Correlation of VLA-4 integrin expression with metastatic potential in various human tumour cell lines

Kindlin-1 Promotes Pulmonary Breast Cancer Metastasis

In breast cancer, increased expression of the cytoskeletal adaptor protein Kindlin-1 has been linked to increased risks of lung metastasis, but the functional basis is unknown. Here, we show that in a mouse model of polyomavirus middle T antigen-induced mammary tumorigenesis, loss of Kindlin-1 reduced early pulmonary arrest and later development of lung metastasis. This phenotype relied on the ability of Kindlin-1 to bind and activate β integrin heterodimers. Kindlin-1 loss reduced α4 integrin-mediated adhesion of mammary tumor cells to the adhesion molecule VCAM-1 on endothelial cells. Treating mice with an anti-VCAM-1 blocking antibody prevented early pulmonary arrest. Kindlin-1 loss also resulted in reduced secretion of several factors linked to metastatic spread, including the lung metastasis regulator tenascin-C, showing that Kindlin-1 regulated metastatic dissemination by an additional mechanism in the tumor microenvironment. Overall, our results show that Kindlin-1 contributes functionally to early pulmonary metastasis of breast cancer.Significance: These findings provide a mechanistic proof in mice that Kindin-1, an integrin-binding adaptor protein, is a critical mediator of early lung metastasis of breast cancer. Cancer Res; 78(6); 1484-96. ©2018 AACR.

Integrin α4-positive human trophoblast progenitors: functional characterization and transcriptional regulation

STUDY QUESTION

What are the functional characteristics and transcriptional regulators of human trophoblast progenitor cells (TBPCs)?

SUMMARY ANSWER

TBPC lines established from the human smooth chorion by cell sorting for integrin α4 expressed markers of stemness and trophoblast (TB) stage-specific antigens, invaded Matrigel substrates and contributed to the cytotrophoblasts (CTBs) layer of smooth chorion explants with high-mobility group protein HMGI-C (HMGA2) and transcription factor GATA-4 (GATA4) controlling their progenitor state and TB identity.

WHAT IS KNOWN ALREADY

Previously, we reported the derivation of TBPC lines by trypsinization of colonies that formed in cultures of chorionic mesenchyme cells that were treated with an activin nodal inhibitor. Microarray analyses showed that, among integrins, α4 was most highly expressed, and identified HMGA2 and GATA4 as potential transcriptional regulators.

STUDY DESIGN, SIZE, DURATION

The aim of this study was to streamline TBPC derivation across gestation. High-cell surface expression of integrin α4 enabled the use of a fluorescence-activated cell sorter (FACS) approach for TBPC isolation from the human smooth chorion (n = 6 lines). To confirm their TBPC identity, we profiled their expression of stemness and TB markers, and growth factor receptors. At a functional level, we assayed their invasive capacity (n = 3) and tropism for the CTB layer of the smooth chorion (n = 3). At a molecular level, we studied the roles of HMGA2 and GATA4.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Cells were enzymatically disassociated from the human smooth chorion across gestation. FACS was used to isolate the integrin α4-positive population. In total, we established six TBPC lines, two per trimester. Their identity was determined by immunolocalization of a suite of antigens. Function was assessed via Matrigel invasion and co-culture with explants of the human smooth chorion. An siRNA approach was used to down-regulate HMGA2 and GATA4 expression and the results were confirmed by immunoblotting and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analyses. The endpoints analyzed included proliferation, as determined by 5-bromo-2'-deoxyuridine (BrDU) incorporation, and the expression of stage-specific antigens and hormones, as determined by qRT-PCR and immunostaining approaches.

MAIN RESULTS AND THE ROLE OF CHANCE

As with the original cell lines, the progenitors expressed a combination of human embryonic stem cell and TB markers. Upon differentiation, they primarily formed CTBs, which were capable of Matrigel invasion. Co-culture of the cells with smooth chorion explants enabled their migration through the mesenchyme after which they intercalated within the chorionic CTB layer. Down-regulation of HMGA2 showed that this DNA-binding protein governed their self-renewal. Both HMGA2 and GATA4 had pleitropic effects on the cells' progenitor state and TB identity.

LIMITATIONS, REASONS FOR CAUTION

This study supported our hypothesis that TBPCs from the chorionic mesenchyme can contribute to the subpopulation of CTBs that reside in the smooth chorion. In the absence of in vivo data, which is difficult to obtain in humans, the results have the limitations common to all in vitro studies.

WIDER IMPLICATIONS OF THE FINDINGS

The accepted view is that progenitors reside among the villous CTB subpopulation. Here, we show that TBPCs also reside in the mesenchymal layer of the smooth chorion throughout gestation. We theorize that they can contribute to the CTB layer in this region. This phenomenon may be particularly important in pathological situations when CTBs of the smooth chorion might provide a functional reserve for CTBs of the placenta proper.

STUDY FUNDING/COMPETING INTERESTS

Research reported in this publication was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health under award P50HD055764. O.G., N.L., K.O., A.P., T.G.-G., M.K., A.B., M.G. have nothing to disclose. S.J.F. received licensing fees and royalties from SeraCare Life Sciences for trisomic TBPC lines that were derived according to the methods described in this manuscript.

TRIAL REGISTRATION NUMBER

N/A.

Role of the host stroma in cancer and its therapeutic significance

Current cancer research focuses mainly upon the cancer cells in malignant tumours and is providing a growing database about aberrations in their genetic composition. However, tumours also contain non-cancerous host tissue, referred to as the stroma, which plays an active and indispensable role in tumour growth and influences the virulence of the neoplasm towards the host. Many cell types inhabit the stroma, amidst apparently inert fibrous and viscous matrix material, composed of complex polysaccharides, proteins and other molecules. Actually, all of these elements are in constant turnover, causing unpredictable evolution in the properties of the community. This article provides pathologic observations and data on reciprocal interactions between these stromal and neoplastic components of tumours and how they change during the course of the disease. Malignant progression depends upon dauntingly intricate communications between different specialised lineages within the cellular society, which enable rapid adaptation to changing circumstances. Opportunistic misuse of such communication networks enables tumour cells to recruit and incorporate adjacent normal stroma into their midst, so that they may grow, infiltrate and parasitise the host. The absolute dependency of primary tumours and metastases on their diverse stromal components for survival and their insatiable need to continuously recruit more stroma to support expansion, renders them vulnerable to strategies capable of disrupting the cellular interactions involved. This dependency is of critical importance for cancer therapy research, and proposed methods for turning this parasitic behaviour of tumours against themselves are suggested below.

Functional role of endothelial adhesion molecules in the early stages of brain metastasis

BACKGROUND

Cellular adhesion molecules (CAMs), which are normally associated with leukocyte trafficking, have also been shown to play an essential role in tumor metastasis to non-CNS sites. However, the role played by CAMs in brain metastasis is largely unexplored. It is known that leukocyte recruitment to the brain is very atypical and that mechanisms of disease in peripheral tissues cannot be extrapolated to the brain. Here, we have established the spatiotemporal expression of 12 key CAMs in the initial phases of tumor seeding in 2 different models of brain metastasis.

METHODS

BALB/c or SCID mice were injected intracardially (10(5) cells/100 μL phosphate-buffered saline with either 4T1-GFP or MDA231BR-GFP cells, respectively (n = 4-6/group), and expression of the CAMs was determined by immunohistochemistry and immunofluorescence colocalisation.

RESULTS

Endothelial expression of E-selectin, VCAM-1, ALCAM, ICAM-1, VLA-4, and β4 integrin was markedly increased early in tumor seeding. At the same time, the natural ligands to these adhesion molecules were highly expressed on the metastatic tumor cells both in vitro and in vivo. Two of these ligands showed particularly high tumor cell expression (ALCAM and VLA-4), and consequently their functional role in tumor seeding was determined. Antibody neutralization of either ALCAM or VLA-4 significantly reduced tumor seeding within the brain (>60% decrease in tumor number/mm(2) brain; P < .05-0.01).

CONCLUSIONS

These findings suggest that ALCAM/ALCAM and VLA-4/VCAM-1 interactions play an important functional role in the early stages of metastasis seeding in the brain. Moreover, this work identifies a specific subset of ligand-receptor interactions that may yield new therapeutic and diagnostic targets for brain metastasis.

Inappropriate gene expression in human cancer and its far-reaching biological and clinical significance

This article provides a broad overview of the field of inappropriate gene expression in many organisms across the animal and plant kingdoms as well as its importance to human disease in general and cancer in particular. Study of the topic is especially important for understanding how the chaotic maelstrom of evolving and cascading regulatory genetic interactions in an advancing cancer produces its clinical effects and for designing pragmatic solutions to how such disorder might eventually be tamed. It is emphasized that the topic warrants much more attention in research and in clinical practice because of the added value it brings to refining cancer diagnosis and treatment and to the assessment of prognostic markers. It is also particularly relevant to understanding the etiology and extensive clinical manifestations of paraneoplastic syndromes affecting multiple organs remote from the tumor and the treatment or amelioration of the substantial morbidity that they cause in cancer patients. More broadly, inappropriate expression can be caused by a number of mechanisms including mutations, rearrangements of the genome, and viral insertions and, under prolonged selection pressures, also has the potential to be an agent of evolutionary change.

Molecular MRI enables early and sensitive detection of brain metastases

Metastasis to the brain is a leading cause of cancer mortality. The current diagnostic method of gadolinium-enhanced MRI is sensitive only to larger tumors, when therapeutic options are limited. Earlier detection of brain metastases is critical for improved treatment. We have developed a targeted MRI contrast agent based on microparticles of iron oxide that enables imaging of endothelial vascular cell adhesion molecule-1 (VCAM-1). Our objectives here were to determine whether VCAM-1 is up-regulated on vessels associated with brain metastases, and if so, whether VCAM-1-targeted MRI enables early detection of these tumors. Early up-regulation of cerebrovascular VCAM-1 expression was evident on tumor-associated vessels in two separate murine models of brain metastasis. Metastases were detectable in vivo using VCAM-1-targeted MRI 5 d after induction (<1,000 cells). At clinical imaging resolutions, this finding is likely to translate to detection at tumor volumes two to three orders of magnitude smaller (0.3-3 × 10(5) cells) than those volumes detectable clinically (10(7)-10(8) cells). VCAM-1 expression detected by MRI increased significantly (P < 0.0001) with tumor progression, and tumors showed no gadolinium enhancement. Importantly, expression of VCAM-1 was shown in human brain tissue containing both established metastases and micrometastases. Translation of this approach to the clinic could increase therapeutic options and change clinical management in a substantial number of cancer patients.

Micrometastatic disease and metastatic outgrowth: clinical issues and experimental approaches

Metastasis from the primary tumor to distant organs is the principal cause of mortality in patients with cancer. While prognostic factors can predict which patients are likely to have their cancer recur, these are not perfect predictors, and some patient's cancers recur even decades after apparently successful treatment. This phenomenon is referred to as dormancy. Data from experimental studies have revealed two categories of metastatic dormancy: cellular dormancy, with solitary cancer cells in cell-cycle arrest; and micrometastatic dormancy, characterized by a balanced state of proliferation and apoptosis, but with no net increase in size. Development of new models and imaging techniques to track the fate of dormant cancer cells is beginning to shed some light on dormancy. Elucidation of the molecular pathways involved in dormancy will advance clinical understanding and may suggest new avenues for treatment to inhibit the revival of these dormant cells, thereby reducing cancer mortality rates.

Expression of melanocyte-related genes in human breast cancer and its implications

We report the expression of melanocyte-related genes (MRG) in freshly resected, histopathologically confirmed, human breast cancer specimens and describe experiments illuminating similar observations on a variety of breast cancer cell lines including MDA-MB-435. This finding has implications for research on breast cancer, for clinical investigation of cancer patients presenting with metastases from occult primary tumors and for understanding aberrant differentiation in cancer cells. For example, higher expression of six MRG correlated inversely with propensity for metastatic spread in clones isolated from the human breast cancer cell line MDA-MB-435. Comparisons of MRG expression in cells growing in vitro with those seen in tumors generated by the same lines in vivo showed that the levels of activity of these genes are influenced by the surrounding environment. Also, silencing of expression of the melanocyte-related transcription factor MITF, by transduction of the non-metastatic clone NM2C5 with a construct expressing a specific anti-MITF shRNA, resulted in decreased production of 5 of the melanocyte-related proteins including TYRP1, Pmel 17, MART 1(Melan-A) and TYRP2, but no increase in metastatic capability. Hence MRG expression reproducibly ear-marked, but did not cause, metastatic incompetence. We also report cytogenetic and other data that conflict with the recent suggestion that MDA-MB-435 is of melanocytic origin and are more consistent with its original designation as being of mammary lineage. We conclude that detection of MRG expression profiles in freshly excised breast cancers and in cultured breast cancer cells reflects the operationally important clinical phenomenon of inappropriate gene expression in malignant neoplasms. Concomitantly, we suggest that the evidence we have obtained (i) collectively supports the continued widespread use of the MDA-MB-435 cell line in breast cancer and metastasis research and (ii) advances knowledge of the diversity of aberrant differentiation programs in malignant cells, which is valuable for making accurate diagnoses and treatment decisions in clinical oncology.

Osteopontin gene expression determines spontaneous metastatic performance of orthotopic human breast cancer xenografts

A major problem in the therapeutic management of cancer is the growth of metastases in distant organs, but the genes orchestrating the process need to be identified for the rational design of new treatment. Here, we provide decisive experimental evidence demonstrating the causal involvement of a specific gene, osteopontin (OPN), in the pathogenesis of metastasis by human breast cancer cells and implicating some of its probable partners. Stable long-term depletion, or up-regulation, of OPN gene expression in a matched, isogenic pair of human breast cancer cell lines of differing metastatic proficiency reproducibly changed their ability to colonize distant organs. OPN down-regulation was achieved by transduction of the metastatic line with a DNA construct encoding a small hairpin RNA in a vector labeled with red fluorescent protein and resulted in a marked reduction of metastatic load (P < 0.01). Up-regulation of OPN in the negligibly metastatic line, with a green fluorescent protein-marked retroviral vector containing OPN cDNA driven by a strong promoter, resulted in heavy colonization of the lungs and lymph nodes (P < 0.005). The reciprocal changes in behavior of these matched cell lines cross-corroborate each other. Concomitant changes were seen in the expression of other metastasis-related genes in both modulated lines. The data indicate that therapeutic targeting of tumor OPN molecules could reset metastatically relevant gene networks, resulting in clinical benefit.

Gene expression profiling of human lymph node metastases and matched primary breast carcinomas: clinical implications

The genetic program that drives tumor metastasis and the mode and timing of its initiation are of great practical significance to clinical management. Modern technical advances open new opportunities for gaining useful relevant information. Gene expression profiles of histologically-verified viable tissue from lymph node metastases were compared with those of matched primary breast cancers from 10 different patients, among samples from over 400 cases, using high-throughput oligonucleotide arrays comprising probes for 22,000 genes. It was observed that metastases have very similar expression signatures to their parent tumors. However, detailed computational analysis revealed that a small number of genes were consistently differentially expressed between 100% of tumors and metastases, suggesting that these are mechanistically important. Lists of such candidate genes, of potential clinical interest, are provided. We interpret these results in the framework of a meta-analysis of previous investigations by others and ourselves and of existing clinical knowledge on the behavior of human tumors. The collective data show that metastases resemble their primary tumors but the signatures obtained in different studies are not sufficiently reproducible or informative to be prognostically useful, although they do give valuable insights into the pathogenesis and biology of human tumor metastasis. The findings indicate that the genetic program encoding metastasis is implemented progressively over time although, occasionally, this evolution can occur rapidly, early in the life of the neoplasm. The important clinical significance of this deduction is that, in most patients, early detection provides time for appropriate therapeutic intervention to be effective in obstructing metastasis.

Expression of coxsackie and adenovirus receptor reduces the lung metastatic potential of murine tumor cells

The coxsackie and adenovirus receptor (CAR) is involved in the epithelial cell tight junction, the downregulated expression of which is observed in different cancer types. In the present study, we examined CAR's role in tumor metastasis using a B16 melanoma and CT26 colon adenocarcinoma model of experimental metastasis. In lung metastasis, the colony number of B16 cells stably expressing CAR (B16CAR) was significantly lower than that of the control CAR-negative B16 cells. B16 and CT26 cells transiently expressing CAR, which were transduced with adenovirus (Ad) vector expressing CAR, also reduced lung metastasis, suggesting that CAR plays a role in the early stage of metastasis. CAR expression significantly decreased the accumulation of B16 cells in the lung after i.v. injection and the migration in vitro. CAR expression reduced expression of alpha(v), alpha(4), beta(3) and beta(1) integrin, which play important roles in attachment to cells or basement membrane. Thus, CAR expression likely acts as a metastatic suppressor.

Dormant cancer cells retrieved from metastasis-free organs regain tumorigenic and metastatic potency

This study shows that solitary, dormant human cancer cells, retrieved from metastasis-free organs of animals carrying spontaneously metastatic primary tumors, can reactivate their tumorigenic and metastatic potency. The tumors were produced by MDA-MB-435 CL16 breast cancer cells permanently labeled with green fluorescent protein and the neomycin resistance gene. This enabled unequivocal identification of tumor cells emerging from organ explants cultured in neomycin to eliminate nonneoplastic host cells. Rescued cells resumed proliferation and generated lines that were tumorigenic and metastatic in fresh animals. All resulting primary and secondary tumors were uniformly labeled. Cells recovered from bone marrows and spleens, where there were no metastases, were as tumorigenic and metastatic as cells recovered from lungs and lymph nodes, which are the preferred sites of colonization for this tumor line. This evidence that malignant growth of disseminated cancer cells is suspended indefinitely by microenvironmental conditions in metastasis-free organs, although it is still active in others of the same host, shows that neoplastic progression can be arrested and has far-reaching biological and clinical implications. Specifically, it predicts the existence of natural, nonimmune host mechanisms that stimulate or inactivate tumor growth in different anatomical sites, which may be exploitable for therapeutic benefit.

Tumor-stromal interactions reciprocally modulate gene expression patterns during carcinogenesis and metastasis

This study used a unique xenogeneic breast cancer model to study the effects of tumor cells and neighboring host cells upon each other in tumor growth and metastasis. It exploited species differences between the interacting components to determine how the host influenced the tumor and vice versa. It was found that the gene expression profiles of highly and poorly metastatic clones from the same human breast carcinoma changed differentially when the cells were transferred from growth in vitro to the mammary gland. We describe novel sets of genes, validated by human-specific probes, which were induced in the 2 isogenic, but phenotypically different, tumor lineages by the mammary environment. Conversely, the tumor cells also induced changes in gene expression in the neighboring host stromal (i.e., mesenchymal) cell lineages, validated by mouse-specific probes. Reciprocal inductive interactions were also demonstrated in the tumor deposits formed preferentially in the lungs and lymph nodes by the highly metastatic tumor cells. Subtraction of the induced gene changes in the primary site from those in the metastases revealed that the number and magnitude of specific gene inductions in colonized organs were moderate. This finding indicates that the gene expression program causing metastasis has only limited flexibility and fits well with clinical observations that tumor cells form metastases preferentially in select organs, although tumor cells are scattered ubiquitously. This dependency on suitable host niches suggests new molecular therapeutic avenues that target genes in the host-support system that is manipulated by the malignant cells.

Expression profiling of primary tumors and matched lymphatic and lung metastases in a xenogeneic breast cancer model

Using a purpose-designed experimental model, we have defined new, statistically significant, differences in gene expression between heavily and weakly metastatic human breast cancer cell populations, in vivo and in vitro. The differences increased under selection pressures designed to increase metastatic proficiency. Conversely, the expression signatures of primary tumors generated by more aggressive variants, and their matched metastases in the lungs and lymph nodes, all tended to converge. However, the few persisting differences among these selectively enriched malignant growths in the breast, lungs, and lymph nodes were highly statistically significant, implying potential mechanistic involvement of the corresponding genes. The evidence that has emerged from the current work indicates that selective enhancement of metastatic proficiency by serial transplantation co-purifies a subliminal gene expression pattern within the tumor cell population. This signature most likely includes genes participating in metastasis pathogenesis, and we document manageable numbers of candidates for this role. The findings also suggest that metastasis to at least two different organs occurs through closely similar genetic mechanisms.

Tumor–host interactions contribute to the elevated expression level of α1-antichymotrypsin in metastatic breast tumor xenografts

We investigated alpha1-antichymotrypsin (ACT) gene expression in xenograft tumors generated by two isogenic human breast cancer cell lines derived from the same parent, MDA-MB-435, which display opposite metastatic behaviors. Microarray and real-time PCR experiments showed an overexpression of this serine protease inhibitor in the metastatic tumors (M-4A4T) and its derived metastases (M4-Mets) compared with the weakly metastatic tumors (NM-2C5T), and its release into the blood was confirmed by western-blotting. However, functional assays in vivo using genetically engineered tumor cells demonstrated that ACT up-regulation was not, by itself, responsible for the metastatic phenotype. We also made observations that ACT gene regulation was sensitive to tumor-host interactions: inoculation of these lines into the mouse mammary gland greatly increased ACT production and accentuated the intrinsic difference observed when they are cultured in vitro. Sensitivity of tumor cells to their environment was further analyzed by in vitro experiments, which demonstrated that a purified ECM environment and soluble components from normal host mammary cells were both able to significantly promote ACT expression. In addition, we took advantage of the xenogeneic nature of the model to measure ACT expression by the host cells (mouse) and the tumor cells (human) within the neoplasm using species-specific primers in real-time PCR experiments. It was found that the presence of tumor cells, irrespective of their metastatic capabilities, induced local ACT production by host cells at the primary and secondary tumor sites. Thus, this work indicates that there is a specific association of ACT overexpression with the metastatic phenotype in our breast cancer metastasis model. Moreover, because of the xenogeneic nature of our system, we were able to provide evidence of tumor-host reciprocal regulation of ACT production.

Altered metastatic behavior of human breast cancer cells after experimental manipulation of matrix metalloproteinase 8 gene expression

Previous work in our laboratory led to the cloning, from the same parent tumor cell line (MDA-MB-435), of two human breast cancer cell lines (M-4A4 and NM-2C5) with opposite metastatic phenotypes. Additional investigations revealed that the nonmetastatic cell line NM-2C5 overexpressed the neutrophil collagenase, matrix metalloproteinase (MMP)-8, relative to its partner. Because other studies have implicated the MMP family in promoting tumor metastasis, we investigated the apparently paradoxical expression of MMP-8 in these cell lines. By genetic engineering, we inverted its relative levels of expression in the two partners and studied the effects on the behavior of the tumors that they generated in athymic mice. Knock-down of expression in NM-2C5 cells by transduction with a sequence encoding a specific ribozyme and overexpression of MMP-8 in M-4A4 cells by retroviral transduction both strikingly changed metastatic performance in opposite directions, indicating that this gene plays a role in the regulation of tumor metastasis.

Soluble adhesion molecules (E-selectin, ICAM-1 and VCAM-1) in breast carcinoma

Adhesion molecules are important in cell-cell and cell-basement membrane interactions. They are intimately involved in inflammatory reactions and a role in tumour progression has been postulated. E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) play a role in cell adhesion to the vascular endothelium, and may have a role in tumour cell dissemination. Soluble forms of these molecules have been described and this study was established to examine these adhesion molecules in patients with breast carcinoma. Serum was obtained from 92 patients with breast carcinoma and 31 age-matched patients with benign breast disease. All samples were obtained prior to surgery. Soluble levels of E-selectin, ICAM-1, and VCAM-1 were significantly elevated in patients with Stage 4 disease compared with controls. (E-selectin 88.6 (47.9) versus 51.4 (18.4) ng/ml; P<0.001: ICAM-1 447 (249) versus 244 (79) ng/ml; P<0.001: VCAM-1 779 (159) versus 552 (135) ng/ml; P<0.001 results expressed on mean (SEM) SD placed above this.). The prognostic value of the adhesion molecules was examined. In patients with Stage 2 disease, elevated VCAM-1 was predictive of decreased survival, even when corrected for T and N status. Adhesion molecules are elevated in patients with advanced disease and elevation in VCAM-1 has prognostic significance in patients with breast carcinoma.

PTEN expression is maintained in sporadic colorectal tumours

Loss of PTEN (phosphatase and tensin homologue deleted from chromosome 10) function has been implicated in the progression of several types of cancer. Allele loss close to the PTEN locus occurs in sporadic colon cancer and germline PTEN mutations cause Cowden disease, an inherited cancer syndrome characterized by an increased incidence of gastrointestinal tract lesions that can progress to colorectal carcinoma. However, although PTEN is a good candidate for involvement in the pathogenesis of sporadic colon cancer, previous analyses have not revealed a high frequency of somatic mutations in colorectal tumours. Alternative mechanisms which could lead to a loss of PTEN expression in colon cancer have not been investigated. This study monitored PTEN mRNA and protein levels in a panel of 50 tumour tissues obtained from 35 patients with sporadic colon cancer. RT-PCR and immunohistochemistry were used to evaluate the expression of mRNA and protein, respectively, in normal, adenoma and adenocarcinoma colorectal tissues as well as in metastatic lesions. To overcome the problem of heterogeneity and normal stromal cell contamination in homogenized tissue specimens, specific cell types were isolated by microdissection prior to PCR analysis. No loss of PTEN expression was evident in any of the colon tissues examined. PTEN protein was localized exclusively in the cytoplasm of normal and tumour cells and no correlation of immunostaining intensity and tumour stage or grade was revealed. As with previous deletion and mutation analyses, the present study suggests that loss of PTEN expression is not prevalent in sporadic colon cancer.

Adoptive transfer of human natural killer cells in mice with severe combined immunodeficiency inhibits growth of Hsp70-expressing tumors

In vitro, tumor-selective Hsp70 plasma membrane localization correlates with increased sensitivity to lysis mediated by a subpopulation of human natural killer (NK) cells that adhere to plastic following cytokine stimulation. In the present study, we analyzed the capacity of adoptively transferred human NK cells in SCID/beige mice for local tumor control and prevention of metastatic dissemination of Hsp70-expressing CX(+) and non-expressing CX(-) tumors following orthotopic (o.t.) injection. Both tumor sublines were derived by cell sorting of the original cell line, CX2, and thus exhibit an identical MHC and adhesion molecule expression pattern but differ with respect to Hsp70 plasma membrane expression. Viability of adherent, human NK cells in SCID/beige mice up to 18 days and the capacity to migrate have been demonstrated. Growth of Hsp70-expressing and non-expressing CX(+) and CX(-) tumor cells was completely suppressed when 10 x 10(6) NK cells were injected into the i.p. cavity on day 4 after inoculation of 2.5 x 10(6) tumor cells. Although a single injection of 5 or 2.5 x 10(6) NK cells was not sufficient to suppress tumor growth completely in all mice, the reduction in size of CX(+) tumors was significantly greater than that of CX(-) tumors. To mimic the clinical situation, ex vivo stimulated NK cells were injected i.v. on day 4 after o.t. injection of tumor cells. Under these conditions, growth of Hsp70-expressing primary tumors and metastases was suppressed. If CX(-) tumor cells were injected, 3 of 9 mice developed Hsp70-negative primary tumors. However, none of these mice developed distant metastases. In summary, our data indicate that Hsp70 acts as a recognition structure for adherent NK cells in a SCID/beige mouse model.

Cell adhesion molecules and intermediate filaments on embryonal childhood tumors

We describe the expression of 18 different cell adhesion molecules, intermediate filaments and Ki-67 antigen in embryonal childhood tumors. 5 microns frozen sections from 15 nephroblastomas, 13 neuroblastomas, six rhabdomyosarcomas, one Ewing sarcoma and one pulmonary blastoma were analyzed by the alkaline phosphatase anti-alkaline phosphatase (APAAP) method using murine monoclonal antibodies. All tumors exhibited high proliferation rates as did, surprisingly, the nephroblastoma specimens despite pre-treatment with chemotherapy. Polysialylated NCAM was demonstrated on all tumor types, but Ewing sarcoma and expression correlated inversely with cell differentiation. In contrast, E-cadherin was present solely on tubulus like cells in nephroblastomas. This cell type showed a coexpression of cytokeratin and vimentin, giving evidence of its intermediate position between the mesenchyme and epithelium. In neuroblastomas, CD44s (hyaluronate receptor) expression was increased with cell differentiation. ICAM-1, VCAM-1 and E-selectin were mostly expressed in regressive areas of pretreated nephroblastoma specimens where a considerable infiltration of leukocytes was noted as well. Since endothelial and leukocyte adhesion molecules were distinctly less expressed in all other tumors investigated, these findings may indicate immunological processes as a consequence of or as supplement to the chemotherapeutical effect on nephroblastoma cells. Integrin receptors were not found on the surface of tumor cells, and therefore, at least those investigated seem to be of secondary importance to the biology of the tumors studied herein. In conclusion, our investigations demonstrate that, besides achieving a secure and prompt differentiation between various embryonal tumors, applying the panel of monoclonal antibodies proposed herein gives interesting insights into the histogenesis, biology and metastatic potential of pediatric malignancies.

Differential Hsp70 plasma-membrane expression on primary human tumors and metastases in mice with severe combined immunodeficiency

To study the role of cell-surface expression of a tumor-selective heat-shock protein 70 (Hsp70) in vivo, the colon-carcinoma cell line CX2, and the clonal sub-lines CX+ and CX-, which differ in Hsp70 cell-surface expression, but not in MHC and adhesion-molecule expression, were implanted into immunodeficient SCID/beige mice by s.c., i.p., i.v. and orthotopic (o.t.) inoculation. On day 18 after s.c. injection, all animals developed s.c. tumors, ranging in size from 2.5 to 3 cm2. Phenotypic characterization of single-cell suspensions generated from freshly isolated tumor material revealed that the pattern of cell-surface expression is identical to that of the injected tumor cells from cell culture. Comparable results were obtained following i.p. inoculation of CX+ and CX- cells. Macroscopic and microscopic evaluation of lymph nodes, lung, liver and spleen at autopsy of tumor-bearing mice showed no tumor burden except the primary tumor, following s.c. or i.p. injection. After i.v. inoculation of CX+ and of CX- cells, weak tumor growth was observed in lung and liver, the Hsp70 cell-surface-expression pattern on these tumors being identical to that of the injected cells. However, o.t. injection of colon-carcinoma cell lines CX+ and CX- into the cecum resulted in tumor growth at the injection site and in spread of distant metastases in lung, liver and spleen. Most interestingly, and in contrast to the primary colon carcinomas, metastases of CX+ and of CX- tumor cells both revealed strong Hsp70 plasma-membrane expression, although the total amount of cytoplasmic Hsp70 was comparable.

The disintegrin eristostatin interferes with integrin alpha 4 beta 1 function and with experimental metastasis of human melanoma cells

Peptides containing the integrin recognition sequence, RGD, can inhibit experimental metastasis of mouse melanoma cells, but the integrin(s) affected in these experiments is unknown. Besides "classical" RGD-binding integrins such as alpha 5 beta 1 and alpha v beta 3, RGD has been reported to bind alpha 4 beta 1, and mAbs to alpha 4 beta 1 can inhibit melanoma metastasis. We investigated the mode of action of the disintegrin eristostatin, an RGD-containing peptide isolated from snake venom, in a human melanoma experimental metastasis model. Lung colonization following i.v. injection of MV3 cells in nude mice was strongly inhibited by eristostatin. MV3 cells bound FITC-eristostatin and adhered to eristostatin-coated wells. This adhesion was partially inhibited by a GRGDSP peptide and by alpha 4 mAb. Binding of FITC-eristostatin to Jurkat cells and adhesion of Jurkat (but not K562) cells to eristostatin-coated wells further suggested that eristostatin binds alpha 4 beta 1, even though, again, alpha 4 mAb only partially inhibited adhesion. Expression of alpha 4 beta 1 was enhanced in metastatic melanoma cells compared to normal melanocytes and nonmetastatic melanoma cells. Finally, eristostatin inhibited adhesion of both MV3 and CHO alpha 4 cells to the alpha 4 beta 1-ligand VCAM-1, while adhesion to other ligands via other integrins was not affected. These findings demonstrate that inhibition of melanoma cell metastasis by RGD-containing peptides such as eristostatin, may be due to interference with alpha 4 beta 1-VCAM binding, in addition to inhibition of the classical RGD-binding integrins.

Orthotopic engraftment of human lung tumours in SCID mice for the study of metastasis

This study presents a new technique for the orthotopic engraftment of human lung tumours in SCID mice and demonstrates the importance of a more clinically relevant route of tumour propagation for the study of metastatic potential. The orthotopic engraftment of human lung tumour biopsy specimens was performed via an anterior thoracotomy into SCID mice. Engraftment of non-small cell lung cancer specimens from nine patients into 52 SCID mice yielded a 31% engraftment rate and a 50% metastasis rate. Unlike subcutaneous inoculation, the engraftment rates following the orthotopic inoculation did not vary between squamous cell carcinomas and adenocarcinomas. Direct visceral pleural invasion was seen in most cases. Orthotopically placed tumours grew 5-fold by 4 to 6 months. Unique to this model was the observation of metastasis to clinically relevant sites, such as the adrenal gland and supraclavicular lymph nodes. Contralateral lung metastases were also noted in 37.5%, and one ovarian metastasis occurred. The procedure was well tolerated, with survival rates of 98%.

Ectopic expression of human and feline CD9 in a human B cell line confers beta 1 integrin-dependent motility on fibronectin and laminin substrates and enhanced tyrosine phosphorylation

Few molecules have been shown to confer cell motility. Although the motility-arresting properties of anti-CD9 monoclonal antibody (mAb) suggest the transmembrane 4 superfamily (TM4SF) member CD9 can induce a motorgenic signal, gene transfection studies have failed to confirm this hypothesis. We report here that ectopic expression of human CD9 (CD9h) and feline CD9 (CD9f) in the CD9-negative, poorly motile, human B cell line Raji dramatically enhances migration across fibronectin- and laminin-coated polycarbonate filters. Migration of Raji/CD9h and Raji/CD9f on either substrate was inhibited by the anti-CD9 mAb 50H.19 and by the anti-beta 1 integrin mAb AP-138. Migration of Raji/CD9h on laminin was potently inhibited by the anti-VLA-6 integrin mAb GoH3 and by the anti-VLA-4 integrin mAb 44H6, whereas migration of Raji/CD9h on fibronectin was inhibited only by mAb 44H6. Since CD9h-transfected Raji cells adhered to fibronectin as effectively as mock transfectants, expression of CD9 enhanced motility, but not adhesion. CD9-enhanced migration was inhibited by the protein tyrosine kinase inhibitor herbimycin A suggesting that tyrosine phosphorylation played a role in the generation of a motorgenic signal. Raji/CD9h transfectants adherent to fibronectin expressed 6-fold higher levels of phosphotyrosine than Raji. Raji/CD9f transfectants also phosphorylated proteins on tyrosine more effectively than Raji including a protein of 110 kDa which was phosphorylated on the motility-inducing substrates laminin and fibronectin, but not on bovine serum albumin. Our results support a role for CD9 in the amplification of a motorgenic signal in B cells involving beta 1 integrins and the activation of protein tyrosine kinases.

Aspartate 698 within a novel cation binding motif in alpha 4 integrin is required for cell adhesion

The interactions of alpha 4 beta 1 integrin with vascular cell adhesion molecule (VCAM) and fibronectin play important roles in many physiological and pathological processes. To understand the mechanism of alpha 4 beta 1 integrin-mediated cell adhesion, we made mutant alpha 4 constructs. Three aspartic acid (Asp) residues in alpha 4, Asp-489, Asp-698, and Asp-811, were replaced with glutamic acids (Glu). The wild-type and mutant alpha 4 constructs were transfected into K562 cells, and stable transfectants with similar levels of alpha 4 surface expression were established. The Asp-->Glu substitutions did not affect alpha 4 beta 1 association or heterodimer formation as demonstrated by immunoprecipitation analysis. However, the glutamate substitutions at Asp-489 and Asp-698 severely impaired cell adhesion to VCAM and fibronectin, whereas the substitution at Asp-811 had no detectable effect on cell adhesion. In contrast to these results, isolated alpha 4 beta 1, containing the D489E or D698E substitution, was able to bind to VCAM, suggesting that these two residues are not critical for ligand recognition. In searching for a mechanism to explain inhibition of adhesion by Asp-489 and Asp-698 mutations, we found that the sequences flanking Asp-698 resemble the DxxxxxD-S-Sx divalent cation/ligand binding motif in beta integrins and the I-domains of alpha integrins. This suggests that Asp-698 in the alpha 4 integrin, which does not possess an I-domain, may also be involved in cation binding and may be part of a sequence functionally similar to that found in the I-domains of other alpha integrins.

The role of alpha 4 beta 1 integrin in cell motility and fibronectin matrix assembly

The alpha 4 beta 1 integrin has been suggested to play important roles in embryogenesis and pathogenesis of many diseases which involve both cell adhesion and cell migration. Previous studies using anti-alpha 4 beta 1 antibodies and fibronectin (Fn) fragments have suggested that alpha 4 beta 1 integrins may be involved in cell motility on Fn and vascular cell adhesion molecule-1 (VCAM-1). However, the cells used in these studies also express other Fn integrin receptors including alpha 5 beta 1 integrin, which is known to function in cell motility on Fn. To test whether alpha 4 beta 1 integrins mediate cell motility on Fn and VCAM-1 in the absence of alpha 5 beta 1 integrin, we expressed human alpha 4 integrin in a Chinese hamster ovary (CHO) cell line that is deficient in alpha 5 beta 1 integrin (CHO B2). The parental alpha 5 deficient CHO B2 cells were unable to adhere, spread or migrate on Fn, nor could they assemble a fibrillar Fn matrix. Expression of alpha 4 beta 1 integrin in the CHO B2 cells enabled the cells to adhere, spread and migrate on Fn and on VCAM-1 but not to assemble a fibrillar Fn matrix. The cellular processes mediated by the interaction of alpha 4 beta 1 with Fn or VCAM-1 were inhibited by the CS1 peptide derived from the major alpha 4 beta 1 binding site on Fn. These findings demonstrate that alpha 4 beta 1 integrins not only function as cell adhesion receptors but also as cell motility receptors for Fn and VCAM-1 independent of alpha 5 beta 1. Moreover, they reveal important functional differences between Fn binding integrins. The alpha 4-positive, alpha 5-negative CHO cells described in this report will be useful tools in studying the mechanism of molecular signalling during integrin mediated cellular processes.

Recent advances in the study of tumour invasion and metastasis

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Deranged activity of the CD44 gene and other loci as biomarkers for progression to metastatic malignancy

About one in three people in modern industrialised countries die of the consequences of malignant tumours or are found to carry an unsuspected one at the time of autopsy. Early resection of such lesions and appropriate adjuvant therapy is very effective in curing the disease. There is therefore a strong clinical incentive to find effective methods of early diagnosis, assessment of prognosis and treatment of neoplastic lesions and research on this topic is directed at a numerically significant medical problem. Recently it has been found that many human tumours show severe abnormalities in the expression of the CD44 gene which increase with progression to metastatic malignancy. By alternative splicing mechanisms this gene codes for a family of heavily glycosylated cell surface proteins involved in many important cellular activities. In neoplasia there is gross overexpression of various products of the gene associated with disorderly splicing, which can be detected in clinical samples with the sensitive technique of reverse transcription-polymerase chain reaction (RT-PCR). These disturbances begin early in the neoplastic process and can be detected in very small biopsy samples. It has also been shown that it is possible to achieve non-invasive diagnosis of malignancy by analysis of CD44 expression in exfoliated cells in body fluids and waste products. The potential significance of these observations for early diagnosis of symptomatic cancer and for screening of the population for asymptomatic lesions are readily seen and await further investigation. Separate work in our laboratory has succeeded in DNA-mediated transfer of metastatic capability through two rounds of transfection into non-metastatic tumour cells and a metastasis-associated human DNA fragment has been recovered from the transfectants and sequenced. Using primers designed to anneal to a coding region identified by computer analysis within the novel sequence, it has been shown with RT-PCR that it is heavily expressed in metastatic cancer tissues, but not in corresponding normal ones. This could be of value in assessing the prognosis of patients using small biopsy samples from their primary tumours and the potential of this sequence for such purposes and for possible therapeutic intervention is currently being explored. Recent work in several laboratories has shown that elevated expression of certain other specific growth factor genes, including c-met and EGFR, correlates with metastatic capability. Combined evaluation of such markers in further studies will in time give useful information on the prognosis of individual patients to guide therapeutic decisions and the implications of these recent advances for clinical practice and future research are discussed below.