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.

Inhibition of CXCR4 by CTCE-9908 inhibits breast cancer metastasis to lung and bone

Metastasis occurs, in part, due to tumor cell responses to chemokine secretion by ectopic organs or tissues. SDF-1 is constitutively expressed in tissues where metastases frequently develop while breast carcinoma cells express the receptor for SDF-1, CXCR4, which is correlated with increased bone metastasis and poor overall survival. We hypothesized that treatment with a CXCR4 antagonist, CTCE-9908, would decrease incidence of bone and lung metastasis. Treatment with CTCE-9908 (25 mg/kg) began the day prior to or the day of intravenous or intracardiac tumor cell inoculation of MDA-MB-231 human breast carcinoma cells expressing enhanced green fluorescent protein (GFP) into athymic mice. After 5 or 8 weeks (i.c. and i.v. injections, respectively), the presence of fluorescent foci at metastatic sites was assessed. Somewhat surprisingly, CTCE-9908 treatment did not decrease incidence of metastasis as hypothesized. However, CTCE-9908 did decrease metastatic burden (i.e., size of metastases) in all organs examined (lungs, bone, heart, liver, kidneys, pancreas and spleen). Based upon this and other studies, the use of CTCE-9908 is promising as an adjuvant therapy for metastatic disease.

Breast cancer metastasis suppressor 1 up-regulates miR-146, which suppresses breast cancer metastasis

Breast cancer metastasis suppressor 1 (BRMS1) is a predominantly nuclear protein that differentially regulates expression of multiple genes, leading to suppression of metastasis without blocking orthotopic tumor growth in multiple human and murine cancer cells of diverse origins. We hypothesized that miR-146 may be involved in the ability of BRMS1 to supress metastasis because miR-146 expression is altered by BRMS1 and because BRMS1 and miR-146 are both associated with decreased signaling through the nuclear factor-kappaB pathway. BRMS1 significantly up-regulates miR-146a by 6- to 60-fold in metastatic MDA-MB-231 and MDA-MB-435 cells, respectively, and miR-146b by 40-fold in MDA-MB-435 as measured by real-time quantitative reverse transcription-PCR. Transduction of miR-146a or miR-146b into MDA-MB-231 down-regulated expression of epidermal growth factor receptor, inhibited invasion and migration in vitro, and suppressed experimental lung metastasis by 69% and 84%, respectively (mean +/- SE: empty vector = 39 +/- 6, miR-146a = 12 +/- 1, miR-146b = 6 +/- 1). These results further support the recent notion that modulating the levels of miR-146a or miR-146b could have a therapeutic potential to suppress breast cancer metastasis.

BRMS1 contributes to the negative regulation of uPA gene expression through recruitment of HDAC1 to the NF-kappaB binding site of the uPA promoter

The BRMS1 metastasis suppressor was recently shown to negatively regulate NF-kappaB signaling and down regulate NF-kappaB-dependent uPA expression. Here we confirm that BRMS1 expression correlates with reduced NF-kappaB DNA binding activity in independently derived human melanoma C8161.9 cells stably expressing BRMS1. We show that knockdown of BRMS1 expression in these cells using small interfering RNA (siRNA) leads to the reactivation of NF-kappaB DNA binding activity and re-expression of uPA. Further, we confirm that BRMS1 expression does not alter IKKbeta kinase activity suggesting that BRMS1-dependent uPA regulation does not occur through inhibition of the classical upstream activators of NF-kappaB. BRMS1 has been implicated as a corepressor of HDAC1 and consistent with this, we show that BRMS1 promotes HDAC1 recruitment to the NF-kappaB binding site of the uPA promoter and is associated with reduced H3 acetylation. We also confirm that BRMS1 expression stimulates disassociation of p65 from the NF-kappaB binding site of the uPA promoter consistent with its reduced DNA binding activity. These data suggest that BRMS1 recruits HDAC1 to the NF-kappaB binding site of the uPA promoter, modulates histone acetylation of p65 on the uPA promoter, leading to reduced NF-kappaB binding activity on its consensus sequence, and reduced transactivation of uPA expression.

Over-expression of the BRMS1 family member SUDS3 does not suppress metastasis of human cancer cells

BRMS1 and SUDS3 are related members of SIN3-HDAC chromatin remodeling complexes. We hypothesized that they might have overlapping functions and that SUDS3 over-expression could compensate for BRMS1 deficiency. SUDS3 expression was ubiquitous in seven breast cell lines, regardless of metastatic potential. SUDS3 over-expression in BRMS1-non-expressing metastatic cells did not suppress metastasis, motility, osteopontin secretion, or EGF receptor expression, phenotypes associated with BRMS1-mediated metastasis suppression. This study demonstrates functional differences for BRMS1 family members and highlights how the composition of SIN3-HDAC (BRMS1/SUDS3) complexes uniquely affects protein expression and biological behaviors.

Expressing connexin 43 in breast cancer cells reduces their metastasis to lungs

Recently the concept that gap junctions play a role in cancer cell metastasis has emerged. However, the mechanism by which this might occur is unknown. To examine this issue a metastatic breast cancer cell line, MDA-MB-435, was stably transfected with human Cx43 cDNA. Four clones of 435 transfectants (435/Cx43(+) c1, c6, c8, c14) and two clones of plasmid control (435/hy) were isolated and examined in this study. We found that expressing Cx43 in MDA-MB-435 cells decreased their expression of Cx32 but did not affect gap junctional intercellular communication, migration or invasion through Matrigel((R)). However, forced expression of Cx43 decreased the growth of MDA-MB-435 cells, decreased expression of N-cadherin, which is frequently associated with an aggressive phenotype, and increased MDA-MB-435 sensitivity to apoptosis. More importantly, there were fewer lung metastases in mice injected with 435/Cx43(+) cells relative to mice injected with 435/hy. These results suggest that expressing Cx43 in breast cancer cells decreases their metastatic potential through a mechanism independent of gap junctional communication but, rather, related to N-cadherin expression and apoptosis.

Breast cancer metastasis suppressor-1 differentially modulates growth factor signaling

That metastatic tumor cells grow in selective non-native environments suggests an ability to differentially respond to local microenvironments. BRMS1, like other metastasis suppressors, halts ectopic growth (metastasis) without blocking orthotopic tumor formation. BRMS1-expressing tumor cells reach secondary sites but do not colonize distant tissues, compelling the hypothesis that BRMS1 selectively restricts the ability of tumor cells to respond to exogenous regulators in different tissues. Here we report that BRMS1 expression in metastatic human breast cancer cells leads to a selective reduction in epidermal growth factor receptor expression and downstream (AKT) signaling. Signaling through another receptor tyrosine kinase, hepatocyte growth factor receptor (c-Met), remains unaltered despite reduced levels of the signaling intermediate phosphatidylinositol (4,5)-bisphosphate. Interestingly, reduced downstream calcium signaling is observed following treatment with platelet-derived growth factor, consistent with decreased phosphatidylinositol (4,5)-bisphosphate. However, platelet-derived growth factor receptor expression is unaltered. Thus, BRMS1 differentially attenuates cellular responses to mitogenic signals, not only dependent upon the specific signal received, but at varying steps within the same signaling cascade. Specific modulation of signaling responses received from the microenvironment may ultimately dictate which environments are permissive/restrictive for tumor cell growth and provide insights into the biology underlying metastasis.

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.

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.

Microarray analysis reveals potential mechanisms of BRMS1-mediated metastasis suppression

We used Affymetrix microarrays to compare gene expression profiles of the metastatic parental breast cancer cell line MDA-MB-435 (435) and the non-metastatic daughter cell line created by the stable expression of the BReast cancer Metastasis Suppressor 1 (BRMS1) gene in 435 cells, MDA-MB-435-BRMS1 (435/BRMS1). Analysis of microarray data provided insight into some of the potential mechanisms by which BRMS1 inhibits tumor formation at secondary sites. Furthermore, due to the importance of the microenvironment, we also examined gene expression under different growth conditions (i.e., plus or minus serum). Expression of 565 genes was significantly (adjusted P-value <0.05) altered regardless of in vitro growth conditions. BRMS1 expression significantly increased multiple major histocompatability complex (MHC) genes and significantly decreased expression of several genes associated with protein localization and secretion. The pattern of gene expression associated with BRMS1 expression suggests that metastasis suppression may be mediated by enhanced immune recognition, altered transport, and/or secretion of metastasis-associated proteins.

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.

C16 laminin peptide increases angiotropic extravascular migration of human melanoma cells in a shell-less chick chorioallantoic membrane assay

BACKGROUND

As distinct from intravascular dissemination, extravascular migratory metastasis (EVMM) has been described as a potential additional mechanism of melanoma spread in which tumour cells migrate along the external surfaces of vessels. Recent experimental studies strongly suggest a correlation of angiotropism of melanoma cells with EVMM. Angiotropic melanoma cells are linked to the endothelium by an amorphous matrix confirmed to contain laminin.

OBJECTIVES

To investigate whether laminin plays a role in this extravascular mechanism of tumour spread.

METHODS

We tested the effect of the C16 laminin peptide on melanoma spread in a shell-less chick chorioallantoic membrane model.

RESULTS

After 3 days, green fluorescent protein-expressing melanoma cells were observed spreading along or in the immediate proximity of vessels. The C16 laminin peptide significantly lengthened the distance of extravascular, angiotropic migration of melanoma cells. Histopathology confirmed the angiotropism of melanoma cells without intravasation, compatible with that observed with human angiotropic melanoma.

CONCLUSIONS

The results of this study suggest that the C16 laminin gamma1 chain peptide has angiotropic, extravascular migration-promoting activity on human melanoma cells, and might be a molecular target for preventing melanoma metastasis.

Do we need to redefine a cancer metastasis and staging definitions?

Metastasis is the most lethal attribute of cancer cells and clinical decisions regarding treatment are based largely upon the likelihood of developing metastases. However, improvements in detection as well as recent experimental data have raised questions about the most appropriate definition of a metastasis, especially whether the mere presence of cells at secondary sites constitute a metastatic lesion. After reviewing the experimental basis of metastasis, a definition of metastasis is proffered along with a proposal to consider regarding modification of staging parameters.

Metastasis: recent discoveries and novel treatment strategies

Most cancer deaths are due to the development of metastases, hence the most important improvements in morbidity and mortality will result from prevention (or elimination) of such disseminated disease. Some would argue that treatments directed against metastasis are too late because cells have already escaped from the primary tumour. Such an assertion runs contrary to the significant but (for many common adult cancers) fairly modest improvements in survival following the use of adjuvant radiation and chemotherapy designed to eliminate disseminated cells after surgical removal of the primary tumour. Nonetheless, the debate raises important issues concerning the accurate early identification of clonogenic, metastatic cells, the discovery of novel, tractable targets for therapy, and the monitoring of minimal residual disease. We focus on recent findings regarding intrinsic and extrinsic molecular mechanisms controlling metastasis that determine how, when, and where cancers metastasise, and their implications for patient management in the 21st century.

Human breast fibroblasts inhibit growth of the MCF10AT xenograft model of proliferative breast disease

Stromal fibroblasts are important for normal breast homeostasis and regulation of epithelial growth; however, this regulatory function is altered during carcinogenesis. To study the role of fibroblasts in the development of breast cancer, fibroblasts derived from normal breast (NAFs) were incorporated into the MCF10AT xenograft model of progressive proliferative breast disease. The persistence of human NAFs in xenografts was established by intracellular labeling and tyramide-coupled fluorescent in situ hybridization. Overall, the number of MCF10AT epithelial structures was decreased, and the rate of epithelial cell apoptosis was increased in xenografts containing NAFs. However, these changes were primarily in low-grade epithelial structures, corresponding to normal or mildly hyperplastic ductal epithelium. The level and rate of apoptosis of high-grade epithelial structures, corresponding to in situ and invasive carcinoma, were not consistently altered by NAFs. In addition, there was variability in the growth-inhibitory capacity of NAFs derived from different individuals. NAFs induced changes in the morphology of high-grade MCF10AT structures and in xenograft stroma, including the composition of extracellular matrix, and increased angiogenesis and lymphocytic infiltration. These findings imply that NAFs can inhibit the growth of normal and hyperplastic epi-thelium but are less able to regulate the more transformed epithelial cells that arise during carcino-genesis.

Requirement of KISS1 secretion for multiple organ metastasis suppression and maintenance of tumor dormancy

BACKGROUND

The KISS1 protein suppresses metastasis of several tumor models without blocking orthotopic tumor growth, but the mechanism remains elusive. For its role in human sexual maturation, KISS1 protein is secreted and processed to kisspeptins, which bind to the G protein-coupled receptor GPR54. We tested the hypothesis that KISS1 secretion is required for metastasis suppression via GPR54.

METHODS

KISS1 containing an internal FLAG epitope with (KFM) or without (KFMdeltaSS) a signal sequence was transfected into C8161.9 human melanoma cells, which do not express endogenous KISS1. Whole-cell lysates and conditioned medium from C8161.9(KFM) and C8161.9(KFMdeltaSS) cells were collected and analyzed for kisspeptins by immunoprecipitation and enzyme-linked immunosorbent assay. GPR54 levels were measured using real-time reverse transcription-polymerase chain reaction. The ability of conditioned medium from C8161.9(KFM) and C8161.9(KFMdeltaSS) cells to stimulate calcium mobilization in GPR54-expressing Chinese hamster ovary cells (CHO-G) and in C8161.9 cells was evaluated. Metastasis was monitored in athymic mice (groups of 10 per experiment) that were injected with C8161.9(KFM) or C8161.9(KFMdeltaSS) cells labeled with enhanced green fluorescent protein. Survival of mice injected with C8161.9 or C8161.9(KFM) cells was analyzed by Kaplan-Meier methods.

RESULTS

Full-length KFM and KFMdeltaSS were detected in whole-cell lysates of C8161.9(KFM) and C8161.9(KFMdeltaSS) cells, respectively, but kisspeptins were detected only in conditioned medium of C8161.9(KFM) cells. In vivo, C8161.9(KFM), but not C8161.9(KFMdeltaSS), cells were suppressed for metastasis to lung, eye, kidney, and bone, with corresponding differences in mouse survival (median > 120 versus 42 days). C8161.9(KFM) cells seeded mouse lungs but did not form macroscopic metastases. Conditioned medium from C8161.9(KFM), but not C8161.9(KFMdeltaSS), cells stimulated calcium mobilization in CHO-G cells. GPR54 expression was low in C8161.9 cells, which were not stimulated by conditioned medium from C8161.9(KFM) cells.

CONCLUSIONS

KISS1 secretion was required for multiple organ metastasis suppression and for maintenance of disseminated cells in a dormant state. The absence of GPR54 expression in C8161.9 cells (whose metastatic spread was suppressed by KFM) suggests that metastasis suppression is not mediated through this receptor. The results imply the existence of another KISS1 receptor and/or paracrine signaling. The findings raise the possibility that soluble KISS1, kisspeptins, or mimetics could be used to maintain tumor dormancy, rendering treatment of already disseminated tumor cells (i.e., micrometastases) a legitimate target.

Loss of breast cancer metastasis suppressor 1 protein expression predicts reduced disease-free survival in subsets of breast cancer patients

PURPOSE

This study aims to determine the effect of loss of breast cancer metastasis suppressor 1 (BRMS1) protein expression on disease-free survival in breast cancer patients stratified by estrogen receptor (ER), progesterone receptor (PR), or HER2 status, and to determine whether loss of BRMS1 protein expression correlated with genomic copy number changes.

EXPERIMENTAL DESIGN

A tissue microarray immunohistochemical analysis was done on tumors of 238 newly diagnosed breast cancer patients who underwent surgery at the Cleveland Clinic between January 1, 1995 and December 31, 1996, and a comparison was made with 5-year clinical follow-up data. Genomic copy number changes were determined by array-based comparative genomic hybridization in 47 breast cancer cases from this population and compared with BRMS1 staining.

RESULTS

BRMS1 protein expression was lost in nearly 25% of cases. Patients with tumors that were PR negative (P=0.006) or HER2 positive (P=0.039) and <50 years old at diagnosis (P=0.02) were more likely to be BRMS1 negative. No overall correlation between BRMS1 staining and disease-free survival was observed. A significant correlation, however, was seen between loss of BRMS1 protein expression and reduced disease-free survival when stratified by either loss of ER (P=0.008) or PR (P=0.029) or HER2 overexpression (P=0.026). Overall, there was poor correlation between BRMS1 protein staining and copy number status.

CONCLUSIONS

These data suggest a mechanistic relationship between BRMS1 expression, hormone receptor status, and HER2 growth factor. BRMS1 staining could potentially be used in patient stratification in conjunction with other prognostic markers. Further, mechanisms other than genomic deletion account for loss of BRMS1 gene expression in breast tumors.