Nitric oxide attenuates IGF-I-induced aortic smooth muscle cell motility by decreasing Rac1 activity: essential role of PTP-PEST and p130cas

Recent data support the hypothesis that reactive oxygen species (ROS) play a central role in the initiation and progression of vascular diseases. An important vasoprotective function related to the regulation of ROS levels appears to be the antioxidant capacity of nitric oxide (NO). We previously reported that treatment with NO decreases phosphotyrosine levels of adapter protein p130(cas) by increasing protein tyrosine phosphatase-proline, glutamate, serine, and threonine sequence protein (PTP-PEST) activity, which leads to the suppression of agonist-induced H(2)O(2) elevation and motility in cultured rat aortic smooth muscle cells (SMCs). The present study was performed to investigate the hypotheses that 1) IGF-I increases the activity of the small GTPase Rac1 as well as H(2)O(2) levels and 2) NO suppresses IGF-I-induced H(2)O(2) elevation by decreasing Rac1 activity via increased PTP-PEST activity and dephosphorylation of p130(cas). We report that IGF-I induces phosphorylation of p130(cas) and activation of Rac1 and that NO attenuates these effects. The effects of NO are mimicked by the overexpression of PTP-PEST or dominant-negative (dn)-p130(cas) and antagonized by the expression of dn-PTP-PEST or p130(cas). We conclude that IGF-I induces rat aortic SMC motility by increasing phosphotyrosine levels of p130(cas) and activating Rac1 and that NO decreases motility by activating PTP-PEST, inducing dephosphorylating p130(cas), and decreasing Rac1 activity. Decreased Rac1 activity lowers intracellular H(2)O(2) levels, thus attenuating cell motility.

Essential role of protein kinase G and decreased cytoplasmic Ca2+ levels in NO-induced inhibition of rat aortic smooth muscle cell motility

Hyperinsulinemia is a major risk factor for the development of vascular disease. We have reported that insulin increases the motility of vascular smooth muscle cells via a hydrogen peroxide-mediated mechanism and that nitric oxide (NO) attenuates insulin-induced motility via a cGMP-mediated mechanism. Events downstream of cGMP elevation have not yet been investigated. The aim of our study was to test the hypothesis that antimotogenic effects of NO and cGMP in cultured rat aortic smooth muscle cells are mediated via PKG, followed by reduction of cytoplasmic Ca(2+) levels and increased protein tyrosine phosphatase-proline, glutamate, serine, and threonine activity, leading to suppression of agonist-induced elevation of hydrogen peroxide levels and cell motility. Treatment of primary cultures with adenovirus expressing PKG-1alpha mimicked NO-induced inhibition of insulin-elicited hydrogen peroxide elevation and cell motility, whereas treatment with the pharmacological PKG inhibitor Rp-8-bromo-3',5'-cyclic monophosphorothioate (Rp-8-Br-cGMPS) rescued the stimulatory effects of insulin that were suppressed by NO donor. Treatment of cells with insulin failed to increase cytoplasmic Ca(2+) levels, whereas NO donor decreased cytoplasmic Ca(2+) levels in the presence or absence of insulin. Treatment of cells with the Ca(2+) chelator BAPTA mimicked the effects of PKG and the NO donor and increased the activity of PTP-PEST. Finally, treatment with a dominant negative allele of PTP-PEST reversed the inhibitory effect of BAPTA on cell motility and hydrogen peroxide elevation. We conclude that NO-induced inhibition of cell motility occurs via PKG-mediated reduction of basal cytoplasmic Ca(2+) levels, followed by increased PTP-PEST activity, leading to decreased hydrogen peroxide levels and reduced cell motility.

Nitric oxide attenuates insulin- or IGF-I-stimulated aortic smooth muscle cell motility by decreasing H2O2 levels: essential role of cGMP

Insulin and insulin-like growth factor I (IGF-I) both play important roles in vascular remodeling. Moreover, nitric oxide (NO) is well established as a counterregulatory agent that opposes the actions of several vascular agonists, in part by decreasing smooth muscle motility. We tested the hypothesis that NO blocks insulin or IGF-I-induced rat aortic smooth muscle cell motility via a mechanism involving the attenuation of agonist-induced elevation of hydrogen peroxide levels and cGMP as mediator. Insulin or IGF-I induced an increase of hydrogen peroxide levels and cell motility. Both effects were blocked by catalase or diphenyleneiodonium, indicating that hydrogen peroxide elevation is necessary for induction of cell motility. Two NO donors mimicked the effects of catalase, indicating that NO decreases cell motility by suppressing agonist-induced elevation of hydrogen peroxide. A cGMP analogue mimicked the effect of NO, whereas a guanyl cyclase inhibitor blocked the effect of NO on hydrogen peroxide levels, indicating that elevation of cGMP is both necessary and sufficient to account for the reduction of hydrogen peroxide levels. A NO donor as well as a cGMP analogue attenuated insulin-stimulated NADPH activity, indicating that NO decreases hydrogen peroxide levels by inhibiting the generation of superoxide, via a cGMP-mediated mechanism. Finally, exogenous hydrogen peroxide increased cell motility and reversed the inhibitory effect of cGMP. These results support the view that NO plays an antioxidant role via reduction of hydrogen peroxide in cultured rat aortic smooth muscle cells and that this effect is both necessary and sufficient to account for its capacity to decrease cell motility.

Expression of mammalian Rab Escort protein-1 and -2 in yeast Saccharomyces cerevisiae

Rab GTPases are post-translationally geranylgeranylated on their C-terminal cysteines by Rab geranylgeranyl transferase (RabGGTase) and this modification is essential for their biological activity. Rab Escort Protein (REP) is a molecular chaperone that assists in the prenylation reaction carried out by RabGGTase. Mutations in the REP-1 gene lead to progressive retinal degradation and blindness in humans. Despite the significant interest in REP proteins, their preparative production remains challenging. We report here an inducible expression system for the production of REP-1 and REP-2 in yeast Saccharomyces cerevisiae at levels 3.5 and 2mg/L, respectively. The REP-1 was found to be toxic for yeast cells and its toxicity is proposed to be associated with the formation of unproductive Ypt:REP-1 complexes. To minimize the toxic effect of REP-1, the recombinant protein expression was induced at the end of the exponential phase. Under these conditions, the GAL1 promoter is no longer repressed due to exhaustion of glucose and utilization of ethanol as a carbon source. This expression procedure was successfully scaled up to 30L for both proteins. The REP-1 and REP-2 were purified using a combination of affinity and anion-exchange chromatography. Purified proteins were functionally active, as determined by a fluorescent Rab binding assay and in vitro prenylation. The reported procedure provides a reliable source of REP proteins for biochemical and structural studies.

Interaction of yeast Rab geranylgeranyl transferase with its protein and lipid substrates

Small GTPases from the Rab/Ypt family regulate events of vesicular traffic in eukaryotic cells. For their activity, Rab proteins require a posttranslational modification that is conferred by Rab geranylgeranyltransferase (RabGGTase), which attaches geranylgeranyl moieties onto two cysteines of their C terminus. RabGGTase is present in both lower and higher eukaryotes in the form of heterodimers composed of alpha and beta subunits. However, the alpha subunits of RabGGTases from lower eukaryotes, including Saccharomyces cerevisiae (yRabGGTase), are half the size of the corresponding subunit of the mammalian enzyme. This difference is due to the presence of additional immunoglobulin (Ig)-like and leucine rich (LRR) domains in the mammalian transferase. To understand the possible evolutionary implications and functional consequences of structural differences between RabGGTases of higher and lower eukaryotes, we have investigated the interactions of yeast RabGGTase with its lipid and protein substrate. We have demonstrated that geranylgeranyl pyrophosphate binds to the enzyme with an affinity of ca. 40 nM, while binding of farnesyl pyrophosphate is much weaker, with a K(d) value of ca. 750 nM. This finding suggests that despite the structural difference, yRabGGTase selects its lipid substrate in a fashion similar to mammalian RabGGTase. However, unlike the mammalian enzyme, yRabGGTase binds prenylated and unprenylated Ypt1p:Mrs6p complexes with similar affinities (K(d) ca. 200 nM). Moreover, in contrast to the mammalian enzyme, phosphoisoprenoids do not influence the affinity of Mrs6p for yRabGGTase. Using an in vitro prenylation assay, we have demonstrated that yRabGGTase can prenylate Rab proteins in complex with mammalian REP-1, thus indicating that neither the LRR nor the Ig-like domains, nor the recently discovered alternative pathway of catalytic complex assembly, are essential for the catalytic activity of RabGGTase. Despite the ability to function in concert with yRabGGTase in vitro, expression of mammalian REP-1 could not complement deletion of MRS6 gene in S. cerevisiae in vivo. The implications of these findings are discussed.

Parentage analysis for three Romanian families by DNA-fingerprinting

In forensic medicine, DNA fingerprinting for human identification and paternity testing is becoming a necessary procedure. The genetic locus D1S80 (MCT118) with Hinf I polymorphism of its 5' flanking sequence, HUMTH01 and D21S11 have been successfully amplified from human genomic DNA isolated from blood (50 ng from each sample) by the polymerase chain reaction (PCR) using oligonucleotide primers complementary to the flanking sequences as primers for amplification. DNA bands were detected by ethidium bromide staining after electrophoresis on agarose gels or high-resolution SDS-PAGE. Analysis of these VNTR loci was thus achieved without the need for Southern blot or radioactive material. The small size of the DNA fragments produced in the PCR amplification permitted good resolution of individual alleles. The precise specification of the number of tandem repeats present in each allelic fragment was reproducible from one analysis to another. The aim of this study includes three paternity testing cases; they are the first three human DNA-fingerprints performed in Romania.