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The purpose of this study was to investigate the role of the Zn finger protein CTCF in the establishment of genetic borders and in controlling spatially-restricted activity of a mammary-specific super-enhancer (SE) known to selectively activate gene expression during pregnancy. CRISPR/Cas9 gene editing was used to generate mice with deletions in CTCF binding sites (CBSs) separating the Wap SE from the Ramp3 gene. ChIP-seq and qRT-PCR were used to investigate protein-DNA interactions and changes in gene expression, respectively. RNA-seq data demonstrated that expression of the mammary-specific Wap and widely-expressed Ramp3 gene was activated in mammary tissue at the onset of lactation. To investigate the possibility that the Wap SE can regulate both genes, mice carrying deletions in the SE were established. In these mice, both Wap and downstream Ramp3 were downregulated to the same extent, supporting the notion that the SE regulates both genes. Given these results, we investigated the contributions of several intervening CBSs in dampening SE activity on Ramp3. Mice harboring individual and combinatorial deletions of three CBSs (A, B and C) between the Wap SE and Ramp3 were generated. While loss of CTCF at site B (ΔB) had no apparent effect, loss of site A (ΔA) led to an expansion of H3K27ac from the adjacent SE in mammary tissue. The site C mutation (ΔC) resulted in a two-fold induction of Ramp3 in mammary tissue. Mice lacking all three binding sites demonstrated a marked increase in Ramp3 expression, which indicates that the CBSs block expression in an additive manner. To test the possible insulator function of these in a tissue with opposing gene expression, cerebellum was chosen as Ramp3 is actively transcribed while Wap is silent. The ΔA and ΔB mice showed no phenotype, but surprisingly ΔC mice demonstrated an 80% reduction in Ramp3 expression. Analysis of ChIP-seq and DNAse-seq demonstrated that site C coincides with a cerebellum-specific enhancer, which appears to regulate Ramp3 expression. These data demonstrate that a SE can activate two genes, albeit to different degrees. Furthermore, we demonstrate that CBSs do not serve as tight genetic boundaries encapsulating transcriptional enhancers and their associated genes, but are porous borders that allow for fine tuning of transcriptional activity. Individual CBSs have a modest ability to insulate genes, but a cluster of CTCF proteins is required to adjust the enhancer activity on genes and prevent deregulation. In addition, we show that CBSs are not restricted to a unique function and can act in a tissue-specific manner to contribute to gene regulation. These data help us to develop a more nuanced understanding of SE function as well as the roles of CTCF in regulating gene expression. Previous studies have shown that SEs and CBSs are mutational hotspots in cancer, implicating them in tumorigenesis. A more complete understanding of their biology will allow a better understanding of their role in cancer. Citation Format: Michaela Willi, Tyler M. Kuhns, Kyung Hyun Yoo, Fabian Reinisch, Christian Reinbold, Teresa Mohr, Chaochen Wang, Lothar Hennighausen. The role of super-enhancers and genetic boundaries in gene regulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4993. doi:10.1158/1538-7445.AM2017-4993

JAK/STAT signaling pathways are critical for cell response to cytokines across multiple tissues, genetic variation in this pathway could associate with neoplastic diseases. STAT5, the most common used STAT family member, differently activates two distinct classes of genes. It activates cell-specific genes up to two orders of magnitude higher than shared genes expressed across different cell types. Socs2 (Suppressors of cytokine signaling 2), a widely expressed STAT5 target gene and a negative regulator of cytokine feedback loops, contains STAT5 response element within its promoter region. In our study, we demonstrated that STAT5 preferentially binds to promoter sequence of shared STAT5 targeted genes and to distal putative enhancers of lineage-specific genes. DNase-seq demonstrated that chromatin accessibility of STAT5-based enhancers was greatly dependent on cytokine exposure, while common STAT5 promoter targets were constitutively accessible. CRIPSR /Cas9 gene editing was used to delete the generic STAT5 binding sites in Socs2 locus in mice. Prolactin induction of Socs2 was abrogated both in liver and mammary gland, and resulted in elevated STAT5 activation and precocious mammary development in mutant mice. Taken together, we demonstrated that promoter-bound STAT5 modulates cytokine responses of universal STAT5 target genes, while enhancer-bound STAT5 is necessary for linage-specific target gene activation. This study provides new insight into the mechanism of used by a generic cytokine response element controlling lineage-specific transcription. Citation Format: xianke zeng, Michaela Willi, Ha Youn Shin, Chaochen Wang, Lothar Hennighausen. Lineage-specific and shared cytokine-sensing genes respond distinctly to the master regulator STAT5 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5511. doi:10.1158/1538-7445.AM2017-5511

Background: p73 is a member of the p53 family transcription factors and known tumor suppressor. However, its transcriptional activity is complex owing to its multiple isoforms, and limited information is available regarding the transcriptional and functional regulation of the p73 gene in colorectal cancer. In this study, we examined the role of p73 in colorectal cancer. Methods: We established a TAp73 overexpressing cell line using the Tet-on inducible expression system and analyzed global RNA expression by RNA-sequencing (RNA-seq). We studied the effects of TAp73 expression on the migration, invasiveness, and EMT of colon cancer cells. We conducted experiments in animals with liver metastasis of colorectal cancer. To investigate the roles of p73 in colon cancer, we examined the samples from patients, who had undergone surgical resection for colorectal cancer between 2009 and 2013. mRNA expression of TAp73 and KAI1 was analyzed in 108 colorectal cancer specimen and adjacent non-cancerous tissues by real-time RT-PCR. Results: RNA-seq showed the association between TAp73 and KAI1 expression. Migration and invasiveness of colon cancer cells were reduced by TAp73 expression, but induced by KAI1 knockdown. TAp73 regulates KAI1 expression in colon cancer cell lines. TAp73-induced decrease in invasiveness and epithelial-mesenchymal transition (EMT) was abrogated by KAI1 knockdown in TAp73 overexpressing cells. Migration ability of TAp73 overexpressing cells was recovered by KAI1 knockdown. Hepatic metastases were significantly reduced in mice injected with TAp73 overexpressing cells and increased in those injected with TAp73 overexpressing cells with KAI1 knockdown. mRNA expression of TAp73 and KAI1 was higher in colorectal cancer tissues than in adjacent non-cancerous tissues. Significant correlation between TAp73 and KAI1 mRNA expression was detected in early stage primary colorectal cancer, but not in the advanced stage. Conclusions: This study suggests that p73 (TAp73) acts as a tumor suppressor in the progression of colorectal cancer and regulates the expression of KAI1, which is a key target of p73 in colorectal cancer liver metastases. Note: This abstract was not presented at the meeting. Citation Format: Woo Kyun Bae, Kyung Hyun Yoo, Keunsoo Kang, Lothar Hennighausen, Ik-Joo Chung. Transcriptional regulation of KAI1 by p73 in colorectal cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1879. doi:10.1158/1538-7445.AM2017-1879

MOZ-TIF2 is a leukemogenic fusion oncoprotein that confers self-renewal capability to hematopoietic progenitor cells and induces acute myelogenous leukemia (AML) with long latency in bone marrow transplantation assays. Here, we report that FLT3-ITD transforms hematopoietic cells in cooperation with MOZ-TIF2 in vitro and in vivo. Coexpression of FLT3-ITD confers growth factor independent survival/proliferation, shortens disease latency, and results in an increase in the number of leukemic stem cells (LSC). We show that STAT5, a major effector of aberrant FLT3-ITD signal transduction, is both necessary and sufficient for this cooperative effect. In addition, STAT5 signaling is essential for MOZ-TIF2–induced leukemic transformation itself. Lack of STAT5 in fetal liver cells caused rapid differentiation and loss of replating capacity of MOZ-TIF2–transduced cells enriched for LSCs. Furthermore, mice serially transplanted with Stat5−/− MOZ-TIF2 leukemic cells develop AML with longer disease latency and finally incomplete penetrance when compared with mice transplanted with Stat5+/+ MOZ-TIF2 leukemic cells. These data suggest that STAT5AB is required for the self-renewal of LSCs and represents a combined signaling node of FLT3-ITD and MOZ-TIF2 driven leukemogenesis. Therefore, targeting aberrantly activated STAT5 or rewired downstream signaling pathways may be a promising therapeutic option. Cancer Res; 73(1); 373–84. ©2012 AACR.

To investigate the role of EZH1 and EZH2 in liver homeostasis, mice were generated that carried Ezh1-/- and EZH2fl/fl alleles and an Alb-Cre transgene. Only combined loss of EZH1 and EZH2 in mouse hepatocytes caused a depletion of global H3K27me3 marks and the specific loss over ∼1900 genes at 3 months of age. Ezh1-/-,Ezh2fl/flAlb-Cre mice exhibited progressive liver abnormalities manifested by development of regenerative nodules and concomitant periportal fibrosis, inflammatory infiltration and activation of A6-positive hepatic progenitor cells at 8 months of age. In response to chronic treatment with CCl4, all experimental mice but none of the controls (n = 27 each) showed increased hepatic degeneration associated with liver dysfunction and reduced ability to proliferate. After 2/3ds partial hepatectomy, mutant mice (n = 5) displayed increased liver injury and a blunted regenerative response. Genome-wide analyses at 3-months of age identified 51 genes that had lost H3K27me3 marks and their expression was significantly increased. These genes were involved in regulation of cell survival, fibrosis, and proliferation. H3K27me3 levels and liver physiology were unaffected in mice lacking either EZH1 globally or EZH2 specifically in hepatocytes. This work demonstrates a critical redundancy of EZH1 and EZH2 in maintaining hepatic homeostasis and regeneration. Next, we checked the expression EZH2 and H3K27me3 status in 67 human hepatocellular carcinoma (HCC) samples. We also checked the gene expression by the next-generation sequencing based on EZH2 expression. This work demonstrates candidate EZH2 target genes in human HCC. Citation Format: Woo Kyun Bae, Hyun Jeong Shim, Sang Hee Cho, Ik-Joo Chung, In-Kyu Park, Lothar Hennighausen. The role of methyltransferase, enhancer of zeste homolog 2 (EZH2) in mouse hepatocyte and human hepatocellular carcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2304. doi:10.1158/1538-7445.AM2015-2304

Brca2 is an important tumor suppressor associated with susceptibility to breast cancer. Although increasing evidence indicates that the primary function of Brca2 is to facilitate the repair of DNA damage via the homologous recombination pathway, how Brca2 prevents breast cancer is largely unknown. To study the role of Brca2 specifically in mammary epithelium development, we crossed mice bearing the conditionally deficient allele Brca2flox9–10 to mouse mammary tumor virus- or whey acidic protein-Cre transgenic lines. Analysis of these animals showed that Brca2 is not required for epithelial expansion in mammary glands of pregnant mice. In addition, examination of mammary gland involution revealed normal kinetics of mammary alveolar cell apoptosis after weaning of litters. Nevertheless, Brca2-deficient mice developed mammary adenocarcinomas after a long latency (average, 1.6 years). Detailed histopathological analysis of four of these tumors demonstrated that three of them showed abnormal p53 protein expression. A mutation in the p53 gene was detected in one case. Moreover, homozygosity versus heterozygosity for the Brca2 mutation heavily skewed the tumor spectrum toward mammary adenocarcinoma development in p53+/− mice. Our data indicate that Brca2 is not essential for mammary epithelium development but that Brca2 deficiency and down-regulated p53 expression can work jointly to promote mammary tumorigenesis.

Insulin-like growth factors (IGFs) play a crucial role in regulating cell proliferation and differentiation. The aim of this study was to examine the potential relationship between serum IGF-I levels and breast cancer risk. To do this, we studied liver-specific IGF-I gene-deleted (LID) mice, in which circulating IGF-I levels are 25% of that in control mice. Mammary tumors were induced in two ways: (a) by exposing mice to the carcinogen 7,12-dimethybenz (a)anthracene; and (b) by crossing LID mice with C3(1)/SV40 large T-antigen transgenic mice. In both models, LID mice exhibited a delayed latency period of mammary tumor development. In the 7,12-dimethybenz (a)anthracene-induced mammary tumor model, the incidence of palpable mammary tumors was significantly lower in LID mice (26% versus 56% in controls), and the onset of the tumors was delayed (74 +/- 1.2 days in LID mice versus 59.5 +/- 1.1 days in controls). Histological analysis showed extensive squamous metaplasia in late-stage mammary tumors of control mice, whereas late-stage tumors from LID mice exhibited extensive hyperplasia, but little metaplasia. In control mice, the onset of C3(1)/SV40-large T-antigen-induced mammary tumors occurred at 21.6 +/- 1.8 weeks of age, whereas in LID mice the average age of onset was 30.2 +/- 1.7 weeks. In addition, 60% of the mice in the control group developed two or more mammary tumors per mouse, whereas in the LID mice only 30% developed more than one mammary tumor per mouse. Our data demonstrate that circulating IGF-I levels play a significant role as a risk factor in the onset and development of mammary tumors in two well-established animal models of breast cancer.

To examine the behavior of tumor cells in tumors developing directly from mammary tissue in transgenic models, we have evaluated transgenic mice expressing green fluorescent protein (GFP). Using the mouse mammary virus promoter (MMTV) to directly drive expression of GFP, we find low levels of fluorescence in the mammary and salivary glands of transgenic animals. Using MMTV-Cre or WAP-Cre in combination with the Cre-activatable CAG-CAT-EGFP construct, we find stronger expression of GFP that is still tissue specific. These animals provide a range of expression of GFP that is suitable for analysis of transgenic mammary tumors and metastases in vivo at the single cell level of resolution.

It has been shown previously that slight elevations in serum levels of insulin-like growth factor-I (IGF-I) are correlated with an increased risk for developing prostate, breast, colon, and lung cancer. The aim of this study was to determine the role of serum IGF-I levels in the process of stimulating tumor growth and metastasis in a mouse model of colon cancer. Colon 38 adenocarcinoma tissue fragments were orthotopically transplanted by attachment to the surface of the cecum in control and liver-specific IGF-I-deficient (LID) mice in which serum IGF-I levels are 25% of that in control mice. A total of 156 male mice at 5 weeks of age (74 control mice and 82 LID mice) received tumor transplants. Mice were divided randomly into two groups; one group was injected i.p. with recombinant human IGF-I (2 mg/kg) twice daily for 6 weeks, and the other group received saline injections. IGF-I treatment increased the serum levels of IGF-I and IGFBP-3 in both control and LID mice. In the saline-injected group, the incidence of tumor growth on the cecum as well as the frequency of hepatic metastasis was significantly higher in control mice as compared with LID mice. Both control and LID mice treated with recombinant human IGF-I displayed significantly increased rates of tumor development on the cecum and metastasis to the liver, as compared with saline-injected mice. The number of metastatic nodules in the liver was significantly higher in control mice as compared with LID mice. The expression of vascular epithelial growth factor (VEGF) as well as vessel abundance in the cecum tumors was dependent on the levels of serum IGF-I. This study supports the hypothesis that circulating IGF-I levels play an important role in tumor development and metastasis.

Background: Efficient acquisition of primary cancer cells for genetic and pharmacological testing is a means towards individualized cancer treatment. Genetically engineered mouse models of triple negative mammary cancer were used to compare culture conditions conditionally reprogrammed cell culture CRC with a rho kinase inhibitor (Y-27632) and irradiated J2 feeder cells, EpiCult™, DMEM for establishment efficiency, differentiation, fibroblast contamination, and allograft generation. Goals: 1) Evaluate mammary cancer progenitor cells by allograft and secondary culture 2) Compare RNA-seq transcriptomes in cells and allografts with different Brca1 gene dosages (100%, 50%, 0%) Methods: Triple negative invasive adenocarcinomas from 4 mouse genotypes, all carrying a p53-null allele, were analyzed: A) 1 mutant Brca1 allele; B) 2 mutant Brca1 alleles; C) 1 mutant Brca1 allele and 1 human aromatase transgene; D) human aromatase transgene. Cancers were divided and growth assessed in CRC, EpiCult™ and DMEM cultures. Illumina (V2scriptseq) RNA-seq libraries were prepared from cell pellets and allografts. One million cells injected into mammary gland fat pads of nude mice generated allografts divided for histology/DNA analyses, secondary culture and RNAseq. Transcript abundance and differentially expressed genes were determined after assembling transcriptomes with Cufflinks. Results: CRC was the most efficient methodology based on rapidity and percentage cancer specimens successfully cultured and paucity of fibroblasts. Brca1 gene dosage made no difference in culture efficiency. Differentiation markers were expressed at significantly higher levels in CRC whereas markers of epithelial mesenchymal transition were expressed higher in EpiCult™. Allografts were derived from CRC and EpiCult™ but not DMEM. Genetic testing confirmed allografts were derived from original endogenous cancer cells. Some individual allografts derived from the same culture exhibited different growth curves and histology, suggesting tumor cell heterogeneity within cultures. Overall, palpable EpiCult™ allografts appeared significantly earlier than CRC allografts (p Citation Format: Ahmad M. Alamri, Svenja Groeneveld, Keunsoo Kang, Sarah Dabydeen, Weisheng Wang, Lothar Hennighausen, Bhaskar Kallakury, Xuefeng Liu, Priscilla A. Furth. Characterizing growth features, allograft generation and transcriptomes of cultured conditionally reprogrammed cells (CRC) prepared from primary triple negative cancer from Brca1-mutant mice. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3918. doi:10.1158/1538-7445.AM2014-3918

Thermo-responsive hydrogel consisting of conjugated linoleic acid-coupled Pluronic F127 (Plu-CLA) is an optimized drug delivery system with anti-cancer activity for controlled release of the hydrophobic drug, docetaxel. In this study, we evaluated the effect of Plu-CLA as a potential new intraperitoneal docetaxel delivery system for peritoneal dissemination of gastric cancer. We have established a peritoneal metastasis models using BALB/c mice by injection with TMK-1 human gastric cancer cells. Mice were injected intraperitoneally with docetaxel alone and docetaxel loaded Plu-CLA at 1 week after TMK1 cells were injected. Tumor progression and response to therapy were monitored by micro-positron emission tomography. The total number of peritoneal tumors and ascites volume were also measured. Compared to docetaxel alone, the combination of docetaxel and Plu-CLA significantly and synergistically reduced cell survival. The combination of docetaxel and Plu-CLA showed excellent anti-tumor activity inducing stronger apoptosis than docetaxel alone. The combination of docetaxel and Plu-CLA also significantly reduced number of peritoneal metastatic nodules and increased the survival in the peritoneal gastric cancer xenograft model. Our results showed that intraperitoneal administration of docetaxel combined with Plu-CLA synergistically inhibited peritoneal metastasis and prolonged the survival in peritoneal gastric cancer model. Therefore, Plu-CLA could be a potential intraperitoneal carrier for hydrophobic docetaxel for the effective treatment of peritoneal metastatic gastric cancer. Citation Format: Woo Kyun Bae, Lothar Hennighausen, Ji Hee Lee, Dae Eun Kim, Jun Eul Hwang, Hyun Jeong Shim, Sang Hee Cho, In-Kyu Park, Ik-Joo Chung. Intraperitoneal administration of docetaxel loaded in thermo-responsive conjugated linoleic acid-incorporated poloxamer hydrogel for the suppression of peritoneal dissemination of gastric cancer. [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 4344. doi:10.1158/1538-7445.AM2013-4344