The role of CXCL1 in crosstalk between endocrine resistant breast cancer and fibroblast.

BACKGROUND: ER positive breast cancer is currently targeted using various endocrine therapies. Despite the proven therapeutic efficacy, resistance to the drug and reoccurrence of tumor appears to be a complication that many patients deal with. Molecular pathways underlying the development of resistance are being widely studied. METHODS AND RESULTS: In this study, using four established endocrine resistant breast cancer (ERBC) cell lines, we characterized CXCL1 as a secreted factor in crosstalk between ERBC cells and fibroblasts. Protein array revealed upregulation of CXCL1 and we confirmed the CXCL1 expression by real-time qRT-PCR and U-Plex assay. Co-culturing ERBC cells with fibroblasts enhanced the cell growth and migration compared to monoculture. The crosstalk of ERBC cells with fibroblasts significantly activates ERK/MAPK signaling pathway while reparixin, CXCR1/2 receptor inhibitor, attenuates the activity. Reparixin displayed the ERBC cell growth inhibition and the combination treatment with reparixin and CDK4/6 inhibitor (palbociclib and ribociclib) increased these inhibitory effect. CONCLUSIONS: Taken together, our study implicates CXCL1 as a critical role in ERBC growth and metastasis via crosstalk with fibroblast and cotargeting CXCR1/2 and CDK4/6 could potentially overcome endocrine resistant breast cancer.

HOXB13 interaction with MEIS1 modifies proliferation and gene expression in prostate cancer.

BACKGROUND: The recurrent p.Gly84Glu germline mutation (G84E) in HOXB13 is consistently associated with prostate cancer (PCa), although the mechanisms underlying such linkage remain elusive. The majority of the PCa-associated HOXB13 mutations identified are localized to two conserved domains in HOXB13 that have been shown to mediate the interaction with MEIS cofactors belonging to the TALE family of homeodomain transcription factors. In this study, we sought to interrogate the biochemical and functional interactions between HOXB13 and MEIS in prostatic cells with a goal of defining how the HOXB13-MEIS complex impacts PCa pathobiology and define the extent to which the oncogenic activity of G84E is related to its effect on HOXB13-MEIS interaction/function. METHODS: HOXB13 and MEIS paralog expression in prostate epithelial cells and PCa cell lines was characterized by qPCR and immunoblot analyses. HOXB13 and MEIS1 co-expression in human prostate tissue was confirmed by IHC, followed by co-IP mapping of HOXB13-MEIS1 interactions. Proliferation of the PCa cell line LAPC4 following shRNA-mediated knockdown of each gene or both genes was assessed using DNA- and metabolic-based assays. Transcriptional targets of HOXB13 and MEIS1 were identified by gene expression profiling and qPCR. Finally, protein stability of HOXB13 in the context of MEIS1 was determined using pulse-chase assays. RESULTS: HOXB13 and MEIS1 are co-expressed and interact in prostate cells. Both of the putative MEIS interacting domains (MID) within HOXB13 were shown to be capable of mediating the interaction between HOXB13 and MEIS1 independently and such interactions were not influenced by the G84E mutation. The inhibitory effect of either HOXB13 or MEIS1 knockdown on cellular proliferation was augmented by knockdown of both genes, and MEIS1 knockdown abolished HOXB13-driven regulation of BCHE and TNFSF10 mRNA expression. Notably, we demonstrated that MEIS1 stabilized the HOXB13 protein in LAPC4 cells. CONCLUSIONS: Our study provides evidence for functional HOXB13-MEIS1 interactions in PCa. MEIS1 may contribute to the cancer-promoting actions of HOXB13 in cellular proliferation and gene regulation by prolonging HOXB13 half-life. Our data demonstrates that G84E is not a loss-of-function mutation that interferes with HOXB13 stability or ability to interact with MEIS1.

Simultaneous blockade of IL-6 and CCL5 signaling for synergistic inhibition of triple-negative breast cancer growth and metastasis.

BACKGROUND: Metastatic triple-negative breast cancer (TNBC) is a heterogeneous and incurable disease. Numerous studies have been conducted to seek molecular targets to treat TNBC effectively, but chemotherapy is still the main choice for patients with TNBC. We have previously presented evidence of the important roles of interleukin-6 (IL-6) and chemokine (C-C motif) ligand 5 (CCL5) in TNBC tumor growth and metastasis. These experiments highlighted the importance of the crosstalk between cancer cells and stromal lymphatic endothelial cells (LECs) in tumor growth and metastasis. METHODS: We examined the viability and migration of MDA-MB-231-LN, SUM149, and SUM159 cells co-cultured with LECs when treated with maraviroc (CCR5 inhibitor) and tocilizumab (anti-IL-6 receptor antibody). To assess the anti-tumor effects of the combination of these two drugs in an athymic nude mouse model, MDA-MB-231-LN cells were implanted in the mammary fat pad and maraviroc (8 mg/kg, orally daily) and cMR16-1 (murine surrogate of the anti-IL-6R antibody, 10 mg/kg, IP, 3 days a week) were administrated for 5 weeks and effects on tumor growth and thoracic metastasis were measured. RESULTS: In this study, we used maraviroc and tocilizumab to confirm that IL-6 and CCL5 signaling are key pathways promoting TNBC cell proliferation and migration. Further, in a xenograft mouse model, we showed that tumor growth was dramatically inhibited by cMR16-1, the mouse version of the anti-IL6R antibody. The combination of maraviroc and cMR16-1 caused significant reduction of TNBC tumor growth compared to the single agents. Significantly, the combination of maraviroc and cMR16-1 abrogated thoracic metastasis. CONCLUSION: Taken together, these findings show that IL-6 and CCL5 signaling, which promote crosstalk between TNBC and lymphatic vessels, are key enhancers of TNBC tumor growth and metastasis. Furthermore, these results demonstrate that a drug combination inhibiting these pathways may be a promising therapy for TNBC patients.

Modeling triple-negative breast cancer heterogeneity: Effects of stromal macrophages, fibroblasts and tumor vasculature.

A hallmark of breast tumors is its spatial heterogeneity that includes its distribution of cancer stem cells and progenitor cells, but also heterogeneity in the tumor microenvironment. In this study we focus on the contributions of stromal cells, specifically macrophages, fibroblasts, and endothelial cells on tumor progression. We develop a computational model of triple-negative breast cancer based on our previous work and expand it to include macrophage infiltration, fibroblasts, and angiogenesis. In vitro studies have shown that the secretomes of tumor-educated macrophages and fibroblasts increase both the migration and proliferation rates of triple-negative breast cancer cells. In vivo studies also demonstrated that blocking signaling of selected secreted factors inhibits tumor growth and metastasis in mouse xenograft models. We investigate the influences of increased migration and proliferation rates on tumor growth, the effect of the presence on fibroblasts or macrophages on growth and morphology, and the contributions of macrophage infiltration on tumor growth. We find that while the presence of macrophages increases overall tumor growth, the increase in macrophage infiltration does not substantially increase tumor growth and can even stifle tumor growth at excessive rates.

HOX genes: Major actors in resistance to selective endocrine response modifiers.

Long term treatment with therapies aimed at blocking the estrogen- (ER) or androgen receptor (AR) action often leads to the development of resistance to selective modulators of the estrogen receptor (SERMs) in ERα-positive breast cancer, or of the androgen receptor (SARMs) in AR-positive prostate cancer. Many underlying molecular events that confer resistance are known, but a unifying theme is yet to be revealed. Receptor tyrosine kinases (RTKs) such EGFR, ERBB2 and IGF1R are major mediators that can directly alter cellular response to the SERM, tamoxifen, but the mechanisms underlying increased expression of RTKs are not clear. A number of HOX genes and microRNAs and non-coding RNAs residing in the HOX cluster, have been identified as important independent predictors of endocrine resistant breast cancer. Recently, convincing evidence has accumulated that several members belonging to the four different HOX clusters contribute to endocrine therapy resistant breast cancer, but the mechanisms remain obscure. In this article, we have reviewed recent progress in understanding of the functioning of HOX genes and regulation of their expression by hormones. We also discuss, in particular, the contributions of several members of the HOX gene family to endocrine resistant breast cancer.

The HOXB7 protein renders breast cancer cells resistant to tamoxifen through activation of the EGFR pathway.

Multiple factors including long-term treatment with tamoxifen are involved in the development of selective estrogen receptor (ER) modulator resistance in ERα-positive breast cancer. Many underlying molecular events that confer resistance are known but a unifying theme is yet to be revealed. In this report, we provide evidence that HOXB7 overexpression renders MCF-7 cells resistant to tamoxifen via cross-talk between receptor tyrosine kinases and ERα signaling. HOXB7 is an ERα-responsive gene. Extended treatment of MCF-7 cells with tamoxifen resulted in progressively increasing levels of HOXB7 expression, along with EGFR and EGFR ligands. Up-regulation of EGFR occurs through direct binding of HOXB7 to the EGFR promoter, enhancing transcriptional activity. Finally, higher expression levels of HOXB7 in the tumor significantly correlated with poorer disease-free survival in ERα-positive patients with breast cancer on adjuvant tamoxifen monotherapy. These studies suggest that HOXB7 acts as a key regulator, orchestrating a major group of target molecules in the oncogenic hierarchy. Functional antagonism of HOXB7 could circumvent tamoxifen resistance.

Overview of the therapeutic strategies for ER positive breast cancer.

Estrogen Receptor is the driving transcription factor in about 75% of all breast cancers, which is the target of endocrine therapies, but drug resistance is a common clinical problem. ESR1 point mutations at the ligand binding domain are frequently identified in metastatic tumor and ctDNA (Circulating tumor DNA) derived from ER positive breast cancer patients with endocrine therapies. Although endocrine therapy and CDK4/6 inhibitor therapy have demonstrated preclinical and clinical benefits for breast cancer, the development of resistance remains a significant challenge and the detailed mechanisms, and potential therapeutic targets in advanced breast cancer yet to be revealed. Since a crosstalk between tumor and tumor microenvironment (TME) plays an important role to grow tumor and metastasis, this effect could serve as key regulators in the resistance of endocrine therapy and the transition of breast cancer cells to metastasis. In this article, we have reviewed recent progress in endocrine therapy and the contribution of TME to ER positive breast cancer.

Crosstalk between triple negative breast cancer and microenvironment.

Although many advances have been made in the treatment of breast cancer, for the triple negative breast cancer (TNBC) these therapies have not significantly increased overall survival. Tumor microenvironment (TME) plays an essential role to develop and control TNBC progression. Many preclinical and clinical studies are ongoing to treat patients with TNBC disease, but the effective therapies are currently not available. Here, we have reviewed recent progress in understanding of TNBC and advance in defining mechanisms of TNBC therapies and potential therapeutic strategies to overcome TNBC.

Mirk regulates the exit of colon cancer cells from quiescence.

Mirk/Dyrk1B is a serine/threonine kinase widely expressed in colon cancers. Serum starvation induced HD6 colon carcinoma cells to enter a quiescent G0 state, characterized by a 2N DNA content and a lower RNA content than G1 cells. Compared with cycling cells, quiescent cells exhibited 16-fold higher levels of the retinoblastoma protein p130/Rb2, which sequesters E2F4 to block entry into G1, 10-fold elevated levels of the CDK inhibitor p27kip1, and 10-fold higher levels of Mirk. However, depletion of Mirk did not prevent entry into G0, but enabled quiescent HD6, SW480, and colo320 colon carcinoma cells to acquire some biochemical characteristics of G1 cells, including increased levels of cyclin D1 and cyclin D3 because of slower turnover, increased activity of their CDK4/cyclin D complexes, and increased phosphorylation and decreased E2F4 sequestering ability of the CDK4 target, p130/Rb2. As a result, depletion of Mirk allowed some cells to escape quiescence and enabled cells released from quiescence to traverse G1 more quickly. The kinase activity of Mirk was increased by the chemotherapeutic drug 5-fluorouracil (5-FU). Treatment of p53 mutant colon cancer cells with 5-FU led to an elongated G1 in a Mirk-dependent manner, as G1 was shortened by ectopic overexpression of cyclin D1 mutated at the Mirk phosphorylation site (T288A), but not by wild-type cyclin D1. Mirk, through regulating cyclin D turnover, and the CDK inhibitor p27, as shown by depletion studies, functioned independently and additively to regulate the exit of tumor cells from quiescence.

BRCA1: linking HOX to breast cancer suppression.

Homeobox (HOX) genes play key roles in embryogenesis and tissue differentiation. Recently, a number of groups have reported altered HOX gene expression in breast cancer. However, the mechanism of HOX gene regulation and the search for direct targets of its transcriptional regulatory function have been minimally fruitful. Recently, Gilbert and colleagues reported that HOXA9 restrains breast cancer progression by upregulation of BRCA1, a tumor suppressor. This finding raises our hope that more, rather elusive targets of HOX genes important in tumor progression or suppression will be found in the future.

Cytokines secreted by stromal cells in TNBC microenvironment as potential targets for cancer therapy.

In triple-negative breast cancer (TNBC), the lack of therapeutic markers and effective targeted therapies result in an incurable metastatic disease associated with a poor prognosis. Crosstalks within the tumor microenvironment (TME), including those between cancer and stromal cells, affect the tumor heterogeneity, growth, and metastasis. Previously, we have demonstrated that IL-6, IL-8, and CCL5 play a significant role in TNBC growth and metastasis. In this study, we performed a systematic analysis of cytokine factors secreted from four stromal components (fibroblasts, macrophages, lymphatic endothelial cells, and blood microvascular endothelial cells) induced by four TNBC cell types. Through bioinformatic analysis, we selected putative candidates of secreted factors from stromal cells, which are involved in EMT activity, cell proliferation, metabolism, and matrisome pathways. Among the candidates, LCN2, GM-CSF, CST3, IL-6, IL-8, and CHI3L1 are ranked highly. Significantly, Lipocalin-2 (LCN2) is upregulated in the crosstalk of stromal cells and four different TNBC cells. We validated the increase of LCN2 secreted from four stromal cells induced by TNBC cells. Using a specific LCN2 antibody, we observed the inhibition of TNBC cell growth and migration. Taken together, these results propose secreted factors as molecular targets to treat TNBC progression via crosstalk with stromal components.

The survival kinase Mirk/Dyrk1B is a downstream effector of oncogenic K-ras in pancreatic cancer.

The kinase Mirk is overexpressed in many resected pancreatic adenocarcinomas and is amplified in a subset of pancreatic cancer cell lines. Depletion of Mirk has been shown to lead to apoptosis in pancreatic cancer cell lines, and thus to inhibit their clonogenic growth. Mirk is activated by signaling from activated Rac1 to MKK3 in MDCK cells, but the mechanism of activation of Mirk in pancreatic cancers is unknown. In this report, Mirk is shown to be a novel effector of K-ras, a gene mutated in approximately 90% of pancreatic cancers. Activation of Mirk signaling from oncogenic K-ras through Rac1 was shown in transient expression systems and reporter assays. Mirk activation in pancreatic cancer cells was blocked by RNA interference using three different synthetic duplex RNAis to K-ras, or two RNAis to Rac1, by pharmacologic inhibition of Rac1, or by expression of dominant negative K-rasS17N. Rac1 was activated in four out of five pancreatic cancer cell lines, and was activated by signaling from oncogenic K-ras. Mirk knockout does not induce embryonic lethality, and depletion of Mirk had no effect on the survival of normal diploid fibroblasts. In contrast, the clonogenic ability of Panc1 and AsPc1 pancreatic cancer cell lines was reduced 8- to 12-fold by the depletion of Mirk, with a greater reduction seen following the depletion of K-ras or both genes. Mirk is a novel downstream effector of oncogenic K-ras and mediates some of the survival signals activated by ras signaling.

Crosstalk between stromal components and tumor cells of TNBC via secreted factors enhances tumor growth and metastasis.

Triple negative breast cancer (TNBC) as a metastatic disease is currently incurable. Reliable and reproducible methods for testing drugs against metastasis are not available. Stromal cells may play a critical role in tumor progression and metastasis. In this study, we determined that fibroblasts and macrophages secreted IL-8 upon induction by tumor cell-conditioned media (TCM) from MDA-MB-231 cancer cells. Our data showed that the proliferation of MDA-MB-231 cells co-cultured with fibroblasts or macrophages was enhanced compared to the monoculture. Furthermore, TNBC cell migration, a key step in tumor metastasis, was promoted by conditioned media (CM) from TCM-induced fibroblasts or macrophages. Knockdown of the IL-8 receptor CXCR2 by CRISPR-Cas9 reduces MDA-MB-231 cell proliferation and migration compared to wild type. In a mouse xenograft tumor model, the growth of MDA-MB-231-CXCR2-/- tumor was significantly decreased compared to the growth of tumors from wild-type cells. In addition, the incidence of thoracic metastasis of MDA-MB-231-CXCR2-/- tumors was reduced compared to wild type. We found that the auto- and paracrine loop exists between TNBC cells and stroma, which results in enhanced IL-8 secretion from the stromal components. Significantly, inhibition of the IL-8 signaling pathway by reparixin, an inhibitor of the IL-8 receptor, CXCR1/2, reduced MDA-MB-231 tumor growth and metastasis. Taken together, these findings implicate IL-8 signaling as a critical event in TNBC tumor growth and metastasis via crosstalk with stromal components.

Inhibitors of STAT3, ß-catenin, and IGF-1R sensitize mouse PIK3CA-mutant breast cancer to PI3K inhibitors.

Although mutations in the phosphoinositide 3-kinase catalytic subunit (PIK3CA) are common in breast cancer, PI3K inhibitors alone have shown modest efficacy. We sought to identify additional pathways altered in PIK3CA-mutant tumors that might be targeted in combination with PI3K inhibitors. We generated two transgenic mouse models expressing the human PIK3CA-H1047R- and the -E545K hotspot-mutant genes in the mammary gland and evaluated their effects on development and tumor formation. Molecular analysis identified pathways altered in these mutant tumors, which were also targeted in multiple cell lines derived from the PIK3CA tumors. Finally, public databases were analyzed to determine whether novel pathways identified in the mouse tumors were altered in human tumors harboring mutant PIK3CA. Mutant mice showed increased branching and delayed involution of the mammary gland compared to parental FVB/N mice. Mammary tumors arose in 30% of the MMTV-PIK3CA-H1047R and in 13% of -E545K mice. Compared to MMTV-Her-2 transgenic mouse mammary tumors, H1047R tumors showed increased upregulation of Wnt/ß-catenin/Axin2, hepatocyte growth factor (Hgf)/Stat3, insulin-like growth factor 2 (Igf-2), and Igf-1R pathways. Inhibitors of STAT3, ß-catenin, and IGF-1R sensitized H1047R-derived mouse tumor cells and PIK3CA-H1047R overexpressing human HS578T breast cancer cells to the cytotoxic effects of PI3K inhibitors. Analysis of The Cancer Genome Atlas database showed that, unlike primary PIK3CA-wild-type and HER-2+ breast carcinomas, PIK3CA-mutant tumors display increased expression of AXIN2, HGF, STAT3, IGF-1, and IGF-2 mRNA and activation of AKT, IGF1-MTOR, and WNT canonical signaling pathways. Drugs targeting additional pathways that are altered in PIK3CA-mutant tumors may improve treatment regimens using PI3K inhibitors alone.

The Widening Sphere of Influence of HOXB7 in Solid Tumors.

Strong lines of evidence have established a critical role for the homeodomain protein HOXB7 in cancer. Specifically, molecular and cellular studies have demonstrated that HOXB7 is a master regulatory gene, capable of orchestrating a variety of target molecules, resulting in the activation of several oncogenic pathways. HOXB7 overexpression correlates with clinical progression and poor outcome of cancer patients. Specific inhibition of HOXB7 is particularly relevant in cancers still lacking effective therapies, such as tamoxifen-resistant breast cancer and melanoma. Mechanistic studies are providing additional targets of therapy, and biomarker studies are further establishing its importance in early diagnosis and prognosis. Cancer Res; 76(10); 2857-62. ©2016 AACR.

Effective treatment of ductal carcinoma in situ with a HER-2- targeted alpha-particle emitting radionuclide in a preclinical model of human breast cancer.

The standard treatment for ductal carcinoma in situ (DCIS) of the breast is surgical resection, followed by radiation. Here, we tested localized therapy of DCIS in mice using the immunoconjugate 225Ac linked-trastuzumab delivered through the intraductal (i.duc) route. Trastuzumab targets HER-2/neu, while the alpha-emitter 225Ac (half-life, 10 days) delivers highly cytotoxic, focused doses of radiation to tumors. Systemic 225Ac, however, elicits hematologic toxicity and at high doses free 213Bi, generated by its decay, causes renal toxicity. I.duc delivery of the radioimmunoconjugate could bypass its systemic toxicity. Bioluminescent imaging showed that the therapeutic efficacy of intraductal 225Ac-trastuzumab (10-40 nCi per mammary gland; 30-120 nCi per mouse) in a DCIS model of human SUM225 cancer cells in NSG mice was significantly higher (p<0.0003) than intravenous (120 nCi per mouse) administration, with no kidney toxicity or loss of body weight. Our findings suggest that i.duc radioimmunotherapy using 225Ac-trastuzumab deserves greater attention for future clinical development as a treatment modality for early breast cancer.

Combined Treatment with Epigenetic, Differentiating, and Chemotherapeutic Agents Cooperatively Targets Tumor-Initiating Cells in Triple-Negative Breast Cancer.

Efforts to induce the differentiation of cancer stem cells through treatment with all-trans retinoic acid (ATRA) have yielded limited success, partially due to the epigenetic silencing of the retinoic acid receptor (RAR)-ß The histone deacetylase inhibitor entinostat is emerging as a promising antitumor agent when added to the standard-of-care treatment for breast cancer. However, the combination of epigenetic, cellular differentiation, and chemotherapeutic approaches against triple-negative breast cancer (TNBC) has not been investigated. In this study, we found that combined treatment of TNBC xenografts with entinostat, ATRA, and doxorubicin (EAD) resulted in significant tumor regression and restoration of epigenetically silenced RAR-ß expression. Entinostat and doxorubicin treatment inhibited topoisomerase II-ß (TopoII-ß) and relieved TopoII-ß-mediated transcriptional silencing of RAR-ß Notably, EAD was the most effective combination in inducing differentiation of breast tumor-initiating cells in vivo Furthermore, gene expression analysis revealed that the epithelium-specific ETS transcription factor-1 (ESE-1 or ELF3), known to regulate proliferation and differentiation, enhanced cell differentiation in response to EAD triple therapy. Finally, we demonstrate that patient-derived metastatic cells also responded to treatment with EAD. Collectively, our findings strongly suggest that entinostat potentiates doxorubicin-mediated cytotoxicity and retinoid-driven differentiation to achieve significant tumor regression in TNBC. Cancer Res; 76(7); 2013-24. ©2016 AACR.

A pivotal role for HOXB7 protein in endocrine resistant breast cancer.

HOXB7 is a homeodomain containing transcription factor which plays a pivotal role in tamoxifen resistant breast cancer. Our work has shown that overexpression of HOXB7 renders cells tamoxifen resistant by mobilizing a number of receptor tyrosine kinase pathways. EGFR expression is upregulated by direct binding of HOXB7 to the EGFR promoter, while HOXB7 functions as a cofactor with ERα to cause overexpression of multiple ER-target genes, including HER2, in tamoxifen resistant breast cancer cells. Probing the pathway further, we found that miR-196a and MYC are upstream regulators of HOXB7 expression. Mechanistically, HOXB7 and ERα jointly upregulate HER2 which phosphorylates MYC. Thus stabilized, MYC in turn suppresses miR-196a. Loss of miR-196a results lifts the quelling influence of miR-196a on HOXB7 expression. Besides shedding light on the intricate interplay of events occurring in tamoxifen resistant breast cancer, the work identifies a number of new therapeutic targets capable of restoring sensitivity of breast cancer cells to tamoxifen.

HOXB7 promotes malignant progression by activating the TGFß signaling pathway.

Overexpression of HOXB7 in breast cancer cells induces an epithelial-mesenchymal transition and promotes tumor progression and lung metastasis. However, the underlying mechanisms for HOXB7-induced aggressive phenotypes in breast cancer remain largely unknown. Here, we report that phosphorylation of SMAD3 was detected in a higher percentage in primary mammary tumor tissues from double-transgenic MMTV-Hoxb7/Her2 mice than tumors from single-transgenic Her2/neu mice, suggesting activation of TGFß/SMAD3 signaling by HOXB7 in breast tumor tissues. As predicted, TGFß2 was high in four MMTV-Hoxb7/Her2 transgenic mouse tumor cell lines and two breast cancer cell lines transfected with HOXB7, whereas TGFß2 was low in HOXB7-depleted cells. HOXB7 directly bound to and activated the TGFß2 promoter in luciferase and chromatin immunoprecipitation assays. Increased migration and invasion as a result of HOXB7 overexpression in breast cancer cells were reversed by knockdown of TGFß2 or pharmacologic inhibition of TGFß signaling. Furthermore, knockdown of TGFß2 in HOXB7-overexpressing MDA-MB-231 breast cancer cells dramatically inhibited metastasis to the lung. Interestingly, HOXB7 overexpression also induced tumor-associated macrophage (TAM) recruitment and acquisition of an M2 tumor-promoting phenotype. TGFß2 mediated HOXB7-induced activation of macrophages, suggesting that TAMs may contribute to HOXB7-promoted tumor metastasis. Providing clinical relevance to these findings, by real-time PCR analysis, there was a strong correlation between HOXB7 and TGFß2 expression in primary breast carcinomas. Taken together, our results suggest that HOXB7 promotes tumor progression in a cell-autonomous and non-cell-autonomous manner through activation of the TGFß signaling pathway.