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L T Williams

Publications and source records attributed to L T Williams.

At least 163 records · Page 9Linked to original sources
PubMed1986

Thrombin stimulates c-sis gene expression in microvascular endothelial cells.

We have determined whether expression of the c-sis gene product, platelet-derived growth factor (PDGF), is regulated in cultured renal microvascular endothelial cells by factors to which vascular endothelial cells may be exposed at sites of perivascular cellular proliferation. Thrombin exposure increased endothelial cell levels of c-sis message by 3-5-fold over a time course that peaked at 4 h after exposure. Similarly, thrombin-exposed microvascular endothelial cells released increased amounts of PDGF activity into their media. The thrombin effect was not mediated through the proteolytic activity of thrombin, as proteolytically inactive thrombin stimulated the c-sis expression as well as native thrombin. This stimulation was mimicked by exposure of cells to biologically active phorbol esters, suggesting that thrombin action may be mediated through activation of kinase C (Ca2+/phospholipid-dependent enzyme). Thus, thrombin regulates the expression and release of PDGF activity from endothelial cells in culture and may act in vivo to stimulate mitogen release from endothelial cells, thereby inducing proliferation of perivascular cells.

Angiotensin II↗
PubMed1986

Cardiac myocyte hypertrophy is associated with c-myc protooncogene expression.

The mechanism of hormonally induced cell hypertrophy is unknown. Stimulation of cardiac myocytes by alpha 1-adrenergic agents, phorbol esters, and serum induces an increase in the cell size of nondividing cardiac myocytes in primary culture. Expression of the c-myc gene, known to be increased in growth factor-induced cell division, was studied in this model of cell hypertrophy. The alpha-adrenergic agonist norepinephrine (0.002-20 microM) increased levels of c-myc-encoded mRNA to 10-fold over control levels. This increase was detectable at 30 min, peaked at 2 hr, and returned to baseline by 6 hr after stimulation. The norepinephrine response was abolished by the alpha 1-antagonist terazosin (2 microM) but was not affected by the beta-adrenergic antagonist propranolol (2 microM) and was only slightly (25%) attenuated by the alpha 2-adrenergic antagonist yohimbine (2 microM). Serum and the phorbol ester tumor promoter phorbol 12-myristate 13-acetate also enhanced c-myc expression in cardiac myocyte cultures. These findings show that the induction of cardiac myocyte hypertrophy is associated with enhanced expression of the c-myc gene and suggest that hormonally induced cell hypertrophy and cell division share common mechanistic pathways.

Animals↗
PubMed1986

Dental care for patients receiving chemotherapy.

Common oral complications of chemotherapy include mucositis, infections secondary to profound bone marrow aplasia, and gingival bleeding. Mucositis and infections were treated with appropriate antibiotic therapy; a symptomatic tooth was extracted before chemotherapy was begun. Transfusions were performed to obtain adequate platelet levels. A regimen of ticarcillin disodium and gentamicin sulfate is recommended for antibiotic prophylaxis for selected dental procedures.

Adult↗
PubMed1986

The sis gene and PDGF.

The aberrant expression of a protein that is involved in normal growth regulatory pathways can cause cell transformation. One of the best examples of this phenomenon is the transformation of fibroblasts by the simian sarcoma virus (SSV). An oncogene (v-sis) of this virus encodes a protein whose amino acid sequence is highly homologous to one of the subunits of a mesenchymal cell mitogen, platelet-derived growth factor (PDGF). How does expression of the v-sis or related genes transform cells? Clearly, this process uses biochemical pathways involved in the normal actions of growth factors. For example, the v-sis-encoded protein appears to act through cellular PDGF receptors. The biochemical consequences of PDGF receptor activation include increased tyrosine kinase activity, enhanced expression of a set of genes associated with cell proliferation, the dramatic alteration in cellular cytoskeleton, a rapid turnover of membrane phospholipids and the commitment of the cell to proceed through a series of responses culminating in the replication of DNA. An important issue is whether, in SSV transformed cells, these biochemical pathways are simply overstimulated by an abundance of self-made growth factor, or are there qualitative alterations in the pathways that are unique to these cells. Several specific related questions are addressed in this discussion: Is the protein encoded by the v-sis gene functionally identical to PDGF? Does the v-sis-encoded protein act at the cell surface or at intracellular sites? In the action of PDGF-like compounds, what are the biochemical steps distal to receptor stimulation?(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Transformation, Neoplastic↗
PubMed1985

Human tumor cell lines with EGF receptor gene amplification in the absence of aberrant sized mRNAs.

A survey of human tumor cell lines for increased PDGF or EGF receptors identified 5 lines which bind from 6 to 13 times more EGF than normal human fibroblasts. Immunoprecipitation analysis links the elevated binding activity to increased quantities of the EGF receptor protein. EGF receptor gene amplification was detected in 2 of the cell lines. No evidence for EGF receptor gene rearrangements was found at the level of DNA or RNA structure. The results suggest that elevated levels of EGF receptor can be associated with at least three distinct mechanisms. These include gene amplification accompanied by rearrangement, gene amplification without accompanied alteration of mRNA transcripts, and extensive expression without gene amplification.

Epidermal Growth Factor↗
PubMed1985

Evidence that the v-sis gene product transforms by interaction with the receptor for platelet-derived growth factor.

A scheme for partial purification of biologically active v-sis-coded protein from cells transformed with simian sarcoma virus (SSV) has made possible a functional comparison of the transforming protein with platelet-derived growth factor (PDGF). The SSV-transforming gene product is capable of specifically binding PDGF receptors, stimulating tyrosine phosphorylation of PDGF receptors, and inducing DNA synthesis in quiescent fibroblasts. Each of these activities was specifically inhibited by antibodies to different regions of the v-sis gene product. Moreover, viral infection of a variety of cell types revealed a strict correlation between those cells possessing PDGF receptors and those susceptible to transformation by SSV. These findings provide evidence that SSV-transforming activity is mediated by the interaction of a virus-coded mitogen with PDGF receptors.

Animals↗
PubMed1985

c-myc gene expression is stimulated by agents that activate protein kinase C and does not account for the mitogenic effect of PDGF.

The role of the phosphoinositide turnover-protein kinase C pathway in mediating PDGF-stimulated c-myc expression and cell proliferation was studied. Both direct activators of kinase C (e.g. phorbol ester analogues) and hormones that activate kinase C via receptor-mediated phosphoinositide turnover (e.g. PDGF, bradykinin, or vasopressin) elicited a rapid increase in c-myc mRNA expression. Desensitization of the kinase C pathway by prolonged exposure to phorbol abolished the induction of c-myc by subsequent phorbol challenge and attenuated c-myc induction by PDGF and bradykinin, but did not affect PDGF-stimulated mitogenesis. Bradykinin and phorbol esters stimulated the same magnitude of c-myc expression as PDGF but elicited less than one-tenth the PDGF-induced mitogenic response. We conclude that stimulation of c-myc expression is a common response to a diverse group of agents that elicit phosphoinositide turnover and activate protein kinase C, and that neither activation of protein kinase C nor enhanced c-myc expression is sufficient for the mitogenic action of PDGF.

Animals↗
PubMed1985

Purification of the platelet-derived growth factor receptor by using an anti-phosphotyrosine antibody.

The platelet-derived growth factor (PDGF) receptor is a 180-kDa membrane glycoprotein. A protein of identical size, lectin affinity, and isoelectric point has been identified as a major substrate for PDGF-activated tyrosine kinase in stimulated 3T3 cells. We have purified this tyrosine-phosphorylated protein to homogeneity by using anti-phosphotyrosine immunoaffinity and lectin affinity steps. Demonstration that this purified tyrosine phosphoprotein is the PDGF receptor necessitated development of an assay capable of identifying specific 125I-labeled PDGF binding activity in soluble receptor preparations. PDGF receptor solubilized from 3T3 cell membranes with the detergent octyl beta-D-glucoside was precipitated on an artificial liposome matrix after receptor aggregation with concanavalin A. Precipitated binding sites display affinity and kinetic characteristics of PDGF receptors in cells and membranes. Preparations of the 180-kDa phosphoprotein that are greater than 90% homogeneous by silver stain and by [35S]methionine protein autoradiography have specific high affinity 125I-labeled PDGF binding sites (equilibrium dissociation constant, 0.1 X 10(-9) M). Binding activity enrichment in this preparation reflects an 11,000-fold purification of binding activity in intact cells. These data demonstrate that the 180-kDa substrate of the PDGF-stimulated tyrosine kinase is the PDGF receptor. Furthermore, these methods provide a means of purifying this and other tyrosine kinase substrates from growth factor-stimulated cells.

Animals↗
PubMed1984

A v-sis oncogene protein produced in bacteria competes for platelet-derived growth factor binding to its receptor.

The oncogene of simian sarcoma virus, v-sis, encodes a protein which is homologous to human platelet-derived growth factor (PDGF). This v-sis-encoded protein was expressed in bacteria using an inducible promotor of lambda phage. Soluble extracts from these bacteria contained a substance which competed with 125I-PDGF for PDGF receptor sites in fibroblast membranes. The receptor competition activity was correlated with the presence of the v-sis-encoded protein as assessed by genetic and immunochemical criteria. These results directly demonstrate that the v-sis oncogene product is functionally related to PDGF.

Binding, Competitive↗
PubMed1984

Evidence for the platelet-derived growth factor-stimulated tyrosine phosphorylation of the platelet-derived growth factor receptor in vivo. Immunopurification using a monoclonal antibody to phosphotyrosine.

The addition of platelet-derived growth factor (PDGF) to intact BALB/c 3T3 cells results in the rapid (less than 1 min), dose-dependent phosphorylation of a number of proteins that could be isolated by a monoclonal antiphosphotyrosine antibody. The predominant tyrosinephosphorylated protein shared many characteristics with the PDGF receptor, including its molecular weight (170,000), isoelectric point (pI of about 4.2), its binding to DEAE-cellulose, and its pattern of binding to lectins. This 170-kDa protein, labeled with [35S] methionine, was substantially purified from PDGF-stimulated cells using the monoclonal anti-phosphotyrosine antibody but was not significantly immunopurified from unstimulated cells. At 37 degrees C, phosphorylation of the 170-kDa protein was maximal by 5-10 min of exposure to PDGF, and thereafter decreased rapidly. However, at 4 degrees C, the phosphorylation continued to increase after 3 h of exposure to PDGF. Subsequently, shifting the cells from 4 to 37 degrees C resulted in an additional rapid burst of tyrosine phosphorylation. Among the other PDGF-stimulated molecules, the most prominent and consistently observed was a cytosolic, acidic (pI of about 4.2), 74-kDa protein. These findings indicate that the action of PDGF in vivo is associated with the rapid and transient tyrosine phosphorylation of several membrane and cytosolic proteins; the most prominent of these proteins, isolated by monoclonal antibody to phosphotyrosine, is likely to be the PDGF receptor. The use of this antibody provides a new approach for purification of the PDGF receptor.

Animals↗
PubMed1984

Platelet-derived growth factor receptors form a high affinity state in membrane preparations. Kinetics and affinity cross-linking studies.

The specific binding of 125I-PDGF (platelet-derived growth factor) to intact fibroblasts becomes relatively nondissociable during incubation at 37 degrees C. To characterize the interaction of PDGF with its receptors under conditions in which there is no receptor internalization, we have studied the binding of 125I-PDGF to membrane preparations derived from mouse 3T3 cells and rat liver. The binding sites had the affinity and specificity characteristics expected of PDGF receptors. At 37 degrees C (but not at 4 degrees C) the specific binding of 125I-PDGF to membranes gradually became nondissociable as assessed by either dilution or by addition of excess unlabeled PDGF. This tight binding was not due to a covalent interaction since the polyanionic compound suramin readily dissociated specifically bound 125I-PDGF. This property of suramin was used to expose rat liver PDGF receptors which were occupied by endogenous PDGF. Affinity cross-linking studies demonstrated that the formation of the nondissociable state of 125I-PDGF binding was associated with the binding of 125I-PDGF to a 160,000-dalton protein and to a 110,000-dalton species. The cross-linked binding sites could be adsorbed to wheat germ agglutinin and to anion exchange resins. The isoelectric point of both cross-linked species determined by two-dimensional gel electrophoresis was approximately 4.7. These data demonstrate that in membrane preparations, PDGF binds to an anionic 160,000-dalton glycoprotein which is likely to be the receptor. A high affinity state of PDGF binding, which is formed rapidly at 37 degrees C, can be dissociated by suramin.

Animals↗
PubMed1984

Blockade of autocrine stimulation in simian sarcoma virus-transformed cells reverses down-regulation of platelet-derived growth factor receptors.

The viral (v)-sis oncogene encodes a protein (p28sis) that is structurally homologous to platelet-derived growth factor (PDGF). We have shown that simian sarcoma virus (SSV)-transformed cells containing the v-sis oncogene release a Mr 20,000 substance that is recognized by antisera to synthetic peptide sequences contained in p28sis. Medium conditioned by SSV-transformed cells competes with 125I-labeled PDGF for specific PDGF receptor sites, initiates DNA synthesis, and stimulates tyrosine phosphorylation of the PDGF receptor when added to normal cells. When normal cells are co-cultured with SSV-transformed cells, the PDGF receptors of the normal cells are down-regulated by factors released from the transformed cells. Thus, SSV-transformed cells release material that is functionally similar to PDGF. We have used anti-phosphotyrosine antibodies to purify PDGF receptors and to detect PDGF-stimulated receptors in normal cells. SSV-transformed cells have no PDGF receptors detectable by these antibodies or by 125I-labeled PDGF binding studies. However, when SSV-transformed cells are exposed to suramin, a compound that blocks binding of PDGF to its receptors, the receptors reappear on the cell surface and within 8 hr are present at the same levels as in control cells. These "new" receptor sites can be phosphorylated in response to PDGF. Thus, the absence of PDGF receptors in SSV-transformed cells is due to down-regulation of the receptors by an autocrine mechanism that can be blocked by suramin.

Animals↗
PubMed1983

An unusual instance of leukemic infiltrate. Diagnosis and management of periapical tooth involvement.

The clinical course of an adult patient with relapsed acute myelogenous leukemia and leukemic infiltrate periapical to the dentition is described. While the oral symptoms were indicative of pulpal disease requiring dental therapy to resolve the patient's complaint, roentgenographic, dental pulp testing, and histologic analysis revealed extramedullary infiltrate apical to a mandibular molar. The findings developed coincident with relapse of leukemia; the medical and dental testing described above were essential in establishing an accurate diagnosis. While most oral leukemic infiltrates affect the gingiva, in this patient the infiltrate involved periapical tissue which was not clinically observable.

Adult↗
PubMed1983

Platelet-derived growth factor stimulates mouse 3T3 cell mitogenesis and leukocyte chemotaxis through different structural determinants.

Platelet-derived growth factor (PDGF) stimulates both proliferation of fibroblasts and chemotaxis of leukocytes. In this study we compared the mitogenic and chemotactic activities of native PDGF and reduced PDGF. Reduction of PDGF (Mr = 32,000) to its constituent polypeptides (Mr = 14,000 and 17,000) caused a loss of the ability to stimulate proliferation of Balb/c 3T3 cells. However, reduced PDGF retained virtually all of its activity as a chemotactic agent for human neutrophils and monocytes. A half-maximal chemotactic response to both native and reduced PDGF occurred at a concentration of approximately 0.08 nM for neutrophils and 0.1 nM for monocytes. The maximal chemotactic response to reduced PDGF was at least as great as the maximal response to native PDGF. Both native and reduced PDGF stimulated the release of the lysosomal enzyme, beta-glucosaminidase, from neutrophils with a half-maximal response at less than 0.1 nM. However, the net maximum release of this enzyme by PDGF (and reduced PDGF) was significantly less than that stimulated by a maximal concentration of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine. These results indicate that different structural determinants are required for the proliferative response of 3T3 cells to PDGF and for the chemotactic response of leukocytes to PDGF.

Animals↗
PubMed1983

Human platelet-derived growth factor: structure and function.

Human platelet-derived growth factor (PDGF) is a heat-stable, cationic polypeptide transported in blood in the alpha granules of platelets. It is released from platelets during blood clotting. PDGF has been resolved into at least two closely related active polypeptides, PDGF-I and PDGF-II, each consisting of two inactive chains linked together by disulfide bonds. PDGF stimulates the growth of normal cells in culture, including fibroblasts, arterial smooth muscle cells, and glial cells. In addition, PDGF has been shown to stimulate cell migration and many diverse metabolic functions such as amino acid transport, protein synthesis, cholesterol ester synthesis, phospholipid turnover, and prostacyclin synthesis. It modulates receptor binding of other active components such as epidermal growth factor, luteinizing hormone, low-density lipoprotein, and somatomedin C. Specific cell membrane receptors for PDGF have been demonstrated in arterial smooth muscle cells and fibroblasts.

Amino Acids↗
PubMed1982

Dental extractions in patients with acute nonlymphocytic leukemia.

Dental extractions in patients with leukemia are controversial, since they may lead to hemorrhage, delayed wound healing and infection. However, the retention of diseased teeth in these patients may also lead to infectious complications during chemotherapy. With adequate hematologic values and specific surgical techniques, 119 extractions were performed on 28 patients with acute nonlymphocytic leukemia. No serious adverse sequelae occurred, and the prevalence of other adverse affects was comparable with that in nonleukemic patients. It is concluded that with proper precautions, extractions can be performed on these patients.

Acute Disease↗