Circular economy in the valorisation of food and other biowaste: case studies in small and medium-sized enterprises in the Belgian construction sector

The construction sector has significant impacts on the environment due to the consumption of resources and the production of waste. The implementation of circular economy strategies can improve the environmental performance of the sector, optimising the current production and consumption patterns, slowing and closing material loops, and using waste as a source of raw materials. Biowaste represents a key waste flow at the European scale. However, research on its application in the construction sector is still limited and product-oriented, with little insights into the processes of valorisation undertaken at the company's level. This study presents eleven case studies of Belgian small and medium-sized enterprises involved in biowaste valorisation in the construction sector in order to tackle this research gap in the Belgian context. Semi-structured interviews were conducted to identify the enterprise's business profile and its current marketing practices, as well as to analyse opportunities and barriers for market expansion and highlight current research interests. Results show that the overall picture is extremely heterogeneous in terms of sourcing, production methods, and products, while the barriers and success factors that have been identified are recurrent. This study contributes to the circular economy research in the construction sector by providing insights into innovative waste-based materials and business models.

High-Resolution Mapping of Material Stocks in Belgian Road Infrastructure: Material Efficiency Patterns, Material Recycling Potentials, and Greenhouse Gas Emissions Reduction Opportunities

Road infrastructure is an integral part of built environment stocks, as it delivers essential social and economic services. While previous work has assessed material stocks, flows, and embodied emissions, spatially refined mapping of materials accumulated in road infrastructure can highlight hitherto underappreciated synergies between improved spatial planning, material stock efficiency, and urban mining. In this study, we mapped the materials stocked in road infrastructure across Belgium, explored the patterns of material stock efficiency and the recyclability of end-of-life road materials, and examined the greenhouse gas (GHG) emissions reductions of improving stock efficiency and recycling. We assembled data scattered across various governmental sources and crowdsourced platforms and developed a comprehensive database to warehouse locational information on road typology, layer geometry and thickness, material characteristics, traffic volume, climatic conditions, and soil conditions. Our results reveal a strong but nonlinear correlation between material stock efficiency and population density, indicating that spatial planning can reduce the required road stocks and associated GHG emissions. Urban mining potentials in road infrastructure hinge on multiple factors, such as the proximity to recycling facilities and the degradation of pavements during use. Our counterfactual analysis shows that urban road planning and reusing recycled asphalt can cut GHG emissions by up to 53 and 70%, respectively. Therefore, material-efficient road planning and improved material recycling can help realize circular economy potentials and mitigate GHG emissions moving forward.

The use of urban biowaste and excavated soil in the construction sector: A literature review

Soil has been used as building material for thousands of years with a decrease in popularity after the industrial revolution. Nowadays, there is a growing interest in the implementation of unfired soil-based building solutions for their low environmental impact, performances and availability. Traditional soil construction techniques have recurrently included vegetal fibres to enhance soil performance and recent studies highlight a predominant use of agro- and non-agro-waste for unfired soil construction. The article reviews the state-of-the-art of the use of excavated soil and biowaste in the construction industry including a novel focus on urban-only waste and on building technologies using the integration of these two secondary construction material flows. Our literature review highlights a lack of references about the joint use of these secondary resources. Finally, future research orientations are suggested to promote their implementation in the building sector, which could improve urban waste management.

Pharmacological targeting of miR-155 via the NEDD8-activating enzyme inhibitor MLN4924 (Pevonedistat) in FLT3-ITD acute myeloid leukemia

High levels of microRNA-155 (miR-155) are associated with poor outcome in acute myeloid leukemia (AML). In AML, miR-155 is regulated by NF-κB, the activity of which is, in part, controlled by the NEDD8-dependent ubiquitin ligases. We demonstrate that MLN4924, an inhibitor of NEDD8-activating enzyme presently being evaluated in clinical trials, decreases binding of NF-κB to the miR-155 promoter and downregulates miR-155 in AML cells. This results in the upregulation of the miR-155 targets SHIP1, an inhibitor of the PI3K/Akt pathway, and PU.1, a transcription factor important for myeloid differentiation, leading to monocytic differentiation and apoptosis. Consistent with these results, overexpression of miR-155 diminishes MLN4924-induced antileukemic effects. In vivo, MLN4924 reduces miR-155 expression and prolongs the survival of mice engrafted with leukemic cells. Our study demonstrates the potential of miR-155 as a novel therapeutic target in AML via pharmacologic interference with NF-κB-dependent regulatory mechanisms. We show the targeting of this oncogenic microRNA with MLN4924, a compound presently being evaluated in clinical trials in AML. As high miR-155 levels have been consistently associated with aggressive clinical phenotypes, our work opens new avenues for microRNA-targeting therapeutic approaches to leukemia and cancer patients.

Bcl-xL anti-apoptotic network is dispensable for development and maintenance of CML but is required for disease progression where it represents a new therapeutic target

The dismal outcome of blast crisis chronic myelogenous leukemia (CML-BC) patients underscores the need for a better understanding of the mechanisms responsible for the development of drug resistance. Altered expression of the anti-apoptoticBcl-xL has been correlated with BCR-ABL leukemogenesis; however, its involvement in the pathogenesis and evolution of CML has not been formally demonstrated yet. Thus, we generated an inducible mouse model in which simultaneous expression of p210-BCR-ABL1 and deletion of bcl-x occurs within hematopoietic stem and progenitor cells. Absence of Bcl-xL did not affect development of the chronic phase-like myeloproliferative disease, but none of the deficient mice progressed to an advanced phenotype, suggesting the importance of Bcl-xL in survival of progressing early progenitor cells. Indeed, pharmacological antagonism of Bcl-xL, with ABT-263, combined with PP242-induced activation of BAD markedly augmented apoptosis of CML-BC cell lines and primary CD34(+) progenitors but not those from healthy donors, regardless of drug resistance induced by bone marrow stromal cell-generated signals. Moreover, studies in which BAD or Bcl-xL expression was molecularly altered strongly support their involvement in ABT-263/PP242-induced apoptosis of CML-BC progenitors. Thus, suppression of the antiapoptotic potential of Bcl-xL together with BAD activation represents an effective pharmacological approach for patients undergoing blastic transformation.

Where are we going with CML research?

The introduction of Abl tyrosine kinase inhibitors (TKI; that is, imatinib, dasatinib and nilotinib) as front-line therapy completely changed the course of chronic myelogenous leukemia (CML) to the point that most of the TKI-responsive newly diagnosed CML patients can be considered 'clinically' cured and their progression into blast crisis (BC) a rare event. However, a therapy for those patients who transform is still lacking, and TKIs do not eradicate CML at the stem cell level, therefore leaving a reservoir of cancer stem cells in a dormant stage. Thus, it is not surprising that the focus of CML research has shifted significantly toward the dissection of the mechanisms regulating the survival and self-renewal of TKI-resistant Philadelphia-positive leukemic chronic phase and BC stem cells, with the ultimate goal of developing small molecules capable of selectively killing leukemic but not normal hematopoietic stem cells, thereby achieving a 'biological' cure for this disease.

Chronic myeloproliferative diseases with and without the Ph chromosome: some unresolved issues

Ph-positive chronic myeloid leukemia (CML) and Ph-negative chronic myeloproliferative diseases (MPDs), characterized in many cases by the presence of the JAK2(V617F) mutation, have many features in common and yet also show fundamental differences. In this review, we pose five discrete and related questions relevant to both categories of hematological malignancy, namely: What are the mechanisms that underlie disease progression from a relatively benign or chronic phase? By what therapeutic methods might one target residual leukemia stem cells in CML? Is JAK2(V617F) the original molecular event in MPD? What epigenetic events must have a role in dictating disease phenotype in MPDs? And finally, Will the benefits conferred by current or future JAK2(V617F) inhibitors equal or even surpass the clinical success that has resulted from the use of tyrosine kinase inhibitors in CML? These and others questions must be addressed and in some cases should be answered in the foreseeable future.

Jak2 inhibition deactivates Lyn kinase through the SET-PP2A-SHP1 pathway, causing apoptosis in drug-resistant cells from chronic myelogenous leukemia patients

Chronic myelogenous leukemia (CML) patients treated with imatinib mesylate (IM) become drug resistant by mutations within the kinase domain of Bcr-Abl, and by other changes that cause progression to advanced stage (blast crisis) and increased expression of the Lyn tyrosine kinase, the regulation of which is not understood yet. In Bcr-Abl+ cells inhibition of Jak2, a downstream target of Bcr-Abl, by either Jak2 inhibitors or Jak2-specific short interfering RNA (siRNA) reduced the level of the SET protein, and increased PP2A Ser/Thr phosphatase and Shp1 tyrosine phosphatase activities, which led to decreased levels of activated Lyn. Activation of PP2A combined with Jak2 inhibition enhanced the reduction of activated Lyn kinase compared with Jak2 inhibition alone. In contrast, inhibition of either PP2A or Shp1 combined with Jak2 inhibition interfered with the loss of Lyn kinase activation more so than Jak2 inhibition alone, indicating the involvement of PP2A and Shp1 in the inactivation of the Lyn kinase caused by Jak2 inhibition. Inhibition of Jak2 induced apoptosis and reduced colony formation in IM-sensitive and -resistant Bcr-Abl mutant cell lines. Jak2 inhibition also induced apoptosis in CML cells from blast crisis patients but not in normal hematopoietic cells. These results indicate that Lyn is downstream of Jak2, and Jak2 maintains activated Lyn kinase in CML through the SET-PP2A-Shp1 pathway.

ReSETting PP2A tumour suppressor activity in blast crisis and imatinib-resistant chronic myelogenous leukaemia

The deregulated kinase activity of p210-BCR/ABL oncoproteins, hallmark of chronic myelogenous leukaemia (CML), induces and sustains the leukaemic phenotype, and contributes to disease progression. Imatinib mesylate, a BCR/ABL kinase inhibitor, is effective in most of chronic phase CML patients. However, a significant percentage of CML patients develop resistance to imatinib and/or still progresses to blast crisis, a disease stage that is often refractory to imatinib therapy. Furthermore, there is compelling evidence indicating that the CML leukaemia stem cell is also resistant to imatinib. Thus, there is still a need for new drugs that, if combined with imatinib, will decrease the rate of relapse, fully overcome imatinib resistance and prevent blastic transformation of CML. We recently reported that the activity of the tumour suppressor protein phosphatase 2A (PP2A) is markedly inhibited in blast crisis CML patient cells and that molecular or pharmacologic re-activation of PP2A phosphatase led to growth suppression, enhanced apoptosis, impaired clonogenic potential and decreased in vivo leukaemogenesis of imatinib-sensitive and -resistant (T315I included) CML-BC patient cells and/or BCR/ABL⁺ myeloid progenitor cell lines. Thus, the combination of PP2A phosphatase-activating and BCR/ABL kinase-inhibiting drugs may represent a powerful therapeutic strategy for blast crisis CML patients.

Mutations of KIT tyrosine kinase (TK) gene predict relapse in adult patients (pts) with core binding factor acute myeloid leukemia (CBF AML): A Cancer and Leukemia Group B (CALGB) study

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Background: Multi-course high-dose cytarabine (HDAC) has largely improved the outcome of CBF AML pts with t(8;21)(q22;q22) and inv(16)(p13q22). Yet, ∼50% of pts relapse within 5 years (yrs), indicating the need for markers identifying high-risk pts who require more aggressive and/or novel therapies. KIT mutations (mKIT) of exons 17 (mKIT17) and 8 (mKIT8) are good candidates to be such markers. Previous studies showed that mKIT17 impacted adversely on outcome of t(8;21), but not inv(16), pts. Methods: Sixty-one pts with inv(16) and 49 with t(8;21), assigned to HDAC consolidation on CALGB protocols,were analyzed at diagnosis for mKIT17 and mKIT8 by denaturing high-performance liquid chromatography and direct sequencing. The median follow-up was 5.3 yrs. Results: Among pts with inv(16), 10 had mKIT17 (3 with concurrent mKIT8) and 8 sole mKIT8; among pts with t(8;21), 9 had mKIT17 (2 with mKIT8) and 2 sole mKIT8. In each cytogenetic group, complete remission rates were similar for pts with wild-type KIT (wtKIT) and those with mKIT or mKIT17. In both groups, cumulative incidence of relapse (CIR) was higher for pts with any mKIT [inv(16), P=.050, 5-yr CIR 56% vs 29%; t(8;21), P=.017, 5-yr CIR 70% vs 36%], and also for the subsets of pts with mKIT17 [inv(16), P=.002, 5-yr CIR 80% vs 29%; t(8;21), P=.014, 5-yr CIR 75% vs 36%] compared to wtKIT. Neither mKIT nor mKIT17 significantly affected overall survival (OS). In multivariable analyses (see table ), mKIT [in t(8;21)] and mKIT17 [in inv(16) and t(8;21)] independently predicted worse CIR; worse OS correlated significantly with mKIT only in inv(16) pts. Conclusions: We show for the first time that mKIT17 confer significantly higher relapse rates in inv(16) pts and confirm their adverse impact on t(8;21) pts. Thus, this subset of pts may benefit from more aggressive treatment and/or, since mKIT17 lead to constitutive KIT activation, from therapy that includes TK inhibitors, such as imatinib or PKC412.

[Table: see text]

No significant financial relationships to disclose.

Bcl-2 expression restores the leukemogenic potential of a BCR/ABL mutant defective in transformation

Growth factor-dependent hematopoietic cell lines expressing the BCR/ABL oncoprotein of the Ph chromosome show growth factor-independent proliferation and resistance to apoptosis. Apoptosis resistance of BCR/ABL-expressing cells may depend on enhanced expression of anti-apoptotic proteins as well as reduced expression and/or inactivation of pro-apoptotic proteins. Compared to myeloid precursor 32Dcl3 cells expressing wild type BCR/ABL, cells expressing a BCR/ABL mutant lacking amino acids 176-426 in the BCR domain (p185 delta BCR) are susceptible to apoptosis induced by interleukin-3 (IL-3) deprivation. These cells exhibited the hypophosphorylated apoptotic BAD and markedly reduced levels of Bcl-2. Upon ectopic expression of Bcl-2, these cells showed no changes in BAD phosphorylation, but they became apoptosis-resistant and proliferated in the absence of IL-3, albeit more slowly than cells expressing wild type BCR/ABL. Moreover, the p185 delta BCR/Bcl-2 double transfectants were leukemogenic when injected into immunodeficient mice, but Bcl-2 expression did not restore the leukemia-inducing effects of p185 delta BCR to the levels of wild type BCR/ABL. Leukemic cells recovered from the spleen of mice injected with p185 delta BCR/Bcl-2 cells did not show rearrangements in the Bcl-2 genomic locus, but they exhibited enhanced proliferation in culture and induced a rapidly fatal disease process when inoculated in secondary recipient mice. Together, these data support the importance of anti-apoptotic pathways for BCR/ABL-dependent leukemogenesis and suggest that Bcl-2 expression promotes secondary changes leading to a more aggressive tumor phenotype. (Blood. 2000;96:3915-3921)

BCR-ABL prevents c-jun-mediated and proteasome-dependent FUS (TLS) proteolysis through a protein kinase CbetaII-dependent pathway

The DNA binding activity of FUS (also known as TLS), a nuclear pro-oncogene involved in multiple translocations, is regulated by BCR-ABL in a protein kinase CbetaII (PKCbetaII)-dependent manner. We show here that in normal myeloid progenitor cells FUS, although not visibly ubiquitinated, undergoes proteasome-dependent degradation, whereas in BCR-ABL-expressing cells, degradation is suppressed by PKCbetaII phosphorylation. Replacement of serine 256 with the phosphomimetic aspartic acid prevents proteasome-dependent proteolysis of FUS, while the serine-256-to-alanine FUS mutant is unstable and susceptible to degradation. Ectopic expression of the phosphomimetic S256D FUS mutant in granulocyte colony-stimulating factor-treated 32Dcl3 cells induces massive apoptosis and inhibits the differentiation of the cells escaping cell death, while the degradation-prone S256A mutant has no effect on either survival or differentiation. FUS proteolysis is induced by c-Jun, is suppressed by BCR-ABL or Jun kinase 1, and does not depend on c-Jun transactivation potential, ubiquitination, or its interaction with Jun kinase 1. In addition, c-Jun-induced FUS proteasome-dependent degradation is enhanced by heterogeneous nuclear ribonucleoprotein (hnRNP) A1 and depends on the formation of a FUS-Jun-hnRNP A1-containing complex and on lack of PKCbetaII phosphorylation at serine 256 but not on FUS ubiquitination. Thus, novel mechanisms appear to be involved in the degradation of FUS in normal myeloid cells; moreover, the ability of the BCR-ABL oncoprotein to suppress FUS degradation by the induction of posttranslational modifications might contribute to the phenotype of BCR-ABL-expressing hematopoietic cells.

The nucleoside diphosphate kinase activity of DRnm23 is not required for inhibition of differentiation and induction of apoptosis in 32Dcl3 myeloid precursor cells

DRnm23 belongs to a multigene family which includes nm23-H1, the first bona fide metastasis suppressor gene, nm23-H2, nm23-H4, and nm23-H5. Like nm23-H1, nm23-H2, and nm23-H4, DRnm23 possesses nucleoside diphosphate kinase (NDPK) activity. Upon overexpression in myeloid precursor 32Dcl3 cells, DRnm23 inhibits granulocytic differentiation and promotes apoptosis. Two specific mutants of DRnm23 (H134Q and S136P), at residues required for the NDPK activity, inhibit differentiation and promote apoptosis of 32Dcl3 cells. By contrast, substitution of serine 61 with proline (S61P) or deletion of the RGD domain (DeltaRGD) abrogates the effects of wild-type DRnm23. Like wild-type DRnm23, all four mutants show a predominantly mitochondrial subcellular localization. These studies indicate that the enzymatic activity of DRnm23 is not required for the effects observed in 32Dcl3 cells. Moreover, the inability of the S61P and DeltaRGD DRnm23 mutants to inhibit differentiation and promote apoptosis may be due to defective protein-protein interactions at the mitochondria, the predominant site of DRnm23 subcellular localization.

The interferon regulatory factors 1 and 2 bind to a segment of the human c-myb first intron: possible role in the regulation of c-myb expression

The preferential expression of the protooncogene c-myb in hematopoietic cells is in part regulated by a mechanism of transcriptional block in the first intron. By electrophoresis mobility shift assays using probes corresponding to different segments of the putative human c-myb intron 1 transcription pause region and nuclear extracts from myeloid leukemia HL 60 and fibroblast WI 38 cells, we detected a HL-60-specific DNA-protein complex with a 123-bp fragment containing binding sites for the interferon regulatory factors (IRFs) nuclear proteins. Formation of the DNA-protein complex was abrogated by competition with an oligomer containing the wild-type, but not the mutated, IRF binding site and the complex was specifically supershifted by the anti-IRF-1 or the anti-IRF-2 antibody. Moreover, in vitro translated IRF-1 or IRF-2 protein did interact with the 123-bp c-myb intron 1 fragment. Upon TPA-induced differentiation, c-myb expression was readily down-modulated in parental HL 60 cells, but not in cells transfected with an antisense IRF-1 plasmid. Moreover, chloramphenicol acetyltransferase activity driven by a c-myb promoter containing the entire intron 1 was suppressed upon IRF-1, but not IRF-2 expression. Together, these results are consistent with the existence of a functional relationship between IRF-1 and c-myb in which IRF-1 negatively regulates c-myb expression at the transcriptional level by a mechanism that may depend on the interaction of IRF-1 with a segment of the c-myb gene implicated in transcription pausing.

Resistance to apoptosis in CTLL-2 cells overexpressing B-Myb is associated with B-Myb-dependent bcl-2 induction

Transcriptional regulators of the Myb family play important roles in cell proliferation, differentiation, and survival. To investigate the role of Myb proteins in the regulation of apoptosis, we studied the apoptotic response of interleukin 2-dependent CTLL-2 cells stably transfected with B-Myb. B-Myb-overexpressing cells showed a diminished cytokine dependence and were resistant to apoptosis induced by doxorubicin, ceramide, and dexamethasone. Overexpression of B-Myb was associated with enhanced expression of bcl-2, which was dependent, at least in part, on increased transcription. In transient transfection assays in T-lymphoblastic cells, B-Myb was able to stimulate the promoter activity of the bcl-2 5' flanking region linked to the chloramphenicol acetyltransferase reporter gene. A segment of the bcl-2 promoter (nucleotides +34 to +58 relative to the transcription initiation site) contained a putative Myb-binding site and was shown to specifically interact with B-Myb and to confer B-Myb responsiveness to a bcl-2/chloramphenicol acetyltransferase reporter construct. These results indicate that B-Myb promotes T cells survival by enhancing the expression of bcl-2 and identify bcl-2 as a B-Myb target gene regulated in a DNA binding-dependent manner.

Cooperative action of germ-line mutations in decorin and p53 accelerates lymphoma tumorigenesis

Ectopic expression of decorin in a wide variety of transformed cells results in growth arrest and the inability to generate tumors in nude mice. This process is caused by a decorin-mediated activation of the epidermal growth factor receptor, which leads to a sustained induction of endogenous p21(WAF1/CIP1) (the cyclin-dependent kinase inhibitor p21) and growth arrest. However, mice harboring a targeted disruption of the decorin gene do not develop spontaneous tumors. To test the role of decorin in tumorigenesis, we generated mice lacking both decorin and p53, an established tumor-suppressor gene. Mice lacking both genes showed a faster rate of tumor development and succumbed almost uniformly to thymic lymphomas within 6 months [mean survival age (T50) approximately 4 months]. Mice harboring one decorin allele and no p53 gene developed the same spectrum of tumors as the double knockout animals, but had a survival rate similar to the p53 null animals (T50 approximately 6 months). Ectopic expression of decorin in thymic lymphoma cells isolated from double mutant animals markedly suppressed their colony-forming ability. When these lymphoma cells were cocultured with fibroblasts derived from either wild-type or decorin null embryos, the cells grew faster in the absence of decorin. Moreover, exogenous decorin proteoglycan or its protein core significantly retarded their growth in vitro. These results indicate that the lack of decorin is permissive for lymphoma tumorigenesis in a mouse model predisposed to cancer and suggest that germ-line mutations in decorin and p53 may cooperate in the transformation of lymphocytes and ultimately lead to a more aggressive phenotype by shortening the tumor latency.

TLS/FUS, a pro-oncogene involved in multiple chromosomal translocations, is a novel regulator of BCR/ABL-mediated leukemogenesis

The leukemogenic potential of BCR/ABL oncoproteins depends on their tyrosine kinase activity and involves the activation of several downstream effectors, some of which are essential for cell transformation. Using electrophoretic mobility shift assays and Southwestern blot analyses with a double-stranded oligonucleotide containing a zinc finger consensus sequence, we identified a 68 kDa DNA-binding protein specifically induced by BCR/ABL. The peptide sequence of the affinity-purified protein was identical to that of the RNA-binding protein FUS (also called TLS). Binding activity of FUS required a functional BCR/ABL tyrosine kinase necessary to induce PKCbetaII-dependent FUS phosphorylation. Moreover, suppression of PKCbetaII activity in BCR/ABL-expressing cells by treatment with the PKCbetaII inhibitor CGP53353, or by expression of a dominant-negative PKCbetaII, markedly impaired the ability of FUS to bind DNA. Suppression of FUS expression in myeloid precursor 32Dcl3 cells transfected with a FUS antisense construct was associated with upregulation of the granulocyte-colony stimulating factor receptor (G-CSFR) and downregulation of interleukin-3 receptor (IL-3R) beta-chain expression, and accelerated G-CSF-stimulated differentiation. Downregulation of FUS expression in BCR/ABL-expressing 32Dcl3 cells was associated with suppression of growth factor-independent colony formation, restoration of G-CSF-induced granulocytic differentiation and reduced tumorigenic potential in vivo. Together, these results suggest that FUS might function as a regulator of BCR/ABL leukemogenesis, promoting growth factor independence and preventing differentiation via modulation of cytokine receptor expression.

Myb and ets proteins are candidate regulators of c-kit expression in human hematopoietic cells

Kit is a tyrosine kinase receptor that plays an important role in human hematopoietic cell growth. The promoter elements that modulate the gene's expression have not been extensively studied. Because of c-kit's acknowledged importance in hematopoiesis, we sought to address this issue in more detail. To perform these studies we analyzed a human c-kit 5' flanking fragment approximately 1 kilobase in length. Deletion constructs showed a region approximately 139 nucleotides upstream from the translation initiation site that was critical for promoter activity. A region containing a potential silencing element was also identified. Sequence analysis indicated several potential Myb- and Ets-binding sites. The functional significance of these sites was explored by showing that both wild-type Myb and Ets-2 protein, but not a DNA binding-deficient Myb mutant protein, bound to distinct 5' flanking fragments that included these sites. Furthermore, binding of recombinant Myb and Ets-2 protein to these fragments could be competed with an excess of double stranded oligodeoxynucleotides containing canonical, but not mutated, Myb- or Ets-binding sites. We also showed that the 5' flanking region of c-kit exhibited promoter activity in nonhematopoietic cells only when the cells were transfected with c-myb or ets-2 expression vectors. Moreover, Myb and Ets-2 coexpression in such cells augmented transactivation of c-kit promoter constructs in comparison to that observed in cells transfected with either construct alone. Promoter constructs lacking various Myb and Ets sites deleted were much less effective in this same system. Finally, Myb and Ets-2 mRNA expression was detected in CD34+, Kit low as well as CD34+, Kit bright cells. In aggregate, these data further define the human c-kit promoter's functional anatomy and suggest that Myb and Ets proteins play an important, perhaps cooperative, role in regulating expression of this critical hematopoietic cell receptor.

Transformation of hematopoietic cells by BCR/ABL requires activation of a PI-3k/Akt-dependent pathway

The BCR/ABL oncogenic tyrosine kinase activates phosphatidylinositol 3-kinase (PI-3k) by a mechanism that requires binding of BCR/ABL to p85, the regulatory subunit of PI-3k, and an intact BCR/ABL SH2 domain. SH2 domain BCR/ABL mutants deficient in PI-3k activation failed to stimulate Akt kinase, a recently identified PI-3k downstream effector with oncogenic potential, but did activate p21 RAS and p70 S6 kinase. The PI-3k/Akt pathway is essential for BCR/ABL leukemogenesis as indicated by experiments demonstrating that wortmannin, a PI-3k specific inhibitor at low concentrations, suppressed BCR/ABL-dependent colony formation of murine marrow cells, and that a kinase-deficient Akt mutant with dominant-negative activity inhibited BCR/ABL-dependent transformation of murine bone marrow cells in vitro and suppressed leukemia development in SCID mice. In complementation assays using mouse marrow progenitor cells, the ability of transformation-defective SH2 domain BCR/ABL mutants to induce growth factor-independent colony formation and leukemia in SCID mice was markedly enhanced by expression of constitutively active Akt. In retrovirally infected mouse marrow cells, the BCR/ABL mutant lacking the SH2 domain was unable to upregulate the expression of c-Myc and Bcl-2; in contrast, expression of a constitutively active Akt mutant induced Bcl-2 and c-Myc expression, and stimulated the transcription activation function of c-Myc. Together, these data demonstrate the requirement for the BCR/ABL SH2 domain in PI-3k activation and document the essential role of the PI-3k/Akt pathway in BCR/ABL leukemogenesis.

Granulocytic differentiation of normal hematopoietic precursor cells induced by transcription factor PU.1 correlates with negative regulation of the c-myb promoter

Numerous transcription factors allow hematopoietic cells to respond to lineage- and stage-specific cytokines and/or to act as their effectors. The transcription factors PU.1 and c-Myb are essential for hematopoiesis, most likely acting at distinct stages of differentiation, but sharing a common set of target genes. To determine whether PU.1 and c-Myb are functionally interrelated, murine bone marrow (BM) cells and 32Dcl3 murine myeloid precursor cells were infected with a retrovirus carrying a PU.1 cDNA and assessed for myeloid colony formation and for granulocytic differentiation, respectively. Compared with noninfected normal BM cells or to cells infected with an empty virus, hematopoietic precursor cells expressing PU.1 formed an increased number of interleukin-3 (IL-3) and granulocyte colony-stimulating factor (G-CSF)-stimulated colonies. Moreover, granulocytic differentiation of 32Dcl3 cells constitutively expressing PU.1 was accelerated, as indicated by morphology and by expression of differentiation markers. Downregulation of c-Myb protein levels by expression of an antisense c-myb construct was also associated with a faster kinetics of 32Dcl3 granulocytic differentiation. Sequence analysis of the 5' flanking region of the c-myb gene revealed a consensus PU box at position +16 to +21 able to specifically interact in electrophoretic mobility shift assays with either bacterially synthesized PU.1 protein or whole cell extracts from differentiated 32Dcl3 cells. Transient expression of PU.1 in cotransfection assays in different cell lines resulted in inhibition of chloramphenicol acetyl transferase activity driven by different segments of the c-myb promoter. Moreover, such an effect was dependent on an intact PU box. Thus, the ability of PU.1 to potentiate terminal myeloid differentiation appears to involve downregulation of c-myb expression, an essential step during differentiation of hematopoietic precursor cells.

Antileukemia effect of c-myc N3'-->P5' phosphoramidate antisense oligonucleotides in vivo

In vitro, uniformly modified oligonucleotide N3'-->P5' phosphoramidates are apparently more potent antisense agents than phosphorothioate derivatives. To determine whether such compounds are also effective in vivo, severe combined immunodeficiency mice injected with HL-60 myeloid leukemia cells were treated systemically with equal doses of either phosphoramidate or phosphorothioate c-myc antisense or mismatched oligonucleotides. Compared with mice treated with mismatched oligodeoxynucleotides, the peripheral blood leukemic load of mice treated with the antisense sequences was markedly reduced, and such effects were associated with significantly prolonged survival of the antisense-treated mice. Moreover, with each of three different treatment schedules (100, 300, or 900 microg/day for 6 consecutive days), survival of the phosphoramidate-treated mice was significantly longer than that of the phosphorothioate-treated mice. Both phosphoramidate and phosphorothioate oligonucleotides were efficiently taken up by leukemic cells in vivo and were capable of specifically down-regulating c-Myc expression. Moreover, tissue distribution of the phosphoramidate derivatives was undistinguishable from that of the phosphorothioate derivatives. Collectively, these studies suggest that phosphoramidate oligonucleotides can serve as potent and specific antisense agents in the treatment of human leukemia and probably of other malignancies.

Resistance to apoptosis in CTLL-2 cells constitutively expressing c-Myb is associated with induction of BCL-2 expression and Myb-dependent regulation of bcl-2 promoter activity

c-Myb, the cellular homologue of the transforming gene of the avian myeloblastosis virus, is preferentially expressed in all hematopoietic lineages, including T and B lymphocyte lineages. In T lymphocytes, c-Myb expression appears to be required for cell cycle progression and proliferation. To further investigate the role of c-Myb in T cell proliferation and survival, interleukin (IL) 2-dependent CTLL-2 cells were transfected with a constitutively active c-myb or with a c-myb antisense construct able to down-regulate endogenous Myb levels, and the transfectants were assessed for proliferation and survival in low concentrations of IL-2 and for susceptibility to dexamethasone-induced apoptosis. Compared with control cells, CTLL-2 cells constitutively expressing c-Myb proliferate in low concentrations of IL-2 and are less susceptible to apoptosis induced by IL-2 deprivation or treatment with dexamethasone. In contrast, cells transfected with an antisense c-myb construct do not proliferate in low concentrations of IL-2 and undergo apoptosis upon IL-2 deprivation or dexamethasone treatment more rapidly than parental cells. Overexpression of c-Myb was accompanied by up-regulation of BCL-2 expression. In transient transfection assays, the murine bcl-2 promoter was efficiently transactivated by c-Myb, but such effect was observed also in cells transfected with a DNA binding-deficient c-myb construct. Moreover, in gel retardation assays, a 38-bp oligomer in the shortest bcl-2 promoter segment regulated by c-Myb formed a specific complex with nuclear extracts from c-Myb-transfected CTLL-2 cells. Thus, these results strongly suggest that c-Myb, in addition to regulating T cell proliferation, protects T lymphocytes from apoptosis by induction of BCL-2 expression, which involves a c-Myb-dependent mechanism of promoter regulation.

Sepsis-induced regulation of lipoprotein lipase expression in rat adipose tissue and soleus muscle

Hypertriglyceridemia of sepsis is associated with suppressed tissue lipoprotein lipase (LPL) activities. We investigated the effect of sepsis on lipoprotein lipase gene expression in epididymal fat and soleus muscle from control and septic rats in the fasted and fed state. After 24 h of sepsis, LPL activity decreased significantly in epididymal fat from fasted rats by 45% along with a 57% reduction in LPL mRNA levels and LPL mass. Transcription rate, measured by nuclear run-on assay, decreased by 70% in epididymal fat from fasted septic rats compared to fasted control rats. The synthesis rate of LPL in epididymal fat decreased by 31% while the LPL relative synthesis declined by 50% during sepsis. The turnover rate was not altered. Sepsis in fed rats did not lead to a significant decrease in LPL mRNA in epididymal fat but did lower LPL activity and LPL mass by 45%. The sepsis-induced suppression in soleus LPL activity, LPL mRNA levels, and LPL mass in the fasted state also was observed when septic rats were fed. The results indicate that during fasting sepsis, LPL expression in epididymal fat and possibly soleus muscle involves transcriptional regulation. During sepsis in the fed state, the regulation of LPL in adipose tissue may involve posttranslational mechanisms.

Gene structure, promoter activity, and chromosomal location of the DR-nm23 gene, a related member of the nm23 gene family

DR-nm23 cDNA was cloned recently by differential screening of a cDNA library derived from chronic myelogenous leukemia-blast crisis primary cells. It is highly homologous to the putative metastasis suppressor nm23-H1 gene and the closely related nm23-H2 gene. When overexpressed in the myeloid precursor 32Dcl3 cell line, it inhibited granulocyte colony-stimulating factor-stimulated granulocytic differentiation and induced apoptosis. We have now found that the expression of DR-nm23 is not restricted to hematopoietic cells but is also detected in an array of solid tumor cell lines, including carcinoma of the breast, colon, and prostate, as well as the glioblastoma cell line T98G. We have also isolated both the gene and its 5'-flanking region and found that DR-nm23 localizes on chromosome 16q13. The gene consists of six exons and five introns. When fused in-frame to the nucleotide sequence for the green fluorescent protein and transfected in SAOS-2 cells, it generates a protein of the predicted size that localizes to the cytoplasm. The 5'-flanking region of DR-nm23 does not contain a canonical TATA box or a CAAT box, but it is G+C rich and contains two binding sites for the developmentally regulated transcription factor activator protein 2 (AP-2). Transient expression assays of DR-nm23 promoter-chloramphenicol acetyltransferase constructs demonstrated that the segment from nucleotides -1028 to +123 has the highest activity in hematopoietic K562 cells and in TK-ts13 hamster fibroblasts. Moreover, AP-2 induced a 3-fold transactivation of the DR-nm23 5'-flanking segment from nucleotides -1676 to +123 and interacted specifically with oligomers containing putative AP-2 binding sites (-936 to -909, and -548 to -519) as indicated by electrophoretic mobility shift assay. Furthermore, nuclear run-on assays from high and low DR-nm23-expressing cells (K562 and CCRF-CEM, respectively) revealed similar transcription rates. Therefore, the regulation of the DR-nm23 gene expression might involve other mechanisms occurring at posttranscriptional and/or translational levels.

Treatment of Philadelphia leukemia in severe combined immunodeficient mice by combination of cyclophosphamide and bcr/abl antisense oligodeoxynucleotides

BACKGROUND

Philadelphia cells are human chronic myelogenous leukemia (CML) cells that contain the BCR/ABL oncogene (a fusion of the BCR and ABL genes). Selective eradication of these cells in vitro can be achieved by combined treatment with antisense phosphorothioate oligodeoxynucleotides ([S]ODNs) specifically targeted to this oncogene (bcr/abl [S]ODNs) and a suboptimal (for use as a single agent) dose of mafosfamide (the in vitro active form of cyclophosphamide).

PURPOSE

We evaluated the ability of bcr/abl antisense [S]ODNs, alone or subsequent to treatment with a single injection of cyclophosphamide, to suppress the leukemic process induced in severe combined immunodeficient (SCID) mice by Philadelphia cells (i.e., primary CML-blast crisis [CML-BC] cells). In addition, we studied potential mechanisms that might explain the efficacy of the bcr/abl antisense [S]ODN-mafosfamide combination against Philadelphia cells in vitro.

METHODS

The effects of treating leukemic mice with cyclophosphamide (25 mg/kg body weight; 25% of the dose required to eradicate evidence of leukemia in SCID mice) and/or bcr/abl antisense [S]ODNs were assessed by analysis of survival, by examination of bone marrow for the presence of leukemia cells (using a colony formation assay or using coupled reverse transcription and the polymerase chain reaction to screen for bcr/abl messenger RNA), and by examination of a variety of tissues for the presence of infiltrating leukemia cells. The induction of apoptosis (a cell death program) in vitro in primary CML-BC cells following treatment with bcr/abl antisense [S]ODNs plus or minus prior treatment with mafosfamide was monitored by use of a commercial assay. Relative cellular uptake of [S]ODNs by CML-BC cells treated in vitro with or without prior treatment with mafosfamide was determined by use of confocal microscopy and flow cytometry (for fluorescent [S]ODNs) or by use of blotting techniques that employed radioactively labeled probes (for extracted, unlabeled [S]ODNs). Levels of specific proteins in treated and untreated cells were determined by use of western blotting methods. Reported P values are two-sided.

RESULTS

The disease process in leukemic mice was retarded substantially by combination treatment with cyclophosphamide and specific bcr/abl antisense [S]ODNs (P < .001, relative to treatment with specific antisense [S]ODNs alone, cyclophosphamide alone, or cyclophosphamide plus nonspecific [i.e., control] antisense [S]ODNs); 50% of the mice treated with cyclophosphamide and specific antisense [S]ODNs appeared to be cured of leukemia. The combination treatment was associated with increased induction of apoptosis. In addition, cellular uptake of bcr/abl antisense [S]ODNs appeared to be increased twofold to sixfold by prior treatment with mafosfamide. This increased uptake of [S]ODNs was associated with enhanced suppression of p210bcr/abl protein levels.

CONCLUSIONS AND IMPLICATIONS

Combination therapy with antisense [S]ODNs targeted to specific oncogenes and less toxic doses of anticancer drugs may represent a rational strategy to purpose for the treatment of human leukemias.

Beta 4 integrin subunit expression is downregulated in low metastatic carcinoma variants

Organization and expression of the gene coding for beta 4 integrin subunit were investigated in murine carcinoma lines endowed with low and high metastatic potential maintained both in vivo and in vitro. Probes corresponding to either the extracellular or the cytoplasmic domains of the protein were generated and employed for Southern and Northern blot hybridization experiments. Southern blot analysis demonstrates a restriction fragment-length polymorphism between BALB/c and C57BI/6J DNAs. The different genomic organization of the beta 4 gene apparently does not generate variation in mRNA length. Northern blot analysis reveals a 7-kb transcript encoding full-length beta 4 protein and shorter transcripts that apparently correspond to nonfunctional mRNAs. In carcinoma cells endowed with low metastatic capacity, the 7-kb mRNA cannot be revealed in spite of the presence of shorter transcripts. In contrast, the 7-kb transcript is always present in tumor cells endowed with high metastatic capacity. Accordingly, the beta 4 protein is detectable, either by immunofluorescence or by Western blot analyses, only in highly metastatic carcinoma cells. In conclusion, the data presented show that in these murine carcinoma cell lines (i) the 7-kb mRNA is associated with a more invasive phenotype, and (ii) missing expression of the beta 4 integrin subunit in low metastatic carcinoma cells depends, at least in part, on mechanisms acting at a post-transcriptional level. The possibility that beta 4 subunit expression is a consequence of specific differentiation stages of lung carcinoma cells is discussed.

Blastic transformation of p53-deficient bone marrow cells by p210bcr/abl tyrosine kinase

Blastic transformation of chronic myelogenous leukemia (CML) is characterized by the presence of nonrandom, secondary genetic abnormalities in the majority of Philadelphia1 clones, and loss of p53 tumor suppressor gene function is a consistent finding in 25-30% of CML blast crisis patients. To test whether the functional loss of p53 plays a direct role in the transition of chronic phase to blast crisis, bone marrow cells from p53+/+ or p53-/- mice were infected with a retrovirus carrying either the wild-type BCR/ABL or the inactive kinase-deficient mutant, and were assessed for colony-forming ability. Infection of p53-/- marrow cells with wild-type BCR/ABL, but not with the kinase-deficient mutant, enhanced formation of hematopoietic colonies and induced growth factor independence at high frequency, as compared with p53+/+ marrow cells. These effects were suppressed when p53-/- marrow cells were coinfected with BCR/ ABL and wild-type p53. p53-deficient BCR/ABL-infected marrow cells had a proliferative advantage, as reflected by an increase in the fraction of S+G2 phase cells and a decrease in the number of apoptotic cells. Immunophenotyping and morphological analysis revealed that BCR/ABL-positive p53-/- cells were much less differentiated than their BCR/ABL-positive p53+/+ counterparts. Injection of immunodeficient mice with BCR/ABL-positive p53-/- cells produced a transplantable, highly aggressive, poorly differentiated acute myelogenous leukemia. In marked contrast, the disease process in mice injected with BCR/ABL-positive p53+/+ marrow cells was characterized by cell infiltrates with a more differentiated phenotype and was significantly retarded, as indicated by a much longer survival of leukemic mice. Together, these findings directly demonstrate that loss of p53 function plays an important role in blast transformation in CML.

A cell proliferation-dependent multiprotein complex NC-3A positively regulates the CD34 promoter via a TCATTT-containing element

The CD34 cell surface antigen is a glycoprotein expressed by hematopoietic stem and progenitor cells and also by certain nonhematopoietic cell-types. Because CD34 expression is regulated both at the transcriptional and the posttranscriptional level, we attempted to identify factors that, by interacting with the 5' flanking region of the human CD34 gene, may regulate its promoter activity in proliferating hematopoietic cells. By electrophoretic mobility shift assay, UV cross-linking and DNase I footprinting analyses, we identified a multiprotein complex, designated NC-3A, that specifically interacts with the CD34 promoter region from nucleotides -375 to -351. Sequence analysis of this region revealed the presence of a distinct motif, TCATTT. Chloramphenicol acetyl-transferase assays used to assess promoter activity in transiently transfected cells showed that this TCATTT-containing element, which is conserved in both the human and the murine CD34 genes, mediates positive regulatory activity in hematopoietic and nonhematopoietic cells, and acts as an enhancer when placed upstream of a heterologous promoter. Moreover, loss of CD34 promoter activity was caused by mutation of the TCATTT motif. In addition, the interaction of the nuclear multiprotein complex NC-3A with this enhancer element is proliferation-dependent. These data indicate that, although not cell-type specific, the formation of a multiprotein complex NC-3A interacting with the region from nucleotides -375 to 351 plays an important role in controlling CD34 promoter activity in proliferating hematopoietic cells.

Overexpression of the zinc finger protein MZF1 inhibits hematopoietic development from embryonic stem cells: correlation with negative regulation of CD34 and c-myb promoter activity

Zinc finger genes encode proteins that act as transcription factors. The myeloid zinc finger 1 (MZF1) gene encodes a zinc finger protein with two DNA-binding domains that recognize two distinct consensus sequences, is preferentially expressed in hematopoietic cells, and may be involved in the transcriptional regulation of hematopoiesis-specific genes. Reverse transcription-PCR analysis of human peripheral blood CD34+ cells cultured under lineage-restricted conditions demonstrated MZF1 expression during both myeloid and erythroid differentiation. Sequence analysis of the 5'-flanking region of the CD34 and c-myb genes, which are a marker of and a transcriptional factor required for hematopoietic proliferation and differentiation, respectively, revealed closely spaced MZF1 consensus binding sites found by electrophoretic mobility shift assays to interact with recombinant MZF1 protein. Transient or constitutive MZF1 expression in different cell types resulted in specific inhibition of chloramphenicol acetyltransferase activity driven by the CD34 or c-myb 5'-flanking region. To determine whether transcriptional modulation by MZF1 activity plays a role in hematopoietic differentiation, constructs containing the MZF1 cDNA under the control of different promoters were transfected into murine embryonic stem cells which, under defined in vitro culture conditions, generate colonies of multiple hematopoietic lineages. Constitutive MZF1 expression interfered with the ability of embryonic stem cells to undergo hematopoietic commitment and erythromyeloid colony formation and prevented the induced expression of CD34 and c-myb mRNAs during differentiation of these cells. These data indicate that MZF1 plays a critical role in hematopoiesis by modulating the expression of genes involved in this process.

C-RAF-1 serine/threonine kinase is required in BCR/ABL-dependent and normal hematopoiesis

BCR/ABL oncogenic tyrosine kinase is responsible for initiating and maintaining the leukeic phenotype of Philadelphia chromosome-positive cells. c-RAF-1 serine/threonine kinase is known to be activated by receptor and nonreceptor tyrosine kinases. To determine whether c-RAF-1 plays a role in the growth of BCR/ABL-dependent cells, we examined whether c-RAF-1 associates with and/or is regulated by BCR/ABL and, if so, whether this interaction is functionally significant for BCR/ABL-dependent growth of chronic myelogenous leukemia cells and for growth factor-dependent proliferation of normal bone marrow cells. We show that c-RAF-1 enzymatic activity is regulated by BCR/ABL, although the protein does not associate with BCR/ABL. Downregulation of c-RAF-1 expression with antisense oligodeoxynucleotides or cDNA constructs, and inhibition of c-RAF-1 activity by its dominant negative mutants, inhibited both BCR/ABL-dependent growth of chronic myelogenous leukemia cells and growth factor-dependent proliferation of normal hematopoietic progenitors and the MO7 cell line without affecting the BCR/ABL-and growth factor-independent proliferation of HL-60 cells. These results indicate that c-RAF-1 plays an important role in Philadelphia chromosome-positive and normal hematopoiesis.

Structure and growth-dependent regulation of the human cyclin B1 promoter

As a step toward defining the signals important for the regulation of cyclin B1 expression, we cloned, sequenced, and partially characterized a 1012-bp genomic fragment encompassing the human cyclin B1 promoter. By transient expression experiments, we found that promoter activity resides within a -150/+182-bp DNA fragment. The activity of this promoter fragment was high in asynchronous NIH-3T3 cells, but dramatically decreased in quiescent cells. Time-course experiments, using stable transfectants expressing the CAT gene under the control of this fragment, were performed after releasing the cells from serum starvation. The results showed that the promoter becomes active at the end of the S phase and its activity increases during the cell cycle. Similar experiments performed with a shorter promoter region (-58/+182) showed that this 5' deletion mutant is active throughout the cell cycle. In good agreement with promoter activity, Northern analysis indicated that the endogenous gene is negatively regulated in quiescent murine NIH-3T3 cells. The data presented here demonstrate that in NIH-3T3 cells the cyclin B1 promoter is growth regulated, and important regulatory elements must exist in the region spanning -150 to -58 bp.

Inhibition of leukemia cell proliferation by receptor-mediated uptake of c-myb antisense oligodeoxynucleotides

Exposure of human leukemia HL-60 cells to an oligodeoxynucleotide complementary to an 18-base sequence (codons 2-7) of c-myb-encoded mRNA has previously been shown to result in inhibition of cell proliferation. Because HL-60 cells express high levels of transferrin receptor we adapted a DNA delivery system based on receptor-mediated endocytosis to introduce myb oligomers complexed with a transferrin-polylysine conjugate into those cells. A DNA.RNA duplex resistant to S1 nuclease digestion was detected as early as 12 hr after culture of HL-60 cells in the presence of the myb antisense/transferrin-polylysine complex. Exposure of HL-60 cells to the myb antisense/transferrin-polylysine complex resulted in rapid and profound inhibition of proliferation and loss of cell viability much more pronounced than that occurring in cells exposed to free myb antisense oligodeoxynucleotides. The transferrin-polylysine/myb sense complex or the transferrin-polylysine conjugate alone had no effect on HL-60 cell proliferation and viability. These findings indicate that myb synthetic oligodeoxynucleotides enter efficiently into HL-60 by transferrin receptor-mediated endocytosis and exert a profound biological effect. Such a delivery system could exploit other ligand-receptor interactions for the selective delivery of oncogene-targeted antisense oligodeoxynucleotides.

Differential expression of transforming growth factor-beta 1 gene in 3LL metastatic variants

In vitro and in vivo metastatic variants derived from Lewis lung carcinoma (3LL) were examined for the level of the expression of several growth-regulated genes, oncogenes, and transforming growth factor (TGF) genes. To determine whether the proliferative advantage of metastatic cells is due to an increased growth fraction of the cell population or to a deregulated expression of some growth-regulated genes, the mRNA levels of the S-phase-specific H3 histone gene were compared with that of some cell cycle-related genes (vimentin, calcyclin, c-myc, and p53) and oncogenes (Ki-ras, Ha-ras, c-sis, c-src, c-fes, and c-erb). In addition, to evaluate whether an autocrine pattern of cell proliferation is responsible for the proliferative advantage of metastatic cells, the level of the expression of TGF genes (alpha and beta 1) was studied. Northern blot analysis demonstrated that in 3LL metastatic variants the expression of TGF-alpha as well as the expression of all growth-regulated genes and oncogenes studied are similar. Only the TGF-beta 1 gene is expressed at higher levels in highly metastatic 3LL variants maintained either in vitro or in vivo. Data suggest that the proliferative advantage of 3LL metastatic cells is not due to a deregulated expression of some growth-regulated genes and oncogenes, but more likely is acquired through the expression of genes which might interfere with the ability of the tumor cells to escape hostile microenvironmental conditions.

Metastatic phenotype: growth factor dependence and integrin expression

Homogeneous subpopulations, which are endowed with low or high metastatic potential, were selected from Lewis lung carcinoma (3LL) in an attempt to correlate metastatic phenotype with specific properties of tumor cells. Since the growth of malignant cells at secondary sites could depend on their ability to respond to microenvironments, the growth factor dependence of 3LL variants has been studied. The ability of variant lines to grow in monolayer and in soft agar cultures, either in the presence or absence of different growth factors or serum, was analyzed and correlated with their metastatic potential. The reported results demonstrate that tumor cells expressing higher metastatic potential also exhibit higher capacity to grow and proliferate in all the culture conditions tested, independently of the addition of exogenous growth factors or serum. Moreover, since highly metastasizing cells express a significant amount of TGF-beta 1 mRNA, a pattern of autocrine growth is postulated for 3LL metastatic cells. One relevant aspect of the phenotype of transformed cells is their reduced adhesion to solid substrates; this phenomenon is thought to reflect the invasive and metastatic potential of tumor cells. Since the adhesion of the cells to substrata is mediated by molecules of the extracellular matrix, the expression of extracellular matrix receptors (integrins) was studied on 3LL metastatic variants. In particular, through immunochemical and biochemical studies we investigated the expression of the laminin receptor(alpha 6/beta 1) and of a novel receptor (integrin: alpha 6/beta 4), of unknown function. The receptors were quantitated on the cell surface of 3LL variants by the use of specific monoclonal antibodies which recognize, respectively, different epitopes of alpha 6, beta 4 or beta 1 subunits. Results demonstrate that the novel integrin alpha 6/beta 4, is specifically expressed in highly metastasizing 3LL cells, whereas the laminin receptor alpha 6/beta 1 is expressed in all 3LL variants. In conclusion, data presented demonstrate that 3LL cells endowed with higher metastatic potential are more independent of the microenvironmental conditions in that they possess a higher autocrine capacity than the lower metastasizing ones, and could acquire higher capacity to invade through the expression on their cell surface of specific receptors for cell adhesion (the novel integrin, defined as alpha 6/beta 4).