Stimulation of histamine H1 receptor up-regulates histamine H1 receptor itself through activation of receptor gene transcription

Histamine is a major mediator in allergy acting mainly through the histamine H(1) receptor (H1R). Although H1R up-regulation has been suggested as an important step for induction of allergic symptoms, little is known about the regulation of H1R level. Here we report that the activation of H1R up-regulates H1R through augmentation of H1R mRNA expression in HeLa cells. Histamine stimulation significantly increased both H1R promoter activity and mRNA level without alteration in mRNA stability. H1R protein was also up-regulated by histamine. An H1R antagonist but not histamine H(2) receptor antagonist blocked histamine-induced up-regulation of both promoter activity and mRNA expression. A protein kinase C (PKC) activator, phorbol-12-myristate-13-acetate, increased H1R mRNA expression, whereas an activator of PKA or PKG (8-Br-cAMP or 8-Br-cGMP, respectively) did not. Furthermore, histamine-induced up-regulation of both promoter activity and mRNA level were completely suppressed by the PKC inhibitor Ro-31-8220. H1R antagonists have long been thought to block H1R and inhibit immediate allergy symptoms. In addition to this short-term effect, our data propose their long-term inhibitory effect against allergic diseases by suppressing PKC-mediated H1R gene transcription. This finding provides new insights into the therapeutic target of H1R antagonist in allergic diseases.

Seven cases of pelvic exenteration combined with sacral resection for locally recurrent rectal cancer

Local recurrence of rectal cancer following abdominoperineal resection is rarely amenable to limited resection. Carcinoembryonic antigen assay is valuable for diagnosing most recurrent rectal cancers, but it is inadequate for early detection. Pelvic computed tomography examination is very valuable for the early detection and localization of recurrence in relation to pelvic structures and can also serve as a guide in percutaneous needle biopsy of the tumor. Seven patients with deeply invading recurrent lesions underwent pelvic exenteration combined with sacral resection. The ileal segment conduit was used for ureteral urinary diversion. The mean operation time and blood loss were 8.8 hours and 6,200 ml, respectively. No operative deaths were encountered. One patient is alive 22 months postoperatively with no evidence of disease, and another patient is alive 32 months postoperatively with pelvic wall recurrence. This procedure seems a reasonable treatment for palliation and full recovery in certain patients.

Surface morphology and function of human pulmonary alveolar macrophages from smokers and non-smokers

Pulmonary alveolar macrophages were obtained by saline lavage from 23 healthy male volunteers--10 non-smokers and 13 cigarette smokers. Lavage produced three times as many alveolar macrophages in smokers than in non-smokers. When macrophages from smokers and from non-smokers were incubated in vitro, more cells from smokers adhered to glass, spread out, and showed enhanced nitroblue tetrazolium (NBT) reduction. The surface morphology of alveolar macrophages from smokers showed more with a plate like appearance and ridge like membrane surface, while the macrophages from non-smokers were predominantly spherical with ruffles. The proportions of cells which stained highly for beta galactosidase were 55% in smokers and 11% in non-smokers. Thus, in a resting state in vitro, alveolar macrophages from smokers were more active than those from non-smokers. When, however, macrophages from smokers and non-smokers were incubated with immunobeads and with opsonised or non-opsonised BCG, the phagocytic activity and stimulated NBT reduction of alveolar macrophages from smokers were similar to or somewhat less than those of non-smokers.

Suplatast tosilate inhibits histamine signaling by direct and indirect down-regulation of histamine H1 receptor gene expression through suppression of histidine decarboxylase and IL-4 gene transcriptions

Allergic rhinitis (AR) is an inflammatory disorder typified by symptoms such as sneezing, congestion, and rhinorrhea. Histamine plays important roles in eliciting AR symptoms. Up-regulation of the histamine H(1) receptor (H1R) and histidine decarboxylase (HDC) mRNAs was observed in AR patients. Th2 cytokines are also involved in the pathogenesis of AR. We examined the effect of suplatast tosilate on nasal symptoms, and H1R, HDC, and IL-4 gene expression using toluene-2,4-diisocyanate (TDI)-sensitized rats and HeLa cells expressing endogenous H1R. Provocation with TDI increased nasal symptoms, HDC activity, the histamine content of nasal lavage fluid, and the expression of H1R, HDC, and IL-4 mRNAs in TDI-sensitized rats. Pretreatment with suplatast for 2 wk significantly suppressed TDI-induced nasal symptoms and elevation of H1R, HDC, and IL-4 mRNAs. Suplatast also suppressed HDC activity in the nasal mucosa and the histamine content of the nasal lavage fluid. Bilateral injection of IL-4 into the nasal cavity of normal rats up-regulated H1R mRNA, while intranasal application of histamine up-regulated IL-4 mRNA. Suplatast suppressed IL-4-induced up-regulation of H1R mRNA in HeLa cells. However, it did not inhibit histamine-induced H1R mRNA elevation. These results suggest that suplatast alleviates nasal symptoms by inhibiting histamine signaling in TDI-sensitized rats through the suppression of histamine- and IL-4-induced H1R gene expression by the inhibitions of HDC and IL-4 gene transcriptions, respectively.

A new method of inhalation challenge with propranolol: comparison with methacholine-induced bronchoconstriction and role of vagal nerve activity

To establish a safe procedure for examining propranolol-induced bronchoconstriction, we have developed a new method for performing inhalation challenge with propranolol. Monitoring respiratory resistance during tidal breathing with continuous inhalation of propranolol in 1.5-fold increasing concentrations from 0.78 to 30 mg/ml for 1 minute at each concentration, we tested 43 subjects with stable asthma and 10 normal subjects. We also compared bronchial responsiveness with responsiveness to inhaled methacholine on separate days. In addition, to determine the role of vagal nerve activity in propranolol-induced bronchoconstriction, we studied the effect of atropine. Inhaled propranolol caused dose-related bronchoconstriction in all subjects with asthma but not in normal subjects. None of the subjects suffered severe asthmatic attack during the test, which was performed in 15 minutes or less. The minimum cumulative dose of methacholine and of propranolol, at the point where respiratory conductance began to decrease, was not significantly correlated. Increased respiratory resistance was reversed by atropine in 70% of the subjects with asthma with marked individual differences. These data suggest that, although in most subjects with asthma, vagal nerve activity contributes in varying degree to bronchoconstriction, other constricting factors may contribute in the remaining subjects. It is also suggested that the mechanism of bronchial response to propranolol differs from that of the nonspecific airway reactivity estimated by methacholine challenge.

Two threonine residues and two serine residues in the second and third intracellular loops are both involved in histamine H1receptor downregulation

Human histamine H1 receptor (H1R) contains five possible phosphorylation residues (Thr140, Thr142, Ser396, Ser398 and Thr478) and the substitution of all these five residues to alanine completely impairs agonist-induced receptor downregulation. In the present study, to determine which residue(s) are responsible for receptor downregulation, we used mutant H1Rs in which single or multiple residues were substituted with alanine. The results suggested that two groups, i.e., residues Thr140 and Thr142, and residues Ser396 and Ser398, independently contributed to H1R downregulation. Thr140 and Ser398 mainly contributed to downregulation, and Thr142 or Ser396 had a slight inhibitory effect on Thr140- or Ser398-mediated process, respectively.

Anatomically corrected malposition of the great arteries--case reports and a review

Anatomically corrected malposition of the great arteries (ACM) is an extremely uncommon cardiac disease in which the great arteries arise from their appropriate ventricles despite abnormal spatial interrelations. Two patients with this malformation underwent successful surgical intervention for their associated anomalies. One was of situs solitus, d-loop and l-malposition and the other of situs inversus, l-loop and d-malposition of the great arteries. Fifty-three cases with accurate anatomical description were collected from the literature, and anatomical characteristics and associated anomalies were investigated. From the standpoint of anatomy and hemodynamics, we considered that ACM should be classified into atrioventricular concordant ACM, atrioventricular discordant ACM and ACM with situs ambiguus. Heart position and conus were variable. Dextrocardia and mesocardia were frequent. Bilateral conus was characteristic in concordant ACM, and subpulmonary conus was prominent in discordant ACM. The hypoplasia of the right heart and juxtaposition of the atrial appendages were in high incidence in cases of ACM. Surgical intervention was also discussed.

Heterologous up-regulation of the histamine H1 receptor by M3 muscarinic receptor-mediated activation of H1-receptor gene transcription

Histamine H(1) receptor (H1R) level varies under various pathological conditions, and these changes may be responsible for some pathogenesis, such as allergic rhinitis. Previously, we showed that H1R was heterologously down-regulated (through degradation of H1R) by prolonged stimulation with muscarinic M(3) receptor (M3R) in Chinese hamster ovary (CHO) cells stably expressing H1R and M3R. However, this cell was inadequate for studying the effects on H1R gene regulation, because the cell expresses H1R, which is under the control of the SV40 promoter. Therefore, in this study, we have investigated the possible role of M3R stimulation in the H1R gene transcription and H1R mRNA stability by using U373 astrocytoma cells that express endogenous H1R and transfected M3R. Stimulation of M3R significantly increased H1R promoter activity and H1R mRNA level without alteration in H1R mRNA stability. The H1R level was also up-regulated by M3R activation (150% of control by treatment with carbachol for 24 h). These M3R-mediated events were almost completely blocked by the protein kinase C (PKC) inhibitor, Ro 31-8220, suggesting the involvement of PKC. These results indicated that M3R was involved in the up-regulation of H1R by activating H1R gene transcription through a PKC-dependent process.

Identification of Amino Acid Residues Responsible for Agonist-Induced Down-Regulation of Histamine H1 Receptors

The histamine H(1) receptor (H1R) level is dynamically regulated in vivo under various physiological and pathological conditions. The H1R regulation may consist of various processes, and this study focused on the process of receptor trafficking, that is, receptor internalization to endosomes and the following receptor degradation. First, we identified five possible phosphorylation residues of human H1R, Thr(140), Thr(142), Ser(396), Ser(398), and Thr(478), based on in vitro phosphorylation studies. Then to determine the role of these residues, we constructed a mutant H1R in which all of these five residues were substituted with alanine. Both wild-type and the mutant receptors expressed in Chinese hamster ovary (CHO) cells had similar values of K(d) for [(3)H]mepyramine binding and K(i) for histamine, and these cells showed similar levels of histamine-stimulated inositol phosphate formation. Both types of H1Rs were internalized essentially in the same way upon stimulation with histamine (100 microM) for 30 min. However, down-regulation of the mutant H1R was completely impaired, whereas that of wild-type H1R occurred by approximately 60% by the treatment with 100 microM histamine for 24 h. These results suggest that these residues are responsible for receptor down-regulation but not for receptor internalization. Possibly, phosphorylation of the residues is required for receptor transport from endosomes to lysosomes.

Temperature-dependence of desensitization induced by acetylcholine and histamine in guinea-pig ileal longitudinal muscle

1. The effects of temperature on the time course of desensitization induced by acetylcholine and histamine, and on the recovery from desensitization were studied in the longitudinal muscle of the guinea-pig ileum. 2. Self- and cross-desensitization produced by acetylcholine (10(-5) M) occurred rapidly in the first 10 min of exposure to the agonist, with the same time course and the same degree of desensitization over the temperature range of 11 degrees C to 31 degrees C. 3. Self-desensitization produced by histamine (10(-5) M) also occurred rapidly in the first 10 min of exposure to the agonist, and showed great temperature-dependence, especially at 11 degrees C and 21 degrees C, but scarcely occurred at 6 degrees C. 4. Cross-desensitization produced by histamine developed gradually with time and showed a moderate temperature-dependence between 11 degrees C and 31 degrees C, but scarcely occurred at 6 degrees C. 5. The recovery processes from desensitization showed marked temperature-dependence. Recovery was halted completely at 11 degrees C. 6. These studies suggest that acetylcholine-induced desensitization may be attributed to a single non-specific mechanism. Histamine-induced desensitization may be due to at least two mechanisms: it occurs in both a specific and non-specific manner. Each of these desensitizations can be characterized by its unique temperature-dependence.

Recent advances in molecular pharmacology of the histamine systems: regulation of histamine H1 receptor signaling by changing its expression level

Histamine H1 receptor (H1R) signaling is regulated by changing its expression level. Two mechanisms are involved in this regulation. One is down-regulation through receptor desensitization. Receptor phosphorylation seemed crucial because stimulation of the mutant H1R lacking five putative phosphorylation sites did not show down-regulation. The phosphorylation level of the mutant receptor was much smaller than that of the wild type ones by several protein kinases. The other is up-regulation through activation of receptor gene expression. Protein kinase C (PKC) signaling was suggested to be involved in this up-regulation. Regulation of H1R expression level was mediated not only through H1R but also autonomic nerve receptors. Stimulation of M3 muscarinic receptors (M3R) induced both down-regulation and up-regulation of H1R. Down-regulation of M3R-mediated H1R seemed not to be mediated by PKC activation, although PKC activation induced H1R phosphorylation. Elevation of H1R expression was induced by the stimulation of M3Rs. PKC was suggested to be involved in this up-regulation. Stimulation of beta2-adrenergic receptors induced H1R down-regulation through several mechanisms. One of them is enhanced receptor degradation after desensitization and another is suppression of receptor synthesis that includes the suppression of receptor gene expression and enhanced degradation of the receptor mRNA. Protein kinase A was suggested to be involved in enhanced degradation and the activation of the receptor gene expression. Elevation of both H1R expression and its mRNA was observed in nasal mucosa of nasal hypersensitivity allergy model rat after toluene diisocyanate provocation. These results suggest that activation of H1R gene expression plays an important patho-physiological role in allergy. Elevation of the mRNA was partially but significantly suppressed by antihistamines.

Improving symptoms of senile dementia by a night-time spa bathing

In our medical and welfare facilities, many patients with senile dementia require aid in taking a bath. In most institutions, patients usually take a bath in the daytime within the working hours of the staff. However, most of these patients used to take a bath in the evening or at night at their homes. Some patients even fall asleep after daylight bathing. Thus, we studied the stabilizing effects of night-time spa bathing on symptoms associated with dementia. Ten patients (two male and eight females, aged 75-88) in special nursing institution for the aged, were enrolled in this study. They were all assessed as +4 on the Karasawa's clinical criteria for grading dementia. For 9 weeks, night-time spa bathing was performed at 18:00-19:00 twice a week. Except for the night-time spa bathing period, the bathing hour was 14:00-15:00 as usual. The observations of symptoms including restlessness, wandering and aggression were carried out ten times daily along with those on sleeping condition five times daily, to compare symptoms and conditions during 2 weeks of baseline daytime bathing periods, 9 weeks of night-time bathing periods and 2 weeks of daytime bathing periods, totaling 13 weeks. The results showed that sleeping conditions were ameliorated in more than 60-90% of the subjects. Their sleeping conditions began to improve 2 weeks after the start of night-time spa bathing with a remarkably improvement 4-6 weeks after the start. Restlessness was recognized in six subjects, wandering in eight and aggression in four at baseline, and 75-100% of the subjects with such symptoms improved markedly.

Alterations in histamine receptors of guinea-pig ileal smooth muscle produced during agonist-induced desensitization

1. The effects of prolonged treatment with histamine (10(-4) M, 30 min) on desensitization at histamine H1-receptors of guinea-pig ileal longitudinal muscle were investigated. 2. This treatment did not change either the maximum amount or dissociation constant (Kd) of [3H]-mepyramine binding to membranes of guinea-pig ileal muscle. 3. In contrast, this treatment shifted the histamine inhibition curves of [3H]-mepyramine binding to the right both in the presence and absence of 0.5 mM guanosine-5'-triphosphate (GTP). This rightward shift of the curves occurred rapidly in the first 10 min of exposure to histamine. 4. The histamine inhibition curves were analyzed with a two binding sites model. It was shown that the histamine-induced affinity change of the receptor for the agonist occurred with the high affinity binding component (which comprise about 80% of the total), whereas no significant change occurred with the low affinity component. The GTP-dependent decrease in the affinity of the receptor for the agonist also occurred with the high affinity component both in control and histamine-treated preparations. 5. These studies suggest that histamine-induced desensitization was caused by alteration in the affinity of the receptor for the agonist rather than reduction in the number of the receptors and that the interaction of the receptor with a guanine nucleotide regulatory protein was retained in the desensitized state.

Beta(2)-adrenergic receptor-mediated histamine H(1) receptor down-regulation: another possible advantage of beta(2) agonists in asthmatic therapy

To clarify heterologous regulation of a receptor is important in considering medication. Histamine constricts the airway smooth muscle through the action to the H(1) receptor (H1R), which contributes to asthma. beta(2)-Adrenergic receptor (beta2R) agonists are widely used in asthmatic therapy for their bronchodilating effects. In this study, we investigated the effect of beta2R activation on the H1R function using Chinese hamster ovary cells stably co-expressing human histamine H1R and beta2R (CHO-H1/beta2 cell). The stimulation of beta2R resulted in the decrease of H1R in the membrane. Heterologous H1R down-regulation was significantly reversed in the presence of the cyclic AMP-dependent protein kinase (PKA) inhibitor KT5720. Since phosphorylation of G protein-coupled receptor (GPCR) by second messenger-dependent kinases, is proposed to be a key step initiating heterologous receptor desensitization, we examined whether heterologous H1R down-regulation was accompanied by H1R phosphorylation. H1R was phosphorylated by beta2R stimulation; however, a PKA inhibitor did not inhibit heterologous H1R phosphorylation. Our results suggest that H1R was heterologously regulated by beta2R. Not only a direct action of beta2R agonist to beta2R causing bronchodilation but also indirect action that reduces the number of H1R responsible for bronchoconstriction might contribute to a decrease in the bronchial resistance, which proposes another possible advantage of beta2R agonists for asthmatic medication.

Histamine H1 Receptor Down-Regulation Mediated by M3 Muscarinic Acetylcholine Receptor Subtype

Heterologous down-regulation of histamine H(1) receptor (H1R) mediated by muscarinic acetylcholine receptor subtype was investigated using five kinds of Chinese hamster ovary (CHO) cells stably co-expressing the human H1R and one of the five (M(1) - M(5)) muscarinic acetylcholine receptors, CHO-H1/M1, CHO-H1/M2, CHO-H1/M3, CHO-H1/M4, and CHO-H1/M5 cells. Among the CHO-H1/M1, CHO-H1/M3, and CHO-H1/M5 cells, carbachol treatment of the CHO-H1/M3 cells time-dependently led to remarkable down-regulation of the H1R to 60% of the control level. In contrast, stimulation of CHO-H1/M1 cells by carbachol induced negligible effect on the down-regulation. Stimulation of CHO-H1/M5 cells by carbachol induced significant but only small H1R down-regulation. M(2) and M(4) muscarinic receptors showed negligible effect on the down-regulation. H1R-mediated accumulation of inositol phosphates in CHO-H1/M3 cells with long-term expose to carbachol was decreased to 60% compared with non-treated cells. Heterologous phosphorylation of H1R was induced by the stimulation of each muscarinic receptor. H1R was phosphorylated by about twofold from the basal level through five subtypes of muscarinic receptor. The M(3) muscarinic receptor-mediated phosphorylation of H1R was reversed by the inhibition of protein kinase C. In the present study we demonstrated that the M(3) muscarinic acetylcholine receptor mediated remarkable down-regulation of the H1R with decreased receptor signaling.

Direct phosphorylation of histamine H1 receptor by various protein kinases in vitro

Phosphorylation of G protein-coupled receptors (GPCRs) by various kinases is suggested to be an important step in initiating receptor desensitization. Some reports have indirectly demonstrated the involvement of protein kinase C (PKC)-mediated receptor phosphorylation in the desensitization of the histamine H1 receptor (H1R). In this study, human c-myc-epitope-tagged H1R (hm mcH1R) was expressed in Sf9 cells, and an in vitro approach was taken to obtain direct evidence that H1R could be phosphorylated by various kinases. When hm mcH1R, which had been immunoprecipitated with anti-c-myc antibody from Sf9 cell membranes, was incubated with PKC, cAMP-dependent protein kinase (PKA), calcium/calmodulin-dependent protein kinase II (CaMKII) or cGMP-dependent protein kinase (PKG), the immunoprecipitated receptor was phosphorylated by these kinases. Membrane-bound hm mcH1R, whose conformation is closer to its physiological state than that of the immunoprecipitated receptor, was also phosphorylated by PKC, PKA, CaMKII and PKG. Phosphorylation of immunoprecipitated and membrane-bound hm mcH1R was inhibited by kinase inhibitors. These data are the first demonstration of the phosphorylation of H1R by four protein kinases, i.e., PKC, PKA, CaMKII and PKG, and provide fundamental information to help us further understand the relationship between H1R phosphorylation and desensitization of this receptor.

Changes in bronchial reactivity to acetylcholine with type C influenza virus infection in dogs

To investigate the mechanisms involved in increasing bronchial reactivity, we made a model of airway reactivity increase in dogs after Type C influenza virus infection. Five beagle dogs were inoculated intranasally with the virus, and the time courses of changes in the hemagglutination inhibition (HI) antibody titer and the bronchial reactivity were determined. To assess bronchial reactivity the dogs were anesthetized, and dose-response curves of pulmonary resistance were obtained against increasing concentrations of acetylcholine aerosol. The dogs infected with the virus showed mild symptoms of rhinorrhea and cough. The HI antibody titer was significantly increased in all dogs, with peak values at 1 to 3 wk after infection. The bronchial reactivity to acetylcholine began to increase towards Day 3, reached a peak at 1 to 2 wk, and returned to a normal level at 4 wk. The airway reactivity to acetylcholine at 2 wk after infection was increased by 2.3 to 6.5 times the normal value in terms of the acetylcholine provocative concentration. The mean increase was significant at 1 wk (p less than 0.05), 2 wk (p less than 0.01), and 3 wk (p less than 0.05). Although both the HI antibody titer and the airway responsiveness increased together towards 1 to 2 wk, no close relationship between these factors was observed thereafter. The present dog model of airway hyperreactivity may be useful for further investigation of the mechanism governing increase in bronchial reactivity with respiratory viral infection in normal subjects as well as in patients with asthma.

Interaction of local anaesthetics with histamine H1 receptors in guinea-pig ileum

The interaction of amine local anaesthetics and related compounds with histamine H1 receptors was investigated in guinea-pig ileal longitudinal muscle. Quinacrine, chloroquine, tetracaine and procaine inhibited [3H]mepyramine binding to solubilized membrane from ileal muscle with pKi values of 5.27 +/- 0.11, 5.66 +/- 0.01, 4.28 +/- 0.08 and 3.97 +/- 0.11, respectively. The pKB values obtained from the initial parallel shift of the dose-response curves for histamine in the presence of these drugs were 5.49 +/- 0.11, 6.14 +/- 0.09, 4.86 +/- 0.06 and 4.58 +/- 0.06, respectively, in reasonable agreement with the pKi values. The combined dose-ratio test with both local anaesthetics and antagonist (mepyramine) present showed that tetracaine and procaine were competitive and chloroquine was partially competitive, but that quinacrine was not competitive at histamine H1 receptors. These local anaesthetics inhibited histamine-induced desensitization in guinea-pig ileum. Receptor occupancy (%) by agonist decreased from 95.2 (without inhibitor) to 73.9, 42.8, 35.9 and 33.9 in the presence of quinacrine, chloroquine, tetracaine or procaine, respectively, under the conditions where each inhibitor drug induced half maximum inhibition of desensitization. The results suggested that most of these local anaesthetics interacted competitively at histamine H1 receptors and inhibited desensitization through their antagonizing actions, whereas quinacrine interacted allosterically and inhibited desensitization through a separate action.

Role of cellular Na+ accumulation in acetylcholine-induced desensitization of guinea pig ileal longitudinal muscle

The role of cellular Na+ accumulation in acetylcholine-induced desensitization was investigated in guinea pig ileal longitudinal muscle. Desensitization was induced by the pretreatment with acetylcholine (10(-4) M, 30 min) and was expressed by the rightward shift in the concentration-response curve for acetylcholine after the treatment. The same treatment with acetylcholine caused accumulation of cellular Na+ that amounted to about 3.5-fold of the control level. To study the relationship between the gain of cellular Na+ and the development of desensitization, we treated the muscle strips with acetylcholine under the condition in which the external Na+ concentration ranged from zero to 149.2 mM. The result showed that cellular Na+ content is closely related to the extent of desensitization; that is, desensitization was at the lowest level when acetylcholine induced no increase in cellular Na+, while desensitization developed in proportion to the increase in cellular Na+ content. However, when cellular Na+ was increased by another method (by the treatment with ouabain), the inhibition of the acetylcholine response was far less than that observed in the case of desensitization. We concluded that both muscarinic stimulation and the accompanying accumulation of cellular Na+ are required for desensitization to occur in full. This desensitization could be the result of a muscarinic stimulated and cellular Na+-dependent mechanism.

Down-regulation of histamine H1 receptors by beta2-adrenoceptor-mediated inhibition of H1 receptor gene transcription

Histamine H1 receptor (H1R) levels vary under various pathological conditions, and these changes may be responsible for some pathogenesis such as in allergic rhinitis. Several stimulants, including histamine, muscarinic agonists and platelet-activating factor, have now been shown to regulate H1R levels and may have roles in regulating the H1R level in physiological and pathological conditions. Results for beta2-adrenoceptor (beta2AR) stimulation are conflicting, however.beta2AR up-regulated H1R in bovine tracheal smooth muscle, but down-regulated human H1R expressed in Chinese hamster ovary (CHO) cells. It is possible that this discrepancy comes from the differences in the preparations used for each study: the former cell expressed bovine H1R and the latter cell expressed human H1R. Moreover, CHO cells have been shown to be inadequate for studying the effects on H1R gene expression, because the cells express non-endogenous stably transfected H1R under the control of the SV40 promoter. Therefore, in this study, we have investigated the role of beta2AR stimulation in H1R gene regulation using human U373 astrocytoma cells that express endogenous H1R and transfected beta2AR. Stimulation of beta2AR significantly reduced H1R promoter activity and H1R mRNA levels. H1R mRNA stability was slightly reduced by beta2AR stimulation, although this was not significant. The decrease of H1R mRNA by beta2AR stimulation was blocked by the protein kinase A (PKA) inhibitor KT5720, suggesting the involvement of PKA. These results indicate that the beta2AR is involved in the down-regulation of human H1R by inhibiting H1R gene transcription through a PKA-dependent process.

Inhibition of histamine H1 receptor downregulation by KT5823, a protein kinase G inhibitor

The role of various protein kinases in the downregulation of histamine H(1) receptors was studied by using their inhibitors and activators. Human histamine H(1) receptors (H(1)Rs) expressed in CHO cells were downregulated by histamine in a dose- and time-dependent manner, and this downregulation continued to increase over a 24-h period. KT5823, an inhibitor of protein kinase G, remarkably but not completely reversed the histamine-induced H(1)R downregulation over 24 h. HA1004, another inhibitor of protein kinase G, showed a similar inhibitory effect. However, both 8-Br-cGMP and 8-pCPT-cGMP, membrane-permeable analogues of cGMP, did not show any effects on H(1)R downregulation in the absence or presence of histamine. Ro 31-8220, an inhibitor of protein kinase C (PKC), did not affect histamine-induced downregulation of H(1)R; nor did phorbol 12-myristate 13-acetate, a PKC-activating phorbol ester. Similarly, histamine-induced downregulation of H(1)R was unaffected by either H-89, an inhibitor of protein kinase A, or 8-Br-cAMP, a membrane-permeable analogue of cAMP.

Localized expression of histamine H1 receptors in syncytiotrophoblast cells of human placenta

The previous Northern blot analysis and in situ hybridization studies showed that histamine H1-receptor (H1R) mRNA is expressed in human placenta and suggested that H(1)R plays some roles in the function of placenta in pregnancy. To investigate further, it is essential to show the precise location of H1R in the placenta. In the present study, we investigated H1R expression in human placenta by radioligand binding assay and immunohistochemical study using an antibody against human H1R. Placentas were obtained from normal uncomplicated deliveries. Membranes prepared from the tissue exhibited saturable [3H]mepyramine binding (K(d) = 4.0 +/- 0.6 nM and B(max) = 91.4 +/- 4.9 fmol/mg of protein). Stereoisomers of chlorpheniramine inhibited [(3)H]mepyramine binding; d-chlorpheniramine inhibited more potently than l-chlorpheniramine, K(i) values being 1.1 +/- 0.4 and 270 +/- 170 nM, respectively. The placenta tissues were positively immunostained with anti-H1R antibody only in the region of the syncytiotrophoblast of chorionic villus. The tissues were double stained with anti-H1R antibody and an antibody against human chorionic gonadotoropin (hCG) that is solely expressed in placental syncytiotrophoblast cells. The results showed that H1R and hCG were expressed on the same cells, that is, syncytiotrophoblast cells. These results indicate that H1Rs are specifically expressed in syncytiotrophoblast cells of human placenta organ.

Homologous and heterologous phosphorylations of human histamine H1 receptor in intact cells

Homologous and heterologous phosphorylations of histamine H1 receptor (H1R) in intact cells were investigated using Chinese hamster ovary cells stably co-expressing c-myc-tagged human histamine H1 and muscarinic M3 receptors. Increase in histamine-induced homologous phosphorylation of H1R was induced in a dose- and time-dependent manner. Maximum phosphorylation of H1R by 8-fold over the basal level was induced 1 min after the stimulation, and the increased phosphorylation level was maintained over 40 min. M3 receptor-mediated heterologous phosphorylation of H1R reached maximum by 2-fold over the basal level at 5 min after the stimulation and then rapidly returned to the basal level by 40 min after the stimulation. Histamine-induced phosphorylation of H1R was partially inhibited by three protein kinase inhibitors including Ro-31-8220 for protein kinase C (PKC), KN-93 for calcium/calmodulin-dependent kinase II (CaMKII), and KT5823 for protein kinase G (PKG), while, M3-receptor-mediated phosphorylation of H1R was completely inhibited by Ro 31-8220. Protein kinase activators including phorbol 12-myristate 13-acetate (PMA), 8-bromo-cyclic GMP (8-Br-cGMP), and 8-bromo-cyclic AMP (8-Br-cAMP) induced increases in H1R phosphorylation. Increased phosphorylation of H1R, by 5-fold over the basal level, induced with a combination of PMA, 8-Br-cGMP, and 8-Br-cAMP was still lower than that with histamine. It was suggested that H1R-mediated H1R phosphorylation involves the activation of PKC, CaMKII, PKG, and other unidentified kinases including G-protein coupled receptor kinases (GRKs) and that PKC is solely involved in M3 receptor-mediated H1R phosphorylation.