Breast Cancer Metastasis Suppressor 1 (BRMS1) Forms Complexes with Retinoblastoma-binding Protein 1 (RBP1) and the mSin3 Histone Deacetylase Complex and Represses Transcription

Breast cancer metastasis suppressor 1 (BRMS1) suppresses metastasis of multiple human and murine cancer cells without inhibiting tumorigenicity. By yeast two-hybrid and co-immunoprecipitation, BRMS1 interacts with retinoblastoma binding protein 1 and at least seven members of the mSin3 histone deacetylase (HDAC) complex in human breast and melanoma cell lines. BRMS1 co-immunoprecipitates enzymatically active HDAC proteins and represses transcription when recruited to a Gal4 promoter in vivo. BRMS1 exists in large mSin3 complex(es) of approximately 1.4-1.9 MDa, but also forms smaller complexes with HDAC1. Deletion analyses show that the carboxyl-terminal 42 amino acids of BRMS1 are not critical for interaction with much of the mSin3 complex and that BRMS1 appears to have more than one binding point to the complex. These results further show that BRMS1 may participate in transcriptional regulation via interaction with the mSin3.HDAC complex and suggest a novel mechanism by which BRMS1 might suppress cancer metastasis.

A small molecule antagonist of the αvβ3integrin suppresses MDA-MB-435 skeletal metastasis

INTRODUCTION

Breast cancer is one of the most common malignancies affecting women in the United States and Europe. Approximately three out of every four women with breast cancer develop metastases in bone which, in turn, diminishes quality of life. The alpha(v)beta3 integrin has previously been implicated in multiple aspects of tumor progression, metastasis and osteoclast bone resorption. Therefore, we hypothesized that the alpha(v)beta3-selective inhibitor, S247, would decrease the development of osteolytic breast cancer metastases.

MATERIALS AND METHODS

Cells were treated in vitro with S247 and assessed for viability and adhesion to matrix components. Athymic mice received intracardiac (left ventricle) injections of human MDA-MB-435 breast carcinoma cells expressing enhanced green-fluorescent protein. Mice were treated with vehicle (saline) or S247 (1, 10, or 100 mg/kg/d) using osmotic pumps beginning either one week before or one week after tumor cell inoculation. Bones were removed and examined by fluorescence microscopy and histology. The location and size of metastases were recorded.

RESULTS AND CONCLUSIONS

IC50 for S247 adhesion to alpha(v)beta3 or alpha(IIB)beta3a substrates was 0.2 nM vs. 244 nM, respectively. Likewise, S247 was not toxic at doses up to 1000 microM. However, osteoclast cultures treated with S247 exhibited marked morphological changes and impaired formation of the actin sealing zone. When S247 was administered prior to tumor cells, there was a significant, dose-dependent reduction (25-50% of vehicle-only-treated mice; P = 0.002) in osseous metastasis. Mice receiving S247 after tumor cell inoculation also developed fewer bone metastases, but the difference was not statistically significant. These data suggest that, in the MDA-MB-435 model, the alpha(v)beta3 integrin plays an important role in early events (e.g., arrest of tumor cells) in bone metastasis. Furthermore, the data suggest that alpha(v)beta3 inhibitors may be useful in the treatment and/or prevention of breast cancer metastases in bone.

Microarrays bring new insights into understanding of breast cancer metastasis to bone

Using a microarray approach, Kang and colleagues identified several genes involved in the generation of breast cancer metastasis in bone and demonstrated their roles in bone colonization in vivo. Their findings and interpretations are reviewed in the context of recent array studies that compared gene expression in primary tumors and metastases. RNA expression array results have already demonstrated value in predicting whether metastases will develop in patients. They have also shown that expression patterns are similar in primary tumors and metastases. The latter data have invited re-examination of long-held notions related to mechanisms of metastasis. While the arrays show promise for improving diagnostic capability in breast cancers, ascribing mechanistic interpretations to correlative data should be done with extreme caution. Kang and colleagues' paper in Cancer Cell elegantly reinforces the concepts that efficiency of the metastatic process is dependent on the coordinated expression of multiple genes and that the expression of metastasis-associated genes is sometimes dependent on the microenvironment in which cells find themselves.

Effects of alpha-difluoromethylornithine on local recurrence and pulmonary metastasis from MDA-MB-435 breast cancer xenografts in nude mice

We have recently shown that administration of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), the first and rate-limiting enzyme in polyamine (PA) biosynthesis reduces pulmonary metastasis from MDA-MB-435 breast cancer xenografts in nude mice. The present experiments were designed to further explore PA involvement in breast cancer metastasis, using GFP-tagged MDA-MB-435 cells that can be tracked at the single cell level. Administration of DFMO significantly reduced the number of mice with pulmonary metastasis as well as the number of metastases per mouse. Both single-cell and multicellular metastatic deposits were similarly suppressed, thus suggesting that DFMO was inhibiting lung colonization by tumor cells rather than preventing progression of single-cell deposits to overt metastasis. DFMO administration also significantly reduced local recurrences following removal of the primary tumor. Prolongation of DFMO treatment to 14 weeks did not yield a superior antimetastatic effect beyond that provided by a 10-week course of therapy. Discontinuation of DFMO, on the other hand, was associated with local regrowth of the tumors and, possibly, recurrence of pulmonary metastasis. These data provide a rationale for testing the efficacy of anti-PA treatment within the context of adjuvant therapy of breast cancer.

MDA-MB-435 human breast carcinoma metastasis to bone

Breast cancer metastasizes to bone with high frequency and incidence. However, studies of breast cancer metastasis to bone have been limited by two factors. First, the number of models that colonize bone are limited. Second, detection of bone metastases is too insensitive or too laborious for routine, large-scale studies or for studying the earliest steps in bone colonization. To partially alleviate these problems, the highly metastatic MDA-MB-435 (435) human breast carcinoma cell line was engineered to constitutively express enhanced green fluorescent protein (GFP). While 435GFP cells did not form femoral metastases following orthotopic or intravenous injections, they produced widespread osteolytic skeletal metastases following injection into the left ventricle of the heart. All mice developed at least one femur metastasis as well as a mandibular metastasis. As in humans, osseous metastases localized predominantly to trabecular regions, especially proximal and distal femur, proximal tibia, proximal humerus and lumbar vertebrae. 435GFP cells also developed metastases in adrenal glands, brain and ovary following intracardiac injection, suggesting that this model may also be useful for studying organotropism to other tissues as well. Additionally, GFP-tagging permitted detection of single cells and microscopic metastases in bone at early time points following arrival and at stages of proliferation prior to coalescence of individual metastases.

Metastasis suppressor pathways--an evolving paradigm

A greater understanding of the processes of tumor invasion and metastasis, the principal cause of death in cancer patients, is essential to determine newer therapeutic targets. Metastasis suppressor genes, by definition, suppress metastasis without affecting tumorigenicity and, hence, present attractive targets as prognostic or therapeutic markers. This short review focuses on those twelve metastasis suppressor genes for which functional data exist. We also outline newly identified genes that bear promising traits of having metastasis suppressor activity, but for which functional data have not been completed. We also summarize the biochemical mechanism(s) of action (where known), and present a working model assembling potential metastasis suppression pathways.

The skeleton as a unique environment for breast cancer cells

Bone is a favored location for several cancer metastases especially breast, prostate and myeloma. This review evaluates various properties of the skeleton that contribute to its successful colonization by breast cancer cells. The first consideration is the unique aspects of the vasculature of metaphyseal bone, which may account for the initial lodging of breast cancer cells in specific regions of the skeleton. Metasphyseal bone, found at the ends of long bone, in ribs and in vertebrae, is comprised of trabecular bone interspersed with marrow and a rich vasculature. The chemotactic factors that arise from bone marrow and bone cells are discussed in terms of cancer cell migration out of the vasculature and entry of cancer cells into the marrow cavity. Once the breast cancer cells have migrated into the metaphysis, they interact both directly and indirectly with bone cells and other cells in the marrow. As tumor growth progresses, functional bone cells are lost, most likely through apoptosis.

Mucosally-derived HPV-40 can infect both human genital foreskin and cutaneous hand skin tissues grafted into athymic mice

HPV-40 is a rare HPV type that has been detected only in genital mucosal tissues. This HPV type is very closely related to HPV-7, which has a predominantly cutaneous tissue tropism. We have shown, previously, that an isolate of HPV-40 (described here as HPV-40(Hershey) or HPV-40(H)) productively infected genital tissues. In this study, HPV-40(H) was tested for productive infection of cutaneous tissue. Fetal hand skin fragments were incubated with infectious HPV-40(H) and implanted subrenally into athymic mice. After 120 days, xenografts showed morphological changes consistent with HPV-40(H) infection and were HPV-40 DNA in situ positive and capsid antigen positive. The results demonstrated that hand skin can support HPV-40(H) infection thereby indicating that this viral type has the capacity to infect both genital mucosal and cutaneous tissues.

Breast cancer metastasis suppressor 1: update

This article reviews information related to the BRMS1 (BReast Metastasis Suppressor 1) metastasis suppressor gene. BRMS1 was identified by differential display comparing metastasis-suppressed chromosome 11 hybrids with metastatic, parental MDA-MB-435 human breast carcinoma cells. BRMS1 has subsequently been shown to suppress metastasis, but not tumorigenicity of human melanoma cells. The murine version, Brms1, also suppresses metastasis and exhibits a high level of homology to the human gene at the structure, nucleotide and amino acid levels. The mechanisms of action remain to be determined; however, BRMS1 transfectant cells have restored gap junctional intercellular communication. Recent data suggest that BRMS1 is part of the mSin3A histone deacetylase complex.

KISS1 metastasis suppression and emergent pathways

Metastatic disease is the most critical impediment to cancer patient survival. However, comparatively little is known concerning the intricate pathways which govern the complex phenotypes associated with metastasis. The KISS1 metastasis suppressor gene inhibits metastasis in both in vivo melanoma and breast carcinoma models. Despite its clear physiological activity, the mechanism of KISS1 remains unclear. Recent identification of a 54 amino acid peptide of KISS1, termed metastin or kisspeptin-54, and its cognate G-protein coupled receptor (hOT7T175, AXOR12, GPR54) have provided additional clues and avenues of research. While studies have attributed KISS1 with modulation of NFkappaB regulation, experiments with metastin and its receptor implicate MAP kinase pathways and also suggest the potential of autocrine, paracrine and endocrine roles. Impacts on motility, chemotaxis, adhesion and invasion have each been documented in disparate cell lines and conflicting observations require resolution. Nevertheless, mounting clinical evidence, particularly the loss of KISS1 in metastases, correlates KISS1 and metastin receptor expression with human tumor progression. Together, the data substantiate roles for these molecules in metastasis regulation.

Melanoma metastasis suppression by chromosome 6: evidence for a pathway regulated by CRSP3 and TXNIP

Loss of genetic material on chromosome 6 has been associated with progression of human melanomas. We showed previously that introducing chromosome 6 into metastatic human melanoma cell lines suppresses metastasis without affecting the ability of the hybrids to form progressively growing tumors. By subtractive hybridization comparing nonmetastatic chromosome 6-containing (neo6/C8161) versus parental (C8161) metastatic cells, the KISS1 metastasis suppressor gene was isolated. However, KISS1 mapped to chromosome 1q32. To identify upstream regulator(s) of (and downstream effectors of) KISS1, microarray hybridization comparing C8161 and neo6/C8161 variants was performed. TXNIP/VDUP1, a thioredoxin-binding protein, was expressed more highly in neo6/C8161 and in nonmetastatic melanomas. Increased TXNIP expression inhibited metastasis and up-regulated KISS1. Surprisingly, TXNIP also mapped to chromosome 1q. PCR karyotyping that refined the region on chromosome 6 identified CRSP3/DRIP130, a transcriptional coactivator, as a metastasis suppressor. CRSP3 transfectant cells had up-regulated KISS1 and TXNIP expression and were suppressed for metastasis. Quantitative real-time reverse-transcription PCR of clinical melanoma samples showed that loss of CRSP3 expression correlated with decreased KISS1 expression and increased metastasis. Thus, we implicated a specific gene on chromosome 6 in the etiology of melanoma metastasis and identified potential up-stream regulators of KISS1 and TXNIP.

B16F10 melanoma cell colonization of mouse lung is enhanced by partial pneumonectomy

Surgical resection of lung tissue is employed clinically as a therapy for pulmonary metastases; however, local cancer recurrence is a frequent post-surgical complication. In a variety of small mammals, left pneumonectomy (PNX) initiates rapid compensatory hyperplasia of the remnant lung lobes restoring normal tissue mass, structure and function. Post-PNX compensatory lung growth is known to promote lung tumor formation in carcinogen-treated mice. The present study tests the hypothesis that PNX enhances experimental metastasis to lung. C57B1/6 mice subjected to PNX were given an intravenous injection of B16F10 melanoma cells at various stages of compensatory lung growth. Animals injected with B16F10 cells during the linear phase of the response had 77% to 260% more pulmonary metastases than mice subjected to thoracotomy (P < 0.01). Moreover, measurements of tumor area (mm2) revealed that PNX mice harbored a substantially larger lung tumor burden than control animals. Normalization of the tumor cell inoculum to lung mass yielded similar results. PNX had no effect on growth of sub-cutaneous B16F10 melanoma tumors, suggesting that experimental melanoma metastasis was enhanced by local alterations in the lung microenvironment. These results suggest (1) that PNX is a relevant model in which to investigate mechanisms of local cancer recurrence and, (2) melanoma cell metastatic potential is influenced, at least in part, by local factors modified during post-PNX compensatory lung growth.

Influence of polyamines on in vitro and in vivo features of aggressive and metastatic behavior by human breast cancer cells

Increased cellular activity of ornithine decarboxylase (ODC), the first and rate-limiting enzyme in polyamine (PA) synthesis, is an independent adverse prognostic factor for overall survival in human breast cancer, thus suggesting an important role for PA in tumor progression. The experiments presented here were designed to investigate the role of PA in invasion and metastasis, using the highly aggressive MDA-MB-435 and MDA-MB-231 human breast cancer cell lines. Administration of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, significantly reduced, in a dose-dependent manner, the invasiveness in matrigel of both MDA-MB-435 and MDA-MB-231 cells by approximately 70%. DFMO treatment also inhibited (P < 0.0001) 'stellate' colony formation (an indicator of aggressive phenotype) by MDA-MB-435 cells plated in the matrigel outgrowth assay. Administration of DFMO (2% in drinking water) reduced the growth rate of both cell lines implanted orthotopically in nude mice. To evaluate metastasis while minimizing effects on proliferation, DFMO-treated mice were sacrificed later to allow their tumors to reach the same size of the tumors in the control mice. The most striking finding was that DFMO, while ineffective in reducing local invasion, nearly totally abolished (P = 0.0152) pulmonary metastasis in mice bearing MDA-MB-435 xenografts. These results support a role of PA in promoting breast cancer aggressiveness, particularly with regard to the development of distant metastasis. Furthermore, the data suggest that PA involvement is distal to local invasion in the metastatic cascade.

Analysis of mechanisms underlying BRMS1 suppression of metastasis

Introduction of normal, neomycin-tagged human chromosome 11 (neo11) reduces the metastatic capacity of MDA-MB-435 human breast carcinoma cells by 70-90% without affecting tumorigenicity. Differential display comparing MDA-MB-435 and neo11/435 led to the discovery of a human breast carcinoma metastasis suppressor gene, BRMS1, which maps to chromosome 11q13.1-q13.2. Stable transfectants of MDA-MB-435 and MDA-MB-231 breast carcinoma cells with BRMS1 cDNA still form progressively growing, locally invasive tumors when injected in mammary fat pads of athymic mice but exhibit significantly lower metastatic potential (50-90% inhibition) to lungs and regional lymph nodes. To begin elucidating the mechanism(s) of action, we measured the ability of BRMS1 to perturb individual steps of the metastatic cascade modeled in vitro. Consistent differences were not observed for adhesion to extracellular matrix components (laminin, fibronectin, type IV collagen, type I collagen, Matrigel); growth rates in vitro or in vivo; expression of matrix metalloproteinases, heparanase, or invasion. Likewise. BRMS1 expression did not up regulate expression of other metastasis suppressors, such as NM23, Kai1, KiSS1 or E-cadherin. Motility of BRMS1 transfectants was modestly inhibited (30-60%) compared to parental and vector-only transfectants. Ability to grow in soft agar was also decreased in MDA-MB-435 cells by 80-89%, but the decrease for MDA-MB-231 was less (13-15% reduction). Also, transfection and re-expression of BRMS1 restored the ability of human breast carcinoma cells to form functional homotypic gap junctions. Collectively, these data suggest that BRMS1 suppresses metastasis of human breast carcinoma by complex, atypical mechanisms.

Suppression of human melanoma metastasis by the metastasis suppressor gene, BRMS1

We recently identified a novel metastasis suppressor gene, BRMS1, in breast cancer. Since the BRMS1 gene maps to chromosome 11q13.1-q13.2 and since chromosome 11q defects have been described in various stages of human melanoma progression, we hypothesized that BRMS1 may function as a tumor or metastasis suppressor in melanomas as well. Quantitative real-time RT-PCR revealed that BRMS1 mRNA expression was high in melanocytes, considerably reduced in early melanoma-derived cell lines, and barely detectable in advanced/metastatic cell lines. Stable transfectants of BRMS1 in the human melanoma cell lines MelJuSo and C8161.9 did not alter the tumorigenicity of either cell line, but significantly suppressed metastasis compared to vector-only transfectants. Orthotopic tumors continued to express BRMS1, but expression was lost in lung metastases. In vitro morphology, growth rate, and histology of BRMS1 transfectants were similar to controls. BRMS1 transfectants were less invasive in a collagen sandwich assay and had restored homotypic gap junctional intercellular communication (GJIC). Thus, BRMS1 functions as a metastasis suppressor in more than one tumor type (i.e., breast carcinoma and cutaneous melanoma) by modifying several metastasis-associated phenotypes.