Upregulation of the Oct3/4 Network in Basal Breast Cancer Is Associated with Its Metastatic Potential and Shows Tissue Dependent Variability.

Adaptive plasticity of Breast Cancer stem cells (BCSCs) is strongly correlated with cancer progression and resistance, leading to a poor prognosis. In this study, we report the expression profile of several pioneer transcription factors of the Oct3/4 network associated with tumor initiation and metastasis. In the triple negative breast cancer cell line (MDA-MB-231) stably transfected with human Oct3/4-GFP, differentially expressed genes (DEGs) were identified using qPCR and microarray, and the resistance to paclitaxel was assessed using an MTS assay. The tumor-seeding potential in immunocompromised (NOD-SCID) mice and DEGs in the tumors were also assessed along with the intra-tumor (CD44+/CD24-) expression using flow cytometry. Unlike 2-D cultures, the Oct3/4-GFP expression was homogenous and stable in 3-D mammospheres developed from BCSCs. A total of 25 DEGs including Gata6, FoxA2, Sall4, Zic2, H2afJ, Stc1 and Bmi1 were identified in Oct3/4 activated cells coupled with a significantly increased resistance to paclitaxel. In mice, the higher Oct3/4 expression in tumors correlated with enhanced tumorigenic potential and aggressive growth, with metastatic lesions showing a >5-fold upregulation of DEGs compared to orthotopic tumors and variability in different tissues with the highest modulation in the brain. Serially re-implanting tumors in mice as a model of recurrence and metastasis highlighted the sustained upregulation of Sall4, c-Myc, Mmp1, Mmp9 and Dkk1 genes in metastatic lesions with a 2-fold higher expression of stem cell markers (CD44+/CD24-). Thus, Oct3/4 transcriptome may drive the differentiation and maintenance of BCSCs, promoting their tumorigenic potential, metastasis and resistance to drugs such as paclitaxel with tissue-specific heterogeneity.

Gliomagenesis is orchestrated by the Oct3/4 regulatory network.

Glioblastoma multiforme (GBM) is a lethal brain tumor characterized by developmental hierarchical phenotypic heterogeneity, therapy resistance and recurrent growth. Neural stem cells (NSCs) from human central nervous system (CNS), and glioblastoma stem cells from patient-derived GBM (pdGSC) samples and cultured in both 2D well-plate and 3D monoclonal neurosphere culture system (pdMNCS). The pdMNCS model shows promise to establish a relevant 3D-tumor environment that maintains GBM cells in the stem cell phase within suspended neurospheres. Utilizing the pdMNCS, we examined GBM cell-lines for a wide spectrum of developmental cancer stem cell markers, including the early blastocyst inner-cell mass (ICM)-specific Nanog, Oct3/4,B, and CD133. We observed that MNCS epigenotype is recapitulated using gliomasphere-derived cells. CD133, the marker of GSC is robustly expressed in 3D-gliomaspheres and localized within the plasma membrane compartment. Conversely, gliomasphere cultures grown in conventional 2D culture quickly lost CD133 expression, indicating its variable expression is dependent on cell-culture conditions. Critically, this experiment demonstrates incomplete differentiation of cytoskeleton microtubules and intermediate filaments (IFs) of patient derived cells, similar to commercially available GBM cell lines. Subsequently, in order to determine whether Oct3/4 it was necessary for CD133 expression and cancer stemness, we transfected 2D and 3D culture with siRNA against Oct3/4 and found a significant reduction in gliomasphere formation. These results suggest that expression of Oct3/4,Aand CD133 suppress differentiation of GSCs.

Stem-like cells in bone sarcomas: implications for tumorigenesis.

Bone sarcomas are a clinically and molecularly heterogeneous group of malignancies characterized by varying degrees of mesenchymal differentiation. Despite advances in medical and surgical management, survival rates for high-grade tumors have remained static at 50% to 70%. Tumor stem cells have been recently implicated in the pathogenesis of other heterogeneous, highly malignant tumors. We demonstrate here the existence of a small subpopulation of self-renewing bone sarcoma cells that are capable of forming suspended spherical, clonal colonies, also called "sarcospheres," in anchorage-independent, serum-starved conditions. These bone sarcoma cells as well as tissue specimens express activated STAT3 and the marker genes of pluripotent embryonic stem (ES) cells, Oct 3/4 and Nanog. Expression levels of Oct 3/4 and Nanog are greater in sarcospheres than in adherent cultures. A subset of bone sarcoma cells displays several surface markers of mesenchymal stem cells (Stro-1, CD105, and CD44) as well as attributes of mesodermal, ectodermal, and endodermal differentiation. Although previously documented in brain and breast tumors, our results support the extension of the cancer stem cell hypothesis to include tumors of mesenchymal lineage. Furthermore, they suggest the participation of ES cell homeobox proteins in non-germ cell tumorigenesis.

ATF5 regulates the proliferation and differentiation of oligodendrocytes.

The transcription factor ATF5 is expressed in cells of the embryonic and neonatal ventricular zone/subventricular zone (VZ/SVZ), and must be down-regulated for their differentiation into neurons and astrocytes. Here, we show that ATF5 plays a major role in directing oligodendrocyte development. ATF5 is expressed by oligodendrocyte precursors but is absent from mature oligodendroglia. Constitutively expressed ATF5 maintains SVZ cells and O4(+) oligodendrocyte precursors in cycle and inhibits their differentiation into oligodendrocytes in vitro and in vivo. In contrast, ATF5 loss-of-function (LOF; produced by a dominant-negative form of the protein) accelerates oligodendrocyte differentiation of O4(+) cells in vitro and of SVZ cells in vivo. Significantly, the accelerated oligodendrocyte differentiation promoted by ATF5 LOF in vivo results in aberrant migration. Thus, appropriately regulated expression of ATF5 is required for proper expansion of oligodendroglial progenitors as well as for their timely differentiation. Regulation of oligodendrocyte, astrocyte, and neuronal differentiation indicates that ATF5 operates as a general regulator of the timing of differentiation, independent of cell lineage.

Downregulation of activating transcription factor 5 is required for differentiation of neural progenitor cells into astrocytes.

The mechanisms that regulate neural progenitor cell differentiation are primarily unknown. The transcription factor activating transcription factor 5 (ATF5) is expressed in neural progenitors of developing brain but is absent from mature astrocytes and neurons. Here, we demonstrate that ATF5 regulates the conversion of ventricular zone (VZ) and subventricular zone (SVZ) neural progenitors into astrocytes. Constitutive ATF5 expression maintains neural progenitor cell proliferation and blocks their in vitro and in vivo differentiation into astrocytes. Conversely, loss of ATF5 function promotes cell-cycle exit and allows astrocytic differentiation in vitro and in vivo. CNTF, a promoter of astrocytic differentiation, downregulates endogenous ATF5, whereas constitutively expressed ATF5 suppresses CNTF-promoted astrocyte genesis. Unexpectedly, constitutive ATF5 expression in neonatal SVZ cells both in vitro and in vivo causes them to acquire properties and anatomic distributions of VZ cells. These findings identify ATF5 as a key regulator of astrocyte formation and potentially of the VZ to SVZ transition.

Lysophosphatidic acid induces clonal generation of mouse neurospheres via proliferation of Sca-1- and AC133-positive neural progenitors.

Neural stem/progenitor cells are clonogenic in vitro and produce neurospheres in serum-free medium containing epidermal growth factor (EGF) and fibroblast growth factor (FGF2). Here, we demonstrate that lysophosphatidic acid (LPA) instigated the clonal generation of neurospheres from dissociated mouse postnatal forebrain in the absence of EGF and FGF2. LPA induced proliferation of cells which co-expressed Sca-1 antigen and AC133, markers of primitive hematopoietic and neural stem/progenitor cells. Clonal expansion of these cells induced by LPA was inhibited by diacylglycerol- pyrophosphate (DGPP), an antagonist of the LPA receptor subtypes LPA1 and LPA3. Moreover, Sca-1- and AC133-positive cells of these neurospheres expressed LPA1, LPA2, and LPA3, suggesting important roles for these LPA receptors in proliferation of neural progenitors. LPA induced neurospheres to differentiate on an adherent laminin/poly-L-ornithine matrix. In differentiating neurospheres, LPA receptors co-localized with betaIII-tubulin, nestin, and CNPase, but not with glial fibrillary acidic protein (GFAP), a marker of astrocyte lineage. Our results demonstrate for the first time that lysophosphatidic acid induces clonal neurosphere development via proliferation of AC133/Sca-1-positive stem cells by a receptor-dependent mechanism. This differentiation was characterized by the initial co-localization of neural specific antigens at sites of LPA receptor expression upon their interaction with the inducing agonist.

Mouse myeloma cell line Sp2/0 multidrug-resistant variant as parental cell line for hybridoma construction.

The use of multidrug-resistant variant of Sp2/0 mouse myeloma cell line SpEBr-5 as a partner for making mouse hybridoma producing monoclonal antibodies is described here. The resulting hybridoma cell line 1F7 was characterized with a high level of monoclonal antibody production and karyotype containing all normal mouse chromosomes. 1F7 cells were separately selected for resistance to ethidium bromide (EBr) and adriamycin (ADR) and different mechanisms of drug resistance were found in these cell variants. The resistance in ADR-selected 1F7 cells was due to amplification and overexpression of mdr genes. In EBr-resistant 1F7 cells, mdr genes were overexpressed without amplification. Substantially decreased level of Topo II activity in both cell lines also suggests the existence of additional mechanisms for MDR phenotype of hybridoma cells. Finally, adriamycin-resistant 1F7 hybridoma cell variant was found to produce higher level of specific immunoglobulins due to the increased level of Iggamma(2b) heavy chain mRNA.

Regulated expression of ATF5 is required for the progression of neural progenitor cells to neurons.

An important milestone in brain development is the transition of neuroprogenitor cells to postmitotic neurons. We report that the bZIP transcription factor ATF5 plays a major regulatory role in this process. In developing brain ATF5 expression is high within ventricular zones containing neural stem and progenitor cells and is undetectable in postmitotic neurons. In attached clonal neurosphere cultures ATF5 is expressed by neural stem/progenitor cells and is undetectable in tau-positive neurons. In PC12 cell cultures nerve growth factor (NGF) dramatically downregulates endogenous ATF5 protein and transcripts, whereas exogenous ATF5 suppresses NGF-promoted neurite outgrowth. Such inhibition requires the repression of CRE sites. In contrast, loss of function conferred by dominant-negative ATF5 accelerates NGF-promoted neuritogenesis. Exogenous ATF5 also suppresses, and dominant-negative ATF5 and a small-interfering RNA targeted to ATF5 promote, neurogenesis by cultured nestin-positive telencephalic cells. These findings indicate that ATF5 blocks the differentiation of neuroprogenitor cells into neurons and must be downregulated to permit this process to occur.

Neural stem cell heterogeneity demonstrated by molecular phenotyping of clonal neurospheres.

Neural stem cells (NSCs) in vitro are able to generate clonal structures, "neurospheres," that exhibit intra-clonal neural cell-lineage diversity; i.e., they contain, in addition to NSCs, neuronal and glial progenitors in different states of differentiation. The present study focuses on a subset of neurospheres derived from fresh clinical specimens of human brain by using an in vitro system that relies on particular growth factors, serum, and anchorage withdrawal. Thirty individual and exemplary cDNA libraries from these neurosphere clones were clustered and rearranged within a panel after characterization of differentially expressed transcripts. The molecular phenotypes that were obtained indicate that clonogenic NSCs in our in vitro system are heterogeneous, with subsets reflecting distinct neural developmental commitments. This approach is useful for the sorting and expansion of NSCs and facilitates the discovery of genes involved in cell proliferation, communication, fate control, and differentiation.

Human cortical glial tumors contain neural stem-like cells expressing astroglial and neuronal markers in vitro.

Neural stem cells from neurogenic regions of mammalian CNS are clonogenic in an in vitro culture system exploiting serum and anchorage withdrawal in medium supplemented with methyl cellulose and the pleiotropic growth factors EGF, FGF2, and insulin. The aim of this study was to test whether cortical glial tumors contain stem-like cells capable, under this culture system, of forming clones showing intraclonal heterogeneity in the expression of neural lineage-specific proteins. The high frequencies of clone-forming cells (about 0.1-10 x 10(-3)) in clinical tumor specimens with mutated p53, and in neurogenic regions of normal human CNS, suggest that the ability to form clones in this culture system is induced epigenetically. RT-PCR analyses of populations of normal brain- and tumor-derived sister clones revealed transcripts for nestin, neuron-specific enolase, and glial fibrillary acidic protein (GFAP). However, the tumor-derived clones were different from clones derived from neurogenic regions of normal brain in the expression of transcripts specific for genes associated with neural cell fate determination via the Notch-signaling pathway (Delta and Jagged), and cell survival at G2 or mitotic phases (Survivin). Moreover, the individual glioma-derived clones contain cells immunopositive separately for GFAP or neuronal beta-III tubulin, as well as single cells coexpressing both glial and neuronal markers. The data suggest that the latent critical stem cell characteristics can be epigenetically induced by growth conditions not only in cells from neurogenic regions of normal CNS but also in cells from cortical glial tumors. Moreover, tumor stem-like cells with genetically defective responses to epigenetic stimuli may contribute to gliomagenesis and the developmental pathological heterogeneity of glial tumors.