Abstract 629: The impact of BMP4 on breast cancer metastasis in an in vivo xenograft mouse model

Background. Breast cancer is the most common cancer in women worldwide. Bone morphogenetic proteins (BMPs), members of the transforming growth factor β superfamily, are known to regulate cell proliferation, differentiation and motility, and have also been shown to be involved in cancer pathogenesis, also in breast cancer. We have previously demonstrated that BMP4 is able to consistently reduce breast cancer cell proliferation through G1 cell cycle arrest and to simultaneously induce migration and invasion in a subset of breast cancer cell lines. Similarly, our clinical data revealed a correlation between elevated BMP4 expression in primary breast tumors and reduced proliferation as well as increased risk of recurrence. The growth inhibitory effects of BMP4 have also been demonstrated in vivo but its possible metastasis promoting functions are less well characterized. Here we set out to investigate this topic using a xenograft mouse model.

Methods. MDA-MB-231 breast cancer cells were transduced with a luciferase-expressing vector to allow monitoring of the metastasis formation using bioluminescence imaging. Cells (2 × 105) were injected into the mice intracardially and BMP4 (100 ng/g, 10 animals) or vehicle control (11 animals) was administered through tail vein three times a week. After seven weeks, the mice were sacrificed and metastases collected for histological analyses.

Results. The overall amount of metastases was similar in both groups (13 in BMP4-treatment group vs. 12 in control group). There was a slight but non-significant trend of metastases developing earlier in the BMP4 group compared to controls. Most of the metastases occurred in bone and adrenal glands. There were somewhat more metastases in bone in the BMP4-treated mice (10 vs. 7) and more adrenal gland metastases in vehicle-treated animals (5 vs. 1). To assess the contribution of BMP4 to the characteristics of the metastases, the tumors were stained for pSMAD1/5/9 (BMP signaling activation), Ki67 (proliferation), MECA32 (blood vessels), mesenchymal marker vimentin, α-SMA (cancer-associated fibroblasts) and basal markers K5 and K14. No major dissimilarities were observed between the BMP4 and vehicle tumor groups in the staining patterns. Interestingly, the osteoclast marker Tartrate-resistant acid phosphatase (TRAP) was expressed in both groups in the cancer cells whereas Toluidine Blue staining revealed that the bone morphology was not detrimentally affected by BMP4 treatment.

Conclusions. Despite its ability to enhance breast cancer cell migration and invasion in vitro, BMP4 does not seem to have a dramatic impact on in vivo metastasis formation, although a small acceleration in appearance of the metastases was observed. However, the limitations of the xenograft model do not allow us to exclude the possible long-term effects of BMP4 that might be more applicable to human situation.

Citation Format: Minna Ampuja, Emma L. Alarmo, Philip Owens, Riikka Havunen, Agnes E. Gorska, Harold L. Moses, Anne Kallioniemi. The impact of BMP4 on breast cancer metastasis in an in vivo xenograft mouse model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 629.

Abstract 2676: Inhibition of bmp signaling suppresses metastasis in mammary cancer

Bone Morphogenetic Proteins (BMPs) are secreted cytokines/growth factors that play differing roles in cancer. BMPs are overexpressed in human breast cancers, but loss of BMP signaling in mammary carcinomas can accelerate metastasis. We show that human breast cancers display active BMP signaling, which is rarely downregulated or homozygously deleted. We hypothesized that systemic inhibition of BMP signaling in both the tumor and the surrounding microenvironment could prevent tumor progression and metastasis. To test this hypothesis, we used DMH1, a BMP antagonist in MMTV.PyVmT expressing mice. Treatment with DMH1 reduced lung metastasis and the tumors were less proliferative and more apoptotic. In the surrounding tumor microenvironment, treatment with DMH1 altered fibroblasts, lymphatic vessels and macrophages to be less tumor promoting. These results indicate that inhibition of BMP signaling may successfully target both the tumor and the surrounding microenvironment to reduce tumor burden and metastasis.

Citation Format: Philip Owens, Michael W. Pickup, Sergey V. Novitskiy, Jennifer M. Giltnane, Agnes E. Gorska, Corey R. Hopkins, Charles C. Hong, Harold L. Moses. Inhibition of bmp signaling suppresses metastasis in mammary cancer. [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 2676. doi:10.1158/1538-7445.AM2014-2676

Abstract 1500: Bone morphogenetic proteins stimulate mammary fibroblasts to promote mammary tumorigenesis

Bone Morphogenetic Proteins (BMPs) are secreted cytokines/growth factors belonging to the Transforming Growth Factor ≤ (TGFβ) superfamily. BMPs have recently been shown to be overexpressed in human breast cancers, however loss of BMP signaling in mammary carcinomas has also been shown to accelerate metastases. Stimulation of dermal fibroblasts with BMP4 can enhance pro-tumorigenic factors uniquely from the epidermal response. Additionally, treatment of carcinoma-associated fibroblasts (CAFs) derived from a mouse prostate carcinoma with BMP have been reported to stimulate tumor-associated angiogenesis. We sought to determine the effect of BMP treatment on mammary fibroblasts and determine their response during mammary tumor progression. We first identified secreted pro-inflammatory cytokines and matrix-metalloproteinases (MMPs) upregulated in response to BMP4 treatment. We found that fibroblasts stimulated with BMP4 could enhance tumor invasion, which was inhibited by a BMP receptor kinase antagonist. We next demonstrated that BMP signaling was specifically absent in the stroma of human ductal and lobular carcinoma in situ (DCIS & LCIS). Yet after progression to invasion, breast tumors of many distinct subtypes contained a stroma active for BMP signaling. We further extended these observations with human normal mammary fibroblasts and compared them to human fibroblasts from breast cancer and found that BMP was capable of inducing MMP3 and IL-6 secretion in normal fibroblasts. However carcinoma associated fibroblasts had constitutively elevated levels of MMP3 and IL-6 that corresponded to enhanced BMP signaling in addition to loss of secreted BMP antagonists. These experiments demonstrate that BMP may play important tumor promoting functions within the tumor microenvironment.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1500. doi:1538-7445.AM2012-1500

Overexpression of a kinase-deficient transforming growth factor-beta type II receptor in mouse mammary stroma results in increased epithelial branching

Members of the transforming growth factor-beta (TGF-beta) superfamily signal through heteromeric type I and type II serine/threonine kinase receptors. Transgenic mice that overexpress a dominant-negative mutation of the TGF-beta type II receptor (DNIIR) under the control of a metallothionein-derived promoter (MT-DNIIR) were used to determine the role of endogenous TGF-betas in the developing mammary gland. The expression of the dominant-negative receptor was induced with zinc and was primarily localized to the stroma underlying the ductal epithelium in the mammary glands of virgin transgenic mice from two separate mouse lines. In MT-DNIIR virgin females treated with zinc, there was an increase in lateral branching of the ductal epithelium. We tested the hypothesis that expression of the dominant-negative receptor may alter expression of genes that are expressed in the stroma and regulated by TGF-betas, potentially resulting in the increased lateral branching seen in the MT-DNIIR mammary glands. The expression of hepatocyte growth factor mRNA was increased in mammary glands from transgenic animals relative to the wild-type controls, suggesting that this factor may play a role in TGF-beta-mediated regulation of lateral branching. Loss of responsiveness to TGF-betas in the mammary stroma resulted in increased branching in mammary epithelium, suggesting that TGF-betas play an important role in the stromal-epithelial interactions required for branching morphogenesis.

Identification of STRAP, a novel WD domain protein in transforming growth factor-beta signaling

Transforming growth factor-beta1 (TGF-beta1) is the prototype of a large family of proteins that regulate a variety of biological processes. The pleiotropic responses to TGF-beta are mediated via ligand-induced heteromeric complex formation by type I (TbetaR-I) and type II (TbetaR-II) serine-threonine kinase receptors. Several studies have shown that TbetaR-II acts as a primary receptor, binding TGF-beta and phosphorylating TbetaR-I, whose kinase activity then propagates the signals. Therefore, intracellular proteins that interact with type I receptors are likely to play important roles in TGF-beta signaling. We have identified a novel WD domain-containing protein, designated STRAP (serine-threonine kinase receptor-associated protein), which interacts with TbetaR-I in a yeast two-hybrid system. STRAP associates with both functional TbetaR-I and TbetaR-II in vivo. Overexpression of STRAP leads to inhibition of TGF-beta-mediated transcriptional activation. It also shows synergistic inhibition of TGF-beta signaling in concert with Smad7, but not with Smad6, as measured by TGF-beta-dependent transcriptional reporters. The existence of the STRAP gene from yeast to mammals indicates an evolutionarily conserved function in eukaryotes. The data suggest a potential role for STRAP in TGF-beta signal transduction.

Dominant-negative interference of the transforming growth factor beta type II receptor in mammary gland epithelium results in alveolar hyperplasia and differentiation in virgin mice

Transforming growth factor (TGF)-beta1 and TGF-beta3 are normally expressed at high levels in the mammary gland during quiescence and at all stages of development, except lactation. Exogenously added TGF-beta1, -beta2, and -beta3 have been shown to regulate growth and differentiation of mammary epithelial cells in vitro and in vivo. TGF-betas signal through a heteromeric complex of type I and type II serine/threonine kinases. The type II receptor is necessary for ligand binding and growth suppression by TGF-betas. Deletions of the cytoplasmic domains of several kinase receptors known to function in multimeric complexes have been shown to act as dominant-negative mutations. To evaluate the role of endogenous TGF-betas in the growth and differentiation of the mammary gland in vivo, we have targeted expression of a truncated, kinase-defective TGF-beta type II receptor to mammary epithelial cells in transgenic mice using the mouse mammary tumor virus promoter/enhancer. Transgene expression was localized to the epithelial cells of terminal ducts and alveolar buds. At approximately 20 weeks of age, virgin female transgenic mice demonstrated varying degrees of mammary epithelial hyperplasia. Mammary glands from transgenic, virgin animals exhibited alveolar development and expression of the milk protein, beta-casein. The data suggest that impaired responsiveness in the epithelium to endogenous TGF-betas results in inappropriate alveolar development and differentiation in the mammary gland. We conclude that endogenous TGF-betas signal to the epithelium to maintain quiescence in the mammary glands of virgin animals.

Mammary tumor suppression by transforming growth factor beta 1 transgene expression

In cell culture, type alpha transforming growth factor (TGF-alpha) stimulates epithelial cell growth, whereas TGF-beta 1 overrides this stimulatory effect and is growth inhibitory. Transgenic mice that overexpress TGF-alpha under control of the mouse mammary tumor virus (MMTV) promoter/enhancer exhibit mammary ductal hyperplasia and stochastic development of mammary carcinomas, a process that can be accelerated by administration of the chemical carcinogen 7,12-dimethylbenz[a]anthracene. MMTV-TGF-beta 1 transgenic mice display mammary ductal hypoplasia and do not develop mammary tumors. We report that in crossbreeding experiments involving the production of mice carrying both the MMTV-TGF-beta 1 and MMTV-TGF-alpha transgenes, there is marked suppression of mammary tumor formation and that MMTV-TGF-beta 1 transgenic mice are resistant to 7,12-dimethylbenz[a]anthracene-induced mammary tumor formation. These data demonstrate that overexpression of TGF-beta 1 in vivo can markedly suppress mammary tumor development.

Inhibition of cell growth by TGF beta 1 is associated with inhibition of B-myb and cyclin A in both BALB/MK and Mv1Lu cells

The concept of positive and negative regulation of normal cellular growth by diffusible factors is well illustrated by the effects of epidermal growth factor and transforming growth factor beta 1 (TGF beta 1) on mouse keratinocytes (MK) and mink lung epithelial cells (Mv1Lu). MK and Mv1Lu are nontransformed cell lines that reversibly arrest at a point in late G1 in response to TGF beta 1. Previously, we have shown that expression of the protooncogene c-myc is induced upon epidermal growth factor stimulation of quiescent MK and Mv1Lu cells and that transcriptional suppression of c-myc by TGF beta 1 treatment is important in the TGF beta 1 growth inhibition pathway. Using epidermal growth factor-stimulated synchronized MK and Mv1Lu cells, we have investigated the mRNA expression of a large number of growth factor-inducible genes that are critical regulators of growth in G1 and at the G1/S transition. These genes, often found to be dysregulated in cancer, include transcription factors as well as cyclins and their associated kinases, that promote growth, and tumor suppressor genes, that inhibit growth. As reported here, TGF beta 1 significantly inhibited mRNA expression of B-myb and cyclin A in both cell lines, suggesting that these may be important common downstream targets in the growth inhibition pathway. In contrast, the expression patterns of cyclins D1 and D2 and the transcription factors E2F1 and E2F2 were unaffected in MK cells treated with TGF beta 1 but were significantly inhibited in TGF beta 1-treated Mv1Lu cells. We cite the evidence suggesting that the inhibition of B-myb and cyclin A may contribute to the late G1 arrest caused by TGF beta 1 and that these events may be linked through the actions of the product of the retinoblastoma susceptibility gene (Rb) or an Rb family member.