3D Matrigel Research Articles

Abstract 1909: Multiple Mdm2 isoforms promote tumorigenesis, disrupt mammary tissue architecture, and are endogenously expressed in cancers.

Abstract Mdm2 is a key regulator of the tumor suppressor p53 and over expression of Mdm2 is a negative prognostic marker for many cancers. Mdm2 expression is increased in estrogen-receptor positive breast cancer cells that have the mdm2 G/G single nucleotide polymorphism at position 309 (mdm2 SNP309). In such cells, estrogen activates cell proliferation in an Mdm2 dependent manner. Alternatively spliced mdm2 transcripts have been observed in cancers, however, endogenous protein isoforms have not been detected. The exogenous expression of mdm2 splice variants encodes proteins, transforms cell lines in culture, and in the absence of p53 causes tumors in mice. Therefore we hypothesized that endogenous human Mdm2 protein isoforms participate in p53-independent tumorigenesis. We created a specific human Mdm2-C antibody to the splice junction of exons four and ten (Mdm2 C410) and validated the C410 antibody using in vitro translated Mdm2 compared to Mdm2-C. We detected, for the first time in human cancer cell lines, expression of endogenous Mdm2-C. This was particularly high in G/G mdm2 SNP309 breast cancer cells. In addition, using immunohistochemistry analysis three out of three Liposarcoma tissue samples tested positive for Mdm2-C expression. Using the C410 antibody we detected endogenous Mdm2-C protein in estrogen receptor positive T47D and MCF-7 breast cancer cells. T47D cells (with mutant p53), and MCF-7 cells (with wild-type p53), both showed increased Mdm2-C protein expression after estrogen treatment. We also determined that Mdm2-C did not interact with p53. Interestingly, Mdm2-C protein localized in nucleolar and cytoplasmic speckles. The exogenous expression of Mdm2-C increased colony formation ability indicating that it had transforming capability. However contrary to results with exogenously expressed Mdm2-FL, exogenously expressed Mdm2-C did not influence p53 stability, or p53 transactivation activity. Importantly, siRNA-mediated knockdown of Mdm2-C in T47D cells induced cell death. We engineered miR30-based inducible mdm2 knockdown cell lines of MCF-7 and T47D to evaluate the impact of multiple Mdm2 isoforms. The down-regulation of Mdm2 in MCF-7.shmdm2 and T47D.shmdm2 inhibited cell proliferation in 2D culture and in 3D laminin-rich matrigel. The knockdown of Mdm2 in T47D cells reduced colony size, reverted to cells to more normal mammary architecture, and decreased E2F protein expression. We suggest that survival of estrogen-influenced breast cancer is through a p53-independent, and thus non-canonical, Mdm2 isoform mediated mechanism. Special thanks to Gerard Evan for help with immunogen peptide design. This work was supported by The Breast Cancer Research Foundation and The NSF (grant MCB-0744316) to J.B. D.O. was partially supported by a CUNY Magnet Award and M.R. was supported by MBRS-RISE Program to Hunter College 3R25-GM060665. Citation Format: Danielle Okoro, Chong Gao, Cindy Puente, Alla Polotskaia, Nicoleta Arva, Melissa Rosso, Jill Bargonetti. Multiple Mdm2 isoforms promote tumorigenesis, disrupt mammary tissue architecture, and are endogenously expressed in cancers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1909. doi:10.1158/1538-7445.AM2013-1909

Abstract LB-280: Inhibition of SHP2 in basal-like and triple-negative breast cancer cells induces basal-to-luminal transition, suppresses tumorigenesis, and blocks metastasis.

Abstract One of the factors that contribute to the disproportionately high mortalities in basal-like and triple-negative breast cancer (BTBC) is the lack of targeted therapies. Identifying and characterizing potential targets is therefore critical for future development of such therapies. In the current report, we show that silencing the expression of the Src homology phosphotyrosyl phosphatase 2 (SHP2) in BTBC cell lines (MDA-MB231 and MDA-MB468) suppresses cell proliferation, reverses transformation, and blocks invasiveness. Unexpectedly, we have discovered that inhibition of SHP2 induces basal-to-luminal transition (BLT) in BTBC cells as evidenced by a decrease in the expression of mesenchymal markers and/or drivers (vimentin, ZEB1, Snail, and alpha smooth muscle actin) and an increase in the expression of the luminal marker cytokeratin 18. Furthermore, we have discovered that inhibition of SHP2 induces the expression of the estrogen receptor alpha in otherwise triple-negative breast cancer cells. Intramammary transplantation studies in the NOD/SCID mice demonstrated that inhibition of SHP2 suppresses tumorigenesis and blocks metastasis. Analyses of total cell lysates prepared from cells grown in 3D matrigel cultures demonstrated that SHP2 mediates the activation of the Ras-ERK, the PI3K, and the β-catenin signaling pathways to promote the tumorigenic, invasive, and metastatic potential of BTBC cells. By and large, the results presented in this report suggest that SHP2 plays an essential role in the biology of BTBC. Citation Format: Fatimah Matalka, Hua Zhao, Yehenew M. Agazie. Inhibition of SHP2 in basal-like and triple-negative breast cancer cells induces basal-to-luminal transition, suppresses tumorigenesis, and blocks metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-280. doi:10.1158/1538-7445.AM2013-LB-280

Abstract 3794: The role of LMTK3 in breast cancer cell growth and invasion.

Abstract Abstract Title: The role of LMTK3 in breast cancer cell growth and invasion Background: We have identified Lemur tyrosine kinase-3 (LMTK3) as a novel regulator of estrogen receptor α (ERα) that is associated with disease free and overall survival and predicted response to endocrine therapies in breast cancer. In addition, inhibition of LMTK3 in tamoxifen (tam)-sensitive and tam-resistant xenograft mouse models led to tumor volume reduction. Moreover, a genome microarray analysis revealed various genes modulated by LMTK3 implicated in different canonical pathways. Herein we present evidence that further elucidates the mechanism of LMTK3 involvement in breast cancer growth and invasion. Methods: Stable over-expressed and depleted LMTK3 breast cancer cell lines were generated to study the effects of LMTK3 on proliferation and invasion. Various molecular and cellular biology techniques (including RT-PCR, immunofluorescence, immunoprecipitation and invasion assays) were carried out to elucidate the participation of LMTK3 in various signalling pathways. Stable isotope labelling by amino acids in cell culture (SILAC) was undertaken to identify and analyse novel LMTK3-regulated proteins. Results: Transwell and collagen 1 invasion assays results demonstrated that over-expression of LMTK3 in non-invasive MCF7 cells promote invasion while conversely knockdown of LMTK3 in MDA-MB-231 cells significantly inhibited invasion. Moreover, stable LMTK3 over-expressing cells form larger and looser acini structures compared to parental cells in 3D matrigel overlay assays. Wound healing assays demonstrated an increased motility of cells that over-express LMTK3 compared to LMTK3 knock-out cell lines. Cell adhesion assays revealed preferential binding of LMTK3 over-expressing cell lines to different ECM ligands. RT-qPCR analysis indicated up-regulation of an invasive gene signature (including MMPs, vimentin, and others) associated with LMTK3 over-expression. SILAC analysis identified various novel LMTK3-regulated proteins and phospho-proteins. In addition, modulation of LMTK3 affected the expression of specific members of the integrin family, as well as proteins involved in the focal adhesion complex. Co-immunoprecipitation and immunofluorescence experiments further helped us identify interacting partners of LMTK3 pertaining to the pathways conferring the observed pro-invasive phenotypic results. Finally, the involvement of LMTK3 in promoting tumorigenicity was confirmed in an in vivo xenograft mouse model. Conclusion: We show that LMTK3 is important for mediating breast cancer cell growth and invasion and propose a model of the mechanism of LMTK3 action in these processes. These data position LMTK3 in the map of well-known oncogenic signaling cascades. Citation Format: Yichen Xu, Aleksandra Filipovic, Hua Zhang, Lei Cheng Lit, Ylenia Lombardo, Justin Stebbing, Georgios Giamas. The role of LMTK3 in breast cancer cell growth and invasion. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3794. doi:10.1158/1538-7445.AM2013-3794

Abstract 924: FAK inhibition preferentially attenuates growth of Merlin-negative malignant mesotheliomas: role of cancer stem cells.

Abstract Malignant pleural mesothelioma (MPM) is an aggressive tumor in the pleural lining of the lung often caused by asbestos exposure. MPM patients are usually diagnosed at an advanced stage of the disease and the prognosis is poor. Median survival after diagnosis is 9 to 12 months and standard-of-care agents such as pemetrexed are relatively ineffective in increasing median survival time for MPM patients. New therapeutic modalities are urgently needed for MPM patients. Neurofibromatosis 2 (NF2) is a tumor suppressor gene that encodes the protein Merlin. Biallelic inactivation of NF2 by mutation and/or deletion occurs in ∼40% of MPMs leading to inactive or absent Merlin. Merlin has been demonstrated to play roles in cell adhesion, invasion and cell motility in tumor cell lines partially through regulation of focal adhesion kinase (FAK) which in turn mediates signal transduction by integrins and growth factor receptors. Increased activation of FAK has been demonstrated in NF2-mutated mesothelioma cells, indicating that FAK may represent an important therapeutic target for MPM. A potent and selective FAK inhibitor VS-4718 was evaluated in a panel of MPM cell lines with wild-type or mutated NF2. Mutant NF2 MPM cells were found to be especially sensitive to the FAK inhibitor VS-4718 in a 3D Matrigel assay with EC50 values below 100 nM, in contrast to wild type NF2 MPM cell lines which were less sensitive with EC50 values above 1 μM. Decrease in cell growth in response to FAK inhibitor treatment was found to result from reduction of cell proliferation and induction of apoptosis. Ectopic expression of a non-phosphorylatable mutant form of NF2 (NF2-S518A) in NF2 mutant MPM cells abolished the enhanced sensitivity to VS-4718 in both proliferation and apoptosis assays, confirming the hypothesis that Merlin loss confers hypersensitivity to FAK inhibition. In addition, VS-4718 inhibited tumor cell growth in an orthotopic Merlin-negative mesothelioma xenograft model in a dose-dependent manner with corresponding inhibition of tumor FAK autophosphorylation. It has been reported that cancer stem cells (CSCs) are enriched in pemetrexed-resistant mesothelioma. Using Aldefluor activity as a measure of CSCs, we have found that the FAK inhibitor VS-4718 preferentially reduced the percentage of CSCs in Merlin-negative MPM in contrast to the standard-of-care agent pemetrexed which increased the percentage of CSCs. In summary, our results indicate that the FAK inhibitor VS-4718 is especially potent in Merlin-negative MPM tumor cells, and that NF2 status may be a valuable stratification marker for response to FAK inhibition. Furthermore, cancer stem cells in Merlin-negative mesotheliomas appear to be particularly resistant to pemetrexed, but sensitive to VS-4718. These data support the clinical development of a selective FAK inhibitor for treatment of Merlin-negative malignant mesothelioma. Citation Format: Irina M. Shapiro, Vihren N. Kolev, Christian M. Vidal, Jennifer E. Ring, Mitchell Keegan, Qunli Xu, Craig W. Menges, Joseph R. Testa, Jonathan A. Pachter. FAK inhibition preferentially attenuates growth of Merlin-negative malignant mesotheliomas: role of cancer stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 924. doi:10.1158/1538-7445.AM2013-924

Cellular behavior in micropatterned hydrogels by bioprinting system depended on the cell types and cellular interaction

The fabrication of patterned microstructures within three-dimensional (3D) matrices is a challenging subject in tissue engineering and regenerative medicine. A 3D, free-moving bioprinting system was developed and hydrogels were patterned by varying the process parameters of z-axis moving velocity and ejection velocity. The patterning of hydrogel based microfibers in a 3D matrigel was achieved with dimensions of 4.5mm length and widths from 79 to 200μm. Hyaluronan-based hydrogels mixed with fibroblasts (L929), mouse endothelial cells (MS1), or human mesenchymal stem cells (hMSCs) were patterned using a 3D moving axis bioprinter and cell behavior was monitored in culture for up to 16 days. L929 and MS1 cells and hMSCs in patterned hydrogel revealed cell-cell interactions and a morphological dependency on cell types. HMSCs formed spheres through cell aggregation, while L929 cells increased in cellular mass without cell aggregation and MS1 dispersed into the matrix instead of aggregating. The aggregation of hMSCs was attenuated by treatment with Rho kinase (ROCK) inhibitor and cadherin antibody. This reflected the close relationship between cell aggregation and migration with RhoA and cell-cell adhesion molecules. Angiogenic-specific gene expression profiles showed that expression of CD105 decreased to 22% in the ROCK inhibitor group compared to control group. These results showed that cell-based patterns in a 3D matrix are highly dependent on both cell aggregation and migration over time.

Protein kinase Cδ is required for ErbB2-driven mammary gland tumorigenesis and negatively correlates with prognosis in human breast cancer

Protein kinase C δ (PKCδ) regulates apoptosis in the mammary gland, however, the functional contribution of PKCδ to the development or progression of breast cancer has yet to be determined. Meta-analysis of ErbB2-positive breast cancers shows increased PKCδ expression, and a negative correlation between PKCδ expression and prognosis. Here, we present in-vivo evidence that PKCδ is essential for the development of mammary gland tumors in a ErbB2-overexpressing transgenic mouse model, and in-vitro evidence that PKCδ is required for proliferative signaling downstream of the ErbB2 receptor. Mouse mammary tumor virus (MMTV)-ErbB2 mice lacking PKCδ (δKO) have increased tumor latency compared with MMTV-ErbB2 wild-type (δWT) mice, and the tumors show a dramatic decrease in Ki-67 staining. To explore the relationship between PKCδ and ErbB2-driven proliferation more directly, we used MCF-10A cells engineered to express a synthetic ligand-inducible form of the ErbB2 receptor. Depletion of PKCδ with short hairpin RNA inhibited ligand-induced growth in both two-dimensional (2D) (plastic) and three-dimensional (3D) (Matrigel) culture, and correlated with decreased phosphorylation of the ErbB2 receptor and reduced activation of Src and MAPK/ERK pathways. Similarly, in human breast cancer cell lines in which ErbB2 is overexpressed, depletion of PKCδ suppresses proliferation, Src and ERK activation. PKCδ appears to drive proliferation through the formation of an active ErbB2/PKCδ/Src signaling complex, as depletion of PKCδ disrupts association of Src with the ErbB2 receptor. Taken together, our studies present the first evidence that PKCδ is a critical regulator of ErbB2-mediated tumorigenesis, and suggest further investigation of PKCδ as a target in ErbB2-positive breast cancer.

Role of CX3CR1 Receptor in Monocyte/Macrophage Driven Neovascularization

Monocyte/Macrophages are implicated in initiation of angiogenesis, tissue/organ perfusion and atherosclerosis biology. We recently showed that chemokine receptor CX3CR1 is an essential regulator of monocyte/macrophage derived smooth muscle cell differentiation in the vessel wall after injury. Here we hypothesised the contribution of CX3CR1- CX3CL1 interaction to in vivo neovascularization and studied the functional consequences of genetic and pharmacologic targeting of CX3CR1 in formation, maturation and maintenance of microvascular integrity. Cells functionally deficient in CX3CR1 lacked matrix tunnelling and tubulation capacity in a 3D Matrigel assay. These morphogenic and cytokinetic responses were driven by CX3CL1-CX3CR1 interaction and totally abrogated by a Rho antagonist. To evaluate the role of CX3CR1 system in vivo, Matrigel plugs were implanted in competent CX3CR1+/gfp and functionally deficient CX3CR1gfp/gfp mice. Leaky microvessels (MV) were formed in the Matrigel implanted in CX3CR1gfp/gfp but not in CX3CR1+/gfp mice. In experimental plaque neovascularization immature MV phenotype was observed in CX3CR1gfp/gfp mice, lacking CX3CR1 positive smooth muscle-like cells, extracellular collagen and basement membrane (BM) laminin compared to competent CX3CR1+/gfp mice. This was associated with increased extravasation of platelets into the intima of CX3CR1gfp/gfp but not functionally competent CX3CR1 mice. Pharmacologic targeting using CX3CR1 receptor antagonist in wild type mice resulted in formation of plaque MV with poor BM coverage and a leaky phenotype. Our data indicate a hitherto unrecognised role for functional CX3CR1 in Matrigel and experimental plaque neovascularization in vivo, which may buttress MV collectively in favour of a more stable non-leaky phenotype.

Combined Inhibition of ErbB1/2 and Notch Receptors Effectively Targets Breast Ductal Carcinoma In Situ (DCIS) Stem/Progenitor Cell Activity Regardless of ErbB2 Status

Pathways involved in DCIS stem and progenitor signalling are poorly understood yet are critical to understand DCIS biology and to develop new therapies. Notch and ErbB1/2 receptor signalling cross talk has been demonstrated in invasive breast cancer, but their role in DCIS stem and progenitor cells has not been investigated. We have utilised 2 DCIS cell lines, MCF10DCIS.com (ErbB2-normal) and SUM225 (ErbB2-overexpressing) and 7 human primary DCIS samples were cultured in 3D matrigel and as mammospheres in the presence, absence or combination of the Notch inhibitor, DAPT, and ErbB1/2 inhibitors, lapatinib or gefitinib. Western blotting was applied to assess downstream signalling. In this study we demonstrate that DAPT reduced acini size and mammosphere formation in MCF10DCIS.com whereas there was no effect in SUM225. Lapatinb reduced acini size and mammosphere formation in SUM225, whereas mammosphere formation and Notch1 activity were increased in MCF10DCIS.com. Combined DAPT/lapatinib treatment was more effective at reducing acini size in both DCIS cell lines. Mammosphere formation in cell lines and human primary DCIS was reduced further by DAPT/lapatinib or DAPT/gefitinib regardless of ErbB2 receptor status. Our pre-clinical human models of DCIS demonstrate that Notch and ErbB1/2 both play a role in DCIS acini growth and stem cell activity. We report for the first time that cross talk between the two pathways in DCIS occurs regardless of ErbB2 receptor status and inhibition of Notch and ErbB1/2 was more efficacious than either alone. These data provide further understanding of DCIS biology and suggest treatment strategies combining Notch and ErbB1/2 inhibitors should be investigated regardless of ErbB2 receptor status.

Abstract B62: ADAM8 promotes tumorigenesis, angiogenesis, and spreading of circulating tumor cells in breast cancer

Abstract ADAM (a disintegrin and metalloprotease) proteins mediate cell adhesion and shedding of receptors and proteins of the extracellular matrix via their disintegrin and metalloproteinase domains, respectively. Recently, using microarray analysis we identified ADAM8 as a target of a pathway mediated by NF-κB RelB/Ras to B lymphocyte-induced maturation protein (Blimp-1) that promotes a more aggressive breast cancer cell phenotype. ADAM8 is a membrane-anchored protein that is synthesized as a pro-form and needs to multimerize to autocatalytically clip off its prodomain leaving an active processed form. Using the Oncomine and bc-GenExMiner databases, ADAM8 mRNA levels were found overexpressed in invasive breast tumors compared to normal breast tissue, and high ADAM8 levels were correlated with metastatic relapse in breast cancer patients. As ADAM8 is not essential under physiological conditions as evidenced by the lack of phenotype in ADAM8 deficient mice, here we tested the hypothesis that ADAM8 represents a novel target for the treatment of aggressive breast cancer. Immunohistochemical analysis revealed that ADAM8 is abundantly expressed in 34.0% (17/50) of triple-negative breast tumors and in 48.2% (27/56) of breast cancer metastases. In particular, ADAM8 was highly expressed in brain metastases (63.0%). In contrast, ADAM8 was not observed in normal mammary tissue and was only detected in 13.5% of Ductal Carcinoma In Situ tumors. Consistently, we found that ADAM8 promotes aggressive breast cancer cell behavior in culture. ADAM8 siRNA knockdown reduced the migratory and invasive properties of triple-negative breast cancer lines MDA-MB-231 and Hs578T in Boyden chamber and 3D Matrigel assays. MDA-MB-231 clones stably expressing an ADAM8 shRNA or Control shRNA showed equal rates of growth and survival in vitro. However, when these clones were used in a mammary fat pad mouse model (n=7/group), tumors derived from ADAM8 shRNA MDA-MB-231 clone uniformly failed to grow significantly beyond a palpable size over the 33 day-time course in contrast to the Control shRNA clone (0.08 g versus 2.0 g). Angiogenesis was also significantly decreased in ADAM8 shRNA cell-derived tumors as measured by CD31 staining. As the clones were stably expressing Green Fluorescent Protein, spreading of circulating tumor cells (CTCs) into the blood was analyzed by flow cytometry. The CTC numbers in mice bearing ADAM8 shRNA tumors did not exceed background level. In contrast, the Control shRNA group showed a high number of CTCs. To address the mechanism causing tumorigenesis and tumor cell spreading, we investigated the effects of hypoxia, which is an early event that promotes tumor angiogenesis. In vitro, hypoxia (1% oxygen) induced levels of ADAM8 pro-form and processed protein by ~3-fold in the Control shRNA clone, but not in the ADAM8 shRNA clone. As an early step in migration of cancers cells requires β1-integrin activation, we tested the effects of ADAM8 knockdown. Immunofluorescence demonstrated an essential role of ADAM8 in activation of β1-integrin in the MDA-MB-231 clones. Consistently, expression and activity of the matrix metalloprotease MMP-9, which is induced downstream of β1-integrin pathway, were reduced by ADAM8 knockdown, suggesting this is an essential pathway whereby ADAM8 promotes matrix remodeling and angiogenesis. Despite recent advances in diagnosis and treatment of breast cancer, in many patients the disease still progresses to invasive carcinoma with fatal metastatic spread of primary tumors to distant organs. Our findings suggest that ADAM8 constitutes a promising new target for the treatment of these aggressive breast cancers. Citation Format: Mathilde Romagnoli, Nora D. Mineva, Delphine Loussouarn, Sophie Barillé-Nion, Mike Polmear, Irene Georgakoudi, Catharina Conrad, Uwe Schlomann, Joerg W. Bartsch, Maddy Parsons, Gail E. Sonenshein. ADAM8 promotes tumorigenesis, angiogenesis, and spreading of circulating tumor cells in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B62.

N-Cadherin Dependent Collective Cell Invasion of Prostate Cancer Cells Is Regulated by the N-Terminus of α-Catenin

Cancer cell invasion is the critical first step of metastasis, yet, little is known about how cancer cells invade and initiate metastasis in a complex extracellular matrix. Using a cell line from bone metastasis of prostate cancer (PC3), we analyzed how prostate cancer cells migrate in a physiologically relevant 3D Matrigel. We found that PC3 cells migrated more efficiently as multi-cellular clusters than isolated single cells, suggesting that the presence of cell-cell adhesion improves 3D cell migration. Perturbation of N-cadherin function by transfection of either the N-cadherin cytoplasmic domain or shRNA specific to N-cadherin abolished collective cell migration. Interestingly, PC3 cells do not express α-catenin, an actin binding protein in the cadherin complex. When the full-length α-catenin was re-introduced, the phenotype of PC3 cells reverted back to a more epithelial phenotype with a decreased cell migration rate in 3D Matrigel. Interestingly, we found that the N-terminal half of α-catenin was sufficient to suppress invasive phenotype. Taken together, these data suggest that the formation of N-cadherin junctions promotes 3D cell migration of prostate cancer cells, and this is partly due to an aberrant regulation of the N-cadherin complex in the absence of α-catenin.

Novel role of microRNA146b in promoting mammary alveolar progenitor cell maintenance

In this report, we have shown that miR146b promotes the maintenance of pregnancy-derived mammary luminal alveolar progenitors. MiR146b expression was significantly higher in the mammary glands of pregnant and lactating mice than in virgin mice. Furthermore, miR146b levels were significantly higher in mouse mammary glands exposed to the sex hormones, estrogen and progesterone, compared with those of untreated control animals. Pregnancy-derived primary mouse mammary epithelial cells in which miR146b was knocked down showed a significant reduction in the number of hollow acinar organoid structures formed on three-dimensional Matrigel and in β-casein expression. This demonstrates that miR146b promotes the maintenance of pregnancy-derived mammary luminal alveolar progenitors. It has been shown that mouse mammary luminal progenitors give rise to hollow organoid structures, whereas solid organoid structures are derived from stem cells. Among several miR146b targets, miR146b knockdown resulted in preferential STAT3β overexpression. In the primary mouse mammary epithelial cells, overexpression of STAT3β isoform caused mammary epithelial cell death and a significant reduction in β-casein mRNA expression. Therefore, we conclude that during pregnancy miR146b is involved in luminal alveolar progenitor cell maintenance, at least partially, by regulating STAT3β.

Abstract P6-04-24: Overexpression of protein kinase C alpha differentially activates transcription factors in T47D breast cancer cells in the presence of 17β-estradiol both in the 2D and 3D environments.

Abstract Background: Our lab has previously shown that overexpression of protein kinase C alpha (PKCα) results in a hormone independent, tamoxifen resistant phenotype in the T47D:A18 breast cancer cell line. Moreover, 17β-estradiol (E2) inhibits colony formation of T47D/PKCα in 3D Matrigel and tumor growth in vivo but not in the 2D environment (Zhang et al, Mol. Cancer Res, 2009). Differential transcriptional activation may account for the phenotypic changes observed in T47D/PKCα cells. In this study, we sought to identify transcription factors (TF) differentially activated in T47D:A18/neo versus T47D:A18/PKCα grown in 3D Matrigel in the presence and absence of E2, and compare these TFs with those activated in the 2D environment using a high-throughput screening (HTS) technology. Methods: A system for rapid, non-invasive, large scale, dynamic quantification of TF activity was developed (Weiss et al, PLoS ONE, 2010). Reporter constructs were created containing a TF binding site that preceeds a basal promoter to produce firefly luciferase (Fluc) using a lentiviral backbone. The control construct contained only the basal promoter and was used for normalization. T47D/PKCα and T47D/neo cells were infected with lentiviral reporter constructs. Cells were seeded either on top of Matrigel or without Matrigel in 384 well plates in E2-free media. After 3 days, cells were treated with either E2 (10–9M) or vehicle (0.1% ethanol). Fluc activity was assessed by bioluminescence imaging at 24, 48 and 72 hours following treatment using Xenogen IVIS Spectrum imaging system. Results: Initial findings showed differential transcriptional activities between the parental T47D/neo and T47D/PKCα cell lines at the basal level (without E2 treatment) in the 3D environment. Specifically, TFs involved in tumorigenesis (such as ETS1, STAT5) or the EMT process (such as SNAI1) were more highly activated in T47D/PKCα cells. Furthermore, E2 has a modulating effect on the activities of TFs in the two cell lines over time; observed both in the 2D and 3D environments. In particular, some TFs, such as Oct4, ETS1, and Stat5; were modulated (either induced or suppressed) by E2 only in T47D/PKCα cells. Conclusion: These findings suggest that overexpression of PKCα alters TF activity in T47D breast cancer cells both basally and in response to E2. This HTS technology allowed us to reveal the dynamic regulation of TF activation in PKCα overexpressing T47D breast cancer cells. We are now beginning to understand the mechanism whereby PKCα may mediate differential response to E2 dependent on the microenvironment. This HTS approach is likely to lead to the identification of new therapeutic targets. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-04-24.

Abstract P1-04-04: KSR1 is involved in functional interaction between p53 and BRCA1 and is an independent predictor of overall survival in breast cancer

Abstract Background: Our recent human kinome screening to identify new regulators of estrogen receptor α (ERα) suggested an important role of kinase suppressor of ras 1 (KSR1) in breast cancer. KSR1 was originally identified as a positive regulator interacting with both RAS and RAF in the mitogen-activated protein kinase (MAPK) pathway. Recent studies have suggested that KSR1 may have dual functions as a scaffolding protein and also a protein kinase. Although KSR1 has been implicated in Ras-dependent cancers, its clinical significance and function in breast cancer have not been elucidated. Methods: The clinical significance of KSR1 was assessed by analyzing its expression in breast cancer tissue microarrays (TMAs, n=1000) by immunohistochemistry. Pearson chi2 and Fisher's Exact Test were used to correlate the expression levels with various tumor biomarkers; Kaplan Meier analyses were used to investigate impact on disease-free (DFS) and overall survival (OS). Multivariate Cox-proportional hazards analysis was also performed to evaluate the significant of KSR1 as an independent factor in breast cancer-specific survival (BCSS) and disease-free interval (DFI). The expression levels of KSR1 in breast cancer cell lines were measured by RT-qPCR and western blotting. A KSR1 stable over-expression breast cancer cell line (MCF7-KSR1) was generated to study its effect on growth and colony formation by 3D matrigel assay and soft agar assay in vitro. Furthermore, MCF7-KSR1 stable cells were also used in nude mice xenograft model in vivo. Luciferase reporter assay was employed to examine the effect of KSR1 on p53 transcriptional activity. Further immunofluorescence staining, western blotting and reporter assays were performed to elucidate the interaction between KSR1, BRCA1 and p53. Results: KSR1 was expressed with low (60%) and high levels (40%) in breast cancer patients. High expression correlated significantly with longer DFS (p = 0.014) and longer OS (p = 0.012) in more than 20 yrs follow-up. Interestingly, KSR1 was positively associated with BRCA1 (p = 0.002) and reversely with p53 (p = 0.038). High KSR1 levels were a significant predictor of longer breast cancer-specific survival BCSS (p = 0.001) and longer disease free interval DFI (p = 0.002) independent of tumour stage, grade and size. RT-qPCR and western blotting demonstrated that KSR1 is ubiquitously expressed in breast cancer cell lines. In vitro 3D matrigel and soft agar assay showed that MCF7-KSR1 cells had a significant decreased number of colonies and formed smaller size colonies compared to MCF7-vector cells. Furthermore, over-expression of KSR1 (MCF7-KSR1) significantly suppressed the growth of breast cancer xenografts in nude mice. Finally, KSR1 was involved in the functional interaction between BRCA1 and p53 and elevated KSR1 potentially resulted in up-regulated BRCA1. KSR1 also inhibited p53-dependent transcriptional activity through suppression of p53 acetylation and promotion of p53 neddylation. Conclusion: KSR1 is an independent prognostic factor in breast cancer and high KSR1 expression correlates with longer DFS and OS. Furthermore, it is potential that KSR1 is important in tumour suppression by its involvement in functional feedback regulation of BRCA1 and p53. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-04-04.

ARTEMIN Promotes De Novo Angiogenesis in ER Negative Mammary Carcinoma through Activation of TWIST1-VEGF-A Signalling

The neurotrophic factor ARTEMIN (ARTN) has been reported to possess a role in mammary carcinoma progression and metastasis. Herein, we report that ARTN modulates endothelial cell behaviour and promotes angiogenesis in ER-mammary carcinoma (ER-MC). Human microvascular endothelial cells (HMEC-1) do not express ARTN but respond to exogenously added, and paracrine ARTN secreted by ER-MC cells. ARTN promoted endothelial cell proliferation, migration, invasion and 3D matrigel tube formation. Angiogenic behaviour promoted by ARTN secreted by ER-MC cells was mediated by AKT with resultant increased TWIST1 and subsequently VEGF-A expression. In a patient cohort of ER-MC, ARTN positively correlated with VEGF-A expression as measured by Spearman’s rank correlation analysis. In xenograft experiments, ER-MC cells with forced expression of ARTN produced tumors with increased VEGF-A expression and increased microvessel density (CD31 and CD34) compared to tumors formed by control cells. Functional inhibition of ARTN by siRNA decreased the angiogenic effects of ER-MC cells. Bevacizumab (a humanized monoclonal anti-VEGF-A antibody) partially inhibited the ARTN mediated angiogenic effects of ER-MC cells and combined inhibition of ARTN and VEGF-A by the same resulted in further significant decrease in the angiogenic effects of ER-MC cells. Thus, ARTN stimulates de novo tumor angiogenesis mediated in part by VEGF-A. ARTN therefore co-ordinately regulates multiple aspects of tumor growth and metastasis.

Vincristine enhances amoeboid-like motility via GEF-H1/RhoA/ROCK/Myosin light chain signaling in MKN45 cells

BackgroundAnti-cancer drugs are widely used in cancer treatment frequently combined with surgical therapy and/or radiation therapy. Although surgery and radiation have been suggested to facilitate invasion and metastasis of tumor cells in some cases, there is so far little information about the effect of anti-cancer drugs on cellular invasive ability and metastasis. In this study, using four different anti-cancer drugs (vincristine, paclitaxel, cisplatin and etoposide), we examined whether these drugs influence the invasive ability of tumor cells.MethodsHuman gastric adenocarcinoma MKN45 cells were used to evaluate the effect of anti-cancer drugs. After drug treatment, cellular invasive ability was assessed using the Matrigel invasion chamber. Cytoskeletal changes after treatment were examined microscopically with F-actin staining. In addition, we monitored cellular motility in 3D matrigel environment by time-lapse microscopic analysis. The drug-induced activation of RhoA and ROCK was evaluated by pull-down assay and Western blotting using an antibody against phosphorylated myosin light chain (MLC), respectively. Where necessary, a ROCK inhibitor Y27632 and siRNA for guanine nucleotide exchange factor-H1 (GEF-H1) were applied.ResultsAmong all drugs tested, only vincristine stimulated the invasive ability of MKN45 cells. Microscopic analysis revealed that vincristine induced the formation of non-apoptotic membrane blebs and amoeboid-like motility. Vincristine significantly enhanced RhoA activity and MLC phosphorylation, suggesting the involvement of RhoA/ROCK pathway in the vincristine-induced cytoskeletal reorganization and cellular invasion. Furthermore, we found that Y27632 as well as the siRNA for GEF-H1, a RhoA-specific activator, attenuated MLC phosphorylation, the formation of membrane blebs and the invasive ability after vincristine treatment.ConclusionsThese results indicate that vincristine activates GEF-H1/RhoA/ROCK/MLC signaling, thereby promoting amoeboid-like motility and the invasive ability of MKN45 cells.

P210 bcr‐abl induces amoeboid motility by recruiting ADF/destrin through RhoA/ROCK1

We previously demonstrated that the Bcr-Abl oncogene, p210(bcr-abl), through its unique GEF domain, specifically activates RhoA and induces spontaneous amoeboid motility. We intend to study the pathways downstream RhoA controlling amoeboid motility. Mouse prolymphoblastic cells (Ba/F3 cell line) expressing different forms of Bcr-Abl were embedded in 3-dimensional (3D) Matrigel to study motility and explore the effects of inhibiting Rho pathway (inhibitors and siRNAs). The phosphorylation levels of cofilin-1 and destrin were analyzed by 2-dimensional electrophoresis. Composition of Bcr-Abl signalplex in different conditions was determined by coimmunoprecipitation. Ba/F3p190 and Ba/F3 expressing a mutant form of p210(bcr-abl) (unable to activate RhoA) cells presented a spontaneous motility, but not an amoeboid type. p210(bcr-abl)-induced amoeboid motility in a 3D matrix requires isoform-specific RhoA/ROCK-1/destrin signaling. Next to the conventional Rho/ROCK/MLC/myosin pathway, this pathway is a crucial determinant for amoeboid motility, specific for the destrin isoform (and not its coexpressed homologue cofilin-1). Also, the presence of destrin (and not cofilin-1) in the p210(bcr-abl) complex is dependent on ROCK1, and this signalplex is required for amoeboid motility. This underscores isoform-specific function within the ADF/cofilin family and provides new insight into Bcr-Abl signaling to amoeboid motility and possible impact on understanding chronic myeloid leukemia progression.

Nicastrin regulates breast cancer stem cell properties and tumor growth in vitro and in vivo

Nicastrin (NCT) is a crucial component of the γ-secretase (GS) enzyme, which prompted investigations into its biological role in cancer. We have previously shown that nicastrin is overexpressed in breast cancer (BC), conferring worse overall survival in invasive, ERα negative patients. Here, we used 2D and 3D Matrigel, anchorage-independent growth conditions and a breast cancer xenograft mouse model to assess the impact of nicastrin on breast cancer stem cell (BCSC) propagation and invasion in vitro and tumor growth in vivo. Stable knockdown of nicastrin in HCC1806 breast cancer cells reduced cell invasion by 51.4 ± 1.7%, accompanied by a morphological change to a rounded cell phenotype and down-regulation of vimentin, Snail, Twist, MMP2, and MMP9. We observed a reduction of the pool of CD44(+)/CD24(-) and ALDH1 high breast cancer stem cells by threefold and twofold, respectively, and a reduction by 2.6-fold of the mammospheres formation. Nicastrin overexpression in nontransformed MCF10A cells caused an induction of epithelial to mesenchymal regulators, as well as a fivefold increased ALDH1 activity, a threefold enrichment for CD44(+)/CD24(-) stem cells, and a 3.2-fold enhanced mammosphere-forming capacity. Using the γ-sescretase inhibiton, Notch1/4 siRNA, and Akt inhibition, we show that nicastrin regulates breast cancer stem cells partly through Notch1 and the Akt pathway. Exploiting serial dilution transplantation of the HCC1806 cells expressing nicastrin and HCC1806 stably depleted of nicastrin, in vivo, we demonstrate that nicastrin inhibition may be relevant for the reduced tumorigenicity of breast cancer cells. These data could serve as a benchmark for development of nicastrin-targeted therapies in breast cancer.

TIMP-1 Induces an EMT-Like Phenotypic Conversion in MDCK Cells Independent of Its MMP-Inhibitory Domain

Matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs) regulate epithelial-mesenchymal transition (EMT) critical for the development of epithelial organs as well as cancer cell invasion. TIMP-1 is frequently overexpressed in several types of human cancers and serves as a prognostic marker. The present study investigates the roles of TIMP-1 on the EMT process and formation of the lumen-like structure in a 3D Matrigel culture of MDCK cells. We show that TIMP-1 overexpression effectively prevents cell polarization and acinar-like structure formation. TIMP-1 induces expression of the developmental EMT transcription factors such as SLUG, TWIST, ZEB1 and ZEB2, leading to downregulation of epithelial marker and upregulation of mesenchymal markers. Importantly, TIMP-1′s ability to induce the EMT-like process is independent of its MMP-inhibitory domain. To our surprise, TIMP-1 induces migratory and invasive properties in MDCK cells. Here, we present a novel finding that TIMP-1 signaling upregulates MT1-MMP and MMP-2 expression, and potentiates MT1-MMP activation of pro-MMP-2, contributing to tumor cell invasion. In spite of the fact that TIMP-1, as opposed to TIMP-2, does not interact with and inhibit MT1-MMP, TIMP-1 may act as a key regulator of MT1-MMP/MMP-2 axis. Collectively, our findings suggest a model in which TIMP-1 functions as a signaling molecule and also as an endogenous inhibitor of MMPs. This concept represents a paradigm shift in the current view of TIMP-1/MT1-MMP interactions and functions during cancer development/progression.

Angiogenesis Potential of Human Limbal Stromal Niche Cells

The perivascular localization of stem cell (SC) niches suggests the presence of a vascular niche. We aimed to determine the angiogenesis potential of limbal niche cells (NCs). Human limbal NCs were isolated and serially passaged on plastic or coated Matrigel in embryonic SC medium containing BFGF and leukemia inhibitory factor before being reseeded in 3D Matrigel. Expression of angiogenesis markers was assessed by RT-qPCR and immunofluorescence staining. Their angiogenesis potential was measured by differentiation into vascular endothelial cells and by supporting vascular tube network formed by human umbilical vein endothelial cells (HUVEC) on Matrigel. Their support of limbal epithelial progenitor cells (LEPC) was examined in sphere growth formed by reunion in 3D Matrigel. On plastic, limbal NC could be cultured only up to four passages before turning into myofibroblasts. In contrast, on coated Matrigel, they could be expanded for up to 12 passages with upregulation of markers suggestive of angiogenesis progenitors when reseeded in 3D Matrigel because they could differentiate into vascular endothelial cells and pericytes stabilizing the tube network formed by HUVEC. Although both expanded limbal NCs and HUVEC rejoined with LEPC to form spheres to upregulate expression of ΔNp63α, CK15, and CEBPδ, the former but not the latter abolished expression of CK12 keratin. Human limbal NCs continuously expanded on the basement membrane differentiate into angiogenesis progenitors that prevent differentiation of LEPC/SCs. They may partake in formation of the vascular niche and contribute to angiogenesis during wound healing.

31P-Magnetic resonance spectra of ovarian cancer cells exposed to chemotherapy within a three-dimensional Matrigel construct

We aimed to determine the metabolic profile and effects of chemotherapy on ovarian cancer cell metabolism in a three-dimensional (3D) vs. a two-dimensional (2D) construct using 31P-magnetic resonance spectroscopy (MRS). Three ovarian cancer cell lines were embedded in a 3D perfused Matrigel construct or grown in a 2D monolayer. Metabolic differences between the three cell lines were determined using 31P-MRS both in the 3D and in the 2D constructs. Cells were incubated with three different cytotoxic drugs at LC50 for 44h and evaluated for metabolic changes using 31P-MRS. While the 3D construct allowed MRS assessment of viable cells, the 2D monolayer permitted evaluation of non-viable cell extracts. In both cells embedded in Matrigel (CEM) and cells grown in monolayers (CGM) different cancer cell lines showed characteristic metabolic fingerprints, which differed significantly between CEM and CGM. In contrast to the cell monolayer, CEM allowed continuous monitoring of the changes in 31P-MRS spectra over time following exposure to chemotherapy, demonstrating a progressive decrease in specific phosphorylated metabolites. The metabolic response of CEM and CGM to various antimitotic agents was significantly different. We conclude that different ovarian cancer cell lines show characteristic 31P-MRS fingerprints and specific metabolic changes in response to cytotoxic drug treatment. The perfused 3D Matrigel construct is superior to the 2D tissue monolayer for 31P-MRS studies, because it simulates the invivo conditions more closely and facilitates MRS evaluation of viable cells as well as continuous monitoring of metabolic changes in response to chemotherapy over time.