Matrix-degrading proteinases are shed in membrane vesicles by ovarian cancer cells in vivo and in vitro

The in vitro release of matrix-degrading proteinases from breast cancer cells is associated in part with shed membrane vesicles. To determine whether shed vesicles might play a similar role in ovarian cancer cells, we analyzed the shedding phenomenon in vivo and in vitro as well as the enzymatic content of their vesicles. This is the first time that an immunoelectron microscopical analysis revealed membrane vesicles carrying tumor-associated antigen alpha-Folate Receptor (alpha-FR), circulating in biological fluids (ascites and serum) of an ovarian carcinoma patient. These vesicles were trapped in a fiber network with characteristic fibrin periodicity. An ovarian cancer cell line (CABA I) established from ascitic fluid cells of this patient, grew in Matrigel and formed tubular structures suggesting invasive capability. Immunofluorescence analysis demonstrated strong cytoplasmic staining of CABA I cells with anti-matrix metalloproteinase-9 (MMP-9) and anti-urokinase-type plasminogen activator (uPA) antibodies. CABA I cells shed membrane vesicles, which were morphologically similar to those identified in vivo, as determined by electron microscopy. Gelatin zymography of vesicles isolated both in vivo and in vitro revealed major gelatinolytic bands of the MMP family, identified as the zymogen and active forms of gelatinase B (MMP-9) and gelatinase A (MMP-2). By casein-plasminogen zymography we observed high-molecular weight (HMW)-uPA and plasmin bands. Incubation of purified vesicles from CABA I cells with Matrigel led to cleavage of Matrigel components. Taken together, our results point to a possible role of shed vesicles, both in vivo and in vitro, in proteolysis that mediates invasion and spread of ovarian epithelial carcinoma cells.

Participant satisfaction and comfort with multidisciplinary pediatric telemedicine consultations

PURPOSE

The aim of this study was to measure both satisfaction and comfort levels and estimates of cost savings of families with children receiving health care services from a distant pediatric tertiary care center by readily available telecommunications technologies.

METHODS

From February 1996 to September 1997, 140 children at a site 840 miles from the tertiary care center were seen during an evaluative trial of telemedicine consultations (TMC). The TMC visit was the initial encounter with the tertiary care specialist for 31 children. After consultation, each family was asked to complete an anonymous quality management survey that asked for estimates of cost savings and assessed their level of comfort and satisfaction with 13 other aspects of the TMC encounter. A 3- or 5-point Likert scale was used for each question. Comfort scores before and after each consultation were compared by chi2 analysis. Logistic regression was used to determine the independent predictors of satisfaction.

RESULTS

104 of the 140 (74%) families responded. Mean patient estimated cost savings was $1,318+/-677. The highest level of comfort was noted by 58% of respondents before TMC and by 77% after (P = .005). On a 5-point scale, 71% scored 5 (completely satisfied). None scored less than 3. The independent statistically significant predictors of satisfaction were concerns about privacy, comfort with the camera, and perceived specialist comfort.

CONCLUSIONS

In addition to providing financial savings, TMC is well accepted by families and children. Those using this new technology must give special attention to issues of patient privacy, camera comfort, and specialist comfort.

A novel mechanism of CD4 down-modulation induced by monosialoganglioside GM3. Involvement of serine phosphorylation and protein kinase c delta translocation

In this report the molecular mechanism(s) involved in the rapid and selective endocytosis of cell surface glycoprotein CD4 induced by exogenous monosialoganglioside GM3 in human peripheral blood lymphocytes have been investigated. Inhibition of the GM3-induced CD4 down-modulation was observed in the presence of specific protein kinase C (PKC) inhibitors. Scanning confocal microscopy revealed the translocation and clustering on the cell surface of PKC isozymes delta and theta (more evidently than alpha and beta) after GM3 treatment, suggesting the involvement of these isozymes in the ganglioside-induced CD4 down-modulation. Exogenous GM3 induced phosphorylation of CD4 molecule, which then dissociated from p56(lck), as early as after 5 min. Moreover, addition of GM3 resulted in a rapid (1 min) cytosolic phospholipase A2 activation with consequent arachidonic acid release, whereas no phosphatidylinositol-phospholipase C activity was observed. Both PKC translocation and CD4 down-modulation were blocked by the trifluoromethylketone analog of arachidonic acid, a selective inhibitor of cytosolic phospholipase A2 and by mitogen-activated protein kinase inhibitor PD98059. Taken together, these findings strongly suggest that GM3 may trigger a novel mechanism of modulation of the CD4 surface expression through the activation of enzyme(s) involved in the regulation of cellular functions.

Colocalization and complex formation between prosaposin and monosialoganglioside GM3 in neural cells

Prosaposin, the precursor of saposins A, B, C, and D, was recently identified as a neurotrophic factor in vitro as well as in vivo. Its neurotrophic activity has been localized to a linear 12-amino acid sequence located in the NH2-terminal portion of the saposin C domain. In this study, we show the colocalization of prosaposin and ganglioside GM3 on NS20Y cell plasma membrane by scanning confocal microscopy. Also, TLC and western blot analyses showed that GM3 was specifically associated with prosaposin in immunoprecipitates; this binding was Ca2+-independent and not disassociated during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The association of prosaposin-GM3 complexes on the cell surface appeared to be functionally important, as determined by differentiation assays. Neurite sprouting, induced by GM3, was inhibited by antibodies raised against a 22-mer peptide, prosaptide 769, containing the neurotrophic sequence of prosaposin. In addition, pertussis toxin inhibited prosaptide-induced neurite outgrowth, as well as prosaptide-enhanced ganglioside concentrations in NS20Y cells, suggesting that prosaposin acted via a G protein-mediated pathway, affecting both ganglioside content and neuronal differentiation. Our findings revealed a direct and tight GM3-prosaposin association on NS20Y plasma membranes. We suggest that ganglioside-protein complexes are structural components of the prosaposin receptor involved in cell differentiation.

Selective localization of matrix metalloproteinase 9, beta1 integrins, and human lymphocyte antigen class I molecules on membrane vesicles shed by 8701-BC breast carcinoma cells

The shedding of membrane vesicles from the cell surface is a vital process considered to be involved in cell-cell and cell-matrix interactions and in tumor progression. By immunoelectron microscopic analysis of surface replicas of 8701-BC human breast carcinoma cells, we observed that membrane vesicles shed from plasma membranes contained densely clustered gelatinase B [matrix metalloproteinase 9 (MMP-9)], beta1 integrins, and human lymphocyte antigen class I molecules. By contrast, alpha-folate receptor was uniformly distributed on the smooth cell membrane and shedding areas. Both cell surface clustering of selected molecules and membrane vesicle release were evident only when cells were cultured in the presence of serum. Vesicle shedding occurred preferentially at the edge or along narrow protrusions of the cell. Specific accumulation of proMMP-9 and active forms of MMP-9 in shed vesicles was also demonstrated by gelatin zymography. In addition, Western blotting analysis showed the presence of a large amount of proMMP-9/tissue inhibitor of metalloproteinase 1 complex. The release of selected areas of plasma membranes enriched with MMP-9 and beta1 integrins indicates that membrane vesicle shedding from tumor cells plays an important role in the directional proteolysis of the extracellular matrix during cellular migration. The presence of human lymphocyte antigen class I antigens suggests a mechanism for tumor cells to escape from immune surveillance.

Thermal behavior of human melanoma cell line in vitro and enhancement of hyperthermic response by bupivacaine

The effect of hyperthermia and bupivacaine, alone and in combination, on the clonogenic activity of a human melanoma cell line was investigated. The time-temperature relationship of exponentially growing cells was defined in the range of 41-45 degrees C. All the survival curves were exponential and the Arrhenius plot was linear over the temperature range tested. The survival curve of bupivacaine-treated cells was also exponential after an initial shoulder. Bupivacaine affected cell survival mainly through an ATP depletion because of deep alterations of mitochondria, essentially due to changes in the physical state of membrane lipids. The analysis of the interaction between hyperthermia and bupivacaine, performed with an isobolar method, demonstrated a synergism of response at all combinations tested, but only with simultaneous exposure. Such a response did not depend on an impairment of the energy-yielding processes, but may be ascribed to combined effects of both agents on cell structure and function. The hyperthermic enhancement achieved by low bupivacaine concentrations allowed to achieve a preestablished cell killing with a reduced exposure time (e.g., 50 min) and with a temperature (42 degrees C) generally accepted as clinically achievable. Therefore, a combined modality in which local treatment with bupivacaine was coupled to local heating could result in high local damage with reduced systemic complications.

Plasminogen activator system modulates invasive capacity and proliferation in prostatic tumor cells

The malignant phenotype of prostatic tumor cells correlates with the expression of both uPA and its cell-membrane receptor (uPAR); however, there is little information concerning the role of cell-bound uPA in matrix degradation and invasion. Our results suggest that cell-associated uPA plays a key role in regulating the amount of plasmin present at the surface of prostatic carcinoma (PRCA) cells and show that differential production of uPA corresponds with the capacity to bind and activate plasminogen. In addition, we provide direct evidence that both uPA secretion and the presence of uPA-uPAR complexes characterize the invasive phenotype of PRCA cells and suggest the existence of several pathways by which tumor cells acquire plasmin activity. LNCaP cells (which do not produce uPA but express uPAR) may activate plasmin through exogenous uPA. In vivo, the source of uPA may be infiltrating macrophages and/or fibroblasts as observed in several other systems. PAI-1 accumulation in the conditioned medium (CM) limits plasmin action to the pericellular microenvironment. Our results indicate that MMP-9 and MMP-2 are also activated by plasmin generated by cell-bound but not by soluble, extracellular uPA. Plasmin activation and triggering of the proteolytic cascade involved in Matrigel invasion is blocked by antibodies against uPA (especially by anti- A-chain of uPA which interacts with uPAR) and by PA inhibitors such as p-aminobenzamidine which may regulate levels of cell-bound uPA. uPA may also regulate growth in PRCA cells. Indeed, antibodies against uPA A-chain (and also p-aminobenzamidine treatment) interfere with the ATF domain and inhibit cell growth in uPA-producing PC3 and DU145 prostate cancer cell lines, whereas exogenous uPA (HMW-uPA with ATF) induces growth of LNCaP prostate tumor cell line. These data support the hypothesis that in prostatic cancer patients at risk of progression, uPA/plasmin blockade may be of therapeutic value by blocking both growth of the primary tumor and dissemination of metastatic cells.

Regulation by thyroid hormone of the expression of basement membrane components in rat prepubertal Sertoli cells

The present study reports the modulation of basement membrane (BM) components, laminin, entactin, and type IV collagen, expression in prepubertal rat Sertoli cell by the thyroid hormone T3. Immunocytochemical studies of permeabilized Sertoli cells in culture showed that T3 treatment (10[-7] M for 24 h) increased the number of cells staining positive for laminin and/or entactin (from 58 +/- 5.3% to 86.4 +/- 6.5%, P < 0.01). In contrast, a strong inhibition of type IV collagen immunopositivity was observed. Western blot analysis of Sertoli cell-conditioned media indicated that T3 treatment significantly (P < 0.01) increased the level of secreted entactin by 60-65% without affecting the levels of laminin A and B1/B2 chains. Moreover, thyroid hormone treatment of Sertoli cells significantly reduced type IV collagen secretion by 62% (P < 0.05). Slot blot analysis of poly-A RNA demonstrated a significant (P < 0.01) increase in the level of entactin messenger RNA (mRNA) by 140% (P < 0.01) and a 50% reduction of type IV collagen alpha1 chain mRNA after thyroid hormone treatment. No effect of the hormone was observed on the accumulation of the laminin B1 and B2 chain mRNAs in Sertoli cell cultures. These effects cannot be ascribed to changes in the degradation of BM components, because no effect of thyroid hormone was observed on plasminogen activators or metalloproteinase secretion by Sertoli cells. These observations indicate the Sertoli cell as a source of entactin within the testis, demonstrate the ability of T3 to differentially regulate the expression of BM components, and can be regarded as a part of the integrated mechanism by which thyroid hormone affects testicular development and differentiation.

Circulating Vdelta1+ T cells are activated and accumulate in the skin of systemic sclerosis patients

OBJECTIVE

An increased percentage of Vdelta1+/gamma/delta T cells has been detected both in the peripheral blood and bronchoalveolar lavage fluid of patients with systemic sclerosis (SSc). This study evaluated the subset distribution, activation status, and expression of cellular adhesion molecules, such as intercellular adhesion molecule 1 (CD54), very late activation antigen alpha4 (CD49d), and lymphocyte function-associated antigen 1alpha (CD11a), on circulating gamma/delta T cells, as well as their presence in the skin of SSc patients.

METHODS

We studied 12 patients with SSc and 16 healthy volunteer donors. The distribution, activation status, and expression of cellular adhesion molecules were studied by flow cytometry; their presence in SSc patient skin was evaluated by immunohistochemistry.

RESULTS

We found that the percentages and absolute numbers of peripheral blood gamma/delta T cells, CD16, CD8, CD45RO, CD25, HLA-DR, CD54, and CD11a coexpression did not differ significantly from those of the controls. CD49d gamma/delta T cells were significantly increased in SSc patients (2.3%) compared with controls (0.5%). A marked increase in the ratio of Vdelta1+ cells to gamma/delta cells was observed in the patients (72%) compared with the controls (31%). The Vdelta1+ subset showed a significant expression of both HLA-DR (83% of total Vdelta1+ cells) and CD49d (90% of total Vdelta1+ cells) compared with the controls (20.5% and 60%, respectively). In the skin, the absolute numbers of gamma/delta T cells were found in striking amounts in perivascular areas, particularly in the early edematous phase of SSc (22.58 in patients and 0 in controls); the majority of gamma/delta T cells were Vdelta1+ (19 in patients and 0 in controls). In the advanced phase of SSc, Vdelta1+ T cells were also increased compared with controls (3.5 versus 0).

CONCLUSION

Our results show that Vdelta1+ T cells express both adhesion molecules and activation markers, and strongly support gamma/delta T cell homing to sites of inflammation. The increase in the Vdelta1 subset suggests a selective V gene subset expansion.

Evidence for the existence of ganglioside-enriched plasma membrane domains in human peripheral lymphocytes

In human peripheral blood lymphocytes (PBL) monosialoganglioside GM3 appears to be the major ganglioside on the cell plasma membrane. We have analyzed the expression and distribution pattern of GM3 molecules on the lymphocyte plasma membrane by flow cytometry, immunofluorescence, and immunoelectron microscopy, using an anti-GM3 monoclonal antibody. Both CD4+ and CD8+ T lymphocyte subpopulations showed substantial GM3 expression, as determined by thin-layer chromatography and flow cytometric analysis. A clustered distribution of GM3 molecules on the cell surface, revealed by immunofluorescence and immunogold electron microscopy, clearly indicated the presence of GM3 molecule-enriched plasma membrane domains. To better define these domains, we analyzed the ganglioside and protein composition of buoyant low-density Triton-insoluble (LDTI) lymphocyte fractions. The results show that GM3 is enriched approximately 20-fold in LDTI fraction, as compared with total cell lysates. In addition, CD4 and lck molecules are selectively recovered in the same LDTI fraction isolated from human PBL. These findings, together with the observation that anti-CD4 co-immunoprecipitated GM3, support the hypothesis of a possible GM3-CD4 interaction and suggest a role for gangliosides as structural components of the membrane multimolecular signaling complex involved in T-cell activation, antigen recognition, and other dynamic lymphocytic plasma membrane functions.

Ultrastructural and phenotypic characterization of CABA I, a new human ovarian cancer cell line

We have established an ovarian cancer cell line (CABA I) from ascitic fluid obtained from a patient with papillary adenocarcinoma of the ovary prior to drug treatment. The epithelial origin of the cell line was confirmed by morphology and by immunofluorescence analysis using anticytokeratin antibodies. Ultrastructural analysis revealed a very irregular membrane surface and a clear cytoplasm rich in electron-lucent vesicles. CABA I cells grow rapidly in culture (doubling time 18 h) in an anchorage-independent manner. Exogenously added beta-estradiol and epidermal growth factor (EGF) treatments did not influence cell growth rate. FACS analysis to determine the phenotypic profile of tumor-associated antigen, membrane receptor, and adhesion molecule expression indicated that the cell line was positive for different members of the c-erbB family, for alpha 6 and beta 1 integrin receptors, and intensively positive for HLA class I antigens and the folate receptor. Molecular characterization revealed no mutations for c-myc and c-k-ras genes, but did detect an exon 5 mutation in the p53 gene. CABA I cells grew poorly as heterotransplants in nude mice, and tumors showed long latency periods. Because early (15-20) and late (55-60) passage cells maintain the same growth and phenotypic characteristics, the CABA I cell line might provide a good in vitro model system to investigate the cellular and molecular events involved in ovarian carcinogenesis.

Overexpression of monosialoganglioside GM3 on lymphocyte plasma membrane in patients with HIV infection

SUMMARY

This study was undertaken to analyze both the GM3 expression on peripheral blood lymphocytes of HIV-infected patients and the relationship between ganglioside content and anti-GM3 reactivity. GM3 expression was determined as a percentage of lipid-bound sialic acid and by cytofluorimetric analysis in 25 AIDS patients, 20 anti-HIV+ asymptomatic subjects, 25 patients with different viral disease, and 25 healthy donors. GM3 distribution was analyzed by immunofluorescence and immunoelectron microscopy. A follow-up study to detect anti-lymphocytic GM3 antibodies was performed in progressive and nonprogressive anti-HIV+ subjects. Lymphocytes from HIV-infected patients showed a significant increase of plasma membrane GM3 content; no difference was found between CD4+ and CD8+ cells. Immunofluorescence and immunoelectron microscopic analysis showed that GM3 was distributed in large clusters over the cell plasma membrane. The follow-up study revealed that the occurrence of anti-lymphocytic GM3 antibodies was significantly higher in patients with progressive disease, compared with asymptomatic non-progressive subjects. These findings revealed that (1) the increased GM3 content in HIV-infected patients is detected at the plasma membrane level, (2) GM3 overexpression is able to induce an increased reactivity with anti-GM3 antibodies, and (3) the appearance of anti-lymphocytic GM3 antibodies in asymptomatic anti-HIV+ subjects could have prognostic relevance for the risk of developing AIDS.

Intravenous propafenone in paroxysmal atrial fibrillation: a randomized, placebo-controlled, double-blind, multicenter clinical trial. Paroxysmal Atrial Fibrillation Italian Trial (PAFIT)-2 Investigators

BACKGROUND

Pharmacological conversion of paroxysmal atrial fibrillation is frequently necessary. The aim of this study was to compare intravenous propafenone, a class Ic antiarrhythmic agent, with placebo in paroxysmal atrial fibrillation (AF) of recent onset (< 72 h).

PATIENTS AND METHODS

We randomly allocated 75 patients, aged 18 to 70 years, with paroxysmal AF to receive intravenous propafenone (2 mg/kg in 15 min followed by 1 mg/kg in 2 h) or the matching placebo. Patients were followed for 3 h. Exclusion criteria were the presence of one of the following: clinical heart failure, recent acute myocardial infarction, hypotension, atrioventricular block, Wolff-Parkinson-White syndrome, or current treatment with antiarrhythmic agents or digitalis.

RESULTS

No sign of heart disease was found in 74.7% of the patients. Echocardiographically determined left atrium diameter was similar in the two groups. Conversion to sinus rhythm occurred in 24 of 41 patients allocated to propafenone and in 10 of 34 patients allocated to placebo (odds ratio 3.2, 95% confidence intervals 1.3-7.9; p < 0.01). Mean conversion time was 34 +/- 29 and 71 +/- 55 min, respectively, for propafenone and placebo. Mean heart rate in nonconverters decreased from 146 to 109 beats/min in patients treated with propafenone while it remained virtually unchanged in those treated with placebo. Only minor side effects were noted.

CONCLUSIONS

Intravenous propafenone is an effective therapeutic option for restoring sinus rhythm in patients with paroxysmal AF of recent onset.

Monosialoganglioside GM3 induces CD4 internalization in human peripheral blood T lymphocytes

Gangliosides modulate the expression of CD4 molecules on the cell surface of T lymphocytes. We report here that treatment of human peripheral blood lymphocytes with exogenous monosialoganglioside GM3 induces a rapid down-modulation of the CD4 molecules on the plasma membrane of CD4+ T lymphocytes, as assessed by cytofluorimetric analysis and quantitative immunoelectron microscopy. The CD4 down-modulation was ganglioside-dose dependent and was already evident after 5 min of treatment, reaching the maximum after 20 min. The expression of other surface antigens was not affected by GM3 treatment. The immunoelectron microscopic analysis showed that, following GM3 addition, gold labelled CD4 molecules were rapidly redistributed on the cell surface, clustered and internalized via endocytic pits and vesicles. These results indicate that CD4 down-modulation induced by GM3 occurs through an endocytic mechanism. A persistent low level of CD4 expression on the cell surface up to 24 h after GM3 treatment, compared with a stable expression of either CD4 in untreated cells and CD3 in GM3-treated cells, suggests intracellular degradation of the internalized CD4 molecules.

Enhancing medical database semantics

Medical Databases deal with dynamic, heterogeneous and fuzzy data. The modeling of such complex domain demands powerful semantic data modeling methodologies. This paper describes GSM-Explorer a Case Tool that allows for the creation of relational databases using semantic data modeling techniques. GSM Explorer fully incorporates the Generic Semantic Data Model-GSM enabling knowledge engineers to model the application domain with the abstraction mechanisms of generalization/specialization, association and aggregation. The tool generates a structure that implements persistent database-objects through the automatic generation of customized SQL ANSI scripts that sustain the semantics defined in the higher lever. This paper emphasizes the system architecture and the mapping of the semantic model into relational tables. The present status of the project and its further developments are discussed in the Conclusions.

Platelet proaggregating activity of human colorectal tumour cell lines does not correlate with the degree of differentiation

Six human colorectal tumour cell lines with various degrees of differentiation were studied. Each of the cell lines studied showed an in vitro platelet proaggregating activity, represented by the induction of typical aggregation waves. This activity was dose-dependent and probably related to a thrombin-dependent mechanism. However, the degree of cell differentiation did not correlate with the proaggregating activity. In fact, significant differences were observed between the two well differentiated cell lines, while a comparison between well and poorly differentiated cell lines did not reveal any difference. These results were confirmed by the ultrastructural observations, indicating that similar platelet-tumour cell interaction may be found in all the cell lines studied. The present results suggest that platelet proaggregating activity of the human colorectal tumour cell lines under investigation is unrelated to their degree of differentiation.

Infection by human herpesvirus 6 (HHV-6) of human lymphoid T cells occurs through an endocytic pathway

We have analyzed by immunoelectron microscopy the early events of binding and internalization of human herpesvirus 6 (HHV-6, strain GS) on a susceptible T-lymphoblastoid cell line, HSB-2. The virions bound to the cell surface at 4 degrees C were tightly associated with the plasma membrane. Gold immunolabeling of the viral envelope proteins was strong and specific. Warming at 37 degrees C for different times showed viral internalization through smooth surfaced pits and vesicles. Fusion events of the virions with the cell plasma membrane were never observed. Gold immunolabeling performed in parallel experiments before or after viral internalization showed: (1) absence of viral envelope proteins on the cell plasma membranes at all times of internalization, again excluding fusion events; (2) entry of the virions with their envelopes. Treatment of the cells with chloroquine, a drug known to affect the endocytic pathway, led to an almost complete inhibition of viral infectivity, suggesting that the endocytosed virions are responsible for a successful infection. Comparable results were obtained using a second strain of HHV-6 (BA92), with biologic and molecular characteristics similar to the prototype strain Z29. The chloroquine inhibition was effective on two different T cell lines (HSB-2 and J-Jhan), as well as on phytohemagglutinin-stimulated peripheral blood mononuclear cells.

Patching and capping of LFA-1 molecules on human lymphocytes

The distribution and dynamics of LFA-1 molecules over the surface of human lymphocytes were analysed using immunogold label-fracture and fracture-flip methods. Patching and capping were induced by incubation at 37 degrees C with antibodies directed against the alpha and beta chains respectively of the heterodimeric LFA-1 molecule, and were followed by immunofluorescence. Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) to link LFA-1 molecules to the cytoskeleton increased the percentage of capped cells, implying a faster and more efficient process of capping. At all times of clustering or upon phorbol ester treatment, the concentration of LFA-1 in patches and then in caps was not accompanied by a parallel concentration of membrane particles on the freeze-fractured plasma membranes. Our results support the role of the cytoskeleton in regulating the capping phenomenon and in controlling the structural organization of the plasma membranes.

Dynamics of transmembrane proteins during Sindbis virus budding

Label-fracture and immunogold fracture-flip techniques are used to address at the ultrastructural level the dynamics of viral and cellular transmembrane proteins during the budding of Sindbis virus on the plasma membrane of infected cells. Immunolabeling with anti-Sindbis spike antibodies shows that the viral proteins are mostly in clusters, all associated with budding viruses. Ultrastructural observation of the unlabeled freeze-fractured plasma membranes shows that membrane particles aggregate over the budding viruses. These results indicate that the concentration of viral transmembrane proteins gives rise to a parallel concentration of membrane particles. Immunolabeling with anti-CD8 antibodies of cells expressing by transfection the CD8 transmembrane protein and infected with Sindbis virus shows absence of labeling on the particle aggregates over the forming virions. These findings indicate the exclusion of CD8 proteins from the portions of the membrane where budding occurs.

Herpes simplex virus envelopment and maturation studied by fracture label

Herpes simplex virus envelopment and maturation were investigated by thin-section fracture label. The distribution of glycoproteins B and D was analyzed by labeling with antibodies; the precursor and mature forms of the glycoproteins were differentiated by labeling with the lectins concanavalin A (ConA) and wheat germ agglutinin (WGA), respectively. We report that the two glycoproteins were readily detected in the intracellular virion, whether located between the inner and outer nuclear membranes or within cytoplasmic membrane-bound vesicles and in the inner and outer nuclear membranes themselves. The enveloped virion between the inner and outer nuclear membranes labeled with ConA but not with WGA. During the transit to the extracellular space the reactivity of the virion membranes with ConA decreased and that with WGA ensued. The results document that herpes simplex viruses acquire at the inner nuclear membrane an envelope carrying the immature forms of the glycoproteins and that during the transit to the extracellular space the envelope glycoproteins become of the fully processed type.

Partition of epidermal growth factor receptors on freeze-fractured plasma membranes of A431 cells is affected by the ligand

The fracture immunolabel technique, which permits assessment of the partition of transmembrane proteins with the inner or outer leaflets of the freeze-fractured membrane, was used to analyze the behavior on fracture of epidermal growth factor (EGF) receptors over the plasma membranes of A431 cells. The receptors partition mainly with the outer leaflet of the freeze-fractured plasma membranes, whereas they become associated with the inner leaflet when they are occupied by the ligand. This modified partition is even more evident after receptor clustering induced by incubation with EGF at 37 degrees C. Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) decreases the number of receptors over both inner and outer leaflets. An effect similar to that induced by the ligand is obtained when receptor aggregation is achieved using anti-receptor monoclonal antibodies (MAb). The modified partition therefore indicates receptor activation and appears to be a consequence of receptor cross-linking rather than to reflect a conformational change of the receptor molecule. Parallel immunolabeling with anti-phosphotyrosine antibodies of freeze-fractured EGF-treated A431 cells reveals that the receptors, when activated, are associated only with the inner leaflet of the plasma membrane.