Antiproliferative effects of calcitonin gene-related peptide in aortic and pulmonary artery smooth muscle cells

Pulmonary hypertension is characterized by vascular remodeling involving smooth muscle cell proliferation and migration. Calcitonin gene-related peptide (CGRP) and nitric oxide (NO) are potent vasodilators, and the inhibition of aortic smooth muscle cell (ASMC) proliferation by NO has been documented, but less is known about the effects of CGRP. The mechanism by which overexpression of CGRP inhibits proliferation in pulmonary artery smooth muscle cells (PASMC) and ASMC following in vitro transfection by the gene coding for prepro-CGRP was investigated. Increased expression of p53 is known to stimulate p21, which inhibits G(1) cyclin/cdk complexes, thereby inhibiting cell proliferation. We hypothesize that p53 and p21 are involved in the growth inhibitory effect of CGRP. In this study, CGRP was shown to inhibit ASMC and PASMC proliferation. In PASMC transfected with CGRP and exposed to a PKA inhibitor (PKAi), cell proliferation was restored. p53 and p21 expression increased in CGRP-treated cells but decreased in cells treated with CGRP and PKAi. PASMC treated with CGRP and a PKG inhibitor (PKGi) recovered from inhibition of proliferation induced by CGRP. ASMC treated with CGRP and then PKAi or PKGi recovered only when exposed to the PKAi and not PKGi. Although CGRP is thought to act through a cAMP-dependent pathway, cGMP involvement in the response to CGRP has been reported. It is concluded that p53 plays a role in CGRP-induced inhibition of cell proliferation and cAMP/PKA appears to mediate this effect in ASMC and PASMC, whereas cGMP appears to be involved in PASMC proliferation.

Vasorelaxant responses to endomorphins, nociceptin, albuterol, and adrenomedullin in isolated rat aorta

The endogenous peptides endomorphins 1 and 2 are newly discovered, potent, selective mu-opioid receptor agonists. In the present study, the effects of endomorphins 1 and 2 on vascular smooth muscle tone were investigated on isolated rings from rat aorta with and without endothelium. In rings precontracted with phenylephrine, endomorphins 1 and 2 at concentrations of 0.1 and 1.0 microM, nociceptin at concentrations of 1-100 microM, and adrenomedullin at concentrations of 0.01-1.0 microM induced concentration dependent relaxant responses. The endomorphins and nociceptin were less potent than adrenomedullin. No relaxation was induced by endomorphins 1 and 2 in aortic rings denuded of endothelium and precontracted with phenylephrine. The results of the present studies demonstrate that the endomorphins relax aortic vascular smooth muscle from the rat aorta by an endothelium-dependant mechanism.

Gene transfer of endothelial nitric oxide synthase to the lung of the mouse in vivo. Effect on agonist-induced and flow-mediated vascular responses

The effects of transfer of the endothelial nitric oxide synthase (eNOS) gene to the lung were studied in mice. After intratracheal administration of AdCMVbetagal, expression of the beta-galactosidase reporter gene was detected in pulmonary airway cells, in alveolar cells, and in small pulmonary arteries. Gene expression with AdCMVbetagal peaked 1 day after administration and decayed over a 7- to 14-day period, whereas gene expression after AdRSVbetagal transfection peaked on day 5 and was sustained over a 21- to 28-day period. One day after administration of AdCMVeNOS, eNOS protein levels were increased, and there was a small reduction in mean pulmonary arterial pressure and pulmonary vascular resistance. The pressure-flow relationship in the pulmonary vascular bed was shifted to the right in animals transfected with eNOS, and pulmonary vasodepressor responses to bradykinin and the type V cGMP-selective phosphodiesterase inhibitor zaprinast were enhanced, whereas systemic responses were not altered. Pulmonary vasopressor responses to endothelin-1 (ET-1), angiotensin II, and ventilatory hypoxia were reduced significantly in animals transfected with the eNOS gene, whereas pressor responses to norepinephrine and U46619 were not changed. Systemic pressor responses to ET-1 and angiotensin II were similar in eNOS-transfected mice and in control mice. Intratracheal administration of AdRSVeNOS attenuated the increase in pulmonary arterial pressure in mice exposed to the fibrogenic anticancer agent bleomycin. These data suggest that transfer of the eNOS gene in vivo can selectively reduce pulmonary vascular resistance and pulmonary pressor responses to ET-1, angiotensin II, and hypoxia; enhance pulmonary depressor responses; and attenuate pulmonary hypertension induced by bleomycin. Moreover, these data suggest that in vivo gene transfer may be a useful therapeutic intervention for the treatment of pulmonary hypertensive disorders.

Dexniguldipine hydrochloride, a protein-kinase-C-specific inhibitor, affects the cell cycle, differentiation, P-glycoprotein levels, and nuclear protein phosphorylation in Friend erythroleukemia cells

Dexniguldipine hydrochloride (DNIG) is a potent antineoplastic agent with well-documented anti-(protein kinase C) activity and an ability to reverse multidrug resistance. Given the importance of protein kinase C (PKC) activity in proliferation and differentiation, we examined the effect of DNIG on several parameters of Friend erythroleukemia cell (FELC) activity. Particular attention was paid to proliferation, hexamethylene-bisacetamide-(HMBA)-induced differentiation, nuclear localization of protein kinase C, and nuclear protein phosphorylation. P-glycoprotein expression was also followed as an indicator of changes in multidrug resistance. At 2.5 microM, DNIG caused a significant decrease in the rate of FELC proliferation, while maintaining a cellular viability of greater than 80%, whether exposure to the drug was continuous over 96 h or took the form of a 6-h pulse/chase. DNA synthesis was decreased in cells exposed to DNIG for 20 h. Flow cytometry showed a marked increase in the percentage of cells in S phase of the cell cycle. Phosphorylation studies revealed decreased phosphorylation of two nuclear proteins (80 kDa and 47 kDa) following a 4-h exposure to the drug. HMBA-induced differentiation was significantly inhibited with continuous exposure to DNIG, and this effect appears to be a pre-commitment one, as 6-h pulse/chase exposures also resulted in inhibition of differentiation. Cells induced to differentiate with HMBA also demonstrated a decrease in the quantity of the 80-kDa phosphoprotein. Western blotting revealed that, even in the face of decreased phosphorylation, exposure to this PKC inhibitor resulted in an increase in the amount of nuclear PKC alpha. Finally, levels of P-glycoprotein were decreased in the presence of this drug. Our work identifies several effects of the PKC inhibitor DNIG on FELC and suggests several roles for PKC in regulating FELC proliferation and differentiation. Additionally, these results suggest that this PKC inhibitor may increase the effect of other chemotherapeutic drugs, particularly S-phase-specific ones, by increasing the length of S phase and decreasing multidrug resistance. The possibility of combination therapy with DNIG and other antineoplastic agents should be investigated further in light of these findings.

Protein kinase C beta from Friend erythroleukemia cells is associated with chromatin and DNA

Certain protein kinase C (PKC) isotypes are localized to the nucleus during cellular proliferation in murine erythroid cells, as well as in human promyelocytic leukemia and erythroleukemia cells. Because the structure of these PKC isotypes contains a conserved cysteine-rich region that contains the zinc finger DNA binding motif, we tested the hypothesis that selected PKC isotypes found in Friend erythroleukemia cells can bind to DNA. Cell lysates from murine Friend erythroleukemia cells, which express alpha, beta I, and beta II PKC, expressed greater amounts of the beta isoforms than the alpha isoform of PKC in their nuclei, and PKC beta I was found in the chromatin of these cells. Lysates of these cells were tested for their ability to bind to a DNA-cellulose column. Bound proteins were eluted with a step gradient of increasing KCl concentrations, and eluant fractions were then subjected to immunoblot analysis using isotype-specific antibodies to the alpha and beta I isotypes of PKC. DNA binding was detected for the PKC beta I isotype, which is present in the nucleus, but not for the more abundant PKC alpha isotype, which resides primarily in the cytoplasm. These results demonstrate that PKC can associate with DNA, and that this association is isotype specific in Friend erythroleukemia cells.

Interleukin-3 or erythropoietin induced nuclear localization of protein kinase C beta isoforms in hematopoietic target cells

Protein kinase C (PKC) has been implicated in the signal transduction pathways for the biological effect of both interleukin-3 (IL-3) and erythropoietin (EPO) in hematopoietic target cells. The goal of this study was to identify specific classical isoforms of PKC and their localization in hematopoietic cells in response to the growth factors, IL-3 or EPO. In addition to murine fetal liver cells as a source of normal erythroid progenitor cells, we have utilized the B6SUt.EP cell line, a non-transformed hematopoietic cell line that requires IL-3 for proliferation, but for which EPO can substitute as a growth factor. With polyclonal antibodies prepared against peptide sequences specific for the alpha, beta I, beta II and gamma isoforms of PKC, we have identified beta I and beta II as the predominant nuclear isoforms in target cells that proliferate in response to IL-3 or EPO.

Changes in protein kinase activity within 30 min of induced differentiation in Friend erythroleukemia cells

Induction of maturation in Friend erythroleukemia cells is accompanied by a programmed cessation in cell proliferation and a concomitant increase in hemoglobin production. To investigate the role of protein kinase activity in the initiation of Friend erythroleukemia cell differentiation, autoradiographs of one-dimensional, nondenaturing gels were prepared from Friend erythroleukemia cells either untreated or preincubated with dimethyl sulfoxide (DMSO) or aphidicolin for a 30-min period. Extracts were treated with cAMP or cGMP prior to electrophoresis and assayed for protein kinase activity in the presence of endogenous or exogenously added histone substrates. The data demonstrated differences in protein kinase activity following exposure of Friend erythroleukemia cells to either DMSO or aphidicolin for 30 min. These changes in enzyme activity varied with the treatment of the cells and the substrate used. Two sets of protein kinases, one responsive to cAMP and the other responsive to cGMP, were activated in control cultures. A different cAMP-responsive enzyme was active only in differentiating cells. Another protein kinase, activated by cGMP, was associated with both DMSO and aphidicolin treatment. All of these protein kinases had a histone substrate preference. One noncyclic nucleotide activated protein kinase phosphorylating endogenous substrates was associated only with DMSO-induced cells. These findings suggest a multifaceted role for protein kinases early in the maturation of Friend erythroleukemia cells.

Proliferation is required for induction of terminal differentiation of Friend erythroleukemia cells

The relationship between cell proliferation and differentiation has long been a source of controversy. Stimulation of normal erythroid maturation results in a finite number of cell divisions accompanied by a concomitant accumulation of hemoglobin. Friend erythroleukemia cells treated with hexamethylene bisacetamide differentiate in a similar manner, while agents such as hemin apparently induce differentiation without limiting cell proliferation. Aphidicolin, an inhibitor of DNA synthesis, has been reported to induce differentiation in the absence of cell proliferation. Using these three chemicals we have investigated the relationship between cell proliferation and erythrocytic maturation by exposing Friend erythroleukemia cells to either hexamethylene bisacetamide (5 mM), hemin (100 microM), or aphidicolin 1.2 microM) and examining the effects on cell growth, morphology, and hemoglobin production. Proliferation in the presence of hexamethylene bisacetamide is limited to four to five rounds of cell division, while hemin has no inhibitory effect. Hexamethylene bisacetamide initiates the complete erythrocytic maturation program, including cellular structural changes and hemoglobin synthesis. Hemin stimulates only globin gene transcription, not differentiation. Aphidicolin inhibits cell growth within 24 h, but does not induce differentiation. Furthermore, inhibition of proliferation by aphidicolin prevents subsequent hexamethylene bisacetamide induced differentiation. These results indicate that at least one round of cell division is required for initiation of erythrocytic differentiation.

Accumulation of phosphatidic acid mass and increased de novo synthesis of glycerolipids in platelet-activating-factor-activated human neutrophils

Incubation of human neutrophils with 100 nM-platelet-activating factor (PAF) but without cytochalasin B resulted in a rapid (5 s) accumulation (1.6-fold) of phosphatidic acid (PtdOH) mass. The increased PtdOH mass reached a maximum (2.8-fold) at 1 min and remained elevated (1.7-fold) at 10 min. No methylamine-stable lyso-PtdOH was detectable in the total lipid extract from control or from PAF-activated cells, suggesting that diacyl-PtdOH was the predominant species. In PAF-activated cells, changes in 1,2-diacylglycerol (DG) mass were not detectable at 5 or 15 s. Increased DG mass (1.7-fold) was detected between 30 s and 2 min, but then it declined to basal levels by 10 min. PAF enhanced [3H]glycerol incorporation into PtdOH and DG by 2- and 3-fold respectively during 1-10 min incubations. PAF also increased the radioactivity but not the mass of phosphatidylinositol and of choline glycerophospholipid by 8-fold and 4-fold respectively at 10 min. In addition, PAF-activated cells showed increased (2-fold) glycerol incorporation into triacylglycerol. These results demonstrate that PAF enhances rapid accumulation of diacyl-PtdOH mass, and that increased de novo synthesis may contribute to PtdOH mass accumulation.

15-Lipoxygenase products affect protein phosphorylation in Friend erythroleukemia cells

Endogenous arachidonic acid metabolism and protein phosphorylation have been examined in Friend erythroleukemia cells in response to the induction of differentiation by dimethyl sulfoxide and hexamethylene bisacetamide. 15-Hydroxyeicosatetraenoic acid levels were elevated in cells differentiated with hexamethylene bisacetamide or dimethyl sulfoxide compared with undifferentiated cells. Protein phosphorylation decreased markedly in differentiated cells compared with undifferentiated cells and the addition of 15-hydroperoxyeicosatetraenoic acid specifically decreased the phosphorylation of a 28-kilodalton protein. These findings indicate that products of 15-lipoxygenase may act as intracellular messengers in Friend erythroleukemia cells by affecting protein phosphorylation.

Effect of aphidicolin on Friend erythroleukemia cell maturation

Aphidicolin, a specific and reversible inhibitor of DNA polymerase alpha, was examined as a potential tool to evaluate the relationship between proliferative and differentiative events in Friend erythroleukemia cell (FELC) maturation. Since FELC can be induced to differentiate along the erythrocytic pathway with a variety of inducing agents, the effects of aphidicolin were tested on proliferating FELC and cells which were induced to differentiate with the potent inducer, hexamethylene bisacetamide (HMBA). Exposure of FELC to aphidicolin resulted in unbalanced growth within 24 h, as reflected by abnormally large cells, compared with untreated cells. In the presence of 10 or 50 microM aphidicolin, 75-90% of cells became differentiated (benzidine+ cells) within 48 h, although by 72 h cells treated with aphidicolin were non-viable as determined by trypan blue staining. A wider range of aphidicolin concentrations was tested in an effort to determine the optimal concentration of aphidicolin that maximally induced differentiation with minimal loss of cell viability. Continuous exposure of FELC from 24-96 h with doses of aphidicolin ranging from 0.5 to 50 microM was more effective for differentiation induction than was short-term exposure (1, 2, 4, 12 h) to the drug, although 1 h of exposure significantly (p less than 0.01) increased differentiation (28.1 +/- 7.8%) compared with untreated cells (2.7 +/- 1.0%). When cells were treated with HMBA (5 mM) and aphidicolin (1, 5, 10 microM), in combination, aphidicolin shifted the time of onset of differentiation from 72 to 48 h, but did not act synergistically or additively with HMBA; nor was the induction effect of aphidicolin changed by HMBA. In contrast, suboptimal doses of aphidicolin (0.5 microM) in combination with HMBA (2.5 mM) produced an additive effect on FELC differentiation. In addition, [3H]thymidine experiments demonstrated that aphidicolin reversibly blocked FELC in S phase and at G1-S interface of the cell cycle. These results indicate that aphidicolin can induce the differentiation of FELC, and that a complete round of replicative DNA synthesis is not required for differentiation to occur.

Cell-cycle-specific activity of cyclic nucleotide phosphodiesterase in Physarum polycephalum

The cell-cycle-related activities of the cAMP- and cGMP-dependent phosphodiesterases of Physarum polycephalum were assayed. The activities of plasmodial homogenate and of selected subcellular fractions were measured. The results suggested the presence of both cAMP- and cGMP-dependent phosphodiesterase in the isolated nuclei of P. polycephalum. In addition, they reveal that the cAMP- and cGMP-dependent phosphodiesterase activities of the subcellular fractions fluctuate throughout the cell cycle. The whole-cell homogenates exhibit no cell-cycle-related changes in the presence of 5 X 10(-4) M cGMP. Kinetic data suggest the presence of multiple phosphodiesterase activities in the homogenate and its particulate fractions for the cGMP-dependent enzyme. Multiple cAMP activities are also suggested for the particulate fractions. The Km values indicate that the substrate affinities of the phosphodiesterases from P. polycephalum are similar to those found previously in mammalian systems.

Activation induced by luteinizing hormone of type II protein kinase dependent on cyclic adenosine monophosphate and phosphorylation of soluble proteins in porcine granulosa cells

The present experiments were designed to study whether exogenous LH could elicit acute cyclic AMP-mediated activation of cyclic AMP-dependent protein kinase and phosphorylation of cellular protein in intact porcine granulosa cells. Incubation of porcine granulosa cells (from 3 to 5 mm diameter follicles) with 2 microgram luteinizing hormone/ml (LH) caused a significant rise of cellular cyclic AMP content within 2 min of the addition of LH. The increase was dose-dependent and occurred between doses of 0.2 and 2.0 microgram LH/ml. Luteinizing hormone also caused a time- and dose-dependent dissociation of the type II cyclic AMP-dependent protein kinase isozyme in porcine granulosa cells. Luteinizing hormone (0.05--2 microgram/ml) significantly dissociated the cyclic AMP-dependent protein kinase between 2 and 30 min after stimulation. The protein kinase dissociation was a specific effect of LH and was not elicited by either adrenocorticotrophic hormone or prolactin. During the period of LH-induced protein kinase activation, several soluble granulosa cell proteins, ranging in molecular weights from about 43 000 to 99 000, became phosphorylated in a time-dpeendent and hormone-specific manner. The results suggest that cyclic AMP-mediated activation of granulosa cell type II cyclic AMP-dependent protein kinase may be a prerequisite in the short-term molecular action of LH leading to LH-specific phosphorylation of several soluble granulosa cell proteins of an as yet unidentified function.

Chromatin substructure: an electron microscopic study of thin-sectioned chromatin subjected to sequential protein extraction and water swelling procedures

Electron microscopic observations and measurements were made on thin-sectioned chromatin fibers and fibrils obtained from nuclei of mature chicken erythrocytes. The nuclei were isolated in low ionic strength gum arabic and octanol then extracted sequentially with (1) 0.14 M NaCl, (2) 0.25 N HCl, (3) buffer saturated phenol, (4) hot 5% SDS and 0.14 M 2-mercaptoethanol and, (5) 0.4 N NaOH. The amount of nuclear protein removed at each of the first four extraction steps was 1, 86, 3 and 11% of the total, respectively. Each extract was characterized by electrophoretic profiles. At each extraction the chromatin was fixed by adding large quantities of a mixture of equal volumes of sodium cacodylate buffered 8% (w/v) glutaraldehyde (pH 6.8) and 2% OsO4 (w/v), directly into (1) an aliquot of the chromatin in extraction fluid, and (2) an aliquot of the chromatin after water washing and swelling. Three size classes of chromatin structure were seen in thin sections prepared for high resolution transmission electron microscopy and stained with uranyl acetate and lead citrate. A thick fiber of about 25 + nm diameter was the predominant large fiber seen in freshly isolated nuclei or in nuclei after salt extraction. This 25 + nm fiber has a substructure consisting of 3.2-5.2 nm diameter fibrils. After water swelling of such freshly isolated or salt extracted nuclei a fiber of about 10 nm diameter was the predominant large fiber instead of the 25 nm diameter fiber. The HCl extraction step which is known to remove histones, caused the disappearance of both the 25 nm and the 10 nm fibers. High magnification (600,000 x) micrographs of the chromatin at all procedural steps, except the last NaOH step, reveal the fibril to be omnipresent. This fibril tends to decrease somewhat in diameter during the protein extraction steps to a 2.5 nm diameter fibril after the hot SDS extraction. A fibril of 2.5 nm diameter is expected of naked double helical DNA stained with a positive stain. The NaOH, which is known to denature DNA, completely destroyed the remaining fibril. We inerpret our results to indicate that the larger chromatin fiber seen in micrographs of thin-sectioned chromatin has a fibrillar substructure which probably represents a double coil of native DNA which may have a thin protein coating of its own. The latter fibril may in turn be wrapped around a hydrophobic histone domain, perhaps reflected in the 10 nm diameter fiber which is seen upon swelling of the chromatin. This 10 nm diameter fiber is thought to be further packaged by folding into the 25 + nm diameter chromatin fiber most frequently reported in thin sections of eukaryotic cell nuclei in situ.

High-density induction of a quiescent cell state in Physarum polycephalum

The non-histone protein complement of Physarum polycephalum changes rapidly when microplasmodia are subjected to conditions of high density. The changes in these proteins induced by high density are similar to the changes observed during starvation-induced encystment. A 50% decrease in DNA synthesis, observed after 7 h of starvation, is observed after only 1 h of high density. High density also results in a decrease in RNA synthesis comparable to decreases induced by prolonged starvation. Total heterochromatin increases in response to either high density or starvation. Increased heterochromatization is preceded by an increase in nuclear actin. Mitochondrial morphology and cytoplasmic organization are also similarly altered by starvation and high density. These observations suggest the possibility of a generalized mechanism for cellular transition from active growth to a non-proliferative cell state.