The mouse insulin-like growth factor type-2 receptor is imprinted and closely linked to the Tme locus

T-associated maternal effect (Tme) is the only known maternal-effect mutation in the mouse. The defect is nuclear-encoded and embryos that inherit a deletion of the Tme locus from their mother die at day 15 of gestation. There are many genomically imprinted regions known in the mouse genome but so far no imprinted genes have been cloned. The Tme locus is absent in two chromosome-17 deletion mutants, Thp and the tLub2, and its position has been localized using these deletions to a 1-cM region. We report here that the genes for insulin-like growth factor type-2 receptor (Igf2r) and mitochondrial superoxide dismutase-2 (Sod-2) are absent from both deletions. Probes for these genes and for plasminogen (Plg) and T-complex peptide 1 (Tcp-1) were used in pulsed-field gel mapping to show that Tme must lie within a region of 800-1,100 kb. We also demonstrate that embryos express Igf2r only from the maternal chromosome, and that Tcp-1, Plg and Sod-2 are expressed from both chromosomes. Therefore Igf2r is imprinted and closely linked or identical to Tme.

The transcription factor ZEB1 (deltaEF1) promotes tumour cell dedifferentiation by repressing master regulators of epithelial polarity

Epithelial to mesenchymal transition (EMT) is implicated in the progression of primary tumours towards metastasis and is likely caused by a pathological activation of transcription factors regulating EMT in embryonic development. To analyse EMT-causing pathways in tumourigenesis, we identified transcriptional targets of the E-cadherin repressor ZEB1 in invasive human cancer cells. We show that ZEB1 repressed multiple key determinants of epithelial differentiation and cell-cell adhesion, including the cell polarity genes Crumbs3, HUGL2 and Pals1-associated tight junction protein. ZEB1 associated with their endogenous promoters in vivo, and strongly repressed promotor activities in reporter assays. ZEB1 downregulation in undifferentiated cancer cells by RNA interference was sufficient to upregulate expression of these cell polarity genes on the RNA and protein level, to re-establish epithelial features and to impair cell motility in vitro. In human colorectal cancer, ZEB1 expression was limited to the tumour-host interface and was accompanied by loss of intercellular adhesion and tumour cell invasion. In invasive ductal and lobular breast cancer, upregulation of ZEB1 was stringently coupled to cancer cell dedifferentiation. Our data show that ZEB1 represents a key player in pathologic EMTs associated with tumour progression.

Imprinted expression of the Igf2r gene depends on an intronic CpG island

Gametic imprinting is a developmental process that induces parental-specific expression or repression of autosomal and X-chromosome-linked genes. The mouse Igf2r gene (encoding the receptor for insulin- like growth factor type-2) is imprinted and is expressed from the maternal allele after embryonic implantation. We previously proposed that methylation of region 2, a region rich in cytosine-guanine doublets (a 'CpG island') in the second intron of Igf2r, is the imprinting signal that maintains expression of the maternal allele. Here we use mouse transgenes to test the role of region 2 and the influence of chromosome location on Igf2r imprinting. Yeast artificial chromosome transgenes successfully reproduced the imprinted methylation and expression pattern of the endogenous Igf2r gene; deletion of region 2 from these transgenes caused a loss of imprinting and restored biallelic Igf2r expression. These results define a primary role for region 2 and a negligible role for chromosomal location in Igf2r imprinting; they also show that methylation imprints can maintain allelic expression. Short transgenes containing only region 2 and yeast artificial chromosome transgenes with an inactive Igf2r promoter do not attract parental-specific methylation. All transgenes showing paternal-specific repression of Igf2r produced an antisense RNA whose transcription was dependent on region 2. The production of an antisense RNA by the repressed parental allele is reminiscent of the imprinting of the Igf2/H19 gene pair and may indicate that expression competition could play a general role in imprinting.

Transcriptional plasticity promotes primary and acquired resistance to BET inhibition

Following the discovery of BRD4 as a non-oncogene addiction target in acute myeloid leukaemia (AML), bromodomain and extra terminal protein (BET) inhibitors are being explored as a promising therapeutic avenue in numerous cancers. While clinical trials have reported single-agent activity in advanced haematological malignancies, mechanisms determining the response to BET inhibition remain poorly understood. To identify factors involved in primary and acquired BET resistance in leukaemia, here we perform a chromatin-focused RNAi screen in a sensitive MLL-AF9;Nras(G12D)-driven AML mouse model, and investigate dynamic transcriptional profiles in sensitive and resistant mouse and human leukaemias. Our screen shows that suppression of the PRC2 complex, contrary to effects in other contexts, promotes BET inhibitor resistance in AML. PRC2 suppression does not directly affect the regulation of Brd4-dependent transcripts, but facilitates the remodelling of regulatory pathways that restore the transcription of key targets such as Myc. Similarly, while BET inhibition triggers acute MYC repression in human leukaemias regardless of their sensitivity, resistant leukaemias are uniformly characterized by their ability to rapidly restore MYC transcription. This process involves the activation and recruitment of WNT signalling components, which compensate for the loss of BRD4 and drive resistance in various cancer models. Dynamic chromatin immunoprecipitation sequencing and self-transcribing active regulatory region sequencing of enhancer profiles reveal that BET-resistant states are characterized by remodelled regulatory landscapes, involving the activation of a focal MYC enhancer that recruits WNT machinery in response to BET inhibition. Together, our results identify and validate WNT signalling as a driver and candidate biomarker of primary and acquired BET resistance in leukaemia, and implicate the rewiring of transcriptional programs as an important mechanism promoting resistance to BET inhibitors and, potentially, other chromatin-targeted therapies.

p38alpha suppresses normal and cancer cell proliferation by antagonizing the JNK-c-Jun pathway

The mitogen-activated protein kinase (MAPK) p38alpha controls inflammatory responses and cell proliferation. Using mice carrying conditional Mapk14 (also known as p38alpha) alleles, we investigated its function in postnatal development and tumorigenesis. When we specifically deleted Mapk14 in the mouse embryo, fetuses developed to term but died shortly after birth, probably owing to lung dysfunction. Fetal hematopoietic cells and embryonic fibroblasts deficient in p38alpha showed increased proliferation resulting from sustained activation of the c-Jun N-terminal kinase (JNK)-c-Jun pathway. Notably, in chemical-induced liver cancer development, mice with liver-specific deletion of Mapk14 showed enhanced hepatocyte proliferation and tumor development that correlated with upregulation of the JNK-c-Jun pathway. Furthermore, inactivation of JNK or c-Jun suppressed the increased proliferation of Mapk14-deficient hepatocytes and tumor cells. These results demonstrate a new mechanism whereby p38alpha negatively regulates cell proliferation by antagonizing the JNK-c-Jun pathway in multiple cell types and in liver cancer development.

Negative and positive regulation of gene expression by mouse histone deacetylase 1

Histone deacetylases (HDACs) catalyze the removal of acetyl groups from core histones. Because of their capacity to induce local condensation of chromatin, HDACs are generally considered repressors of transcription. In this report, we analyzed the role of the class I histone deacetylase HDAC1 as a transcriptional regulator by comparing the expression profiles of wild-type and HDAC1-deficient embryonic stem cells. A specific subset of mouse genes (7%) was deregulated in the absence of HDAC1. We identified several putative tumor suppressors (JunB, Prss11, and Plagl1) and imprinted genes (Igf2, H19, and p57) as novel HDAC1 targets. The majority of HDAC1 target genes showed reduced expression accompanied by recruitment of HDAC1 and local reduction in histone acetylation at regulatory regions. At some target genes, the related deacetylase HDAC2 partially masks the loss of HDAC1. A second group of genes was found to be downregulated in HDAC1-deficient cells, predominantly by additional recruitment of HDAC2 in the absence of HDAC1. Finally, a small set of genes (Gja1, Irf1, and Gbp2) was found to require HDAC activity and recruitment of HDAC1 for their transcriptional activation. Our study reveals a regulatory cross talk between HDAC1 and HDAC2 and a novel function for HDAC1 as a transcriptional coactivator.

Microarray Gene Expression Profiling of B-Cell Chronic Lymphocytic Leukemia Subgroups Defined by Genomic Aberrations and VH Mutation Status

Purpose

Genomic aberrations and mutational status of the immunoglobulin variable heavy chain (VH) gene have been shown to be among the most important predictors for outcome in patients with B-cell chronic lymphocytic leukemia (B-CLL). In this study, we report on differential gene expression patterns that are characteristic for genetically defined B-CLL subtypes.

Materials and Methods

One hundred genetically well-characterized B-CLL samples, together with 11 healthy control samples, were analyzed using oligonucleotide arrays, which test for the expression of some 12,000 human genes.

Results

Aiming at microarray-based subclassification, class predictors were constructed using sets of differentially expressed genes, which yielded in zero or low misclassification rates. Furthermore, a significant number of the differentially expressed genes clustered in chromosomal regions affected by the respective genomic losses/gains. Deletions affecting chromosome bands 11q22-q23 and 17p13 led to a reduced expression of the corresponding genes, such as ATM and p53, while trisomy 12 resulted in the upregulation of genes mapping to chromosome arm 12q. Using an unsupervised analysis algorithm, expression profiling allowed partitioning into predominantly VH-mutated versus unmutated patient groups; however, association of the expression profile with the VH mutational status could only be detected in male patients.

Conclusion

The finding that the most significantly differentially expressed genes are located in the corresponding aberrant chromosomal regions indicates that a gene dosage effect may exert a pathogenic role in B-CLL. The significant difference in the partitioning of male and female B-CLL samples suggests that the genomic signature for the VH mutational status might be sex-related.

Modeling colon adenocarcinomas in vitro a 3D co-culture system induces cancer-relevant pathways upon tumor cell and stromal fibroblast interaction

Activated tumor stroma participates in tumor cell growth, invasion, and metastasis. Normal fibroblasts and cancer-associated fibroblasts (CAFs) have been shown to display distinct gene expression signatures. This molecular heterogeneity may influence the way tumor cells migrate, proliferate, and survive during tumor progression. To test this hypothesis and to better understand the molecular mechanisms that control these interactions, we established a three-dimensional (3D) human cell culture system that recapitulates the tumor heterogeneity observed in vivo. Human colon tumor cells were grown as multicellular spheroids and subsequently co-cultured with normal fibroblasts or CAFs in collagen I gels. This in vitro model system closely mirrors the architecture of human epithelial cancers and allows the characterization of the tumor cell-stroma interactions phenotypically and at the molecular level. Using GeneChip analysis, antibody arrays, and enzyme-linked immunosorbent assays, we demonstrate that the interaction of colon cancer cells with stromal fibroblasts induced different highly relevant cancer expression profiles. Genes involved in invasion, extracellular matrix remodeling, inflammation, and angiogenesis were differentially regulated in our 3D carcinoma model. The modular setup, reproducibility, and robustness of the model make it a powerful tool to identify target molecules involved in signaling pathways that mediate paracrine interactions in the tumor microenvironment and to validate the influence of these molecular targets during tumor growth and invasion in the supporting stroma.

Chemically Induced Degradation of the Oncogenic Transcription Factor BCL6

The transcription factor BCL6 is a known driver of oncogenesis in lymphoid malignancies, including diffuse large B cell lymphoma (DLBCL). Disruption of its interaction with transcriptional repressors interferes with the oncogenic effects of BCL6. We used a structure-based drug design to develop highly potent compounds that block this interaction. A subset of these inhibitors also causes rapid ubiquitylation and degradation of BCL6 in cells. These compounds display significantly stronger induction of expression of BCL6-repressed genes and anti-proliferative effects than compounds that merely inhibit co-repressor interactions. This work establishes the BTB domain as a highly druggable structure, paving the way for the use of other members of this protein family as drug targets. The magnitude of effects elicited by this class of BCL6-degrading compounds exceeds that of our equipotent non-degrading inhibitors, suggesting opportunities for the development of BCL6-based lymphoma therapeutics.

Identification of a novel gene, CDCP1, overexpressed in human colorectal cancer

We report the identification of a novel human tumor associated gene, CDCP1 (Cub Domain Containing Protein), which was identified using representational difference analysis and cDNA chip technology. The gene consists of eight exons, the upstream region of which neither contains a TATA- nor a CCAAT-box. However, a CpG island is located around the transcription start, which is found in approximately 60% of known genes. The CDCP1 gene was mapped to chromosome 3p21-p23 by fluorescence in situ hybridization. For expression profiling real time quantitative RT--PCR was performed using cell lines and laser capture microdissected colon cancer biopsies. CDCP1 mRNA is approximately 6 kb and highly overexpressed in human colon cancer and lung cancer. CDCP1 represents a putative transmembrane protein, containing three CUB domains in the extracellular part most likely involved in cell adhesion or interacting with the extracellular matrix.

Blood and lymphatic endothelial cell-specific differentiation programs are stringently controlled by the tissue environment

The discovery of marker proteins of human blood (BECs) and lymphatic endothelial cells (LECs) has allowed researchers to isolate these cells. So far, efforts to unravel their transcriptional and functional programs made use of cultured cells only. Hence, it is unknown to which extent previously identified LEC- and BEC-specific programs are representative of the in vivo situation. Here, we define the human BEC- and LEC-specific in vivo transcriptomes by comparative genomewide expression profiling of freshly isolated cutaneous EC subsets and of non-EC skin cells (fibroblasts, mast cells, dendritic cells, epithelial cells). Interestingly, the expression of most of the newly identified EC subset-discriminating genes depends strictly on the in vivo tissue environment as revealed by comparative analyses of freshly isolated and cultured EC subsets. The identified environment-dependent, EC subset-restricted gene expression regulates lineage fidelity, fluid exchange, and MHC class II–dependent antigen presentation. As an example for a BEC-restricted in vivo function, we show that non-activated BECs in situ, but not in vitro, assemble and display MHC class II protein complexes loaded with self-peptides. Thus, our data demonstrate the key importance of using precisely defined native ECs for the global identification of in vivo relevant cell functions.

Cloning of the mouse and human solute carrier 22a3 (Slc22a3/SLC22A3) identifies a conserved cluster of three organic cation transporters on mouse chromosome 17 and human 6q26-q27

Here we report the isolation of the mouse and human solute carrier genes Slc22a3/SLC22A3. Slc22a3 is specifically expressed in placenta, but the levels of expression decline toward the end of gestation. A BAC contig spanning the mouse Slc22a3 gene was constructed, and Slc22a3 was mapped between the Igf2r and Plg genes in close association with two additional members of the Slc22a gene family, mouse Slc22a1 and Slc22a2. A partial cDNA sequence of the human SLC22A3 gene was reconstituted from sequenced EST clones. SLC22A3 is expressed in first-trimester and term placenta, but also in skeletal muscle, prostate, aorta, liver, fetal lung, salivary gland, and adrenal gland. Using a somatic cell hybrid panel and a human YAC clone, SLC22A3 was mapped to the syntenic region on human chromosome 6q26-q27, between the IGF2R and APO(a)-like genes. SLC22A1 and SLC22A2 localized to the same locus, demonstrating the conservation of the close physical linkage of these three organic cation transporter genes in mouse and human.

IGFBP7, a novel tumor stroma marker, with growth-promoting effects in colon cancer through a paracrine tumor-stroma interaction

The activated tumor stroma participates in many processes that control tumorigenesis, including tumor cell growth, invasion and metastasis. Cancer-associated fibroblasts (CAFs) represent the major cellular component of the stroma and are the main source for connective tissue components of the extracellular matrix and various classes of proteolytic enzymes. The signaling pathways involved in the interactions between tumor and stromal cells and the molecular characteristics that distinguish normal 'resting' fibroblasts from cancer-associated or '-activated' fibroblasts remain poorly defined. Recent studies emphasized the prognostic and therapeutic significance of CAF-related molecular signatures and a number of those genes have been shown to serve as putative therapeutic targets. We have used immuno-laser capture microdissection and whole-genome Affymetrix GeneChip analysis to obtain transcriptional signatures from the activated tumor stroma of colon carcinomas that were compared with normal resting colonic fibroblasts. Several members of the Wnt-signaling pathway and gene sets related to hypoxia, epithelial-to-mesenchymal transition (EMT) and transforming growth factor-β (TGFβ) pathway activation were induced in CAFs. The putative TGFβ-target IGFBP7 was identified as a tumor stroma marker of epithelial cancers and as a tumor antigen in mesenchyme-derived sarcomas. We show here that in contrast to its tumor-suppressor function in epithelial cells, IGFPB7 can promote anchorage-independent growth in malignant mesenchymal cells and in epithelial cells with an EMT phenotype when IGFBP7 is expressed by the tumor cells themselves and can induce colony formation in colon cancer cells co-cultured with IGFBP7-expressing CAFs by a paracrine tumor-stroma interaction.

CDNA microarray gene expression analysis of B-cell chronic lymphocytic leukemia proposes potential new prognostic markers involved in lymphocyte trafficking

Human cancer is characterized by complex molecular perturbations leading to variable clinical behavior, often even in single-disease entities. We performed a feasibility study systematically comparing large-scale gene expression profiles with clinical features in human B-cell chronic lymphocytic leukemia (B-CLL). cDNA microarrays were employed to determine the expression levels of 1,024 selected genes in 54 peripheral blood lymphocyte samples obtained from patients with B-CLL. Statistical analyses were applied to correlate the expression profiles with a number of clinical parameters including patient survival and disease staging. We were able to identify genes whose expression levels significantly correlated with patient survival and/or with clinical staging. Most of these genes code either for cell adhesion molecules (L-selectin, integrin-beta2) or for factors inducing cell adhesion molecules (IL-1beta, IL-8, EGR1), suggesting that prognosis of this disease may be related to a defect in lymphocyte trafficking. This report demonstrates the feasibility of a systematic integration of large-scale gene expression profiles with clinical data as a general approach for dissecting human diseases.

The transcription factor ZEB1 (deltaEF1) represses Plakophilin 3 during human cancer progression

Plakophilin 3 (PKP3) belongs to the p120ctn family of armadillo-related proteins predominantly functioning in desmosome formation. Here we report that PKP3 is transcriptionally repressed by the E-cadherin repressor ZEB1 in metastatic cancer cells. ZEB1 physically associates with two conserved E-box elements in the PKP3 promoter and partially represses the activity of corresponding human and mouse PKP3 promoter fragments in reporter gene assays. In human tumours ZEB1 is upregulated in invasive cancer cells at the tumour-host interface, which is accompanied by downregulation of PKP3 expression levels. Hence, the transcriptional repression of PKP3 by ZEB1 contributes to ZEB1-mediated disintegration of intercellular adhesion and epithelial to mesenchymal transition.

Balance between NF-κB and JNK/AP-1 activity controls dendritic cell life and death

The life cycle of dendritic cells (DCs) must be precisely regulated for proper functioning of adaptive immunity. However, signaling pathways actively mediating DC death remain enigmatic. Here we describe a novel mechanism of hierarchical transcriptional control of DC life and death. Ligation of tumor necrosis factor receptor superfamily (TNFR-SF) members on DCs and cognate contact with T cells resulted in quantitatively balanced nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK)–mediated activator protein-1 (AP-1) induction and strongly enhanced DC longevity. Specific blockade of NF-κB in DCs induced strongly augmented JNK/AP-1 activity because of elevated levels of reactive oxygen species. In this scenario, DC activation by TNFR-SF members or T cells induced DC apoptosis. Specific inhibition of JNK/AP-1 rescued DCs from this activation-induced cell death program and restored TNFR-SF member- and T-cell–mediated survival. We conclude that JNK/AP-1 activity is under negative feedback control of NF-κB and can execute apoptosis in DCs. Thus, feedback-controlled signaling amplitudes of 2 transcriptional pathways decide the fate of a DC.

CDCP1 identifies a broad spectrum of normal and malignant stem/progenitor cell subsets of hematopoietic and nonhematopoietic origin

CUB-domain-containing protein 1 (CDCP1) is a novel transmembrane molecule that is expressed in metastatic colon and breast tumors as well as on the surface of hematopoietic stem cells. In this study, we used multiparameter flow cytometry and antibodies against CDCP1 to analyze the expression of CDCP1 on defined hematopoietic cell subsets of different sources. In addition, CDCP1 expression on leukemic blasts and on cells with nonhematopoietic stem/progenitor cell phenotypes was determined. Here we demonstrate that a subset of bone marrow (BM), cord blood (CB), and mobilized peripheral blood (PB) CD34+ cells expressed this marker and that CDCP1 was detected on CD34(+)CD38- BM stem/progenitor cells but not on mature PB cells. Analysis of leukemic blasts from patients with acute lymphoblastic leukemia, acute myeloid leukemia, and chronic myeloid leukemia in blast crisis revealed that CDCP1 is predominantly expressed on CD34(+)CD133+ myeloid leukemic blasts. However, CDCP1 was not strictly correlated with CD34 and/or CD133 expression, suggesting that CDCP1 is a novel marker for leukemia diagnosis. Stimulation of CD34+ BM cells with CDCP1-reactive monoclonal antibody CUB1 resulted in an increased (approximately twofold) formation of erythroid colony-forming units, indicating that CDCP1 plays an important role in early hematopoiesis. Finally, we show that CDCP1 is also expressed on cells phenotypically identical to mesenchymal stem/progenitor cells (MSCs) and neural progenitor cells (NPCs). In conclusion, CDCP1 is not only a novel marker for immature hematopoietic progenitor cell subsets but also unique in its property to recognize cells with phenotypes reminiscent of MSC and NPC.

Atad2 is a generalist facilitator of chromatin dynamics in embryonic stem cells

Although the conserved AAA ATPase and bromodomain factor, ATAD2, has been described as a transcriptional co-activator upregulated in many cancers, its function remains poorly understood. Here, using a combination of ChIP-seq, ChIP-proteomics, and RNA-seq experiments in embryonic stem cells where Atad2 is normally highly expressed, we found that Atad2 is an abundant nucleosome-bound protein present on active genes, associated with chromatin remodelling, DNA replication, and DNA repair factors. A structural analysis of its bromodomain and subsequent investigations demonstrate that histone acetylation guides ATAD2 to chromatin, resulting in an overall increase of chromatin accessibility and histone dynamics, which is required for the proper activity of the highly expressed gene fraction of the genome. While in exponentially growing cells Atad2 appears dispensable for cell growth, in differentiating ES cells Atad2 becomes critical in sustaining specific gene expression programmes, controlling proliferation and differentiation. Altogether, this work defines Atad2 as a facilitator of general chromatin-templated activities such as transcription.

The Lx1 gene maps to mouse chromosome 17 and codes for a protein that is homologous to glucose and polyspecific transmembrane transporters

A novel mouse gene, provisionally named Lx1, has been cloned and sequenced. Lx1 most likely represents the mouse homolog of the rat gene OCT1, which encodes a polyspecific transmembrane transporter that is possibly involved in drug elimination. The LX1 predicted protein is highly hydrophobic, possesses twelve putative transmembrane domains, and also shares significant homology with members of the sugar transporter family, particularly the novel liver-specific transporter NLT. Lx1 mRNA is expressed at high levels in mouse liver, kidney, and intestine, and at low levels in the adrenals and in lactating mammary glands. The Lx1 gene maps very close to the imprinted Igf2r/Mpr300 gene on mouse Chromosome (Chr) 17, in a region that is syntenic to human Chr 6q. Chr 6q has been previously associated with transient neonatal diabetes mellitus and breast cancer.

A Novel RAF Kinase Inhibitor with DFG-Out-Binding Mode: High Efficacy in BRAF-Mutant Tumor Xenograft Models in the Absence of Normal Tissue Hyperproliferation

BI 882370 is a highly potent and selective RAF inhibitor that binds to the DFG-out (inactive) conformation of the BRAF kinase. The compound inhibited proliferation of human BRAF-mutant melanoma cells with 100× higher potency (1-10 nmol/L) than vemurafenib, whereas wild-type cells were not affected at 1,000 nmol/L. BI 882370 administered orally was efficacious in multiple mouse models of BRAF-mutant melanomas and colorectal carcinomas, and at 25 mg/kg twice daily showed superior efficacy compared with vemurafenib, dabrafenib, or trametinib (dosed to provide exposures reached in patients). To model drug resistance, A375 melanoma-bearing mice were initially treated with vemurafenib; all tumors responded with regression, but the majority subsequently resumed growth. Trametinib did not show any efficacy in this progressing population. BI 882370 induced tumor regression; however, resistance developed within 3 weeks. BI 882370 in combination with trametinib resulted in more pronounced regressions, and resistance was not observed during 5 weeks of second-line therapy. Importantly, mice treated with BI 882370 did not show any body weight loss or clinical signs of intolerability, and no pathologic changes were observed in several major organs investigated, including skin. Furthermore, a pilot study in rats (up to 60 mg/kg daily for 2 weeks) indicated lack of toxicity in terms of clinical chemistry, hematology, pathology, and toxicogenomics. Our results indicate the feasibility of developing novel compounds that provide an improved therapeutic window compared with first-generation BRAF inhibitors, resulting in more pronounced and long-lasting pathway suppression and thus improved efficacy.

The novel BET bromodomain inhibitor BI 894999 represses super-enhancer-associated transcription and synergizes with CDK9 inhibition in AML

Bromodomain and extra-terminal (BET) protein inhibitors have been reported as treatment options for acute myeloid leukemia (AML) in preclinical models and are currently being evaluated in clinical trials. This work presents a novel potent and selective BET inhibitor (BI 894999), which has recently entered clinical trials (NCT02516553). In preclinical studies, this compound is highly active in AML cell lines, primary patient samples, and xenografts. HEXIM1 is described as an excellent pharmacodynamic biomarker for target engagement in tumors as well as in blood. Mechanistic studies show that BI 894999 targets super-enhancer-regulated oncogenes and other lineage-specific factors, which are involved in the maintenance of the disease state. BI 894999 is active as monotherapy in AML xenografts, and in addition leads to strongly enhanced antitumor effects in combination with CDK9 inhibitors. This treatment combination results in a marked decrease of global p-Ser2 RNA polymerase II levels and leads to rapid induction of apoptosis in vitro and in vivo. Together, these data provide a strong rationale for the clinical evaluation of BI 894999 in AML.

Impact of constitutive IGF1/IGF2 stimulation on the transcriptional program of human breast cancer cells

Insulin-like growth factor (IGF) signaling is a key regulator of breast development and breast cancer. We have analyzed the expression of the IGF signaling cascade in 17 human breast cancer and 4 mammary epithelial cell lines. Five cell lines expressed high levels of IGF1 receptor, insulin (INS)/IGF receptor substrate 1, IGF-binding proteins 2 and 4, as well as the estrogen receptor (ESR), indicating a co-activation of IGF and ESR signaling. Next, we stably overexpressed IGF1 and IGF2 in MCF7 breast cancer cells, which did not affect their epithelial characteristics and the expression and localization of the epithelial marker genes E-cadherin and beta-catenin. Conversely, IGF1 and IGF2 overexpression potently increased cellular proliferation rates and the efficiency of tumor formation in mouse xenograft experiments, whereas the resistance to chemotherapeutic drugs such as taxol was unaltered. Expression profiling of overexpressing cells with whole-genome oligonucleotide microarrays revealed that 21 genes were upregulated >2-fold by both IGF1 and IGF2, 9 by IGF1, and 9 by IGF2. Half of the genes found to be upregulated are involved in transport and biosynthesis of amino acids, including several amino acid transport proteins, argininosuccinate and asparagine synthetases, and methionyl-tRNA synthetase. Upregulation of these genes constitutes a novel mechanism apparently contributing to the stimulatory effects of IGF signaling on the global protein synthesis rate. We conclude that the induction of cell proliferation and tumor formation by long-term IGF stimulation may primarily be due to anabolic effects, in particular increased amino acid production and uptake.

Expression of stromal cell markers in distinct compartments of human skin cancers

BACKGROUND

The importance of changes in the supporting tumor stroma for cancer initiation and progression is well established. The characteristics of an activated tumor stroma, however, are not completely understood. In an effort to better characterize the desmoplastic response to human skin tumors, we evaluated the expression pattern of three stromal cell markers, fibroblast-activation protein (FAP), endoglyx-1, and endosialin, in a series of melanocytic and epithelial skin tumors.

METHODS

Immunohistochemistry using antibodies against FAP, endoglyx-1, and endosialin was carried out in skin samples obtained from 43 patients. Furthermore, microarray data from an independent set of human skin cancers were analyzed.

RESULTS

FAP-positive fibroblasts were detected in all tumor tissues tested, including cases of melanocytic nevi, melanoma metastases, basal cell carcinomas, and squamous cell carcinomas. In cutaneous melanoma metastases, we identified different compartments within the stromal response on the basis of the regions of FAP expression. Endoglyx-1 expression was confined to normal and tumor blood vessel endothelium including 'hot spots' of neoangiogenesis within the cutaneous melanoma metastases. Endosialin was selectively induced in subsets of small- and medium-sized tumor blood vessels in melanoma metastases and squamous cell carcinomas.

CONCLUSIONS

These data describe novel aspects of stromal marker expression in distinct compartments of human skin tumors and may point to potential targets for novel therapeutic strategies aimed at the tumor stroma.

CDCP1 is a novel marker for hematopoietic stem cells

CDCP1 is a transmembrane protein that contains three CUB domains within the extracellular region and a hexalysine stretch within the cytoplasmic region. CDCP1 mRNA is highly expressed in lung and colon tumors and in the erythroleukemic cell line K562. To analyze CDCP1 protein expression, monoclonal antibodies against the extracellular domain of CDCP1 were raised. For this purpose, CDCP1 was overexpressed in NIH-3T3 cells. Balb/c mice were then immunized with the resultant cell line NIH-3T3/huCDCP1. After fusion of SP2/0 cells with immune spleen cells, hybridoma clones were selected that secreted antibodies reacting with NIH-3T3/huCDCP1 cells but not with parental cells. Four antibodies (CUB1-CUB4) were obtained that fulfilled these criteria. Screening of peripheral blood cells revealed that the antibodies did not recognize mature lymphocytes, monocytes, granulocytes, erythrocytes, or platelets. In contrast, multi-color analyses revealed that CDCP1 protein is almost exclusively expressed on a subset of CD34(+) stem/progenitor cells in bone marrow. Transplantation of purified CDCP1(+) cells into NOD/SCID mice resulted in engraftment of human cells with multi-lineage differentiation potential, suggesting that CDCP1 is a novel marker for hematopoietic stem cells.

Characterization of the C3 YAC contig from proximal mouse chromosome 17 and analysis of allelic expression of genes flanking the imprinted Igf2r gene

The imprinted mouse insulin-like growth factor type 2 receptor (Igf2r) maps to the middle of a gene-rich region in band A2 of mouse chromosome 17. The t(Lub2) chromosome 17 variant contains a small deletion that removes at least seven genes including Igf2r. We have constructed a YAC contig spanning the entire t(Lub2) deletion and created a restriction map that covers 700 kb. The position, transcription orientation, and imprinted status of the genes immediately flanking Igf2r have been assessed. We show here that the Mas gene, which lies 65 kb upstream to Igf2r, contains a novel 5' exon and is not imprinted in adult tissues. We further show that the recently identified Lx1 gene lies immediately downstream and is also expressed from both parental alleles in adult tissues. The remaining genes in this region have previously been shown to be biallelically expressed.