Heparin suppresses sgk, an early response gene in proliferating vascular smooth muscle cells

Characterization of bone morphology in CCN5/WISP5 knockout mice

CCN5/WISP2 is part of the CCN family of matricellular proteins, but is distinct in that it lacks the C-terminal (CT) domain. Although CCN5 has been shown to impact cell proliferation and differentiation in vitro, its role in vivo is unclear. We therefore generated mice using ES cells developed by the Knockout Mouse Project (KOMP) in which exons 2-5, which encode the all of the conserved protein coding regions, are replaced by a lacZ cassette. Ccn5 ^LacZ/LacZ mice were viable and apparently normal. Based on previous studies showing that CCN5 impacts osteoblast proliferation and differentiation, we performed an analysis of adult bone phenotype. LacZ expression was examined in adult bone, and was found to be strong within the periosteum, but not in trabecular bone or bone marrow. Micro-CT analysis revealed no apparent changes in bone mineral density (BMD) or bone tissue volume (BV/TV) in Ccn5 ^LacZ/LacZ mice. These studies indicate that CCN5 is not required for normal bone formation, but they do not rule out a role in mechanotransduction or repair processes. The availability of Ccn5 ^LacZ mice enables studies of CCN5 expression and function in multiple tissues.

CCN5 in alveolar epithelial proliferation and differentiation during neonatal lung oxygen injury

Lung immaturity is the major cause of morbidity and mortality in premature infants, especially those born <28 weeks of gestation. These infants are at high risk of developing respiratory distress syndrome (RDS), a lung disease caused by insufficient surfactant production and immaturity of saccular/alveolar type II epithelial cells in the lung. RDS treatment includes oxygen and respiratory support that improve survival but also increase the risk for bronchopulmonary dysplasia (BPD), a chronic lung disease characterized by arrested alveolarization, airway hyperreactivity, and pulmonary hypertension. The mechanisms regulating normal alveolar development and how injury disrupts normal development to cause BPD are not well understood. We examined the role of the matricellular protein CCN5 (Cysteine-rich protein 61/Connective tissue growth factor/Nephroblastoma-overexpressed protein) in the development of BPD. Cultured non-proliferating alveolar type II cells expressed low levels of CCN5 protein, and displayed higher levels during proliferation. siRNA targeting of CCN5 reduced alveolar type II cell proliferation and migration in cell culture. In a mouse model of hyperoxia-induced BPD, CCN5 protein was increased only in proliferating alveolar type I cells. Alveolar epithelial cells co-expressing markers of type II cells and type I cells also appeared. The results suggest that hyperoxic injury in immature lungs induces proliferation of type I cells and trans-differentiation of type II cells into type I cells. We propose that the mechanism of the injury response in BPD includes CCN5 expression. Study of CCN5 in neonatal alveolar injury will further our understanding of BPD pathophysiology while providing a mechanistic foundation for therapeutic approaches.

Serum and glucocorticoid kinase 1 promoted the growth and migration of non-small cell lung cancer cells

Serum and glucocorticoid kinase 1 (SGK1) has been reported to be up-regulated in non-small cell lung cancer (NSCLC). However, its functions in NSCLC remained unclear. Here, SGK1 was found to be up-regulated in NSCLC samples. Over-expression of SGK1 promoted the growth and migration of NSCLC cells, while down-regulation of SGK1 inhibited the growth, migration and metastasis of NSCLC cells. SGK1 promoted the phosphorylation of GSK3 beta and the accumulation of beta-catenin, up-regulation of the target genes downstream of beta-catenin/TCF signaling, and activating the transcriptional activity of beta-catenin/TCF complex. Collectively, SGK1 might promote the progression of NSCLC through activating beta-catenin/TCF signaling.

Explants of porcine coronary artery in culture: A paradigm for studying the influence of heparin on vascular wall cell proliferation

Explant cultures of porcine coronary artery provided a coculture model, used as a paradigm of arterial wall in contact with vascular prosthesis which allowed the study of spatial and temporal changes in cell phenotype. First cells emerging from the explant had an endothelial phenotype monitored by cytoimmunostaining. Percentages of anti-smooth muscle alpha-actin labelled cells were assessed at early and late phase by flow cytofluorometric analysis to control the effect of heparin. At 100 mug ml(-1), no effect on alpha-actin labelled cell growth has been detected. This result contrasted with the inhibition of monolayer cell cultures. At 500 mug ml(-1), the proliferation of smooth muscle cells was reduced. This explant system should be useful for testing drugs susceptible to interfere with restenosis.

(Patho)physiological significance of the serum- and glucocorticoid-inducible kinase isoforms

The serum- and glucocorticoid-inducible kinase-1 (SGK1) is ubiquitously expressed and under genomic control by cell stress (including cell shrinkage) and hormones (including gluco- and mineralocorticoids). Similar to its isoforms SGK2 and SGK3, SGK1 is activated by insulin and growth factors via phosphatidylinositol 3-kinase and the 3-phosphoinositide-dependent kinase PDK1. SGKs activate ion channels (e.g., ENaC, TRPV5, ROMK, Kv1.3, KCNE1/KCNQ1, GluR1, GluR6), carriers (e.g., NHE3, GLUT1, SGLT1, EAAT1-5), and the Na+-K+-ATPase. They regulate the activity of enzymes (e.g., glycogen synthase kinase-3, ubiquitin ligase Nedd4-2, phosphomannose mutase-2) and transcription factors (e.g., forkhead transcription factor FKHRL1, beta-catenin, nuclear factor kappaB). SGKs participate in the regulation of transport, hormone release, neuroexcitability, cell proliferation, and apoptosis. SGK1 contributes to Na+ retention and K+ elimination of the kidney, mineralocorticoid stimulation of salt appetite, glucocorticoid stimulation of intestinal Na+/H+ exchanger and nutrient transport, insulin-dependent salt sensitivity of blood pressure and salt sensitivity of peripheral glucose uptake, memory consolidation, and cardiac repolarization. A common ( approximately 5% prevalence) SGK1 gene variant is associated with increased blood pressure and body weight. SGK1 may thus contribute to metabolic syndrome. SGK1 may further participate in tumor growth, neurodegeneration, fibrosing disease, and the sequelae of ischemia. SGK3 is required for adequate hair growth and maintenance of intestinal nutrient transport and influences locomotive behavior. In conclusion, the SGKs cover a wide variety of physiological functions and may play an active role in a multitude of pathophysiological conditions. There is little doubt that further targets will be identified that are modulated by the SGK isoforms and that further SGK-dependent in vivo physiological functions and pathophysiological conditions will be defined.

The serum- and glucocorticoid-inducible kinase Sgk-1 is involved in pulmonary vascular remodeling: role in redox-sensitive regulation of tissue factor by thrombin

The stress-responsive serum- and glucocorticoid-inducible kinase Sgk-1 is involved in osmoregulation and cell survival and may contribute to fibrosis and hypertension. However, the function of Sgk-1 in vascular remodeling and thrombosis, 2 major determinants of pulmonary hypertension (PH), has not been elucidated. We investigated the role of Sgk-1 in thrombin signaling and tissue factor (TF) expression and activity in pulmonary artery smooth muscle cells (PASMC). Thrombin increased Sgk-1 activity and mRNA and protein expression. H2O2 similarly induced Sgk-1 expression. Antioxidants, dominant-negative Rac, and depletion of the NADPH oxidase subunit p22phox diminished thrombin-induced Sgk-1 expression. Inhibition of p38 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and phosphoinositide-dependent kinase-1 prevented thrombin-induced Sgk-1 expression. Thrombin or Sgk-1 overexpression enhanced TF expression and procoagulant activity, whereas TF upregulation by thrombin was diminished by kinase-deficient Sgk-1 and was not detectable in fibroblasts from mice deficient in sgk-1 (sgk1(-/-)). Similarly, dexamethasone treatment failed to induce TF expression and activity in lung tissue from sgk1(-/-) mice. Transcriptional induction of TF by Sgk-1 was mediated through nuclear factor kappaB. Finally, Sgk-1 and TF proteins were detected in the media of remodeled pulmonary vessels associated with PH. These data show that thrombin potently induces Sgk-1 involving NADPH oxidases, phosphatidylinositol 3-kinase, p38 mitogen-activated protein kinase, and phosphoinositide-dependent kinase-1, and that activation of nuclear factor kappaB by Sgk-1 mediates TF expression and activity by thrombin. Because enhanced procoagulant activity can promote pulmonary vascular remodeling, and Sgk-1 and TF were present in the media of remodeled pulmonary vessels, this pathway may play a critical role in vascular remodeling in PH.

Expression of serum- and glucocorticoid-inducible kinase is regulated in an experience-dependent manner and can cause dendrite growth

The interaction of an animal with its environment during a critical period in early postnatal life has lifelong effects on the structure and function of sensory and motor systems. To gain insight into the molecular mechanisms of experience-dependent development, we challenged young rats to adapt to a new environment that engenders novel motor behavior. Rats born in the gravitational field (1G) of the earth subsequently were reared for 2 weeks either in the absence of gravity (microgravity) or at 1G. A comparison of gene expression using microarrays led to the identification of a panel of differentially regulated transcripts. We report here that the abundance of serum- and glucocorticoid-inducible kinase (SGK) is increased in spinal cord tissue from animals reared in microgravity in comparison with 1G-reared controls. The induction of SGK expression also can be achieved by administration of glucocorticoids to animals at 1G or neurons in vitro. Expression of constitutively active SGK in neurons leads to the elaboration of neuronal dendrites and their branching. Glucocorticoids also lead to dendrite elaboration, and this effect can be abrogated by inhibiting SGK activity. Changes in the level of expression of SGK could be part of the mechanism for experience-dependent acquisition of mature neuronal properties.

Identification, structural, and functional characterization of a new early gene (6A3-5, 7 kb): implication in the proliferation and differentiation of smooth muscle cells

Arterial smooth muscle cells (SMCs) play a major role in atherosclerosis and restenosis. Differential display was used to compare transcription profiles of synthetic SMCs to proliferating rat cultured SMC line. An isolated cDNA band (6A3-5) was shown by northern (7 kb) to be upregulated in the proliferating cell line. A rat tissue northern showed differential expression of this gene in different tissues. Using 5' RACE and screening of a rat brain library, part of the cDNA was cloned and sequenced (5.4 kb). Sequence searches showed important similarities with a new family of transcription factors, bearing ARID motifs. A polyclonal antibody was raised and showed a protein band of 175 kd, which is localized intracellularly. We also showed that 6A3-5 is upregulated in dedifferentiated SMC (P9) in comparison to contractile SMC ex vivo (P0). This work describes cloning, structural, and functional characterization of a new early gene involved in SMC phenotype modulation.

Heparin modulates the growth and adherence and augments the growth-inhibitory action of TNF-alpha on cultured human keratinocytes

Previous works suggest the involvement of mast cells in the epithelialization of chronic wounds. Since heparin is a major mediator stored in the secretory granules of mast cells, the purpose of this work was to elucidate the function of heparin in epithelialization using in vitro culture models. For this, low- and high-calcium media in monolayer and epithelium cultures of keratinocytes were used. Also, an assay based on keratinocyte adherence onto plastic surface was used as well. Heparin (0.02-200 microg/ml) inhibited keratinocyte growth in a non-cytotoxic and dose-dependent manner in low- and high-calcium media, Keratinocyte-SFM and DMEM, in the absence of growth factors and serum. Also, heparin inhibited the growth of keratinocyte epithelium in the presence of 10% fetal calf serum and DMEM. Instead, in the presence of Keratinocyte-SFM and growth factors, heparin at 2 microg/ml inhibited the growth by 18% but at higher heparin concentrations the inhibition was reversed to baseline. TNF-alpha is another preformed mediator in mast cell granules and it inhibited keratinocyte growth in monolayer and epithelium cultures. Interestingly, heparin at 2-20 microg/ml augmented or even potentiated this growth-inhibitory effect of TNF-alpha. The association of TNF-alpha with heparin was shown by demonstrating that TNF-alpha bound tightly to heparin-Sepharose chromatographic material. However, heparin could not augment TNF-alpha-induced cell cycle arrest at G0/G1 phase or intercellular adhesion molecule-1 expression in keratinocytes. In the cell adherence assay, heparin at 2 microg/ml inhibited significantly by 12-13% or 33% the adherence of keratinocytes onto the plastic surface coated with fibronectin or collagen, respectively, but this inhibition was reversed back to baseline at 20 or 200 microg/ml heparin. Also, heparin affected the cell membrane rather than the protein coat on the plastic surface. In conclusion, heparin not only inhibits or modulates keratinocyte growth and adherence but it also binds and potentiates the growth-inhibitory function of TNF-alpha.

Identification of dietary copper- and iron-regulated genes in rat intestine

Copper and iron act at different levels on gene expression. Due to their chemical reactivity, both metals could play a role in the regulation of the protein machinery involved in their metabolism, and/or of the metabolic function they are involved in. Experimental and clinical evidences raise also the hypothesis of the existence of genes commonly regulated by both metals. Purpose of this work was to find genes modulated by copper and iron in the rat intestine. A panel of 24 animals was randomly divided into three nutritional treatments including a control, a copper-deficient and an iron-deficient diet. The positive regulation of iron responsive element (IRE)-DMT1 gene was found, with different extent, in both experimental groups. A differential display reverse transcription (DDRT)-polymerase chain reaction (PCR) analysis carried out on the rat intestinal mRNAs demonstrated the differential expression of five cDNA fragments. Among these, the Cytochrome c oxidase (COX) subunit II mitochondrial gene resulted to be regulated by both metals, the Serum and Glucocorticoids-regulated Kinase (SGK) gene mainly by iron, and an Ebnerin-like 2 kb mRNA dramatically down-regulated by copper. Two residual clones showed low identity scores with sequences present in data bank. Finally, we observed that both iron and copper are able to modulate the expression of the three characterized genes in some tissues, other than intestine.

The oncogene Nup98-HOXA9 induces gene transcription in myeloid cells

The nucleoporin Nup98 gene is frequently rearranged in acute myelogenous leukemia (AML). In most cases this results in fusion of the N terminus of Nup98 to the DNA binding domain of a homeodomain transcription factor. The prototype of these fusions, Nup98-HOXA9, is associated with human AML and induces AML in mouse models. To understand the mechanisms by which Nup98-HOXA9 causes AML, we expressed it in myeloid cells and identified its target genes using high density oligonucleotide microarrays. The analysis was performed in triplicate and was confirmed by quantitative real time PCR. Of the 102 Nup98-HOXA9 target genes identified, 92 were up-regulated, and only 10 were down-regulated, suggesting a transcriptional activation function. A similar analysis of wild-type HOXA9 revealed 13 target genes, 12 of which were up-regulated, and 1 was down-regulated. In contrast, wild-type Nup98 had no effect on gene expression, demonstrating that the HOXA9 DNA binding domain is required for gene regulation. Co-transfection experiments using a luciferase reporter linked to the promoter of one of the Nup98-HOXA9 target genes confirmed up-regulation at the transcriptional level by Nup98-HOXA9 but not by either HOXA9 or Nup98. These data indicate that Nup98-HOXA9 is an aberrant transcription factor whose activity depends on the HOXA9 DNA binding domain but has a stronger and wider transcriptional effect than HOXA9. Several of the genes regulated by Nup98-HOXA9 are associated with increased cell proliferation and survival as well as drug metabolism, providing insights into the pathogenesis and epidemiology of Nup98-HOXA9-induced AML.

Importin-alpha mediates the regulated nuclear targeting of serum- and glucocorticoid-inducible protein kinase (Sgk) by recognition of a nuclear localization signal in the kinase central domain

The transcriptionally regulated serum and glucocorticoid inducible protein kinase (Sgk) is localized to the nucleus in a serum-dependent manner, and a yeast two-hybrid genetic screen uncovered a specific interaction between Sgk and the importin-alpha nuclear import receptor. In vitro GST pull down assays demonstrated a strong and direct association of importin-alpha with endogenous Sgk and exogenously expressed HA-tagged Sgk, whereas both components coimmunoprecipitate and colocalize to the nucleus after serum stimulation. Consistent with an active mechanism of nuclear localization, the nuclear import of HA-Sgk in permeabilized cells required ATP, cytoplasm, and a functional nuclear pore complex. Ectopic addition of a 107 amino acid carboxy-terminal fragment of importin-alpha, which contains the Sgk binding region, competitively inhibited the ability of endogenous importin-alpha to import Sgk into nuclei in vitro. Mutagenesis of lysines by alanine substitution defined a KKAILKKKEEK sequence within the central domain of Sgk between amino acids 131-141 that functions as a nuclear localization signal (NLS) required for the in vitro interaction with importin-alpha and for nuclear import of full-length Sgk in cultured cells. The serum-induced nuclear import of Sgk requires the NLS-dependent recognition of Sgk by importin-alpha as well as the PI3-kinase-dependent phosphorylation of Sgk. Our results define a new role importin-alpha in the stimulus-dependent control of signal transduction by nuclear localized protein kinases.

The nephroblastoma overexpressed gene (NOV/ccn3) protein associates with Notch1 extracellular domain and inhibits myoblast differentiation via Notch signaling pathway

We demonstrate a novel interaction of the nephroblastoma overexpressed gene (NOV), a member of the CCN gene family, with the Notch signaling pathway. NOV associates with the epidermal growth factor-like repeats of Notch1 by the CT (C-terminal cysteine knot) domain. The promoters of HES1 and HES5, which are the downstream transducers of Notch signaling, were activated by NOV. Expressions of NOV and Notch1 were concomitant in the presomitic mesoderm and later in the myocytes and chondrocytes, suggesting their synergistic effects in mesenchymal cell differentiation. In C2/4 myogenic cells, elevated expression of NOV led to down-regulation of MyoD and myogenin, resulting in inhibition of myotube formation. These results indicate that NOV-Notch1 association exerts a positive effect on Notch signaling and consequently suppresses myogenesis.

A chemically modified dextran inhibits smooth muscle cell growth in vitro and intimal in stent hyperplasia in vivo

PURPOSE

Intimal smooth muscle cell (SMC) hyperplasia is a main component of the arterial wall response to injury. We have investigated the capacity of a water-soluble nonanticoagulant functionalized dextran (E9) in inhibition of SMC growth in vitro and in vivo.

METHODS

E9 was obtained with chemical substitutions with anionic and hydrophobic groups on the dextran backbone. SMC proliferation (cell counting, thymidine uptake, cell cycle analysis) was followed in culture in the presence of E9. Western blot analysis against phosphorylated mitogen-activated protein kinase (MAPK), extracellular signal-regulated protein kinase 1/2, and assessment of MAPK activity on serum-stimulated SMCs also were investigated. Binding/displacement experiments, electron microscopy, and cell fractionations were used to follow the binding and internalization of radiolabeled and fluorescentlabeled E9. New Zealand white rabbit iliac arteries were injured with balloon dilatation and stent deployment. Animals were treated for 14 days with saline solution or E9 (5 mg/kg injected subcutaneously, twice daily). Morphometric analyses were carried out in each group (n = 6 arteries, 18 sections).

RESULTS

Nonanticoagulant E9 inhibited SMC proliferation in vitro. Tyrosine phosphorylation of MAPK 1/2 and MAPK activity were inhibited with E9 within 5 minutes of incubation. The binding and rapid cytoplasmic internalization of the synthetic compound was evidenced, but, in contrast to heparin, we did not detect any nuclear localization of the antiproliferative E9. In the in vivo model, qualitative modifications of neointimal structure with a thinner fibrocellular neointima were noticed after E9 treatment. Morphometric analyses of stented arteries in E9-treated animals indicated an important reduction (P <.01) of intimal growth: 33% and 45% for intimal area and intima/media ratio, respectively.

CONCLUSION

Cytoplasmic internalization of the synthetic polysaccharide correlated to the SMC growth inhibition that involved the MAPK pathway. In vivo inhibition of intimal instent hyperplasia with this nonanticoagulant derived dextran is shown providing a new candidate for a potential selective treatment of SMC proliferation.

Influence of Class I interferons on performance of vascular cells on stent material in vitro

PURPOSE

Numerous reports suggest that Class 1 interferons (IFNs), particularly IFN-gamma, inhibit migration and proliferation of different types of human cells. The objective of the present study was to determine the effect of Class I IFNs on viability and growth characteristics of human aortic endothelial cells (ECs), smooth muscle cells (SMC) and fibroblasts (FBs) in vitro.

METHODS

Stainless-steel (316-l) disks were coated with fibrin meshwork containing IFN-gamma or IFN-alpha. The discs and IFN embedded meshwork were incubated with human EC, SMC and FB, and then cultured, whereas control cells were seeded onto uncoated surfaces or plain fibrin meshwork. Concentrations of recombinant IFN varied from 5 to 20 ng/cm(2). Assessment of effect on cell viability, growth and attachment was performed utilizing Alamar Blue (AB) assay. Cell morphology was assessed by scanning electron microscopy (SEM).

RESULTS

We have now shown inhibitory capacity of IFN-gamma on all three types of unstimulated cells. The growth-inhibitory effect was maximal with SMC, while it was minimal with FB and EC. IFN-gamma abrogated mitogenic responses of SMC but not EC and partially FB to VEGF and FGF stimulation. IFN-alpha was able to inhibit EC growth and, to a lesser extent, FB, and did influence growth rates of SMC. Biochemical analysis of lactate dehydrogenase activity suggested that IFN was not toxic to vascular cells. We also measured the expression of cell adhesive molecules: P- and E-selections, PECAM and ICAM-1. These molecules were upregulated by IFN in EC. Media derived from quiescent human SMC displayed low immunoreactive elastase activity, while conditional media after IFN-gamma treatment but not IFN-alpha treatment had approximately a threefold greater activity.

CONCLUSION

These data suggest that IFN-gamma significantly inhibits SMC growth in the absence of significant endothelial toxicity and is dose-dependent; however, animal experiments are needed to further explore the antirestenotic effects of IFNs.

sgk, a primary glucocorticoid-induced gene, facilitates memory consolidation of spatial learning in rats

By using differential display PCR, we have identified 98 cDNA fragments from the rat dorsal hippocampus that are expressed differentially between the fast learners and slow learners in the water maze learning task. One of these cDNA fragments encodes the rat serum- and glucocorticoid-inducible kinase (sgk) gene. Northern blot analysis revealed that the sgk mRNA level was approximately 4-fold higher in the hippocampus of fast learners than slow learners. In situ hybridization results indicated that sgk mRNA level was increased markedly in CA1, CA3, and dentate gyrus of hippocampus in fast learners. Transient transfection of the sgk mutant DNA to the CA1 area impaired, whereas transfection of the sgk wild-type DNA facilitated water maze performance in rats. These results provide direct evidence that enhanced sgk expression facilitates memory consolidation of spatial learning in rats. These results also elucidate the molecular mechanism of glucocorticoid-induced memory facilitation in mammals.

Heparin and coumadin versus acetylsalicylic acid for prevention of restenosis after coronary angioplasty

The purpose of the present study was to determine whether postprocedural antithrombotic therapy with prolonged heparin infusion followed by 6 months of oral anticoagulation in addition to acetylsalicylic acid (ASA) reduces the incidence of angiographic restenosis after successful PTCA. One hundred ninety-one patients with uncomplicated PTCA were randomized into two groups: one group was discharged with ASA 100 mg only (G1) and the other group was additionally treated with 12-24 hr of heparin infusion and overlapping oral anticoagulation with coumadin for 6 months (G2). The two groups were comparable with respect to age, gender, coronary risk profile, clinical presentation, and angiographic lesion characteristics. Stents were implanted in 33% and 36% of the G1 and G2 patients, respectively. In-hospital myocardial infarction occurred in 4% of the G1 and 3% of the G2 patients. One patient in G1 died of subacute stent thrombosis (day 3). Six-month angiographic follow-up was obtained in 90% of G1 patients and 94% of G2 patients. Restenosis occurred in 30% and 33% of the patients and mean diameter stenoses at follow-up were 40% +/- 28% and 39% +/- 24%, respectively. Thrombin inhibition with heparin infusion followed by 6 months of oral anticoagulation did not reduce angiographic restenosis among patients undergoing PTCA with or without stent implantation. The occurrence of acute ischemic complications was also comparable in the two groups.

Regulation and physiological roles of serum- and glucocorticoid-induced protein kinase isoforms

Serum- and glucocorticoid-induced protein kinase 1 (SGK1) was identified in 1993 as an immediate early gene whose mRNA levels increase dramatically within 30 minutes when cells are exposed to serum or glucocorticoids, or both. Subsequently, many other agonists, acting through a variety of signal transduction pathways, have been shown to induce SGK1 gene transcription in cells and tissues. SGK1 is a member of the "AGC" subfamily, which includes protein kinases A, G, and C, and its catalytic domain is most similar to protein kinase B (PKB). Like PKB, SGK1 is activated by phosphorylation in response to signals that stimulate phosphatidylinositol 3-kinase, and this is mediated by 3-phosphoinositide-dependent protein kinase 1 (PDK1) and another protein kinase that has yet to be identified. Thus, SGK1 is remarkable in being activated at both the transcriptional and posttranslational levels by a huge number of extracellular signals. In contrast, little is known about the transcriptional regulation of the two closely related isoforms SGK2 and SGK3, although they can be activated by phosphorylation. The substrate specificity of SGK isoforms superficially resembles that of PKB in that serine and threonine residues lying in Arg-Xaa-Arg-Xaa-Xaa-Ser/Thr sequences (where Xaa is a variable amino acid) are phosphorylated. However, although they may have some substrates in common, evidence is emerging that SGK1 and PKB phosphorylate distinct proteins and have different functions in vivo. In particular, SGK1 plays an important role in activating certain potassium, sodium, and chloride channels, suggesting an involvement in the regulation of processes such as cell survival, neuronal excitability, and renal sodium excretion. Moreover, sustained high levels of SGK1 protein and activity may contribute to conditions such as hypertension and diabetic nephropathy. This raises the possibility that specific inhibitors of SGK1 may have therapeutic potential for the treatment of several diseases.

COP-1, a member of the CCN family, is a heparin-induced growth arrest specific gene in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) hyperplasia is responsible for the failure of 15-30% of vascular surgical procedures such as coronary artery bypass grafts and angioplasties. We and others have shown that heparin suppresses VSMC proliferation in vivo and in cell culture. We hypothesize that heparin inhibits VSMC proliferation by binding to cell surface receptors, resulting in selective modulation of mitogenic signal transduction pathways and altered transcription of a specific subset of growth regulatory genes. To test this idea, we used subtractive hybridization to identify differentially expressed mRNAs in heparin-treated and untreated VSMC. We identified a heparin induced mRNA identical to Cop-1, a member of the CCN family of proteins which are secreted, cysteine-rich modular proteins involved in growth regulation and migration. Cop-1 from smooth muscle cells appears to have a different expression pattern and possibly different functions than Cop-1 from other cells. Cop-1 mRNA is expressed at high levels in quiescent VSMC and at low levels in proliferating VSMC, an expression pattern highly characteristic of growth arrest specific genes. Cop-1 mRNA is expressed at high levels in heparin treated VSMC and COP-1 protein is secreted into culture medium. In tissues, Cop-1 expression is observed in the uninjured rat aorta suggesting a possible role for Cop-1 in vivo. We found PDGF, but not EGF, inhibits the expression of Cop-1 in VSMC. Neither TGF-beta nor interferon-beta, two inhibitors of VSMC proliferation, were able to induce Cop-1 expression. In addition, heparin does not induce Cop-1 mRNA in endothelial cells and VSMC resistant to the antiproliferative effect of heparin. Conditioned medium from cells over-expressing COP-1 protein inhibits VSMC proliferation in culture. Together, our data indicate that COP-1 may play a role in the antiproliferative mechanism of action of heparin.

Tissue-specific expression of the transcriptionally regulated serum and glucocorticoid-inducible protein kinase (Sgk) during mouse embryogenesis

In situ hybridization of mouse embryo whole mounts and sagittal sections revealed a tissue- and stage-specific expression pattern of the transcriptionally regulated serum and glucocorticoid-inducible protein kinase (sgk) during embryogenesis. Sgk expression is first observed at embryonic day 8.5 (E8.5) in the decidua and yolk sac, and then during developmental stages E9.5 through E12.5 this kinase is highly localized in the heart chamber, otic vesicle, blood vessels surrounding the somites, and lung buds. At the later stages of mouse embryogenesis, E13.5 through E16.5, sgk expression becomes highly concentrated in brain (choroid plexus), distal epithelium and the terminal bronchi/bronchioles, adrenal gland, liver, thymus and intestines, remains high in heart tissue, and is expressed at a low level in the other embryonic tissues.

Hyperosmotic stress stimulates promoter activity and regulates cellular utilization of the serum- and glucocorticoid-inducible protein kinase (Sgk) by a p38 MAPK-dependent pathway

We have established that the serum- and glucocorticoid-inducible protein kinase (Sgk) is a new component of the hyperosmotic stress response. Treatment of NMuMg mammary epithelial cells with the organic osmolyte, sorbitol, caused the stable accumulation of Sgk transcripts and protein after an approximately 4-h lag. Transient transfection of a series of sgk-CAT reporter plasmids containing either 5' deletions or continuous 6-base pair substitutions identified a hyperosmotic stress-regulated element that is GC-rich and is necessary for the sorbitol stimulation of sgk gene promoter activity. Gel shift analysis identified four major DNA-protein complexes in the hyperosmotic stress-regulated element that, by competition with excess consensus wild type and mutant oligonucleotides and by antibody supershifts, contains the Sp1 transcription factor. Several lines of evidence suggest that the p38 MAPK signaling pathway mediates the hyperosmotic stress stimulation of sgk gene expression. Treatment with pharmacological inhibitors of p38 MAPK or with a dominant negative form of MKK3, an upstream regulator of p38 MAPK, significantly reduced or ablated the sorbitol induction of sgk promoter activity or protein production. Using an in vitro peptide transphosphorylation assay, sorbitol treatment activates either endogenous or exogenous Sgk that is localized to the cytoplasmic compartment. Thus, we propose that the stimulated expression of enzymatically active Sgk after sorbitol treatment is a newly defined component of the p38 MAPK-mediated response to hyperosmotic stress.

Heparin-like molecules inhibit pulmonary vascular pericyte proliferation in vitro

Proliferation of vascular pericytes (PCs), smooth muscle-like cells found in the distal microvasculature, contributes to vascular remodeling in pulmonary hypertension. The factors controlling lung PC quiescence in normal states are poorly understood. We demonstrate that exogenous heparin and heparan sulfate proteoglycans inhibit rat lung PC proliferation in vitro as does pulmonary vascular subendothelial matrix, particularly its heparan sulfate component. Heparin inhibits the intracellular alkalinization essential to proliferation, and we show that inhibition of alkalinization by 5-(N, N-dimethyl)amiloride also reduces PC proliferation. As shown by DNA staining and fluorescence-activated cell sorting analysis, heparin does not induce apoptosis in PCs. However, heparin maintains lung PCs in the G(0)/G(1) growth phase. Heparin induces production of p21, a potent inhibitor of cyclin-dependent kinases, thereby potentially identifying a fundamental mechanism by which heparin inhibits proliferation in smooth muscle-like cells. These studies establish additional similarities between lung PCs and smooth muscle cells and provide further understanding of growth control in the lung microvasculature. They also further support the rationale that heparin-like molecules might be therapeutically beneficial in pulmonary hypertension.

Regulation of the epithelial Na+ channel by aldosterone: open questions and emerging answers

Aldosterone is the principal adrenal steroid controlling Na+ retention in amphibians and mammalians. It acts primarily by increasing the apical Na+ permeability through activation of the epithelial Na+ channel (ENaC). The cellular events mediating the hormonal action are mostly unknown. Early studies have provided evidence that the hormone functions to activate or translocate pre-existing channels by a yet undefined mechanism. In addition, enhanced de novo channel synthesis appears to take place as well. The molecular cloning of the three ENaC subunits has provided new powerful tools for testing and confirming this hypothesis, as well as for characterizing mechanisms by which ENaC is regulated. Another important development is the recent identification of several cDNAs corresponding to aldosterone-induced and suppressed mRNAs. The study of these genes and their putative interactions with ENaC is likely to provide important clues to the mechanisms by which aldosterone controls the apical Na+ permeability of tight epithelia. This article reviews recent developments in the field that may lead to the elucidation of the mechanisms by which the hormone controls Na+ transport.

Regulation of sgk by aldosterone and its effects on the epithelial Na(+) channel

Aldosterone is the major corticosteroid regulating Na(+) absorption in tight epithelia and acts primarily by activating the epithelial Na(+) channel (ENaC) through unknown induced proteins. Recently, it has been reported that aldosterone induces the serum- and glucocorticoid-dependent kinase sgk and that coexpressing ENaC with this kinase in Xenopus laevis oocytes increases the amiloride-sensitive Na(+) current (Chen SY, Bhargava A, Mastroberardino L, Meijer OC, Wang J, Buse P, Firestone GL, Verrey F, and Pearce D. Proc Natl Acad Sci USA 96: 2514-2519, 1999). The present study was done to further characterize regulation of sgk by aldosterone in native mammalian epithelia and to examine its effect on ENaC. With both in vivo and in vitro protocols, an almost fivefold increase in the abundance of sgk mRNA has been demonstrated in rat kidney and colon but not in lung. Induction of sgk by aldosterone was detected in kidney cortex and medulla, whereas the papilla expressed a constitutively high level of the kinase. The increase in sgk mRNA was detected as early as 30 min after the hormonal application and was independent of de novo protein synthesis. The observed aldosterone dose-response relationships suggest that the response is mediated, at least in part, by occupancy of the mineralocorticoid receptor. Coexpressing sgk and ENaC in Xenopus oocytes evoked a fourfold increase in the amiloride-blockable Na(+) channel activity. A point mutation in the beta-subunit known to impair regulation of the channel by Nedd4 (Y618A) had no significant effect on the response to sgk.

Sustained release of heparin from polymeric particles for inhibition of human vascular smooth muscle cell proliferation

Vascular smooth muscle cell (SMC) growth plays an important role in atherosclerosis, restenosis and venous bypass graft disease. With systemic drug administration no effective therapy for restenosis and venous bypass graft disease is available. This could be due to low local concentrations of the drugs at the target site. A directed delivery of drugs to tissues with a sustained release system during percutaneous transluminal coronary angioplasty (PTCA) or during bypass surgery could provide high concentrations of drugs at the target site and avoid systemic side effects. In the present study heparin was encapsulated by spray-drying into biodegradable poly(D, L-lactic-co-glycolic acid) (PLGA) to obtain a system for prolonged drug release. SMC were cultured from saphenous vein explants obtained from patients undergoing coronary bypass surgery. Cell proliferation was measured by [(3)H]thymidine incorporation. Heparin release from PLGA 50:50 microspheres in an isoosmolar PBS buffer (pH=7.4) showed a triphasic profile with an initial burst (completed after 24 h), a dormant period and a final stage with increased release rate, which lasted about 10-14 days. Cell proliferation as measured by [(3)H]thymidine incorporation was markedly stimulated by platelet-derived growth factor-BB (PDGF-BB) (5 ng/ml) or serum (5%). Proliferation of SMC was equally reduced (50%; P<0.05; n=9-11) by native heparin or heparin released from PLGA microspheres, while PLGA microspheres without heparin loading had no effect on [(3)H]thymidine incorporation in human SMC. Similar results were also obtained when SMC were stimulated with 5% serum instead of PDGF-BB (50%; P<0.05; n=6). Thus, heparin encapsulated into PLGA microspheres was released over a prolonged period of time and thereby effectively reduced human SMC proliferation stimulated either with PDGF or serum. Biodegradable PLGA microspheres may also be used to encapsulate other antiproliferative agents and provide a new approach for local drug delivery after PTCA. This may help to prevent restenosis after PTCA or to reduce graft disease after coronary bypass graft surgery.

Identification and cloning of a new gene (2A3-2), homologous to human translational elongation factor, upregulated in a proliferating rat smooth muscle cell line and in carotid hyperplasia

Smooth muscle cells (SMCs), before migration and proliferation in the intima of the vessel wall, change from a normal contractile to a pathological proliferating phenotype. The molecular regulatory mechanisms implicated in such phenotypic changes remain poorly understood. In this study, using differential display, we have isolated for the first time a new gene (2A3-2) that is overexpressed in a rapidly proliferating, but not synthetic, rat SMC line. This was further confirmed by northern blot performed on the 2 cell types. Moreover, balloon catheter injury of rat carotids showed, by a virtual northern technique, an upregulation of this new gene in hyperplasia vessels. This new gene (2A3-2, 1.2 kb) was present in skeletal muscle, heart, aorta, lung, liver, kidney, and spleen. In addition, 5' rapid amplification of cDNA ends (5' RACE) allowed the cloning and sequencing of this 1.2-kb gene. Comparison of this newly identified gene sequence with data banks showed a strong homology to human and bovine mitochondrial translational elongation factor. The 2A3-2 gene, identified in this study, may play a vital role in the cascade of events implicated in switching SMC phenotype from a quiescent to a proliferate one.

Serum and glucocorticoid-inducible kinase (SGK) is a target of the PI 3-kinase-stimulated signaling pathway

Serum and glucocorticoid-inducible kinase (SGK) is a novel member of the serine/threonine protein kinase family that is transcriptionally regulated. In this study, we have investigated the regulatory mechanisms that control SGK activity. We have established a peptide kinase assay for SGK and present evidence demonstrating that SGK is a component of the phosphoinositide 3 (PI 3)-kinase signaling pathway. Treatment of human embryo kidney 293 cells with insulin, IGF-1 or pervanadate induced a 3- to 12-fold activation of ectopically expressed SGK. Activation was completely abolished by pretreatment of cells with the PI 3-kinase inhibitor, LY294002. Treatment of activated SGK with protein phosphatase 2A in vitro led to kinase inactivation. Consistent with the similarity of SGK to other second-messenger regulated kinases, mutation of putative phosphorylation sites at Thr256 and Ser422 inhibited SGK activation. Cotransfection of PDK1 with SGK caused a 6-fold activation of SGK activity, whereas kinase-dead PDK1 caused no activation. GST-pulldown assays revealed a direct interaction between PDK1 and the catalytic domain of SGK. Treatment of rat mammary tumor cells with serum caused hyperphosphorylation of endogenous SGK, and promoted translocation to the nucleus. Both hyperphosphorylation and nuclear translocation could be inhibited by wortmannin, but not by rapamycin.

Characterization of [3H]-heparin binding in human vascular smooth muscle cells and its relationship to the inhibition of DNA synthesis

1. The glycosaminoglycan heparin inhibits vascular smooth muscle cell (VSMC) proliferation and migration, but the mechanism of its antiproliferative action remains unclear. Heparin has been reported to bind to high affinity cell surface sites on animal VSMC before undergoing receptor mediated endocytosis resulting in signal transduction into the cytoplasm and modulation of genes involved in proliferation. In this study, we have characterized the binding of [3H]-heparin to human saphenous vein-derived VSMC and examined whether there is any relationship between the affinity of [3H]-heparin binding and the inhibitory effect of heparin and its structural analogues on DNA synthesis. 2. At 4 degrees C [3H]-heparin binding to human VSMC occurred in a specific, time and concentration-dependent manner and was not influenced by the removal of calcium ions. Binding of the ligand appeared to occur to the cell surface and was both saturable and reversible. Kinetic and steady state data indicated a single class of binding sites. 3. The pharmacology of [3H]-heparin binding was examined in displacement studies using unlabelled heparin and structural analogues. A comparison of the rank potencies of heparin, heparan sulphate fraction II, low molecular weight heparin and trehalose octasulphate showed that there was a marked discrepancy between their estimated affinities in the binding assays and their effect on DNA synthesis. 4. In summary, we have characterized the heparin binding site on human saphenous vein-derived VSMC. Our findings suggest that the action of heparin and its analogues on DNA synthesis does not simply reflect an interaction with the cell-associated heparin binding site defined in these studies, but may also be determined by the internalization and metabolism of the glycosaminoglycan(s).

Heparin rapidly and selectively regulates protein tyrosine phosphorylation in vascular smooth muscle cells

Aberrant vascular smooth muscle cell (VSMC) hyperplasia is the hallmark of atherosclerosis and restenosis seen after vascular surgery. Heparin inhibits VSMC proliferation in animal models and in cell culture. To test our hypothesis that heparin mediates its antiproliferative effect by altering phosphorylation of key mitogenic signaling proteins in VSMC, we examined tyrosine phosphorylation of cellular proteins in quiescent VSMC stimulated with serum in the presence or absence of heparin. Western blot analysis with anti-phosphotyrosine antibodies shows that heparin specifically alters the tyrosine phosphorylation of only two proteins (42 kDa and 200 kDa). The 200 kDa protein (p200) is dephosphorylated within 2.5 min after heparin treatment with an IC50 that closely parallels the IC50 for growth inhibition. Studies using the tyrosine phosphatase inhibitor, sodium orthovanadate, indicate that heparin blocks p200 phosphorylation by inhibiting a kinase. Phosphorylation of p200 is not altered in heparin-resistant cells, supporting a role for p200 in mediating the antiproliferative effect of heparin. Purification and sequence analysis indicate that p200 exhibits very high homology to the heavy chain of nonmuscle myosin IIA. The 42 kDa protein, identified as mitogen activated protein kinase (MAPK), undergoes dephosphorylation within 15 min after heparin treatment, and this effect is also not seen in heparin-resistant cells. The identification of only two heparin-regulated tyrosine phosphoproteins suggests that they may be key mediators of the antiproliferative effect of heparin.