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

Metastasis suppressor genes at the interface between the environment and tumor cell growth

The molecular mechanisms and genetic programs required for cancer metastasis are sometimes overlapping, but components are clearly distinct from those promoting growth of a primary tumor. Every sequential, rate-limiting step in the sequence of events leading to metastasis requires coordinated expression of multiple genes, necessary signaling events, and favorable environmental conditions or the ability to escape negative selection pressures. Metastasis suppressors are molecules that inhibit the process of metastasis without preventing growth of the primary tumor. The cellular processes regulated by metastasis suppressors are diverse and function at every step in the metastatic cascade. As we gain knowledge into the molecular mechanisms of metastasis suppressors and cofactors with which they interact, we learn more about the process, including appreciation that some are potential targets for therapy of metastasis, the most lethal aspect of cancer. Until now, metastasis suppressors have been described largely by their function. With greater appreciation of their biochemical mechanisms of action, the importance of context is increasingly recognized especially since tumor cells exist in myriad microenvironments. In this chapter, we assemble the evidence that selected molecules are indeed suppressors of metastasis, collate the data defining the biochemical mechanisms of action, and glean insights regarding how metastasis suppressors regulate tumor cell communication to-from microenvironments.

Sorting nexin 6 interacts with breast cancer metastasis suppressor-1 and promotes transcriptional repression

Sorting nexin 6 (SNX6), a predominantly cytoplasmic protein involved in intracellular trafficking of membrane receptors, was identified as a TGF-β family interactor. However, apart from being a component of the Retromer, little is known about SNX6 cellular functions. Pim-1-dependent SNX6 nuclear translocation has been reported suggesting a putative nuclear role for SNX6. Here, we describe a previously non-reported association of SNX6 with breast cancer metastasis suppressor 1 (BRMS1) protein detected by a yeast two-hybrid screening. The interaction can be reconstituted in vitro and further FRET analysis confirmed the novel interaction. Additionally, we identified their coiled-coil domains as the minimal binding motives required for interaction. Since BRMS1 has been shown to repress transcription, we sought the ability of SNX6 to interfere with this nuclear activity. Using a standard gene reporter assay, we observed that SNX6 increases BRMS1-dependent transcriptional repression. Moreover, over-expression of SNX6 was capable of diminishing trans-activation in a dose-dependent manner.

Protein Signatures in Human MDA-MB-231 Breast Cancer Cells Indicating a More Invasive Phenotype Following Knockdown of Human Endometase/Matrilysin-2 by siRNA

Human matrix metalloproteinase-26 (MMP-26/endometase/matrilysin-2) is a putative biomarker for carcinomas of breast, prostate, and other cancers of epithelial origin. MMP-26 expression was silenced using small interfering RNA (siRNA) in the human breast cancer cell line MDA-MB-231. Immunological and proteomics approaches, including two-dimensional gel electrophoresis and matrix assisted laser desorption/ionization time-of-flight mass spectrometry, were employed to identify differential protein expression in MMP-26 knockdown cells. A comparison of the protein expression profiles of control and MMP-26 knockdown cells revealed nine differentially regulated proteins. Five of the proteins (heat shock protein 90, glucose-regulated protein 78 (GRP78), annexin V, tropomyosin, and peroxiredoxin II) were up-regulated, while alpha-tubulin, cystatin SA-III, breast cancer metastasis suppressor 1 (BRMS1) and beta-actin were down-regulated. This decrease of BRMS1 expression is concomitant with an increase of invasion through matrix-coated membranes. These results suggest an important role for MMP-26 in the regulation of proteins involved in invasive and metastatic breast cancers.

Genetic factors in metastatic progression of cutaneous melanoma: the future role of circulating melanoma cells in prognosis and management

The greatest potential for improvement of outcome for patients with Cutaneous Malignant Melanoma lies in the prevention of systemic metastasis. Despite extensive investigation, current prognostic indicators either alone or in combination, although related to melanoma progression, are not sufficient to accurately predict the pattern of progression and outcome for any individual patient. Metastasis related death has been recorded in patients initially diagnosed with early stage tumour as well as in patients many years after initial tumour removal. The trouble finding a predictable pattern in the puzzle of melanoma progression may be linked to the fact that most of the material studied for prognosis is either, cutaneous primaries or metastatic deposits, rather than the melanoma cells in the circulatory system which are responsible for disease progression. In this review article we discuss the potential use of circulating tumour cell (CTC) detection and quantification for identifying patients at risk of metastatic deposits. We also discuss current therapies for the treatment of metastatic melanoma and analyse how CTCs may be used to evaluate the effectiveness of current therapies and to pinpoint patients who require further treatment.

Gene signatures of breast cancer progression and metastasis

Breast cancer is a heterogeneous disease. Patient outcome varies significantly, depending on prognostic features of patients and their tumors, including patient age, menopausal status, tumor size and histology, nodal status, and so on. Response to treatment also depends on a series of predictive factors, such as hormone receptor and HER2 status. Current treatment guidelines use these features to determine treatment. However, these guidelines are imperfect, and do not always predict response to treatment or survival. Evolving technologies are permitting increasingly large amounts of molecular data to be obtained from tumors, which may enable more personalized treatment decisions to be made. The challenge is to learn what information leads to improved prognostic accuracy and treatment outcome for individual patients.

Decoding melanoma metastasis

Metastasis accounts for the vast majority of morbidity and mortality associated with melanoma. Evidence suggests melanoma has a predilection for metastasis to particular organs. Experimental analyses have begun to shed light on the mechanisms regulating melanoma metastasis and organ specificity, but these analyses are complicated by observations of metastatic dormancy and dissemination of melanocytes that are not yet fully malignant. Additionally, tumor extrinsic factors in the microenvironment, both at the site of the primary tumor and the site of metastasis, play important roles in mediating the metastatic process. As metastasis research moves forward, paradigms explaining melanoma metastasis as a step-wise process must also reflect the temporal complexity and heterogeneity in progression of this disease. Genetic drivers of melanoma as well as extrinsic regulators of disease spread, particularly those that mediate metastasis to specific organs, must also be incorporated into newer models of melanoma metastasis.

Metastasis suppressors and the tumor microenvironment

The most lethal and debilitating attribute of cancer cells is their ability to metastasize. Throughout the process of metastasis, tumor cells interact with other tumor cells, host cells and a variety of molecules. Tumor cells are also faced with a number of insults, such as hemodynamic sheer pressure and immune selection. This brief review explores how metastasis suppressor proteins regulate interactions between tumor cells and the microenvironments in which tumor cells find themselves.

Homotypic gap junctional communication associated with metastasis suppression increases with PKA activity and is unaffected by PI3K inhibition

Loss of gap junctional intercellular communication (GJIC) between cancer cells is a common characteristic of malignant transformation. This communication is mediated by connexin proteins that make up the functional units of gap junctions. Connexins are highly regulated at the protein level and phosphorylation events play a key role in their trafficking and degradation. The metastasis suppressor breast cancer metastasis suppressor 1 (BRMS1) upregulates GJIC and decreases phosphoinositide-3-kinase (PI3K) signaling. On the basis of these observations, we set out to determine whether there was a link between PI3K and GJIC in tumorigenic and metastatic cell lines. Treatment of cells with the well-known PI3K inhibitor LY294002, and its structural analogue LY303511, which does not inhibit PI3K, increased homotypic GJIC; however, we found the effect to be independent of PI3K/AKT inhibition. We show in multiple cancer cell lines of varying metastatic capability that GJIC can be restored without enforced expression of a connexin gene. In addition, while levels of connexin 43 remained unchanged, its relocalization from the cytosol to the plasma membrane was observed. Both LY294002 and LY303511 increased the activity of protein kinase A (PKA). Moreover, PKA blockade by the small molecule inhibitor H89 decreased the LY294002/LY303511-mediated increase in GJIC. Collectively, our findings show a connection between PKA activity and GJIC mediated by PI3K-independent mechanisms of LY294002 and LY303511. Manipulation of these signaling pathways could prove useful for antimetastatic therapy.

Prognostic significance of BRMS1 expression in human melanoma and its role in tumor angiogenesis

Breast cancer metastasis suppressor 1 (BRMS1) has been reported to suppress metastasis without significantly affecting tumorigenicity in breast cancer and ovarian cancer. To investigate the role of BRMS1 in human melanoma progression and prognosis, we established tissue microarray and BRMS1 expression was evaluated by immunohistochemistry in 41 dysplastic nevi, 90 primary melanomas and 47 melanoma metastases. We found that BRMS1 expression was significantly decreased in metastatic melanoma compared with primary melanoma or dysplastic nevi (P=0.021 and 0.001, respectively, χ(2) test). In addition, reduced BRMS1 staining was significantly correlated with American Joint Committee on Cancer stages (P=0.011, χ(2) test), but not associated with tumor thickness, tumor ulceration and other clinicopathological parameters. Furthermore, BRMS1 expression was significantly correlated with disease-specific 5-year survival of melanoma patients (P=0.007, log-rank test). Multivariate Cox regression analysis revealed that BRMS1 staining was an independent prognostic factor for melanoma patients (relative risk=0.51; confidence interval=0.29-0.91; P=0.022). Moreover, we demonstrated that BRMS1 overexpression inhibited endothelial cell growth and tube formation ability by suppressing NF-κB activity and IL-6 expression in vitro. We also showed that knockdown of BRMS1 increased IL-6 expression and promoted endothelial cell growth and tube formation. In addition, our data revealed that the BRMS1-mediated IL-6 expression is dependent on NF-κB. Strikingly, our in vivo studies using nude mice confirmed that BRMS1 inhibited blood vessel formation and the recruitment of CD31-positive cells in matrigel plugs. Taken together, BRMS1 expression was decreased in metastatic melanomas, which resulted in deficient suppression of angiogenesis and contributed to melanoma progression. BRMS1 may serve an important prognostic marker and therapeutic target for melanoma patients.

BRMS1 transcriptional repression correlates with CpG island methylation and advanced pathological stage in non-small cell lung cancer

Breast cancer metastasis suppressor gene-1 (BRMS1) mRNA and protein expression are significantly decreased in non-small cell lung cancer (NSCLC) and this is a poor prognostic indicator. Given that the BRMS1 promoter region contains a promoter-associated CpG island (CGI) that encompasses the transcriptional start site, we hypothesized that decreased BRMS1 mRNA and protein levels in NSCLC was secondary to increased BRMS1 promoter methylation. Methylation-specific PCR (MSP) of the two known CGIs (-3477 to - 2214 and - 531 to + 608) in the BRMS1 genome was performed in NSCLC cells. This demonstrated a robust increase in methylation of the promoter-associated CGI (-531 to + 608) but not of the upstream CGI (-3477 to - 2214). To experimentally verify that methylation contributes to BRMS1 transcriptional repression, we cloned the BRMS1 promoter region, including the promoter-associated CGI, into a luciferase reporter gene and found that BRMS1 promoter activity was dramatically inhibited under methylated conditions. We then assessed the BRMS1 methylation profile with MSP and bisulphite-sequencing PCR in human NSCLC adenocarcinoma (n = 20) and squamous cell carcinoma (n = 20) relative to adjacent non-cancerous bronchial epithelium. There was a significant increase in BRMS1 promoter methylation in all NSCLC specimens relative to non-cancerous tissues, with the most dramatic difference in squamous cell cancer histology. Subsequent immunostaining demonstrated that nuclear BRMS1 expression is reduced in lung cancer specimens compared to normal bronchial epithelium. The association between BRMS1 promoter methylation and specific clinical and histopathological variables was examined using a general linear model. Pathological tumour stage was associated with increased BRMS1 methylation in squamous cell cancers. These observations demonstrate that methylation of the promoter-associated CGI in BRMS1 results in its transcriptional repression, and highlight the potential clinical relevance of this methylation event with respect to NSCLC tumour histology and pathological stage.

The epigenetics of breast cancer

Epigenetic changes can be defined as stable molecular alterations of a cellular phenotype such as the gene expression profile of a cell that are heritable during somatic cell divisions (and sometimes germ line transmissions) but do not involve changes of the DNA sequence itself. Epigenetic phenomena are mediated by several molecular mechanisms comprising histone modifications, polycomb/trithorax protein complexes, small non-coding or antisense RNAs and DNA methylation. These different modifications are closely interconnected. Epigenetic regulation is critical in normal growth and development and closely conditions the transcriptional potential of genes. Epigenetic mechanisms convey genomic adaption to an environment thereby ultimately contributing towards given phenotype. In this review we will describe the various aspects of epigenetics and in particular DNA methylation in breast carcinogenesis and their potential application for diagnosis, prognosis and treatment decision.

Breast cancer metastasis suppressor 1 coordinately regulates metastasis-associated microRNA expression

Breast cancer metastasis suppressor 1 (BRMS1) suppresses metastasis of multiple tumor types without blocking tumorigenesis. BRMS1 forms complexes with SIN3, histone deacetylases and selected transcription factors that modify metastasis-associated gene expression (e.g., EGFR, OPN, PI4P5K1A, PLAU). microRNA (miRNA) are a recently discovered class of regulatory, noncoding RNA, some of which are involved in neoplastic progression. Based on these data, we hypothesized that BRMS1 may also exert some of its antimetastatic effects by regulating miRNA expression. MicroRNA arrays were done comparing small RNAs that were purified from metastatic MDA-MB-231 and MDA-MB-435 and their nonmetastatic BRMS1-transfected counterparts. miRNA expression changed by BRMS1 were validated using SYBR Green RT-PCR. BRMS1 decreased metastasis-promoting (miR-10b, -373 and -520c) miRNA, with corresponding reduction of their downstream targets (e.g., RhoC which is downstream of miR-10b). Concurrently, BRMS1 increased expression of metastasis suppressing miRNA (miR-146a, -146b and -335). Collectively, these data show that BRMS1 coordinately regulates expression of multiple metastasis-associated miRNA and suggests that recruitment of BRMS1-containing SIN3:HDAC complexes to, as yet undefined, miRNA promoters might be involved in the regulation of cancer metastasis.

Linking metastasis suppression with metastamiR regulation

Cancer metastasis requires the coordinate expression of multiple genes during every step of the metastatic cascade. Molecules that regulate these genetic programs have the potential to impact metastasis at multiple levels. Breast cancer metastasis suppressor 1 (BRMS1) suppresses metastasis by inhibiting multiple steps in the cascade through regulation of many protein-encoding, metastasis-associated genes as well as metastasis-regulatory microRNA, termed metastamiR. In this Feature , we will highlight connections between BRMS1 biology and regulation of metastamiR.

A shift from nuclear to cytoplasmic breast cancer metastasis suppressor 1 expression is associated with highly proliferative estrogen receptor-negative breast cancers

BACKGROUND/AIMS

To determine breast cancer metastasis suppressor 1 (BRMS1) expression in breast cancers and the efficacy of BRMS1 as a prognostic indicator, BRMS1 expression was assessed in two sets of breast cancer tissues.

METHODS

Epithelial cells from 36 frozen samples of breast cancers and corresponding normal breast were collected by laser capture microdissection and assessed for BRMS1 by quantitative RT-PCR and immunohistochemistry. BRMS1 was also evaluated by immunohistochemistry in a tissue microarray of 209 breast cancers and correlated with indicators of prognosis [estrogen receptor (ER), progesterone receptor (PR), ErbB2, p53, p27(Kip1), Bcl2 and Ki-67].

RESULTS

BRMS1 mRNA and protein were higher in 94 and 81%, respectively, of breast cancers than in corresponding normal epithelium. BRMS1 localization was predominantly nuclear, but 60-70% of cancers also exhibited cytoplasmic immunostaining. Breast cancers with lower nuclear than cytoplasmic BRMS1 (nuclear score - cytoplasmic score < or =0; 11% of cancers) had lower ER, lower PR and higher Ki-67 expression. There was also a trend toward poorer overall survival in this group of cancers, but this was only of borderline significance (p = 0.073). In Cox proportional hazards models, loss of nuclear BRMS1 was not a significant predictor of overall survival.

CONCLUSIONS

Loss of nuclear BRMS1 was associated with ER-negative cancers and a high rate of proliferation, but was not an independent indicator of prognosis.

Expression of the Breast Cancer Metastasis Suppressor 1 (BRMS1) maintains in vitro chemosensitivity of breast cancer cells

The Breast Cancer Metastasis Suppressor 1 (BRMS1) belongs to an expanding category of proteins called metastasis suppressors that demonstrate in vivo metastasis suppression while still allowing growth of the orthotopic tumor. Since BRMS1 decreases either the expression or function of multiple mediators implicated in resistance to chemotherapy (NF-kappaB, AKT, EGFR), we asked whether breast carcinoma cells expressing BRMS1 could be sensitized upon exposure to commonly used therapeutic agents that inhibit some of these same cellular mediators as BRMS1. In this report, we demonstrate that chemosensitivity of breast cancer cells is preserved in the presence of BRMS1. Further, BRMS1 does not change expression of AKT isoforms or PTEN, implicated in chemoresistance to common drug agents. Overall, our data with two different metastatic breast cancer cell lines indicates that BRMS1 expression status may not interfere with the response to commonly used chemotherapeutic agents in the management of solid tumors such as breast cancer. Since tumor protein expression analysis increasingly guides therapy decisions, our data may be of clinical benefit in disease management including profiling for BRMS1 expression before start of therapy.

Spheroid-forming subpopulation of breast cancer cells demonstrates vasculogenic mimicry via hsa-miR-299-5p regulated de novo expression of osteopontin

The growth of cancer cells as multicellular spheroids has frequently been reported to mimic the in vivo tumour architecture and physiology and has been utilized to study antitumour drugs. In order to determine the distinctive characteristics of the spheroid-derived cells compared to the corresponding monolayer-derived cells, we enriched multicellular spheroid-forming subpopulations of cells from three human breast cancer cell lines (MCF7, MCF10AT and MCF10DCIS.com). These spheroid-derived cells were injected into female athymic nude mice to assess their tumorigenic potential and were profiled for their characteristic miRNA signature. We discovered that the spheroid-derived cells expressed increased levels of osteopontin (OPN), an oncogenic protein that has been clinically correlated with increased tumour burden and adverse prognosis in patients with breast cancer metastasis. Our studies further show that increased OPN levels are brought about in part, by decreased levels of hsa-mir-299–5p in the spheroid-forming population from all three cell lines. Moreover, the spheroid-forming cells can organize into vascular structures in response to nutritional limitation; these structures recapitulate a vascular phenotype by the expression of endothelial markers CD31, Angiopoeitin-1 and Endoglin. In this study, we have validated that hsa-mir-299–5p targets OPN; de novo expression of OPN in turn plays a critical role in enhancing proliferation, tumorigenicity and the ability to display vasculogenic mimicry of the spheroid-forming cells.

Purification and characterisation of the breast cancer metastasis suppressor, BRMS1

The breast cancer metastasis suppressor 1 (BRMS1) is a member of a family of proteins that actively suppress tumour metastasis. Understanding BRMS1 mediated metastasis suppression is critical to the development of new therapies designed to prevent and treat patients with late stage breast cancer. To aid research into the functional aspects that underpin BRMS1 mediated metastasis suppression we have expressed and purified recombinant BRMS1 and produced BRMS1 polyclonal antibodies. Using these antibodies to immunoprecipitate endogenous BRMS1 containing complexes from MCF7 breast cancer cell lines we have identified, by mass spectrometry, the small heat shock protein Hsp27 in complex with BRMS1. We also show that the expression of both BRMS1 and Hsp27 are inversely correlated with metastatic potential.

Breast cancer metastasis suppressor 1 (BRMS1) suppresses metastasis and correlates with improved patient survival in non-small cell lung cancer

Breast cancer metastasis suppressor 1 (BRMS1) is a metastasis suppressor gene in several solid tumors. The role of BRMS1 in non-small cell lung cancer (NSCLC) is not well established. To assess in vitro and in vivo metastatic behavior H1299 NSCLC cells stably expressing BRMS1 or a vector control were created. BRMS1 expression significantly decreases both migration and invasion of NSCLC cells in vitro. Importantly, in flank xenografts, BRMS1 suppresses the formation of pulmonary and hepatic metastases but does not significantly affect primary tumor growth. To evaluate whether BRMS1 is related to the progression of NSCLC, we examined BRMS1 expression in human NSCLC. Both BRMS1 mRNA and protein levels are diminished in NSCLC compared to adjacent non-cancerous lung. BRMS1 expression is also lower in squamous cell carcinoma compared to adenocarcinoma. Moreover, preservation of tumor BRMS1 expression is associated with improved patient survival. Thus, BRMS1 functions as a metastasis suppressor and may be a prognostic indicator for human NSCLC.

Multiple forms of BRMS1 are differentially expressed in the MCF10 isogenic breast cancer progression model

Clinical studies evaluating the mRNA expression level of the BRMS1 metastasis suppressor in the progression of breast cancer have not been consistent. The purpose of this study was to characterize endogenous BRMS1 mRNA and protein in a model of the progression of breast cancer. BRMS1 protein expression was evaluated in the genetically related MCF10 cell lines representing 'normal' breast epithelial cells (MCF10A), pre-malignant breast disease (MCF10AT), comedo ductal carcinoma in situ (MCF10DCIS.com), and metastatic carcinoma (MCF10CAa.1 and MCF10CAd.1alpha) with two antibodies that recognize distinct epitopes in the BRMS1 protein. Nuclear expression of the characteristic *35 kDa BRMS1 protein was detected in all cell lines. Because BRMS1 was expressed in the metastatic MCF10 variants, the BRMS1 exons were sequenced to scan for possible genetic mutations. BRMS1 was wild-type with the exception of a synonymous T/C transition in exon 7. However, alternatively spliced variants were detected by RT-PCR. Two variants, BRMS1.v2 and BRMS1.v4 were only detected in the MCF10A and AT cell lines, while BRMS1 and BRMS1.v3 were detected in all lines. These results demonstrate that expression of the characteristic *35 kDa BRMS1 protein is not sufficient to prevent metastasis. The differential expression of alternative splice variants suggests caution should be taken when evaluating BRMS1 mRNA in clinical samples.

Downregulation of osteopontin contributes to metastasis suppression by breast cancer metastasis suppressor 1

Breast cancer metastasis suppressor 1 (BRMS1) inhibits the ability of multiple human and murine cancer cell lines to metastasize to lymph nodes, bones and lungs. Comparison of mRNA expression in metastatic MDA-MB-435 human carcinoma cells (435) and metastasis-suppressed BRMS1 transfectants (435/BRMS1) showed a marked (>90%) reduction of osteopontin (OPN) mRNA and protein expression in BRMS1-overexpressing cells. OPN expression is associated with disease progression in patients, with higher levels of OPN produced by cancer cells associated with poorer patient survival. Furthermore, OPN has been suggested to promote survival of cancer cells in response to stress, although the mechanisms by which this may occur remain poorly understood. This study tested the hypothesis that re-expression of OPN in metastasis-suppressed 435/BRMS1 cells would reverse metastasis suppression and confer protection from stress-induced apoptosis. A stable pooled population of OPN overexpressing 435/BRMS1 cells was created (435/BRMS1/OPN). OPN re-expression did not affect in vitro cell growth rates; however, increased anchorage independent growth/survival and protection from hypoxia-induced apoptosis was observed (p < 0.05). In vivo, OPN re-expression in BRMS1 transfected cells did not affect in vivo primary tumor growth but did increase the incidence of spontaneous metastasis to lymph nodes and lungs in mice. These novel findings suggest that OPN downregulation by BRMS1 may be responsible, at least in part, for BRMS1-mediated metastasis suppression by sensitizing cancer cells to stress induced apoptosis. These studies clarify one mechanism by which BRMS1 can suppress metastasis.

Epigenetic silencing contributes to the loss of BRMS1 expression in breast cancer

Breast Cancer Metastasis Suppressor 1 (BRMS1) suppresses metastasis of human breast cancer, ovarian cancer and melanoma in athymic mice. Studies have also shown that BRMS1 is significantly downregulated in some breast tumors, especially in metastatic disease. However, the mechanisms which regulate BRMS1 expression are currently unknown. Upon examination of the BRMS1 promoter region by methylation specific PCR (MSP) analysis, we discovered a CpG island (-3477 to -2214), which was found to be hypermethylated across breast cancer cell lines. A panel of 20 patient samples analyzed showed that 45% of the primary tumors and 60% of the matched lymph node metastases, displayed hypermethylation of BRMS1 promoter. Furthermore, we found a direct correlation between the methylation status of the BRMS1 promoter in the DNA isolated from tissues, with the loss of BRMS1 expression assessed by immunohistochemistry. There are several studies investigating the mechanism by which BRMS1 suppresses metastasis; however thus far there is no study that reports the cause(s) of loss of BRMS1 expression in aggressive breast cancer. Here we report for the first time that BRMS1 is a novel target of epigenetic silencing; and aberrant methylation in the BRMS1 promoter may serve as a cause of loss of its expression.

Breast cancer metastasis suppressor 1 inhibits SDF-1alpha-induced migration of non-small cell lung cancer by decreasing CXCR4 expression

This report shows that over-expression of BRMS1 reduces SDF-induced chemotaxis and suppresses nuclear factor-kappaB (NF-kappaB) activity in NSCLC cell line. Inhibition of NF-kappaB activity impairs SDF-1alpha-dependent migration and NF-kappaB can directly bind to the chemokine (C-X-C motif) receptor 4 (CXCR4) promoter invivo. However, knockdown of BRMS1 promotes NSCLC cell migration and CXCR4 expression. Furthermore, BRMS1 and CXCR4 expression levels are inversely correlated in the NSCLC cases. The level of BRMS1 mRNA is found to be markedly lower in the distant metastasis group than in the non-distant metastasis group (P=0.003). However, CXCR4 mRNA was higher in the distant metastasis group than in the non-distant metastasis group (P=0.032). These results indicate that BRMS1 regulates metastatic potential at least in part through the down-regulation of CXCR4, to be indirectly regulated by BRMS1 through nuclear factor-kappaB activation.

Ezrin, a key component in tumor metastasis

Identification of the key regulatory molecules in metastasis is crucial for understanding tumor dissemination and for the development of novel interventions. The recent identification of ezrin as a necessary component in the metastasis of osteosarcoma and rhabdomyosarcoma is, therefore, an important advance. Ezrin has been implicated in many roles, for example, as a conduit for signals between metastasis-associated cell-surface molecules and signal transduction components. This suggests that ezrin and, potentially, other members of the ERM (ezrin-radixin-moesin) family have key roles in the coordination of signals and cellular complexes that are required for the successful metastasis of these and other malignancies.

Epigenetic contributions to cancer metastasis

The molecular basis of cancer encompasses both genetic and epigenetic alterations. These epigenetic changes primarily involve global DNA methylation changes in the form of widespread loss of methylation along with concurrent hypermethylation events in gene regulatory regions that can repress tissue-specific gene expression. Increasingly, the importance of these epigenetic changes to the metastatic process is being realized. Cells may acquire an epi-genotype that permits their dissemination from the primary tumour mass or the ability to survive and proliferate at a secondary tissue site. These epigenetic changes may be cancer-type specific, or in some cases may involve a common target gene providing a selective advantage to multiple metastatic cell types. In this review, I examine the growing volume of literature related to the epigenetic contributions to cancer metastasis. I discuss the functional importance of these epigenetic phenomena and how new epigenetic biomarkers may permit the identification of diagnostic signatures of metastasis and the development of new cancer therapies.

Alterations of BRMS1-ARID4A interaction modify gene expression but still suppress metastasis in human breast cancer cells

The BRMS1 metastasis suppressor interacts with the protein AT-rich interactive domain 4A (ARID4A, RBBP1) as part of SIN3.histone deacetylase chromatin remodeling complexes. These transcriptional co-repressors regulate diverse cell phenotypes depending upon complex composition. To define BRMS1 complexes and their roles in metastasis suppression, we generated BRMS1 mutants (BRMS1(mut)) and mapped ARID4A interactions. BRMS1(L174D) disrupted direct interaction with ARID4A in yeast two-hybrid genetic screens but retained an indirect association with ARID4A in MDA-MB-231 and -435 human breast cancer cell lines by co-immunoprecipitation. Deletion of the first coiled-coil domain (BRMS1(DeltaCC1)) did not disrupt direct interaction in yeast two-hybrid screens but did prevent association by co-immunoprecipitation. These results suggest altered complex composition with BRMS1(mut). Although basal transcription repression was impaired and the pro-metastatic protein osteopontin was differentially down-regulated by BRMS1(L174D) and BRMS1(DeltaCC1), both down-regulated the epidermal growth factor receptor and suppressed metastasis in MDA-MB-231 and -435 breast cancer xenograft models. We conclude that BRMS1(mut), which modifies the composition of a SIN3.histone deacetylase chromatin remodeling complex, leads to altered gene expression profiles. Because metastasis requires the coordinate expression of multiple genes, down-regulation of at least one important gene, such as the epidermal growth factor receptor, had the ability to suppress metastasis. Understanding which interactions are necessary for particular biochemical/cellular functions may prove important for future strategies targeting metastasis.

BRMS1 suppresses breast cancer experimental metastasis to multiple organs by inhibiting several steps of the metastatic process

Breast cancer metastasis suppressor 1 (BRMS1) inhibits formation of macroscopic lung metastases in breast, ovary, and melanoma xenograft models. Because it is unclear which step(s) of the metastatic cascade are affected by BRMS1, the major aim of this study was to determine when and how BRMS1 acts to suppress metastasis. We also examined whether BRMS1 expression globally blocks metastasis or selectively inhibits metastatic outgrowths in specific tissues. Metastatic human breast carcinoma cell lines MDA-MB-231 and -435 expressing enhanced green fluorescent protein (GFP; 231 GFP and 435 GFP) and cell lines transduced with the BRMS1 gene (231 GFP-BRMS1 and 435 GFP-BRMS1) were injected into the left cardiac ventricle to achieve the widest possible cellular distribution, by minimizing first-pass clearance in the lungs. Compared with parental cells, BRMS1-expressing clones formed significantly fewer metastases in all organs tested. When cells were injected directly into the vasculature, fewer of the BRMS1-expressing cells reached lungs or bone compared with parental cells, suggesting that restoration of BRMS1 expression increased cell death during transit. Susceptibility to anoikis was verified in vitro by demonstrating decreased survival on poly-hydroxyethyl methacrylate-coated dishes. Most of the BRMS1-expressing cells reaching secondary sites failed to proliferate, suggesting that BRMS1 also inhibits colonization. Coupled with previous reports showing modest effects of BRMS1 on adhesion and invasion, our results indicate that BRMS1 inhibits metastases in multiple organs by blocking several steps in the metastatic cascade.

Metastasis suppressors and the tumor microenvironment

The most dangerous attribute of cancer cells is their ability to metastasize. Throughout the process of metastasis, tumor cells interact with other tumor cells, host cells and extracellular molecules. This brief review explores how a new class of molecules – metastasis suppressors – regulate tumor cell–microenvironmental interactions. Data are presented which demonstrate that metastasis suppressors act at multiple steps of the metastatic cascade. A brief discussion for how metastasis suppressor regulation of cellular interactions might be exploited is presented.

Metastasis suppressors and their roles in breast carcinoma

Metastasis remains the most deadly aspect of cancer and still evades direct treatment. Clinically and experimentally, primary tumor development and metastasis are distinct processes-locally growing tumors can progress without the development of metastases. The discovery of endogenous molecules that exclusively inhibit metastasis suggests that metastasis is an amenable therapeutic target. By definition, metastasis suppressors inhibit metastasis without inhibiting tumorigenicity and are thus distinct from tumor suppressors. As the biology underlying functional mechanisms of metastasis suppressors becomes clearer, it is evident that metastasis suppressors could be harnessed as direct drug targets, prognostic markers, and to understand the fundamental biology of the metastatic process. Metastasis suppressors vary widely in their cellular localization: they are found in every cellular compartment and some are secreted. In general, metastasis suppressors appear to regulate selectively how cells respond to exogenous signals, by affecting signaling cascades which regulate downstream gene expression. This review briefly summarizes current functional and biochemical data on metastasis suppressors implicated in breast cancer. We also present a schematic integrating known mechanisms for these metastasis suppressors highlighting potential targets for therapeutic intervention.

Rac1 activity regulates proliferation of aggressive metastatic melanoma

Molecular mechanisms underlying the different capacity of two in vivo selected human melanoma cell variants to form experimental metastases were studied. The doubling times of the FEMX-I and FEMX-V cell sublines in vitro were 15 and 25 h, respectively. The invasive capacity of FEMX-I cells was 8-fold higher than FEMX-V cells, and the time to form approximately 10 mm s.c. tumors in nude mice was 21 versus 35 days. FEMX-I displayed a spindle-like formation in vitro, whereas FEMX-V cells had a rounded shape. Hence, we examined known determinants of cell shape and proliferation, the small GTPases. The four studied showed equal expression in both cell types, but Rac1 activity was significantly decreased in FEMX-V cells. Rac1 stimulates NFkappaB, and we found that endogenous NFkappaB activity of FEMX-V cells was 2% of that of FEMX-I cells. Inhibition of Rac1 resulted in blocked NFkappaB activity. Specific inhibition of either Rac1 or NFkappaB significantly reduced proliferation and invasion of FEMX-I cells, the more pronounced effects observed with Rac1 inhibition. These data indicate that Rac1 activity in FEMX cells regulates cell proliferation and invasion, in part via its effect on NFkappaB, signifying Rac1 as a key molecule in melanoma progression and metastasis.

A list of candidate cancer biomarkers for targeted proteomics

We have compiled from literature and other sources a list of 1261 proteins believed to be differentially expressed in human cancer. These proteins, only some of which have been detected in plasma to date, represent a population of candidate plasma biomarkers that could be useful in early cancer detection and monitoring given sufficiently sensitive specific assays. We have begun to prioritize these markers for future validation by frequency of literature citations, both total and as a function of time. The candidates include proteins involved in oncogenesis, angiogenesis, development, differentiation, proliferation, apoptosis, hematopoiesis, immune and hormonal responses, cell signaling, nucleotide function, hydrolysis, cellular homing, cell cycle and structure, the acute phase response and hormonal control. Many have been detected in studies of tissue or nuclear components; nevertheless we hypothesize that most if not all should be present in plasma at some level. Of the 1261 candidates only 9 have been approved as "tumor associated antigens" by the FDA. We propose that systematic collection and large-scale validation of candidate biomarkers would fill the gap currently existing between basic research and clinical use of advanced diagnostics.

Tumor dormancy and the role of metastasis suppressor genes in regulating ectopic growth

Metastasis, or tumor growth in an ectopic site, may occur several years after apparently successful treatment of the primary malignancy. Clinical dormancy is seen in a large number of cancer patients, but once growth in an ectopic site initiates, current adjuvant therapies are inadequate and the majority of patients with metastatic disease will die. Many genes may regulate ectopic growth in a secondary site, including a small subset, termed the metastasis suppressor genes. Investigation into this class of genes holds promise in terms of gaining a greater understanding of tumor dormancy and how the process of metastasis may be naturally inhibited. This review will focus on the role of metastasis suppressor genes in tumor dormancy. Insights into the metastatic process from studies of metastasis suppressor genes may lead to novel targets for antimetastatic therapy through drug-induced reactivation of one or more of these genes and/or their respective signaling pathways.

Breast cancer metastasis suppressor 1 (BRMS1) inhibits osteopontin transcription by abrogating NF-kappaB activation

Background

Osteopontin (OPN), a secreted phosphoglycoprotein, has been strongly associated with tumor progression and aggressive cancers. MDA-MB-435 cells secrete very high levels of OPN. However metastasis-suppressed MDA-MB-435 cells, which were transfected with breast cancer metastasis suppressor 1 (BRMS1), expressed significantly less OPN. BRMS1 is a member of mSin3-HDAC transcription co-repressor complex and has been shown to suppress the metastasis of breast cancer and melanoma cells in animal models. Hence we hypothesized that BRMS1 regulates OPN expression.

Results

The search for a BRMS1-regulated site on the OPN promoter, using luciferase reporter assays of the promoter deletions, identified a novel NF-κB site (OPN/NF-κB). Electrophoretic mobility shift assays and chromatin immunoprecipitations (ChIP) confirmed this site to be an NF-κB-binding site. We also show a role of HDAC3 in suppression of OPN via OPN/NF-κB.

Conclusion

Our results show that BRMS1 regulates OPN transcription by abrogating NF-κB activation. Thus, we identify OPN, a tumor-metastasis activator, as a crucial downstream target of BRMS1. Suppression of OPN may be one of the possible underlying mechanisms of BRMS1-dependent suppression of tumor metastasis.

High level of messenger RNA forBRMS1 in primary breast carcinomas is associated with poor prognosis

BRMS1 is regarded as a metastasis suppressor gene for its ability to reduce metastatic potential of human and murine breast cancer cells as well as human melanoma cells. However, BRMS1 association to human tumor progression is not clearly understood. In the present study we analyzed BRMS1 mRNA expression in tumor progression and its potential prognostic value for breast carcinoma. BRMS1 mRNA expression level was quantified by real-time PCR in 47 tumoral, in 14 peritumoral and in 15 metastatic microdissected cellular populations from 47 breast cancer patients with 10-year follow up. We found BRMS1 expression to be higher in carcinoma cells than in matching normal epithelial cell populations in 10 out of 14 cases (p = 0.0005), while lymph-nodal carcinoma cells showed lower BRMS1 expression in 9 out of 15 cases (p = 0.001). Using both in vivo (human mammary breast carcinomas) and in vitro systems (breast cancer cell lines) we were able to demonstrate that BRMS1 overexpression was not a bias effect induced by cell proliferation rate. BRMS1 expression levels did not correlate with standard breast cancer prognostic factors but BRMS1 higher expression was associated with patient shorter disease-free and overall survival. Our findings are apparently inconsistent with the concept of BRMS1 as a metastasis suppressor gene. One possible explanation is that epithelial cells increase their BRMS1 expression as a compensatory response to tumor formation or metastasis progression, which is elevated in proportion to tumor aggressiveness, whereas those cells of the primary tumor that cannot upregulate BRMS1 escape to form metastasis.

Suppression of human ovarian carcinoma metastasis by the metastasis-suppressor gene, BRMS1

Metastasis-suppressor genes, by definition, suppress metastasis without affecting tumorigenicity and, hence, present attractive targets as prognostic or therapeutic markers. BRMS1 (breast cancer metastasis suppressor) has recently been identified as a metastasis-suppressor gene for human breast cancer and melanoma. Expression of BRMS1 messenger RNA (mRNA) in multitissue including normal prostate, ovarian, testis, and colon has been detected by northern blot analysis. We hypothesize that the role of BRMS1 in tumor progression may not be limited to breast cancer and melanoma. We previously found that BRMS1 mRNA levels in primary ovarian epithelial carcinomas were significantly lower than that in normal ovarian and benign tumors (P < 0.05), and statistical analysis of BRMS1 mRNA levels revealed that BRMS1 mRNA levels were significantly higher in early tumor stages (I, II) compared with advanced tumor stages (III, IV) in which lymph node or distant metastases were present (P < 0.01). Our data showed that reduced BRMS1 mRNA seems to influence ovarian carcinoma metastatic ability. Therefore, we transfected BRMS1 plasmid into highly malignant ovarian carcinoma cell line, HO-8910PM, and examined cell biologic behaviors including proliferation, adhesion, invasion, and metastasis in vitro and in vivo. BRMS1 expression did not alter the proliferation of HO-8910PM cells in vitro and primary tumor formation in vivo. But, BRMS1 expression significantly suppressed the cell adhesion to extracellular matrix components and in vitro cell invasion in BRMS1-transfected HO-8910PM cells compared to parental HO-8910PM and vector-only transfectants (HO-8910PM-vect). Furthermore, motility of BRMS1 transfectants was inhibited. lung colony formation of intravenously injected BRMS1 transfectants in nude mice was significantly reduced. Also, BRMS1 transfectants form significantly less metastatic to organs of peritoneal cavity in orthotopically implanted ovarian tumor nude models. We further discovered that BRMS1 expression did downregulate expression of an actin-bundling protein associated with cell motility -fascin, which perhaps is the mechanism underlying BRMS1 suppression of metastasis. These data suggested that in addition to its already described role in breast cancer and melanoma, BRMS1 functions as a metastasis-suppressor gene in ovarian carcinoma by modifying several metastatic-associated phenotypes, offering a new target for therapeutic intervention.

Breast cancer metastasis suppressor 1 functions as a corepressor by enhancing histone deacetylase 1-mediated deacetylation of RelA/p65 and promoting apoptosis

The antiapoptotic transcription factor NF-kappaB is constitutively activated in many cancers and is important for cytokine-mediated progression and metastatic movement of tumors. Breast cancer metastasis suppressor 1 (BRMS1) is a metastasis suppressor gene whose mechanisms of action are poorly understood. In this report, we demonstrate that BRMS1 decreases the transactivation potential of RelA/p65 and ameliorates the expression of NF-kappaB-regulated antiapoptotic gene products. BRMS1 immunoprecipitates with the RelA/p65 subunit of NF-kappaB with protein-protein interactions occurring at the C terminus region of the rel homology domain but not at its known transactivation domains. Moreover, BRMS1 functions as a corepressor by promoting binding of HDAC1 to RelA/p65, where it deacetylates lysine K310 on RelA/p65, which suppresses RelA/p65 transcriptional activity. Selective small interfering RNA knockdown of BRMS1 confirms that chromatin-bound BRMS1 is required for deacetylation of RelA/p65, while enhancing chromatin occupancy of HDAC1 onto the NF-kappaB-regulated promoters cIAP2 and Bfl-1/A1. We observed in cells lacking BRMS1 a dramatic increase in cell viability after the loss of attachment from the extracellular matrix. Collectively, these results suggest that BRMS1 suppresses metastasis through its ability to function as a transcriptional corepressor of antiapoptotic genes regulated by NF-kappaB.

Breast cancer metastasis suppressor 1 (BRMS1) is stabilized by the Hsp90 chaperone

Breast cancer metastasis suppressor 1 (BRMS1) is a member of the mSin3-HDAC transcription co-repressor complex. However, the proteins associated with BRMS1 have not been fully identified. Yeast two-hybrid screen, immuno-affinity chromatography, and co-immunoprecipitation experiments were performed to identify BRMS1 interacting proteins (BIPs). In addition to known core mSin3 transcriptional complex components RBBP1 and mSDS3, BRMS1 interacted with other proteins including three chaperones: DNAJB6 (MRJ), Hsp90, and Hsp70. Hsp90 is a known target of HDAC6 and reversible acetylation is one of the mechanisms that is implicated in regulation of Hsp90 chaperone complex activity. BRMS1 interacted with class II HDACs, HDAC 4, 5, and 6. We further found that BRMS1 is stabilized by Hsp90, and its turnover is proteasome dependent. The stability of BRMS1 protein may be important in maintaining the functional role of BRMS1 in metastasis suppression.

Osteopontin knockdown suppresses tumorigenicity of human metastatic breast carcinoma, MDA-MB-435

Elevated expression of osteopontin (OPN), a secreted phosphoglycoprotein, is frequently associated with many transformed cell lines. Various studies suggest that OPN may contribute to tumor progression as well as metastasis in multiple tumor types. High levels of OPN have been reported in patients with metastatic cancers, including breast. We found that the expression of OPN corroborates with the aggressive phenotype of the breast cancer cells i.e. the expression of OPN is acquired as the breast cancer cells become more aggressive. To assess the role(s) of OPN in breast carcinoma, expression of endogenous OPN was knocked down in metastatic MDA-MB-435 human breast carcinoma cells using RNA interference. We targeted multiple regions of the OPN transcript for RNA interference, along with 'scrambled' and 'non-targeting siRNA pool' controls to distinguish between target-specific and potential off-target effects including interferon-response gene (PeIF2-alpha) induction. The OPN knockdown by shRNA suppressed tumor take in immunocompromised mice. The 'silenced' cells also showed significantly lower invasion and migration in modified Boyden chamber assays and reduced ability to grow in soft agar. Thus, in addition to the widely reported roles of OPN in late stages of tumor progression, these results provide functional evidence that OPN contributes to breast tumor growth as well.

Metastasis suppressor proteins: discovery, molecular mechanisms, and clinical application

Clinically and experimentally, primary tumor formation and metastasis are distinct processes — locally growing tumors can progress without the development of metastases. This observation prompted the hypothesis that the molecular processes regulating tumorigenicity and metastasis are distinguishable and could be targeted therapeutically. During the process of transformation and subsequent progression to a malignant phenotype, both genetic and epigenetic alterations alter a cell’s ability to perceive and respond to signals that regulate normal tissue homeostasis. A minority of tumorigenic cells accrue the full complement of alterations that enables them to disseminate from the primary tumor, survive insults from the immune system and biophysical forces, and respond to growth-promoting and/or inhibitory signals from the distant tissues and thrive there. Identification of genes and proteins that specifically inhibit the ability of cells to form metastases (e.g., metastasis suppressors) is providing new insights into the molecular mechanisms that regulate this complex process. This review will highlight: (a ) the functional identification of metastasis suppressors, (b ) the signaling cascades and cellular phenotypes which are controlled or modulated by metastasis suppressors, and (c ) op portunities for translation and clinical trials that are based on mechanistic studies regarding metastasis suppressors.

Suppression of murine mammary carcinoma metastasis by the murine ortholog of breast cancer metastasis suppressor 1 (Brms1)

The murine ortholog (Brms1) of human breast cancer metastasis suppressor 1 shares 95% identity to the human metastasis suppressor, BRMS1, in amino acid structure. We tested Brms1 for suppression of metastasis of mouse mammary carcinoma cell line 4T1 in syngenic BALB/c mice, using orthotopic (mammary fat pad) injection as well as intravenous injection. As observed for BRMS1, transfection with Brms1 did not inhibit 4T1 primary tumor formation, but significantly suppressed lung colonization. We also show that Brms1 protein interacts with histone deacetylases, indicating involvement of Brms1 in murine Sin3-HDAC complex, like its human counterpart. Thus, because of similarities with its human ortholog, the results suggest that Brms1 will be useful as a model for studying mechanism of action of BRMS1.

Breast Cancer Metastasis Suppressor 1 Inhibits Gene Expression by Targeting Nuclear Factor-κB Activity

Breast cancer metastasis suppressor 1 (BRMS1) functions as a metastasis suppressor gene in breast cancer and melanoma cell lines, but the mechanism of BRMS1 suppression remains unclear. We determined that BRMS1 expression was inversely correlated with that of urokinase-type plasminogen activator (uPA), a prometastatic gene that is regulated at least in part by nuclear factor-kappaB (NF-kappaB). To further investigate the role of NF-kappaB in BRMS1-regulated gene expression, we examined NF-kappaB binding activity and found an inverse correlation between BRMS1 expression and NF-kappaB binding activity in MDA-MB-231 breast cancer and C8161.9 melanoma cells stably expressing BRMS1. In contrast, BRMS1 expression had no effect on activation of the activator protein-1 transcription factor. Further, we showed that suppression of both constitutive and tumor necrosis factor-alpha-induced NF-kappaB activation by BRMS1 may be due to inhibition of IkappaBalpha phosphorylation and degradation. To examine the relationship between BRMS1 and uPA expression in primary breast tumors, we screened a breast cancer dot blot array of normalized cDNA from 50 breast tumors and corresponding normal breast tissues. There was a significant reduction in BRMS1 mRNA expression in breast tumors compared with matched normal breast tissues (paired t test, P < 0.0001) and a general inverse correlation with uPA gene expression (P < 0.01). These results suggest that at least one of the underlying mechanisms of BRMS1-dependent suppression of tumor metastasis includes inhibition of NF-kappaB activity and subsequent suppression of uPA expression in breast cancer and melanoma cells.

Pathobiology of brain metastases

Brain metastasis is a major cause of systemic cancer morbidity and mortality. Many factors participate in the development and maintenance of brain metastases. The survival of the metastasis depends upon crucial interactions between tumour cells and the brain microenvironment during its development at the new site. This review focuses on the pathobiological mechanisms involved in the establishment and regulation of brain metastases. Developments in molecular biology have vastly expanded our knowledge about the mechanisms of invasion, proliferation, metastatic cell signalling, and angiogenesis in brain metastases. Advances in this understanding of the pathobiology of brain metastasis may lead to novel targeted treatment paradigms and a better prognosis for patients with brain metastatic disease.

Reduced metastasis-suppressor gene mRNA-expression in breast cancer brain metastases

PURPOSE

Brain metastases are an increasingly common complication in breast cancer patients. The Metastasis Suppressor Genes (MSG) Nm23, KISS1, KAI1, BRMS1, and Mkk4 have been associated with the metastatic potential of breast cancer in vitro and in vivo.

METHODS

The mRNA expression of Nm23, KISS1, KAI1, BRMS1, and Mkk4 in fresh frozen tissue samples of brain metastases from ductal invasive breast cancer specimens was examined in relation to primary tumors. In a first step, mRNA expression screening was carried out using a semi-quantitative RT-PCR approach, in a second step quantitative real-time RT-PCR was performed on selected specimens. By immunohistochemical staining, gene products were visualized on the protein level.

RESULTS

Semi-quantitative RT-PCR revealed reduced mRNA expression of Nm23, KISS1, KAI1, BRMS, and Mkk4 in brain metastases. Results for KISS1, KAI1, BRMS, and Mkk4 were confirmed by real-time RT-PCR. In detail, mRNA expression reduction in breast cancer brain metastases was tenfold. Expression of MSG could be confirmed by immunohistochemical staining on protein level.

CONCLUSIONS

Our investigations revealed significantly reduced mRNA expression of metastases suppressor genes KISS1, KAI1, BRMS1, and Mkk4 in breast cancer brain metastasis. Particularly, in the case of KISS1 and Mkk4, an important role for future treatment of patients with breast cancer brain metastatic lesions can be assumed.

Identification of a novel BRMS1-homologue protein p40 as a component of the mSin3A/p33(ING1b)/HDAC1 deacetylase complex

Repression of gene transcription is mediated by histone deacetylases containing repressor-co-repressor complexes, which are recruited to promoters of target genes via interactions with sequence-specific transcription factors. The mammalian Sin3A co-repressor complex contains a core of at least seven proteins including the pRb-interacting protein RBP1 and a putative tumor suppressor p33(ING1b). By biochemical purification and mass spectrometry, we have identified a novel component p40 from this complex. p40 bears homology to both yeast Sds3, a component of yeast histone deacetylase complexes, and its mammalian homologue mSds3. The p40-associated complex purified from human cells shows a strong histone deacetylase activity. When tethered to a Gal-DNA binding domain, the Gal-p40 is able to significantly repress transcription of a Gal-luciferase promoter. Interestingly, database analysis reveals that p40 is also highly homologous to BRMS1, a breast carcinoma metastasis suppressor, and overexpression of p40 in human cells can significantly inhibit cell growth. Thus, our data indicate that p40 may be critically involved in transcription repression of cell growth-associated gene expression by recruiting the HDAC1 deacetylase complex.

Metastasis suppressor genes: signal transduction, cross-talk and the potential for modulating the behavior of metastatic cells

In the past decade, research from various disciplines has stimulated a re-evaluation of our ideas of how cancers metastasize. Two important findings have been fundamental to this re-evaluation: that cancer cells are subject to growth regulation at the secondary site and that a specific class of proteins suppresses the metastatic phenotype. These proteins are encoded by metastasis suppressor genes, which are operationally defined as genes that suppress in vivo metastasis without inhibiting primary tumor growth when transfected into metastatic cell lines and injected into experimental animals. Recent biochemical studies have shown that certain metastasis suppressor proteins participate in highly conserved signal transduction cascades that mediate cellular responses to growth factors, cytokines and cellular stresses. Further elucidation of the biochemical foundations of these pathways coupled with strong in vivo studies should give us insight into the mechanisms of cancer metastasis, and may hold important implications for the future of cancer staging and therapy, using both existing and novel modalities.

Identification of metastasis-associated proteins through protein analysis of metastatic MDA-MB-435 and metastasis-suppressed BRMS1 transfected-MDA-MB-435 cells

BRMS1 (breast cancer metastasis suppressor 1) was recently identified as a novel breast cancer metastasis suppressor gene. To further characterize BRMS1-mediated metastasis suppression, we applied two-dimensional proteomic and mass spectrometry (LC-tandem MS and MALDI-TOF) analysis to identify proteins differentially expressed between highly metastatic MDA-MB-435 cells and metastasis-suppressed BRMS1-transfected MDA-MB-435 cells. Quadruplicate independent 2D gels were run and analyzed under identical conditions. Following in-gel trypsin digestion of seven differentially expressed proteins, amino acid sequence and mass profiles of the peptides were generated. Proteins were identified from the NCBI non-redundant database using the search program TurboSequest. Differential expression was confirmed for five proteins, including annexin I and alpha B-crystallin, by Northern blot analysis and immunostaining. Furthermore, we showed that both proteins were expressed in vivo in lungs containing metastasized MDA-MB-435 cells but not expressed in normal lung tissue of athymic mice. Our results suggest that annexin I and alpha B-crystallin are important cellular proteins that are down regulated through BRMS1 mediated metastasis suppression.