Molecular mechanisms of cell adhesion in normal and transformed cells

In vitro mesenchymal-epithelial transition in NIH3T3 fibroblasts results in onset of low-dose radiation hypersensitivity coupled with attenuated connexin-43 response

BACKGROUND

Mesenchymal-to-epithelial transition (MET) is associated with altered cell adhesion patterns. Independent studies showed that cellular adhesion regulates low-dose hyper-radiosensitivity (HRS), a phenomenon reported widely in tumour cells. Therefore, present study aimed to investigate whether MET and associated cellular adhesion alterations affect cellular radiosensitivity.

METHODS

We established multiple stages of MET by in vitro transformation of NIH3T3 mouse embryonic fibroblasts. Nutritional deprivation followed by repetitive treatment cycles of 3-methylcholanthrene and phorbol-12-myristate-13-acetate with frequent isolation of foci established three progressive strains (NIH3T3.1, NIH3T3x3, NIH3T3x8x3) depicting MET, and one strain (NIH3T3x12) with partial reversion. Alterations in morphology, cell adhesion properties, expression/intracellular localization of cell adhesion proteins, microRNA expression and cellular radiosensitivity were studied in these stably transformed cell strains.

RESULTS

All four transformants had increased proliferation rate, saturation density, bipolarity, E-cadherin expression; coupled with reduced cell size/spreading, pseudopodia/migration, and fibroblast marker protein and vimentin. The most aggressive trans-differentiated (phenotypically epithelial) cell strain, NIH3T3x8x3 acquired ~30% higher growth potential associated with more than two-fold reduction in cell size and migration. These phenotypic changes accompanied ~40% reduction in endogenous or radiation-induced connexin-43 expression/mitochondrial translocation. Incidentally, all three progressive strains displayed prominent HRS (α_s/α_r: 7.95-37.29) whereas parental (NIH3T3) and reverting (NIH3T3x12) strains lacked HRS and had distinct radiation-induced Cx43 translocation into mitochondria.

CONCLUSION

Our study shows that trans-differentiating fibroblasts progressively acquiring epithelial features during MET process, display low-dose hyper-radiosensitivity associated with altered Cx43 behaviour.

GENERAL SIGNIFICANCE

This study demonstrates that MET progression triggers low-dose hyper-radiosensitivity in trans-differentiating cells, which has significant therapeutic implications.

The combined expression of metaplasia biomarkers predicts the prognosis of gastric cancer

BACKGROUND

Our previous study indicated that gene expression profiling of intestinal metaplasia (IM) or spasmolytic polypeptide-expressing metaplasia (SPEM) can identify useful prognostic markers of early-stage gastric cancer, and seven metaplasia biomarkers (MUC13, CDH17, OLFM4, KRT20, LGALS4, MUC5AC, and REG4) were selectively expressed in 17-50% of gastric cancer tissues. We investigated whether the combined expression of these metaplasia biomarkers could predict the prognosis of advanced stage gastric cancer.

METHODS

The expression of seven metaplasia biomarkers was evaluated immunohistochemically using tissue microarrays comprised of 450 gastric cancer patients. The clinicopathologic correlations and the prognostic impact were analyzed according to the expression of multiple biomarkers.

RESULTS

MUC13, CDH17, LGALS4, and REG4 were significant prognostic biomarkers in univariate analysis. No expression of four markers was found in 56 cases (14.2%); 1 marker was seen in 67 cases (17%), 2 in 106 cases (27%), 3 in 101 cases (25.7%), and 4 in 63 cases (16%). Patients in which two or fewer proteins were expressed (group B) showed younger age, undifferentiated or diffuse type cancer, larger tumor size, larger number of metastatic lymph nodes, and more advanced stage than those in which three or more proteins were expressed (group A). In undifferentiated or stage II/III gastric cancer, the prognosis of group B was significantly poorer than that of group A by multivariate analysis.

CONCLUSIONS

The combined loss of expression of multiple metaplasia biomarkers is considered an independent prognostic indicator in undifferentiated or stage II/III gastric cancer.

Adhesion mechanisms in embryogenesis and in cancer invasion and metastasis

Cell-substratum and cell-cell adhesion mechanisms contribute to the development of animal form. The adhesive status of embryonic cells has been analysed during epithelial-mesenchymal cell interconversion and in cell migrations. Clear-cut examples of the modulation of cell adhesion molecules (CAMs) have been described at critical periods of morphogenesis. In chick embryos the three primary CAMs (N-CAM. L-CAM and N-cadherin) present early in embryogenesis are expressed later in a defined pattern during morphogenesis and histogenesis. The axial mesoderm derived from gastrulating cells expresses increasing amounts of N-cadherin and N-CAM. During metamerization these two adhesion molecules become abundant at somitic cell surfaces. Both CAMs are functional in an in vitro aggregation assay; however, the calcium-dependent adhesion molecule N-cadherin is more sensitive to perturbation by specific antibodies. Neural crest cells which separate from the neural epithelium lose their primary CAMs in a defined time-sequence. Adhesion to fibronectins via specific surface receptors becomes a predominant interaction during the migratory process, while some primary and secondary CAMs are expressed de novo during the ontogeny of the peripheral nervous system. In vitro, different fibronectin functional domains have been identified in the attachment, spreading and migration of neural crest cells. The fibronectin receptors which transduce the adhesive signals play a key role in the control of cell movement. All these results have prompted us to examine whether similar mechanisms operate in carcinoma cell invasion and metastasis. In vitro, rat bladder transitional carcinoma cells convert reversibly into invasive mesenchymal cells. A rapid modulation of adhesive properties is found during the epithelial-mesenchymal carcinoma cell interconversion. The different model systems analysed demonstrate that a limited repertoire of adhesion molecules, expressed in a well-defined spatiotemporal pattern, is involved in tissue formation and in key processes of tumour spread.

An anti-invasive concentration of the alkyl-lysophospholipid ET-18-OCH3 enhances the motility of embryonal chick heart cells cultured on solid substrate

Pretreatment of embryonal chick heart fragments with ET-18-OCH3 is known to induce resistance to invasion by several malignant cell lines. Embryonal chick heart fragments or cell suspensions prepared from such fragments were explanted on solid substrate and treated in medium with 10 micrograms/ml ET-18-OCH3 or with drug-free medium (control) for 48 h. This medium was washed away and replaced by drug-free fresh medium. Twenty-four to 48 h later the fast plasma membrane movements (involved in ruffling, blebbing, fast shape change and fast translocation) were quantified using a simple method based on subtracting two video images taken with an interval of 28 s. The ET-18-OCH3-treated cells showed a higher intensity of fast plasma membrane movements than control cells. Cells around a treated explant did not show the same radial alignment as in controls, suggesting loss of contact inhibition of movement. Cells from a cell suspension derived from a treated fragment showed faster translocation on solid substrate and faster shape change. We speculate that increased motility of host cells may be involved in resistance to invasion.

Increasing N-CAM-mediated cell-cell adhesion does not reduce invasion of RSV-transformed WC5 rat cerebellar cells

The WC5 rat cerebellar cell line, infected with a Rous sarcoma virus (RSV) that is temperature-sensitive for pp60v-src transformation, expresses high levels of the neural cell adhesion molecule, N-CAM, when grown at the non-permissive temperature for pp60v-src activity. At the permissive temperature, N-CAM expression is 4- to 10-fold reduced and the cells aggregate poorly. To evaluate the effects of variations in N-CAM expression, we compared the invasive ability of transformed WC5 cells that express low levels of N-CAM with transformed cells in which N-CAM-mediated adhesion was restored. WC5 cells were transfected with expression vectors containing cDNAs encoding the 120 or 180 kDa forms of chicken N-CAM linked to constitutive promoters. Several permanently transfected lines that expressed chicken N-CAM at the cell surface were isolated. These cell lines showed enhanced aggregation at the permissive temperature relative to untransfected WC5 cells or cells transfected with control constructs. By comparing the ability of control and transfected WC5 cells to invade reconstituted extracellular matrix, we tested the effect of variations in N-CAM-mediated adhesion on invasion. Clones that expressed high levels of N-CAM showed invasion rates that were similar to control cells, indicating that increasing N-CAM-mediated adhesion does not inhibit the invasiveness of RSV-transformed WC5 cells.

Role of the host tissue in the anti-invasive activity of the alkyllysophospholipid, ET-18-OCH3, in vitro

The alkyllysophospholipid, racemic-l-O-octadecyl-2-O-methylglycero-3- phosphocholine (ET-18-OCH3) was previously shown to inhibit invasion of malignant cells into precultured heart fragments (PHF) in vitro. In particular, pretreatment of PHF with 10 micrograms ET-18-OCH3 for 48 h was sufficient to induce in the host tissue resistance towards invasion by mouse MO4 cells. Resistance was obvious when MO4 cells were confronted either immediately (the pretreatment experiment) or after withdrawal of the drug 7 days prior to confrontation (the reversibility experiment). In the present study, the survival of PHF cells in the pretreatment and reversibility experiments was similar to that of untreated PHF cells as determined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) test and by the PHF explantation test. The effective anti-invasive concentration was 6 micrograms/ml in the pretreatment experiment while 3 micrograms/ml was sufficient to inhibit invasion in the reversibility experiment. Induction of resistance towards invasion in pretreated PHF was shown to occur not only with MO4 cells but also with mouse LLC-H61 Lewis lung carcinoma and mouse BW-O-Li1 T-lymphoma cells. The increase in molecular weight of N-linked cell surface glycosylpeptides (N-GP) of PHF was apparent in the pretreatment experiment and was enhanced in the reversibility experiment. This effect was completely abolished in cells obtained from pretreated PHF which were converted into a cell suspension and further cultured as a monolayer on tissue culture plastic without drug for 7 days. The results reported here provide additional evidence for the causal involvement of N-GP of the PHF host tissue in the anti-invasive activity of ET-18-OCH3 in vitro.

Characterization of NCAM expression and function in BT4C and BT4Cn glioma cells

The neural cell adhesion molecule, NCAM, plays an important role in cell-cell adhesion. Therefore, we have studied NCAM expression in the glioma cell lines BT4C and BT4Cn. We demonstrate that the 2 cell lines differ in their metastatic ability; while BT4C cells have a very low capacity for producing experimental metastases, that of BT4Cn cells is high. In BT4C cells NCAM is synthesized as 4 polypeptides with Mr's of 190,000, 140,000, 115,000 and 97,000. The 140,000, 115,000 and 97,000 polypeptides are glycosylated and for the 140,000 and 115,000 polypeptides sulfatation is observed. Conversely, no NCAM protein synthesis is observed in BT4Cn cells, even though NCAM mRNA is expressed. Thus, development of an increased metastatic capacity is accompanied by the disappearance of NCAM protein expression in this model system. The functional importance of NCAM expression was studied by a cell-substratum binding assay in which the binding of BT4C and BT4Cn cells to NCAM immobilized to glass was assessed. We found that BT4C cells adhere specifically to NCAM, and that adhesion is inhibited by anti-NCAM Fab'-fragments, while no specific binding of BT4Cn cells to NCAM was observed. The BT4C and BT4Cn cell lines thus constitute an important new model system for the study of tumor invasion and metastasis and of the role of cell adhesion molecules in these processes.

Organ specificity of tumor metastasis: role of preferential adhesion, invasion and growth of malignant cells at specific secondary sites

The locations of distant secondary tumors in many clinical cancers and animal tumors are nonrandom, and their distributions cannot be explained by simple anatomical or mechanical hypotheses based on the simple lodgment or trapping of tumor cell emboli in the first capillary bed encountered. Evidence from certain experimental tumor systems supports Paget's 'seed and soil' hypothesis on the nonrandom distributions of metastases, in which the unique properties of particular tumor cells ('seeds') and the different characteristics of each organ microenvironment ('soil') collectively determine the organ preference of metastasis. Experimentally, differential tumor cell adhesion to organ-derived microvessel endothelial cells and organ parenchymal cells, differential invasion of basement membranes and organ tissues, and differential responses to organ-derived growth-stimulatory and -inhibitory factors all appear to be important determinants in explaining the organ preference of metastasis. Each tumor system may achieve organ specificity because of its own unique set of multiple metastasis-associated properties and responses to host microenvironments. As neoplasms progress to more highly malignant states multisite metastases are more likely and organ-specific metastases may be masked or circumvented owing to stochastic events, tumor cell diversification, host selection processes, and increased production of tumor autocrine molecules that may modulate adhesion, invasion, growth, and other properties important in metastasis. The importance of each of these properties, however, appears to vary considerably among different metastatic tumor systems. These and other tumor cell and host properties may eventually be used to predict and explain the unique metastatic distributions of certain human malignancies.

Homing receptors and metastasis

As discussed in the preceding sections, there are several indications that the lymphocyte homing receptors involved in the normal process of lymphocyte recirculation are also relevant to the behavior of metastatic cells. Cell fusion experiments indicate that previously nonmetastatic cells can acquire metastatic capacity from fusion with normal lymphocytes. Murine T lymphomas that bear high levels of functional homing receptors can metastasize to peripheral lymphoid organs, whereas those lymphomas lacking homing receptors cannot. Virtually all lymph node metastases of lymphomas contain a high proportion of MEL-14hi cells, even if the primary tumor has been selected to be relatively deficient in these cells. Further investigations of the biology of lymphocyte homing receptors will reveal whether or not there are additional lymphocyte homing receptors and will clarify the role of lymphocyte homing receptors in metastasis. Antibodies against three lymphocyte homing receptors could therefore be useful for diagnosis and treatment of metastatic disease.

Effects of dimethyl sulfoxide (DMSO) on microfilament organization, cellular adhesion, and growth of cultured mouse B16 melanoma cells

Cell shape is involved in a variety of cellular activities including proliferation, adhesion, migration, and transformation. Agents known to promote differentiation, such as retinoic acid, butyrate, and dibutyryl cyclic AMP, induce marked alterations in cell shape which are often accompanied by changes in cell functions. In this paper we study the effects of the differentiating polar solvent dimethyl sulfoxide (DMSO) on cytoskeleton, adhesion, and growth properties of cultured mouse B16 melanoma cells. DMSO induced a progressive reorganization of the cytoskeleton which was fully developed in 4 days of continuous exposure to the agent. DMSO-treated cells developed thick and regularly oriented microfilament bundles of the stress fiber type ending at vinculin-rich areas of focal contact between the ventral membrane and the substratum (interference reflection microscopy-dark adhesion plaques). Such a rearrangement of the cytoskeleton resulted in increased adhesion to the substratum and inhibition of cell growth in comparison to control untreated cells. Cells which became highly flattened and tightly adherent after exposure to DMSO for 4 days progressively reverted their phenotype to that of control untreated cells within 3 days of DMSO withdrawal. Namely, they lost stress fibers and adhesion plaques, became rounded and less adherent, and increased their growth rate. These results indicate that DMSO can change the transformed appearance of B16 mouse melanoma cells to a phenotype which is typical of a variety of nontransformed cells in culture.

Bone metastases: pathogenesis, treatment, and rationale for use of resorption inhibitors

Tumors in bone are usually metastatic, with breast, prostate, and lung tumors accounting for more than 80 percent of clinically manifest lesions. Untreated, such metastases can produce the symptoms that most concern cancer patients--pain, pathologic fractures, and paralysis through epidural cord compression. Recent advances in the understanding of the metastatic cascade and the regulation of bone formation and resorption provide unique therapeutic approaches for prevention and treatment of these lesions. This article reviews the prevalence, distribution, diagnosis, and treatment of metastatic cancer in the skeleton, as well as the processes involved in the development of such metastases, the local mediators responsible for some of the destructive changes in bone, and their pathologic results. In addition to considering some of the conventional therapeutic approaches, a rationale for the use of bone resorption inhibitors, such as the diphosphonates (bisphosphonates), is presented for the prevention and amelioration of the pathologic consequences of skeletal metastases.