store-operated Ca2+ and/or second messenger-activated non-selective cation channels in ASM cells.

Cardiac effects of hexarelin in hypopituitary adults

Growth hormone (GH)-releasing peptides possess specific pituitary, hypothalamic, and myocardial receptors. Seven adult male patients with GH deficiency (GHD) (age, mean+/-S.E.M.: 42.0+/-4.0 year) were studied by equilibrium radionuclide angiocardiography after i.v. administration of hexarelin, a peptide GH secretagogue. Data for these patients were compared with those for nine adult male controls (37.0+/-2.7 year). The GH response to hexarelin was negligible in patients with GHD compared to control subjects (CS) (peak: 1.9+/-0.9 vs. 45.7+/-3.6 microg/l, P<0.001). Basal left ventricular ejection fraction (LVEF) in patients with GHD was lower than that in CS (50+/-1% vs. 63+/-2%, P<0.001). Hexarelin administration increased LVEF both in patients with GHD and in CS (peak: 57+/-2 vs. 70+/-2, respectively, P<0.05 vs. baseline) without changing catecholamine levels, mean blood pressure (MBP), or cardiac output in either group. In conclusion, the acute administration of hexarelin exerts a short-lasting positive inotropic effect in humans, probably GH-independent and mediated by specific myocardial receptors for GH secretagogues.

Stoichiometry of the atrial natriuretic factor-R1 receptor complex in the bovine zona glomerulosa

The atrial natriuretic R1 receptor is a membrane protein that is present as an apparently preassociated noncovalent oligomer in the absence of ligand as suggested by steric exclusion studies and cross-linking experiments in physiological and recombinant receptor expression systems. The association state of this receptor oligomer was studied in the presence of amiloride and ATP, two known modulators of the R1 receptor functions with both the intact receptor and a cytoplasmic domain-deleted form obtained by limited proteolysis with trypsin. It was shown by steric exclusion on Superose 6 column that amiloride increased the affinity of ANF for the native and truncated receptor, in contrast with ATP, whose destabilizing effect on ANF binding was abolished by truncation of the cytoplasmic domain. Neither amiloride nor ATP exerts its effects by altering the aggregation state of the receptor. Comparison of the measured number of ANF binding sites with immunoassayable receptor protein revealed that the stoichiometry of ANF binding to the R1 receptor was 1:2. This was confirmed by using an ANF analog that bears a photoactivatable group at both of its ends, showing that ANF, as for the growth hormone/receptor complex, interacts with both the receptor subunits and specifically cross-links a dimeric form of the receptor. The potential pharmacological consequences of this 1:2 stoichiometric ratio of the ANF-receptor complex are discussed.