Factor VIII, ABO blood group and the incidence of ischaemic heart disease

Relations of factor VIII activity, FVIIIC, and von Willebrand factor antigen (vWFAg), with ischaemic heart disease (IHD) were examined in 1393 men aged between 40 and 64 years at entry to the Northwick Park Heart Study (NPHS) who experienced 178 first major episodes of IHD during an average follow-up period of 16.1 years. After allowing for the large factor VIII differences between the main ABO blood groups, FVIIIC was probably associated with IHD incidence, possibly more strongly with fatal than non-fatal episodes. Thus, an increase of 1 standard deviation in FVIIIC raised the risk of fatal IHD by about 28%. vWFAg was also significantly associated with fatal events. The observed relation of FVIIIC with IHD incidence probably underestimates the true strength of the association because of the considerable within-person and laboratory variability in factor VIII measurements. FVIIIC and vWFAg were strongly correlated (r = 0.57) and in statistical terms there may be little to choose between them in long-term studies of IHD. Taking account of evidence that haemophiliacs seem to experience less IHD than expected, high factor VIII levels may contribute to the incidence of IHD by increasing thrombogenic potential. The incidence of IHD was significantly higher in those of blood group AB than in those of groups O, A or B, particularly for fatal events. There was no evidence that the FVIIIC and vWFAg associations with IHD are determined by ABO group. The factor VIII and ABO blood group effects therefore appeared to be independent. Group AB may be a genetic marker of characteristics influencing other indices of IHD risk such as short stature, NPHS men (though not women) of group AB being about 2 cm shorter than those of other groups.

Differential localization and sequence analysis of capping protein beta-subunit isoforms of vertebrates

Capping protein nucleates the assembly of actin filaments and stabilizes actin filaments by binding to their barbed ends. We describe here a novel isoform of the beta subunit of chicken capping protein, the beta 2 isoform, which arises by alternative splicing. The chicken beta 1 isoform and the beta 2 isoform are identical in their amino acid sequence except for a short region at the COOH terminus; this region of the beta subunit has been implicated in binding actin. Human and mouse cDNAs of the beta 1 and beta 2 isoforms also were isolated and among these vertebrates, the COOH-terminal region of each isoform is highly conserved. In contrast, comparison of the sequences of the vertebrate beta subunit COOH-termini to those of lower eukaryotes shows no similarities. The beta 2 isoform is the predominant isoform of nonmuscle tissues and the beta 1 isoform, which was first characterized in studies of capping protein from chicken muscle, is the predominant isoform of muscle tissues, as shown by immunoblots probed with isoform-specific antibodies and by RNAse protection analysis of mRNAs. The beta 2 isoform also is a component of dynactin complex from brain, which contains the actin-related protein Arp1. Both beta-subunit isoforms are expressed in cardiac muscle but they have non-overlapping subcellular distributions. The beta 1 isoform is at Z-discs of myofibrils, and the beta 2 isoform is enriched at intercalated discs; in cardiac myocytes grown in culture, the beta 2 isoform also is a component of cell-cell junctions and at sites where myofibrils contact the sarcolemma. The biochemical basis for the differential distribution of capping protein isoforms is likely due to interaction with specific proteins at Z-discs and cell-cell junctions, or to preferential association with different actin isoforms. Thus, vertebrates have developed isoforms of capping protein that associate with distinct actin-filament arrays.

A yeast actin-related protein homologous to that in vertebrate dynactin complex is important for spindle orientation and nuclear migration

Spindle orientation controls nuclear migration and segregation during mitosis. In yeast, defects in dynein and astral microtubules lead to abnormal spindle orientation and nuclear migration. Dynactin complex is necessary for dynein-mediated vesicle motility in vitro. The major polypeptide of dynactin complex is an actin-related protein in the family Arp1. We have identified in S. cerevisiae a novel actin-related gene, ACT5, in the Arp1 family. An act5 null mutant has defects in spindle orientation and nuclear migration, as does overexpression of Act5p. The phenotype of a double mutant lacking dynein and Act5p is similar to that of single mutants. Therefore, dynactin complex is in the same pathway as dynein and may be necessary for the action of dynein in vivo.

Csk suppression of Src involves movement of Csk to sites of Src activity

Csk phosphorylates Src family members at a key regulatory tyrosine in the C-terminal tail and suppresses their activities. It is not known whether Csk activity is regulated. To examine the features of Csk required for Src suppression, we expressed Csk mutants in a cell line with a disrupted csk gene. Expression of wild-type Csk suppressed Src, but Csk with mutations in the SH2, SH3, and catalytic domains did not suppress Src. An SH3 deletion mutant of Csk was fully active against in vitro substrates, but two SH2 domain mutants were essentially inactive. Whereas Src repressed by Csk was predominantly perinuclear, the activated Src in cells lacking Csk was localized to structures resembling podosomes. Activated mutant Src was also in podosomes, even in the presence of Csk. When Src was not active, Csk was diffusely located in the cytosol, but when Src was active, Csk colocalized with activated Src to podosomes. Csk also localizes to podosomes of cells transformed by an activated Src that lacks the major tyrosine autophosphorylation site, suggesting that the relocalization of Csk is not a consequence of the binding of the Csk SH2 domain to phosphorylated Src. A catalytically inactive Csk mutant also localized with Src to podosomes, but SH3 and SH2 domain mutants did not, suggesting that the SH3 and SH2 domains are both necessary to target Csk to places where Src is active. The failure of the catalytically active SH3 mutant of Csk to regulate Src may be due to its inability to colocalize with active Src.

Hyperoxia stimulates interleukin-8 release from alveolar macrophages and U937 cells: attenuation by dexamethasone

Pulmonary oxygen toxicity is associated with histological evidence of polymorphonuclear neutrophil (PMN) infiltration into lung parenchyma. What guides infiltration of these cells is unknown. A number of chemoattractants for PMN have been documented including interleukin-8 (IL-8), a cytokine released by alveolar macrophages (AM) and other cell types. The purposes of this study were to 1) determine whether human AM and the histiocytic U937 cell line release IL-8 in response to hyperoxia, 2) assess whether hyperoxia results in increased IL-8 steady-state mRNA levels in U937 cells and 3) establish whether dexamethasone could attenuate noted effects of hyperoxia. Our study shows that hyperoxia stimulates human AM and U937 cell release of IL-8. Hyperoxia also increases IL-8 mRNA levels in U937 cells. IL-8 released in response to hyperoxia by AM was biologically active as evidenced by ability to induce PMN chemotaxis. A polyclonal antibody to IL-8 partially attenuated this chemotactic activity. Finally, dexamethasone at concentrations of 10 microM, 1 microM, and 100 nM markedly reduced hyperoxia-induced IL-8 release and mRNA synthesis by U937 cells. We conclude that IL-8 may be important in the pathogenesis of pulmonary oxygen toxicity and that therapeutic concentrations of dexamethasone can suppress production of this cytokine.

The effects of intravenous Triton WR-1339 on factor VII coagulant activity and plasma lipoproteins in normocholesterolaemic and hypercholesterolaemic rabbits

The hypothesis that lipolysis of large lipoproteins by lipoprotein lipase (LPL) has an important influence on the activation of the contact system of coagulation and subsequently on factor VII activation was tested in rabbits rendered hyperlipidaemic by dietary means and/or by injection of Triton WR-1339. The dietary treatment involved a control diet and two isocaloric diets containing either a 0.5% cholesterol or 0.5% cholesterol and 7.5% safflower oil supplement. Other groups of rabbits were given either a standard diet or the standard diet supplemented with 1% cholesterol. All supplemented diets increased many-fold the concentrations of cholesterol associated with the chylomicron, very low-(VLDL), intermediate-(IDL) and low-density (LDL) lipoprotein fractions. Factor VII coagulant activity (FVIIc) increased significantly in all groups of rabbits fed the cholesterol supplement. The intravenous injection of Triton WR-1339 into rabbits fed either the standard or 1% cholesterol-supplemented diet resulted in increases of plasma cholesterol and triglyceride concentrations up to 36-48 h thereafter, followed by decreases up to completion of the experiment at 72 h. Most of these increases in plasma lipids were associated with the chylomicron and VLDL fractions. Following injection of Triton into rabbits fed either the standard or cholesterol-supplemented diet, changes in FVIIc were biphasic with a decrease in activity in the early intervals when rates of accumulation of plasma lipid were constant, and a progressive increase in activity at later intervals when rates of lipid accumulation declined and then reversed.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient localized accumulation of actin in Caenorhabditis elegans blastomeres with oriented asymmetric divisions

During Caenorhabditis elegans embryogenesis, specific cells in the P1 lineage rotate their duplicated centrosome pair onto the anterior-posterior axis; this rotation is correlated with and necessary for a differential inheritance of cytoplasmic determinants in the daughter cells. Centrosome pair rotation is sensitive to inhibitors of actin and microtubule polymerization and may require microtubule attachment to a specific cortical site. We show that actin and the barbed-end binding protein, capping protein, transiently accumulate at this cortical site, possibly by assembly onto persistent remnants of previous cell divisions. Based on these observations, we propose a model for the molecular basis of centrosome rotation that is consistent with the dependence of rotation on actin filaments and microtubules.

Ultrastructural analysis of the dynactin complex: an actin-related protein is a component of a filament that resembles F-actin

The dynactin complex visualized by deepetch electron microscopy appears as a short filament 37-nm in length, which resembles F-actin, plus a thinner, laterally oriented filament that terminates in two globular heads. The locations of several of the constituent polypeptides were identified on this structure by applying antibodies to decorate the dynactin complex before processing for electron microscopy. Antibodies to the actin-related protein Arp1 (previously referred to as actin-RPV), bound at various sites along the filament, demonstrating that this protein assembles in a polymer similar to conventional actin. Antibodies to the barbed-end actin-binding protein, capping protein, bound to one end of the filament. Thus, an actin-binding protein that binds conventional actin may also bind to Arp1 to regulate its polymerization. Antibodies to the 62-kD component of the dynactin complex also bound to one end of the filament. An antibody that binds the COOH-terminal region of the 160/150-kD dynactin polypeptides bound to the globular domains at the end of the thin lateral filament, suggesting that the dynactin polypeptide comprises at least part of the sidearm structure.

Clustering of human T lymphotropic virus type I seropositive in Montserrat, West Indies: evidence for an environmental factor in transmission of the virus

A community survey of human T cell lymphotropic virus type I (HTLV-I) in Montserrat, West Indies, identified 22 instances in which 2 HTLV-I-seropositive adults lived within 60 m of each other (close pairs), compared with 7.8 expected (P < .001). Five of these close pairs were mother-offspring or husband-wife. The remaining 17 pairs were of unrelated members in separate households. The percentages of male-female (41%), female-female (41%), and male-male (18%) types in these 17 pairs were very similar to those among the 1377 similarly defined pairs in which neither or only 1 member was seropositive, affording no support for extramarital heterosexual activity as an explanation for the clustering observed. Thus, the demography of HTLV-I was not accounted for completely by sexual and mother-to-offspring transmission. The predominance of clustering of unrelated HTLV-I-seropositive individuals in locations with high mosquito infestation raised the possibility of sporadic transmission of HTLV-I by hematophagous insects.

Alteration of cellular cytosolic calcium and chemotactic peptide binding by an inhibitor of neutrophil function

The lung is frequently exposed to particulate material that can potentially stimulate release of factors that attract polymorphonuclear neutrophils (PMN). However, few PMN are noted in the airways of normal subjects, suggesting there is some mechanism to dampen influx of these cells. We have isolated from bronchial lavage a peptide that inhibits PMN chemotaxis to formyl-methionyl-leucyl-phenylalanine (FMLP). In the present study we examined effects of this molecule on 1) chemotaxis to other agonists, 2) FMLP-stimulated PMN superoxide production, 3) PMN calcium fluxes, and 4) binding of FMLP. Our results show that purified inhibitor attenuates PMN chemotaxis to C5a and leukotriene B4. This molecule also inhibits PMN superoxide release in response to FMLP. Exposure to this inhibitor causes an abrupt rise in cytosolic calcium concentration due to a pertussis toxin-sensitive shift of intracellular calcium and attenuates subsequent influx of extracellular calcium in response to FMLP. Binding studies demonstrate the inhibitor induces increased FMLP binding at 37 degrees C but has no effects at 4 degrees C. Inhibition of chemotaxis and increased FMLP binding mediated by this molecule are attenuated by buffering PMN calcium transients. These studies suggest an inhibitor of neutrophil function present in the bronchial environment alters PMN through effects on calcium homeostasis.

A single amino acid change in Raf-1 inhibits Ras binding and alters Raf-1 function

Ras and Raf-1 are key proteins involved in the transmission of developmental and proliferative signals generated by receptor and nonreceptor tyrosine kinases. Genetic and biochemical studies demonstrate that Raf-1 functions downstream of Ras in many signaling pathways. Although Raf-1 directly associates with GTP-bound Ras, an effect of this interaction on Raf-1 activity in vivo has not been established. To examine the biological consequence of the Ras/Raf-1 interaction in vivo, we set out to identify key residues of Raf-1 required for Ras binding. In this report, we show that a single amino acid mutation in Raf-1 (Arg89 to Leu) disrupted the interaction with Ras in vitro and in the yeast two-hybrid system. This mutation prevented Ras-mediated but not tyrosine kinase-mediated enzymatic activation of Raf-1 in the baculovirus/Sf9 expression system. Furthermore, kinase-defective Raf-1 proteins containing the Arg89-->Leu mutation were no longer dominant-inhibitory or capable of blocking Ras-mediated signal transduction in Xenopus laevis oocytes. These results demonstrate that the association of Raf-1 and Ras modulates both the kinase activity and the biological function of Raf-1 and identify Arg89 as a critical residue involved in this interaction. In addition, the finding that tyrosine kinases can stimulate the enzymatic activity of Raf-1 proteins containing a mutation at the Ras-interaction site suggests that Raf-1 can be activated by Ras-independent pathways.

Slowed central processing in simple and go/no-go reaction time tasks in Parkinson's disease

Studies of cognition and motor control have independently suggested that patients with Parkinson's disease show deficits in both attentional control and the preprogramming of movement. However, few studies have examined directly the involvement of cognitive processes in the origin of their slowed response. We examined the performance of 100 Parkinson's disease patients on simple reaction time (SRT) and a series of go/no-go cross-modality choice reaction time (CRT) tasks, in which motor response was constant; correct positive responses required attention to a progressively increasing number of dimensions of visual and auditory stimuli. The results showed that Parkinson's disease patients became increasingly impaired in response speed as choice complexity increased. Slowed response speed in Parkinson's disease involved two factors: (i) a 'perceptuomotor' factor which was constant across conditions and independent of choice complexity. Depression affected this factor selectively and independently of confounding associations with impoverished motor control; (ii) a 'cognitive-analytical' factor, which played an increasingly important role as complexity of choice increased. The characteristics of the relationship between response latency and cognitive complexity indicate that the deficit was due to a constant proportional slowing in cognitive speed across all SRT and CRT conditions. A cognitive deficit affecting the monitoring of stimulus-response compatibility may contribute to delayed response in Parkinson's disease. This cognitive-analytical deficit is present in early, untreated cases and, in contrast to perceptuomotor processes, is weakly related to depression.

Tomographic imaging of the distal extremities using cone-beam collimation

We evaluated the feasibility of cone-beam tomography (SPECT with a converging collimator) for detecting bone pathology of the distal extremities.

METHODS

We examined 11 patients: seven with hand or wrist pain, three with ankle pain and one with tibial pain. Cone-beam tomography was performed using a high-resolution converging collimator with a 45-cm focal length. Tomograms were then compared to high-resolution planar images.

RESULTS

Cone-beam tomography was successfully performed in all patients and tomograms were reconstructed in time for inclusion in the clinical report. In five patients, cone-beam tomography identified abnormalities that were equivocal or poorly defined on planar images. All other cone-beam studies provided the same information as the planar images.

CONCLUSIONS

Tomographic imaging of the distal extremities can be successfully performed by using cone-beam tomography which has been found to be feasible and potentially useful in the clinical setting.

Serine/threonine phosphorylation of the gamma-subunit after activation of the high-affinity Fc receptor for immunoglobulin G

In this report we show that interferon gamma treatment of U937 cells induces increased expression of the gamma-subunit of the high-affinity Fc receptor for IgG (Fc gamma RI). Interferon treatment results in a 10-fold increased expression of the gamma-subunit and induces expression of a phosphorylated form (gamma 1). The increased expression of the gamma-subunit correlates with its ability to transmit a signal via Fc gamma R, as measured by activation of the respiratory burst using insoluble immune complexes. During Fc gamma R activation, a mobility shift occurs in the phosphorylated form of this gamma 1-subunit. Phosphoamino acid analysis demonstrates that this gamma 1 subunit is threonine phosphorylated in resting differentiated U937 cells and becomes predominantly serine phosphorylated on Fc receptor activation. The mobility shift in the gamma-subunit can be induced by treating U937 cells with phorbol 12-myristate 13-acetate or by monoclonal antibody cross-linking of Fc gamma RI. Hence the gamma-subunit is serine phosphorylated in response to Fc gamma RI and protein kinase C activation. Therefore the gamma-subunit, initially described as a subunit of Fc epsilon RI, now appears to be involved in signal transduction via Fc gamma RI. The data also suggest that the gamma-subunit, in contrast with the zeta-subunit of the T-cell receptor-CD3 complex, is a substrate for serine/threonine kinase(s) in the cell. The serine phosphorylation of the gamma-subunit suggests a divergence of structure and function between the gamma-subunit and its homologue, the zeta-subunit of the T-cell receptor. Phosphorylation of the gamma-subunit on serine may play some regulatory role in Fc gamma RI signal transduction in myeloid cells.

Mediation of lung neutrophil uptake after endotoxin by CD18-integrin-dependent and -independent mechanisms

We studied polymorphonuclear neutrophil (PMN) uptake in lungs of endotoxemic rabbits using 111In-labeled PMN and isotope imaging by gamma scintigraphy. Rabbits were challenged intravenously with 100 micrograms Escherichia coli endotoxin either 4 or 24 h before an intravenous injection of 111In-labeled PMN, which was obtained from donor rabbits. The contribution of CD18 glycoprotein (beta 2-integrin) on PMN was examined using an anti-CD18 monoclonal antibody (MAb) IB4 infused 20 min before 111In-labeled PMN injection. In control rabbits, 111In-labeled PMN uptake in lungs was maximal within 5 min [36 +/- 2% increase above baseline (+/- SE)] and then fell exponentially with a disappearance half-time (t1/2) of 10 +/- 2 min. In rabbits challenged with endotoxin for either 4 or 24 h, maximum 111In-labeled PMN lung uptake and t1/2 values increased to 52 +/- 3 and 56 +/- 3% and to 26 +/- 2 and 31 +/- 6 min, respectively. Pretreatment with MAb IB4 (0.5 mg/kg iv) did not alter the PMN uptake response and t1/2 values in the 4-h endotoxin-challenged rabbits (i.e., maximum uptake of 52 +/- 3% above baseline and t1/2 of 26 +/- 2 min), whereas MAb IB4 prevented the increases in lung PMN uptake and t1/2 in 24-h endotoxin-challenged rabbits (maximum PMN uptake of 26 +/- 5% and t1/2 of 7 +/- 3 min; P < 0.001). In contrast, the control MAb OKM-1 did not prevent lung PMN uptake and the disappearance of PMN from lungs at either times.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein tyrosine phosphatase inhibitors block myeloid signal transduction through the Fc gamma RI receptor

Fc-receptor stimulation in certain myeloid cells results in an increase in oxygen consumption termed the respiratory burst. In this report we examine the effects of protein tyrosine phosphatase inhibitors on the Fc gamma receptor-induced myeloid respiratory burst. Antiphosphotyrosine immunoblotting of neutrophils stimulated with opsonized oil particles shows that Fc-receptor stimulation is associated with the tyrosine phosphorylation of cellular proteins. Pretreatment of neutrophils for 10 min with vanadate or phenylarsine oxide (PAO), protein tyrosine phosphatase inhibitors, augments tyrosine phosphorylation in response to Fc-receptor stimulation. Vanadate and PAO inhibit the respiratory burst in a dose-dependent fashion, but have no effect on Fc gamma receptor-mediated phagocytosis, suggesting that the inhibition of the respiratory burst is not due to a general inhibition of Fc gamma-receptor signaling. Neutrophil phagolysosomal membranes were isolated from vanadate-treated and control neutrophils after Fc-receptor stimulation show a reduction in protein tyrosine phosphatase activity and a reduction in the NADPH-dependent oxidase activity and contain greater amounts of phosphotyrosine, relative to control membranes. Vanadate did not inhibit the NADPH-oxidase directly or interfere with the superoxide assay. Vanadate and PAO also inhibited the respiratory burst of interferon-differentiated U937 cells in response to immune complex and Fc gamma RI crosslinking. Pretreatment of U937 cells with PAO completely blocks the serine phosphorylation of the gamma subunit of the Fc gamma R, a response that is associated with Fc gamma RI-receptor activation. The data supports the recent observation that CD45 modulates signal transduction through the Fc gamma RI receptor, suggesting that protein tyrosine phosphatases play a positive modulatory role in the signal relay pathway(s) involving the myeloid Fc gamma RI receptor, resulting in the phosphorylation of the gamma subunit and the activation of the NADPH-oxidase complex.

A new function for a phosphotyrosine phosphatase: linking GRB2-Sos to a receptor tyrosine kinase

Autophosphorylated growth factor receptors provide binding sites for the src homology 2 domains of intracellular signaling molecules. In response to epidermal growth factor (EGF), the activated EGF receptor binds to a complex containing the signaling protein GRB2 and the Ras guanine nucleotide-releasing factor Sos, leading to activation of the Ras signaling pathway. We have investigated whether the platelet-derived growth factor (PDGF) receptor binds GRB2-Sos. In contrast with the EGF receptor, the GRB2 does not bind to the PDGF receptor directly. Instead, PDGF stimulation induces the formation of a complex containing GRB2; 70-, 80-, and 110-kDa tyrosine-phosphorylated proteins; and the PDGF receptor. Moreover, GRB2 binds directly to the 70-kDa protein but not to the PDGF receptor. Using a panel of PDGF beta-receptor mutants with altered tyrosine phosphorylation sites, we identified Tyr-1009 in the PDGF receptor as required for GRB2 binding. Binding is inhibited by a phosphopeptide containing a YXNX motif. The protein tyrosine phosphatase Syp/PTP1D/SHPTP2/PTP2C is approximately 70 kDa, binds to the PDGF receptor via Tyr-1009, and contains several YXNX sequences. We found that the 70-kDa protein that binds to the PDGF receptor and to GRB2 comigrates with Syp and is recognized by anti-Syp antibodies. Furthermore, both GRB2 and Sos coimmunoprecipitate with Syp from lysates of PDGF-stimulated cells, and GRB2 binds directly to tyrosine-phosphorylated Syp in vitro. These results indicate that GRB2 interacts with different growth factor receptors by different mechanisms and the cytoplasmic phosphotyrosine phosphatase Syp acts as an adapter between the PDGF receptor and the GRB2-Sos complex.

Radiation pneumonitis. Bronchoalveolar lavage assessment and modulation by a recombinant cytokine

A common side effect of radiotherapy is the development of fibrosis in the irradiated tissue. To study the mechanisms of this fibrogenic response, we developed a model system of whole-lung radiation in the rat and studied the evolution of injury by assessment of the cells and protein recovered by lavage. Once the pattern of injury was known, we attempted to modulate this reaction by administering the cytokine interferon-gamma (IFN-gamma). Rats received 15 Gy radiation to the whole thorax and were studied by lung lavage at intervals of 1 to 35 days after radiation. The effect of radiation was an initial (24 h) leak of protein, unaccompanied by cellular alterations, that resolved by 48 h. This was followed 2 wk later by a phase of inflammatory cell recruitment and more significant protein leak. A third phase of increase in inflammatory cells and further increase in protein flux was noted at Day 35. A significant cellular infiltrate was seen in lung sections obtained from animals treated in parallel experiments. IFN-gamma was given by osmotic pump from Day 0 to Day 35. This treatment significantly attenuated the PMN recruitment and protein leak (p < 0.002 and 0.01, respectively) at Days 25 and 35. Histologic sections demonstrated reduced alveolar cellularity and exudate at Day 25 (p < 0.05); however, significant numbers of inflammatory cells and exudate were present in irradiated and IFN-gamma-treated animals at Day 35. These data indicate that inflammatory cell recruitment may play a role in the lung injury following radiation. Furthermore, these preliminary data indicate that a cytokine blocks this reaction.

Evolutionary conservation of Xenopus laevis mitogen-activated protein kinase activation and function

Saccharomyces cerevisiae possesses at least four mitogen-activated protein (MAP) kinase family members, encoded by the FUS3, KSS1, HOG1, and MPK1 genes, that participate in three distinct signaling pathways. We have tested whether a MAP kinase from Xenopus laevis (Xp42) can function in budding yeast, by expressing wild-type and mutant forms of Xp42 in different strains of S. cerevisiae. In Xenopus cells, Xp42 is phosphorylated on threonine188 and tyrosine190 when activated by a MAP kinase kinase (MAPKK). In S. cerevisiae, Xp42 is constitutively phosphorylated on tyrosine190. Since a kinase-inactive mutant of Xp42 is also phosphorylated, this phosphorylation is presumably due to activation by an endogenous MAPKK. Xp42 phosphorylation and kinase activity are dependent on yeast Bck1p, a putative MAPKK kinase (MAPKKK) and indirect upstream activator of Mpk1p. The loss of either Ste7p or Pbs2p, the upstream activators of Fus3p, Kss1p, and Hog1p, does not decrease the phosphorylation stoichiometry of Xp42. We also show that expression of Xenopus MAP kinase permits an mpk1::TRP1 deletion strain to grow at 37 degrees C. We conclude that S. cerevisiae and X. laevis possess evolutionarily conserved cascades, where biochemical activation and substrate specificity of MAP kinase have been maintained.

Mutations that enhance the cap2 null mutant phenotype in Saccharomyces cerevisiae affect the actin cytoskeleton, morphogenesis and pattern of growth

Mutations conferring synthetic lethality in combination with null mutations in CAP2, the gene encoding the beta subunit of capping protein of Saccharomyces cerevisiae, were obtained in a colony color assay. Monogenic inheritance was found for four mutations, which were attributed to three genetic loci. One mutation, sac6-69, is in the gene encoding fimbrin, another actin-binding protein, which was expected because null mutations in SAC6 and CAP2 are known to be synthetic-lethal. The other two loci were designated slc for synthetic lethality with cap2. These loci include the mutations slc1-66, slc1-87 and slc2-107. The slc mutations are semi-dominant, as shown by incomplete complementation in slc/SLC cap2/cap2 heterozygotes. The slc mutations and sac6-69 interact with each other, as shown by enhanced phenotypes in diheterozygotes. Moreover, the haploid slc2-107 sac6-69 double mutant is inviable. In a CAP2 background, the slc mutations lead to temperature and osmotic sensitivity. They alter the distribution of the actin cytoskeleton, including deficits in the presence of actin cables and the polarization of cortical actin patches. The slc mutations also lead to a pseudomycelial growth pattern. Together these results suggest that slc1 and slc2 encode components of the actin cytoskeleton in yeast and that the actin cytoskeleton can regulate the patterns of growth.

Activation of the SH2-containing phosphotyrosine phosphatase SH-PTP2 by its binding site, phosphotyrosine 1009, on the human platelet-derived growth factor receptor

Much progress has been made in elucidating early events in signal transduction by growth factor receptors with intrinsic tyrosine kinase activity. Upon ligand addition, these receptors dimerize and activate, becoming phosphorylated at a number of tyrosyl residues. These phosphorylation sites serve as docking points for proteins containing src homology-2 (SH2) domains. However, little is known about how phosphotyrosine phosphatases (PTPs), participate in these events. Recently, we and others molecularly cloned a ubiquitously expressed SH2 domain-containing PTP, SH-PTP2 (Syp, PTP1D, PTP2C), and found that it interacts directly with several activated growth factor receptors via its SH2 domains. Using a peptide competition assay, we now demonstrate that the major binding site for SH-PTP2 on the platelet-derived growth factor receptor is phosphotyrosine 1009. Immunoprecipitation studies indicate that SH-PTP2 is the previously unidentified "64-kDa" protein known to bind at this site. Addition of a phosphotyrosyl peptide comprising the region around Tyr-1009 stimulates SH-PTP2 activity 5-10-fold, whereas other phosphotyrosyl peptides from the platelet-derived growth factor receptor have no stimulatory effect. Our data suggest that binding of SH-PTP2 to the activated receptor in vivo should result in stimulation of SH-PTP2 activity.

Ras1-dependent signaling by ectopically-expressed Drosophila src gene product in the embryo and developing eye

The cellular functions of the Drosophila src 64B (Dsrc) gene product, Dsrc, and of most vertebrate Src-family kinases, are unknown. We have examined the effects of over-expression of wild type and mutated forms of Dsrc in transgenic Drosophila. Expression of both wild type Dsrc and a C-terminally truncated mutant at high levels during embryonic development induced extensive tyrosine phosphorylation of cellular proteins and caused considerable lethality, correlating with a block to germ-band retraction. Over-expression in the eye imaginal disc led to excess production of photoreceptor cells in the adult ommatidia. In contrast, expression of a kinase-inactive form of Dsrc caused distinct nervous system abnormalities in embryos and decreased the numbers of photoreceptor cells in the adult eye ommatidia. This suggests that active forms of Dsrc alter development by phosphorylation. Both the lethality and the eye roughening caused by activated Dsrc were partially suppressed by mutations in the Drosophila Ras1 gene. These results suggest that over-expressed Dsrc may function through Ras1 to stimulate differentiation in the embryonic nervous system and eye imaginal disc, and that kinase-active Dsrc interferes with these processes.

Incidental and intentional recall in Parkinson's disease: an account based on diminished attentional resources

The recall of common objects and their spatial location was examined in 65 patients with Parkinson's disease (PD) under conditions in which available attentional resources were manipulated by secondary task demands. PD patients were impaired at item recall particularly under intentional learning conditions but were unimpaired at recall of spatial location. These findings were similar in newly diagnosed, untreated cases as well as patients who had suffered with the disease for an average of 9.6 years. Test performance was not improved by levodopa therapy, despite it benefiting motor control, and was not impaired by anticholinergic medication. Item recall correlated significantly with other memory measures (particularly tasks of working memory) but only weakly with indices of physical disability and traditional frontal-lobe measures. Spatial recall, by contrast, correlated with memory quotient but no other cognitive measure and depression and disease duration failed to correlate significantly with performance on either recall task. These results are attributed to a deficit in attentional resources in PD that impairs performance most markedly for tasks and conditions that make the greatest demands upon effort.