Vasoconstrictive drugs increase carbonic anhydrase I in vascular smooth muscle while vasodilating drugs reduce the activity of this isozyme by a direct mechanism of action

Carbonic anhydrase (CA) is a zinc enzyme that catalyses the reversible hydration reaction of CO2 and plays a major role in the acid-base balance. We have previously shown that certain vasoconstrictive therapeutic agents increase CA I activity whereas vasodilating drugs reduce the activity of this isozyme by a direct mechanism of action. In this paper we studied the effect of other vasoconstrictive and vasodilating agents on CA I activity in order to elucidate the involvement of vascular smooth muscle CA I in vasoconstrictive and vasodilating processes. We studied the in vitro effects of noradrenaline, prostaglandin F2 alpha, thromboxane A2, leukotriene B4, angiotensin II, vasopressin, indomethacin, prazosin, hydralazine, clonidine, reserpine, prostaglandin I2, indapamide, furosemide, amlodipine, verapamil and irbesartan on purified human red blood cell CA I and vascular smooth muscle CA I isolated from rabbits. In vivo, we selected six groups of five rabbits each, which were administered the following substances in acute experiments: orciprenaline (group 1), desmopressin (group 2), verapamil (group 3), irbesartan (group 4), acetazolamide (group 5) and placebo (control group). Vascular smooth muscle CA I activity and systolic blood pressure were determined and compared with those of the control group. In vitro results showed that all the vasoconstrictive agents studied increased purified and human erythrocyte CA I activity as well as vascular smooth muscle CA I, while vasodilating substances reduced the activity of isozyme by a direct mechanism of action. The same results obtained in vivo showed that activation of vascular smooth muscle CA I increased blood pressure while its inhibition reduced blood pressure. The results of this study suggest that pHi changes, induced by activating or inhibiting CA I in vascular smooth muscle, might be responsible for changes in vascular tonus.

Indomethacin activates carbonic anhydrase and antagonizes the effect of the specific carbonic anhydrase inhibitor acetazolamide, by a direct mechanism of action

OBJECTIVES

In this paper we investigated the effect of indomethacin, acetazolamide and their combination in vitro and in vivo on carbonic anhydrase (CA) isozymes.

METHOD

In vitro experiments followed the effect of the two substances at concentrations between 10(-8)-10(-4) M on purified human red cell CA I and II as well as on human gastric mucosa CA IV using dose-response relationships. Kinetic studies were also performed. The effects of single and combined administration of indomethacin and acetazolamide on red cell CA and on gastric acid secretion were studied in vivo.

RESULTS

Indomethacin, in vitro and in vivo. induces an increase in erythorcyte CA I and CA II activity. Acetazolamide, a specific inhibitor of CA, reduces the activity of CA I and CA II from red cells. Indomethacin completely antagonizes CA activity, i.e. abolishes the inhibitory effect of acetazolamide on CA. In humans, an increase or decrease in erythrocyte CA II activity is correlated with an increase or decrease in gastric acid secretion.

CONCLUSIONS

Our results show that indomethacin, a known cyclooxygenase (COX) inhibitor, is also an activator of CA. Our data also prove that indomethacin is not only an activator of CA but also antagonizes the effect of acetazolamide, a specific inhibitor of this enzyme. In view of the role of CA in acid-base balance as well as the fact that an increase or decrease in its activity is accompanied by an increase or decrease in intra- and extracellular pH, our results suggest that: firstly, CA activation induced by indomethacin might cause changes in COX activity; secondly, PGs are synthetized as a consequence of the changes in COX activity, a hypothesis that requires further study.

The mechanism of action of angiotensin II is dependent on direct activation of vascular smooth muscle carbonic anhydrase I

Our previous studies have shown that angiotensin II increases carbonic anhydrase activity both in vitro and in vivo. In this study we investigated in vitro the effect of angiotensin II on carbonic anhydrase I and II from erythrocytes and on arteriolar vascular smooth muscle carbonic anhydrase I. We also studied in vitro and in vivo the effect of angiotensin II receptor blockers (irbesartan and candesartan) on purified carbonic anhydrase I and II, on vascular smooth muscle carbonic anhydrase I and on arterial blood pressure in humans and in animals. In vitro results showed that angiotensin II is a direct and stronger activator of carbonic anhydrase I than II. Angiotensin II receptor blockers reduced mainly carbonic anhydrase I activity and completely antagonized the activating effect of angiotensin II both on purified and on vascular smooth muscle carbonic anhydrase I. Our in vivo experiments showed that irbesartan and candesartan are powerful inhibitors of carbonic anhydrase I both in erythrocytes (in humans) and in vascular smooth muscles (in animals). In humans, irbesartan and candesartan progressively reduce arterial blood pressure in hypertensive subjects, in parallel with progressive reduction of erythrocyte carbonic anhydrase I activity. We believe that angiotensin II could have a dual mechanism of action: (1) angiotensin interacting with its receptor to form a stimulus-receptor complex; (2) the same stimulus directly acts on the carbonic anhydrase I isozyme (which might be coupled with angiotensin II receptors), ensuring an adequate pH for stimulus-receptor coupling for signal transmission into the cell and hence vasoconstriction.

Catecholamine-induced vasoconstriction is sensitive to carbonic anhydrase I activation

We studied the relationship between alpha- and beta-adrenergic agonists and the activity of carbonic anhydrase I and II in erythrocyte, clinical and vessel studies. Kinetic studies were performed. Adrenergic agonists increased erythrocyte carbonic anhydrase as follows: adrenaline by 75%, noradrenaline by 68%, isoprenaline by 55%, and orciprenaline by 62%. The kinetic data indicated a non-competitive mechanism of action. In clinical studies carbonic anhydrase I from erythrocytes increased by 87% after noradrenaline administration, by 71% after orciprenaline and by 82% after isoprenaline. The increase in carbonic anhydrase I paralleled the increase in blood pressure. Similar results were obtained in vessel studies on piglet vascular smooth muscle. We believe that adrenergic agonists may have a dual mechanism of action: the first one consists of a catecholamine action on its receptor with the formation of a stimulus-receptor complex. The second mechanism proposed completes the first one. By this second component of the mechanism, the same stimulus directly acts on the carbonic anhydrase I isozyme (that might be functionally coupled with adrenergic receptors), so that its activation ensures an adequate pH for stimulus-receptor coupling for signal transduction into the cell, resulting in vasoconstriction.

Hypotensive effect of calcium channel blockers is parallel with carbonic anhydrase I inhibition

In this article we studied in vitro and in vivo the effect of calcium channel blockers (verapamil and amlodipine) on erythrocyte carbonic anhydrase I activity, on carbonic anhydrase I isolated from vascular smooth muscles, and on arterial blood pressure values in human beings and in animals. Our in vitro and in vivo results have shown that verapamil and amlodipine are strong inhibitors of carbonic anhydrase I both in erythrocytes (in human beings) and in vascular smooth muscles (in animals). In human beings calcium channel blockers reduce arterial blood pressure in subjects with hypertension and progressively reduce erythrocyte carbonic anhydrase I activity. We assume that verapamil and amlodipine possess a dual mechanism of action: the first mechanism consists of their action on calcium channels, and the second mechanism, proposed by us, shows that verapamil and amlodipine inhibit vascular smooth muscle carbonic anhydrase I activity with consecutive pH increase. The increase of pH might be an additional factor involved in intracellular calcium influx through calcium channels. This dual mechanism of action would bring new data regarding the hypotensive effect of verapamil and amlodipine, effects that might also be parallel and dependent on carbonic anhydrase I inhibition.

Calcium channel blockers reduce blood pressure in part by inhibiting vascular smooth muscle carbonic anhydrase I

Calcium channel blockers are a group of drugs used for the treatment of hypertension. Carbonic anhydrase (CA) I detected in vascular smooth muscle and in other cells in the organism has a major role in the acid-base balance and in vascular processes. Our previous work has proven that verapamil inhibits CA activity by a direct mechanism of action. Starting from our results in this article we studied in vitro and in vivo the effect of calcium channel blockers (verapamil and amlodipine) on erythrocyte CA I, on vascular smooth muscles CA I, and on arterial blood pressure values in human and in animals. Our in vitro and in vivo results have proved that verapamil and amlodipine are strong CA I inhibitors both in human erythrocytes and also in vascular smooth muscles in animals. In humans, calcium channel blockers studied here progressively reduce arterial blood pressure in hypertensive subjects, in parallel with progressive lowering of erythrocyte CA I activity in the normal range in normotensive subjects. From our point of view verapamil and amlodipine possess a dual mechanism of action: the first well-known action consists of their action on calcium channels. The second mechanism, suggested by us, directly acts on the vascular smooth muscle CA I isozyme, so that its inhibition should ensure an adequate pH for calcium ions transport through the channels, having as result vasodilation. This double mechanism could explain the hypotensive effect of verapamil and amlodipine, with a mechanism that partially dependent on CA I inhibition.

Curbing the nuclear activities of beta-catenin. Control over Wnt target gene expression

Wnt molecules control numerous developmental processes by altering specific gene expression patterns, and deregulation of Wnt signaling can lead to cancer. Many Wnt factors employ beta-catenin as a nuclear effector. Upon Wnt stimulation, beta-catenin heterodimerizes with T-cell factor (TCF) DNA-binding proteins to form a transcriptional activator complex. As the activating subunit of this complex, beta-catenin performs dual tasks: it alleviates repression of target gene promoters and subsequently it activates them. Beta-catenin orchestrates these effects by recruiting chromatin modifying cofactors and contacting components of the basal transcription machinery. Although beta-catenin and TCFs are universal activators in Wnt signaling, their target genes display distinct temporal and spatial expression patterns. Apparently, post-translational modifications modulate the interactions between TCFs and beta-catenin or DNA, and certain transcription factors can sequester beta-catenin from TCFs while others synergize with beta-catenin-TCF complexes in a promoter-specific manner. These mechanisms provide points of intersection with other signaling pathways, and contribute to the complexity and specificity of Wnt target gene regulation.

The p300/CBP acetyltransferases function as transcriptional coactivators of beta-catenin in vertebrates

Wnt growth factors regulate a variety of developmental processes by altering specific gene expression patterns. In vertebrates beta-catenin acts as transcriptional activator, which is needed to overcome target gene repression by Groucho/TLE proteins, and to permit promoter activation as the final consequence of Wnt signaling. However, the molecular mechanisms of transcriptional activation by beta-catenin are only poorly understood. Here we demonstrate that the closely related acetyltransferases p300 and CBP potentiate beta-catenin-mediated activation of the siamois promoter, a known Wnt target. beta-catenin and p300 also synergize to stimulate a synthetic reporter gene construct, whereas activation of the cyclin D1 promoter by beta-catenin is refractory to p300 stimulation. Axis formation and activation of the beta-catenin target genes siamois and Xnr-3 in Xenopus embryos are sensitive to the E1A oncoprotein, a known inhibitor of p300/CBP. The C-terminus of beta-catenin interacts directly with a region overlapping the CH-3 domain of p300. p300 could participate in alleviating promoter repression imposed by chromatin structure and in recruiting the basal transcription machinery to promoters of particular Wnt target genes.

Vasodilatory effect of diuretics is dependent on inhibition of vascular smooth muscle carbonic anhydrase by a direct mechanism of action

Five years ago, our in vitro and in vivo studies demonstrated for the first time that diuretic agents such as furosemide, hydrochlorothiazide, amiloride, triamterene and spironolactone inhibit carbonic anhydrase (CA) I, II and renal CA IV by a direct mechanism of action. In this paper we investigate the relationship between diuretics and CA I in the vasodilatory mechanism. Both in vitro (on purified CA I, erythrocyte CA I and smooth muscle CA I) and in vivo (in human and rabbits) we studied the effect of acetazolamide, hydrochlorothiazide, indapamide, furosemide, amiloride and triamterene on purified CA I, on human erythrocyte CA I, as well as on CA I isolated from vascular smooth muscle. Our results demonstrate that in vitro all diuretics inhibit CA I by a direct mechanism of action. Inhibition reached 100% with acetazolamide, 45% with hydrochlorothiazide, 82% with indapamide, 85% with furosemide, 68% with amiloride and 58% with triamterene. In vivo, similar inhibition of erythrocyte and smooth muscle CA I was obtained, being parallel with a reduction in arterial blood pressure values. Our data show that in addition to their already known mechanisms, diuretics also inhibit CA in vascular smooth muscle. Our results suggest that this mechanism is achieved by means of pH changes induced by CA I inhibition.

Functional characterization of multiple transactivating elements in beta-catenin, some of which interact with the TATA-binding protein in vitro

beta-Catenin, a member of the family of Armadillo repeat proteins, plays a dual role in cadherin-mediated cell adhesion and in signaling by Wnt growth factors. Upon Wnt stimulation beta-catenin undergoes nuclear translocation and serves as transcriptional coactivator of T cell factor DNA-binding proteins. Previously the transactivation potential of different portions of beta-catenin has been demonstrated, but the precise location of transactivating elements has not been established. Also, the mechanism of transactivation by beta-catenin and the molecular basis for functional differences between beta-catenin and the closely related proteins Armadillo and Plakoglobin are poorly understood. Here we have used a yeast system for the detailed characterization of the transactivation properties of beta-catenin. We show that its transactivation domains possess a modular structure, consist of multiple subelements that cover broad regions at its N and C termini, and extend considerably into the Armadillo repeat region. Compared with beta-catenin the N termini of Plakoglobin and Armadillo have different transactivation capacities that may explain their distinct signaling properties. Furthermore, transactivating elements of beta-catenin interact specifically and directly with the TATA-binding protein in vitro providing further evidence that a major function of beta-catenin during Wnt signaling is to recruit the basal transcription machinery to promoter regions of Wnt target genes.

The C-terminal transactivation domain of beta-catenin is necessary and sufficient for signaling by the LEF-1/beta-catenin complex in Xenopus laevis

Beta-catenin is a multifunctional protein involved in cell adhesion and communication. In response to signaling by Wnt growth factors, beta-catenin associates with nuclear TCF factors to activate target genes. A transactivation domain identified at the C-terminus of beta-catenin can stimulate expression of artificial reporter genes. However, the mechanism of target gene activation by TCF/beta-catenin complexes and the physiological relevance of the beta-catenin transactivation domain still remain unclear. Here we asked whether the beta-catenin transactivation domain can generate a Wnt-response in a complex biological system, namely axis formation during Xenopus laevis embryogenesis. We show that a chimeric transcription factor consisting of beta-catenin fused to the DNA-binding domain of LEF-1 induces a complete secondary dorsoanterior axis when expressed in Xenopus. A LEF-1-beta-catenin fusion lacking the C-terminal transactivation domain is impaired in signaling while fusion of just the beta-catenin transactivator to the DNA-binding domain of LEF-1 is sufficient for axis-induction. The latter fusion molecule is blocked by dominant negative LEF-1 but not by excess cadherin indicating that all events parallel or upstream of the transactivation step mediated by beta-catenin are dispensable for Wnt-signaling. Moreover, beta-catenin can be replaced by a heterologous transactivator. Apparently, the ultimate function of beta-catenin in Wnt signaling is to recruit the basal transcription machinery to promoter regions of specific target genes.

Nuclear endpoint of Wnt signaling: neoplastic transformation induced by transactivating lymphoid-enhancing factor 1

The interaction between beta-catenin and LEF-1/TCF transcription factors plays a pivotal role in the Wnt-1 signaling pathway. The level of beta-catenin is regulated by partner proteins, including glycogen synthase kinase-3beta (GSK-3beta) and the adenomatous polyposis coli (APC) tumor suppressor protein. Genetic defects in APC are responsible for a heritable predisposition to colon cancer. APC protein and GSK-3beta bind beta-catenin, retain it in the cytoplasm, and facilitate the proteolytic degradation of beta-catenin. Abrogation of this negative regulation allows beta-catenin to translocate to the nucleus and to form a transcriptional activator complex with the DNA-binding protein lymphoid-enhancing factor 1 (LEF-1). This complex is thought to be involved in tumorigenesis. Here we show that covalent linkage of LEF-1 to beta-catenin and to transcriptional activation domains derived from the estrogen receptor or the herpes simplex virus protein VP16 generates transcriptional regulators that induce oncogenic transformation of chicken embryo fibroblasts. The chimeras between LEF-1 and beta-catenin or VP16 are constitutively active, whereas fusions of LEF-1 to the estrogen receptor are regulatable by estrogen. These experiments document the oncogenicity of transactivating LEF-1 and show that the transactivation domain normally provided by beta-catenin can be replaced by heterologous activation domains. These results suggest that the transactivating function of the LEF-1/beta-catenin complex is critical for tumorigenesis and that this complex transforms cells by activating specific LEF-1 target genes.

CT diagnosis of acquired intercostal lung herniation

Intercostal lung herniation is a rare complication of trauma, best demonstrated by computed tomography. Most intercostal lung herniations are the result of direct trauma to the chest wall or occur at sites of prior percutaneously placed chest tubes. We present two cases of acquired intercostal lung herniation.

Regulation of sucrase and lactase in developing rats: role of nuclear factors that bind to two gene regulatory elements

BACKGROUND & AIMS

Sucrase-isomaltase and lactase-phlorizin hydrolase expressions change remarkably during postnatal development in rats. The aim of this study was to explore the role of transacting nuclear proteins, proteins that bind to the SIF1 cis-regulatory element of the sucrase-isomaltase gene and to the CE-LPH1 cis-regulatory element of the lactase-phlorizin hydrolase gene, in this regulation.

METHODS

Enzyme activity, Northern analysis, and electrophoretic mobility shift assays were used to study the relationship of these nuclear proteins to sucrase-isomaltase and lactase-phlorizin hydrolase gene expression in rats during development.

RESULTS

A rapidly migrating low-molecular-weight SIF1-binding protein was found in suckling animals without sucrase-isomaltase messenger RNA (mRNA), and a higher-molecular-weight-binding protein was found in older animals with expression of sucrase-isomaltase mRNA. Supershift experiments and Western analysis showed that neither protein is Cdx-2, the only previously described SIF1-binding protein. CE-LPH1-binding protein was found only in adult animals (with low lactase activity), and there was no relationship between enzymatic activity and levels of lactase-phlorizin hydrolase mRNA.

CONCLUSIONS

SIF1-binding proteins may regulate sucrase-isomaltase expression during postnatal development, but CE-LPH1-binding proteins do not seem to regulate lactase-phlorizin hydrolase expression during this period.

SIR2 and SIR4 interactions differ in core and extended telomeric heterochromatin in yeast

Yeast core telomeric heterochromatin can silence adjacent genes and requires RAP1, SIR2, SIR3, and SIR4 and histones H3 and H4 for this telomere position effect. SIR3 overproduction can extend the silenced domain. We examine here the nature of these multiprotein complexes. SIR2 and SIR4 were immunoprecipitated from whole-cell extracts. In addition, using formaldehyde cross-linking we have mapped SIR2, SIR4, and RAP1 along telomeric chromatin before and after SIR3 overexpression. Our data demonstrate that SIR2 and SIR4 interact in a protein complex and that SIR2, SIR3, SIR4, and RAP1 map to the same sites along telomeric heterochromatin in wild-type cells. However, when overexpressed, SIR3 spreads along the chromosome and its interactions are dominant to those of SIR4 and especially SIR2, whose detection is decreased in extended heterochromatin. RAP1 binding at the core region is unaffected by SIR3 overproduction and RAP1 shows no evidence of spreading. Thus, we propose that the structure of core telomeric heterochromatin differs from that extended by SIR3.

Spreading of transcriptional repressor SIR3 from telomeric heterochromatin

Telomeric genes and the HM loci in saccharomyces cerevisiae are transcriptionally repressed and adopt a heterochromatin-like structure. The trans-acting factors RAP1, SIR3 and SIR4 are required for telomeric and HM silencing, and are thought to be chromosomal, but how they contribute to histone-dependent repression of adjacent chromatin is unclear. SIR3 suppresses silencing defects in histones, is limiting for silencing adjacent to telomeres, and interacts with the H3 and H4 amino termini in vitro. Here we show that SIR3 co-immunoprecipitates SIR4, RAP1 and histones from cellular extracts, suggesting the presence of large chromatin-associated protein complexes. Crosslinking experiments show that SIR3 is present at HMRa, HMLalpha and telomeres in vivo, and that is spreads from telomeric regions into adjacent chromatin when overexpressed. Thus SIR3 is a structural component of yeast heterochromatin, repressing adjacent genes as it spreads along the chromosome.

Diagnosis and treatment of pneumonia in the nursing home

Risk factors, diagnosis, ethical considerations, and treatment of pneumonia in a nursing home setting are summarized. Risk factors for pneumonia include age-associated changes, co-morbid conditions, declining general health, and iatrogenic factors. Diagnosis can be challenging in geriatric residents because of atypical presentations and complex underlying diseases. Key features of presentation include rhonchi and confusion. An increased respiratory rate can be a sensitive indicator for pneumonia. Ethical dilemmas include identifying a resident's wishes for treatment in the event of an acute illness and the decision on whether to relocate the resident to an acute care facility. Decisions are based on available resources, medical stability of the resident, unimpeded access to a hospital, and the resident's well-informed decision. The common etiologic pathogen(s) of nursing-home-acquired pneumonia reflect a mixture between community-acquired and hospital-acquired pathogens. Multiple pharmacologic interventions are available, as well as supportive measures including oxygen therapy and hydration. Preventive measures are utilized to decrease the incidence of further infection.

Usefulness of increased myocardial cyclic adenosine 3',5'-monophosphate content as a sign of rejection after cardiac transplantation

Cardiac allograft rejection represents a series of cellular and molecular events triggered by the recognition of the graft by the host immune system. One of the second messenger systems involved in mitogenic mechanisms is the cyclic adenosine 3',5'-monophosphate (cAMP)-coupled signaling system. The aim of this preliminary study was to evaluate whether rejection after cardiac transplantation is accompanied by changes in the expression of cAMP. Myocardial cAMP content was determined by radioimmunoassay in endomyocardial biopsy specimens taken during routine follow-up after cardiac transplantation with or without cellular and/or vascular (i.e., coronary vasculopathy) rejection, respectively. Analysis of the different subgroups of patients showed that patients without any signs of rejection (no vasculopathy, no cellular rejection) had the lowest myocardial cAMP content (1.41 +/- 0.12 pmol/mg wet weight). Patients with either cellular or vascular rejection had significantly higher myocardial cAMP levels (2.25 +/- 0.29 and 2.24 +/- 0.59 pmol/mg wet weight, respectively, p < 0.05). Patients with both cellular rejection and coronary vasculopathy had the highest cAMP levels (5.95 +/- 1.6 pmol/mg wet weight; p < 0.001). We speculate that cAMP may play a functional role in mediating rejection induced by mitogenic factors activated after cardiac transplantation, suggesting a possible "cross-talk" between different cellular signaling pathways.

Histone H3 and H4 N-termini interact with SIR3 and SIR4 proteins: a molecular model for the formation of heterochromatin in yeast

The silent mating loci and chromosomal regions adjacent to telomeres of S. cerevisiae have features similar to heterochromatin of more complex eukaryotes. Transcriptional repression at these sites depends on the silent information regulators SIR3 and SIR4 as well as histones H3 and H4. We show here that the SIR3 and SIR4 proteins interact with specific silencing domains of the H3 and H4 N-termini in vitro. Certain mutations in these factors, which affect their silencing functions in vivo, also disrupt their interactions in vitro. Immunofluorescence studies with antibodies against RAP1 and SIR3 demonstrate that the H3 and H4 N-termini are required for the association of SIR3 with telomeric chromatin and the perinuclear positioning of yeast telomeres. Based on these interactions, we propose a model for heterochromatin-mediated transcriptional silencing in yeast, which may serve as a paradigm for other eukaryotic organisms as well.

The regulation of euchromatin and heterochromatin by histones in yeast

Yeast chromosomes may lack the linker histone H1 (normally required to compact 10 nm beads-on-a-string fiber into the 30 nm fiber) and there is no cytological evidence for higher order fiber structure but they do contain regions which correspond to euchromatin and heterochromatin of higher eukaryotes. Both euchromatin and heterochromatin contain nucleosomal particles (composed of two molecules each of H2A, H2B, H3 and H4), however histones have been shown to regulate genes in these regions in quite different ways. The mechanisms by which such regulation occurs are the topic of this paper.