A role for POR1, a Rac1-interacting protein, in ARF6-mediated cytoskeletal rearrangements

The ARF6 GTPase, the least conserved member of the ADP ribosylation factor (ARF) family, associates with the plasma membrane and intracellular endosome vesicles. Mutants of ARF6 defective in GTP binding and hydrolysis have a marked effect on endocytic trafficking and the gross morphology of the peripheral membrane system. Here we report that expression of the GTPase-defective mutant of ARF6, ARF6(Q67L), remodels the actin cytoskeleton by inducing actin polymerization at the cell periphery. This cytoskeletal rearrangement was inhibited by co-expression of ARF6(Q67L) with deletion mutants of POR1, a Rac1-interacting protein involved in membrane ruffling, but not with the dominant-negative mutant of Rac1, Rac1(S17N). A synergistic effect between POR1 and ARF6 for the induction of actin polymerization was detected. Furthermore, we observed that ARF6 interacts directly with POR1 and that this interaction was GTP dependent. These findings indicate that ARF6 and Rac1 function on distinct signaling pathways to mediate cytoskeletal reorganization, and suggest a role for POR1 as an important regulatory element in orchestrating cytoskeletal rearrangements at the cell periphery induced by ARF6 and Rac1.

RAC regulation of actin polymerization and proliferation by a pathway distinct from Jun kinase

The RAC guanine nucleotide binding proteins regulate multiple biological activities, including actin polymerization, activation of the Jun kinase (JNK) cascade, and cell proliferation. RAC effector loop mutants were identified that separate the ability of RAC to interact with different downstream effectors. One mutant of activated human RAC protein, RACV12H40 (with valine and histidine substituted at position 12 and 40, respectively), was defective in binding to PAK3, a Ste20-related p21-activated kinase (PAK), but bound to POR1, a RAC-binding protein. This mutant failed to stimulate PAK and JNK activity but still induced membrane ruffling and mediated transformation. A second mutant, RACV12L37 (with leucine substituted at position 37), which bound PAK but not POR1, induced JNK activation but was defective in inducing membrane ruffling and transformation. These results indicate that the effects of RAC on the JNK cascade and on actin polymerization and cell proliferation are mediated by distinct effector pathways that diverge at the level of RAC itself.

Exercise and resting pulmonary function in sarcoidosis

Patients with sarcoidosis frequently complain of exercise intolerance but reports of the value of static tests of pulmonary function in predicting disability have been contradictory. We studied 32 patients with sarcoidosis and dyspnea, correlating x-ray stages, spirometry and lung volume measurements with graded exercise testing. Patients demonstrated a reduction in maximum workload (Wmax) when compared to an age matched group of 7 normal subjects (p < 0.05). While ventilation (VEmax) at Wmax was lower in patients, when adjusted for workload (V/E/watt) there was relative hyperventilation (p < 0.05). Exercise induced arterial desaturation (PaO2 decrease) was significantly related to resting DLCO% predicted (r = 0.74, p < 0.05). When patients were separated into subgroups of > < DLCO 55% predicted, the lower diffusing capacity group had a lower Wmax and greater fall in exercise PaO2. Chest radiograph staging and the vital capacity proved to be poor predictors of exercise capacity though maximum impairment was associated with advanced x-ray changes and greater decreases in vital capacity. In conclusion, the magnitude of functional impairment may vary widely from apparent histopathologic involvement as reflected by chest x-ray and lung volumes. Actual exercise testing is necessary to accurately characterize and quantitate the impairment in patients with sarcoidosis complaining of dyspnea.

Novel CDC34 (UBC3) ubiquitin-conjugating enzyme mutants obtained by charge-to-alanine scanning mutagenesis

CDC34 (UBC3) encodes a ubiquitin-conjugating (E2) enzyme required for transition from the G1 phase to the S phase of the budding yeast cell cycle. CDC34 consists of a 170-residue catalytic N-terminal domain onto which is appended an acidic C-terminal domain. A portable determinant of cell cycle function resides in the C-terminal domain, but determinants for specific function must reside in the N-terminal domain as well. We have explored the utility of "charge-to-alanine" scanning mutagenesis to identify novel N-terminal domain mutants of CDC34 that are enzymatically competent with respect to unfacilitated (E3-independent) ubiquitination but that nevertheless are defective with respect to its cell cycle function. Such mutants may reveal determinants of specific in vivo function, such as those required for interaction with substrates or trans-acting regulators of activity and substrate selectivity. Three of 18 "single-scan" mutants (in which small clusters of charged residues were mutated to alanine) were compromised with respect to in vivo function. One mutant (cdc34-109, 111, 113A) targeted a 12-residue segment of the Cdc34 protein not found in most other E2s and was unable to complement a cdc34 null mutant at low copy numbers but could complement a null mutant when overexpressed from an induced GAL1 promoter. Combining adjacent pairs of single-scan mutants to produce "double-scan" mutants yielded four additional mutants, two of which showed heat and cold sensitivity conditional defects. Most of the mutant proteins expressed in Escheria coli displayed unfacilitated (E3-independent) ubiquitin-conjugating activity, but two mutants differed from wild-type and other mutant Cdc34 proteins in the extent of multiubiquitination they catalyzed during an autoubiquitination reation-conjugating enzyme function and have identified additional mutant alleles of CDC34 that will be valuable in further genetic and biochemical studies of Cdc34-dependent ubiquitination.

Characterization of novel yeast RAD6 (UBC2) ubiquitin-conjugating enzyme mutants constructed by charge-to-alanine scanning mutagenesis

Ubiquitination of intracellular proteins by the yeast RAD6 (UBC2) ubiquitin-conjugating (E2) enzyme is required for cellular processes as diverse as DNA repair, selective proteolysis, and normal growth. For most RAD6-dependent functions, the relevant in vivo targets, as well as the mechanisms and cofactors that govern RAD6 substrate selectivity, are unknown. We have explored the utility of "charge-to-alanine" scanning mutagenesis to generate novel RAD6 mutants that are enzymatically competent with respect to unfacilitated (E3-independent) ubiquitination but that are nevertheless severely handicapped with respect to several in vivo functions. Five of the nine mutants we generated show defects in their in vivo functions, but almost all of the most severely affected mutants displayed unfacilitated ubiquitin-conjugating activity in vitro. We suggest that E2 mutants obtained by this approach are likely to be defective with respect to interaction with other, trans-acting factors required for their intracellular activity or substrate selectivity and therefore will be useful for further genetic and biochemical studies of ubiquitin-conjugating enzyme function.

Construction and initial characterization of a mouse-human chimeric anti-TNF antibody

Tumor necrosis factor-alpha (TNF) has been implicated in the pathogenesis of a variety of human diseases including septic shock, cachexia, graft-versus-host disease and several autoimmune diseases. Monoclonal antibodies directed against TNF provide an attractive mode of therapeutic intervention in these diseases. We have generated a murine monoclonal antibody (A2) with high affinity and specificity for recombinant and natural human TNF. To increase its therapeutic usefulness, we used genetic engineering techniques to replace the murine constant regions with human counterparts while retaining the murine antigen binding regions. The resulting mouse-human chimeric antibody should have reduced immunogenicity and improved pharmacokinetics in humans. Molecular analysis of light chain genomic clones derived from the murine hybridoma suggests that two different alleles of the same variable region gene have rearranged independently and coexist in the same hybridoma cell. The chimeric A2 antibody (cA2) exhibits better binding and neutralizing characteristics than the murine A2 which was shown to contain a mixture of two kappa light chains. The properties of cA2 suggest that it will have advantages over existing murine anti-TNF antibodies for clinical use.

Lung transplantation in New Jersey

Single- or bilateral-lung transplantation is an effective treatment for end-stage pulmonary diseases. Refinements in the surgical technique and postoperative management of recipients have resulted in a return to normal function in most cases and a one-year survival in 70 percent of patients.

Stable expression of cloned human antibody genes in murine myeloma cells

Human monoclonal antibodies (MAbs) offer potential advantages over murine MAbs for therapy because they are not likely to elicit immune responses and are expected to interact more efficiently with the human immune system to activate therapeutically useful functions. Traditional methods for obtaining human MAbs (i.e., immortalization of B cells by cell fusion or transformation) can result in low and unstable antibody secretion. Recently, methods have been devised for direct cloning of human variable region genes via polymerase chain reaction and phage combinatorial libraries. Both types of human MAb production can benefit from expression systems that support the stable, high-level antibody secretion required for therapeutic use. Using an existing human-derived hybridoma that secretes a human IgM antibody as a convenient source of antibody genes, we have demonstrated that cloned human antibody genes can be efficiently expressed in murine myeloma cells and that cell lines with properties suitable for large-scale economical production can be obtained. We were unable to detect any differences between the antibodies produced by the original hybridoma and the engineered cell line. In addition, we were able to express an IgG form of the antibody, showing that expression of a recombinant human antibody need not be limited to the original antibody class.

Late auditory evoked potentials in alcoholics. Identifying those with a history of epileptic seizures during withdrawal

The N1-P2 wave of the auditory evoked potential was studied in 19 alcoholics, six of whom had withdrawal seizures on previous admissions. The recordings were made at 1 and 5 days after cessation of drinking. Eight nonalcoholic volunteers were used as controls. The latencies of N1 and P2 were slightly prolonged in alcoholics, but during the detoxification period they frequently shortened (p less than 0.05), occasionally attaining the values of the controls. One day after withdrawal, the amplitude of N1-P2 was consistently reduced in the alcoholics compared to the controls (p less than 0.05 and p less than 0.01), but higher in alcoholics with a seizure history compared to alcoholics without seizures (p less than 0.05 and p less than 0.001). Five days after cessation of drinking, the amplitude in the alcoholic groups always increased from the admission values (p less than 0.05 and p less than 0.01). By that time, the alcoholics with a history of withdrawal seizures had significantly (p less than 0.05 and p less than 0.01) higher amplitudes than those of the controls or the alcoholics without seizures. Large N1-P2 amplitude during alcohol withdrawal may reflect increased cerebral excitability and contribute to the identification of alcoholics with high risk for withdrawal seizures.

Cardiac sarcoidosis. A case with unusual manifestation

A 26-year-old woman was hospitalized with new-onset congestive heart failure. M-mode and two-dimensional echocardiography revealed abnormal motion involving the apex and posterolateral wall of the left ventricle. Cardiac catheterization was performed. The left ventriculogram demonstrated apical akinesis and an apical filling defect. The diagnosis of cardiac sarcoidosis was made from an open myocardial biopsy.

Inhibition of platelet phospholipid methylation during platelet secretion

A pathway for the synthesis of membrane phosphatidylcholine involving the N-methylation of phosphatidylethanolamine has been detected in several types of mammalian cells. Furthermore, it has been implicated in the coupling of agonist binding to cell response. We examined whether human platelets exhibit this synthetic pathway and whether platelet agonists influence its activity. When washed platelets were incubated with 0.15 microM L-[methyl-3H]methionine at 37 degrees C, they incorporated methyl-3H into their phospholipids linearly at the rate of 1 pmole/10(9) platelets/hr. When incubated with 20 microM radiolabeled methionine, they incorporated about 15 pmole/10(9) platelets/hr. The radioactivity was found predominantly in phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidylcholine. Thrombin caused an immediate (within 15 sec) and sustained (up to 30 min) decrease in the rate and extent of N-methylation of platelet phospholipids. This was accounted for by a decrease in synthesis of methylated phospholipids rather than an increase in their degradation. This thrombin effect correlated with serotonin release and could be dissociated from platelet aggregation and prostaglandin synthesis. Thrombin also decreased the synthesis of phosphatidylcholine when choline was used as the radiolabeled substrate. Other agonists such as epinephrine, adenosine diphosphate (ADP), or A23187 also decreased phospholipid methylation under conditions in which they stimulated serotonin release. These data demonstrate that platelets are capable of synthesizing phosphatidylcholine from phosphatidylethanolamine by N-methylation and that agonists perturb this pathway as they induce platelet secretion. The precise role of phospholipid methylation in either resting or stimulated platelets remains to be established.

Carbenicillin and penicillin G inhibit platelet function in vitro by impairing the interaction of agonists with the platelet surface

Carbenicillin or penicillin G administered in large doses can cause a bleeding diathesis as a result of platelet dysfunction. These antibiotics also inhibit platelet aggregation in vitro, although several-fold larger concentrations of drug are required to demonstrate this effect. We wondered whether these antibiotics might impair platelet function by interfering with the initial step of platelet activation: the binding of agonists to their specific receptors on the platelet surface.Platelet aggregation and [(14)C]serotonin release induced by epinephrine were competitively inhibited by carbenicillin and penicillin G in vitro. At antibiotic concentrations that inhibited platelet function by more than 80%, the affinity of platelet alpha-adrenergic receptors for the alpha-adrenergic antagonist, [(3)H]dihydroergocryptine, and for epinephrine was reduced twofold by carbenicillin and sixfold by penicillin G (P < 0.01). Platelet aggregation and [(14)C]serotonin release stimulated by ADP were also competitively inhibited by these antibiotics. In addition, carbenicillin reduced the incorporation of an ADP affinity label, 5'-p-fluorosulfonylbenzoyl [(3)H]adenosine, into its binding protein in platelet membranes. Moreover, both carbenicillin and penicillin G impaired the interaction of von Willebrand factor with platelets as evidenced by their inhibition of the agglutination of formalin-fixed platelets by ristocetin, snake venom, or bovine factor VIII. These studies demonstrate that carbenicillin and penicillin G inhibit platelet function in vitro by impairing the interaction of several agonists with their specific receptors on the platelet surface membrane. If this were mechanism operative in vivo, it could account for the hemorrhagic as well as the potential antithrombotic effects of these antibiotics.

Carbenicillin and Penicillin G Impair Platelet Function by Inhibiting the Binding of Agonists to the Platelet Surface

Carbenicillin (carb) and penicillin G (pen) inhibit human platelet function in vivo and can cause a bleeding diathesis. Since the mechanism by which these drugs inhibit platelets is unknown, we investigated whether they might interfere with the binding of epinephrine, ADP, or ristocetin (von Willebrand factor) to the platelet surface in vitro. Pen (10 mM) or carb (20 mM) produced a 6-fold decrease in the affinity of receptors on intact platelets for both epinephrine and for the α-adrenergic antagonist, 3U-dihydroer-gocryptine (p < 0.001). Neither antibiotic changed the maximum number of α-adrenergic binding sites per platelet. Pen and carb at these concentrations completely inhibited 14C-serotonin release induced by 1 μM epinephrine and inhibited primary platelet aggregation by 1 μM. Similarly, these antibiotics inhibited aggregation and serotonin release induced by 1 μM ADP and inhibited the covalent binding of an ADP analogue (5'FSO2BZAdo) to its specific binding protein in platelet membranes. Moreover, pen and carb inhibited competitively the agglutination of platelets by ristocetin. Thus, carbenicillin and penicillin G decrease the affinity of a number of distinct platelet receptors for their specific agonists, and this correlates with inhibition of platelet function induced by these agonists. Interaction of these antibiotics with the platelet surface membrane may account for their hemorrhagic as well as their anti-thrombotic activity.

Platelet function in essential thrombocythemia. Decreased epinephrine responsiveness associated with a deficiency of platelet alpha-adrenergic receptors

Platelets from two patients with essential thrombocythemia failed to aggregate or release serotonin in response to concentrations of epinephrine that aggregated platelets from normal controls. Therefore, we studied their alpha-adrenergic receptors, using 3H-dihydroergocryptine (3H-DHE), an alpha-adrenergic antagonist. These platelets contained an average (mean +/- S.E.) of 210 +/- 18 and 227 +/- 27 3H-DHE binding sites per platelet--less than half that found on control platelets, 464 +/- 37 (P less than 0.01). In contrast, platelets from two other patients with essential thrombocythemia responded to epinephrine and contained a normal number of 3H-DHE sites. Platelets in essential thrombocythemia demonstrated normal kinetics of 3H-DHE binding and normal affinities for 3H-DHE and for epinephrine. When control platelets were preincubated with a half-saturating concentration of 3H-DHE, there was a diminution of epinephrine-induced platelet function comparable to that seen in essential thrombocythemia. Thus, a deficiency of alpha-adrenergic receptors may account for diminished functional responsiveness of platelets to epinephrine in some patients with essential thrombocythemia.

Elevation of platelet factor four in acute myocardial infarction: measurement by radioimmunoassay

A radioimmunoassay has been developed for the measurement of PF-4--a chemically well-defined heparin-neutralizing molecule. PF-4 was iodinated, repurified by affinity chromatography on heparin-Sepharose, and incubated with rabbit antiserum and a source of unlabeled antigen. Following incubation at 4 degrees C for 24 hr, bound PF-4 was precipitated with 2.2M ammonium sulfate. The assay, which could detect 25 pg of purified PF-4, was unaffected by the presence of plasma containing up to 50 U/ml heparin. The plasma concentration of PF-4 in 30 normal subjects was 16 +/- 4 ng/ml. This level was increased in patients with pulmonary emboli, prosthetic cardiac valves, and severe cardiorespiratory failure. In addition, 21 of 50 patients admitted to the hospital with acute chest pain who had sustained a myocardial infarct had a mean level of 95 ng/ml. In contrast, the mean level in 21 patients with chest pain but without evidence of infarction was 29 ng/ml. PF-4 remained elevated for at least 1 week after infarction in six of the eight patients studied and then returned to within the normal range. The data suggest that radioimmunoassay of PF-4 may be a useful test to measure activation of the coagulation system and an aid to the diagnosis and treatment of patients with thromboembolic disorders.