Proteolytic activity of human lymphoid tumor cells. Correlation with tumor progression

Matrix metalloproteinase (MMP) expression and production are associated with advanced-stage tumor and contribute to tumor progression, invasion and metastases. The current study was designed to determine the expression and production of MMP-2 (gelatinase A) and MMP-9 (gelatinase B) by human lymphoid tumor cells. Changes in expression and production were also investigated during tumor progression of multiple myeloma and mycosis fungoides. In situ hybridization analysis revealed that lymphoblastic leukemia B cells (SB cell line), multiple myeloma (MM) cells (U266 cell line) and lymphoblastic leukemia T cells (CEM and Jurkat cell lines) express constitutively the mRNA for MMP-2 and/or MMP-9. We demonstrated by gelatin-zymography of cell culture medium that both enzymes were secreted in their cleaved (activated) form. In situ hybridization of bone marrow plasma cells and gelatin-zymography of the medium showed that patients with active MM (diagnosis, relapse, leukemic progression) express higher levels of MMP-2 mRNA and protein than patients with non-active MM (complete/objective response, plateau) and with monoclonal gammopathies of undetermined significance (MGUS). MMP-9 expression and secretion was similar in all patient groups. In patients with mycosis fungoides (MF), the expression of MMP-2 and MMP-9 mRNAs was significantly upregulated with advancing stage, in terms of lesions both positive for one of two mRNAs and with the greatest intensity of expression. Besides MF cells, the MMP-2 and/or MMP-9 mRNAs were expressed by some stromal cell populations (microvascular endothelial cells, fibroblasts, macrophages), suggesting that these cells cooperate in the process of tumor invasion. Our studies identify MMPs as an important class of proteinases involved in the extracellular matrix (ECM) degradation by human lymphoid tumors, and suggest that MMPs inhibitors may lead to important new treatment for their control.     

Comparative studies on the secretion and activation of MMPs in two reconstructed human skin models using HaCaT- and HaCaT-ras-transfected cell lines

Matrix metalloproteinases play an important role in tissue regeneration, wound healing and tumor invasion. Our previous studies have shown a higher motility of HaCaT-ras-transfected cells compared with HaCaT or normal human keratinocytes (NHK) in correlation with a higher secretion of MMP-2 (72 kDa) or MMP-9 (92 kDa), according to the medium used for cell cultures. Presently, the expression and activity of MMPs were investigated in two reconstructed skin models, using a dead de-epidermized dermis (DED) or a dermal substitute including living fibroblasts. In all experiments, MMP-9 was essentially secreted by NHK and to a greater extent by HaCaT cells. Its active form (86 kDa) was only detected in both reconstructed skin models according to keratinocyte differentiation. MMP-2 was mainly secreted by living fibroblasts included in the dermal substitute skin model. In this case, its activation was up-regulated when HaCaT cell lines were seeded onto the dermal substitute according to their culture at air/liquid interface as shown for MMP-9. The collagenase MMP-1 and stromelysin-1 (MMP-3), susceptible to activate pro-MMP-2 and -9, respectively, were detected in their inactive form by ELISA. MMP-1 was expressed in both models but MMP-3 required the presence of living fibroblasts. Their activities were not detected using specific fluorogenic substrates. In the skin equivalent model using HaCaT, the extensive secretion and activation of MMP-2 and MMP-9 could explain the defect observed in basal membrane reconstruction, suggesting a direct interaction of HaCaT with fibroblasts.     

Ovarian cancer cell invasion is inhibited by paclitaxel

Overproduction of matrix metalloproteinases (MMPs) and alterations in adhesive and migratory behavior are common characteristics of metastatic cancer cells. Ovarian cancer is a highly invasive type of malignancy. The effect of the antineoplastic drug paclitaxel on human ovarian cancer cell (Ovcar-3) invasion was studied using an in vitro invasion assay with reconstituted basement membrane. The effect of treatment with paclitaxel was also determined separately on certain invasion-associated events, such as the secretion of 72 kDa type IV collagenase (gelatinase A/MMP-2), the expression of the tissue inhibitor of metalloproteinase-2 (TIMP-2), cell attachment and migration. Ovcar-3 cell attachment, migration and in vitro invasion were significantly decreased after paclitaxel treatment (P=0.02, P<0.01 and P=0.001, respectively) whereas no alteration in the secretion of latent MMP-2 was noted. However, the intracellular localization of the immunoreactive protein for MMP-2 was altered in response to paclitaxel treatment. Interestingly, paclitaxel increased the appearance of TIMP-2 protein in culture medium (P=0.002) but did not change the expression of mRNA for TIMP-2 in Ovcar-3 cells. These data show that paclitaxel is an effective suppressor of Ovcar-3 cell invasion. It inhibits attachment and migratory activities of the cells but also causes a release of TIMP-2 protein into the tissue culture medium.     

RNA干扰抑制MTA1基因对人乳腺癌细胞ERα表达及浸润能力的影响

目的 通过观察pGenesil-1肿瘤转移相关基因1(MTA1)对人乳腺癌细胞株MDA-MB-231和MCF-7细胞MTA1基因的沉默效应,了解其对ERα表达及浸润能力的影响.方法 设计合成并构建重组质粒pGenesil-1MTA1,将该质粒分别转染MDA-MB-231和MCF-7细胞,荧光显微镜评估转染效率,RT-PCR检测MTA1和基质金属蛋白酶(MMP)-9 mRNA表达,免疫细胞化学检测ERα和MMP-9表达,Western blot检测ERα蛋白表达,用Boyden小室体外侵袭实验检测转染前后两株细胞侵袭力的变化.结果 成功构建重组质粒pGenesil-1MTA1,并成功转染入MDA-MB-231和MCF-7细胞(平均转染效率分别为82.5%和78.2%).两株细胞MTA1 mRNA表达均受到不同程度的抑制(分别为80.2%和58.7%).经干扰MTA1基因后MDA-MB-231细胞ERα蛋白表达得到逆转,呈阳性表达;MMP-9 mRNA表达下降;细胞体外侵袭力减弱(侵袭指数为27.2%±2.1%),与干扰前(76.3%±2.4%)相比差异有统计学意义(P＜0.05).而MCF-7细胞转染重组质粒并干扰MTA1基因后,ERα蛋白、MMP-9 mRNA表达和体外侵袭能力变化均无统计学意义(P＞0.05).结论 重组质粒pGenesil-1MTA1能有效抑制人乳腺癌细胞株MDA-MB-231和MCF-7细胞MTA1基因表达,ERa在MDA-MB-231细胞得到逆转,表达阳性,其高侵袭能力减弱,使干扰肿瘤转移靶基因成为可能.     

Regulation of MMP-9 (92 kDa type IV collagenase/gelatinase B) expression in stromal cells of human giant cell tumor of bone

Matrix metalloproteinases (MMPs) play an important regulatory role in tissue morphogenesis, cell differentiation, tumor invasion and metastasis. Several authors have reported a direct correlation between the production of 72 kDa (MMP-2) and 92 kDa (MMP-9) type IV collagenases/gelatinases and the metastatic potential of cancer cells. Recently, we have identified the expression of both MMP-2 and MMP-9 in primary cultures of human giant cell tumor (GCT) of bone in vitro, and in tissue extracts in vivo. Interestingly, MMP-9 is not secreted by late-passaged GCT cells. It is possible that the production of MMP-9 is regulated by certain factor(s) secreted by the multinucleated giant cells in the primary culture. In order to test this hypothesis, the effect of primary-culture-conditioned medium on the expression of MMP-9 by late-passaged mononuclear stromal cells was examined. Adding conditioned medium from the primary GCT culture to the late-passaged stromal cells induced MMP-9, as evidenced by the presence of lytic bands at Mr 92000 and 72000 on a gelatin zymogram. These enzyme activities were inhibited by EDTA, a well-known inhibitor of the MMPs. We confirmed these results by Western blotting using specific antibodies and RT-PCR for MMP-2 and MMP-9. Immunofluorescence studies with specific antibodies to MMP-9 further confirmed its expression by the passaged stromal cells cultured in the primary-culture-conditioned medium. The data indicate that MMP-2 and MMP-9 are produced by the mononuclear stromal cells when cultured in GCT primary-culture-conditioned medium. This suggests that multinucleated giant cells in primary cultures secrete a factor(s) that stimulates stromal cells to produce MMP-9, which, in turn, may contribute to the aggressive behavior of GCT.     

MMP-9 secretion and MMP-2 activation distinguish invasive and metastatic sublines of a mouse mammary carcinoma system showing epithelial-mesenchymal transition traits

We have investigated the gelatinase profiles and invasiveness of clonal tumour sublines derived from a spontaneously arising mammary tumour in a Balb/cfC3H mouse. The 67NR, 66cl4 and 4T1.2 sublines have low, intermediate and high metastatic potential respectively. In Boyden chamber studies, Matrigel invasion was seen to be progressively higher in the more metastatic lines 4T1.2>66cl4>67NR, consistent with MMP-2 activation potential, MMP-9 secretion, and migration over either type I or IV collagen, which were low in both 67NR and 66cl4 cells compared to 4T1.2 cells. These attributes are consistent with those seen in human breast cancer cell lines which appear to have undergone an epithelial-mesenchymal transition (EMT) as indicated by vimentin expression. We were, however, surprised to find vimentin expression, MT1-MMP expression and stellate Matrigel outgrowth in the non-invasive, non-metastatic 67NR cells, indicating that they had undergone an EMT despite not being invasive. We conclude that the EMT is manifested to differing degrees in these three clonal cell lines, and that the 67NR cells have either undergone a partial EMT or have since lost certain important attributes of the EMT-derived phenotype. This model should prove useful in further characterizing the regulation of MT1-MMP mediated MMP-2 activation and delineating the EMT in breast cancer progression. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metastatic and non-metastatic colorectal cancer (CRC) cells induce host metalloproteinase production in vivo

Numerous studies have demonstrated the persistent localization of matrix metalloproteinase (MMP) expression to the interface between invading human colorectal cancer (CRC) cells and surrounding stroma supporting a role for MMPs in CRC invasion and metastasis. The present study sought to determine whether CRC cells of varying metastatic potential would have differential effects on host MMP release. Subcutaneous CRC tumors were generated in BALB/c nude mice using three CRC cell lines: SW480, SW620, and the highly metastatic SW620S5 clone. Representative samples from the subcutaneous CRC were then orthotopically implanted on the cecum of recipient nude mice. Subcutaneous and cecal tumors were analyzed for MMP expression via zymography, western blot, and RT-PCR. In vitro, none of the three cell lines expressed MMP-2 nor MMP-9. In contradistinction, the subcutaneous tumors expressed limited amounts of MMP-2 and MMP-9 while the cecal tumors expressed significant amounts of MMP-2 and MMP-9 as well as other smaller members of the MMP family. MMP-9 mRNA and protein was confirmed as host in origin by RT-PCR with mouse specific primers and a mouse MMP-9 molecular weight of 105 kDa as determined by zymography and western blot analysis. In situ hybridization also localized the mRNA for MMP-9 to the host stromal cells. In conclusion, CRC cells appear incapable of producing MMP-2 and MMP-9 in vitro but are capable of up-regulating host MMP production in vivo. Enhanced host MMP-9 production in metastatic CRC cell-derived subcutaneous and cecal tumors suggests that metastatic colon cells may acquire the expression of important MMP regulating factor(s) in vivo.     

Tumour-stroma interactions between metastatic prostate cancer cells and fibroblasts

Previous work has shown the importance of tumour-stroma interactions for prostate cancer development at the primary site. The aim of the present study was to find out whether evidence can be found for a tumour-stroma cross- talk also between metastatic prostate cancer cell lines and non-prostatic stromal fibroblasts which are encountered by metastatic cells at most sites. We addressed this issue in cell culture systems using 3 metastatic human prostate cancer cell lines (LnCaP, PC-3 and DU-145) on the one hand, and a human fibroblast line (HFF, human foreskin fibroblasts) on the other. We incubated fibroblasts with tumour cell- and tumour cells with fibroblast-conditioned media and evaluated several parameters important for the establishment of metastases such as cell proliferation, migration and expression of matrix degrading proteases. We also determined in the conditioned media the concentrations of several growth factors and cytokines which might be responsible for the observed effects. We found that media conditioned by all 3 metastatic prostate cancer cell lines stimulated fibroblast proliferation which corresponds to fibrous stroma induction in vivo. DU-145 cell conditioned media induced in fibroblasts expression of mmp-1 mRNA known to be important for tumour invasion. ELISA assays revealed that tumour cells secrete bFGF, PDGF and TNFalpha known to stimulate fibroblast proliferation and/or MMP-1 expression. Cultivation of DU-145 carcinoma cells in fibroblast conditioned medium resulted in an enhanced proliferation and anchorage-independent growth of this cell line in soft agar. Fibroblast conditioned medium also increased migration of PC-3 cells in the wound assay and slightly augmented mmp-1 expression. KGF (able to stimulate proliferation of normal and neoplastic prostate epithelial cells) was secreted by fibroblasts at higher concentrations than by all 3 tumour cell lines. In addition, fibroblasts secreted TNFalpha, bFGF, PDGF, HGF and also VEGF, the most important factor for tumour vascularization. Our results provide evidence that tumour-stroma interactions do not only exist at the primary site but also between metastatic prostate cancer cell lines and their fibroblastic microenvironment. These interactions, which are mediated through secreted factors, affect several steps of the metastatic cascade including proliferation, anchorage-independent growth, migration and the secretion of matrix-degrading proteases.     

Transforming growth factor beta1 acts as an inducer of matrix metalloproteinase expression and activity in human bone-metastasizing cancer cells.

Bone metastases are a common complication in prostate and breast cancer patients. It leads to extensive morbidity and eventually mortality. Matrix metalloproteinases (MMPs) are known to be involved in the metastatic process. MMP activity can be down-regulated by transforming growth factor beta1 (TGF-beta1), a growth-modulating factor, found in high concentrations in the bone. TGF-beta1 acts through the TGF-beta1 inhibitory element (TIE) element, a cis-acting element found in the promoter region of most MMP genes, with the exception of MMP-2. We used three human cell lines relevant for bone metastases, namely prostate adenocarcinoma PC-3, breast adenocarcinoma MDA-MB-231, and adenocarcinoma cells of unknown origin, Hs696, and one human osteosarcoma cell line, SAOS-2, and showed that in these cell lines TGF-beta1 partially lost its repressing action on MMP expression. TGF-beta1 was able to induce MMP-9 activity and protein expression in all three bone-metastatic tumour cell types, whereas MMP-9 protein levels were repressed in SAOS-2 cells. In PC-3 cells, TGF-beta1 repressed MMP-1 expression, whereas in MDA-MB-231 and SAOS-2 cells, an increase in the expression of MMP-1 protein was detected. Additionally, an increase in MMP-3 expression was observed in Hs696 cells. Expression and activity of the tissue inhibitors of matrix metalloproteinases, TIMP-1 and TIMP-2, were found increased in both PC-3 and MDA-MB-231 cells. With respect to cell proliferation, TGF-beta1 was able to induce a dose-dependent growth inhibition of up to 50% in primary human mammary epithelial cells. However, in none of the tumour cell lines was TGF-beta1 able to suppress growth substantially. Data presented in this paper support the hypothesis that TGF-beta1 can potentially disrupt the balance existing between osteoclast- and osteoblast-derived MMP activity by inducing altered expression of matrix metalloproteinases and their tissue inhibitors derived from bone-metastasizing cancer cells. This could eventually lead to skeletal destruction in patients with advanced metastatic disease.     

NGAL knockdown by siRNA in human cholangiocarcinoma cells suppressed invasion by reducing NGAL/MMP-9 complex formation

We studied the role of Neutrophil Gelatinase-associated Lipocalin (NGAL, lipocalin 2) in regulating the invasiveness of a cholangiocarcinoma cell line, RMCCA-1. RMCCA-1 cells expressed multiple forms of 25, 40, 75 and 115/135 kDa NGAL which were detected in the conditioned medium, whereas only the 25 kDa form was detected in the cell lysates. NGAL expression was induced by serum deprivation. NGAL downregulation by siRNA suppressed NGAL mRNA and protein expression by about 70–80%, concommittant with a significant reduction of in vitro invasiveness, migration and pro-MMP-9 activity, but not cell proliferation. Suppression of pro-MMP-9 activity paralleled a reduction of NGAL/MMP-9 complex in the conditioned medium, although MMP-9 mRNA expression was unaffected. Our data suggest that NGAL promotes the invasiveness of the cholangiocarcinoma cells by forming complex with MMP-9, stabilizing its activity and rendering the cancer cells to be more invasive.     

Keratinocyte growth factor-induced motility of breast cancer cells

Endogenous growth factors and cytokines are known to have a major influence on the progression, motility and invasiveness of tumor cells. We have reported previously that conditioned media from mouse fibroblasts increases the motility of breast cancer cells. Further, we determined that keratinocyte growth factor (KGF) was an active factor from mouse fibroblasts responsible for most of the motility response in breast cancer cells. The present study examined the effect of human KGF on the motility of estrogen receptor (ER)-positive and ER-negative human breast cancer cell lines in culture using time-lapse videomicroscopy to quantify cell motility. In the present study we observed that recombinant human KGF enhanced several parameters of cellular motility in ER-positive cells but not in ER-negative cell lines. Further, we observed that the level of KGF receptor (KGFR) expression in ER-positive cells was much greater than in the ER-negative cell lines. The motility response to KGF was found to be both dose-and time-dependent. Of the three ER-positive breast cancer cell lines tested, MCF-7 cells were the most responsive to KGF stimulation. Finally, MCF-7 cells grown in estrogen-depleted media did not respond to KGF. These results suggest that KGF from stromal tissue surrounding a primary tumor mass can enhance tumor cell motility and may be an early signal in the progression of breast cancer cells to a more motile and metastatic phenotype. Thus, KGF, KGFR and/or the KGF signaling pathway may be important therapeutic targets for the treatment or prevention of breast cancer metastasis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Implication of extracellular matrix metalloproteinases in the course of chronic inflammatory airway diseases

Matrix metalloproteinases (MMPs) are major proteolytic enzymes that are involved in extracellular matrix (ECM) turn over. MMP-2 (gelatinase A) and MMP-9 (gelatinase B) cleave type IV collagen, which is an important constituent of basement membrane. These enzymes play an important role in normal tissue homeostasis, but imbalance between MMPs and their tissue inhibitors (TIMPs) is thought to be a critical factor in regulating tissue remodeling. MMP-2 is produced by fibroblasts, endothelial, and epithelial cells, while MMP-9 is mainly produced by inflammatory cells. The role of MMPs was investigated through biochemical analysis or in situ expression, in the pathogenesis of two chronic inflammatory airway diseases, asthma and nasal polyposis. Both are characterized with the accumulation of active inflammatory cells, matrix remodeling and epithelial changes. Increased levels of MMP-9 and TIMP-1 were found in asthmatic subjects and NP. In NP, MMP-9 expression was detected in epithelial, endothelial and inflammatory cells. In this setting, MMP-9 could play a crucial role in the transmigration of basement membrane components by inflammatory cells leading to inflammatory cell accumulation and maintenance of inflammation in airway. Moreover, MMP-9 may contribute to cell migration, an important mechanism involved in the repair of the respiratory epithelium.     

ARK5与乳腺癌侵袭转移关系的研究

目的探讨ARK5在乳腺癌侵袭和转移中的意义。方法采用免疫组化SP法检测58例乳腺癌组织和15例癌旁乳腺组织中MMP-2、MMP-9及ARK5表达。应用小RNA干扰技术,将合成的小RNA干扰质粒转染MDA-MB-435细胞株,采用Western blot法检测瞬时转染后ARK5蛋白表达情况。通过体外侵袭实验检测细胞转染后侵袭能力的变化。ARK5下降后,再次进行Western blot法检测MMP-2、MMP-9蛋白表达。结果乳腺癌组织中MMP-2、MMP-9和ARK5免疫组化阳性结果之间存在正相关性。转染后的细胞株命名:转染ARK5质粒的MDA-MB-435细胞称之为SiARK5/MDA-MB-435,转染对照质粒的MDA-MB-435细胞称之为Scr/MDA-MB-435。转染72 h后,与Scr/MDA-MB-435细胞相比,SiARK5/MDA-MB-435细胞的ARK5蛋白表达水平降低。ARK5表达降低的乳腺癌细胞侵袭并穿透Matrivgel膜基质的细胞数量比对照组少(P<0.01),且MMP-2、MMP-9蛋白表达量降低。结论应用小RNA干扰技术降低ARK5蛋白的表达使MDA-MB-435细胞侵袭转移能力降低,同时MMP-2、MMP-9蛋白表达降低,提示ARK5通过MMP-2、MMP-9在乳腺癌侵袭转移中发挥重要作用。     

Induction of membrane-type matrix metalloproteinase 1 (MT1-MMP) expression in human fibroblasts by breast adenocarcinoma cells

Membrane-type matrix metalloproteinase 1 (MT1-MMP) has been recently described as an activator of proMMP-2 (MMP-2) which is involved in tumor invasion. We have shown by in situ hybridization that MT1-MMP is produced by stromal cells in close contact to preinvasive and invasive tumor cells of breast carcinomas. Of particular interest was the observation that some fibroblasts express this enzyme in focal areas in preinvasive lesions, suggesting that particular tumor cells may stimulate fibroblasts to produce MT1-MMP. We have therefore compared the ability of two different breast cancer cell lines, one non-invasive (MCF7) and one invasive (MDA-MB-231) to stimulate MT1-MMP production in human fibroblasts with consequent proMMP-2-activation. The MDA-MB-231 conditioned medium induced MT1-MMP mRNAs in human fibroblasts and a parallel activation of proMMP-2 whereas MCF7 conditioned medium did not have any effect. These results suggest the existence of soluble factor(s) secreted by invasive or some preinvasive breast tumor cells which stimulate fibroblasts to produce and activate MMPs, and emphasize the cooperation between cancer and stromal cells in tumor invasion.     

布托啡诺调控PBX3基因抑制乳腺癌细胞系MCF7增殖、迁移和侵袭

目的探讨布托啡诺(butorphanol)对乳腺癌细胞增殖、迁移和侵袭的影响以及相关的分子机制。方法用MTT法检测不同浓度布托啡诺对人乳腺癌细胞系MCF7的抑制作用;用Transwell迁移及侵袭实验检测不同浓度布托啡诺对人乳腺癌MCF7细胞迁移及侵袭的影响;RT-qCR与Western blot法分别检测乳腺癌细胞系、正常乳腺上皮细胞以及布托啡诺对MCF7细胞中PBX3 mRNA及蛋白表达的影响;观察转染si-PBX3或si-con后,MCF7细胞增殖、迁移及侵袭能力的变化;PBX3过表达验证布托啡诺对乳腺癌增殖、迁移及侵袭的作用机制。Western blot检测cyclin D1和MMP-2蛋白表达。结果PBX3在乳腺癌细胞系中的表达上调,沉默PBX3表达可明显抑制MCF7细胞增殖、迁移及侵袭,同时抑制cyclin D1和MMP-2的表达;不同浓度的布托啡诺干预能显著抑制MCF7细胞增殖、迁移及侵袭且具有浓度依赖性,还可抑制PBX3、cyclin D1和MMP-2的表达;过表达PBX3可逆转布托啡诺对乳腺癌细胞增殖、迁移及侵袭的抑制作用。结论布托啡诺可通过抑制PBX3降低乳腺癌细胞增殖、迁移及侵袭能力。     

Primary breast myoepithelial cells exert an invasion-suppressor effect on breast cancer cells via paracrine down-regulation of MMP expression in fibroblasts and tumour cells

In normal breast and ductal carcinoma in situ, myoepithelial cells form an incomplete layer separating the epithelial compartment from the stromal environment. Transition to invasive disease is marked by penetration of the myoepithelial-basement membrane (BM) interface. One mechanism involved in tumour invasion is breakdown of extracellular matrices by matrix metalloproteinases (MMPs). It was hypothesized that myoepithelial cells may modulate tumour invasion by controlling MMP gene expression, both in tumour cells and in peri-ductal fibroblasts. To investigate this, myoepithelial cells from normal breast were purified and characterized and their effect on tumour cell invasive potential was assessed. The effect on MMP gene expression of breast cancer cells cultured alone or in combination with primary normal breast fibroblasts was also analysed using RT-PCR with ELISA quantitation, with zymographic analysis to measure enzyme activity. Normal breast myoepithelial cells significantly reduced invasion by the breast cancer cell lines MCF-7, T47D, MDA-MB 231, and MDA-MB 468 when they were cultured alone or in the presence of a fibroblast population. Reduced invasion was associated with changes in MMP gene expression. In those tumour cells expressing MMP, there was a significant down-regulation of MMP-2 (MDA-MB 468, p<0.001), MMP-9 (MDA-MB 231, p=0.05; MDA-MB 468, p<0.001), and MT1-MMP (p<0.001 for both MDA-MB 231 and MDA-MB 468). Myoepithelial cells also caused a significant decrease in MMP gene expression in co-cultured fibroblasts. Furthermore, this was associated with reduced gelatinolytic activity as identified by zymography. This study demonstrates for the first time that primary myoepithelial cells from normal breast reduce breast cancer cell invasion and that this is mediated via modulation of both tumour cell and fibroblast function. This emphasizes the importance of the myoepithelial cell in controlling the breast microenvironment and focuses on the potential significance of the loss of this population with disease progression.