CCR5, CXCR4, and CD4 are clustered and closely apposed on microvilli of human macrophages and T cells.

The chemokine receptors CCR5 and CXCR4 act synergistically with CD4 in an ordered multistep mechanism to allow the binding and entry of human immunodeficiency virus type 1 (HIV-1). The efficiency of such a coordinated mechanism depends on the spatial distribution of the participating molecules on the cell surface. Immunoelectron microscopy was performed to address the subcellular localization of the chemokine receptors and CD4 at high resolution. Cells were fixed, cryoprocessed, and frozen; 80-nm cryosections were double labeled with combinations of CCR5, CXCR4, and CD4 antibodies and then stained with immunogold. Surprisingly, CCR5, CXCR4, and CD4 were found predominantly on microvilli and appeared to form homogeneous microclusters in all cell types examined, including macrophages and T cells. Further, while mixed microclusters were not observed, homogeneous microclusters of CD4 and the chemokine receptors were frequently separated by distances less than the diameter of an HIV-1 virion. Such distributions are likely to facilitate cooperative interactions with HIV-1 during virus adsorption to and penetration of human leukocytes and have significant implications for development of therapeutically useful inhibitors of the entry process. Although the mechanism underlying clustering is not understood, clusters were observed in small trans-Golgi vesicles, implying that they were organized shortly after synthesis and well before insertion into the cellular membrane. Chemokine receptors normally act as sensors, detecting concentration gradients of their ligands and thus providing directional information for cellular migration during both normal homeostasis and inflammatory responses. Localization of these sensors on the microvilli should enable more precise monitoring of their environment, improving efficiency of the chemotactic process. Moreover, since selectins, some integrins, and actin are also located on or in the microvillus, this organelle has many of the major elements required for chemotaxis.

In vitro studies on L-771,688 (SNAP 6383), a new potent and selective alpha1A-adrenoceptor antagonist.

L-771,688 (SNAP 6383, methyl(4S)-4-(3, 4-difluorophenyl)-6-[(methyloxy)methyl]-2-oxo-3-[(¿3-[4-(2-pyridin yl)-1-piperidinyl]propyl¿amino)carbonyl]-1,2,3, 4-tetrahydro-5-pyrimidine carboxylate) had high affinity (Ki less than or = 1 nM) for [3H]prazosin binding to cloned human, rat and dog alpha1A-adrenoceptors and high selectivity (>500-fold) over alpha1B and alpha1D-adrenoceptors. [3H]Prazosin / (+/-)-beta-[125I]-4-hydroxy-phenyl)-ethyl-aminomethylteralone ([125I]HEAT) binding studies in human and animal tissues known to contain alpha1A and non-alpha1A-adrenoceptors further demonstrated the potency and alpha1A-subtype selectivity of L-771,688. [3H]L-771,688 binding studies at the cloned human alpha1A-adrenoceptors and in rat tissues indicated that specific [3H]L-771,688 binding was saturable and of high affinity (Kd=43-90 pM) and represented binding to the pharmacologically relevant alpha1A-adrenoceptors. L-771,688 antagonized norepinephrine-induced inositol-phosphate responses in cloned human alpha1A-adrenoceptors, as well as phenylephrine or A-61603 (N-[5-4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7, 8-terahydro-naphthlen-1-yl] methanesulfonamide hydrobromide) induced contraction in isolated rat, dog and human prostate, human and monkey bladder neck and rat caudal artery with apparent Kb values of 0.02-0.28 nM. In contrast, the contraction of rat aorta induced by norepinephrine was resistant to L-771,688. These data indicate that L-771,688 is a highly selective alpha1A-adrenoceptor antagonist.

Characterization of specific binding of [125I]L-762,459, a selective alpha1A-adrenoceptor radioligand to rat and human tissues.

L-762,459 ((+/-)1-(3-¿[5-carbamoyl-2-2-[(4-hydroxy-3-iodobenzimidoyl)-amino] -ethoxy-methy¿-6-methyl-4-(4-nitropheny)-1,4-dihydropyridine -3-carbonyl]-amino¿-propyl)-4-phenyl-1-piperidine-4-carboxylic acid methyl ester), an analog of a series of dihydropyridines previously reported to be selective alpha1A-adrenoceptor subtype antagonists was found to have alpha1A-adrenoceptor subtype selectivity (Ki (nM), la = 1.3, lb = 240, Id = 280). Specific [125I]L-762,459 binding was detected in rat cerebral cortex, hippocampus, vas deferens, kidney, heart and prostate tissues known to contain the alpha1A-adrenoceptor subtype, but not in tissues known to contain alpha1B-adrenoceptor (spleen, liver) and alpha1D-adrenoceptor (aorta). Scatchard analysis of [125I]L-762,459 binding in rat cerebral cortex and prostate indicated a single binding site with a Kd of 0.7 nM and Bmax of 11 (cerebral cortex) and 1 (prostate) pmole/g tissue. Specific and saturable [125I]L-762,459 binding was also found in human cerebral cortex, liver, prostate and vas deferens (Kd = 0.2-0.4 nM, Bmax = 0.4-4 pmole/g tissue). The specific binding in rat and human tissues was competed by non-selective alpha1-adrenoceptor compounds (Ki values in nM: prazosin (0.14-1.2), terazosin (1.8-5.9) and phentolamine (2.4-11)) and selective alpha1A-adrenoceptor compounds [Ki values in nM: (+) niguldipine (0.04-1.2) and SNAP 5399 ((+/-)-2-((2-aminoethyl)oxy)methyl-5-carboxamido-6-ethyl-4-(4-nitropheny l)-3-N-(3-(4,4-diphenylpiperidin-1-yl)propyl)carboxamido-1,4-dihyd ropyridine hydrate (0.5-4.8)]. The results were consistent with the selective binding of [125I]L-762,459 to the alpha1A-adrenoceptor. The specific labeling of the alpha1A-adrenoceptor subtype by [125I]L-762,459 may make it a useful tool to localize the distribution of the alpha1A-adrenoceptor.

Angiogenic potential of perivascularly delivered aFGF in a porcine model of chronic myocardial ischemia.

A number of heparin-binding growth factors, including basic (bFGF) and acidic (aFGF) fibroblast growth factors have been shown to promote angiogenesis in vivo. In this study, we employed a sustained-release polymer extravascular delivery system to evaluate the angiogenic efficacy of a novel form of genetically modified aFGF in the setting of chronic myocardial ischemia. Fifteen Yorkshire pigs subjected to Ameroid occluder placement on the left circumflex (LCX) artery were treated with perivascularly administered aFGF in ethylene vinyl acetate (EVAc) polymer (10 micrograms, n = 7) or EVAc alone (controls, n = 8). Seven to nine weeks later, after coronary angiography to document Ameroid-induced coronary occlusion, all animals underwent studies of coronary flow and global and regional left ventricular function. Microsphere-determined coronary flow in the Ameroid-compromised territory was significantly increased in aFGF-treated compared with control animals, and this improvement in perfusion was maintained during ventricular pacing. Left ventricular function studies demonstrated improved global and regional function in aFGF-treated animals. We conclude that local perivascular delivery of genetically modified aFGF results in significant improvement in myocardial flow and regional and global left ventricular function.

X-ray crystal structure of human acidic fibroblast growth factor.

Fibroblast growth factors (FGFs) are mitogenic and chemotactic agents for a wide variety of cell types and play a primary role in the regulation of angiogenesis. Angiogenesis is involved in a variety of critical physiological events including organogenesis, wound healing, ischemic collateral circulation, and solid tumor growth. High-resolution structural information is key to understanding the mechanism of action of these growth factors. We report here the X-ray crystal structure of human acidic FGF (aFGF), with data extending to 2.0 angstroms resolution. The crystal contains four independent molecules in the asymmetric unit. Each molecule contains a single bound sulfate ion, in similar juxtapositions. The bound sulfate is stabilized through hydrogen-bond interactions with residues Asn 18, Lys 113, and Lys 118 and defines a potential heparin binding site. The hydrogen bond with the N delta 2 moiety of Asn 18 appears to be the most conserved interaction, being similar to those observed for sulfate ion bound to human basic FGF (bFGF) and similar but not identical to interactions observed for bovine aFGF with heparin analogs. Of the added solvent groups, five ordered water molecules are conserved in each of the four independent structures of human aFGF. These water molecules, located at buried positions, provide hydrogen bonding partnerships with several buried polar groups in the core of the protein. A central interior cavity exists in each of the four structures, with sizes ranging from approximately 20 to 50 angstroms3. The cavity sizes appear to be significantly smaller than that observed in the related protein interleukin-1 beta. The region comprising the high affinity FGF receptor binding site is structurally very similar to the corresponding region from human bFGF, whereas the low affinity site is structurally quite different. The results provide a structural basis for the role of the low affinity binding site in FGF receptor discrimination.

Acidic fibroblast growth factor accelerates dermal wound healing in diabetic mice.

Acidic fibroblast growth factor (aFGF) is a potent mitogenic and chemotactic agent for vascular endothelial cells, dermal fibroblasts, and epidermal keratinocytes, the principal cellular constituents of skin. To explore its potential to heal chronic dermal wounds, we applied pure recombinant human aFGF topically to full-thickness excisional injuries in healing-impaired genetically diabetic mice. Transformation of the nonlinear percent initial wound areas as a function of time to linear rates of tissue ingrowth from the original wound edges showed that aFGF increased wound closure in a dose-dependent manner. Optimal 3-micrograms/cm2 doses of aFGF nearly tripled the linear rate of healing. The median time to complete closure decreased from 46 d in vehicle-treated wounds to only 16 d in those treated with aFGF. Histomorphometric analyses established that aFGF increased granulation tissue formation and reepithelialization throughout healing. Vehicle- and aFGF-treated wounds appeared to be histologically equivalent by the time of closure. Therefore, aFGF has potential therapeutic applications for promoting healing of dermal ulcers, especially in healing-impaired individuals.

Purification and characterization of a naturally occurring vascular endothelial growth factor.placenta growth factor heterodimer.

Vascular endothelial growth factor (VEGF) is a potent and selective mitogen for endothelial cells that is angiogenic in vivo and induced by hypoxia. A homologous protein, placenta growth factor (PlGF), is also reported to be mitogenic for endothelial cells in culture. The rat GS-9L glioma cell line produces not only VEGF homodimers but also PlGF homodimers and a novel heterodimer composed of VEGF and PlGF subunits. All three dimeric forms were purified to apparent homogeneity, and their structures and mitogenic activities were compared. VEGF.PlGF heterodimers are vascular endothelial cell mitogens nearly as potent as VEGF homodimers. Therefore, some of the biological activities attributed to VEGF homodimers might be mediated by VEGF.PlGF heterodimers. In contrast, pure PlGF homodimers are mitogenic for endothelial cells only at high, possibly non-physiologic concentrations; thus the biological relevance of their mitogenic activity for these cells is not obvious. However, the existence of not only homodimers but also heterodimers clearly extends the similarity between the VEGF/PlGF and the homologous platelet-derived growth factor systems.

Specificity of vascular endothelial cell growth factor receptor ligand binding domains.

Vascular endothelial cell growth factor binds with high affinity to FLT and KDR, two homologous tyrosine kinase receptors expressed on vascular endothelial cells. Placental growth factor, a vascular endothelial cell growth factor homologue, also binds with high affinity to the extracellular domains of FLT but not to the extracellular region of KDR. Vascular endothelial cell growth factor binds competitively with placental growth factor to the extracellular ligand binding domains of FLT, indicating that both ligands probably complex to overlapping or identical regions of this receptor.

Polylysine activates smooth muscle actin-myosin interaction without LC20 phosphorylation.

Phosphorylation/dephosphorylation of the 20-kDa light chain of smooth muscle myosin is a major regulator of actin-myosin interaction. Phosphatase inhibitors have thus been shown to enhance contraction in smooth muscle. The activity of type II phosphatase against phosphorylated myosin light chains is inhibited by polylysine. Thus we studied the effects of polylysine (10-13 kDa) on actin-myosin interaction in permeabilized guinea pig taenia coli fibers and in bovine aortic actomyosin. Addition of polylysine (10-20 microM) to Ca-ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid buffered solution ([Ca2+] less than 0.01 microM) elicited a contraction in fibers of 40 +/- 8% (n = 6) of maximally stimulated contractions ([Ca2+] congruent to 1.5 microM). Untreated fibers did not generate any significant force in parallel control experiments. Similarly, polylysine stimulated the ATPase activity both in fibers and actomyosin in a dose-dependent manner. This stimulation could be completely inhibited and abolished upon addition of heparin, a negatively charged heteropolysaccharide. In actomyosin previously phosphorylated with ATP gamma S, polylysine in a concentration range of 2-13 microM did not further stimulate enzyme activity. These increases in activity were not connected with significant changes in the phosphorylation of 20-kDa myosin light chain nor could any incorporation of 32P associated with polylysine stimulation be detected in both skinned fibers and actomyosin by autoradiography of SDS gels. Our data indicate that polylysine increases actin-myosin interaction in both smooth muscle model systems by directly influencing contractile proteins. As such, polylysine may be a useful probe for the mechanism of activation of smooth muscle.

Acidic fibroblast growth factor accelerates dermal wound healing.

Acidic fibroblast growth factor (aFGF) is a potent mitogen in vitro for many cells of ectodermal and mesodermal embryonic origin including skin-derived epidermal keratinocytes, dermal fibroblasts and vascular endothelial cells. Based on the mitogenic activity for these skin-derived cells, we tested the ability of topically applied aFGF to promote healing of full-thickness dermal wounds in healthy rodents. Low doses of aFGF can produce almost a two-fold maximum acceleration in the rate of closure of full-thickness dermal punch biopsy wounds in young healthy mice and rats. The mitogen also produces a 3 to 4 day acceleration in the time to complete closure in rats. Quantitative histomorphometric analysis of wound tissue shows that aFGF induces a marked stimulation of angiogenesis, granulation tissue formation and the growth of new epithelium, but does not promote dermal contraction. Application of aFGF to linear incisions in rat skin produces a transient increase in wound tensile strength accompanied by enhanced cellularity and deposition of collagen. Therefore, aFGF functions as a pharmacological agent that can accelerate dermal wound healing in rodents and could act therapeutically to promote dermal tissue repair in humans.

Conversion of cysteine to serine residues alters the activity, stability, and heparin dependence of acidic fibroblast growth factor.

Acidic fibroblast growth factor (aFGF) is a broad spectrum mitogen that is stabilized by complexation with heparin and heparan proteoglycans. The monomeric human protein contains 3 reduced cysteine residues of unknown function, the first 2 of which are conserved among all seven known fibroblast growth factors. The influence of these free sulfhydryl groups on the level, stability, and heparin dependence of the mitogenic activity at physiological temperature and pH is characterized using a complete set of site-directed mutants in which either any 1, 2, or all 3 of the cysteine residues are converted to serines. Mutants of aFGF in which either any 2 or all 3 cysteine residues are substituted by serines are more active, have longer activity half-lives, and are less heparin dependent than wild-type aFGF. In contrast, wild-type aFGF and the three mutants that each retain 2 cysteine residues inactivate more rapidly in the absence of heparin by a nonproteolytic mechanism but are markedly stabilized by heparin. This cysteine-mediated destabilization of aFGF not only diminishes its activity in the absence of heparin in tissue culture but also could functionally restrict its activity in vivo to the vicinity of mast cell-derived heparins and heparan proteoglycans associated with cell surfaces and basement membranes.

Laminin-mediated process formation in neuronal cells involves protein dephosphorylation.

Laminin mediates neural adhesion and process formation. A possible signal transduction pathway for laminin was investigated in both NG108-15 and PC12 neuronal cells using radiolabeling studies as well as various stimulators and inhibitors of phosphatases and kinases. Using [32P]-ortho-phosphate, laminin caused a decrease in the TCA-precipitable counts. Further, laminin stimulated dephosphorylation of laminin binding proteins of 110 kDa, 67 kDa, and 45 kDa and this dephosphorylation was blocked by the phosphatase inhibitor, okadaic acid, and the protein kinase C stimulator, TPA. The phosphatase inhibitors okadaic acid and vanadate, as well as the protein kinase C stimulators, TPA and DAG, blocked laminin-mediated process formation. Inhibitors of kinase activity such as H-7, H-8, and H-9 increased laminin-mediated neural process formation. Since phosphate incorporation into laminin-binding proteins is decreased by laminin and because both phosphatase inhibitors and kinase stimulators inhibit laminin-mediated process formation, we conclude that dephosphorylation events promote the neural cell response to laminin.

Disulfide bonds are neither required, present, nor compatible with full activity of human recombinant acidic fibroblast growth factor.

Human acidic fibroblast growth factor (aFGF) is a potent broad-spectrum mitogen that contains three Cys residues within its monomeric structure. We have found that site-directed mutants in which any one of these Cys residues is converted to serine remain highly active, although variably dependent on heparin, so none of the three possible intramolecular disulfide bonds that can be formed are required for mitogenic activity. Furthermore, a dispensable disulfide bond that might stabilize the active conformation is not present since all three Cys residues are accessible to chemical modification in recombinant as well as brain-derived aFGFs. Finally, formation of a disulfide bond between the two Cys residues conserved among all seven known members of the FGF family results in a virtually inactive product that can subsequently be reactivated by reduction. Thus, despite the extracellular function of aFGF, its Cys residues do not form intramolecular disulfide bonds in the active conformation.

Modulation of glycogen synthase kinase activity of skeletal and smooth muscle casein kinase I by spermine.

Casein kinase I (CK-I) from skeletal muscle was stimulated 2-3 fold by 0.25-1 mM spermine. The polyamine also stimulated the phosphorylation of glycogen synthase by another casein kinase purified from aortic smooth muscle [DiSalvo et al. (1986) Biochem. Biophys. Res. Commun. 136, 789-796]. Phosphopeptide maps and phosphoamino acid analysis of [32P]glycogen synthase revealed that smooth muscle casein kinase phosphorylated glycogen synthase in the same sites that undergo phosphorylation by CK-I. The stimulatory effect of spermine on glycogen synthase kinase activity of CK-I was accompanied by increased phosphorylation of all peptide sites of glycogen synthase. Increased phosphorylation was observed in both seryl and threonyl residues. Higher concentrations (4 mM) of spermine inhibited CK-I activity by about 50%. These results indicate that aortic smooth muscle casein kinase is a CK-I enzyme and that skeletal and smooth muscle CK-I can be modulated by spermine.

A myosin phosphatase modulates contractility in skinned smooth muscle.

The influence of a purified holoenzyme form of polycation-modulable (PCM-) myosin phosphatase on Ca2+-dependent actin-myosin interactions was studied in detergent-skinned smooth muscle fibers from chicken gizzard. The concentration of Ca2+ required for half maximal isometric contraction (A0.5; 0.26 microM) of fibers incubated in the absence of phosphatase was increased 2-fold when PCM-phosphatase (13 U/ml) was included in the medium. Removal of the phosphatase restored A0.5 to control level showing that the enzyme-mediated decrease in Ca2+-sensitivity was reversible. Two-dimensional electrophoresis of fiber homogenates revealed that PCM-phosphatase decreased Ca2+-sensitivity for phosphorylation of the regulatory myosin light chains in parallel fashion. Ca2+-dependent increases in isometric force were directly correlated to increases in the extent of light chain phosphorylation up to about 0.35 mol PO4/mol light chain; further increases in phosphorylation were not associated with further increases in force. Addition of PCM-phosphatase to fibers which had been contracted with a suboptimal concentration of Ca2+ (0.35 microM) resulted in rapid relaxation. Unloaded shortening velocity, reflecting cross-bridge cycling rate, was reduced by 92% in the presence of PCM-phosphatase and light chain phosphorylation was decreased by 50%. These data show that both tension and unloaded shortening velocity may be related to Ca2+-dependent phosphorylation of the light chains. The results indicate that the level of phosphorylation attained in the fiber preparations studied probably reflects the ratio of myosin kinase to phosphatase activities. Since protein phosphatases are regulated enzymes the results also suggest that modulation of phosphatase activity may participate in control of smooth muscle contractility.

Sindbis virus mutant ts20 of complementation group E contains a lesion in glycoprotein E2.

A technique has been devised to readily obtain the entire structural protein region of Sindbis virus cloned into a plasmid vector. This method uses the fact that the nearest site for restriction enzyme HindIII to the 3' terminal poly(A) occurs at nucleotides 6266-6271 in the genomic RNA. Inserts extending from the poly(A) tract to this HindIII site are 5438 nucleotides long (excluding the poly A tract) and contain the entire 4106-nucleotide structural protein region. Using an oligo(dT)-tailed vector as a primer for first strand cDNA synthesis such clones could be obtained in high yield. We were interested in a precise determination of the mutation responsible for the temperature-sensitive phenotype of ts20, a mutant belonging to complementation group E which has a defect in the function of glycoprotein E2 at the nonpermissive temperature. Using this technique we have cloned and sequenced the structural protein region of ts20 and of several revertants and concluded that the mutation was a change from histidine to leucine at amino acid 291 of E2. Reversion to temperature insensitivity occurred by same site reversion to the parental nucleotide, restoring the original histidine as amino acid 291. Thus, complementation group E of Sindbis virus results from changes in glycoprotein E2 and together with previous results from our laboratory (Arias et al., 1983; Hahn et al., 1985) demonstrates that the three RNA+ complementation groups of Sindbis virus, C, D, and E, result from changes in the three structural proteins of the virus, capsid, glycoprotein E1, and glycoprotein E2, respectively.

Eicosonoid metabolism and beta-adrenergic mechanisms in coronary arterial smooth muscle: potential compartmentation of cAMP.

Beta-Adrenergic relaxation in bovine coronary arteries is enhanced by inhibition of eicosonoid metabolism and inhibited by its stimulation. We investigated the interaction between eicosonoid metabolism and beta-adrenergic mechanisms by studying the effect of perturbations of eicosonoid metabolism on vascular adenosine 3',5'-monophosphate (cAMP) content and the cAMP-dependent relaxation of isometric force and activation of glycogen phosphorylase. KCl (35 mM) elicited a contraction, activated phosphorylase, and slightly decreased cAMP content. Isoproterenol (10(-7) M) relaxed the KCl contraction, further increased phosphorylase activity, and increased cAMP. Neither indomethacin (5 X 10(-6) M) nor arachidonic acid (3 X 10(-5) M) affected the KCl contraction, but arachidonic acid increased both cAMP and phosphorylase activity and indomethacin decreased cAMP. Indomethacin potentiated the relaxation induced by isoproterenol but inhibited the activation of phosphorylase and had no effect on the isoproterenol-induced increase in cAMP. Arachidonic acid, on the other hand, inhibited the isoproterenol-induced relaxation but potentiated both the increases of phosphorylase activity and cAMP. Thus neither relaxation nor phosphorylase activity was related in a straightforward manner to the total cAMP content. A direct relation between cAMP, relaxation, and phosphorylase can be reconciled with the antiparallel effects of alterations of eicosonoid metabolism observed in this study by a proposed model in which the effects of cAMP are assumed to be functionally compartmentalized.

Brain-derived acidic fibroblast growth factor: complete amino acid sequence and homologies.

Bovine brain-derived acidic fibroblast growth factor (aFGF) is a protein mitogen originally identified in partially purified preparations of whole brain. The protein was purified to homogeneity and shown to be a potent vascular endothelial cell mitogen in culture and angiogenic substance in vivo. The homology of aFGF to human interleukin-1 beta was inferred from partial sequence data. The complete amino acid sequence of aFGF has now been determined and observed to be similar to both basic FGF and interleukin-1's. A neuropeptide-like sequence, flanked by basic dipeptides, was observed within the aFGF sequence.