The Department of Veterans Affairs Biorepository Brain Bank: a national resource for amyotrophic lateral sclerosis research

Our objective was to describe a unique national resource to facilitate amyotrophic lateral sclerosis (ALS) research, the Department of Veterans Affairs Biorepository Brain Bank. Enrolled veterans receive biannual telephone follow-up to collect clinical data until death including the ALS Functional Rating Scale-Revised (ALSFRS-R). A comprehensive post mortem examination is performed and a wide range of fixed and frozen brain and spinal cord samples are banked. As of December 2012, 240 veterans were enrolled from 47 states and post mortem tissue recoveries were performed on 100 veterans from 37 states. Average disease duration was 13.5 (range 3-45) years. Average follow-up for living subjects was 3.1 years and average ALSFRS-R score was 23.5 compared to 25.9 (12-24 months earlier), indicating slow disease progression. ALS was confirmed by post mortem examination in 97% of cases. Eighty-six percent of cases were TDP-43-positive. Additional neuropathological diagnoses include Lewy body disease (13%), frontotemporal lobar degeneration (6.3%), chronic traumatic encephalopathy with motor neuron disease (3.2%), and Alzheimer's disease (2.1%). Tissue RIN values were ≥ 4.0 in 88% of cases. In conclusion, the availability of high quality fixed and frozen CNS tissue from this well characterized cohort is an important resource to facilitate research into genetic and environmental risk factors and clinical pathological relationships in ALS.

Rodent models of brain metastasis in melanoma

Metastasis of melanoma to the central nervous system (CNS) remains one of the major barriers to successful treatment of this disease. Available treatment modalities are of limited clinical efficacy. This problem is compounded by the presence of the blood-brain barrier (BBB), an important consideration in the development of new therapeutic agents. Only in animal models can the dual properties of experimental tumours and the BBB be explored in one system. A variety of rodent models have been developed, utilizing both murine and human melanoma cell lines. These models have highlighted the complex biology of cerebral metastasis, involving apparent disease progression through the selection of subclones at each stage, eventually leading to disease in the brain. As demonstrated in a number of animal studies, different subpopulations of metastatic melanoma cells are likely to be responsible for parenchymal and leptomeningeal CNS disease. In addition, these animal systems have been used to demonstrate the potential efficacy of new chemotherapeutic drugs, radiation treatments and immunotherapeutic approaches for the treatment of melanoma brain metastasis. Key biological questions remain to be answered. In particular, the molecular and cellular mechanisms responsible for establishing cerebral melanoma must be clearly delineated. Several molecules, including vascular endothelial growth factor (VEGF) and integrins, appear to play important, but not definitive, roles. Other, as yet undefined, molecules appear to be critical. The identification of these factors in experimental models, with confirmatory studies in humans, will expand our understanding of cerebral melanoma and provide valuable new therapeutic targets for intervention in this difficult clinical problem.

Generation of dendritic cell-tumor cell hybrids by electrofusion for clinical vaccine application

Vaccination with hybrids comprising fused dendritic cells (DCs) and tumor cells is a novel cancer immunotherapy approach designed to combine tumor antigenicity with the antigen-presenting and immune-stimulatory capacities of DCs. For clinical purposes, we have incorporated a large-scale process for the generation of clinical-grade DCs together with novel electrofusion technology. The electrofusion system provides for ease and standardization of method, efficient DC-tumor cell hybrid formation, and large-quantity production of hybrids in a high-volume (6-ml) electrofusion chamber. In addition, we have evaluated DC electrofusion with a variety of allogeneic human tumor cell lines with the rationale that these tumor cell partners would prove a ready, suitable source for the generation of DC-tumor cell hybrid vaccines. The DC production process can generate 6x10(8) to 2x10(9) DCs from a single leukapheresis product (approximately 180 ml). As determined by FACS analysis, electrofusion of 6x10(7) total cells (1:1 ratio of DC and tumor cells) resulted in a consistent average of 8-10% DC-tumor cell hybrids, irrespective of the tumor type used. Hybrids were retained in the population for 48 h postfusion and following freezing and thawing. Upon pre-irradiation of the tumor cell partner for vaccine purposes, the overall fusion efficiency was not altered at doses up to 200 Gy. Evaluation of DC-tumor cell hybrid populations for their ability to stimulate T-cell responses demonstrated that electrofused populations are superior to mixed populations of DCs and tumor cells in generating a primary T-cell response, as indicated by IFN-gamma release. Moreover, hybrids comprising HLA-A*0201 DCs and allogeneic melanoma tumor cells (Colo 829 cell line) stimulated IFN-gamma secretion by antigen-specific CD8+ T cells, which are restricted for recognition of a melanoma gp100 peptide antigen (gp100(209-217)) within the context of the DC HLA haplotype. Maturation of the DC-Colo 829 cell hybrid population served to further improve this T-cell gp100-specific response. Overall, our results are promising for the large-scale generation of electrofused hybrids comprising DCs and allogeneic tumor cells, that may prove useful in human vaccine trials.

alpha-Tocopheryl succinate sensitizes established tumors to vaccination with nonmatured dendritic cells

PURPOSE

Dendritic cells (DCs) are considered potential candidates for cancer immunotherapy due to their ability to process and present antigens to T cells and stimulate immune responses. However, DC-based vaccines have exhibited minimal effectiveness against established tumors in mice and human cancer patients. The use of appropriate adjuvants can enhance the efficacy of DC-based cancer vaccines in treating established tumors.

METHODS

In this study we have employed alpha-tocopheryl succinate (alpha-TOS), a nontoxic esterified analogue of vitamin E, as an adjuvant to enhance the effectiveness of DC vaccines in treating established murine Lewis lung (3LL) carcinomas.

RESULTS

We demonstrate that locally or systemically administered alpha-TOS in combination with nonmatured DCs injected intratumorally (i.t.) or subcutaneously (s.c.) significantly inhibits the growth of preestablished 10-day tumors (mean tumor volume of 77.5 +/- 17.8 mm3 on day 30 post-tumor injection) as compared to alpha-TOS alone (mean tumor volume of 471 +/- 68 mm3 on day 30 post-tumor injection). Additionally, the adjuvant effect of alpha-TOS was superior to that of cyclophosphamide (CTX). The mean tumor volume on day 28 post-tumor injection in mice treated with CTX+DCs was 611 +/- 94 mm3 as compared to 105 +/- 36 mm3 in mice treated with alpha-TOS+DCs. Analysis of purified T lymphocytes from mice treated with alpha-TOS+DC revealed significantly increased secretion of IFN-gamma as compared to T cells from the various control groups.

CONCLUSION

This study demonstrates the potential usefulness of alpha-tocopheryl succinate, an agent nontoxic to normal cell types, as an adjuvant to augment the effectiveness of DC-based vaccines in treating established tumors.

Clinical applications of dendritic cell vaccination in the treatment of cancer

Dendritic cell (DC) immunotherapy has shown significant promise in animal studies as a potential treatment for cancer. Its application in the clinic depends on the results of human trials. Here, we review the published clinical trials of cancer immunotherapy using exogenously antigen-exposed DCs. We begin with a short review of general properties and considerations in the design of such vaccines. We then review trials by disease type. Despite great efforts on the part of individual investigative groups, most trials to date have not yielded data from which firm conclusions can be drawn. The reasons for this include nonstandard DC preparation and vaccination protocols, use of different antigen preparations, variable means of immune assessment, and nonrigorous criteria for defining clinical response. While extensive animal studies have been conducted using DCs, optimal parameters in humans remain to be established. Unanswered questions include optimal cell dose, use of mature versus immature DCs for vaccination, optimal antigen preparation, optimal route, and optimal means of assessing immune response. It is critical that these questions be answered, as DC therapy is labor- and resource-intensive. Cooperation is needed on the part of the many investigators in the field to address these issues. If such cooperation is not forthcoming, the critical studies that will be required to make DC therapy a clinically and commercially viable enterprise will not take place, and this therapy, so promising in preclinical studies, will not be able to compete with the many other new approaches to cancer therapy presently in development. Trials published in print through June 2003 are included. We exclude single case reports, except where relevant, and trials with so many variables as to prevent interpretation about DC therapy effects.

Feasibility to generate monocyte-derived dendritic cell from coculture with melanoma tumor cells in the presence of granulocyte/macrophage colony-stimulating factor (GM-CSF) and interleukin-4

OBJECTIVE

We investigated how melanoma cells and membrane-bound granulocyte/macrophage colony stimulating factor (mbGM-CSF) melanoma cell lines affect the differentiation of dendritic cells (DC) from CD14+ monocytes.

METHOD OF STUDY

The malignant melanoma cell lines (Conley and Jorp) and mbGM-CSF-positive cell lines (Conley B-F8 and Jorp C-E6) were cultured and cell-free supernatants were collected from each cell line cultures to assess the GM-CSF level. Adherent monocytes were cocultured for 6-7 days with irradiated mbGM-CSF and wild type melanoma cells (50 Gy) at each 1:1 and 0.1:1 ratio in six-well culture plates in ex vivo culture medium containing interleukin (IL)-4. Immunophenotyping was performed by triple color immunofluorescence staining with flow cytometry analysis.

RESULTS

GM-CSF was detected at low levels in the culture supernatants of Conley B-F8 (0.48 ng/10(6) cells/24 hr), whereas there was no detectable GM-CSF in that of Conley melanoma cell line. Monocytes cultured with GM-CSF/IL-4 generated the expression of high levels of HLA DR, CD1a and CD86, while the expression of CD14 and CD83 were in low amounts. However, the addition of GM-CSF to these cultures resulted in an increased expression of these markers and decreased that of CD14. Monocytes cocultured with Jorp C-E6 illustrated similar expression pattern of CD1a, HLA DR and CD14 in the presence or absence of GM-CSF as Conley B-F8 melanoma cell line. Monocytes cocultured with Conley B-F8 melanoma cells at 1:1 and 0.1:1 ratio showed no significant difference in expression of CD1a, CD14 and CD83 between the two ratios.

CONCLUSION

Our results illustrate the feasibility to generate monocyte-derived DC from coculture with melanoma tumor cells in the presence of GM-CSF and IL-4. However, mbGM-CSF tumor cells did not significantly enhance the DC differentiation through juxtacrine stimulation unless soluble GM-CSF was added in the culture media.

Antigen-driven oligoclonal expansion of tumor-infiltrating B cells in infiltrating ductal carcinoma of the breast

The objective of this study was to determine whether tumor-infiltrating B cells (TIL-B) of infiltrating ductal carcinoma (IDC) of the breast represent a tumor-specific humoral immune response. Immunohistochemical analysis of three Her-2/neu-negative IDC tumors from geriatric patients showed that TIL-B cluster in structures similar to germinal centers containing CD20(+) B lymphocyte and CD3(+) T lymphocyte zones with interdigitating CD21(+) follicular dendritic cells, suggesting an in situ immune response. A total of 29, 31, and 58 IgG1 H chain clones was sequenced from the three IDC tumors, respectively. Intratumoral oligoclonal expansion of TIL-B was demonstrated by a preponderance (45-68%) of clonal B cells. In contrast, only 7% of tumor-draining lymph node and 0% of healthy donor PBL IgG H chains were clonal, consistent with the larger repertoires of node and peripheral populations. Patterns and levels of TIL-B IgG H chain somatic hypermutation suggested affinity maturation in intratumoral germinal centers. To examine the specificity of TIL-B Ig, a phage-displayed Fab library was generated from the TIL-B of one IDC tumor. Panning with an allogeneic breast cancer cell line enriched Fab binding to breast cancer cells, but not nonmalignant cell lines tested. However, panning with autologous tumor tissue lysate increased binding of Fab to both tumor tissue lysate and healthy breast tissue lysate. These data suggest an in situ Ag-driven oligoclonal B cell response to a variety of tumor- and breast-associated Ags.

Transduction of human dendritic cells with a recombinant modified vaccinia Ankara virus encoding MUC1 and IL-2

The epithelial mucin MUC1 is considered an opportune target antigen for cancer immunotherapy, as it is over-expressed and exhibits aberrant glycosylation in malignant cells. Because dendritic cells (DC) are powerful initiators of immune responses, efforts have focused on tumor antigen-bearing DC as potent cancer vaccines. In this study we have characterized the transduction of monocyte-derived DC with a highly attenuated vaccinia virus vector [modified vaccinia Ankara (MVA)] encoding human MUC1 and the immunostimulatory cytokine IL-2. Analysis of transduced DC cultures generated from a number of donors revealed MUC1 expression in the range of 27-54% of the cells and a co-regulated secretion of bioactive IL-2. As shown by FACS analysis with MUCI-specific antibodies, the MVA-MUC1/IL-2-transduced DC predominantly expressed the fully processed glycoform of MUC1, typical of that displayed by normal epithelia. Over a 3-day period after transduction, transgene expression declined concurrent with an increase in MVA-induced cytopathic effects. The transduced DC stimulated allogeneic lymphocyte proliferation, indicating that DC immunostimulatory function is not impaired by vector transduction. In the presence of IL-2, MVA-transduced DC were able to enhance autologous lymphocyte proliferation. Also, vector expression was analyzed in DC cultures treated with TNF-alpha, a known DC maturation factor. As indicated by the up-regulation of several DC maturation markers, neither virus infection nor transgene expression influenced the maturation capacity of the cells. The MVA-MUC1/IL-2 vector effectively transduced both immature and TNF-alpha-matured DC. Overall, our results are encouraging for the clinical application of MVA-MUC1/IL-2-transduced DC.

Specific targeting of EGP-2+ tumor cells by primary lymphocytes modified with chimeric T cell receptors

A promising strategy for cancer treatment is adoptive immunotherapy with gene-modified lymphocytes expressing a chimeric T cell receptor (cTCR) that directs tumor targeting and stimulates T cell effector functions. In this study, the activities of two novel cTCR molecules (GAgamma and GAHgamma) were investigated. Both encode a single-chain variable fragment (scFv) derived from the monoclonal antibody (MAb) GA733.2, which binds the epithelial glycoprotein 2 (EGP-2) overexpressed on a variety of human carcinomas. In the GAgamma cTCR, the scFv is directly fused to the transmembrane/cytoplasmic portions of the immunoglobulin Fc receptor (Ig FcRI) gamma subunit, which mediates T cell signaling. GAHgamma possesses an extracellular spacer composed of the CD8alpha immunoglobulin hingelike domain inserted between the scFv and gamma chain. Activated T cells (ATCs), stimulated ex vivo using anti-CD3 MAb, were derived from either healthy donors or patients and transduced with recombinant retrovirus encoding the respective GA cTCR molecules. After culture expansion for 14 days, GAgamma-modified ATCs demonstrated enhanced targeting and lysis of EGP-2+ colon cancer cells and increased cytokine secretion. Cells transduced with the GAHgamma cTCR displayed specific lytic activity that was about twofold greater than that of GAgamma-ATCs and produced significantly more cytokine. In addition, reactivation of GAHgamma-ATC with anti-CD3 MAb prior to addition to EGP-2+ tumor target induced a further increase in lytic activity. Because the activation status influences T cell antitumor functions, our data suggest that reactivation prior to adoptive transfer would improve the clinical efficacy of GAHgamma-modified ATCs.

Isolation of endothelial cells and their progenitor cells from human peripheral blood

PURPOSE

We have developed techniques to isolate endothelial cell (EC) progenitors from human peripheral and umbilical cord blood.

METHODS

Human adult peripheral and umbilical cord blood monocytes were isolated by centrifugation, and progenitor cells were separated with the use of magnetic polystyrene beads that were coated with a monoclonal antibody specific for the CD34 cell-membrane antigen. Cells were propagated in selective media, and developing cultures were immunostained for CD31, CD34, factor VIII, and vascular endothelial growth factor cell receptors. ECs that developed were transfected with a gene for prourokinase and used to line ePTFE grafts, which were evaluated in vitro in a pulsatile flow system.

RESULTS

Umbilical cord monocyte cultures demonstrated colonies that resembled ECs at approximately 2 weeks, with growth being best supported by EC growth media plus 20% calf serum with iron. Immunostaining of colonies was positive for CD31 and factor VIII. After 18 days in culture, CD34(+) cells from adult peripheral blood were noted, which had the typical cobblestone appearance of ECs and immunostained positively for CD31 and factor VIII-related antigens. Cultures of umbilical cord-derived cells and adult peripheral blood-derived cells developed complex line formations within 1 week in culture that stained positively for vascular endothelial growth factor receptor-2. Urokinase-transfected ECs were shown to overexpress urokinase. Prosthetic grafts lined with transfected cells showed 87.33% +/- 4.97% cell adherence after 2 hours in a pulsatile flow system at clinically relevant shear stress.

CONCLUSION

We conclude that endothelial progenitor cells can be isolated from human adult peripheral and umbilical cord blood and developed into EC cultures as a source of cells for vascular graft seeding and gene therapy.

T cell activation modulates retrovirus-mediated gene expression

Important considerations for T lymphocyte-based gene therapy include efficient gene delivery and expression in primary, human T cells. In this study, retrovirus-mediated gene transfer and the fate of proviral gene expression were evaluated in human T cells activated using (1) immobilized anti-CD3 monoclonal antibody (MAb) plus interleukin 2, or (2) cis costimulation using beads carrying coimmobilized anti-CD3 and anti-CD28 MAbs. By cross-linking the CD3 and CD28 receptors, these MAbs mimic in vivo signaling events, leading to cytokine production and proliferation. A modified human interleukin 1beta (IL-1beta) cDNA inserted into the MFG retroviral vector served as an indicator gene. Retroviral transduction frequencies were similar for T lymphocytes activated by the respective methods. However, early after MAb stimulation and virus exposure, proviral gene expression was greater at the RNA and protein levels in optimized anti-CD3/anti-CD28 bead-activated T cells, corresponding with augmented endogenous cytokine responses and mitogenesis. Proviral gene expression was not regulated by extrinsic cell factors present in activated T cell supernatants. Regardless of the MAb stimulation method, proviral IL-1beta expression declined in later T cell cultures concomitant with a decrease in cellular cytokines. Restimulation by either method reinduced both T cell activity and vector expression. Our finding that proviral gene regulation is downmodulated in the absence of T cell signaling events has implications for clinical strategies using retrovirus-modified T cells.

Improved adherence of genetically modified endothelial cells to small-diameter expanded polytetrafluoroethylene grafts in a canine model

PURPOSE

A significant limitation to using genetically modified endothelial cells (ECs) to seed prosthetic grafts before implantation has been poor cell adherence to the graft lumen. Methodologic changes to improve cell adherence were evaluated in a canine carotid interposition graft model using 4 mm interior diameter expanded polytetrafluoroethylene.

METHODS

ECs harvested from external jugular veins were grown in culture, with 80% of the cells from each culture transduced by incubation with an LXSN-type retroviral vector carrying a gene for human prourokinase and a neomycin resistance gene for selection in antibiotic G418. Control grafts had passive luminal coating with fibronectin and were seeded with transduced ECs immediately after G418 selection; these grafts were incubated for 2 days before implantation. Experimental grafts had fibronectin forcefully squeezed through the interstices and were seeded with ECs that had recovered in culture for 5 days after G418 selection; these grafts were incubated for 4 days before implantation. For each control (n = 9) and experimental (n = 12) graft, a graft prepared in the same fashion but seeded with the remaining autologous nontransduced cells was placed in the contralateral carotid artery. Grafts were explanted after 30 days and were evaluated for patency, thrombus-free surface area, and cell-free surface area.

RESULTS

No significant differences in patency rates were seen between any groups. The thrombus-free surface area was improved for experimental grafts (90%) compared with control grafts (76%), but this improvement did not achieve statistical significance. The cell-free surface area for transduced cells on experimental grafts was 65% compared with 96% for control grafts (p = 0.021) and was comparable with that for nontransduced cells on both control grafts (62%) and experimental grafts (51%; p = 0.201).

CONCLUSIONS

Adherence of genetically modified endothelial cells to small-diameter expanded polytetrafluoroethylene grafts in an in vivo physiologic flow model is significantly improved when cells have a more prolonged recovery from G418 selection, when the graft lumen is more uniformly coated with fibronectin before EC seeding, and when seeded grafts are left longer in culture before implantation to develop cell lining stability. The short-term patency rate of these seeded grafts is not affected by increased cell retention; long-term graft patency data and luminal healing require further evaluation.

Experimental co-expression of vimentin and keratin intermediate filaments in human breast cancer cells results in phenotypic interconversion and increased invasive behavior

The expression of intermediate filament proteins is remarkably tissue specific, which suggests that the intermediate filament type(s) present in cells is somehow related to their biological function. However, in some cancers, particularly malignant breast carcinoma, there is a strong indication that vimentin is co-expressed with keratins, thus presenting as a dedifferentiated or interconverted (between epithelial and mesenchymal) phenotype. In the present study, we recapitulated the interconverted phenotype by developing stable transfectants of MCF-7 human breast cancer cells, termed MoVi clones, to express both vimentin and keratins. Overexpression of vimentin in these cells led to augmentation of motility and invasiveness in vitra. These activities could be transiently down-regulated by vimentin antisense oligonucleotides in MoVi clones and MDA-MB-231 cells (which constitutively co-express keratins and vimentin). Furthermore, in the MoVi experimental transfectants expressing the highest percentage of vimentin-positive cells, their proliferative capacity, clonogenic potential, and tumorigenicity increased. However, the metastatic ability of the MoVi transfectants remained unchanged compared with MCF-7neo controls. The MDA-MB-231 cells metastasized to axillary lymph nodes in a SCID mouse model. Finally, we explored the possibility that potential changes could occur with respect to cell surface integrins. These studies revealed a decrease in the alpha 2- and alpha 3-containing promiscuous integrins, in addition to beta 1 containing integrins, concomitant with an increase in the alpha 6-containing laminin receptor integrin. Further functional analysis of the alpha 6 observation showed an increase in the baptotactic migration of MoVi transfectants toward a laminin substrate. From these data, it is postulated that the ability to co-express vimentin and keratins confers a selective advantage to breast cancer cells in their interpretation of signaling cues from the extracellular matrix; however the addition of vimentin intermediate filaments alone is not sufficient to confer the metastatic phenotype.

Role of intermediate filaments in migration, invasion and metastasis

The expression of intermediate filament proteins is remarkably tissue-specific which suggests that the intermediate filament (IF) type(s) present in cells is somehow related to their biological function. However, in some cancers-particularly malignant melanoma and breast carcinoma, there is a strong indication that vimentin and keratin IFs are coexpressed, thus presenting as a dedifferentiated or interconverted (between epithelial and mesenchymal) phenotype. In this review, two in vitro models are presented which recapitulate the interconverted phenotype in human melanoma and breast carcinoma, and allow, for the first time, unique observations to be made with respect to the role of IFs in cancer progression. These studies have provided direct evidence linking overexpression of keratin IFs in human melanoma with increased migratory and invasive activity in vitro, which can be down-regulated by substituting dominant-negative keratin mutants. Overexpression of vimentin IFs in the breast carcinoma model leads to augmentation of motility and invasiveness in vitro, which can be transiently down-regulated by treatment with antisense oligonucleotides to vimentin. Additional experimental evidence suggests that the mechanism(s) responsible for the differential expression of metastatic properties associated with the interconverted phenotype rest(s) in the unique interaction, either direct or indirect, of IFs with specific integrins interacting with the extracellular matrix. In this review, we discuss the observations derived from the human melanoma and breast carcinoma models to address the hypothesis that the ability to coexpress vimentin and keratins confers a selective advantage to tumor cells in their interpretation of and response to signaling cues from the extracellular matrix. The ramifications of these observations are discussed with respect to the patholophysiology of the respective in situ tumors.

Urokinase expression in transduced endothelial cells

Increased thromboresistance through the release of lytic agents by endothelial cells may improve the patency of endothelial lined prosthetic grafts. We have evaluated the expression of urokinase from cells transduced with a retrovirus containing the gene for a human preprourokinase. Endothelial cells were enzymatically harvested from canine external jugular vein in nine animals and grown to confluence in culture. One-third of these cells served as controls, and the remaining two-thirds were transduced via incubation with an LXSN-type retroviral vector carrying the urokinase gene and a neomycin resistance gene. Successfully transduced cells were selected by incubation with 400 micrograms/mL G418 and pure cultures grown to confluence. Supernatants from confluent control and experimental cell cultures after 48 hours in defined, serum-free medium were assayed for human urokinase concentration and overall enzyme activity. ELISA quantitation of concentration using mouse antihuman urokinase antibody showed 0.15 +/- 0.11 ng/mL/hr/10(6) cells in the transduced cell supernatant; no measurable concentration was found in the control cells. (P < 0.01) Overall (human plus canine) enzyme activity of urokinase was determined using an indirect spectrophotometric assay based on plasminogen activation (ploug U/mL). Transduced cells showed activities of 0.12 at 10 days and 0.45 at confluence; control cell activity was 0.0 and 0.15, respectively. (P < 0.05) These data show that endothelial cells can be transduced with a urokinase expressing gene that increases the release of this thrombolytic agent. Lining small diameter prosthetic grafts with these cells may improve their thromboresistance and long-term patency.

Structural and biological consequences of increased vimentin expression in simple epithelial cell types

Cytoskeletal intermediate filaments (IFs) constitute a diverse family of proteins whose members are expressed in tissue-specific patterns. Although vimentin IFs are normally restricted to mesenchyme, a variety of cell types express vimentin alone or together with cell-specific IFs during growth, differentiation, and neoplasia. In this study, we have investigated the influence of increased vimentin expression on the simple epithelial cell phenotype. An expression vector encoding a human vimentin cDNA was transfected into murine HR9 endoderm and F9 embryonal carcinoma cell lines, which serve as models for early extraembryonic epithelial differentiation. Stable clones that expressed varying levels of human vimentin were characterized by human vimentin were characterized by immunofluorescence and biochemical analysis. A relatively high level of vimentin expression in HR9 and differentiated F9 epithelial cells resulted in aberrant vimentin structures with co-collapse of keratin K8/K18 filaments and lowered amounts of keratin protein. In F9 epithelial cells, the desmosomal proteins DP I/II did not appear to localize to cell surface desmosome s but rather but rather co-aggregated with the perturbed IFs. Although overall cell morphology was not dramatically altered, individual nuclei were distorted by excess intracellular vimentin. Furthermore, cell proliferation as well as the cell spreading response time were slowed. Ther appears to be a threshold effect regarding overall vimentin levels as cells that expressed lower amounts of the human vimentin exhibited no obvious structural nor biological effects. Our results demonstrate that wild-type vimentin can act as a "mutant" protein when present at high intracellular levels, inducing a variety of phenotypic changes.

Association of vimentin intermediate filaments with the centrosome

SW-13 cells that lack cytoplasmic intermediate filaments (IFs) were stably transfected with a human vimentin cDNA expression vector. Isolated subclones displayed two prevalent patterns of vimentin distribution as observed by indirect immuno-localization: (1) cytoplasmic filaments characteristic of a vimentin IF network; and (2) a distinct, juxtanuclear focus with limited filamentous extensions. Comparative analysis of two subclones that uniquely segregated these patterns of vimentin organization indicated that vimentin accumulated as a perinuclear focus in cells that expressed a 4-fold lower level of the protein. The observed variation in cellular organization was not due to detectable differences in vimentin protein modification, as determined by two-dimensional gel analysis. Increasing the amount of vimentin in a low expressing clone by a secondary transfection with human or mouse vimentin cDNA resulted in well-dispersed, cytoplasmic filaments, suggesting that the distinct juxtanuclear organization of vimentin arose due to lower cellular vimentin levels. Employing anti-gamma-tubulin and anti-vimentin antibodies, dual immunofluorescence together with confocal microscopy revealed that the juxtanuclear focus of vimentin was located in the centrosomal region. Electron microscopy showed a spheroidal, filamentous structure with at least some filaments closely associated with the pericentriolar material (PCM). Because vimentin IF organization is at least partially dependent on microtubules, the effects of nocodazole and taxol on perinuclear vimentin foci were examined. Neither drug affected the juxtanuclear localization of foci, although taxol (10 microM, 5 hours) caused a release of pericentriolar gamma-tubulin from the nuclear region in 50–60% of the cells. These studies indicate that lower, in vivo, levels of vimentin fail to form extended IFs but rather are organized as a perinuclear aggregate. Moreover, the PCM of the centrosome appears to possess attachment sites for vimentin IFs.

Fate of a headless vimentin protein in stable cell cultures: soluble and cytoskeletal forms

The non-alpha-helical head domains of cytoskeletal intermediate filaments (IFs) are considered to play an important role in IF assembly and stability. We have investigated the fate of a "headless" mutant vimentin protein in cell types that either lack cytoplasmic IFs or contain preexisting IF networks (keratin and vimentin). Stable clones expressing a transfected headless vimentin cDNA were individually analyzed in order to avoid variabilities introduced by transient transfection and to compare the levels and effects of the mutant vimentin protein more accurately. In cells lacking IFs, the mutant protein existed in a diffuse, soluble form as determined by immunofluorescence and biochemical protein fractionation. In cells possessing vimentin IFs, the headless vimentin was highly dispersed throughout the cytoplasm, including lamellopodia. Expression levels in individual clones were as high as sevenfold greater than the endogenous vimentin component. Although the majority of the headless vimentin was highly soluble, a residual portion of the mutant vimentin colocalized with vimentin filaments and consistently comprised about 25% of the cytoskeletal vimentin network. These results demonstrate that the mutant protein can be stably expressed at relatively high levels without deleterious cellular effects or disruption of endogenous vimentin filaments. The observed specific ratio of mutant to wild-type vimentin (1:3) in the cytoskeleton supports IF in vivo assembly via specific hybrid tetramer formation and, further, that at least three intact head domains are required for competent tetramer formation and IF assembly.

Chromosomal aberrations in two sporadic gastrinomas

Results of cell culture and cytogenetic analysis (standard and fluorescent in situ hybridization, FISH) of two sporadic gastrinomas are reported. Maintenance of hormonal activity was assessed by detection of gastrin levels during the first 3 months in culture. Case 1 showed clonal aberrations consisting of two marker chromosomes: marker 1 is a large metacentric chromosome and marker 2 is a small acrocentric chromosome. Case 2 showed a constitutional polymorphism with chromosome 15p+ and a clone in the tumor cell culture with trisomy for chromosome 3. To our knowledge, this is the first cytogenetic report of sporadic gastrinomas (Zollinger-Ellison syndrome).

Epithelial-mesenchymal transitions during cell culture of primary thyroid tumors?

Fibroblast contamination of epithelial tumor cell cultures is of great concern when examining tumor cells in vitro for specific biochemical and cytogenetic changes. The observations of normal karyotypes in thyroid tumor cell cultures have raised the concern of whether residual tissue fibroblasts might obscure the cytogenetic analysis of transformed epithelial cells. We have characterized early passaged thyroid tumor cells to examine the proportions of epithelial and fibroblastic cell types. Cells were analyzed by immunocytology using antibodies recognizing the thyroid prohormone thyroglobulin, epithelial cytokeratins, and vimentin, a mesenchyme marker. Tumors consisted of one follicular adenoma and five papillary carcinomas. When examined by day 15 in culture, all cells contained filaments composed of vimentin, which most likely represents an adaptation to culture conditions. Double immunofluorescence staining for thyroglobulin and cytokeratin revealed the presence of not only epithelial but also spindle-like fibroblastoid cells possessing thyroid epithelial cell markers. The results suggest that in thyroid tumor cultures there is a unique cell type intermediate between epithelial and mesenchyme phenotypes that must be considered when performing cytogenetic analysis.

Distribution of desmosomal proteins in F9 embryonal carcinoma cells and epithelial cell derivatives

In diverse epithelia, cytoskeletal keratin intermediate filaments (IFs) associated with the cytoplasmic face of intercellular junctional desmosomes. The processes underlying desmosome formation and keratin IF interactions remain unclear. We have examined F9 embryonal carcinoma (EC) cell differentiation as a model for embryonic development of epithelial surface desmosomes. As determined by immunofluorescence microscopy and biochemical protein techniques, F9 EC cells, which lack surface desmosomes and keratin IFs, express the desmosomal proteins desmoplakins I and II (DP I/II), desmoglein I (DG I) and plakoglobin (PK). DP I/II are present at low level and are relatively soluble in buffer containing Triton X-100. Immunofluorescence localizes DP I/II to the juxtanuclear, centrosomal region. Species of DG I and PK are detected in both the Triton X-100-soluble and -insoluble protein fractions. DG I appears dispersed throughout the cell while PK resides at cell-cell boundaries. In epithelial cell cultures induced by retinoic acid (RA) treatment, each of the desmosomal proteins is organized into punctate desmosome-like structures with the appearance of simple epithelial K8/K18 IFs. The steady-state levels of DP I/II and PK increase with a partitioning of the majority of the desmosomal components into the insoluble fraction. In epithelial cells which lack distinct surface desmosomes, an intracellular association of keratin bundles with DP I/II is observed, suggesting that keratin filaments may facilitate the translocation of these desmosomal components to the cell surface. Parietal endoderm-like cells, derived by treatment with RA and dibutyryl cAMP, are analogous to F9 EC cells in that the cells express desmosomal components and do not display surface desmosomes. Moreover, K8 and K18 do not form distinct filaments, and the protein and RNA levels of K8 are low relative to epithelial cells induced by RA alone. The F9 system appears to be a relevant model for studies of desmosome assembly and the potential interactions of desmosomal proteins and keratin IFs in embryonic epithelial cell types.

Isolation of a variant family of mouse minor satellite DNA that hybridizes preferentially to chromosome 4

Two cosmids (HRS-1 and HRS-2) containing mouse minor satellite DNA sequences have been isolated from a mouse genomic library. In situ hybridization under moderate stringency conditions to metaphase chromosomes from RCS-5, a tumor cell line derived from the SJL strain, mapped both HRS-1 and HRS-2 to the centromeric region of chromosome 4. Sequence data indicate that these cloned minor satellite DNA sequences have a basic higher order repeat of 180 bp, composed of three diverged 60-bp monomers. Digestion of mouse genomic DNA with several restriction enzymes produces a ladder of minor satellite fragments based on a 120-bp repeat. The restriction enzyme NlaIII (CATG) digests all the minor satellite DNA into three prominent bands of 120, 240, and 360 bp and a weak band of 180 bp. Thus, the majority of minor satellite sequences in the genome are arranged in repeats based on a 120-bp dimer, while the family of minor satellite sequences described here represents a rare variant of these sequences. Our results raise the possibility that there may be other variant families of minor satellites analogous to those of alphoid DNA present in humans.

Disruption of keratin filaments in embryonic epithelial cell types

The murine keratins Endo B and Endo A, which are homologs of the human keratins K18 and K8, constitute the intermediate filaments (IFs) that are found in all simple epithelia of the adult and in the first epithelial derivatives of the early embryo. The cellular role of simple epithelial keratins in development and differentiation was investigated by inducing filament collapse in HR9 endoderm and F9 embryonal carcinoma cells in which mutant Endo B protein was constitutively expressed. By immunolocalization techniques a perturbation of the keratin network was revealed as well as concomitant disruption of vimentin IFs and displacement of surface desmosomal proteins, demonstrating an intimate structural association of Endo B/A filaments with these cellular components. In aggregates of differentiating F9 cells displaying altered Endo A/B IFs, the formation of a compact, polarized visceral endoderm layer was significantly compromised. These results indicate that an intact keratin network influences the three-dimensional formation of cell-cell or cell-substratum contacts in embryonic visceral endoderm.