Intracellular Signal-transducing elements involved in transendothelial migration of lymphoma cells

To investigate the molecular mechanisms underlying transendothelial migration of tumor cells, an essential process for their hematogenous dissemination, we developed an in vitro model system that allows the separate monitoring of cell adhesion and transmigration processes. This system uses a human pre-B lymphoma cell line, Nalm-6, and a cultured mouse endothelial cell line, KOP2.16. Nalm-6 cells rapidly adhered to KOP2.16 and subsequently transmigrated underneath them. Using this model, we examined the effects on transendothelial migration, of various reagents which specifically interfere with the function of intracellular signal transduction molecules. Treatment of Nalm-6 cells with wortmannin (WMN), herbimycin A, pertussis toxin, or C3 exoenzyme of Clostridium botulinum, which specifically inhibit P13 kinase and/or myosin light chain kinase, herbimycin-sensitive tyrosine kinases, heterotrimeric G proteins, and the small G proteins, and the small G proteins rho/rac, respectively, reduced transmigration in a dose-dependent manner, Pretreatment of KOP2.16 endothelial cells with WMN also reduced transmigration in a dose-dependent manner. Binding of Nalm-6 binding to KOp2.16 was not affected, even when Nalm-6 or KOP2.16 cells were pretreated with these inhibitors, indicating that the reduction of transmigration was not due to a reduction of Nalm-6 to KOP2.16. These results also indicate that the signal transduction pathway(s) involved in transmigration can be dissociated from that of adhesion. Our results support the notion that endothelial cells are not a passive barrier in lymphoma extravasation, but that they assist lymphoma cell extravasation.

Activation of the osmo-sensitive chloride conductance involves P21rho and is accompanied by a transient reorganization of the F-actin cytoskeleton

Hypo-osmotic stimulation of human Intestine 407 cells rapidly activated compensatory CL- and K+ conductances that limited excessive cell swelling and, finally, restored the original cell volume. Osmotic cell swelling was accompanied by a rapid and transient reorganization of the F-actin cytoskeleton, affecting both stress fibers as well as apical ruffles. In addition, an increase in total cellular F-actin was observed. Pretreatment of the cells with recombinant Clostridium botulinum C3 exoenzyme, but not with mutant enzyme (C3-E173Q) devoid of ADP-ribosyltransferase activity, greatly reduced the activation of the osmo-sensitive anion efflux, suggesting a role for the ras-related GTPase p21rho. In contrast, introducing dominant negative N17-p21rac into the cells did not affect the volume-sensitive efflux. Cell swelling-induced reorganization of F-actin coincided with a transient, C3 exoenzyme-sensitive tyrosine phosphorylation of p125 focal adhesion kinase (p125FAK) as well as with an increase in phosphatidylinositol-3-kinase (PtdIns-3-kinase) activity. Pretreatment of the cells with wortmannin, a specific inhibitor of PtdIns-3-kinase, largely inhibited the volume-sensitive ion efflux. Taken together, our results indicate the involvement of a p21rho signaling cascade and actin filaments in the activation of volume-sensitive chloride channels.

Rhotekin, a new putative target for Rho bearing homology to a serine/threonine kinase, PKN, and rhophilin in the rho-binding domain

Using a mouse embryo cDNA library, we conducted a two-hybrid screening to identify new partners for the small GTPase Rho. One clone obtained by this procedure contained a novel cDNA of 291 base pairs and interacted strongly with RhoA and RhoC, weakly with RhoB, and not at all with Rac1 and Cdc42Hs. Full-length cDNAs were then isolated from a mouse brain library. While multiple splicing variants were common, we identified three cDNAs with an identical open reading frame encoding a 61-kDa protein that we named rhotekin (from the Japanese "teki," meaning target). The N-terminal part of rhotekin, encoded by the initial cDNA and produced in bacteria as a glutathione S-transferase fusion protein, exhibited in vitro binding to 35S-labeled guanosine 5'-3-O-(thio)triphosphate-bound Rho, but not to Rac1 or Cdc42Hs in ligand overlay assays. In addition, this peptide inhibited both endogenous and GTPase-activating protein-stimulated Rho GTPase activity. The amino acid sequence of this region shares approximately 30% identity with the Rho-binding domains of rhophilin and a serine/threonine kinase, PKN, two other Rho target proteins that we recently identified (Watanabe, G., Saito, Y., Madaule, P., Ishizaki, T., Fujisawa, K., Morii, N., Mukai, H., Ono, Y., Kakizuka, A., and Narumiya, S. (1996) Science 271, 645-648). Thus, not only is rhotekin a novel partner for Rho, but it also belongs to a wide family of proteins that bear a consensus Rho-binding sequence at the N terminus. To our knowledge, this is the first conserved sequence for Rho effectors, and we have termed this region Rho effector motif class 1.

Roles of insulin, guanosine 5'-[gamma-thio]triphosphate and phorbol 12-myristate 13-acetate in signalling pathways of GLUT4 translocation

Insulin, guanosine 5'-[gamma-thio]triphosphate (GTP[S] and phorbol 12-myristate 13-acetate (PMA) trigger the translocation of Gl UT4 (type 4 glucose transporter; insulin-sensitive glucose transporter) from an intracellular pool to the cell surface. We have developed a highly sensitive and quantitative method to detect GLUT4 immunologically on the surface of intact 3T3-L1 adipocytes and Chinese hamster ovary (CHO) cells, using c-myc epitope-tagged GLUT4 (GLUT4myc). We examined the roles of insulin, GTP[S] and PMA in the signalling pathways of GLUT4 translocation in the CHO cell system. Among small molecular GTP-binding proteins, ras, rab3D, rad and rho seem to be candidates as signal transmitters of insulin-stimulated GLUT4 translocation. Overexpression of wild-type H-ras and the dominant negative mutant H-rass17N in our cell system respectively enhanced and blocked insulin-stimulated activation of mitogen-activated protein kinase, but did not affect insulin-stimulated GLUT4 translocation. Overexpression of rab3D or rad in the cells did not affect GLUT4 translocation triggered by insulin, GTP[S] or PMA. Treatment with Botulinum C3 exoenzyme, a specific inhibitor of rho, had no effect on GLUT4 translocation induced by insulin, GTP[S] or PMA. Therefore these small molecular GTP-binding proteins are not likely to be involved in GLUT4 translocation. In addition, insulin, GTP[S] and PMA apparently stimulate GLUT4 translocation through independent pathways.

The small GTP-binding protein Rho binds to and activates a 160 kDa Ser/Thr protein kinase homologous to myotonic dystrophy kinase

The small GTP-binding protein Rho functions as a molecular switch in the formation of focal adhesions and stress fibers, cytokinesis and transcriptional activation. The biochemical mechanism underlying these actions remains unknown. Using a ligand overlay assay, we purified a 160 kDa platelet protein that bound specifically to GTP-bound Rho. This protein, p160, underwent autophosphorylation at its serine and threonine residues and showed the kinase activity to exogenous substrates. Both activities were enhanced by the addition of GTP-bound Rho. A cDNA encoding p160 coded for a 1354 amino acid protein. This protein has a Ser/Thr kinase domain in its N-terminus, followed by a coiled-coil structure approximately 600 amino acids long, and a cysteine-rich zinc finger-like motif and a pleckstrin homology region in the C-terminus. The N-terminus region including a kinase domain and a part of coiled-coil structure showed strong homology to myotonic dystrophy kinase over 500 residues. When co-expressed with RhoA in COS cells, p160 was co-precipitated with the expressed Rho and its kinase activity was activated, indicating that p160 can associate physically and functionally with Rho both in vitro and in vivo.

The involvement of the rho gene product, a small molecular weight GTP-binding protein, in polyploidization of a human megakaryocytic cell line, CMK

The role of rho proteins, which are ras p21-related small GTP-binding proteins, in megakaryocyte endomitosis was examined using a botulinum C3 exoenzyme (C3), a rho inactivating enzyme. The megakaryocytic leukemia cell line CMK expressed high levels of rhoA and rhoC mRNAs, whereas rhoB mRNA was expressed at a very low level. The addition of C3 to the culture medium caused ADP-ribosylation of the rho proteins in CMK cells in a dose- and time-dependent manner. This procedure also induced a higher frequency of polyploid cells with increased glycoprotein (GP) IIb/IIIa antigens on the cells. This effect of C3 on both ploidy and the antigen expression was abolished by prior incubation of C3 with an anti-C3 monoclonal antibody. Cytochalasin B, an actin polymerization inhibitor, also induced polyploid cells; however, it did not stimulate the expression of GP IIb/IIIa antigens in CMK cells. This finding suggests that C3-induced increase in the expression of GP IIb/IIIa antigens was not through the actin microfilament disassembly. The present study suggests that the rho p21 is a partly regulatory component in polyploidization and GP IIb/IIIa antigen expression of a human megakaryocytic cell line, CMK.

Protein kinase N (PKN) and PKN-related protein rhophilin as targets of small GTPase Rho

The Rho guanosine 5'-triphosphatase (GTPase) cycles between the active guanosine triphosphate (GTP)-bound form and the inactive guanosine diphosphate-bound form and regulates cell adhesion and cytokinesis, but how it exerts these actions is unknown. The yeast two-hybrid system was used to clone a complementary DNA for a protein (designated Rhophilin) that specifically bound to GTP-Rho. The Rho-binding domain of this protein has 40 percent identity with a putative regulatory domain of a protein kinase, PKN. PKN itself bound to GTP-Rho and was activated by this binding both in vitro and in vivo. This study indicates that a serine-threonine protein kinase is a Rho effector and presents an amino acid sequence motif for binding to GTP-Rho that may be shared by a family of Rho target proteins.

A novel partner for the GTP-bound forms of rho and rac

Using the yeast two hybrid system and overlay assays we identified a putative rholrac effector, citron, which interacts with the GTP-bound forms of rho and rac1, but not with cdc42. Extensive homologies to known proteins were not observed. This 183 kDa protein contains a C6H2 zinc finger, a PH domain, and a long coiled-coil forming region including 4 leucine zippers and the rholrac binding site. We recently identified three others putative rho effectors characterized by a common rho binding motif. Citron does not share this motif and displays a distinctive protein organization, thus defining a separate class of rho partners.

Synergistic activation of rat brain phospholipase D by ADP-ribosylation factor and rhoA p21, and its inhibition by Clostridium botulinum C3 exoenzyme

An activator of rat brain phospholipase D (PLD) that is distinct from the already identified PLD activator, ADP-ribosylation factor (ARF), was partially purified from bovine brain cytosol by a series of chromatographic steps. The partially purified preparation contained a 22-kDa substrate for Clostridium botulinum C3 exoenzyme ADP-ribosyltransferase, which strongly reacted with anti-rhoA p21 antibody, but not with anti-rac1 p21 or anti-cdc42Hs p21 antibody. Treatment of the partially purified PLD-activating factor with both C3 exoenzyme and NAD significantly inhibited the PLD-stimulating activity. These results suggest that rhoA p21 is, at least in part, responsible for the PLD-stimulating activity in the preparation. Recombinant isoprenylated rhoA p21 expressed in and purified from Sf9 cells activated rat brain PLD in a concentration- and GTP gamma S (guanosine 5'-O-(3-thiotriphosphate))-dependent manner. In contrast, recombinant non-isoprenylated rhoA p21 (fused to glutathione S-transferase) expressed in Escherichia coli failed to activate the PLD. This difference cannot be explained by a lower affinity of non-isoprenylated rhoA p21 for GTP gamma S, as the rates of [35S]GTP gamma S binding were very similar for both recombinant preparations and the GTP gamma S-bound form of non-isoprenylated rhoA p21 did not induce PLD activation. Interestingly, recombinant isoprenylated rhoA p21 and ARF synergistically activated rat brain PLD; a similar pattern was seen with the partially purified PLD-activating factor. The synergistic activation was inhibited by C3 exoenzyme-catalyzed ADP-ribosylation of recombinant isoprenylated rhoA p21 in a NAD-dependent manner. Inhibition correlated with the extent of ADP-ribosylation. These findings suggest that rhoA p21 regulates rat brain PLD in concert with ARF, and that isoprenylation of rhoA p21 is essential for PLD regulation in vitro.

Identification of Glu173 as the critical amino acid residue for the ADP-ribosyltransferase activity of Clostridium botulinum C3 exoenzyme

Clostridium botulinum C3 exoenzyme specifically ADP-ribosylates rho-p21 in eukaryotic cells. Trp18 and Glu173 of this enzyme were substituted with other amino acids via site-directed mutagenesis. All substitutions at Glu173 caused a significant reduction in affinity for NAD and diminished ADP-ribosyltransferase activity. On the other hand, the activity of enzymes with the substitution at Trp18 remained intact. Swiss 3T3 cells treated with the enzyme with the Trp18 substitution showed the typical morphologic changes of the C3 exoenzyme phenotype. In contrast, no changes were found in cells incubated with the Glu173-substituted enzyme. These results indicate that the Glu173 residue of the C3 exoenzyme plays a key role in interacting with NAD and in expression of ADP-ribosyltransferase activity, which is essential for the phenotypic change by C3 exoenzyme treatment.

Lysophosphatidic acid-induced activation of protein Ser/Thr kinases in cultured rat 3Y1 fibroblasts. Possible involvement in rho p21-mediated signalling

Renaturation kinase assay was used to detect protein kinases activated by lysophosphatidic acid (LPA) in cultured rat 3Y1 fibroblasts. LPA activated several Ser/Thr protein kinases with apparent molecular weights of 145K, 85K, 64-65K (a doublet), and 60K (each named p145, p85, p64165 and p60, respectively) in addition to p43 mitogen activated protein (MAP)-kinase. Experiments using pertussis toxin and botulinum C3 exoenzyme showed that p145, p85, and p64165 kinases were activated by a pertussis toxin-insensitive rho p21-dependent pathway and that the activation of MAP-kinase was mediated by both the pertussis toxin-sensitive rho p21-independent and the pertussis toxin-insensitive rho p21-dependent pathways.

The small GTP-binding protein, rho p21, is involved in bone resorption by regulating cytoskeletal organization in osteoclasts

Rho protein (rho p21), a p21ras-related small guanine nucleotide binding protein, regulates cytoskeletal organization in a number of different types of cells. Evidence has indicated that Clostridium botulinum-derived ADP-ribosyltransferase (C3 exoenzyme) specifically ADP-ribosylates rho p21 at Asn41 and renders it functionally inactive. In this study, we examined the involvement of rho p21 in osteoclastic bone resorption using the C3 exoenzyme. When osteoclast-like multinucleated cells obtained from cocultures of mouse osteoblastic cells and bone marrow cells were placed on dentine slices, they formed ringed structures of podosomes containing F-actin (corresponding to the clear zone) within 8 hours. Many resorption pits were formed on dentine slices after culture for 24 hours. The C3 exoenzyme at 0.15-10 micrograms/ml added to the culture medium disrupted the ringed structure of podosomes in osteoclast-like cells in a dose-dependent manner. Correspondingly, pit formation by osteoclast-like cells on dentine slices was dose-dependently inhibited also by adding the C3 exoenzyme. Microinjection of the C3 exoenzyme into osteoclast-like cells placed on culture dishes completely disrupted the ringed podosome structure within 20 minutes. The amount of the rho p21 which was ADP-ribosylated by the C3 exoenzyme in vitro was much greater in purified osteoclast-like cells than in osteoblastic cells. Prior exposure of the purified osteoclast-like cell preparation to the C3 exoenzyme in vivo markedly decreased the amount of unribosylated rho p21. This indicated that the C3 exoenzyme incorporated into osteoclast-like cells effectively ADP-ribosylates rho p21 in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Guanosine 5'-3-O-(thio)triphosphate stimulates tyrosine phosphorylation of p125FAK and paxillin in permeabilized Swiss 3T3 cells. Role of p21rho

Addition of guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) to streptolysin O-permeabilized Swiss 3T3 cells induced tyrosine phosphorylation of M(r) 110,000-130,000 and 70,000-80,000 bands. Specifically, GTP gamma S stimulated tyrosine phosphorylation of both focal adhesion kinase (p125FAK) and paxillin. GTP gamma S induced tyrosine phosphorylation was dose-dependent (EC50 of 2.5 microM) and reached maximum levels after 1.5 min for the M(r) 110,000-130,000 band and 2 min for the M(r) 70,000-80,000 paxillin band. Guanosine 5'-O-(2-thiodiphosphate) inhibited GTP gamma S-induced tyrosine phosphorylation with an IC50 of 100 microM. Protein kinase C did not mediate GTP gamma S-induced tyrosine phosphorylation. Varying the Ca2+ concentration from 0 to 6 microM did not increase tyrosine phosphorylation above basal levels and did not affect the ability of GTP gamma S to induce tyrosine phosphorylation. GTP gamma S was able to stimulate tyrosine phosphorylation in the presence of nanomolar concentrations of Mg2+. Furthermore, 30 microM AlF4- only weakly induced tyrosine phosphorylation in permeabilized cells. Pretreatment with the Clostridium botulinum C3 exoenzyme which inactivates p21rho, markedly reduced the ability of GTP gamma S to stimulate tyrosine phosphorylation of M(r) 110,000-130,000 and 70,000-80,000 bands including p125FAK and paxillin in permeabilized Swiss 3T3 cells. Furthermore, a peptide of p21rho (p21rho17-44) inhibited GTP gamma S-induced tyrosine phosphorylation in a dose-dependent manner (IC50 1 microM). This peptide also inhibited tyrosine phosphorylation of p125FAK and paxillin. In contrast, 20 microM p21ras17-44 peptide failed to inhibit GTP gamma S-induced tyrosine phosphorylation. Using permeabilized cells, our findings demonstrate that GTP gamma S stimulates tyrosine phosphorylation of p125FAK and paxillin and that a functional p21rho is implicated in this process.

Botulinum C3 exoenzyme blocks the tyrosine phosphorylation of p125FAK and paxillin induced by bombesin and endothelin

In this study we examined the role of rho p21 in neuropeptide-stimulated tyrosine phosphorylation. Intact Swiss 3T3 cells were treated with the Clostridium botulinum C3 exoenzyme which specifically ADP ribosylates and inactivates rho p21. C3 exoenzyme treatment of cells caused a marked decrease in both bombesin- and endothelin-stimulated tyrosine phosphorylation of multiple proteins, including p125 focal adhesion kinase (FAK) and paxillin. Our results suggest that rho p21 is a component of the signal transduction pathway linking seven transmembrane domain receptors with tyrosine phosphorylation and cytoskeletal events.

Effect of botulinum C3 exoenzyme on cell growth and cytoskeleton organization in transformed human epidermal cells in culture: a possible role for rho protein in epidermal cells

We examined the role of rho gene products (rho proteins) on cell growth and cytoskeleton organization in transformed human epidermal cells in culture (HSC-1), using recombinant botulinum C3 exoenzyme which specifically ADP-ribosylates rho proteins. Incubation of HSC-1 cell lysates with C3 exoenzyme revealed a single [32P]ADP-ribosylated protein with a molecular weight of 23,000. This protein was identified as rhoA protein by isoelectric focusing (pI 6.0). Addition of C3 exoenzyme to the culture medium of HSC-1 cells changed the shape of HSC-1 cells to a round form with beaded processes in a time- and dose-dependent manner. Moreover, C3 treatment reduced the cell growth rate; 72-h treatment with C3 exoenzyme at 1, 3, 10, 30 and 60 micrograms/ml culture medium resulted in 9.0 +/- 1.8%, 20 +/- 2.9%, 26 +/- 2.3%, 50 +/- 1.4% and 40 +/- 2.0% inhibition of the growth rate relative to controls, respectively. Under this condition, actin stress fibers were disassembled, as revealed using fluorescent-labeled phallacidin, whereas keratin intermediate filaments were not affected, visualized by immunofluorescence using anti-keratin antibody. These results suggest that rho proteins are closely related to cell growth and that these proteins regulate, at least in part, the assembly of actin stress fibers in transformed human epidermal cells.

Inhibition of lysophosphatidate- and thrombin-induced neurite retraction and neuronal cell rounding by ADP ribosylation of the small GTP-binding protein Rho

Addition of the bioactive phospholipid lysophosphatidic acid (LPA) or a thrombin receptor-activating peptide (TRP) to serum-starved N1E-115 or NG108-15 neuronal cells causes rapid growth cone collapse, neurite retraction, and transient rounding of the cell body. These shape changes appear to be driven by receptor-mediated contraction of the cortical actomyosin system independent of classic second messengers. Treatment of the cells with Clostridium botulinum C3 exoenzyme, which ADP-ribosylates and thereby inactivates the Rho small GTP-binding protein, inhibits LPA- and TRP-induced force generation and subsequent shape changes. C3 also inhibits LPA-induced neurite retraction in PC12 cells. Biochemical analysis reveals that the ADP-ribosylated substrate is RhoA. Prolonged C3 treatment of cells maintained in 10% serum induces the phenotype of serum-starved cells, with initial cell flattening being followed by neurite outgrowth; such C3-differentiated cells fail to retract their neurites in response to agonists. We conclude that RhoA is essential for receptor-mediated force generation and ensuing neurite retraction in N1E-115 and PC12 cells, and that inactivation of RhoA by ADP-ribosylation abolishes actomyosin contractility and promotes neurite outgrowth.

Inhibitory effects of botulinum toxin on 5-HT1C receptor-induced Cl- current in Xenopus oocytes

Several low molecular weight G proteins have been identified, but their functional roles remain unclear. To clarify the involvement of low molecular weight G protein in receptor-stimulated turnover of polyphosphoinositide (PI) turnover, influences of botulinum toxins on serotonin (5-HT)-stimulated Cl- current mediated by PI turnover were investigated using Xenopus oocytes injected with rat brain mRNA. Treatment with botulinum toxin C, D or purified ADP-ribosyltransferase of botulinum toxin (botulinum toxin C3 enzyme) inhibited the 5-HT-induced Cl- current in oocytes, and ADP-ribosylated 23 kDa proteins. Both botulinum toxin C3 enzyme-induced inhibition of the current and ADP-ribosylation were suppressed by pretreatment with antibotulinum toxin C3 enzyme antibody. Botulinum toxin D treatment of oocytes was ineffective in the response of Cl- current induced by injection of 50 pmol inositol 1,4,5-trisphosphate and 50 pmol Ca2+. It is suggested that low molecular weight G proteins ADP-ribosylated by botulinum toxin C3 enzyme are involved in phospholipase C activation in Xenopus oocytes.

rho GAP of 28 kDa (GAP2), but not of 190 kDa (p190), requires Asp65 and Asp67 of rho GTPase for its activation

Two distinct GTPase-activating proteins (GAPs), i.e. rho GAPs of 28 kDa (GAP2) and of 190 kDa (p190), stimulate the intrinsic GTPase activity of the rho protein. The rho GAP activity of p190 resides in its C-terminal domain (p190C). Neither GAP2 nor p190C activates the ras GTPase. We replaced Asp65 and Asp67 residues of rho GTPase with the corresponding ras residues and examined whether the domain containing them is involved in its activation by rho GAPs. Mutation of either Asp65 to Glu or Asp67 to Ser did not change the Kd value for GTP gamma S of the rho protein. The Ser67 mutation reduced the intrinsic GTPase activity of the rho protein, while no change was observed with the Glu65 mutation. Both mutations abolished activation of rho GTPase by GAP2. The GAP2-dependent activation of rho GTPase was inhibited by the addition of GTP gamma S-bound wild type rho but not by either GTP gamma S-bound Glu65- or Ser67-rho, indicating that both Asp65 and Asp67 are essential for interaction of rho protein with GAP2. On the contrary, p190C activated both Glu65- and Ser67-rho GTPases to the extent and in a dose dependence to those seen in the wild GTPase. These results suggest that GAP2 and p190 interact with different residues or domains of the rho GTPase for their activation.

ADP-ribosylation of rho p21 inhibits lysophosphatidic acid-induced protein tyrosine phosphorylation and phosphatidylinositol 3-kinase activation in cultured Swiss 3T3 cells

Botulinum C3 exoenzyme was used to specifically ADP-ribosylate and inactivate rho p21, and the effects of rho p21 inactivation on lysophosphatidic acid (LPA)-induced tyrosine phosphorylation were examined in cultured Swiss 3T3 cells. LPA induced a rapid increase in the tyrosine phosphorylation of a number of proteins. Pretreatment of the cells with the C3 exoenzyme caused ADP-ribosylation of rho p21 in the cells and selectively attenuated the phosphorylation of several proteins, including p43 mitogen-activated protein kinase, p125 focal adhesion kinase, and two proteins of 72 and 88 kDa. C3 exoenzyme pretreatment did not block the initial phosphorylation and activation of mitogen-activated protein kinase but suppressed its subsequent rise. In contrast, the enzyme treatment inhibited the induction of phosphorylation of the 72- and 88-kDa proteins and suppressed the basal and LPA-induced tyrosine phosphorylation of p125 focal adhesion kinase. In addition, immunoprecipitation of cell lysates with an antibody directed against the 85-kDa subunit of phosphatidylinositol 3-kinase (PI 3-kinase) co-precipitated a tyrosine-phosphorylated band of 180 kDa. C3 exoenzyme pretreatment suppressed both the phosphorylation of this band and PI 3-kinase activation associated with LPA stimulation. These findings suggest that rho p21 works as a link between the LPA receptor signal and the subsequent tyrosine phosphorylation and PI 3-kinase activation in these cells.

A rho-like protein is involved in the organisation of the contractile ring in dividing sand dollar eggs

Sand dollar eggs were microinjected with botulinum C3 exoenzyme, an ADP-ribosyltransferase from Clostridium botulinum that specifically ADP-ribosylates and inactivates rho proteins. C3 exoenzyme microinjected during nuclear division interfered with subsequent cleavage furrow formation. No actin filaments were detected in the equatorial cortical layer of these eggs by rhodamine-phalloidin staining. When microinjected into furrowing eggs, C3 exoenzyme rapidly disrupted the contractile ring actin filaments and caused regression of the cleavage furrows. C3 exoenzyme had no apparent effect on nuclear division, however, and multinucleated embryos developed from the microinjected eggs. By contrast, C3 exoenzyme did not affect the organisation of cortical actin filaments immediately after fertilisation. Only one protein (molecular weight 22,000) was ADP-ribosylated by C3 exoenzyme in the isolated cleavage furrow. This protein co-migrated with ADP-ribosylated rhoA derived from human platelets when analysed by two-dimensional gel electrophoresis. These results strongly suggest that a rho-like, small GTP-binding protein is selectively involved in the organisation and maintenance of the contractile ring.

Lysophosphatidic acid induces tyrosine phosphorylation and activation of MAP-kinase and focal adhesion kinase in cultured Swiss 3T3 cells

Lysophosphatidic acid (LPA) added to serum-starved Swiss 3T3 cells induced, in a time- and concentration-dependent manner, tyrosine phosphorylation of multiple proteins, including proteins of 43, 64, 88 kDa and a group of proteins between 110 and 130 kDa. Among them, two proteins, p43 and p120, were identified as mitogen-activated protein kinase (MAP-kinase) and focal adhesion kinase (FAK), respectively, by immunoprecipitation and immunoblot analysis. Tyrosine phosphorylation of p64 peaked at 1 min and declined rapidly, whereas that of MAP-kinase and FAK peaked at 5 and 10 min after the addition of LPA, respectively. The activity of MAP-kinase determined as phosphorylation of myelin basic protein increased transiently about 3-fold at 5 min, and correlated with tyrosine phosphorylation. These results indicate that tyrosine phosphorylation of these proteins is a part of the signal transduction by LPA and may be involved in its mitogenic responses.

ADP-ribosylation of the rhoA gene product by botulinum C3 exoenzyme causes Swiss 3T3 cells to accumulate in the G1 phase of the cell cycle

Using botulinum C3 exoenzyme, which specifically ADP-ribosylates the rho gene products (rho proteins), we examined the role of these proteins in cell cycle progression in Swiss 3T3 cells. Incubation of cell lysates with C3 exoenzyme revealed a single [32P]ADP-ribosylated protein with an M(r) of 23K. This protein was identified as rhoA protein by isoelectric focusing and peptide mapping. When C3 exoenzyme was added to the culture, it ADP-ribosylated the substrate protein in the cells and reduced their growth rate and saturation density. The reduction was dependent on the amount of C3 exoenzyme and on the extent of ADP-ribosylation of the rho protein in the cells. Flow cytometric analysis of logarithmically growing cells showed that the enzyme treatment concentration-dependently accumulated the cells in the G1 phase of the cell cycle. When G1-enriched cells were treated with C3 exoenzyme and cell cycle progression initiated by the addition of serum was monitored, inhibition of G1-S transition was clearly observed. These results suggest that the rhoA gene product plays a critical role in G1-S progression in cultured Swiss 3T3 cells and that the ADP-ribosylation abolishes this activity and causes the cells to accumulate in G1 phase.

Inhibition of PMA-induced, LFA-1-dependent lymphocyte aggregation by ADP ribosylation of the small molecular weight GTP binding protein, rho

Botulinum C3 exoenzyme specifically ADP-ribosylates a group of ras-related small molecular weight GTP-binding proteins, rho, and inhibits their biological activity. Using this enzyme, we examined the function of rho in PMA-induced activation of lymphocyte function-associated antigen-1 (LFA-1) in a B lymphoblastoid cell line, JY. Northern blot analysis revealed that among the three rho genes, rhoA mRNA was predominantly expressed in JY cells. Consistently, only one [32P]ADP-ribosylated band was found when the lysate of the cells was subjected to ADP ribosylation by C3 exoenzyme. When the cells were cultured with C3 exoenzyme, this substrate was ADP-ribosylated in situ in a time- and concentration-dependent manner. Concomitant with this ADP ribosylation, PMA-induced LFA-1/intercellular adhesion molecule (ICAM)-1-dependent aggregation of JY cells was inhibited. This inhibition was blocked by prior treatment of the enzyme with an anti-C3 monoclonal antibody, and overcome by stimulation with higher concentrations of PMA. The C3 exoenzyme-induced inhibition was not affected by shaking of the cell suspension, while inhibition of aggregation by cytochalasin B was abolished by this procedure, suggesting that the inhibitory effect of the C3 exoenzyme treatment was not due to decrease in cell motility. The C3 exoenzyme treatment affected neither protein phosphorylation in JY cells before and after PMA stimulation, nor affected surface expression of LFA-1 and ICAM-1. These results suggest that rhoA protein works downstream of protein kinase C activation linking PMA stimulation to LFA-1 activation and aggregation in JY cells.

A rho gene product in human blood platelets. II. Effects of the ADP-ribosylation by botulinum C3 ADP-ribosyltransferase on platelet aggregation

In the accompanying paper (Nemoto, Y., Namba, T., Teru-uchi, T., Ushikubi, F., Morii, N., and Narumiya, S. (1992) J. Biol. Chem. 267, 20916-20920), we have identified rhoA protein as the sole substrate protein for botulinum C3 ADP-ribosyltransferase (C3 exoenzyme) in human blood platelets. Here we examined the role of rhoA protein in platelet functions. C3 exoenzyme added to washed platelets dose- and time-dependently ADP-ribosylated rhoA protein in situ in the cells. Concomitant with this modification, inhibition of thrombin-induced platelet aggregation was observed. This inhibition was not reversed by washing the treated platelets, but was not found when C3 exoenzyme was pretreated with mouse monoclonal anti-C3 exoenzyme antibody. C3 exoenzyme treatment did not affect thrombin-induced inositol 1,4,5-trisphosphate production. Secretion of preloaded [14C]serotonin was delayed by the enzyme treatment, but the extent of the secretion was not influenced. In addition, the enzyme treatment did not change the expression of the glycoprotein IIb-IIIa complex on the platelet surface. The enzyme treatment also suppressed platelet aggregation induced by phorbol myristate acetate. These results suggest that rhoA protein plays a role mainly in the aggregation process downstream from receptor-phospholipase C coupling. This, together with the previous finding that rhoA protein modulates stress fiber formation in cultured fibroblasts (Paterson, H. F., Self, A. J., Garrett, M. D., Just, I., Aktories, K., and Hall, A. (1990) J. Cell Biol. 111, 1001-1007), suggests that rhoA protein regulates the assembly of actin filaments and the avidity of the platelet integrin (glycoprotein IIb-IIIa) in the aggregation process.

A rho gene product in human blood platelets. I. Identification of the platelet substrate for botulinum C3 ADP-ribosyltransferase as rhoA protein

A substrate protein for botulinum C3 ADP-ribosyltransferase (C3 exoenzyme) in human platelets was purified to apparent homogeneity from the cytosol by ammonium sulfate fractionation and successive chromatography on columns of DEAE-Sepharose, hydroxylapatite, phenyl-Sepharose, and TSK phenyl-5PW. The purified protein yielded an amino acid sequence identical to that of rhoA protein. When platelet cytosol and membranes were incubated with C3 exoenzyme and [32P]NAD and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing, they gave only one [32P]ADP-ribosylated band on each electrophoresis that showed an M(r) of 22,000 and a pI of 6.0. The radioactive bands from the two fractions co-migrated with each other and with the [32P]ADP-ribosylated purified protein. When these radioactive products were partially digested with either alpha-chymotrypsin or trypsin and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the same digestion pattern was found in the three samples. These results suggest that the ADP-ribosylation substrate for C3 exoenzyme in the platelet cytosol and membrane is rhoA protein and that it is the sole substrate detectable in human platelets.

[ras oncogene-related small molecular weight GTP-binding protein, rho gene product and botulinum C3 ADP-ribosyltransferase]

The ras oncogene products (ras p21s) are 21-KDa proteins with activities of GTP binding and hydrolysis. A number of proteins homologous to ras p21 have been discovered and collectively named small molecular weight GTP-binding proteins. These proteins undergo post-translational modification with isoprenoid residues attached to cysteine in their carboxyl terminal. With this modification, they attach to cellular membranes. The biochemical activities of these proteins, i.e., GTP hydrolysis and binding, are regulated by various regulatory factors such as GDP-GTP exchange proteins and GTPase-activating proteins, but little is known about the cellular functions and physiological pathways through which they regulate these functions. Botulinum C3 ADP-ribosyltransferase, a 23-KDa exoenzyme secreted from certain strains of types C and D Clostridium botulinum, specifically ADP-ribosylates the rho family of these GTP-binding proteins. This ADP-ribosylation occurs at a specific asparagine residue in their putative effector domain, and presumably interferes with their interaction with a putative effector molecule downstream in signal transduction. C3 exoenzyme, when incubated with or microinjected into cultured cells, ADP-ribosylates a rho gene product in the cells, and causes profound cell rounding with loss of adhesion plaques and collapse of stress fiber. Microinjection of an activated mutant of rho A protein, on the contrary, induced extensive adhesion and actin assembly in cultured cells. These results suggest that the rho family of proteins are involved in morphogenesis and motility of cells via assembly and disassembly of cytoskeletal systems, and botulinum ADP-ribosyltransferase is a useful tool for clarifying the molecular mechanism of these processes.

Purification of GTPase-activating protein specific for the rho gene products

A GTPase-activating protein specific for the rho gene products (rho-GAP) was purified from the cytosol of bovine adrenal gland. Purification procedures consisted of ammonium sulfate fractionation, chromatographies on columns of phenyl-Sepharose and CM-Sepharose, gel filtration on a TSK-gel G3000SW, and Mono S fast protein liquid chromatography. By these procedures the activity was purified about 36,000-fold with a recovery of 0.6%. The final preparation showed a major protein band at Mr 28,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and stimulated GTP hydrolysis by the purified rho A protein in a time- and dose-dependent manner. No stimulation was found for ras p21. The ADP-ribosylation on the rho protein by botulinum C3 exoenzyme did not affect its interaction with the purified rho-GAP.

Immunochemical identification of the ADP-ribosyltransferase in botulinum C1 neurotoxin as C3 exoenzyme-like molecule

Botulinum C1 neurotoxin and C3 exoenzyme were purified to apparent homogeneity from the culture filtrate of Clostridium botulinum type C strain 003-9. Both preparations catalyzed ADP-ribosylation of the same substrate, the Mr 22,000 rho gene product (Gb). When the light and heavy chains of C1 toxin were separated, ADP-ribosyltransferase activity in the toxin was quantitatively recovered in the light chain fraction. Anti-C1 toxin antiserum precipitated the ADP-ribosyltransferase activity and the neurotoxicity of C1 toxin in parallel, whereas it had no effect on C3 exoenzyme. On the other hand, anti-C3 exoenzyme antiserum precipitated the ADP-ribosyltransferase activities of both C3 exoenzyme and C1 toxin. This antibody, however, did not precipitate the neurotoxicity of C1 toxin. The ADP-ribosyltransferase in C1 toxin was quantitatively adsorbed onto the anti-C3 antibody column and separated from the majority of C1 toxin protein. The enzyme was then eluted with acidic urea and Western blotting analysis of this eluate revealed the appearance of a protein band positively stained with anti-C3 antibody at a position similar to that of C3 exoenzyme. Quantitative determination by enzyme-linked immunosorbent assay showed that the C3-like immunoreactivity is present in the C1 toxin molecules at the molecular ratio of 1 to 1,000. These results suggest that the ADP-ribosyltransferase activity in C1 toxin is expressed by a C3-like molecule which is present in a small amount in the toxin preparation and appears to bind to the toxin component(s). The above results also indicate that the ADP-ribosyltransferase in C1 toxin is not related to its neurotoxin action.

ADP-ribosylation of the rho/rac proteins induces growth inhibition, neurite outgrowth and acetylcholine esterase in cultured PC-12 cells

Botulinum ADP-ribosyltransferase C3 (C3 exoenzyme) was purified to homogeneity and added to cultured rat pheochromocytoma PC-12 cells. Incubation with this exoenzyme caused inhibition of cell growth and induced neurites as well as acetylcholine esterase in these cells. These changes were dependent on the amount of the enzyme added to the culture, which correlated with the in situ ADP-ribosylation of the rho/rac proteins in the cells. Preincubation with a specific anti-C3 exoenzyme monoclonal antibody inhibited both the ADP-ribosyltransferase activity and the neurite-inducing activity of the enzyme preparation. These results suggest that C3 exoenzyme affected the cellular function of the rho/rac proteins by ADP-ribosylation to induce these changes in the cells.

Chronic blockade of endogenous atrial natriuretic polypeptide (ANP) by monoclonal antibody against ANP accelerates the development of hypertension in spontaneously hypertensive and deoxycorticosterone acetate-salt-hypertensive rats

To explain the pathophysiological significance of endogenous atrial natriuretic polypeptide (ANP) in the development of hypertension, we examined the effect of chronic, repetitive administrations of MAb raised against alpha-rat ANP in two rat models of hypertension, spontaneously hypertensive rats of the stroke prone substrain (SHR-SP), and deoxycorticosterone acetate (DOCA)-salt rats. Weekly intravenous administrations of MAb with high affinity for alpha-rat ANP, named KY-ANP-II (MAb[KY-ANP-II]), started at the age of 6 wk, significantly augmented the rise in blood pressure of SHR-SP, compared with control SHR-SP treated with another MAb with quite low affinity for alpha-rat ANP, named KY-ANP-I (MAb[KY-ANP-I]), throughout the observation period. The administrations of MAb[KY-ANP-II] had no significant effect on blood pressure of age-matched normotensive Wistar Kyoto rats, compared with those receiving MAb[KY-ANP-I]. Weekly administrations of MAb[KY-ANP-II] also significantly aggravated hypertension in DOCA-salt rats. Blood pressure of DOCA-salt rats treated with MAb[KY-ANP-II] was significantly higher than that of DOCA-salt rats treated with MAb[KY-ANP-I] throughout 8 wk of DOCA and 1% saline administration. The administration of MAb[KY-ANP-II] also significantly attenuated exaggerated diuresis and natriuresis in DOCA-salt rats compared with those treated with MAb[KY-ANP-I]. Elevated plasma cGMP levels of both SHR-SP and DOCA-salt rats were significantly reduced by the administration of MAb[KY-ANP-II]. These results suggest the compensatory role of augmented secretion of ANP in these hypertensive rats and support the concept that augmented secretion of ANP could represent an antihypertensive deterrent mechanism.

Expression of atrial natriuretic factor gene in hearts from neonates of spontaneously hypertensive rats and stroke-prone spontaneously hypertensive rats

In order to further elucidate the expression of the atrial natriuretic factor (ANF) gene in spontaneously hypertensive rats (SHR) and the substrain, stroke-prone SHR (SHRSP), ANF messenger (m)RNA levels in the atrium and in the ventricle were measured in neonates of SHR and SHRSP and were compared with those in control Wistar-Kyoto rats (WKY). The levels of ANF mRNA in ventricles of the three strains reached approximately 7% of those in atria; however, no significant difference was observed in atrial and ventricular ANF mRNA levels among the three strains. These results demonstrate that the expression of the ANF gene in hearts from neonates of WKY, SHR and SHRSP is similar among the three strains.

Exaggerated secretion of atrial natriuretic polypeptide during dynamic exercise in patients with essential hypertension

The plasma concentration of atrial natriuretic polypeptide (ANP) was measured in nine patients with essential hypertension during two grades of exercise tests performed in the supine position on a bicycle ergometer. The plasma ANP concentration significantly increased from 97.0 +/- 19.2 pg/ml to 107.6 +/- 23.7 pg/ml (p less than 0.05) during low-grade exercise (50% of the maximal heart rate) and from 96.2 +/- 16.5 pg to 192.8 +/- 30.7 pg/ml (p less than 0.01) during high-grade exercise (75% of the maximal heart rate). During high-grade exercise plasma epinephrine and norepinephrine concentrations showed significant increases. The plasma ANP concentration was significantly correlated with systolic blood pressure (r = 0.51; p less than 0.05). Patients with essential hypertension showed greater absolute increases in the plasma ANP concentration and systolic blood pressure during exercise compared to normotensive subjects. These results suggest that exercise stimulates secretion of ANP in response to its intensity in patients with essential hypertension and that a greater rise in atrial pressure, resulting from a greater elevation of systolic blood pressure, may be involved in the exaggerated secretion of ANP in patients with essential hypertension.

Purification and properties of the cytosolic substrate for botulinum ADP-ribosyltransferase. Identification as an Mr 22,000 guanine nucleotide-binding protein

The substrate for ADP-ribosyltransferase from Clostridium botulinum was purified from the cytosol of bovine adrenal gland. Purification procedures consisted of ammonium sulfate fractionation, chromatographies on columns of DEAE-Sepharose and phenyl-Sepharose, gel filtration on a TSK-gel G3000SW column, and Mono Q fast protein liquid chromatography. On DEAE-Sepharose chromatography, the substrate activity was eluted in two separate peaks, and electrophoretic analyses revealed that the substrates in the two peaks are of similar molecular weight but different isoelectric points. The major peak of the substrate was further purified. It was purified about 1,800-fold with a recovery of 2.2% by the above procedures. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the final preparation showed a single protein band at Mr 22,000. The purified protein served as a substrate for botulinum ADP-ribosyltransferase and was maximally ADP-ribosylated to the extent of about 0.7 mol of ADP-ribose/mol of protein. A guanosine 5'-(3-O-thio)triphosphate (GTP gamma S) binding activity was co-purified with the ADP-ribosylation substrate, and the purified protein maximally bound about 0.5 mol of GTP gamma S/mol. GTP gamma S binding was effectively competed by GTP and GDP but not by GMP, ATP, and ADP. Thus, the ADP-ribosylation substrate is a GTP-binding protein. This protein, designated Gb (b for botulinum), is widely distributed in various tissues. It was rich in brain, pituitary, and adrenal glands, and poor in heart, smooth, and skeletal muscles.

Gamma-atrial natriuretic polypeptide (gamma ANP)-derived peptides in human plasma: cosecretion of N-terminal gamma ANP fragment and alpha ANP

Using RIAs for the N- and C-terminal fragments of the human atrial natriuretic polypeptide (ANP) precursor gamma ANP, that is gamma ANP-(1-25), and alpha ANP [gamma ANP-(99-126)], we studied the secretion of gamma ANP-derived peptides from the heart in normal subjects and patients with heart disease, chronic renal failure, and cirrhosis. We detected gamma ANP-(1-25)-like immunoreactivity (-LI) in plasma from normal subjects (n = 17) in considerable amounts [mean, 510 +/- 62 (+/- SE) pg/mL (174 +/- 21 pmol/L)]; the mean plasma alpha ANP-LI level at the same time in these subjects was 32.8 +/- 4.4 pg/mL (10.7 +/- 1.4 pmol/L). Gel permeation chromatographic analysis of plasma samples from normal subjects and patients with heart disease and chronic renal failure revealed two major components; one was alpha ANP, and the other was the 10K N-terminal gamma ANP fragment (N-peptide) resulting from the removal of alpha ANP (3K) from gamma ANP (13K). In addition, gamma ANP (13K), which possessed both gamma ANP-(1-25)-LI and alpha ANP-LI, and beta ANP, an antiparallel dimer of alpha ANP, were detected in some patients as minor components. A significant positive correlation between plasma levels of the N-terminal gamma ANP fragment and alpha ANP (P less than 0.01) and almost equal step-ups in the coronary sinus plasma levels of the N-terminal gamma ANP fragment and alpha ANP suggest that they are cosecreted in equimolar amounts. The high molar ratio of plasma gamma ANP-(1-25)-LI to alpha ANP-LI (17.4 +/- 1.4) in normal subjects and the significantly higher ratio in patients with chronic renal failure (36.9 +/- 7.1; P less than 0.01) suggest the slower clearance of the N-terminal gamma ANP fragment than alpha ANP and a role for the kidney in its degradation. Since the molar ratio of plasma gamma ANP-(1-25)-LI to alpha ANP-LI in patients with cirrhosis (20.7 +/- 2.7) was similar to that in normal subjects, it is unlikely that the N-terminal gamma ANP fragment is metabolized by the liver. In patients with heart disease, plasma gamma ANP-(1-25)-LI and alpha ANP-LI levels were higher in those with cardiac decompensation and were positively correlated with right atrial pressure, pulmonary arterial pressure, and pulmonary capillary wedge pressure, indicating cosecretion of the N-terminal gamma ANP fragment and alpha ANP in response to atrial stretch.(ABSTRACT TRUNCATED AT 400 WORDS)

A monoclonal antibody to alpha-human atrial natriuretic polypeptide

A monoclonal antibody to alpha-human atrial natriuretic polypeptide (alpha-hANP), KY-ANP-I, has been produced by fusion of a nonproducing mouse myeloma cell line, X63-Ag8.653, with spleen cells from BALB/c mice immunized with synthetic alpha-hANP conjugated to bovine thyroglobulin using the carbodiimide coupling procedure. Hybridomas were screened for antibody production by radioimmunoassay using culture media and 125I-alpha-hANP. They were cloned by the limiting dilution technique, expanded in culture, and injected intraperitoneally into BALB/c mice. The obtained antibody belonged to the immunoglobulin G1 subclass. Analysis by a Scatchard plot revealed a high affinity for alpha-hANP, with an association constant of 3.1 x 10(10) M-1. With this monoclonal antibody, a specific radioimmunoassay for alpha-hANP has been established. The antibody in mouse ascites was available for radioimmunoassay at a final dilution of 1:10(6). Values of IC10 and IC50 in this radioimmunoassay were 3 and 30 fmol/tube, respectively. The radioimmunoassay showed a cross-reactivity of 0.9% with alpha-rat ANP. alpha-hANP-(8-22) and alpha-ANP-(1-6) exhibited less cross-reactivity than alpha-rat ANP on a molar basis. There was no cross-reaction with alpha-ANP-(17-28). Thus, the recognized epitope must be located in the N-terminal half of the ring structure of alpha-hANP including Met12 residue. This radioimmunoassay could detect gamma-hANP and beta-hANP as well as alpha-hANP. The monoclonal antibody was also useful for immunohistochemical studies. ANP-positive cells were finely stained in the human atrium using the avidin-biotin-peroxidase complex technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Potent depressor action of leumorphin, a kappa-opioid agonist, in conscious rats

To investigate the role of leumorphin, a kappa-opioid agonist derived from proenkephalin B (neoendorphin/dynorphin precursor) in the central cardiovascular control, the effects of intracerebroventricular (ICV) administration of leumorphin on basal blood pressure and angiotensin II (AII)-stimulated pressor response were examined in conscious unrestrained rats. The ICV injection of 0.06 and 0.6 nmol of leumorphin caused a significant decrease in basal blood pressure (delta mean arterial pressure (MAP): -6.5 +/- 2.7 and -7.2 +/- 1.7 mm Hg, respectively). The ICV injection of AII (0.1 nmol) elicited a pressor response (delta MAP: 21.4 +/- 1.1 mm Hg). This pressor response was significantly reduced by the simultaneous administration of leumorphin, and furthermore, the blood pressure was lowered below the basal level. These depressor actions of leumorphin were partially antagonized by the preadministration of naloxone, an opiate antagonist. These results together with our previous works on the potent inhibitory actions of leumorphin on drinking and vasopressin secretion suggest the possible involvement of leumorphin in the central regulation of blood pressure and body fluid homeostasis.

Atrial natriuretic polypeptide in bovine adrenal medulla

Two radioimmunoassays for alpha-human atrial natriuretic polypeptide (alpha-hANP) with different specificities were used to study the tissue level and the nature of alpha-hANP-like immunoreactivity in the bovine adrenal gland. A considerable amount of alpha-hANP-like immunoreactivity was detected in the adrenal medulla (90.8 +/- 21.1 and 90.0 +/- 23.1 ng/g with the two radioimmunoassays), while no detectable amount (less than 1.0 ng/g) was present in the cortex. Gel permeation chromatographic analysis showed that ANP in the medulla is composed of two components of alpha-hANP-like immunoreactivity with high and low molecular weights in the approximate ratio of 2:1, eluting at the elution positions of gamma-hANP and alpha-hANP, respectively. Reverse-phase high performance liquid chromatographic analysis revealed that alpha-hANP-like immunoreactivity with a low molecular weight in the medulla consists of two major components, which comigrate with synthetic alpha-hANP(5-28) and alpha-hANP. When cultured bovine adrenal chromaffin cells were incubated in the presence of nicotine (10(-5) M), alpha-hANP-like immunoreactivity was released into the medium concomitantly with catecholamines from chromaffin cells. These findings indicate that a discrete ANP system is present in the adrenal medulla and that ANP is cosecreted with catecholamines from chromaffin cells, suggesting the possible involvement of ANP in the adrenomedullary function.

Effects of intravenously administered beta-human atrial natriuretic polypeptide in humans

beta-Human atrial natriuretic polypeptide (beta-hANP) is an antiparallel dimer of alpha-human ANP (alpha-hANP) that was isolated from human atria. Using synthetic beta-hANP and a radioimmunoassay for alpha-hANP that also detects beta-hANP, we have previously demonstrated that beta-hANP is converted into alpha-hANP in human plasma in vitro. In the present study, we compared the effects of intravenous administration of beta-hANP (100 micrograms) to five normal human volunteers with those of an equimolar administration of alpha-hANP (50 micrograms) to the same subjects, and we also investigated the possible mechanisms of actions of beta-hANP. Although the administration of alpha-hANP caused a significant decrease in blood pressure with a reactional increase of heart rate, beta-hANP elicited minimal change of blood pressure. In contrast, beta-hANP exerted more potent and longer lasting diuretic and natriuretic activities than did alpha-hANP. Net changes in urine volume and sodium excretion induced by beta-hANP (579 +/- 65 ml, 56.0 +/- 9.9 mEq) were significantly greater than those elicited by alpha-hANP (396 +/- 50 ml, 34.7 +/- 4.9 mEq; p less than 0.05, respectively). The administration of beta-hANP revealed a longer retention of the ANP-like immunoreactivity level in plasma, compared with that of alpha-hANP. High performance gel permeation chromatography coupled with the radioimmunoassay revealed that beta-hANP (Mr = 6000) was also converted into alpha-hANP (Mr = 3000) in human plasma in vivo. The demonstrated conversion of beta-hANP into alpha-hANP could be relevant to the observed effects of beta-hANP in humans.

Synthesis of atrial natriuretic polypeptide in human failing hearts. Evidence for altered processing of atrial natriuretic polypeptide precursor and augmented synthesis of beta-human ANP

To elucidate the synthesis of atrial natriuretic polypeptide (ANP) in the failing heart, 20 human right auricles obtained at cardiovascular surgery were studied. The concentration of alpha-human ANP-like immunoreactivity (alpha-hANP-LI) in human right auricles ranged from 13.8 to 593.5 micrograms/g, and the tissue alpha-hANP-LI concentration in severe congestive heart failure (CHF) (New York Heart Association [NYHA] functional class III and class IV) (235.4 +/- 57.2 micrograms/g) was much higher than that in mild CHF (NYHA class I and class II) (52.5 +/- 15.6 micrograms/g). Atrial alpha-hANP-LI levels were significantly correlated with plasma concentrations of alpha-hANP-LI in these patients (r = 0.84, P less than 0.01). High performance gel permeation chromatography and reverse phase high performance liquid chromatography coupled with radioimmunoassay for ANP revealed that the alpha-hANP-LI in the human auricle consisted of three major components of ANP, gamma-human ANP (gamma-hANP), beta-human ANP (beta-hANP) and alpha-human ANP (alpha-hANP). Comparing percentages of gamma-hANP, beta-hANP, and alpha-hANP in alpha-hANP-LI in severe CHF with those in mild CHF, the predominant component of alpha-hANP-LI was gamma-hANP in mild CHF, whereas beta-hANP and/or alpha-hANP were prevailing in severe CHF and, especially, beta-hANP was markedly increased in human failing hearts. These results demonstrate that the total ANP concentration in the atrium of the human heart is increased in severe CHF and that the increase of ANP in the human failing heart is mainly due to the increase of small molecular weight forms of ANP, beta-hANP, and alpha-hANP, especially beta-hANP, and indicate that the processing of ANP precursor, or gamma-hANP, in the human failing heart differs from that in the normal heart, suggesting that the failing heart augments synthesis and secretion of ANP as one of its own compensatory responses.

Augmented expression of atrial natriuretic polypeptide gene in ventricles of spontaneously hypertensive rats (SHR) and SHR-stroke prone

Tissue levels of atrial natriuretic polypeptide (ANP) and ANP messenger RNA (mRNA) in the atrium and ventricle were measured simultaneously in spontaneously hypertensive rats (SHR) and its substrain, SHR-stroke prone (SHRSP), and these levels were compared with those in control Wistar-Kyoto rats (WKY). At 27 weeks of age with established hypertension and ventricular hypertrophy, ANPmRNA levels in ventricles from SHR and SHRSP were markedly increased, and total contents of ventricular ANPmRNA in SHR and SHRSP were approximately 50% and 250%, respectively, of the corresponding atrial contents. However, levels and total contents of atrial ANPmRNA in SHR and SHRSP were similar to those of WKY, and the total content of ventricular ANPmRNA in WKY was only 6% of the content of atrial ANPmRNA. ANP concentrations in ventricles of SHR and SHRSP were increased in association with the augmentation of ANPmRNA levels. During the prehypertensive stage at 6 weeks of age, slight increases in levels and total contents of ANPmRNA and ANP in the ventricle were observed only in SHRSP. These results demonstrate that the expression of the ANP gene is markedly augmented in ventricles of SHR and SHRSP, especially of SHRSP, at the stage of established hypertension and ventricular hypertrophy, and they also suggest that these genetically hypertensive rats are one of the best animal models to investigate the biosynthesis, storage, and secretion of ventricular ANP.