Fire mosaics and reptile conservation in a fire-prone region

Fire influences the distribution of fauna in terrestrial biomes throughout the world. Use of fire to achieve a mosaic of vegetation in different stages of succession after burning (i.e., patch-mosaic burning) is a dominant conservation practice in many regions. Despite this, knowledge of how the spatial attributes of vegetation mosaics created by fire affect fauna is extremely scarce, and it is unclear what kind of mosaic land managers should aim to achieve. We selected 28 landscapes (each 12.6 km(2) ) that varied in the spatial extent and diversity of vegetation succession after fire in a 104,000 km(2) area in the semiarid region of southeastern Australia. We surveyed for reptiles at 280 sites nested within the 28 landscapes. The landscape-level occurrence of 9 of the 22 species modeled was associated with the spatial extent of vegetation age classes created by fire. Biogeographic context and the extent of a vegetation type influenced 7 and 4 species, respectively. No species were associated with the diversity of vegetation ages within a landscape. Negative relations between reptile occurrence and both extent of recently burned vegetation (≤10 years postfire, n = 6) and long unburned vegetation (>35 years postfire, n = 4) suggested that a coarse-grained mosaic of areas (e.g. >1000 ha) of midsuccessional vegetation (11-35 years postfire) may support the fire-sensitive reptile species we modeled. This age class coincides with a peak in spinifex cover, a keystone structure for reptiles in semiarid and arid Australia. Maintaining over the long term a coarse-grained mosaic of large areas of midsuccessional vegetation in mallee ecosystems will need to be balanced against the short-term negative effects of large fires on many reptile species and a documented preference by species from other taxonomic groups, particularly birds, for older vegetation.

Identification of a subpopulation of cells with cancer stem cell properties in head and neck squamous cell carcinoma

Like many epithelial tumors, head and neck squamous cell carcinoma (HNSCC) contains a heterogeneous population of cancer cells. We developed an immunodeficient mouse model to test the tumorigenic potential of different populations of cancer cells derived from primary, unmanipulated human HNSCC samples. We show that a minority population of CD44(+) cancer cells, which typically comprise <10% of the cells in a HNSCC tumor, but not the CD44(-) cancer cells, gave rise to new tumors in vivo. Immunohistochemistry revealed that the CD44(+) cancer cells have a primitive cellular morphology and costain with the basal cell marker Cytokeratin 5/14, whereas the CD44(-) cancer cells resemble differentiated squamous epithelium and express the differentiation marker Involucrin. The tumors that arose from purified CD44(+) cells reproduced the original tumor heterogeneity and could be serially passaged, thus demonstrating the two defining properties of stem cells: ability to self-renew and to differentiate. Furthermore, the tumorigenic CD44(+) cells differentially express the BMI1 gene, at both the RNA and protein levels. By immunohistochemical analysis, the CD44(+) cells in the tumor express high levels of nuclear BMI1, and are arrayed in characteristic tumor microdomains. BMI1 has been demonstrated to play a role in self-renewal in other stem cell types and to be involved in tumorigenesis. Taken together, these data demonstrate that cells within the CD44(+) population of human HNSCC possess the unique properties of cancer stem cells in functional assays for cancer stem cell self-renewal and differentiation and form unique histological microdomains that may aid in cancer diagnosis.

Comparing different sources of sulfur for high-rainfall pastures insouth-western Australia

The dry herbage yield increase (response) of subterranean clover (Trifolium subterraneum L.)-based pasture (>85% clover) to applications of different sources of sulfur (S) was compared in 7 field experiments on very sandy soils in the > 650 mm annual average rainfall areas of south-western Australia where S deficiency of clover is common when pastures grow rapidly during spring (August–November). The sources compared were single superphosphate, finely grained and coarsely grained gypsum from deposits in south-western Australia, and elemental S. All sources were broadcast (topdressed) once only onto each plot, 3 weeks after pasture emerged at the start of the first growing season. In each subsequent year, fresh fertiliser-S as single superphosphate was applied 3 weeks after pasture emerged to nil-S plots previously not treated with S since the start of the experiment. This was to determine the residual value of sources applied at the start of the experiment in each subsequent year relative to superphosphate freshly-applied in each subsequent year. In addition, superphosphate was also applied 6, 12 and 16 weeks after emergence of pasture in each year, using nil-S plots not previously treated with S since the start of the experiment. Pasture responses to applied S are usually larger after mid-August, so applying S later may match plant demand increasing the effectiveness of S for pasture production and may also reduce leaching losses of the applied S.At the same site, yield increases to applied S varied greatly, from 0 to 300%, at different harvests in the same or different years. These variations in yield responses to applied S are attributed to the net effect of mineralisation of different amounts of S from soil organic matter, dissolution of S from fertilisers, and different amounts of leaching losses of S from soil by rainfall. Within each year at each site, yield increases were mostly larger in spring (September–November) than in autumn (June–August). In the year of application, single superphosphate was equally or more effective than the other sources. In years when large responses to S occurred, applying single superphosphate later in the year was more effective than applying single superphosphate 3 weeks after pasture emerged (standard practice), so within each year the most recently applied single superphosphate treatment was the most effective S source. All sources generally had negligible residual value, so S needed to be applied each year to ensure S deficiency did not reduce pasture production.

Stem cells, cancer, and cancer stem cells

Stem cell biology has come of age. Unequivocal proof that stem cells exist in the haematopoietic system has given way to the prospective isolation of several tissue-specific stem and progenitor cells, the initial delineation of their properties and expressed genetic programmes, and the beginnings of their utility in regenerative medicine. Perhaps the most important and useful property of stem cells is that of self-renewal. Through this property, striking parallels can be found between stem cells and cancer cells: tumours may often originate from the transformation of normal stem cells, similar signalling pathways may regulate self-renewal in stem cells and cancer cells, and cancer cells may include 'cancer stem cells' - rare cells with indefinite potential for self-renewal that drive tumorigenesis.

Regulation of p53 localization

Despite intensive study of p53, the regulation of p53 cellular localization is still poorly understood. This is an overview of the elements and molecules involved in p53 nucleocytoplasmic transportation. These include the nuclear import and export signals of p53, inhibition of p53 nuclear import and export by oligomerization, MDM2-mediated p53 nuclear export, and possible roles of p53 phosphorylation in regulating p53 cellular localization. Finally, questions regarding p53 cellular trafficking will also be discussed.

Evaluation of a new dual-specificity promoter for selective induction of apoptosis in breast cancer cells

The conditional expression of lethal genes in tumor cells is a promising gene therapy approach for the treatment of cancer. The identification of promoters that are preferentially active in cancer cells is the starting point for this strategy. The combination of tissue-specific and tumor-specific elements offers the possibility to artificially develop such promoters. We describe the construction and characterization of a hybrid promoter for transcriptional targeting of breast cancer. In many cases, breast cancer cells retain the expression of estrogen receptors, and most solid tumors suffer from hypoxia as a consequence of their aberrant vascularization. Estrogen response elements and hypoxia-responsive elements were combined to activate transcription in cells that present at least one of these characteristics. When a promoter containing these elements is used to control the expression of the pro-apoptotic gene harakiri, the induction of cell death can be activated by estrogens and hypoxia, and inhibited by antiestrogens such as tamoxifen. Finally, we show evidence that these properties are maintained in the context of an adenoviral vector (AdEHhrk). Therefore, infection with this virus preferentially kills estrogen receptor-positive breast cancer cells, or cells growing under hypoxic conditions. We propose the use of this promoter for transcriptional targeting of breast cancer.

Molecular cloning and characterization of a novel regulator of G-protein signaling from mouse hematopoietic stem cells

A novel regulator of G-protein signaling (RGS) has been isolated from a highly purified population of mouse long-term hematopoietic stem cells, and designated RGS18. It has 234 amino acids consisting of a central RGS box and short divergent NH(2) and COOH termini. The calculated molecular weight of RGS18 is 27,610 and the isoelectric point is 8.63. Mouse RGS18 is expressed from a single gene and shows tissue specific distribution. It is most highly expressed in bone marrow followed by fetal liver, spleen, and then lung. In bone marrow, RGS18 level is highest in long-term and short-term hematopoietic stem cells, and is decreased as they differentiate into more committed multiple progenitors. The human RGS18 ortholog has a tissue-specific expression pattern similar to that of mouse RGS18. Purified RGS18 interacts with the alpha subunit of both G(i) and G(q) subfamilies. The results of in vitro GTPase single-turnover assays using Galpha(i) indicated that RGS18 accelerates the intrinsic GTPase activity of Galpha(i). Transient overexpression of RGS18 attenuated inositol phosphates production via angiotensin receptor and transcriptional activation through cAMP-responsive element via M1 muscarinic receptor. This suggests RGS18 can act on G(q)-mediated signaling pathways in vivo.

A novel, conditionally replicative adenovirus for the treatment of breast cancer that allows controlled replication of E1a-deleted adenoviral vectors

The efficiency of gene therapy strategies against cancer is limited by the poor distribution of the vectors in the malignant tissues. To solve this problem, a new generation of tumor-specific, conditionally replicative adenoviruses is being developed. To direct the replication of the virus to breast cancer, we have considered one characteristic present in a great proportion of these cancers, which is the expression of estrogen receptors (ERs). On the basis of the wild-type adenovirus type 5, we have constructed a conditionally replicative adenovirus (Ad5ERE2) in which the E1a and E4 promoters have been replaced by a portion of the pS2 promoter containing two estrogen-responsive elements (EREs). This promoter induces transcriptional activation of the E1a and E4 units in response to estrogens in cells that express the ERs. Ad5ERE2 is able to kill ER(+) human breast cancer cell lines as efficiently as the wild-type virus, but has decreased capacity to affect ER(-) cells. By complementation of the E1a protein in trans, Ad5ERE2 allows restricted replication of a conventional E1a-deleted adenoviral vector. When a virus expressing the proapoptotic gene Bc1-xs (Clarke et al., Proc. Natl. Acad. Sci. U.S.A. 1995;92:11024-11028) is used in combination with Ad5ERE2, the ability of both viruses to induce cell death is dramatically increased, and the effect can be modulated by addition of the antiestrogen tamoxifen.

Complex social organization reflects genetic structure and relatedness in the cooperatively breeding bell miner, Manorina melanophrys

The cooperatively breeding bell miner, Manorina melanophrys, differs from most other cooperative breeding species in the complexity of its social system, where discrete social organization occurs on at least three levels. Microsatellite markers were used to investigate the degree of genetic structure underlying the social organization of M. melanophrys by comparing colonies, coteries and nest contingents. The genetic data confirmed behavioural observations of M. melanophrys living in male kin-based groups between which females disperse short distances to breed. Estimates of FST revealed restricted gene flow between eight colonies located within 30 km that was significantly associated with geographical distance when the two most distant colonies were included. Within a high density colony significant differences were found between coteries; analysis of the degree of relatedness between coterie members showed that this is due to related individuals associating preferentially with each other. Similarly, the contingent of individuals attending a nest were generally close relatives of the young they were aiding, supporting models invoking kin selection as the selective agency mediating helping.

A bipartite nuclear localization signal is required for p53 nuclear import regulated by a carboxyl-terminal domain

Abnormal p53 cellular localization has been considered to be one of the mechanisms that could inactivate p53 function. To understand the regulation of p53 cellular trafficking, we have previously identified two p53 domains involved in its localization. A basic domain, Lys(305)-Arg(306), is required for p53 nuclear import, and a carboxyl-terminal domain, namely the cytoplasmic sequestration domain (CSD) from residues 326-355, could block the nuclear import of Lys(305) or Arg(306) mutated p53. To characterize further the function of these two domains, we demonstrate in this report that the previously described major nuclear localization signal works together with Lys(305)-Arg(306) to form a bipartite and functional nuclear localization sequence (NLS) for p53 nuclear import. The CSD could block the binding of p53 to the NLS receptor, importin alpha, and reduce the efficiency of p53 nuclear import in MCF-7, H1299, and Saos-2 cells. The blocking effect of the CSD is not due to the enhancement of nuclear export or oligomerization of the p53. These results indicate that the CSD can regulate p53 nuclear import by controlling access of the NLS to importin alpha binding.

Germ cell tumor: differentiation of viable tumor, mature teratoma, and necrotic tissue with FDG PET and kinetic modeling

PURPOSE

To evaluate the feasibility of positron emission tomography (PET) with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) in patients with germ cell tumor (GCT) to monitor treatment and differentiate residual masses after chemotherapy.

MATERIALS AND METHODS

Twenty-six FDG PET studies were performed in 21 patients with GCT, FDG uptake of tumors was interpreted visually, and the lean standardized uptake value (SUVlean) was determined. Tumor kinetic rate constants (K1, k2, k3) and net rate of FDG phosphorylation (K = [K1.k3]/[k2 + k3]) in tumors were calculated from the dynamic data by means of a three-compartment model, assuming k4 = 0.

RESULTS

Viable tumors (n = 10) showed intense FDG uptake and could easily be differentiated visually from mature teratoma (n = 6) and necrosis or scar (n = 10). The SUVlean of residual viable tumors (4.51 +/- 1.34 [mean +/- SD]) was higher than that of mature teratoma (1.38 +/- 0.71) and necrosis or scar (1.05 +/- 0.29) (P < .05). Although neither the visual interpretation nor SUVlean differentiated mature teratoma from necrosis or scar, there were statistically significant differences in the kinetic rate constants K1 and K between mature teratoma and necrosis or scar as follows: K1, 0.113 mL/min/g +/- 0.026 versus 0.036 mL/min/g +/- 0.005 (P < .05); K, 0.005 mL/min/g +/- 0.003 versus 0.0008 mL/min/g +/- 0.0001 (P < .05).

CONCLUSION

FDG PET with kinetic analysis appears to be a promising method for management of disease in patients with GCT after treatment.

The nuclear import of p53 is determined by the presence of a basic domain and its relative position to the nuclear localization signal

It has been reported that Lysine-305 is needed for the nuclear import of the p53 protein (Liang et al., 1998). In the present study, further mutagenesis analyses were carried out between Lys-305 and the major nuclear localization signal (NLS I) of p53. It was found that a single mutation of Arg-306 resulted in the defect of p53 nuclear import. This effect is the same as that of Lys-305 mutation. Other mutations between Arg-306 and NLS I have no effect on the nuclear import of p53. However, deletions of more than two amino acids between this region abolished the transport of p53 into the nucleus. These results indicate that a basic domain other than the well defined NLS is required for the nuclear import of p53. A spacer between this basic domain and NLS I is necessary for the entrance of p53 into the cell nucleus.

Role of p53 in the regulation of irradiation-induced apoptosis in neuroblastoma cells

Wild-type p53 plays a crucial role in the control of apoptosis following ionizing radiation (IR); conversely, mutant p53 is associated with IR resistance. Although wild-type p53 is expressed in virtually all neuroblastoma tumors, treatment failures secondary to inadequate local control with radiotherapy are a problem in patients with advanced stage disease. This apparent paradox is the focus of our interest. The Shep-1 neuroblastoma cell line is highly resistant to IR. This cell line contains a wild-type p53 gene and is an ideal model for studying the mechanism of IR resistance in this disease. Following high-dose IR, cell fractionation demonstrated that p53 is induced and targeted to the nucleus. The induced p53 is functional as p53-responsive genes (Waf-1 and MDM-2) are appropriately induced following IR. Intriguingly, overexpression of p53 could reverse the inherent IR resistance of Shep-1 cells. Multiple cell lines expressing variable levels of exogenous temperature-sensitive p53 were generated. Pulse induction of p53 alone did not affect Shep-1 cell viability, while induction of p53, followed by IR, resulted in cell death and DNA fragmentation proportional to the dose of IR and the level of p53 expression. These findings demonstrate that p53 overexpression renders Shep-1 cells IR-sensitive and suggest that large quantities of exogenous p53 can overcome the factors inhibiting p53-mediated, IR-induced apoptosis.

Cooperation of a single lysine mutation and a C-terminal domain in the cytoplasmic sequestration of the p53 protein

Cytoplasmic sequestration of the p53 tumor suppresser protein has been proposed as a mechanism involved in abolishing p53 function. However, the mechanisms regulating p53 subcellular localization remain unclear. In this report, we analyzed the possible existence of cis-acting sequences involved in intracellular trafficking of the p53 protein. To study p53 trafficking, the jellyfish green fluorescent protein (GFP) was fused to the wild-type or mutated p53 proteins for fast and sensitive analysis of protein localization in human MCF-7 breast cancer, RKO colon cancer, and SAOS-2 sarcoma cells. The wild-type p53/GFP fusion protein was localized in the cytoplasm, the nucleus, or both compartments in a subset of the cells. Mutagenesis analysis demonstrated that a single amino acid mutation of Lys-305 (mt p53) caused cytoplasmic sequestration of the p53 protein in the MCF-7 and RKO cells, whereas the fusion protein was distributed in both the cytoplasm and the nucleus of SAOS-2 cells. In SAOS-2 cells, the mutant p53 was a less efficient inducer of p21/CIP1/WAF1 expression. Cytoplasmic sequestration of the mt p53 was dependent upon the C-terminal region (residues 326-355) of the protein. These results indicated the involvement of cis-acting sequences in the regulation of p53 subcellular localization. Lys-305 is needed for nuclear import of p53 protein, and amino acid residues 326-355 can sequester mt p53 in the cytoplasm.

A method of limited replication for the efficient in vivo delivery of adenovirus to cancer cells

Replication-deficient viral vectors are currently being used in gene transfer strategies to treat cancer cells. Unfortunately, viruses are limited in their ability to diffuse through tissue. This makes it virtually impossible to infect the majority of tumor cells in vivo and results in inadequate gene transfer. This problem can be addressed by allowing limited viral replication. Limited viral replication facilitates greater penetration of virions into tissue and can improve gene transfer. We have developed a strategy of limited viral replication using AdRSVlaclys, a chemically modified E1-deleted adenovirus, to codeliver an exogenous plasmid encoding the adenovirus E1 region. This system allows one round of viral replication. We examined the effect of this limited adenovirus replication in vitro and in vivo. In culture, codelivery of virus and pE1 resulted in a large increase in infected cells when compared with control cells exposed to virus and pUC19. In experiments on nude mice bearing HeLa ascites tumors, intraperitoneal injection of AdRSVlaclys/pE1 resulted in a significantly higher percentage of infected HeLa cells as compared with the PBS controls (p < 0.05) or the AdRSVlaclys/pUC19 controls (p < 0.01). These data demonstrate that the transcomplementation of replication-deficient adenovirus with exogenous E1 DNA leads to limited replication, and this controlled replication enhances gene transfer efficiency of adenovirus in vivo.

Targeting cancer cell death with a bcl-XS adenovirus

Transformation is a complex cellular process that requires several genetic abnormalities. In many cases, one of these abnormalities is an inhibition of PCD, which provides a selective advantage for tumor cells. This has been recently shown in an in vivo model, where overexpression of Bcl-XL, is a crucial step in the progression from hyperplasia to neoplasia and is accompanied by a significant decrease in tumor apoptosis [56]. Frequently, overexpression of a member of the Bcl-2 family results in a block in cell death and appears to nullify many built-in cellular defense mechanisms against cancer. Such a block presents a problem because radiation and chemotherapy, standard cancer treatments, ultimately exert their effect by induction of apoptosis and would also be made less effective. Therefore, to better treat cancer it may be necessary to develop novel methods to overcome the effects of the Bcl-2 family. One way to approach this problem is to target the cause--the molecular machinery that allows a cancer cell to survive. Advances in our understanding of apoptosis has identified the Bcl-2 family as a mediator of most apoptosis pathways, including those initiated by oncogenes, tumor suppressor genes, growth factor withdrawal, and external damaging signals. Therefore, functional inhibition of Bcl-2 family members is lethal to many cancer cells. Using gene transfer technology, we can now deliver genes that accomplish this goal. Further investigation will reveal whether this translates to improved therapy in the future.

Prevention of fluorodeoxyuridine-induced cytotoxicity and DNA damage in HT29 colon carcinoma cells by conditional expression of wild-type p53 phenotype

We have examined the effects of conditionally expressing wild-type p53 activity in HT29 cells on DNA damage and cytotoxicity caused by exposure to fluorodeoxyuridine (FdUrd). Expression of wild-type p53 phenotype for 24 hr before FdUrd treatment provided HT29 cells with virtually complete protection from cytotoxicity caused by this drug. In addition, wild-type p53 expression also prevented FdUrd-induced DNA double-strand breaks and, unexpectedly, single-strand breaks in parental (mature) DNA. Temporary expression of wild-type p53 activity in the absence of drug treatment caused some loss of clonogenicity, although the magnitude of this cytotoxic effect was small compared with the level of cell kill obtained by treatment with cytotoxic drugs for similar periods of time, indicating that HT29 cells are not highly sensitive to induction of programmed cell death by wild-type p53. Because these observations conflict with previously suggested models for FdUrd-induced damage to parental DNA, we propose an alternative model to explain how incorporation of uracil into nascent DNA might result in single-strand breaks in the opposite (parental) strand and how these breaks might be converted to the double-strand breaks that produce cell death.

Comparison of immunofiltration assay of plasma D-dimer with diagnostic imaging in deep vein thrombosis

This prospective study was designed to assess the diagnostic sensitivity, specificity and negative predictive value of the NycoCard D-dimer plasma immunofiltration assay in patients with suspected deep vein thrombosis (DVT) confirmed by ultrasonography/venography. 84 medical patients were recruited: 43 patients (51%) had proven venous thrombosis, 33 by venography and 10 by ultrasonography. The sensitivity of NycoCard D-dimer in patients with DVT was 95.3%, the specificity was 22.0% and the negative predictive value was 81.8%. An algorithm including the NycoCard D-dimer test for the acute management of DVT is proposed. This would enable low-risk patients to be discharged early from hospital, without imaging or anticoagulant therapy.

Bcl-xS enhances adenoviral vector-induced apoptosis in neuroblastoma cells

bcl-x is a member of the bcl-2 family of genes and by alternative splicing gives rise to two distinct mRNAs: bcl-xL and bcl-xS. We have previously investigated the expression of Bcl-x in neuroblastoma (NB) cell lines and have shown that Bcl-xL is expressed and functions to inhibit chemotherapy-induced apoptosis. However, none of the NB cell lines expressed Bcl-xS. The aim of the present study was to determine the effects of Bcl-xS expression on the viability of NB cells. A panel of NB cell lines (CHP-382, GOTO, SHEP-1, SHSY-5Y, and GI-CA-N) were infected with either a bcl-xS adenovirus (pAdRSV-bcl-xS) or a control virus (pAdRSV-lac-z). NB cells showed loss of viability with both viruses, although the bcl-xS virus was most toxic. Importantly, infection with the bcl-xS adenovirus resulted in rapid loss of cell viability, DNA fragmentation, and morphological features of apoptosis even in NB cells transfected to overexpress Bcl-2 and Bcl-xL. These findings suggest that deregulated expression of Bcl-xS using an adenovirus may provide a novel mechanism for initiating cell death in tumors that express Bcl-2 or Bcl-xL.

Retroviral infection is limited by Brownian motion

Replication-defective retroviruses are frequently used as gene carriers for gene transfer into target cells. Here we show that the short half-lives of retroviruses limit the distance that they can effectively travel in solution by Brownian motion, and thus the possibility of successful gene transfer. This physiochemical limitation can be overcome, and effective contact between the retroviral gene carrier and the target cell can be obtained, by using net convective flow of retrovirus-containing medium through a layer of target cells. Using model cell lines (NIH-3T3 and CV-1), it was shown that gene transfer rates can be increased by more than an order of magnitude using the same concentration infection medium. High transduction rates could be obtained even in the absence of polycations, such as Polybrene, which heretofore have been required to achieve reasonable transduction rates. This development may play an important role in realizing human gene therapy.

bcl-xs gene therapy induces apoptosis of human mammary tumors in nude mice

Bcl-xs is a dominant negative repressor of Bcl-2 and Bcl-xL, both of which inhibit apoptosis. We used a replication-deficient adenoviral vector to transiently overexpress Bcl-xs in MCF-7 human breast cancer cells, which overexpress Bcl-xL. Infection with this vector induced apoptosis in vitro. We then determined the effects of intratumoral injection of bcl-xs adenovirus on solid MCF-7 tumors in nude mice. Tumors injected four times with the bcl-xs adenovirus showed a 50% reduction in size. Using terminal transferase-mediated dUTP-digoxigenin nick end labeling, we observed apoptotic cells at sites of bcl-xs adenoviral injection. These experiments demonstrate the feasibility of using bcl-xs gene therapy to induce apoptosis in human breast tumors.

A recombinant bcl-x s adenovirus selectively induces apoptosis in cancer cells but not in normal bone marrow cells

Many cancers overexpress a member of the bcl-2 family of inhibitors of apoptosis. To determine the role of these proteins in maintaining cancer cell viability, an adenovirus vector that expresses bcl-xs, a functional inhibitor of these proteins, was constructed. Even in the absence of an exogenous apoptotic signal such as x-irradiation, this virus specifically and efficiently kills carcinoma cells arising from multiple organs including breast, colon, stomach, and neuroblasts. In contrast, normal hematopoietic progenitor cells and primitive cells capable of repopulating severe combined immunodeficient mice were refractory to killing by the bcl-xs adenovirus. These results suggest that Bcl-2 family members are required for survival of cancer cells derived from solid tissues. The bcl-xs adenovirus vector may prove useful in killing cancer cells contaminating the bone marrow of patients undergoing autologous bone marrow transplantation.

Retroviral-mediated gene transfer in human bone marrow cells growth in continuous perfusion culture vessels

Hematopoietic stem cell gene therapy holds the promise of being able to treat a variety of inherited and acquired diseases of the hematopoietic stem cell. However, to date, genetic modification of the human hematopoietic stem cell has been relatively inefficient. Here, we report the results of using a bioreactor system to expand hematopoietic cells after a brief retrovirus infection using a high titer, replication defective virus encoding for murine CD18. The retrovirus transduced culture continued to produce genetically modified hematopoietic progenitors for up to 6 weeks, the duration of the culture period. Up to one-third of the long-term culture initiating cell (LTC-IC) are genetically modified by the culture conditions. Murine CD18 can be expressed on the cell surface of up to 20% of the mature cells generated by the culture system, suggesting that clinically significant levels of gene transfer may be occurring. These results demonstrate the feasibility of using continuous perfusion bioreactors as a method of efficiently modifying human hematopoietic stem cells.

Bcl-XL protects cancer cells from p53-mediated apoptosis

Oncogenesis is a process resulting from genetic events which cause loss of growth control or inhibition of appropriate cell death. The Bcl-XL protein is a recently discovered member of the bcl-2 family which has been shown to protect cells from some forms of programmed cell death, but has not yet been implicated in the genesis of human carcinomas. In this report we explore the role of Bcl-XL overexpression in protecting cancer cells from p53-mediated apoptosis. Increased levels of Bcl-XL were found in a subset of primary human breast carcinomas, as well as in the breast cancer line, T47D. T47D cells were then transfected with a temperature-sensitive mutant of the tumor suppressor p53 (p53ts). Although many tumor cell lines undergo apoptosis when p53 is expressed, the T47D transfectants remained viable at temperatures permitting wild-type p53 phenotype. This suggested that endogenous Bcl-XL could protect cancer cells from p53-mediated apoptosis. To test this hypothesis, murine erythroleukemia cells were transfected with bcl-XL and p53ts. While cell lines expressing p53 alone rapidly died, those cells co-expressing Bcl-XL survived. These results demonstrate that Bcl-XL is capable of protecting cells from p53-mediated apoptosis, and suggest a possible mechanism by which tumors expressing Bcl-XL are able to partly overcome the tumor suppressor functions of p53.

Bcl-2 protects murine erythroleukemia cells from p53-dependent and -independent radiation-induced cell death

To better understand the molecular basis of radiation-induced cell death, we studied the role of the bcl-2 oncogene and the p53 tumor suppressor gene in this process. A temperature-sensitive mutant of murine p53 (p53Val-135) and/or bcl-2 was transfected into murine erythroleukemia cells (MEL, DP16-1, which are null in p53). We demonstrate that radiation-induced cell death occurs by both p53-dependent and -independent pathways and overexpression of bcl-2 modulates both pathways. When viability was measured 24 h post-radiation, cells that had been briefly exposed to wtp53 immediately after X-ray irradiation had decreased survival as compared to unirradiated cells expressing wtp53 or X-ray irradiated DP16-1 cells. However, at later times X-ray irradiated parental DP16-1 cells also had decreased survival compared to the unirradiated control. This decrease in survival began 48 h following radiation. Bcl-2 prevented radiation-induced cell death in DP16-1 cells expressing wtp53 and delayed radiation-induced cell death in DP16-1 cells without wtp53. X-ray irradiated cells expressing wtp53 displayed microscopic and biochemical characteristics consistent with cell death due to apoptosis. DP16-1 cells which were untransfected or co-transfected with wtp53 and bcl-2 displayed characteristics of cells undergoing necrosis. These results suggest that radiation-induced cell death occurs by both p53-dependent and p53-independent pathways. The p53-dependent pathway results in cell death via apoptosis and occurs approximately 24 h following radiation. The p53-independent pathway does not appear to involve apoptosis and occurs at a later time, starting 48 h after X-ray exposure. Thus, bcl-2 protects cells from p53-dependent radiation-induced apoptotic cell death and attenuates p53-independent radiation-induced cell death.

Overexpression of Bcl-XS sensitizes MCF-7 cells to chemotherapy-induced apoptosis

Resistance to apoptosis plays an important role in tumors that are refractory to chemotherapy. We report that Bcl-XL, which functions like Bcl-2 to inhibit apoptosis, is highly expressed in MCF-7 human breast carcinoma cells. We used Bcl-XS, a dominant negative inhibitor of Bcl-2 and Bcl-XL, to demonstrate the role of these genes in modulating chemotherapy-induced apoptosis. Bcl-XS overexpressed in MCF-7 cells by stable transfection does not affect viability by itself but induces a marked increase in chemosensitivity to VP-16 or taxol. Using an ELISA assay which quantitates DNA damage, we demonstrate that this sensitization is due to apoptosis, suggesting the therapeutic utility of targeting this pathway.

The Bcl-2 family of proteins: regulators of cell death and survival

The Bcl-2 protein inhibits apoptosis induced by a variety of signals, in a range of cell types and in diverse organisms, and it is implicated in both normal development and oncogenesis. Despite this central role, the mechanism of action of Bcl-2 is not yet clear. Recent studies have uncovered a number of Bcl-2-related gene products that regulate apoptosis either negatively or positively, and Bcl-2 forms heterodimers with at least one of these proteins, Bax. This article discusses the role of the Bcl-2 family of proteins in the light of these findings.

Alteration of p53 conformation and induction of apoptosis in a murine erythroleukemia cell line by dimethylsulfoxide

Programmed cell death, or apoptosis, may play an important role in the regulation of hematopoiesis. The tumor suppressor protein p53 has been identified as a key regulator of apoptosis in both normal and malignant hematopoietic cells. Modulation of p53 function is of interest, therefore, both in understanding the control of apoptosis and as a potential therapeutic intervention. In this study we describe the effect on murine erythroleukemia cells, transfected with a temperature-sensitive mutant p53, of exposure to the differentiating agent dimethylsulfoxide (DMSO). Rather than terminally differentiating, these cells are induced to undergo apoptosis. Interestingly, exposure to DMSO leads to an alteration of the protein conformation of the p53 mutant to one recognized by a wild-type specific monoclonal antibody. This is accompanied by a translocation of the p53 protein from the cytoplasm to the nucleus. These results suggest that the activity of some mutant p53 proteins can be functionally modified by exogenous compounds.

c-myc and bcl-2 modulate p53 function by altering p53 subcellular trafficking during the cell cycle

We have studied the ability of c-myc and bcl-2 oncogenes to modulate p53 function. Our studies show that coincident expression of human Bcl-2 protein with p53 prolongs survival of murine erythroleukemia cells. This effect was associated with a loss of the G1 specificity of p53-mediated cell cycle arrest. Furthermore, we found that the c-myc and bcl-2 genes cooperate to inhibit p53 functions. Coexpression of bcl-2 and c-myc can totally overcome p53-induced apoptosis and cell cycle arrest by altering the subcellular trafficking of p53 during the cell cycle: the p53 remains in the cytoplasm of the cotransfected cells during a critical period in G1. This finding suggests a mechanism by which normal hematopoietic progenitors can survive and proliferate despite p53 expression and by which the inappropriate expression of bcl-2 and c-myc can cooperate in transformation.

Cell cycle analysis of p53-induced cell death in murine erythroleukemia cells

A temperature-sensitive mutant of murine p53 (p53Val-135) was transfected by electroporation into murine erythroleukemia cells (DP16-1) lacking endogenous expression of p53. While the transfected cells grew normally in the presence of mutant p53 (37.5 degrees C), wild-type p53 (32.5 degrees C) was associated with a rapid loss of cell viability. Genomic DNA extracted at 32.5 degrees C was seen to be fragmented into a characteristic ladder consistent with cell death due to apoptosis. Following synchronization by density arrest, transfected cells released into G1 at 32.5 degrees C were found to lose viability more rapidly than did randomly growing cultures. Following release into G1, cells became irreversibly committed to cell death after 4 h at 32.5 degrees C. Commitment to cell death correlated with the first appearance of fragmented DNA. Synchronized cells allowed to pass out of G1 prior to being placed at 32.5 degrees C continued to cycle until subsequently arrested in G1; loss of viability occurred following G1 arrest. In contrast to cells in G1, cells cultured at 32.5 degrees C for prolonged periods during S phase and G2/M, and then returned to 37.5 degrees C, did not become committed to cell death. G1 arrest at 37.5 degrees C, utilizing either mimosine or isoleucine deprivation, does not lead to rapid cell death. Upon transfer to 32.5 degrees C, these G1 synchronized cell populations quickly lost viability. Cells that were kept density arrested at 32.5 degrees C (G0) lost viability at a much slower rate than did cells released into G1. Taken together, these results indicate that wild-type p53 induces cell death in murine erythroleukemia cells and that this effect occurs predominantly in the G1 phase of actively cycling cells.

c-myb effects on kinetic events during MEL cell differentiation

During dimethylsulfoxide (DMSO)-induced differentiation of Friend mouse erythroleukemia (MEL) cells there is a biphasic fall in c-myb mRNA levels. We have previously shown that constitutive expression of c-myb blocks differentiation. To delineate more accurately the point at which Myb blocks differentiation, MEL cells were transfected with a human c-myb construct under the control of the beta-globin promoter and enhancers. In concert with endogenous DMSO-induced globin transcription during MEL cell differentiation, the beta-globin c-myb transcription unit of the transfected plasmid is activated after 3-5 days of culture in media containing DMSO. Here we describe c-myb-transformed MEL clones which undergo delayed expression of the exogenous c-myb following 3-5 days of culture in DMSO. In contrast to wild-type MEL cells, both clones failed to display phenotypic markers of differentiation and continued to proliferate for up to 10 days of culture. These data suggest that the late fall in c-myb levels may be required in order for differentiation to occur. Additionally, we suggest that constitutive expression of c-myb does not block early commitment events such as activation of histone Hl', subsequent chromatin condensation, and alteration of proliferation-related gene expression. Taken together, these results show that c-myb acts very late in the process of differentiation.

Can Dexter cultures support stem cell proliferation?

The in vitro culture of mouse bone marrow (Dexter cultures) has allowed a detailed analysis of the biology of murine hematopoiesis. However, attempts to develop stable long-term human bone marrow cultures have been unsuccessful. Available culture systems all have finite and relatively short lifetimes. The reasons for the limited longevity are unknown. Utilizing computer-assisted integration techniques, we have theoretically simulated culture cell production kinetics to help identify factors that may be responsible for culture decay, as well as to suggest possible means of improving culture longevity. The simulation demonstrates that removal of stem cells is a possible mechanism leading to culture decline. Under the standard bone marrow culture conditions, even with a high stem cell renewal rate, the cultures appear to be destined to fail. Thus, the development of proper sampling techniques or improved stem cell retention may be critical to obtain successful long-term cultures.

Malignant transformation of NIH 3T3 fibroblasts by human c-sis is dependent upon the level of oncogene expression

High-level expression of the c-sis oncogene, which encodes the beta chain of platelet-derived growth factor, transforms immortalized rodent fibroblasts in vitro to a malignant phenotype. c-sis gene expression has been demonstrated in a variety of human tumors, although generally at levels much lower than those shown to transform cells in vitro. We examined the effect of lower levels of c-sis expression on the phenotype of NIH 3T3 fibroblasts. Clones with various levels of c-sis expression were generated by transfecting NIH 3T3 cells with a plasmid that expressed the human c-sis cDNA and the TN5 neomycin-resistance gene. G418-resistant clones, which expressed the c-sis cDNA, were selected and characterized. Alterations in the phenotype of the clones that expressed c-sis ranged from increased growth in soft agar to malignant tumor formation in nude and syngeneic mice. Increased levels of c-sis cDNA expression correlated with the acquisition of features of transformation in a dose-dependent manner and altered the cellular phenotype in a manner consistent with the progression of cells towards malignancy. These data support a model in which low levels of sis gene expression in tumors contribute to the acquisition of some features of transformation but require complementation by other genes or factors to produce a fully malignant phenotype.

The influence of extra-cellular matrix and stroma remodeling on the productivity of long-term human bone marrow cultures

The stromal cell layer is believed to play an important role in long-term human bone marrow cultures (LTHBMCs). At present, neither the role that the stromal cell extra-cellular matrix (ECM) plays in influencing stroma behavior is well understood nor are the effects of stroma aging. Rapid medium exchanged LTHBMCs were established on surfaces precoated with human natural fibronectin and type 1 rat tail collagen. Although initial adhesion of hematopoietic cells was improved by the presence of both ECMs, the overall progenitor and nonadherent cell productivity was not improved nor did the stroma grow to confluency faster. Thus, the ECMs used did not significantly influence the cell productivity of LTHBMCs. To examine the influence of stromal cell layer aging, conditioned medium was obtained from the first two weeks of LTHBMCs that was subsequently concentrated and used as a medium supplement in a second set of slowly exchanged LTHBMCs. The presence of the concentrated conditioned medium (conCM) enhanced the production of nonadherent cells three-fold compared with control over an eight week culture period. Control cultures that were exposed to conCM after 4 weeks in culture significantly improved their cell productivity during the latter 4 weeks of culture compared with control. The productivity of cultures exposed to conCM for 4 weeks dropped significantly when unsupplemented medium was used for the latter 4 weeks of culture. Interestingly, phytohemagglutin-stimulated leukocyte-conditioned medium stimulated LTHMBCs in a similar fashion, as did conditioned medium from early LTHBMCs. Taken together, these results strongly suggest that the stromal cell layer does produce important factors for active hematopoiesis during its growth to confluence.

In vitro myelopoiesis stimulated by rapid medium exchange and supplementation with hematopoietic growth factors

We studied the effect of the combination of rapid culture medium exchange with the addition of the human hematopoietic growth factors interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and erythropoietin (Epo) on the proliferation and differentiation of human long-term bone marrow cultures (LTBMCs). Individually and in combinations, IL-3, GM-CSF, and Epo were added to the culture medium of LTBMCs that were maintained with 50% medium volume exchange per day. The combination of IL-3 + GM-CSF + Epo generated the most prolific cultures with an order of magnitude increase in nonadherent cell production from weeks 2 through 8 in culture as compared with unsupplemented controls. Under these conditions, the cultures produced as many cells as were inoculated every 2 weeks and led to a greater than 2.5-fold expansion in terms of the number of nonadherent cells produced over a 6- to 8-week period. Furthermore, the LTBMCs produced nonadherent colony-forming unit-GM (CFU-GM) for more than 20 weeks. The rapid medium exchange combined with the addition of human hematopoietic CSFs significantly enhances the proliferation and differentiation of LTBMCs. These results indicate that addition of combinations of hematopoietic CSFs, together with a rapid medium exchange rate, can provide culture conditions that are suitable for the expansion of the progenitor cell pool and perhaps for the increased survival of hematopoietic stem cells in culture. Although these culture conditions still fall short of full reconstitution of functional human bone marrow, they provide an improved approach to hematopoietic cell culture that may permit the expansion and manipulation of progenitor cells in vitro.

Biotinylated granulocyte/macrophage colony-stimulating factor analogues: effect of linkage chemistry on activity and binding

Biotinylated granulocyte/macrophage colony-stimulating factor (GM-CSF) analogues with different linkage chemistries and levels of conjugated biotin were synthesized by reacting recombinant human GM-CSF with sulfosuccinimidyl 6-biotinamidohexanoate or biotin hydrazide/1-[3-(dimethylamino)-propyl]-3-ethylcarbodiimide. These chemically reactive forms of biotin produced derivatives biotinylated at amine or carboxyl groups, respectively. Amine-derivatized analogues of 1.2 and 3.8 mol of biotin/mol of protein (N1-bGM-CSF and N4-bGM-CSF) and a carboxyl-modified analogue of 4.6 mol of biotin/mol of protein (C5-bGM-CSF) were synthesized. These analogues were compared to determine the effect of biotinylation on biological activity and GM-CSF receptor binding characteristics. The biotinylated proteins migrated with the same molecular weight as the native, unmodified protein as determined by SDS-PAGE and could be detected by Western blotting with alkaline phosphatase conjugated streptavidin, thus demonstrating the biotin linkage. All three analogues retained full agonist activity relative to the native protein (EC50 = 10-15 pM) when assayed for the stimulation of human bone marrow progenitor cell growth. Cell surface GM-CSF receptor binding was characterized by the binding of the analogues to human neutrophils, with detection by fluorescein-conjugated avidin and fluorescence-activated cell sorting. The N-bGM-CSFs demonstrated GM-CSF receptor specific binding that was displaceable by excess underivatized protein, with the detected fluorescence signal decreasing with increasing biotin to protein molar ratio. In contrast, C5-bGM-CSF binding above background fluorescence could not be detected using this system, suggesting that this derivative could bind to and activate the receptor, but not simultaneously bind fluorescein-conjugated avidin. The amine-derivatized biotinylated GM-CSF analogues retained biological activity, could specifically label cell surface receptors, and may be useful nonradioactive probes with which to study GM-CSF receptor cytochemistry and receptor modulation by flow cytometry.

The construction of high efficiency human bone marrow tissue ex vivo

The successful ex vivo reconstruction of human bone marrow is an extraordinarily important basic scientific and clinical goal. Fundamentally, the system is the paradigm of a complex interactive tissue, in which the proliferation and regulated differentiation of one parenchymal cell type (the hematopoietic stem cell) is governed by the surrounding stromal cells. Understanding and reproducing the molecular interactions between bone marrow stromal cells and stem cells in tissue culture models is therefore the critical step in successful bone marrow tissue culture. Clinically, successful reconstruction of human bone marrow would permit the controlled production of mature blood cells for transfusion therapy, and immature bone marrow stem cells for bone marrow transplantation. In approaching the bone marrow culture system, we recognize the critical role that hematopoietic growth factors (HGFs) play in hematopoiesis. Since stromal cells in traditional human bone marrow cultures produce little HGFs, we have begun by asking whether local supplementation of hematopoietic growth factors via genetically engineered stromal cells might augment hematopoiesis in liquid cultures. The results indicate that locally produced GM-CSF and IL-3 do augment hematopoiesis for several weeks in culture. In combination with geometric and dynamic approaches to reconstructing physiological bone marrow microenvironments, we believe that this approach has promise for reconstructing human bone marrow ex vivo, thereby permitting its application to a variety of basic and clinical problems.

Influence of medium exchange schedules on metabolic, growth, and GM-CSF secretion rates of genetically engineered NIH-3T3 cells

The metabolic and secretory characteristics of NIH-3T3 fibroblasts transfected with a cDNA encoding human granulocyte-macrophage colony stimulating factor (GM-CSF) were examined as a function of the culture medium exchange schedule. The rates of glucose and glutamine consumption and of lactate and ammonia production were measured over exchange schedules ranging from complete medium replacement weekly (1/week) to complete medium replacement daily (7/week). All measured metabolic rates increased with increased medium exchange rates and accelerated sharply between exchange rates of 3.5/week and 7/week. The lactate/glucose and ammonia/glutamine yield coefficients, however, remained invariant at about 1.9 and 1.0 mol/mol, respectively, under all medium perfusion conditions. A shift-up in medium perfusion rates from 3.5/week to 7/week resulted in increased metabolic rates that resembled those observed in the cultures that were exchanged at the 7/week rate throughout, showing that the metabolic rates could be directly controlled by the perfusion rate. Differential regulation of medium versus serum perfusion demonstrated that increased NIH-3T3 cell metabolism was directly proportional to the serum flux to which the cells were exposed. Thus a limiting serum component is responsible for the altered metabolic and growth rates. The GM-CSF production by the transfected 3T3 cells was stable but exhibited substantial transient increases during periods of cell proliferation, demonstrating that the secretion of transfected gene products can be highly modulated even when the cDNA is driven from a constitutive promoter. These studies show that the metabolic and secretory behavior of genetically engineered cells is influenced by the medium exchange schedule.

Differentiation of mouse erythroleukemia cells enhanced by alternatively spliced c-myb mRNA

C-myb, the normal cellular homolog of the retroviral transforming gene v-myb, encodes a nuclear, transcriptional regulatory protein (p75c-myb). C-myb is involved in regulating normal human hematopoiesis, and inhibits dimethyl sulfoxide-induced differentiation of Friend murine erythroleukemia (F-MEL) cells. An alternately spliced c-myb mRNA encodes a truncated version of p75c-myb (mbm2) that includes the DNA binding region and nuclear localization signal present in the c-myb protein, but does not contain the transcriptional regulatory regions. Constitutive expression of mbm2, in contrast to c-myb, here resulted in enhanced differentiation of F-MEL cells. These data suggest that the c-myb protooncogene encodes alternately spliced mRNA species with opposing effects on differentiation.

Alternative splicing of the human c-myb gene

Two cDNA clones of the human c-myb gene have been isolated from a CCRF-CEM leukemia cell cDNA library and sequenced in their entirety. These sequences, when compared with those previously reported for the human c-myb gene, reveal an alternative splicing process that generates at least four forms of the c-myb message. Three of these forms co-migrate on Northern blots and are co-expressed in several human hematopoietic cell types. Data on sequence comparisons with mouse and chicken homologues of c-myb coupled with oligonucleotide hybridization to genomic clones of the human c-myb gene indicate that this alternative splicing process utilizes three closely spaced splice donor sites and two unique exons present between viral defined exons 5 and 6. In one clone, the alternative splicing would generate a predicted myb protein with a three amino acid deletion in the region involved in transcription activation. In the other clone, incorporation of a new exon leads to introduction of a translation stop codon leading to loss of the entire carboxy terminus of the protein. This includes loss of a portion of the region involved in transcription activation as well as a separate highly conserved domain. The effect of these changes on protein function is currently unknown.