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Biomedical subjects

S Kellie

Publications and source records attributed to S Kellie.

At least 37 records · Page 2Linked to original sources

Postoperative chemotherapy without radiation in young children with malignant non-astrocytic brain tumours. A report from the Australia and New Zealand Childhood Cancer Study Group (ANZCCSG).

Young children with malignant brain tumours have particularly poor survival and manifest severe sequelae of radiation therapy. A multi-institutional pilot study of post-operative primary chemotherapy for children under 3 years with primitive neuroectodermal tumours (PNET) or ependymoma was initiated in 1987. The chemotherapy protocol comprised carboplatin, vincristine and the "eight drugs in 1 day" regimen. Radiation was recommended only if tumour progression or recurrence was documented. A total of 14 patients between 5 and 36 months of age were enrolled. Seven had supratentorial tumours (PNET, pinealoblastoma, intracranial retinoblastoma) with multiple predictors of adverse outcome. Four of these responded to initial chemotherapy but subsequently progressed and all had died by 16 months from diagnosis. The seven patients with infratentorial tumours (three medulloblastomas, four ependymomas) had more favourable predictors of outcome: no meningeal dissemination and gross macroscopic resection in six of the seven cases. One patient progressed rapidly and died within 5 months. The other six are alive at 37-57 months from diagnosis. Four are in continuous complete remission at 57, 51, 41 and 37 months, respectively from the time of their tumour resection. One is described as having stable disease with a persistent radiographic lesion at 41 months from diagnosis. One has relapsed on two occasions and is the only surviving patient to have been irradiated. Intelligence scores for the six long-term survivors have thus for remained within the normal range. It is suggested that some infants with standard-risk ependymoma and, possibly, medulloblastoma may be cured without radiation therapy.

Antineoplastic Combined Chemotherapy Protocols↗

The phosphotyrosine phosphatase inhibitor vanadyl hydroperoxide induces morphological alterations, cytoskeletal rearrangements and increased adhesiveness in rat neutrophil leucocytes.

The functional consequences of treating rat neutrophils with the potent tyrosine phosphatase inhibitor vanadyl hydroperoxide (pervanadate) has been investigated. Pervanadate induced rapid increases in cellular protein phosphotyrosine content in a dose-dependent manner. This treatment also resulted in a change in morphology of the cells from a rounded to a polarised morphology, with many cells exhibiting uropods, pseudopodia and increased membrane activity. Pervanadate induced a transient actin polymerisation and reorganisation similar to that in agonist-stimulated cells. The pervanadate-induced increases in tyrosine phosphorylation, shape change and actin polymerisation were inhibited by the tyrosine kinase inhibitors tyrphostin and erbstatin, indicating that these phenomena were mediated by the constitutive activity of cellular tyrosine kinases. Double fluorescence experiments demonstrated that there was a co-localisation of tyrosine phosphorylated proteins with F-actin in both pervanadate- and agonist-stimulated neutrophils. Pervanadate also induced spreading of neutrophils on tissue culture substrata with concurrent changes in F-actin localisation including unusual F-actin-containing structures. These results demonstrate that morphological changes and cytoskeletal reorganisation in neutrophils are regulated by tyrosine phosphorylation, and that inhibition of tyrosine phosphatase activity in neutrophils is sufficient to activate motile machinery of these cells. These results suggest that an alternative pathway involved in neutrophil stimulation might be via inhibition of endogenous tyrosine phosphatases rather than activation of tyrosine kinases.

Actins↗

Localisation of pp60c-src to the surface membrane of human platelets.

In platelets, pp60c-src has been variously localised to cytosol, dense bodies, or plasma membrane and surface-connected canalicular membranes. We have investigated the localisation of pp60c-src in highly purified human platelet subcellular fractions isolated using density gradient centrifugation and continuous flow electrophoresis followed by quantitative immunoblotting. We have obtained fractions enriched in surface membranes and alpha granule membranes as assessed by the presence of the marker proteins gpIb, gpIIb, thrombospondin, fibrinogen and fibronectin. Quantitative immunoblotting demonstrated that most of the cellular pp60c-src co-purified with markers for surface membrane components and that unlike the situation in fibroblasts, platelet pp60c-src did not associate with non-granule intracellular membranes such as Golgi, endoplasmic reticulum and endosomes. A small subpopulation of the total cellular pp60c-src co-purified with granule components or dense body markers, however this occurred in proportion to the presence of surface membrane markers. Our results demonstrate that the majority of platelet pp60c-src is located on the cytoplasmic face of the plasma membrane in human platelets.

Blood Platelets↗

The interaction of the tyrosine kinase pp60src with membrane and cytoskeletal components.

To study the mechanism of oncogenic transformation we have investigated the association of pp60v-src with the cytoskeleton using a variety of mutants. Transformation is associated with the interaction of pp60v-src with the cytoskeleton, specifically in adhesion plaques. Biochemical analysis has shown a correlation between tyrosine-specific phosphorylation of the fibronectin receptor and the loss of surface-bound fibronectin, but no such correlation with phosphorylation of vinculin or talin. The role of the nontransforming protooncogene product pp60c-src was studied in platelets, which express large amounts of this protein. In resting platelets pp60c-src was soluble in detergent-containing buffers, however it became associated with the cytoskeleton, but not the membrane skeleton, after platelet activation. This association was inhibited by EDTA or RGDS peptides and was therefore dependent on occupancy of a platelet integrin, gpIIb/IIIa. The role of pp60c-src-associated tyrosine phosphorylation in platelet activation was also investigated. Inhibitors of tyrosine phosphorylation inhibited integrin-dependent platelet aggregation and second messenger production, indicating a close linkage between matrix receptor occupancy, pp60c-src association with the cytoskeleton and platelet function.

Animals↗

Translocation of pp60c-src to the cytoskeleton during platelet aggregation.

The high amount of pp60c-src in platelets has led to speculation that this kinase is responsible for tyrosine-specific phosphorylation of cellular proteins during platelet activation by different agonists, and is, therefore, implicated in signal transduction of these cells. Unlike pp60v-src, the association of which with the cytoskeleton appears to be a prerequisite for transformation, pp60c-src is detergent-soluble in fibroblasts overexpressing the c-src gene, and its role in normal cellular function remains elusive. To gain a better understanding of the function of pp60c-src we have investigated the subcellular distribution of pp60c-src and its relationship to the cytoskeleton during platelet activation. Quantitative immunoblotting and immunoprecipitation have revealed that pp60c-src is detergent-soluble in resting platelets, while 40% of total platelet pp60c-src becomes associated with the cytoskeletal fraction upon platelet activation. We have also shown that a small pool of pp60c-src is associated with the membrane skeletal fraction which remains unchanged during the activation process. The interaction of pp60c-src with cytoskeletal proteins strongly correlates with aggregation and is mediated by GPIIb/IIIa receptor-fibrinogen binding. We suggest that the translocation of pp60c-src to the cytoskeleton and its association with cytoskeletal proteins may regulate tyrosine phosphorylation in platelets.

Biological Transport↗

Cytokine gene expression of endothelial cells infected with Trypanosoma cruzi.

Coronary microvascular spasm and platelet hyperreactivity have been implicated in the pathogenesis of Chagas' cardiomyopathy. To clarify further the role of the microvasculature in this disease, alterations in cytokine gene expression due to Trypanosoma cruzi infection of human umbilical vein endothelial cells were examined. Northern blot analysis of total RNA from endothelial cells demonstrated that interleukin (IL)-1 beta, IL-6, and colony-stimulating factor 1 (CSF-1) mRNA expression was absent or minimal in uninfected cells but significantly increased in infected cells. c-sis mRNA levels diminished with increased time of infection. In situ hybridization studies also demonstrated high levels of IL-6 mRNA in individual infected cells. Significant levels of IL-6 and IL-1 beta protein were detected in the supernatants of infected endothelial cells. The serum of an acutely infected individual contained high levels of IL-6 protein, suggesting the potential importance of cytokines secreted by the vascular endothelium in the pathogenesis of Chagas' cardiomyopathy.

Animals↗

Comparison of the role of protein kinase C in platelet functional responses induced by three different mechanisms, PAF, ionomycin and arachidonic acid.

The role of protein kinase C (PKC) in modulating platelet activation has been examined in platelets pre-incubated with either the PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA) or the non-specific protein kinase inhibitor, staurosporine. In order to determine where in the signal transduction pathway PKC is exerting its effect platelets were activated either with a receptor-operated stimulus platelet activating factor (PAF) or by direct elevation of [Ca2+]i (ionomycin) or with arachidonic acid which is converted into thromboxane B2 (TxB2). In PAF-stimulated platelets activation of PKC inhibited both [Ca2+]i elevation and TxB2 generation but had no effect on 5-hydroxytryptamine (5-HT) release whilst staurosporine increased the duration of [Ca2+]i elevation and potentiated TxB2 generation but inhibited 5-HT release. In ionomycin-stimulated platelets modulation of PKC had no effect on [Ca2+]i elevation but in contrast to PAF-stimulated platelets PKC activation caused potentiation of TxB2 generation and 5-HT release whilst inhibition of PKC caused inhibition of TxB2 generation and 5-HT release. Modulation of PKC did not affect arachidonic acid-induced TxB2 generation. These findings suggest that in receptor activated platelets endogenously activated PKC is exerting a negative feedback role, however, when [Ca2+]i elevation is not modified by PKC activation or inhibition (such as in ionomycin stimulated platelets) the relationship between the state of PKC activation and subsequent platelet functional responses corresponds more closely. The findings from this study suggest a different relationship between PKC and TxB2 generation than between PKC and dense granule release in PAF-stimulated platelets.

Alkaloids↗

The relationship between cytosolic Ca2+, sn-1,2-diacylglycerol and inositol 1,4,5-trisphosphate elevation in platelet-activating-factor-stimulated rabbit platelets. Influence of protein kinase C on production of signal molecules.

The temporal and dose-response relationships of platelet-activating-factor (PAF)-induced changes in the concentrations of cytosolic Ca2+ ([Ca2+]i), Ins(1,4,5)P3 and 1,2-diacylglycerol (DAG) were examined. In addition, phosphorylation of protein kinase C (PKC) substrate (40-47 kDa protein) was determined. In high-dose PAF-activated platelets, all three signal molecules increased rapidly and transiently, with the peak Ins(1,4,5)P3 concentration preceding maximal elevation of [Ca2+]i by 5 s. In low-dose PAF-activated platelets there were large increases in [Ca2+]i and dense-granule release, without any increase in Ins(1,4,5)P3 and DAG or 40-47 kDa protein phosphorylation. Staurosporine, a non-specific PKC inhibitor, produced enhanced elevations in the concentrations of Ins(1,4,5)P3, DAG and thromboxane B2, and the duration of the Ca2+ signal in platelets stimulated with a high dose, but not a low dose, of PAF. These results suggest there are both phospholipase C-dependent and -independent changes in Ca2+ homoeostasis. Endogenously activated PKC regulates the formation of signal molecules.

Alkaloids↗

Cell/substratum adhesions in RSV-transformed rat fibroblasts.

Cell/substratum adhesions have been studied in rat fibroblasts transformed by a ts-mutant of Rous sarcoma virus (LA-29) using light and electron microscopy and a variety of preparative methods including immunolabeling. Cells were studied both during the process of transformation, i.e., shifting from 39 degrees to 35 degrees C, and in a fully transformed state (passaged at 35 degrees C continuously). The typical focal contacts observed at 39 degrees C (restrictive temperature) were replaced by "point-contacts" (100-200 per cell) which were classified by immunolabeling as podosome-like adhesions containing actin, beta 1 integrin subunit, vinculin, talin, alpha-actinin, and small membrane patches containing clathrin and integrin. Tyrosine-phosphorylated proteins and pp60src were found in association with groups of small particles on the protoplasmic surface of ventral membranes by gold immunolabeling. Both types of point-contacts were visualized by electron microscopy of ultrathin sections and shadowed replicas and characterized by gold immunolabeling wherever possible. The overall composition of podosome-like adhesions is similar to focal contacts but there are differences in the three-dimensional organization of the microfilaments and in the topography of vinculin which is associated more with actin filaments than with the plasma membrane. The presence of talin and extracellular matrix receptor in podosomes together with the adhesive properties of these actin-containing structures argues against the hypothesis that pp60src affects the interaction of actin with the plasma membrane by phosphorylating the fibronectin receptor and/or other associated proteins.

Actin Cytoskeleton↗

Tyrosine-specific phosphorylation of gpIIIa in platelet membranes.

In vitro phosphorylation of platelet subcellular fractions revealed that most of the alkali-resistant phosphoproteins and the majority of pp60c-src were in the surface membrane fraction. An alkali-resistant phosphoprotein of about 100 kDa was also immune precipitated by an anti-phosphotyrosine antibody and comigrated with gpIIIa. The phosphorylation of gpIIIa, but not gpIIb, was confirmed by the comparison of reduced and non-reduced gels, and this protein was phosphorylated exclusively on tyrosine. In contrast, both gpIIb and gpIIIa were phosphorylated when the purified complex was added to immunopurified, immobilised pp60c-src. A synthetic peptide with partial homology to a putative tyrosine phosphorylation site in the cytoplasmic domain of gpIIIa was phosphorylated by antibody-purified pp60c-src. Our results indicate that tyrosine-specific phosphorylation of gpIIIa by pp60c-src may play a role in the regulation of platelet function.

Amino Acids↗

Relationship of lung function to severity of osteoporosis in women.

To determine if the severity of osteoporosis and its resultant hyperkyphosis cause measurable impairment of lung function, 74 women referred for osteoporosis evaluation underwent pulmonary function testing. Women with thoracic wedge compression fractures secondary to osteoporosis had significantly lower percent predicted FVC than did those without fractures. In hierarchical regression analysis, after controlling for age and arm span, there was a significant effect on FVC of the degree of hyperkyphosis as measured by Cobb's angle (increment in R2 = 0.14, p less than 0.001). The addition of the number of vertebral fractures to the model was also significant (increment in R2 = 0.06, p less than 0.002), but cortical bone volume, bone mineral density, and smoking status did not significantly improve the model. From one half of subjects tested, a regression equation was generated relating %FVC and the number of thoracic fractures: %FVC = 103.4 - 9.4 x number of fractures. When used to predict lung function impairment in the second half of study subjects, the correlation between measured and %FVC was r = 0.59 (p less than 0.002). Kyphosis and thoracic compression fractures caused by osteoporosis produce modest but predictable declines in vital capacity in women.

Adult↗

Regulation of integrin mobility and cytoskeletal association in normal and RSV-transformed chick embryo fibroblasts.

The mobility of the integrin receptor in trypsinised chick embryo fibroblasts (CEF) was investigated using the CSAT monoclonal antibody. The binding of CSAT to trypsinised CEF followed by incubation at 37 degrees C resulted in patching and then capping of the receptor. This capping was dependent on cellular metabolism, since agents such as sodium azide or 2-deoxyglucose inhibited the process. Whereas about 95% of unclustered integrin was soluble in Nonidet P40-containing buffers, after capping more than 25% of surface integrin became detergent-insoluble, indicating a physical association with cytoskeletal elements. Thus the crosslinking of integrin via its beta subunit is sufficient, to induce cytoskeletal association. Unusually, the microfilament-disrupting drugs cytochalasins B and D potentiated CSAT-induced capping in terms of both cell number and the conformation of caps on individual cells. Double immunofluorescent staining demonstrated that in cytochalasin-treated cells both F-actin and talin co-localised with surface CSAT-integrin clusters. The co-distribution of these cytoskeletal components with surface integrin was retained in cytoskeletal preparations, although there was no quantitative increase of either talin or vinculin in the cytoskeletons. The cocapping of talin with integrin clusters on CEF could also be observed in the absence of cytochalasins. No differences were found in capping efficiency, talin and actin co-localisation or cytoskeletal association of surface-modulated integrin in Rous sarcoma virus (RSV)-transformed cells compared with untransformed counterparts, although differences in the response to cytochalasins were observed. These results provide novel evidence for a physiologically relevant association of integrin with cytoskeletal components and its regulation by surface configuration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Differential tyrosine-specific phosphorylation of integrin in Rous sarcoma virus transformed cells with differing transformed phenotypes.

We have investigated the localization and phosphorylation of the fibronectin receptor in chick embryo fibroblasts transformed either by wild-type Prague C strain Rous sarcoma virus, which induces a rounded, less adhesive phenotype with a loss of surface fibronectin and gross cytoskeletal changes, or transformed by rASV2234.3, a variant which induces a flat, adhesive morphology with the retention of surface fibronectin and more normal cytoskeleton. Immunofluorescence showed co-distribution of pp60v-src with integrin and fibronectin fibrils in rASV2234.3-transformed cells. Total levels and surface expression of integrin were unchanged in both transformed cell types compared with untransformed cells. However, whereas integrin band 3 (beta 1 subunit) in Prague C-transformed cells was hyperphosphorylated on tyrosine, this was reduced virtually to normal in rASV2234.3-transformed cells. A similar differential phosphorylation of integrin band 3 could be found in membranes phosphorylated in vitro. rASV2234.3 pp60v-src was less efficient in phosphorylating a synthetic peptide containing the putative integrin tyrosine phosphorylation site, indicating that this variant pp60v-src has an altered substrate specificity compared to Prague C pp60v-src. The correlation between tyrosine-specific phosphorylation of integrin and loss of surface fibronectin suggests that this could play an important role in the induction of the transformed phenotype.

Amino Acids↗

pp60v-src association with the cytoskeleton induces actin reorganization without affecting polymerization status.

The mechanism by which Rous sarcoma virus (RSV) induces a reorganization of actin and its associated proteins and a reduction in microfilament bundles is at present poorly understood. To examine the relationship between the organization of the microfilament system and the polymerization state of actin after transformation, we have investigated these changes in a Rat-1 cell line transformed by LA29, a temperature-sensitive (ts) mutant of RSV. Parallel immunofluorescence and biochemical analysis demonstrated that LA29 pp60v-src was ts for tyrosine kinase activity and cytoskeletal association. Changes in the distribution and organization of actin, alpha-actinin and vinculin were dependent on the association of a kinase-active pp60v-src molecule with the detergent-insoluble cytoskeleton. Whilst there was a transformation-dependent loss of microfilament bundles, biochemical quantitation demonstrated that the polymerization state of the actin in both detergent-soluble and insoluble fractions of these cells grown at temperatures either permissive or restrictive for transformation was quantitatively unchanged. These results indicate that the loss of microfilament bundles after transformation is not due to a net depolymerization of filamentous actin but rather to a reorganization of polymeric actin from microfilament bundles and stress fibers to other polymeric forms within the cell. The polymeric nature of the actin in these cells was confirmed by electron microscopy of cytoskeletons and substrate-adherent membranes.

Actin Cytoskeleton↗