Mitomycin C and its analog trigger cytotoxicity in MCF-7 and K562 cancer cells through the regulation of RAS and MAPK/ERK pathways

Mitomycin C (MC) is an anti-cancer drug which functions by forming interstrand crosslinks (ICLs) between opposing DNA strands. MC analog, 10-decarbamoyl mitomycin C (DMC), unlike MC, has stronger cytotoxic effects on cancer cells with TP53 mutation. We previously demonstrated that MC/DMC could activate p21WAF1/CIP1 in MCF-7 (TP53-proficient) and K562 (TP53 deficient) cells in a TP53-independent mode. We also found that MC/DMC regulate AKT activation in a TP53-dependent manner and that AKT deactivation is not associated with the activation of p21WAF1/CIP1 in response to MC/DMC treatment. RAS proteins are known players in the upstream mediated signaling of p21WAF1/CIP1 activation that leads to control of cell proliferation and cell death. Thus, this prompted us to investigate the effect of both drugs on the expression of RAS proteins and regulation of the MAPK/ERK signaling pathways in MCF-7 and K562 cancer cells. To accomplish this goal, we performed comparative label free proteomics profiling coupled to bioinformatics/complementary phosphoprotein arrays and Western blot validations of key signaling molecules. The MAPK/ERK pathway exhibited an overall downregulation upon MC/DMC treatment in MCF-7 cells but only DMC exhibited a mild downregulation of that same pathway in TP53 mutant K562 cells. Furthermore, treatment of MCF-7 and K562 cell lines with oligonucleotides containing the interstrand crosslinks (ICLs) formed by MC or DMC shows that both ICLs had a stronger effect on the downregulation of RAS protein expression in mutant TP53 K562 cells. We discuss the implication of this regulation of the MAPK/ERK pathway in relation to cellular TP53 status.

PTPN13 Participates in the Regulation of Epithelial-Mesenchymal Transition and Platinum Sensitivity in High-Grade Serous Ovarian Carcinoma Cells

Epithelial ovarian cancer (EOC) is the leading cause of death from gynecological cancers in Western countries. High-Grade Serous Ovarian Carcinoma (HGSOC) accounts for 60-70% of EOC and is the most aggressive subtype. Reduced PTPN13 expression levels have been previously correlated with worse prognosis in HGSOC. However, PTPN13's exact role and mechanism of action in these tumors remained to be investigated. To elucidate PTPN13's role in HGSOC aggressiveness, we used isogenic PTPN13-overexpressing clones of the OVCAR-8 cell line, which poorly expresses PTPN13, and also PTPN13 CRISPR/Cas9-mediated knockout/knockdown clones of the KURAMOCHI cell line, which strongly expresses PTPN13. We investigated their migratory and invasive capacity using a wound healing assay, their mesenchymal-epithelial transition (EMT) status using microscopy and RT-qPCR, and their sensitivity to chemotherapeutic drugs used for HGSOC. We found that (i) PTPN13 knockout/knockdown increased migration and invasion in KURAMOCHI cells that also displayed a more mesenchymal phenotype and increased expression of the SLUG, SNAIL, ZEB-1, and ZEB-2 EMT master genes; and (ii) PTPN13 expression increased the platinum sensitivity of HGSOC cells. These results suggest that PTPN13 might be a predictive marker of response to platinum salts in HGSOC.

The therapeutic effectiveness of 177Lu-lilotomab in B-cell non-Hodgkin lymphoma involves modulation of G2/M cell cycle arrest

Some patients with B-cell non-Hodkin lymphoma Lymphoma (NHL) become refractory to rituximab (anti-CD20 antibody) therapy associated with chemotherapy. Here, the effect of the anti-CD37 antibody-radionuclide conjugate lutetium-177 (¹⁷⁷Lu)-lilotomab (Betalutin^®) was investigated in preclinical models of NHL. In SCID mice bearing DOHH2 (transformed follicular lymphoma, FL) cell xenografts, ¹⁷⁷Lu-lilotomab significantly delayed tumor growth, even at low activity (100 MBq/kg). In athymic mice bearing OCI-Ly8 (diffuse large B-cell lymphoma, DLBCL) or Ramos (Burkitt’s lymphoma) cell xenografts, ¹⁷⁷Lu-lilotomab activity had to be increased to 500 MBq/kg to show a significant tumor growth delay. Clonogenic and proliferation assays showed that DOHH2 cells were highly sensitive to ¹⁷⁷Lu-lilotomab, while Ramos cells were the least sensitive, and U2932 (DLBCL), OCI-Ly8, and Rec-1 (mantle cell lymphoma) cells displayed intermediate sensitivity. The strong ¹⁷⁷Lu-lilotomab cytotoxicity observed in DOHH2 cells correlated with reduced G2/M cell cycle arrest, lower WEE-1- and MYT-1-mediated phosphorylation of cyclin-dependent kinase-1 (CDK1), and higher apoptosis. In agreement, ¹⁷⁷Lu-lilotomab efficacy in vitro, in vivo, and in patient samples was increased when combined with G2/M cell cycle arrest inhibitors (MK-1775 and PD-166285). These results indicate that ¹⁷⁷Lu-lilotomab is particularly efficient in treating tumors with reduced inhibitory CDK1 phosphorylation, such as transformed FL.

The Syk Kinase Promotes Mammary Epithelial Integrity and Inhibits Breast Cancer Invasion by Stabilizing the E-Cadherin/Catenin Complex

While first discovered in immunoreceptor signaling, the Syk protein kinase behaves as a tumor and metastasis suppressor in epithelial cells. Its reduced expression in breast and other carcinomas is correlated with decreased survival and increased metastasis risk, but its action mechanism remains largely unknown. Using phosphoproteomics we found that Syk phosphorylated E-cadherin and α-, β-, and p120-catenins on multiple tyrosine residues that concentrate at intercellular junctions. Increased Syk expression and activation enhanced E-cadherin/catenin phosphorylation, promoting their association and complex stability. In human breast cancer cells, Syk stimulated intercellular aggregation, E-cadherin recruitment and retention at adherens junctions, and promoted epithelial integrity, whereas it inhibited cell migration and invasion. Opposite effects were obtained with Syk knockdown or non-phosphorylatable mutant E-cadherin expression. Mechanistically, Syk stimulated the interaction of the E-cadherin/catenin complex with zonula occludens proteins and the actin cytoskeleton. Conditional Syk knockout in the lactating mouse mammary gland perturbed alveologenesis and disrupted E-cadherin localization at adherens junctions, corroborating the observations in cells. Hence, Syk is involved in the maintenance of the epithelial integrity of the mammary gland via the phosphorylation and stabilization of the E-cadherin/catenin adherens junction complex, thereby inhibiting cell migration and malignant tumor invasion.

FKBP4 connects mTORC2 and PI3K to activate the PDK1/Akt-dependent cell proliferation signaling in breast cancer

Purpose: Among the FKBP family members, FKBP4 has been described to have a potential role in tumorigenesis, and as a putative tissue marker. We previously showed that FKBP4, an HSP90-associated co-chaperone, can elicit immune response as a tumor-specific antigen, and are overexpressed in breast cancer. Experimental design: In this study, we examined how loss of FKBP4 affect breast cancer progression and exploited protein interactomics to gain mechanistic insight into this process. Results: We found that FKBP4 expression is associated with breast cancer progression and prognosis, especially of ER-negative breast cancer. Furthermore, FKBP4 depletion specifically reduces cell growth and proliferation of triple negative breast cancer cell model and xenograft tumor model. Using specific protein interactome strategy by BirA proximity-dependent biotin identification, we demonstrated that FKBP4 is a novel PI3K-Akt-mTOR proximal interacting protein. Conclusion: Our results suggest that FKBP4 interacts with PI3K and can enhance Akt activation through PDK1 and mTORC2.

Detection of known and novel ALK fusion transcripts in lung cancer patients using next-generation sequencing approaches

Rearrangements of the anaplastic lymphoma kinase (ALK) gene in non-small cell lung cancer (NSCLC) represent a novel molecular target in a small subset of tumors. Although ALK rearrangements are usually assessed by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH), molecular approaches have recently emerged as relevant alternatives in routine laboratories. Here, we evaluated the use of two different amplicon-based next-generation sequencing (NGS) methods (AmpliSeq and Archer^®FusionPlex^®) to detect ALK rearrangements, and compared these with IHC and FISH. A total of 1128 NSCLC specimens were screened using conventional analyses, and a subset of 37 (15 ALK-positive, and 22 ALK-negative) samples were selected for NGS assays. Although AmpliSeq correctly detected 25/37 (67.6%) samples, 1/37 (2.7%) and 11/37 (29.7%) specimens were discordant and uncertain, respectively, requiring further validation. In contrast, Archer^®FusionPlex^® accurately classified all samples and allowed the correct identification of one rare DCTN1-ALK fusion, one novel CLIP1-ALK fusion, and one novel GCC2-ALK transcript. Of particular interest, two out of three patients harboring these singular rearrangements were treated with and sensitive to crizotinib. These data show that Archer^®FusionPlex^® may provide an effective and accurate alternative to FISH testing for the detection of known and novel ALK rearrangements in clinical diagnostic settings.

High PTPN13 expression in high grade serous ovarian carcinoma is associated with a better patient outcome

Background

Chromosome 4q loss of heterozygosity (LOH) is frequently observed in high-grade serous ovarian carcinoma (HGSOC). However, this LOH has not been clearly associated with the inactivation of any tumor suppressor gene(s). As the tumor suppressor gene PTPN13 is located on chromosome 4q21, we investigated its expression in HGSOC.

Methods

PTPN13 protein expression was investigated by immunohistochemistry (IHC) in normal ovary epithelium and in 30 HGSOC samples, whereas PTPN13 mRNA expression was quantified by RT-PCR in another independent cohort of 28 HGSOC samples. Patients in both cohorts were followed for more than 8.5 years.

Results

PTPN13 protein expression was lower in one third of HGSOC samples compared with normal ovary epithelium. In both cohorts, high PTPN13 expression level (mRNA or protein) in the tumor was associated with favorable outcome and significantly longer survival (HR=0.27; p=0.0087 and HR=0.42; p=0.03, respectively).

Conclusion

This study demonstrates, for the first time, that high PTPN13 expression level is a prognostic indicator of favorable outcome in patients with HGSOC. This finding, in conjunction with our previous mechanistic studies, suggests that PTPN13 loss, possibly by 4q LOH, enhances HGSOC aggressiveness and highlight the interest of studying PTPN13 signaling in HGSOC to identify new potential therapeutic targets.

An integrated cell line-based discovery strategy identified follistatin and kallikrein 6 as serum biomarker candidates of breast carcinoma

Secreted proteins constitute a relevant source of putative cancer biomarkers. Here, we compared the secretome of a series of four genetically-related breast cancer cell lines as a model of aggressiveness using quantitative mass spectrometry. 537 proteins (59.5% of the total identified proteins) predicted to be released or shed from cells were identified. Using a scoring system based on i) iTRAQ value, ii) breast cancer tissue mRNA expression levels, and iii) immunohistochemical staining (public database), a short list of 10 candidate proteins was selected. Using specific ELISA assays, the expression level of the top five proteins was measured in a verification set of 56 patients. The four significantly differentially expressed proteins were then validated in a second independent set of 353 patients. Finally, follistatin (FST) and kallikrein 6 (KLK6) in serum were significantly higher (p-value < 0.0001) in invasive breast cancer patients compared with non-cancerous controls. Using specific cut-off values, FST distinguished breast cancer samples from healthy controls with a sensitivity of 65% and an accuracy of 68%, whereas KLK6 achieved a sensitivity of 55% and an accuracy of 61%. Therefore, we concluded that FST and KLK6 may have significance in breast cancer detection.

BIOLOGICAL SIGNIFICANCE

Discovery of new serum biomarkers that exhibit increased sensitivity and specificity compared to current biomarkers appears to be an essential field of research in cancer. Most biological markers show insufficient diagnostic sensitivity for early breast cancer detection and, for the majority of them, their concentrations are elevated only in metastatic forms of the disease. It is therefore essential to identify clinically reliable biomarkers and develop effective approaches for cancer diagnosis. One promising approach in this field is the study of secreted proteins through proteomic analysis of in vitro progression breast cancer models. Here we have shown that FST and KLK6 are elevated in breast cancer patient serum compared to healthy controls. We expect that our discovery strategy will help to identify cancer-specific and body-fluid-accessible biomarkers.

Adherens Junction and E-Cadherin complex regulation by epithelial polarity

E-Cadherin-based Adherens Junctions (AJs) are a defining feature of all epithelial sheets. Through the homophilic association of E-Cadherin molecules expressed on neighboring cells, they ensure intercellular adhesion amongst epithelial cells, and regulate many key aspects of epithelial biology. While their adhesive role requires these structures to remain stable, AJs are also extremely plastic. This plasticity allows for the adaptation of the cell to its changing environment: changes in neighbors after cell division, cell death, or cell movement, and changes in cell shape during differentiation. In this review we focus on the recent advances highlighting the critical role of the apico-basal polarity machinery, and in particular of the Par3/Bazooka scaffold, in the regulation and remodeling of AJs. We propose that by regulating key phosphorylation events on the core E-Cadherin complex components, Par3 and epithelial polarity promote meta-stable protein complexes governing the correct formation, localization, and functioning of AJ.

Pro-cathepsin D interacts with the extracellular domain of the beta chain of LRP1 and promotes LRP1-dependent fibroblast outgrowth

Interactions between cancer cells and fibroblasts are crucial in cancer progression. We have previously shown that the aspartic protease cathepsin D (cath-D), a marker of poor prognosis in breast cancer that is overexpressed and highly secreted by breast cancer cells, triggers mouse embryonic fibroblast outgrowth via a paracrine loop. Here, we show the requirement of secreted cath-D for human mammary fibroblast outgrowth using a three-dimensional co-culture assay with breast cancer cells that do or do not secrete pro-cath-D. Interestingly, proteolytically-inactive pro-cath-D remains mitogenic, indicating a mechanism involving protein-protein interaction. We identify the low-density lipoprotein (LDL) receptor-related protein-1, LRP1, as a novel binding partner for pro-cath-D in fibroblasts. Pro-cath-D binds to residues 349-394 of the β chain of LRP1, and is the first ligand of the extracellular domain of LRP1β to be identified. We show that pro-cath-D interacts with LRP1β in cellulo. Interaction occurs at the cell surface, and overexpressed LRP1β directs pro-cath-D to the lipid rafts. Our results reveal that the ability of secreted pro-cath-D to promote human mammary fibroblast outgrowth depends on LRP1 expression, suggesting that pro-cath-D-LRP1β interaction plays a functional role in the outgrowth of fibroblasts. Overall, our findings strongly suggest that pro-cath-D secreted by epithelial cancer cells promotes fibroblast outgrowth in a paracrine LRP1-dependent manner in the breast tumor microenvironment.

Cell membrane extensions, generated by mechanical constraint, are associated with a sustained lipid raft patching and an increased cell signaling

Platelet activation triggers an imbalance in plasma membrane phospholipids by a specific aminophospholipid outflux, resulting in filopodia formation. Similarly, the addition of a phospholipid excess in the outer leaflet of the plasma membrane induces cellular extensions and actin polymerization. The implication of membrane microdomains in sustaining these mechanical constraints remains, however, unknown and was investigated in human platelets and mouse fibroblasts. The disruption of lipid rafts by cholesterol depletion prevents actin polymerization and formation of cellular extensions. Phospholipid excess triggers raft patching underneath the cell extensions, recruitment of protein raft markers and increase of tyrosine phosphorylation of raft proteins. Using a mass spectrometric analysis of isolated platelet rafts, we identified tyrosine kinases and proteins implicated in the formation of cell membrane extensions, cell adhesion and motility. They are recruited to rafts in response to a mechanical constraint. Taken together, our results demonstrate that exogenous phospholipid addition causes a modulation of the lateral plasma membrane organization and an activation of the cell signaling triggering actin remodeling and the formation of cellular protrusions. Raft disruption abolishes these processes, demonstrating that their integrity is crucial for cell shape changes in response to a mechanical constraint on plasma membrane.

Characterization of centrosomal localization and dynamics of Cdc25C phosphatase in mitosis

In mammalian cells, three Cdc25 phosphatases A, B, C coordinate cell cycle progression through activating dephosphorylation of Cyclin-dependent kinases. Whereas Cdc25B is believed to trigger entry into mitosis, Cdc25C is thought to act at a later stage of mitosis and in the nucleus. We report that a fraction of Cdc25C localises to centrosomes in a cell cycle-dependent fashion, as of late S phase and throughout G(2) and mitosis. Moreover, Cdc25C colocalises with Cyclin B1 at centrosomes in G(2) and in prophase and Fluorescence Recovery after Photobleaching experiments reveal that they are both in dynamic exchange between the centrosome and the cytoplasm. The centrosomal localisation of Cdc25C is essentially mediated by its catalytic C-terminal domain, but does not require catalytic activity. In fact phosphatase-dead and substrate-binding hotspot mutants of Cdc25C accumulate at centrosomes together with phosphoTyr15-Cdk1 and behave as dominant negative forms that impair entry into mitosis. Taken together, our data suggest an unexpected function for Cdc25C at the G(2)/M transition, in dephosphorylation of Cdk1. We propose that Cdc25C may participate in amplification of Cdk1-Cyclin B1 activity following initial activation by Cdc25B, and that this process is initiated at the centrosome, then further propagated throughout the cytoplasm thanks to the dynamic behavior of both Cdc25C and Cyclin B1.

Tangeretin inhibits extracellular-signal-regulated kinase (ERK) phosphorylation

Tangeretin is a methoxyflavone from citrus fruits, which inhibits growth of human mammary cancer cells and cytolysis by natural killer cells. Attempting to unravel the flavonoid's action mechanism, we found that it inhibited extracellular-signal-regulated kinases 1/2 (ERK1/2) phosphorylation in a dose- and time-dependent way. In human T47D mammary cancer cells this inhibition was optimally observed after priming with estradiol. The spectrum of the intracellular signalling kinase inhibition was narrow and comparison of structural congeners showed that inhibition of ERK phosphorylation was not unique for tangeretin. Our data add tangeretin to the list of small kinase inhibitors with a restricted intracellular inhibition profile.

Catalytically inactive human cathepsin D triggers fibroblast invasive growth

The aspartyl-protease cathepsin D (cath-D) is overexpressed and hypersecreted by epithelial breast cancer cells and stimulates their proliferation. As tumor epithelial-fibroblast cell interactions are important events in cancer progression, we investigated whether cath-D overexpression affects also fibroblast behavior. We demonstrate a requirement of cath-D for fibroblast invasive growth using a three-dimensional (3D) coculture assay with cancer cells secreting or not pro-cath-D. Ectopic expression of cath-D in cath-D-deficient fibroblasts stimulates 3D outgrowth that is associated with a significant increase in fibroblast proliferation, survival, motility, and invasive capacity, accompanied by activation of the ras-MAPK pathway. Interestingly, all these stimulatory effects on fibroblasts are independent of cath-D proteolytic activity. Finally, we show that pro-cath-D secreted by cancer cells is captured by fibroblasts and partially mimics effects of transfected cath-D. We conclude that cath-D is crucial for fibroblast invasive outgrowth and could act as a key paracrine communicator between cancer and stromal cells, independently of its catalytic activity.

A mutated cathepsin-D devoid of its catalytic activity stimulates the growth of cancer cells

Cathepsin-D, a lysosomal aspartyl proteinase, is highly secreted by breast cancer cells and its over-expression by transfection stimulates cancer cell proliferation. The mechanism by which this protease affects proliferation remains, however, unknown. In order to determine whether proteolytic activity is necessary, we abolished its enzymatic activity using site-directed mutagenesis followed by stable transfection in 3Y1-Ad12 cancer cells. Substitution of the aspartic acid residue 231 by an asparagine residue in its catalytic site abrogated the cathepsin-D proteolytic activity but did not affect its expression level, processing or secretion. However, like wild-type cathepsin-D, this mutated catalytically-inactive cathepsin-D retained its capacity to stimulate proliferation of cells embedded in Matrigel or collagen I matrices, colony formation in soft agar and tumor growth in athymic nude mice. Addition on the mock-transfected cells, of either conditioned media containing the wild-type or the mutated pro-cathepsin-D, or of the purified mutated pro-cathepsin-D, partially mimicked the mitogenic activity of the transfected cathepsin-D, indicating a role of the secreted pro-enzyme. Moreover, addition of two anti-cathepsin-D antibodies on the cathepsin-D transfected cells inhibited their proliferation, suggesting an action of the secreted pro-cathepsin-D via an autocrine loop. A synthetic peptide containing the 27-44 residue moiety of the cathepsin-D pro-fragment was, however, not mitogenic suggesting that a receptor for the pro-fragment was not involved. Furthermore, the cathepsin-D mitogenicity was not blocked by inhibiting the interaction of pro-cathepsin-D with the mannose-6-phosphate receptors. Our results altogether demonstrate that a mutated cathepsin-D devoid of catalytic activity is still mitogenic and suggest that it is acting extra-cellularly by triggering directly or indirectly a yet unidentified cell surface receptor.

Pathophysiology of limb girdle muscular dystrophy type 2A: hypothesis and new insights into the IkappaBalpha/NF-kappaB survival pathway in skeletal muscle

Limb girdle muscular dystrophies (LGMDs) are a group of clinically heterogeneous genetic diseases characterized by progressive weakness and atrophy of scapular and pelvic muscles, with either a dominant or recessive autosomic mode of inheritance. The first symptoms of the disorder appear during the first 20 years of life and progresses gradually, and a walking disability develops 10-20 years later. The gene responsible for LGMD2A has been identified and encodes calpain 3, a protease expressed mainly in skeletal muscle. Apoptotic myonuclei were recently detected in muscular biopsy specimens of LGMD2A patients, and apoptosis was found to be correlated with altered subcellular distribution of inhibitory protein kappaBalpha (IkappaBalpha) and nuclear factor kappaB (NF-kappaB), resulting in sarcoplasmic sequestration of NF-kappaB. Calpain 3 dependent IkappaBalpha degradation was reconstituted in vitro, supporting a possible in vivo sequence of events leading from calpain 3 deficiency to IkappaBkappa accumulation, prevention of nuclear translocation of NF-kappaB, and ultimately apoptosis. Therefore calpain 3, present in healthy muscle as sarcoplasmic and nuclear forms, may control IkappaBalpha turnover and indirectly regulate NF-kappaB dependent expression of survival genes. Recent data reported from a new model of LGMD2A in mice and from other muscular disorders strengthen understanding of the molecular links between calpain 3 and the Ikappaalpha/NF-kappaB pathway. Finally, in light of the lack of apoptosis observed in inflammatory myopathies, a unifying model for the control of cell survival in muscle is proposed and discussed

Heregulin regulates the actin cytoskeleton and promotes invasive properties in breast cancer cell lines

The metastatic process requires changes in tumor cell adhesion properties, cell motility and remodeling of the extracellular matrix. The erbB2 proto-oncogene is overexpressed in approximately 30% of breast cancers and is a major prognostic parameter when present in invasive disease. A ligand for the erbB2 receptor has not yet been identified but it can be activated by heterodimerization with heregulin (HRG)-stimulated erbB3 and erbB4 receptors. The HRGs are a family of polypeptide growth factors that have been shown to play a role in embryogenesis, tumor formation, growth and differentiation of breast cancer cells. The erbB3 and erbB4 receptors are involved in transregulation of erbB2 signaling. The work presented here suggests biological roles for HRG including regulation of the actin cytoskeleton and induction of motility and invasion in breast cancer cells. HRG-expressing breast cancer cell lines are characterized by low erbB receptor levels and a high invasive and metastatic index, while those which overexpress erbB2 demonstrate minimal invasive potential in vitro and are non-tumorigenic in vivo. Treatment of the highly tumorigenic and metastatic HRG-expressing breast cancer cell line MDA-MB-231 with an HRG-neutralizing antibody significantly inhibited proliferation in culture and motility in the Boyden chamber assay. Addition of exogenous HRG to non-invasive erbB2 overexpressing cells (SKBr-3) at low concentrations induced formation of pseudopodia, enhanced phagocytic activity and increased chemomigration and invasion in the Boyden chamber assay. The specificity of the chemomigration response to HRG is demonstrated by inhibition with the anti-HRG neutralizing antibody. These results suggest that either HRG can act as an autocrine or paracrine ligand to promote the invasive behavior of breast cancer cells in vitro or thus may enhance the metastatic process in vivo.

Anti-proliferative and anti-estrogenic effects of ICI 164,384 and ICI 182,780 in 4-OH-tamoxifen-resistant human breast-cancer cells

The effects of the anti-estrogens 4-hydroxytamoxifen (OHTam), ICI 164,384 and ICI 182,780 were tested on the MCF-7/LCC2 breast-carcinoma cell line, which grows significantly in the presence of OHTam and serves as a model for studying anti-estrogen resistance of estrogen-receptor-positive breast cancer. Cell proliferation and cathepsin-D secretion were strongly inhibited by either ICI 182,780 or ICI 164,384 alone or ICI 164,384 in combination with 17-beta-estradiol (E2) or OHTam. ICI 164,384 alone did not affect the cathepsin-D and pS2 mRNA levels, but antagonized the stimulatory effects of E2 or OHTam on these 2 mRNAs. OHTam was more effective than E2 in increasing cathepsin-D mRNA levels, supporting the idea that anti-estrogen-resistant breast cancer continues to overexpress cathepsin-D. These data show that the steroidal anti-estrogens ICI 164,384 and ICI 182,780 retain their ability to inhibit cell proliferation and the estrogen-responsiveness of cathepsin-D and pS2 genes in the OHTam-resistant MCF-7/LCC2 cell lines. These pure anti-estrogens may thus be efficient second-line treatments of some Tamoxifen-resistant tumors.

Laminin binding and internalization by human and murine mammary gland cell lines in vitro

We have studied the binding and internalization of Engelbreth-Holm-Swarm mouse sarcoma laminin labeled with colloidal gold (LN-G40) by human and murine mammary gland cell lines. Interactions between the LN-G40 probe and the cells spread on a glass coverslip were monitored with video-enhanced contrast microscopy (Nanovid). Transmission electron microscopy allowed the quantitation of the LN-G40 probe at various cellular locations. During the first 15 min, a homogeneous binding of LN-G40 probe to the cell surface was observed with all cell lines. This binding did not occur with gold particles that were not conjugated to laminin. Then, the LN-G40 probe began to cluster on the cell surface and was, during the following 20 h, internalized by pits that were not coated. In the cells, the LN-G40 probe sometimes showed saltatory movements along linear tracks. The LN-G40 probe was intracellularly found in vesicles, multivesicular bodies, cisternal structures, and lysosomes, suggesting the degradation of the internalized laminin. However, not all cell surface-bound LN-G40 probe was internalized after 20 h. Differences between the cell lines were quantitative, but no clear correlation could be made between migration of cells on laminin and internalization of laminin.

Arrest of MCF-7 cell migration by laminin in vitro: possible mechanisms

Laminin, a major basement membrane component, arrested the migration of MCF-7/AZ human breast adenocarcinoma cells that were not invasive in vitro. Migration of invasive MCF-7/6 cells was not affected by laminin. Both cell types expressed the 67 kD laminin receptor, at both mRNA and protein level, but did not express the alpha 6 subunit of the VLA-6 integrin-type laminin receptor. The presence of YIGSR peptides (100 micrograms/ml), reported to block the interaction between laminin and its 67 kD receptor, did not change the migratory response of MCF-7/AZ or MCF-7/6 cells when meeting laminin lanes. In addition, the migration of these cell types was not affected by the presence of 17-beta-estradiol (10(-6) M) or all-trans retinoic acid (10(-6) M), which were both reported to increase the number of 67 kD receptors. We could therefore not assign an involvement of the 67 kD receptors in migration of MCF-7 cells on laminin, nor did we find evidence that conditioned medium of MCF-7/6 cells contains factors that are able to initiate migration of MCF-7/AZ cells on laminin.

Effect of oncogene transfection or passage in vivo on malignant phenotypes of rat2 cells

Rat2 cells are thymidine kinase-deficient derivatives from the immortalized rat embryo cell line Rat1. They show no phenotypic correlates of malignancy in vitro and produce tumors in syngeneic Fischer rats after long latency periods. We have investigated how transfection with oncogenes would alter the in vitro and in vivo behavior of Rat2 cells. Thus we have manipulated Rat2 cultures in various ways. The cell lines obtained were categorized as parental, in vitro subclones, untransfected in vivo derivatives, non-oncogene (neor and tk) transfectants, oncogene (mutated c-Ha-ras, polyoma middle-T, FBR v-gag-fos-fox) transfectants, and in vivo derivatives of transfectants. They were tested in vitro for morphotype, colony formation in soft agar, growth in organ culture, invasion in organ culture, and in vivo for latency period of tumor formation, tumor growth rate, invasiveness, and metastasis. Differences between the consequences of various manipulations were found in the number of malignancy-related phenotypic alterations. The following trend could be deduced from our data: induction of invasiveness in organ culture by all manipulations; morphotypic transformation and shortening of tumor-latency period by all oncogene transfections and by passage with tumor formation in vivo; growth in organ culture and increased tumor growth rate in vivo by transfection with ras-, or fos-oncogenes and by passage in vivo. Metastatic capability (present in parental Rat2 cell tumors) and colony formation in soft agar (absent in Rat2 cells) were not affected by the present manipulations. We concluded that differences between the oncogene-transfectants and the untransfected in vivo derivatives do not lie in the expression of malignancy-related phenotypes but in the time needed to acquire them.

Tumorigenicity, invasiveness and metastatic capability of FR3T3 rat cells before and after transfection with bovine papilloma virus type 1 DNA

Fischer rat FR3T3 cells were tested for tumorigenicity, invasive and metastatic capabilities before and after transfection, either with the entire bovine papilloma virus type 1 (BPV-1) genome or with a plasmid (pV69) containing a 69 per cent Bam H1-Hind III fragment of the BPV-1 genome as well as bacterial sequences. Cell lines were grouped as parental, pV69-transfectants, BPV-1 transfectants, in vitro derivatives, and in vivo derivatives. The tumorigenic, invasive and metastatic capabilities of these cell lines were examined in vivo through s.c., and i.p. injections of cell suspensions and through s.c. implantations of cellular aggregates into syngeneic rats. Invasiveness was tested in vitro through confrontations with embryonic chick heart fragments in organ culture. All cell lines including parental lines, were found to be invasive in vitro and tumorigenic in vivo; all tumors were invasive. It is, therefore, not possible to draw conclusions about the role of BPV-1 gene sequences in the acquisition of the invasive phenotype. Transfection with BPV-1 genes conveyed the metastatic phenotype upon parental FR3T3 cells, which were themselves found to be non-metastatic. With regards to this, no differences were found between BPV-1 transfectants compared with pV69 transfectants. Untransfected cells became metastatic also through passage in vivo as an s.c. tumor. The expression of the metastatic phenotype was not noticeably correlated with alterations of growth characteristics of the cell lines. We concluded that the implication of BPV-1 gene sequences in conveying the metastatic phenotype upon FR3T3, if any, was indirect, presumably through alterations of the host cell genome. Our experiments illustrate the need for long-term observations with parental cell lines before drawing conclusions about the role of oncogenes in the acquisition of the malignant phenotype.

The anti-invasive flavonoid (+)-catechin binds to laminin and abrogates the effect of laminin on cell morphology and adhesion

To study the effect of the flavonoid (+)-catechin on cell-matrix interactions two cell types with a different morphology on and adhesion to laminin were used. MO4 virally transformed fetal mouse cells adhere and spread when cultured on top of laminin-coated coverslips or on human amnion basement membrane. M5076 mouse reticulum cell sarcoma cells poorly adhere to these substrates and remain round. Both cell types are invasive in confronting cultures with embryonic chick heart fragments. (+)-Catechin binds to laminin in a pH-dependent way. Pretreatment of laminin-coated coverslips or amnion basement membrane with 0.5 mM (+)-catechin abrogates the effect of laminin on cell morphology and adhesion. MO4 cells do not adhere to the pretreated substrates and remain round, while M5076 cells now adhere and spread. (+)-Catechin inhibits the invasion of MO4 cells but not of M5076 cells into embryonic chick heart in vitro. We speculate that the anti-invasive activity of the flavonoid to MO4 cells is the result of its interference with MO4 cell adhesion to laminin. Invasion of M5076 cells does not imply adhesion to and spreading on laminin.

Pathology of tumours produced in syngeneic Fischer rats by fibroblast-like cells before and after transfection with oncogenes

Fischer rat cells before and after transfection with immortalizing and transforming genes produced tumours after s.c., i.p., or i.v. injection of cell suspensions and after s.c. implantation of cellular aggregates in the tail of syngeneic rats. Tumours were described histologically as fibrosarcoma-like. Virtually all tumours were considered macroscopically to be invasive because they adhered to the neighbouring tissues; in many tumours invasion was confirmed microscopically. All types of cells produced lung colonies (artificial metastases) after i.v. injection. Spontaneous metastases (from a primary tumour) were found with some tumours produced by cells before as well as after transfection. Differences in metastasis between various cell types could not be ascribed to variations in the periods of observation, in the minimum tumour-bearing periods, in the latency periods, or in the volume of primary tumours. We concluded that local invasion and spontaneous metastasis are usefull for the characterization of malignancy in experimental fibrosarcoma-like tumours. Since Fischer rat cells produced invasive and sometimes metastatic tumours before transfection, the present data do not show a rôle of immortalizing and transforming genes in the acquisition of invasiveness and metastatic capability.

Action mechanisms of anti-invasive agents

An anti-invasive activity has been observed with a number of agents in confronting cultures between invasive cell populations and embryonic chick heart fragments. Cytochalasins, microtubule inhibitors and dipyridamole act via intracellular targets. Inhibition of glycosylation of proteins, low temperature and alkyl lysophospholipids alter the plasma membrane. Flavonoids aim at extracellular targets. In a unifying hypothesis we postulate that invasion is due to lack of responsiveness to stop signals that normally retain cells within their tissue boundaries. Some of the anti-invasive agents act on cellular activities that are necessary for invasion; others might act on the stop signal, the perception of and/or the response to this signal.