Sox2 is a transcription factor in neural stem cells and keeps the cells immature and proliferative. Sox2 is expressed in primary human glioma such as glioblastoma multiforme (GBM), primary glioma cells and glioma cell lines and is implicated in signaling pathways in glioma connected to malignancy. Sox21, the counteracting partner of Sox2, has the same expression pattern as Sox2 in glioma but in general induces opposite effects. In this study, Sox21 was overexpressed by using a tetracycline-regulated expression system (tet-on) in glioma cells. The glioma cells were injected subcutaneously into immunodeficient mice. The control tumors were highly proliferative, contained microvascular proliferation and large necrotic areas typical of human GBM. Induction of Sox21 in the tumor cells resulted in a significant smaller tumor size, and the effect correlated with the onset of treatment, where earlier treatment gave smaller tumors. Mice injected with glioma cells orthotopically into the brain survived significantly longer when Sox21 expression was induced. Tumors originating from glioma cells with an induced expression of Sox21 exhibited an increased formation of Sox2:Sox21 complexes and an upregulation of S100β, CNPase and Tuj1. Sox21 appears to decrease the stem-like cell properties of the tumor cells and initiate aberrant differentiation of glioma cells in vivo. Taken together our results indicate that Sox21 can function as a tumor suppressor during gliomagenesis mediated by a shift in the balance between Sox2 and Sox21. The wide distribution of Sox2 and Sox21 in GBM makes the Sox2/Sox21 axis a very interesting target for novel therapy of gliomas.

Glioblastoma multiforme (GBM) is an aggressive brain malignancy characterized by high heterogeneity and invasiveness. It is increasingly accepted that the refractory feature of GBM to current therapies stems from the existence of few tumorigenic cells that sustain tumor growth and spreading, the so-called glioma-initiating cells (GICs). Previous studies showed that cytokines of the bone morphogenetic protein (BMP) family induce differentiation of the GICs, and thus act as tumor suppressors. Molecular pathways that explain this behavior of BMP cytokines remain largely elusive. Here, we show that BMP signaling induces Smad-dependent expression of the transcriptional regulator Snail in a rapid and sustained manner. Consistent with its already established promigratory function in other cell types, we report that Snail silencing decreases GBM cell migration. Consequently, overexpression of Snail increases GBM invasiveness in a mouse xenograft model. Surprisingly, we found that Snail depletes the GBM capacity to form gliomaspheres in vitro and to grow tumors in vivo, both of which are important features shared by GICs. Thus Snail, acting downstream of BMP signaling, dissociates the invasive capacity of GBM cells from their tumorigenic potential.

Abstract Sox2 and Sox21 are two transcription factors important for the developing, as well as the adult, CNS, and they are often co-expressed. Sox2 is an embryonic stem cell marker, whereas ectopic forced expression of Sox21 has been shown to induce differentiation in embryonic stem cells. Further, Sox2 is important for maintenance of neural stem cells whereas Sox21 is important for neurogenesis. These two transcriptionfactors are thus in opposite relation to each other and it is believed that a proper balance between them is needed to regulate target genes. Sox2 is highly expressed in brain tumors and up to 97% of GBM samples express Sox2. While the expression of Sox2 has been shown in GBM, in primary glioma cells and established glioma cell lines, less is known about Sox21 in glioma. We have previously shown that Sox2 and Sox21 are co-expressed in adult and childhood brain tumors and are in a functional relationship in glioma cells. Sox2 keeps glioma cells in a proliferative state whereas over expression of Sox21 reduces Sox2 expression and decreases cell proliferation with an increased tendency of apoptosis and differentiation of the glioma cells. We have now further elucidated this effect in vivo by injecting established inducible-Sox21 glioma cell lines subcutaneously into the flank and orthotopically into the brain of SCID mice. Regardless of the injection site, increased Sox21 expression in these tumors reduces tumor growth. The tumors from treated mice were significantly smaller in size and there is a significant increase in survival time. This effect was dependent on the time of Sox21 induction, where an earlier turn on gives even smaller tumors. Total depletion of Sox2 was not achieved despite forced Sox21 expression. Further we show that Sox2 deficiency leads to an inability to form tumors. With its dual effect, the ability to decrease Sox2 expression and the ability to aberrantly differentiate tumor cells, Sox21 becomes a very important factor for future research around therapeutic possibilities in GBM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 66. doi:1538-7445.AM2012-66

Material and Methods: Recombinant adenoviral vectors with RGD-modified fiber (rAdRGD) and a p53-responsive promoter (PG) were constructed containing genes of p19Arf, IFN or the combination of both.Evaluation of in vitro antiproliferative effect of transgenes in B16F10 cells (B16, mouse melanoma, p53 wt) was done by annexin/PI staining and MTT assays.Bystander effect was revealed by cell cycle analysis of populations transduced with different proportions of the viruses.Antitumor effect in vivo was observed by treatment of established LLC1 tumors (mouse lung carcinoma, p53 wt) with intratumoral injection of rAdRGD in C57BL/6 mice.Involvement of immune response was revealed by second tumor challenge at contralateral flank of mice with a developed and treated first tumor.Results and Discussion: Cell death was resulted from the p19Arf and IFN combined transference (74% subG0), yet single gene transfer yielded only half the number of subG0 cells.A similar result was seen by measurement of cell viability with MTT.Evidence on a bystander effect was revealed when approximately 50% subG0 cells were observed, even though only 10% of the cells had been transduced with IFN.In a population of cells transduced with p19Arf, when 10% of them also expressed IFN, the number of subG0 cells increased to 68%, compared to transduction of p19Arf alone, which results in 45% subG0 cells.This indicates that p19Arf can sensitize cells to death by IFN bystander effect.In vivo assays with the LLC1 model have shown that in situ gene therapy of p19Arf and IFN combination was more effective to inhibit tumor progression and increase survival than application of a single gene.These animals were then challenged with the implantation of a second tumor, revealing greater retardation of growth at the secondary tumor site in mice treated with the combined gene therapy at the primary tumor locus as compared to animals that received single gene treatment. Conclusion:The use of p53-responsive vectors to express p19Arf and IFN represents a potential strategy for melanoma and lung carcinoma tumor suppression.We have shown that complementation of the p53/Arf and interferon pathways in the primary tumor may generate a strong bystander effect as well as immune stimulation.

We have investigated the presence of tentative stem-like cells in the canine mammary tumor cell line CMT-U229. This cell line is established from an atypical benign mixed mammary tumor, which has the property of forming duct-like structures in collagen gels. Stem cells in mammary glands are located in the epithelium; therefore we thought that the CMT-U229 cell line would be suitable for detection of tentative cancer stem-like cells. Side population (SP) analyses by flow cytometry were performed with cells that formed spheroids and with cells that did not. Flow cytometric, single sorted cells were expanded and re-cultured as spheroids. The spheroids were paraffin embedded and characterized by immunohistochemistry. SP analyses showed that spheroid forming cells (retenate) as well as single cells (filtrate) contained SP cells. Sca1 positive cells were single cell sorted and thereafter the SP population increased with repeated SP analyses. The SP cells were positively labeled with the cell surface-markers CD44 and CD49f (integrin alpha6); however the expression of CD24 was low or negative. The spheroids expressed the transcription factor and stem cell marker Sox2, as well as Oct4. Interestingly, only peripheral cells of the spheroids and single cells were positive for Oct4 expression. SP cells are suggested to correspond to stem cells and in this study, we have enriched for tentative tumor stem-like cells derived from a canine mammary tumor. All the used markers indicate that the studied CMT-U229 cell line contains SP cells, which in particular have cancer stem-like cell characteristics.

1.1 Brain tumours/ glioma and medulloblastoma The total amount of brain tumours that effect humans is less than 2%. In children are brain tumours the second most common cancer type after leukaemia. Brain tumours and tumours in CNS (central nervous system) constitute 25% of all childhood tumours and is the most common cause of cancer mortality in children. Medulloblastoma is the most frequent malignant brain tumour type in children, whereas in adult glioblastoma multiforme (GBM) is the most malignant and common form. Although GBM occur in children but the diagnose is more uncommon. Primary brain tumours are classified according to the World Health Organization (WHO) which means grading (I-IV) of the tumours based on tumour histology and pathology (Louis, et al., 2007). However, other criteria such as the age of the patient, tumour location, radiological features, surgical resection, proliferation index and genetic alterations are important when predicting a response of therapy (Louis, et al., 2007).

In this Special Issue, a number of common biological mechanisms are presented that govern both mammary gland development and mammary cancer. About half of the contributors present data on normal growth and differentiation of the gland, while for the others, cancer is the dominating theme. Yet, nearly all of them cross-refer to both research fields, and one of the innovating concepts in this respect is the existence of cellular ecosystems operating in development and cancer. The introductory paper by Marc Mareel and Susana Constantino already underpins the importance of the ecosystem concept by pointing to the existence of cell-cell interactions at multiple levels: between epithelial cells with different phenotypes (stem cells, non-stem cells, ductal cells, myoepithelial cells, etc.), between epithelial cells and stromal elements (endothelial cells, cancer-associated fibroblasts, macrophages, etc.) and, last but not least, between different ecosystems within the organism (primary tumor, metastases, bone marrow, etc.). Strikingly, the research contributions from other authors in this Issue add numerous ecosystem examples in development and cancer, confirming their general occurrence in mammary biology. Historical background information on the ecosystem concept is further provided in the interview with Marc Mareel, translating its relevance also for cancer therapy.Another central issue is the stem cell. Thus, the role of normal adult stem cells in growth and differentiation of the mammary gland is considered from different points of view. Agla Fridriksdottir et al. pay attention to markers for identification and localization of these cells in the mammary …

Numerous studies support a role for Sox2 to keep stem cells and progenitor cells in an immature and proliferative state. Coexpression of Sox2 and GFAP has been found in regions of the adult brain where neural stem cells are present and in human glioma cells. In our study, we have investigated the roles of Sox2 and its counteracting partner Sox21 in human glioma cells. We show for the first time that Sox21 is expressed in both primary glioblastoma and in human glioma cell lines. We found that coexpression of Sox2, GFAP and Sox21 was mutually exclusive with expression of fibronectin. Our result suggests that glioma consists of at least two different cell populations: Sox2(+) /GFAP(+) /Sox21(+) /FN(-) and Sox2(-) /GFAP(-) /Sox21(-) /FN(+) . Reduction of Sox2 expression by using siRNA against Sox2 or by overexpressing Sox21 using a tetracycline-regulated expression system (Tet-on) caused decreased GFAP expression and a reduction in cell number due to induction of apoptosis. We suggest that Sox21 can negatively regulate Sox2 in glioma. Our findings imply that Sox2 and Sox21 may be interesting targets for the development of novel glioma therapy.

Earlier we used a glioma model to identify loci in the mouse genome, which were repeatedly targeted by platelet-derived growth factor (PDGF)-containing Moloney murine leukemia viruses. The gene Prkg2, encoding cyclic guanosine monophosphate (cGMP)-dependent protein kinase II, cGKII, was tagged by retroviral insertions in two brain tumors. The insertions were both situated upstream of the kinase domain and suggested creating a truncated form of the cGKII protein. We transfected different human glioma cell lines with Prkg2 and found an overall reduction in colony formation and cell proliferation compared with controls transfected with truncated Prkg2 (lacking the kinase domain) or empty vector. All glioma cells transfected with the cGKII phosphorylate vasodilator-stimulated phosphoprotein, VASP, after cGMP analog treatment. Glioma cell lines positive for the Sox9 transcription factor showed reduced Sox9 expression when Prkg2 was stably transfected. When cGKII was activated by cGMP analog treatment, Sox9 was phosphorylated, Sox9 protein expression was suppressed and the glioma cell lines displayed loss of cell adhesion, inhibition of Akt phosphorylation and G1 arrest. Sox9 repression by siRNA was similarly shown to reduce glioma cell proliferation. Expression analysis of stem and glial lineage cell markers also suggests that cGKII induces differentiation of glioma cell lines. These findings describe an anti-proliferative role of cGKII in human glioma biology and would further explain the retroviral tagging of the cGKII gene during brain tumor formation in PDGF-induced tumors.

LB-60 We previously used a glioma model to identify loci in the mouse genome that were repeatedly targeted by PDGF-containing Moloney murine leukemia viruses. The gene Prkg2 , encoding cGMP-dependent protein kinase II, cGKII, was tagged by retroviral insertions in two brain tumors. The insertions were both situated upstream of the kinase domain and suggested to create a truncated form of the cGKII protein. Prkg2 is expressed in murine brain tumors but not in established glioma cell lines. We transfected Prkg2 -deficient human glioma cell lines with Prkg2 and found an overall reduction in colony formation and cell proliferation compared to controls transfected with truncated Prkg2 (lacking the kinase domain) or empty vector. More immature glioma cell lines, positive for Sox2 and Sox9 transcription factors, showed a reduced Sox9 expression when Prkg2 was stably transfected. When cGKII was activated by cGMP analog treatment, Sox9 expression was further suppressed and the glioma cell lines displayed loss of cell adhesion, inhibition of Akt phosphorylation and G1 arrest. Expression analysis of stem and glial lineage cell markers suggests that cGKII differentiates glioma cell lines. Moreover, cGKII expression that is often lost in early passages during in vitro culturing in normal oxygen conditions was sustained when primary brain cells were cultured in stem cell conditions or hypoxia. Hypoxic culturing conditions also correlated with lower cGMP levels. The role of cGKII loss during establishing human glioma cell lines is currently evaluated using primary tumor samples. The present findings describe a suppressive role of cGKII in human glioma biology and would further explain the retroviral tagging of the cGKII gene during brain tumor formation in PDGF-induced tumors.

In a previously published insertional mutagenesis screen for candidate brain tumor genes in the mouse using a Moloney mouse leukemia virus encoding platelet-derived growth factor (PDGF)-B, the Sox10 gene was tagged in five independent tumors. The proviral integrations suggest an enhancer effect on Sox10. All Moloney murine leukemia virus/PDGFB tumors had a high protein expression of Sox10 independently of malignant grade or tumor type. To investigate the role of Sox10 in gliomagenesis, we used the RCAS/tv-a mouse model in which the expression of retroviral-encoded genes can be directed to glial progenitor cells (Ntv-a mice). Both Ntv-a transgenic mice, wild-type, and Ntv-a p19Arf null mice were injected with RCAS-SOX10 alone or in combination with RCAS-PDGFB. Infection with RCAS-SOX10 alone did not induce any gliomas. Combined infection of RCAS-SOX10 and RCAS-PDGFB in wild-type Ntv-a mice yielded a tumor frequency of 12%, and in Ntv-a Arf-/- mice the tumor frequency was 30%. This indicates that Sox10 alone is not sufficient to induce gliomagenesis but acts synergistically with PDGFB in glioma development. All induced tumors displayed characteristics of PNET-like structures and oligodendroglioma. The tumors had a strong and widely distributed expression of Sox10 and PDGFR-alpha. We investigated the expression of Sox10 in other human tumors and in a number of gliomas. The Sox10 expression was restricted to gliomas and melanomas. All glioma types expressed Sox10, and tumors of low-grade glioma had a much broader distribution of Sox10 compared with high-grade gliomas.

Malignant primary brain tumors, gliomas, often overexpress both platelet-derived growth factor (PDGF) ligands and receptors providing an autocrine and/or paracrine boost to tumor growth. Glioblastoma multiforme (GBM) is the most frequent glioma. Its aggressive and infiltrative growth renders it extremely difficult to treat. Median survival after diagnosis is currently only 14 months. The present thesis describes the use of retroviral tagging to identify candidate cancer-causing genes that cooperate with PDGF in brain tumor formation. Newborn mice were injected intracerebrally with a Moloney murine leukemia retrovirus carrying the sis/PDGF-B oncogene and a replication competent helper virus. Brain tumors with many characteristics of human glioblastomas developed after 13-42 weeks. Analysis of proviral integrations in the brain tumors identified almost 70 common insertion sites (CISs). These CISs were named brain tumor loci and harbored known but also putative novel cancer-causing genes.An array with over 15000 unique cDNAs was used to screen for differentially expressed genes in the mouse brain tumors compared to normal brain. Known tumor genes and markers of immature cells were upregulated in the tumors. Short latency tumors were further distinguished as fast growing and GBM-like. Long latency tumors resembled slow-growing oligodendrogliomas and contained significantly less integrations as compared to short latency tumors.The gene Prkg2, encoding the cGMP-dependent protein kinase II, was targeted by insertions in two brain tumors. Overexpression of Prkg2 in human glioma cell lines led to a reduction in colony formation, cell proliferation and migration. A glioma cell line expressing markers of immature stem cells showed loss of cell adhesion, G1 cell cycle arrest and decreased activation of the survival signaling protein Akt upon stimulation with a cGMP analog that activates the Prkg2 protein. The present thesis shows that proviral tagging may be a useful tool in the search for candidate glioma genes.

During early mouse embryogenesis, each laminin (Lm) chain of the first described Lm, a heterotrimer of alpha1, beta1, and gamma1 chains (Lm-1), is essential for basement membrane (BM) assembly, which is required for pregastrulation development. individual domains may have other functions, not necessarily structural. The cell binding C terminus of Lm alpha1 chain contains five Lm globular (LG) domains. In vitro, alpha1LG1-3 domains bind integrins, and alpha1LG4 binds dystroglycan, heparin, and sulfatides. A prevailing hypothesis is that alpha1LG4 is crucial as a structural domain for BM assembly, whereas integrin-binding sites conduct signaling. The in vivo role of alpha1LG4-5 (also called E3) has not been studied. Mice lacking alpha1LG4-5 were therefore made. Null embryos implanted, but presumptive epiblast cells failed to polarize and did not survive past day 6.5. BM components including truncated Lm alpha1 were detected in Reichert's membrane. Surprisingly, embryonic BM assembly between visceral endoderm and stem cells was normal in null embryos and in embryoid bodies of alpha1LG4-5-null embryonic stem cells. Yet, stem cells could not develop into polarized epiblast cells. Thus, alpha1LG4-5 provides vital signals for the conversion of stem cells to polarized epithelium.

Murine retroviruses may cause malignant tumors in mice by insertional mutagenesis of host genes. The use of retroviral tagging as a means of identifying cancer-causing genes has, however, almost entirely been restricted to hematopoietic tumors. The aim of this study was to develop a system allowing for the retroviral tagging of candidate genes in malignant brain tumors. Mouse gliomas were induced by a recombinant Moloney murine leukemia virus encoding platelet-derived growth factor (PDGF) B-chain. The underlying idea was that tumors evolve through a combination of PDGF-mediated autocrine growth stimulation and insertional mutagenesis of genes that cooperate with PDGF in gliomagenesis. Common insertion sites (loci that were tagged in more than one tumor) were identified by cloning and sequencing retroviral flanking segments, followed by blast searches of mouse genome databases. A number of candidate brain tumor loci (Btls) were identified. Several of these Btls correspond to known tumor-causing genes; these findings strongly support the underlying idea of our experimental approach. Other Btls harbor genes with a hitherto unproven role in transformation or oncogenesis. Our findings indicate that retroviral tagging with a growth factor-encoding virus may be a powerful means of identifying candidate tumor-causing genes in nonhematopoietic tumors.

Human ECV304 cells respond reproducibly by tube formation to complex basement membrane matrices. Laminins are major glycoproteins of basement membranes. We therefore studied the ability of ECV304 cells to attach to defined laminin isoforms and to fibronectin, and identified the involved laminin receptors. The cells bound poorly to fibronectin, to some extent to laminin-1, whereas laminin-2/4 and -10/11 were strong adhesive substrates. Antibody perturbation assays showed that adhesion to laminin-1 was mediated by integrin alpha6beta1, and adhesion to laminin-2/4 by cooperative activity of integrins alpha3beta1 and alpha6beta1. Adhesion of ECV 304 cells to laminin-10/11 was mainly mediated by integrins alpha3beta1, with minor involvement of alpha6beta1/4 and alphavbeta3. Solid-phase binding assays confirmed that integrin alphavbeta3 binds human laminin-10/11 and -10, in an RGD-dependent fashion. Although integrin alphavbeta3 played a very minor role in cell adhesion to laminin-10/11, this interaction facilitated growth factor-induced proliferation of ECV304 cells. In response to FGF-2 or VEGF, the cells proliferated better when attached on laminin-10/11 than on laminin-1, -2/4, or gelatin. The proliferation induced by the joint application of laminin-10/11 and either one of the growth factors could be blocked by antibodies against integrin alphavbeta3. Fragments of several other basement membrane components are known to interact with alphavbeta3. The current data show that that integrin alphavbeta3 can bind intact alpha5-containing laminin trimers. Since the laminin alpha5 chain is broadly expressed in adult basement membranes, this interaction could be physiologically important. Our data suggest that this interaction is involved in the regulation of cellular responses to growth factors known to be involved in epithelial and endothelial development.

†Department of Cell and Molecular Biology, Lund University, SE-22184 Lund, Sweden; *Department of Cell and Molecular Biology, Uppsala University, SE-75123 Uppsala, Sweden; ‡Department of Physiology, Biophysics, and Neurology, Howard Hughes Medical Institute, University of Iowa, Iowa City, Iowa; §The Netherlands Cancer Institute, Amsterdam, The Netherlands; and Max-PlanckInstitute for Biochemistry, Martinsried, Germany

Laminin-integrin interactions can in some settings activate the extracellular signal-regulated kinases (ERKs) but the control mechanisms are poorly understood. Herein, we studied ERK activation in response to two laminins isoforms (-1 and -10/11) in two epithelial cell lines. Both cell lines expressed beta1-containing integrins and dystroglycan but lacked integrin alpha6beta4. Antibody perturbation assays showed that both cell lines bound to laminin-10/11 via the alpha3beta1and alpha6beta1 integrins. Although laminin-10/11 was a stronger adhesion complex than laminin-1 for both cell lines, both laminins activated ERK in only one of the two cell lines. The ERK activation was mediated by integrin alpha6beta1 and not by alpha3beta1 or dystroglycan. Instead, we found that dystroglycan-binding domains of both laminin-1 and -10/11 suppressed integrin alpha6beta1-mediated ERK activation. Moreover, the responding cell line expressed the two integrin alpha6 splice variants, alpha6A and alpha6B, whereas the nonresponding cell line expressed only alpha6B. Furthermore, ERK activation was seen in cells transfected with the integrin alpha6A subunit, but not in alpha6B-transfected cells. We conclude that laminin-1 and -10/11 share the ability to induce ERK activation, that this is regulated by integrin alpha6Abeta1, and suggest a novel role for dystroglycan-binding laminin domains as suppressors of this activation.