The ten-eleven translocation (TET) family of methylcytosine dioxygenases initiates demethylation of DNA and is associated with tumorigenesis in many cancers; however, the mechanism is mostly unknown. Here we identify upstream activators and downstream effectors of TET1 in breast cancer using human breast cancer cells and a genetically engineered mouse model. We show that depleting the architectural transcription factor high mobility group AThook 2 (HMGA2) induces TET1. TET1 binds and demethylates its own promoter and the promoter of homeobox A (HOXA) genes, enhancing its own expression and stimulating expression of HOXA genes including HOXA7 and HOXA9. Both TET1 and HOXA9 suppress breast tumor growth and metastasis in mouse xenografts. The genes comprising the HMGA2-TET1-HOXA9 pathway are coordinately regulated in breast cancer and together encompass a prognostic signature for patient survival. These results implicate the HMGA2-TET1-HOX signaling pathway in the epigenetic regulation of human breast cancer and highlight the importance of targeting methylation in specific subpopulations as a potential therapeutic strategy. E pigenetic changes play an important role in cancer progression as well as development (1). Recent studies indicate that DNA demethylation can be catalyzed by a class of methylcytosine dioxygenases termed the ten-eleven translocation (TET) family (2-5). TET1 promotes DNA demethylation by catalyzing conversion of 5-methylcytosine (5mC) primarily to 5-hydroxymethylcytosine (5hmC) as well as 5-formylcytosine or 5-carboxylcytosine (3, 5). The modified cytosines are then removed through active or passive mechanisms (2-6). While TET1 is highly expressed in embryonic stem (ES) cells (5, 7-10), loss of TET1 protein and decreased 5hmC levels have been recently shown in solid tumors relative to normal epithelial cells (2,(11)(12)(13)(14). However, the mechanism by which TET1 is suppressed in solid tumors has not been identified. Furthermore, the downstream targets by which TET1 regulates growth and metastasis in cancer are largely unknown.High mobility group AT-hook 2 (HMGA2), a chromatinremodeling factor (15), binds to AT-rich regions in DNA, altering chromatin architecture to either promote or inhibit the action of transcriptional enhancers. HMGA2 is highly expressed in ES cells but is generally low or lacking in normal somatic cells. Interestingly, HMGA2 is highly expressed in most malignant epithelial tumors, including breast (16), pancreas (17), oral squamous cell carcinoma (18), and non-small-cell lung cancer (19). HMGA2 overexpression in transgenic mice causes tumor formation, whereas Hmga2-knockout mice have a pygmy phenotype indicative of a growth defect (20). We have reported that HMGA2 promotes tumor invasion and metastasis in breast cancer in part through regulation of prometastatic genes, including Snail, osteopontin, and CXCR4 (21,22).To systematically identify critical downstream mediators of HMGA2 that regulate invasion and metastasis, we performed gene expression array analysis by knocki...

The non-histone chromatin binding protein HMGA2 is expressed predominantly in the mesenchyme prior to its differentiation, but it is also expressed in tumors of epithelial origin. Ectopic expression of HMGA2 in epithelial cells induces epithelial-mesenchymal transition (EMT), which has been implicated in the acquisition of metastatic characters in tumor cells. However, little is known regarding in vivo modulation of HMGA2 and its effector functions in tumor metastasis. Here we report that HMGA2 loss-of-function in a mouse model of cancer reduces tumor multiplicity. HMGA2-positive cells were identified at the invasive front of human and mouse tumors. Additionally, in a mouse allograft model, HMGA2 overexpression converted non-metastatic 4TO7 breast cancer cells to metastatic cells that homed specifically to liver. Interestingly, expression of HMGA2 enhanced TGFβ signaling by activating expression of the TGFβ type II receptor (TGFβRII), which also localized to the invasive front of tumors. Together our results argued that HMGA2 plays a critical role in EMT by activating the TGFβ signaling pathway, thereby inducing invasion and metastasis of human epithelial cancers.

Triple-negative breast cancer (TNBC) patients have the highest risk of recurrence and metastasis. Because they cannot be treated with targeted therapies, and many do not respond to chemotherapy, they represent a clinically underserved group. TNBC is characterized by reduced expression of metastasis suppressors such as Raf Kinase Inhibitory Protein (RKIP), which inhibits tumor invasiveness. Mechanisms by which metastasis suppressors alter tumor cells are well characterized; however, their ability to regulate the tumor microenvironment, and the importance of such regulation to metastasis suppression is incompletely understood. Here we use species-specific RNA sequencing to show that RKIP expression in tumors markedly reduces the number and metastatic potential of infiltrating TAMs. TAMs isolated from non-metastatic RKIP+ tumors, relative to metastatic RKIP− tumors, exhibit a reduced ability to drive tumor cell invasion and decreased secretion of pro-metastatic factors including PRGN and shed TNFR2. RKIP regulates TAM recruitment by blocking HMGA2, resulting in reduced expression of numerous macrophage chemotactic factors, including CCL5. CCL5 overexpression in RKIP+ tumors restores recruitment of pro-metastatic TAMs and intravasation, while treatment with the CCL5 receptor antagonist Maraviroc reduces TAM infiltration. These results highlight the importance of RKIP as a regulator of TAM recruitment through chemokines such as CCL5. The clinical significance of these interactions is underscored by our demonstration that a signature comprised of RKIP signaling and pro-metastatic TAM factors strikingly separates TNBC patients based on survival outcome. Collectively, our findings identify TAMs as a previously unsuspected mechanism by which the metastasis suppressor RKIP regulates tumor invasiveness, and further suggest that TNBC patients with decreased RKIP activity and increased TAM infiltration may respond to macrophage-based therapeutics.

Elucidating targets of physiological tumor metastasis suppressors can highlight key signaling pathways leading to invasion and metastasis. To identify downstream targets of the metastasis suppressor Raf Kinase Inhibitory Protein (RKIP/PEBP1), we utilized an integrated approach based upon statistical analysis of tumor gene expression data combined with experimental validation. Previous studies from our laboratory identified the architectural transcription factor and oncogene, HMGA2, as a target of inhibition by RKIP. Here we identify two signaling pathways that promote HMGA2-driven metastasis. Using both human breast tumor cells and an MMTV-Wnt mouse breast tumor model, we show that RKIP induces and HMGA2 inhibits expression of miR-200b; miR-200b directly inhibits expression of lysyl oxidase (LOX), leading to decreased invasion. RKIP also inhibits syndecan-2 (SDC2), which is aberrantly expressed in breast cancer, via down-regulation of HMGA2; but this mechanism is independent of miR-200. Depletion of SDC2 induces apoptosis and suppresses breast tumor growth and metastasis in mouse xenografts. RKIP, LOX, and SDC2 are coordinately regulated and collectively encompass a prognostic signature for metastasis-free survival in ER-negative breast cancer patients. Taken together, our findings reveal two novel signaling pathways targeted by the metastasis suppressor RKIP that regulate remodeling of the extracellular matrix and tumor survival.

Carcinomas most often result from the stepwise acquisition of genetic alterations within the epithelial compartment. The surrounding stroma can also play an important role in cancer initiation and progression. Given the rare frequencies of genetic events identified in cancer-associated stroma, it is likely that epigenetic changes in the tumor microenvironment could contribute to its tumor-promoting activity. We use Hmga2 (High-mobility group AThook 2) an epigenetic regulator, to modify prostate stromal cells, and demonstrate that perturbation of the microenvironment by stromal-specific overexpression of this chromatin remodeling protein alone is sufficient to induce dramatic hyperplasia and multifocal prostatic intraepithelial neoplasia lesions from adjacent naïve epithelial cells. Importantly, we find that this effect is predominantly mediated by increased Wnt/β-catenin signaling. Enhancement of Hmga2-induced paracrine signaling by overexpression of androgen receptor in the stroma drives frank murine prostate adenocarcinoma in the adjacent epithelial tissues. Our findings provide compelling evidence for the critical contribution of epigenetic changes in stromal cells to multifocal tumorigenesis.

Tuberous sclerosis (TSC) is a tumor suppressor gene syndrome that is associated with the widespread development of mesenchymal tumor types. Genetically, TSC is said to occur through a classical bi-allelic inactivation of either TSC genes (TSC1, hamartin or TSC2, tuberin), an event that is implicated in the induction of the mTOR pathway and subsequent tumorigenesis. High Mobility Group A2 (HMGA2), an architectural transcription factor, is known to regulate mesenchymal differentiation and drive mesenchymal tumorigenesis in vivo. Here, we investigated the role of HMGA2 in the pathogenesis of TSC using the TSC2+/- mouse model that similarly mirrors human disease and human tumor samples. We show that HMGA2 expression was detected in 100% of human and mouse TSC tumors, and that HMGA2 activation was required for TSC mesenchymal tumorigenesis in genetically engineered mouse models. In contrast to the current dogma, the mTOR pathway was not activated in all TSC2+/- tumors and was elevated in only 50% of human mesenchymal tumors. Moreover, except for a subset of kidney tumors, tuberin was expressed in both human and mouse tumors. Therefore, haploinsufficiency of one TSC tumor suppressor gene was required for tumor initiation, but further tumorigenesis did not require the second hit, as previously postulated. Collectively, these findings demonstrate that tissue-specific genetic mechanisms are employed to promote tumor pathogenesis in TSC, and identify a novel, critical pathway for potential therapeutic targeting.

This abstract is being presented as a short talk in the scientific program. A full abstract is printed in the Proffered Abstracts section (PR02) of the Conference Proceedings. Citation Format: Daniel C. Rabe, Casey Frankenberger, Russell Bainer, Devipriya Sankarasharma, Kiran Chada, Thomas Krausz, Yoav Gilad, Lev Becker, Marsha Rich Rosner. Metastasis suppressors regulate the tumor microenvironment by blocking recruitment of pro-metastatic tumor-associated macrophages. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A01.

Triple-negative breast cancer (TNBC) patients have the highest risk of recurrence and metastasis. Because they cannot be treated with targeted therapies, and many do not respond to chemotherapy, they represent a clinically underserved group. While physiological inhibitors of metastasis (metastasis suppressors) play key roles in regulating tumor growth, invasion and metastasis, their role in regulating the tumor microenvironment and immune system is unknown. We hypothesized that the metastasis suppressor Raf Kinase Inhibitory Protein (RKIP) regulates stromal cells, which then affect tumor invasiveness. Using species-specific RNAseq we determined that expression of RKIP in tumors markedly reduces the number and metastatic potential of infiltrating TAMs. While TAMs isolated from TNBC xenografts drive in vitro invasion, RKIP+ derived TAMs did not drive invasion and had decreased secretion of pro-metastatic factors including SLPI, OPN, MMP-12, Galectin-3, VEGF-A, VEGF-D, TNFR2, and PGRN. We determined that RKIP regulates TAM recruitment by blocking HMGA2, which activates CCL5 expression. CCL5 rescued pro-metastatic TAM infiltration as well as tumor intravasation. We additionally showed that factors decreased in RKIP-derived TAMs were restored in CCL5-derived TAMs. CCL5 derived TAMs were also able to promote metastasis when co-injected with MDA-MB-231 tumors. These tumor cells demonstrated permanent increases in both growth and invasive potential after co-injection with highly pro-metastatic CCL5 derived TAMs. To determine the clinical utility of these TAM genes we combined their expression with RKIP signaling in the tumor to create a signature that strikingly separates TNBC patients based on outcome. Our results demonstrate for the first time that metastasis suppressors can regulate the microenvironment, regulating invasion through TAMs. Our results also suggest aggressive triple negative breast cancers could be controlled by attacking CCL5 derived TAMs crucial for promoting metastasis. Citation Format: Daniel C. Rabe, Casey Frankenberger, Russell Bainer, Devipriya Sankarasharma, Kiran Chada, Thomas Krausz, Yoav Gilad, Lev Becker, Marsha Rich Rosner. Metastasis suppressors regulate the tumor microenvironment by blocking recruitment of pro-metastatic tumor-associated macrophages. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr PR02.