Expression and ligand binding of alpha 2 beta 1 integrin on breast carcinoma cells

Transcriptomics Studies Reveal Functions of Transglutaminase 2 in Breast Cancer Cells Using Membrane Permeable and Impermeable Inhibitors

Transglutaminase 2 (TG2) performs many functions both under physiological and pathological conditions. In cancer, its expression is associated with aggressiveness, propensity to epithelial-mesenchymal transition, and metastasis. Since TG2 performs key functions both outside and inside the cell, using inhibitors with different membrane permeability we analyzed the changes in the transcriptome induced in two triple-negative cell lines (MDA-MB-436 and MDA-MB-231) with aggressive features. By characterizing pathways and gene networks, we were able to define the effects of TG2 inhibitors (AA9, membrane-permeable, and NCEG2, impermeable) in relation to the roles of the enzyme in the intra- and extracellular space within the context of breast cancer. The deregulated genes revealed p53 and integrin signaling to be the common pathways with some genes showing opposite changes in expression. In MDA-MB-436, AA9 induced apoptosis, modulated cadherin, Wnt, gastrin and cholecystokinin receptors (CCKR) mediated signaling, with RHOB and GNG2 playing significant roles, and affected the Warburg effect by decreasing glycolytic enzymes. In MDA-MB-231 cells, AA9 strongly impacted HIF-mediated hypoxia, including AKT and mTOR pathway. These effects suggest an anti-tumor activity by blocking intracellular TG2 functions. Conversely, the use of NCEG2 stimulated the expression of ATP synthase and proteins involved in DNA replication, indicating a potential promotion of cell proliferation through inhibition of extracellular TG2. To effectively utilize these molecules as an anti-tumor strategy, an appropriate delivery system should be evaluated to target specific functions and avoid adverse effects. Additionally, considering combinations with other pathway modulators is crucial.

Vimentin tunes cell migration on collagen by controlling β1 integrin activation and clustering

Vimentin is a structural protein that is required for mesenchymal cell migration and directly interacts with actin, β1 integrin and paxillin. We examined how these interactions enable vimentin to regulate cell migration on collagen. In fibroblasts, depletion of vimentin increased talin-dependent activation of β1 integrin by more than 2-fold. Loss of vimentin was associated with reduction of β1 integrin clustering by 50% and inhibition of paxillin recruitment to focal adhesions by more than 60%, which was restored by vimentin expression. This reduction of paxillin was associated with 65% lower Cdc42 activation, a 60% reduction of cell extension formation and a greater than 35% decrease in cell migration on collagen. The activation of PAK1, a downstream effector of Cdc42, was required for vimentin phosphorylation and filament maturation. We propose that vimentin tunes cell migration through collagen by acting as an adaptor protein for focal adhesion proteins, thereby regulating β1 integrin activation, resulting in well-organized, mature integrin clusters.This article has an associated First Person interview with the first author of the paper.

Tunable synthetic extracellular matrices to investigate breast cancer response to biophysical and biochemical cues

The extracellular matrix (ECM) is thought to play a critical role in the progression of breast cancer. In this work, we have designed a photopolymerizable, biomimetic synthetic matrix for the controlled, 3D culture of breast cancer cells and, in combination with imaging and bioinformatics tools, utilized this system to investigate the breast cancer cell response to different matrix cues. Specifically, hydrogel-based matrices of different densities and modified with receptor-binding peptides derived from ECM proteins [fibronectin/vitronectin (RGDS), collagen (GFOGER), and laminin (IKVAV)] were synthesized to mimic key aspects of the ECM of different soft tissue sites. To assess the breast cancer cell response, the morphology and growth of breast cancer cells (MDA-MB-231 and T47D) were monitored in three dimensions over time, and differences in their transcriptome were assayed using next generation sequencing. We observed increased growth in response to GFOGER and RGDS, whether individually or in combination with IKVAV, where binding of integrin β1 was key. Importantly, in matrices with GFOGER, increased growth was observed with increasing matrix density for MDA-MB-231s. Further, transcriptomic analyses revealed increased gene expression and enrichment of biological processes associated with cell-matrix interactions, proliferation, and motility in matrices rich in GFOGER relative to IKVAV. In sum, a new approach for investigating breast cancer cell-matrix interactions was established with insights into how microenvironments rich in collagen promote breast cancer growth, a hallmark of disease progression in vivo, with opportunities for future investigations that harness the multidimensional property control afforded by this photopolymerizable system.

C-reactive protein binds to integrin α2 and Fcγ receptor I, leading to breast cell adhesion and breast cancer progression

C-reactive protein (CRP) is an acute phase protein synthesized upon the inflammatory responses, associated with breast cancer. The process of tumor cell invasion and metastasis involves the adherence of cells to the extracellular matrix via integrin as a receptor for matrix molecules. The present study investigated the role of CRP in the adhesive phenotype of breast cells and the underlying mechanisms. Here, we first showed that CRP induces adhesion of MCF10A human breast epithelial cells through the activation of integrin α2 signaling. Expression of integrin α2 was induced by CRP in which transcription factors c-fos and SP1 may be involved. Binding of CRP with integrin α2 leads to the activation of focal adhesion kinase (FAK), paxillin and ERKs. CRP also binds to an Fcγ receptor Fcγ receptor I (FcγRI), and induces activation of paxillin, FAK and ERKs. Integrin α2 and FAK have crucial roles in the adhesive and invasive phenotypes as well as MMP-9 upregulation induced by CRP in MCF10A cells. Treatment with an inflammatory lipid sphingosine-1-phosphate induced CRP, which may be secreted and exert an autocrine effect by binding to FcγRI and integrin α2. Involvement of CRP in adhesion, invasion, anchorage-independent growth and upregulation of integrin α2, paxillin and FAK was observed in MDA-MB-231 triple-negative human breast cancer (TNBC) cells. Using an in vivo invasion model and an orthotopic mouse tumor model with MDA-MB-231 cells, we showed that CRP has an important role in intravasation and tumor growth in vivo, demonstrating the in vivo relevance of our in vitro results. The present study elucidates a critical molecular basis between CRP, integrin α2 and FcγRI pathways in MCF10A breast cells and MDA-MB-231 TNBC cells, thereby providing useful information on CRP-induced aggressiveness of breast cells in the inflammatory microenvironment.

Hypoxic tumor environments exhibit disrupted collagen I fibers and low macromolecular transport

Hypoxic tumor microenvironments result in an aggressive phenotype and resistance to therapy that lead to tumor progression, recurrence, and metastasis. While poor vascularization and the resultant inadequate drug delivery are known to contribute to drug resistance, the effect of hypoxia on molecular transport through the interstitium, and the role of the extracellular matrix (ECM) in mediating this transport are unexplored. The dense mesh of fibers present in the ECM can especially influence the movement of macromolecules. Collagen 1 (Col1) fibers form a key component of the ECM in breast cancers. Here we characterized the influence of hypoxia on macromolecular transport in tumors, and the role of Col1 fibers in mediating this transport using an MDA-MB-231 breast cancer xenograft model engineered to express red fluorescent protein under hypoxia. Magnetic resonance imaging of macromolecular transport was combined with second harmonic generation microscopy of Col1 fibers. Hypoxic tumor regions displayed significantly decreased Col1 fiber density and volume, as well as significantly lower macromolecular draining and pooling rates, than normoxic regions. Regions adjacent to severely hypoxic areas revealed higher deposition of Col1 fibers and increased macromolecular transport. These data suggest that Col1 fibers may facilitate macromolecular transport in tumors, and their reduction in hypoxic regions may reduce this transport. Decreased macromolecular transport in hypoxic regions may also contribute to poor drug delivery and tumor recurrence in hypoxic regions. High Col1 fiber density observed around hypoxic regions may facilitate the escape of aggressive cancer cells from hypoxic regions.

CREB3L1 is a metastasis suppressor that represses expression of genes regulating metastasis, invasion, and angiogenesis

The unfolded protein response (UPR) is activated in response to hypoxia-induced stress such as in the tumor microenvironment. This study examined the role of CREB3L1 (cyclic AMP [cAMP]-responsive element-binding protein 3-like protein 1), a member of the UPR, in breast cancer development and metastasis. Initial experiments identified the loss of CREB3L1 expression in metastatic breast cancer cell lines compared to low-metastasis or nonmetastatic cell lines. When metastatic cells were transfected with CREB3L1, they demonstrated reduced invasion and migration in vitro, as well as a significantly decreased ability to survive under nonadherent or hypoxic conditions. Interestingly, in an in vivo rat mammary tumor model, not only did CREB3L1-expressing cells fail to form metastases compared to CREB3L1 null cells but regression of the primary tumors was seen in 70% of the animals as a result of impaired angiogenesis. Microarray and chromatin immunoprecipitation with microarray technology (ChIP on Chip) analyses identified changes in the expression of many genes involved in cancer development and metastasis, including a decrease in those involved in angiogenesis. These data suggest that CREB3L1 plays an important role in suppressing tumorigenesis and that loss of expression is required for the development of a metastatic phenotype.

Mesenchymal-epithelial transition (MET) as a mechanism for metastatic colonisation in breast cancer

As yet, there is no cure for metastatic breast cancer. Historically, considerable research effort has been concentrated on understanding the processes of metastasis, how a primary tumour locally invades and systemically disseminates using the phenotypic switching mechanism of epithelial to mesenchymal transition (EMT); however, much less is understood about how metastases are then formed. Breast cancer metastases often look (and may even function) as 'normal' breast tissue, a bizarre observation against the backdrop of the organ structure of the lung, liver, bone or brain. Mesenchymal to epithelial transition (MET), the opposite of EMT, has been proposed as a mechanism for establishment of the metastatic neoplasm, leading to questions such as: Can MET be clearly demonstrated in vivo? What factors cause this phenotypic switch within the cancer cell? Are these signals/factors derived from the metastatic site (soil) or expressed by the cancer cells themselves (seed)? How do the cancer cells then grow into a detectable secondary tumour and further disseminate? And finally--Can we design and develop therapies that may combat this dissemination switch? This review aims to address these important questions by evaluating long-standing paradigms and novel emerging concepts in the field of epithelial mesencyhmal plasticity.

Expression of matrix metalloproteinases (MMPs) in primary human breast cancer and breast cancer cell lines: New findings and review of the literature

BACKGROUND

Matrix metalloproteinases (MMPs) are a family of structural and functional related endopeptidases. They play a crucial role in tumor invasion and building of metastatic formations because of their ability to degrade extracellular matrix proteins. Under physiological conditions their activity is precisely regulated in order to prevent tissue disruption. This physiological balance seems to be disrupted in cancer making tumor cells capable of invading the tissue. In breast cancer different expression levels of several MMPs have been found.

METHODS

To fill the gap in our knowledge about MMP expression in breast cancer, we analyzed the expression of all known human MMPs in a panel of twenty-five tissue samples (five normal breast tissues, ten grade 2 (G2) and ten grade 3 (G3) breast cancer tissues). As we found different expression levels for several MMPs in normal breast and breast cancer tissue as well as depending on tumor grade, we additionally analyzed the expression of MMPs in four breast cancer cell lines (MCF-7, MDA-MB-468, BT 20, ZR 75/1) commonly used in research. The results could thus be used as model for further studies on human breast cancer. Expression analysis was performed on mRNA and protein level using semiquantitative RT-PCR, Western blot, immunohistochemistry and immunocytochemistry.

RESULTS

In summary, we identified several MMPs (MMP-1, -2, -8, -9, -10, -11, -12, -13, -15, -19, -23, -24, -27 and -28) with a stronger expression in breast cancer tissue compared to normal breast tissue. Of those, expression of MMP-8, -10, -12 and -27 is related to tumor grade since it is higher in analyzed G3 compared to G2 tissue samples. In contrast, MMP-7 and MMP-27 mRNA showed a weaker expression in tumor samples compared to healthy tissue. In addition, we demonstrated that the four breast cancer cell lines examined, are constitutively expressing a wide variety of MMPs. Of those, MDA-MB-468 showed the strongest mRNA and protein expression for most of the MMPs analyzed.

CONCLUSION

MMP-1, -2, -8, -9, -10, -11, -12, -13, -15, -19, -23, -24, -27 and -28 might thus be associated with breast cancer development and tumor progression. Therefore, these MMPs are proper candidates for further functional analysis of their role in breast cancer.

Estradiol and tamoxifen differently affects the inhibitory effects of vitamin A and their metabolites on the proliferation and expression of alpha2beta1 integrins in MCF-7 breast cancer cells

PURPOSE

Retinoids are well known inhibitors of estrogen-dependent breast cancer cell growth and differentiation. alpha2beta1 integrins are involved in the normal growth and differentiation of breast cells, they also take part in many pathological processes including malignancies. The aim of the study was to evaluate the effect of estradiol and tamoxifen on the inhibitory action of retinoids on the proliferation of MCF-7 breast cancer cells and alpha2beta1 integrin expression.

MATERIALS AND METHODS

Evaluation was based on [3H]thymidine incorporation and the proliferative activity of PCNA- and Ki 67-positive cells. Expression of alpha2beta1 was assessed through immunocytochemical analysis.

RESULTS

Treatment of cancer cells with the examined compounds and tamoxifen (10 microM) revealed that only 13-cis retinoic acid (13-cis RA) and all-trans retinoic acid (ATRA) (10(-5) M) decreased cells proliferation compared to the tamoxifen group (30.84%+/-3.32, p<0.01 and 31.05%+/-4.67, p<0.01, respectively). The lowest fraction of PCNA positive cells was also observed after the simultaneous addition ATRA (10(-5) M) and tamoxifen (10 microM) (30.75%+/-0.95, p<0.01, compared to the tamoxifen group). Our results showed that the decrease of alpha2beta1 integrin expression by 13-cis RA (10(-5) M, 49.6+/-3.25%) and ATRA (10-9 M, 15.0%+/-5.0) was augmented by tamoxifen and to a lesser extent by estradiol, particularly in the case of ATRA at 10(-7) or 10(-9) M.

CONCLUSIONS

This data suggest that tamoxifen augments the inhibitory effect of retinoids on proliferation and alpha2beta1 integrin expression in MCF-7 cells.

Salvicine inactivates beta 1 integrin and inhibits adhesion of MDA-MB-435 cells to fibronectin via reactive oxygen species signaling

Integrin-mediated adhesion to the extracellular matrix plays a fundamental role in tumor metastasis. Salvicine, a novel diterpenoid quinone compound identified as a nonintercalative topoisomerase II poison, possesses a broad range of antitumor and antimetastatic activity. Here, the mechanism underlying the antimetastatic capacity of salvicine was investigated by exploring the effect of salvicine on integrin-mediated cell adhesion. Salvicine inhibited the adhesion of human breast cancer MDA-MB-435 cells to fibronectin and collagen without affecting nonspecific adhesion to poly-l-lysine. The fibronectin-dependent formation of focal adhesions and actin stress fibers was also inhibited by salvicine, leading to a rounded cell morphology. Furthermore, salvicine down-regulated beta(1) integrin ligand affinity, clustering and signaling via dephosphorylation of focal adhesion kinase and paxillin. Conversely, salvicine induced extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) phosphorylation. The effect of salvicine on beta(1) integrin function and cell adhesion was reversed by U0126 and SB203580, inhibitors of MAPK/ERK kinase 1/2 and p38 MAPK, respectively. Salvicine also induced the production of reactive oxygen species (ROS) that was reversed by ROS scavenger N-acetyl-l-cysteine. N-acetyl-l-cysteine additionally reversed the salvicine-induced activation of ERK and p38 MAPK, thereby maintaining functional beta(1) integrin activity and restoring cell adhesion and spreading. Together, this study reveals that salvicine activates ERK and p38 MAPK by triggering the generation of ROS, which in turn inhibits beta(1) integrin ligand affinity. These findings contribute to a better understanding of the antimetastatic activity of salvicine and shed new light on the complex roles of ROS and downstream signaling molecules, particularly p38 MAPK, in the regulation of integrin function and cell adhesion.

Novel functions of vimentin in cell adhesion, migration, and signaling

Vimentin is the major intermediate filament (IF) protein of mesenchymal cells. It shows dynamically altered expression patterns during different developmental stages and high sequence homology throughout all vertebrates, suggesting that the protein is physiologically important. Still, until recently, the real tasks of vimentin have been elusive, primarily because the vimentin-deficient mice were originally characterized as having a very mild phenotype. Recent studies have revealed several key functions for vimentin that were not obvious at first sight. Vimentin emerges as an organizer of a number of critical proteins involved in attachment, migration, and cell signaling. The highly dynamic and complex phosphorylation of vimentin seems to be a likely regulator mechanism for these functions. The implicated novel vimentin functions have broad ramifications into many different aspects of cell physiology, cellular interactions, and organ homeostasis.

Biological activity of rainbow trout Ea4-peptide of the pro-insulin-like growth factor (pro-IGF)-I on promoting attachment of breast cancer cells (MDA-MB-231) via alpha2- and beta1-integrin

E-peptide of pro-IGF-I was considered as biologically inactive. We have demonstrated that rainbow trout (rt) Ea4-peptide exerted biological activities in several established tumor cell lines [Chen et al., 2002; Kuo and Chen, 2002]. Here we report the activity of rtEa4-peptide in promoting attachment of human breast cancer cells (MDA-MB-231). While rtEa2-, rtEa3-, and rtEa4-peptides enhanced the attachment of MDA-MB-231 cells in a dose dependent manner, rtEa4-peptide possessed the highest activity. Antibodies specific to alpha2 and beta1 integrins significantly inhibited the attachment of cells to rtEa4-peptide coated-plates by 40%. In addition, rtEa4-peptide induced the expression of fibronectin 1 and laminin receptor genes in MDA-MB-231 cells. Blocking new protein synthesis by cycloheximide significantly reduced the attachment of MDA-MB-231 cells to rtEa4-peptide coated wells by 50%. These results suggest that rtEa4-peptide may promote cell attachment by interacting with alpha2/beta1 integrin receptors at the cell surface and by inducing the expression of fibronectin 1 and laminin receptor genes. Expression of fibronectin 1 gene induced by rtEa4-peptide in MDA-MB-231 cells was abolished by inhibitors of PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signaling transduction molecules. These results suggested that induction of fibronectin 1 gene expression in MDA-MB-231 cells by rtEa4-peptide may be mediated via PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signal transduction molecules.

C60-fullerenes: detection of intracellular photoluminescence and lack of cytotoxic effects

We have developed a new method of application of C₆₀ to cultured cells that does not require water-solubilization techniques. Normal and malignant cells take-up C₆₀ and the inherent photoluminescence of C₆₀ is detected within multiple cell lines. Treatment of cells with up to 200 μg/ml (200 ppm) of C₆₀ does not alter morphology, cytoskeletal organization, cell cycle dynamics nor does it inhibit cell proliferation. Our work shows that pristine C₆₀ is non-toxic to the cells, and suggests that fullerene-based nanocarriers may be used for biomedical applications.

Inhibition of either phosphatidylinositol 3-kinase/Akt or the mitogen/extracellular-regulated kinase, MEK/ERK, signaling pathways suppress growth of breast cancer cell lines, but MEK/ERK signaling is critical for cell survival

The phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen/extracellular signal-regulated kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways are important integrators of growth and survival signals originating from extracellular stimuli. We assessed the importance of these signaling pathways in the growth and survival of 8 breast cell lines (MCF10A, an immortalized line; and 7 cancer cell lines). The cell lines expressed variable levels of both phosphorylated ERK and phosphorylated Akt, but these were unchanged by incubation in serum-free medium. Despite continued activity of these pathways, the cells arrested growth in the absence of serum demonstrating that additional pathways are required for growth. Incubation with the PI3K inhibitor LY294002 suppressed growth of all cell lines, but most remained viable for at least 7-14 days. This long-term survival may be attributable to recovery of phospho-Akt by 24-48 h despite the continued presence of active LY294002, suggesting that alternate pathways may be activating Akt. In contrast, incubation with the MEK inhibitor U0126 not only arrested growth, but also killed all the cell lines within 2-4 days in the absence of serum; the presence of serum only slighted extended viability, except in MCF10A and MDA-MB-468 cells, in which serum provided significantly greater protection. It is likely that these signaling pathways control the level of pro-and anti-apoptotic proteins, yet assessment of Bcl-2 and Bcl-X showed dramatic reduction in level only when large numbers of cells were dead suggesting this may be a consequence rather than cause of death. Overall, the results demonstrate that the MEK/ERK pathway represents the more critical pathway for cell survival of these breast cancer cell lines, and suggest this pathways represents the better target for cancer therapy.

Resensitization of breast cancer cells to anoikis by Tropomyosin-1: role of Rho kinase-dependent cytoskeleton and adhesion

Two most common properties of malignant cells are the presence of aberrant actin cytoskeleton and resistance to anoikis. Suppression of several key cytoskeletal proteins, including tropomyosin-1 (TM1), during neoplastic transformation is hypothesized to contribute to the altered cytoskeleton and neoplastic phenotype. Using TM1 as a paradigm, we have shown that cytoskeletal proteins induce anoikis in breast cancer (MCF-7 and MDA MB 231) cells. Here, we have tested the hypothesis that TM1-mediated cytoskeletal changes regulate integrin activity and the sensitivity to anoikis. TM1 expression in MDA MB 231 cells promotes the assembly of stress fibers, induces rapid anoikis via caspase-dependent pathways involving the release of cytochrome c. Further, TM1 inhibits binding of MDA MB 231 cells to collagen I, but promotes adhesion to laminin. Inhibition of Rho kinase disrupts TM1-mediated cytoskeletal reorganization and adhesion to the extracellular matrix components, whereas the parental cells attach to collagen I, spread and form extensive actin meshwork in the presence of Rho kinase inhibitor, underscoring the differences in parental and TM1-transduced breast cancer cells. Further, treatment with the cytoskeletal disrupting drugs rescues the cells from TM1-induced anoikis. These new findings demonstrate that the aberrant cytoskeleton contributes to neoplastic transformation by conferring resistance to anoikis. Restoration of stress fiber network through enhanced expression of key cytoskeletal proteins may modulate the activity of focal adhesions and sensitize the neoplastic cells to anoikis.

Cripto as a target for cancer immunotherapy

One of the recent, significant advances in cancer immunotherapy is the identification of molecules as targets which regulate cell growth by induction of proliferation and survival signalling pathways. Among them, epidermal growth factor receptor and Her2 have been effectively targeted by monoclonal antibodies. Currently, the treatment of cancer has limitations and most cancer deaths result from the local invasion and distant metastasis of tumour cells. An important insight for the understanding of tumour invasion and metastasis came from the recent discovery that the phenotypic changes of increased motility and invasiveness of cancer cells are reminiscent of the epithelial-mesenchymal transition (EMT) that occurs during embryonic development. The human Cripto, a member of the epidermal growth factor-Cripto, Frl1, and Cryptic (EGF-CFC) protein family and a signalling protein during early embryonic development, plays an important role in cancers. Cripto is attached to the cell membrane through a glycosyl-phosphatidylinositol motif, and is upregulated in a wide range of epithelial cancers. In this paper the authors review the role of Cripto expression in tumourigenesis and in EMT to promote tumour invasion, with emphasis that the unique EGF-like region of Cripto plays a critical role in Cripto signalling-mediated tumour growth and EMT. Therefore, the region should be regarded as a therapeutic point for interruption of the oncogenic and metastatic potential of Cripto for cancer immunotherapy.

Cripto-1: an oncofetal gene with many faces

Human Cripto-1 (CR-1), a member of the epidermal growth factor (EGF)-CFC family, has been implicated in embryogenesis and in carcinogenesis. During early vertebrate development, CR-1 functions as a co-receptor for Nodal, a transforming growth factor beta (TGFbeta) family member and is essential for mesoderm and endoderm formation and anterior-posterior and left-right axis establishment. In adult tissues, CR-1 is expressed at a low level in all stages of mammary gland development and expression increases during pregnancy and lactation. Overexpression of CR-1 in mouse mammary epithelial cells leads to their transformation in vitro and, when injected into mammary glands, produces ductal hyperplasias. CR-1 can also enhance migration, invasion, branching morphogenesis and epithelial to mesenchymal transition (EMT) of several mouse mammary epithelial cell lines. Furthermore, transgenic mouse studies have shown that overexpression of a human CR-1 transgene in the mammary gland under the transcriptional control of the mouse mammary tumor virus (MMTV) promoter results in mammary hyperplasias and papillary adenocarcinomas. Finally, CR-1 is expressed at high levels in approximately 50 to 80% of different types of human carcinomas, including breast, cervix, colon, stomach, pancreas, lung, ovary, and testis. In conclusion, EGF-CFC proteins play dual roles as embryonic pattern formation genes and as oncogenes. While during embryogenesis EGF-CFC proteins perform specific and regulatory functions related to cell and tissue patterning, inappropriate expression of these molecules in adult tissues can lead to cellular proliferation and transformation and therefore may be important in the etiology and/or progression of cancer.

Epithelial mesenchymal transition is a characteristic of hyperplasias and tumors in mammary gland from MMTV-Cripto-1 transgenic mice

Epithelial-mesenchymal transition (EMT) facilitates migration and invasion of epithelial tumor cells. Cripto-1 (CR-1), a member of the epidermal growth factor-CFC protein family increases migration of cells in vitro. Here the expression of molecular markers and signaling molecules characteristic of EMT were assessed in mammary gland hyperplasias and tumors from mice expressing the human CR-1 transgene by the MMTV promoter (MMTV-CR-1) and in mouse mammary epithelial cell line HC-11 overexpressing CR-1 (HC-11/CR-1). Western blot analysis showed decreased expression of E-cadherin in MMTV-CR-1 tumors and in HC-11/CR-1 cells. The expression of N-cadherin, vimentin, cyclin-D1, and of the zinc-finger transcription factor, snail, was increased in MMTV-CR-1 tumors. Increased snail mRNA was also found in HC-11/CR-1 cells. Expression of phosphorylated (P)-c-Src, P-focal adhesion kinase (FAK), P-Akt, P-glycogen synthease kinase 3beta (GSK-3beta), dephosphorylated (DP)-beta-catenin, and various integrins such as, alpha 3, alpha v, beta 1, beta 3, and beta 4 was also increased in MMTV-CR-1 tumors. Immunohistochemistry showed positive staining for vimentin, N-cadherin, cyclin-D1, smooth muscle actin, fibronectin, snail, and beta-catenin in MMTV-CR-1 tumor sections. HC-11/CR-1 cells treated with the c-Src inhibitor PP2 reduced the expression of P-c-Src and of P-FAK, P-Akt, P-GSK-3beta, DP-beta-catenin all known to be activated by c-Src. Migration of HC-11/CR-1 cells was also reduced by PP2 treatment. These results suggest that CR-1 may play a significant role in promoting the increased expression of markers and signaling molecules associated with EMT.

Effect of Progesterone Receptor A Predominance on Breast Cancer Cell Migration into Bone Marrow Fibroblasts

Women exposed to exogenous progesterone have increased breast cancer risk, but the mechanisms of progesterone involvement in breast cancer development are unknown. In human breast and endometrium, progesterone receptor (PR) isoform expression is disrupted in premalignant lesions and predominance of one isoform, usually PRA, in invasive cancers is associated with poorer prognosis. Disrupted PR isoform expression results in disrupted progestin regulation of cell morphology, including rounded morphology and decreased adherence of cells to tissue culture flasks. The purpose of this study was to test the hypothesis that predominance of PRA affects the interaction of breast cancer cells with a physiologically relevant stromal tissue, bone marrow stroma. T-47D breast cancer cells demonstrated the ability to migrate into bone marrow fibroblasts and this was inhibited by progestin treatment. The antiprogestin RU38486 abrogated the progestin effect on migration, demonstrating that it was PR-mediated. In cells expressing a predominance of PRA, after induction of a stably integrated inducible PRA construct, the ability of progestin to inhibit breast cancer cell migration was lost. A number of integrins were progestin regulated in T-47D cells, but there was no difference in the progestin effect in cells with PRA predominance, nor were the levels of focal adhesion proteins altered in these cells. This suggested that the lack of inhibition by progestin of breast cancer cell migration in cells with PRA predominance was not mediated by PRA effects on the membrane components of the adherens junctions. In summary, this study has shown that PRA predominance has a striking functional effect on breast cancer cell migration into stromal layers. PRA predominance may render breast cancer cells relatively resistant to the inhibitory effects of progestins and one consequence of this may be increased invasion of stroma. If borne out in vivo, these findings suggest that tumours with PRA predominance may be predisposed to cancer progression and this may signal a poorer prognosis in patients.

The beta1 cytoplasmic domain regulates the laminin-binding specificity of the alpha7X1 integrin

During muscle development, the laminin-specific alpha7 integrin is alternatively spliced in the putative ligand-binding domain to yield either the alpha7X1 or the alpha7X2 variant. The relative level of alpha7X1 and alpha7X2 is developmentally regulated. Similarly, the partner beta1 integrin cytoplasmic domain is converted from the beta1A to the beta1D splice variant. To determine whether beta1D modulates the activity of the alpha7 receptor, cells were transfected with alpha7X1 and beta1D cDNA. alpha7X1 coupled with beta1A failed to adhere to laminin-1, whereas cotransfectants expressing alpha7X1 and beta1D showed strong adhesion. Interestingly, alpha7X1 complexed with beta1A and beta1D displayed the same level of poor adhesion to laminin-2/4 or strong adhesion to laminin-10/11. These findings indicate that alpha7 function is regulated not only by X1/X2 in its extracellular domain but also by beta1 cytoplasmic splice variants. It is likely that expression of beta1D alters alpha7X1 binding to laminin isoforms by a process related to ligand affinity modulation. Functional regulation of alpha7beta1 by developmentally regulated splicing events may be important during myogenic differentiation and repair because the integrin mediates adhesion, motility, and cell survival.

Collagen-IV and laminin-1 regulate estrogen receptor alpha expression and function in mouse mammary epithelial cells

The expression level and functional activity of estrogen receptor alpha is an important determinant of breast physiology and breast cancer treatment. However, it has been difficult to identify the signals that regulate estrogen receptor because cultured mammary epithelial cells generally do not respond to estrogenic signals. Here, we use a combination of two- and three-dimensional culture systems to dissect the extracellular signals that control endogenous estrogen receptor alpha. Its expression was greatly reduced when primary mammary epithelial cells were placed on tissue culture plastic; however, the presence of a reconstituted basement membrane in combination with lactogenic hormones partially prevented this decrease. Estrogen receptor alpha expression in primary mammary fibroblasts was not altered by these culture conditions, indicating that its regulation is cell type specific. Moreover, estrogen receptor-dependent reporter gene expression, as well as estrogen receptor alpha levels, were increased threefold in a functionally normal mammary epithelial cell line when reconstituted basement membrane was added to the medium. This regulatory effect of reconstituted basement membrane was reproduced by two of its components, collagen-IV and laminin-1, and it was blocked by antibodies against alpha2, alpha6 and beta1 integrin subunits. Our results indicate that integrin-mediated response to specific basement membrane components, rather than cell rounding or cell growth arrest induced by reconstituted basement membrane, is critical in the regulation of estrogen receptor alpha expression and function in mammary epithelial cells.

A rat cell line derived from DMBA-induced mammary carcinoma

A new cell line, designated UHKBR-01, was successfully established from a 7,12-dimethylbenz[a]anthracene (DMBA)-induced rat mammary tumour. DMBA was administered orally at a dose of 4 mg/ml per rat on the first day of the experiment and thereafter at weekly intervals of same dosage, until the rats have reached a weight of around 150-200 g. The tumours grew rapidly after the injection, and were transplanted into nude mice one the harvest size (2.5 x 2 x 1 mm(3)) was reached, it was transplanted onto nude mice. We have developed a cell line from a portion of the DMBA-induced carcinoma of the nude mice. The UHKBR-01 cell exhibited a slow increase in growth rate during the time of culture and was highly tumourigenic in nude mice. The cells have been grown in culture for over 40 passages. Characterization of the cell line was performed. This included morphology by light and transmission electron microscopy, karyotype, growth rate, tumour antigen expression and xenograft implantation into nude mice. These cells exhibit ultrastructural and immunohistochemical features of epithelial cells of mammary origin. The above analyses also demonstrated that UHKBR-01 cells were oestrogen- and progesterone-receptor positive, in likeness to other established breast cancer cell lines such as MDA-MB-231 and MCF-7. The cell line grows as monolayers of oval-shaped cells with large folded nuclei accompanied by a rich supply of mitochondria. This report describes the first in vitro cell line from transplantable DMBA-induced mammary carcinoma of nude mice, which presents unique characteristics that may prove to be a good experimental model for investigating breast cancer biology.

Heregulin and retinoids synergistically induce branching morphogenesis of breast cancer cells cultivated in 3D collagen gels

C-erbB and retinoid receptor signaling control mammary epithelial cell proliferation, differentiation, and morphology. Here, we examined the morphogenetic activities of c-erbB specific ligands such as heregulin and of retinoids on non-malignant (primary, MTSV1-7) and malignant (T47D, SKBR-3) human mammary epithelial cells (HMEC) cultivated in 3D collagen type I gels. These cells are positive for both c-erbB and retinoid receptors. Non-malignant primary HMEC spontaneously formed branched structures in collagen, whereas SV40 large T antigen-immortalized non-tumorigenic MTSV1-7 spontaneously formed balls and required heregulin or retinoid X receptor alpha-selective retinoid Ro 25-7386 for branching, which was further stimulated by combination of both types of agents. In malignant cells, heregulin alone induced ball formation and cooperated either with Ro 25-7386 (T47D) or with retinoic acid receptor alpha-selective AM580 (SKBR-3) for branching morphogenesis, which was accompanied by changes in the subcellular distribution of alpha(2)beta(1)-integrin and E-cadherin, and by down-regulation of c-erbB-2, -3, or -4. Heregulin and/or retinoids correspondingly increased the integrin-dependent adhesion of malignant cells to type I collagen. Our data demonstrate cooperative signaling of c-erbB and retinoid receptor pathways at the levels of morphogenesis and immunophenotypic differentiation.

Latent membrane protein-1 of Epstein-Barr virus inhibits cell growth and induces sensitivity to cisplatin in nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma is closely associated with Epstein-Barr virus (EBV) and the EBV encoded latent membrane protein-1 expression (LMP1) is commonly found in the tumour cells. LMP1 has been shown to be involved in modulation of cell growth in B cells but the biological properties of LMP1 expression in nasopharyngeal carcinoma cells are less defined. In this study, a full length LMP1 gene was introduced into an EBV negative nasopharyngeal carcinoma cell line, CNE2, and five LMP1-expressing clones were isolated. Expression of LMP1 did not confer cell growth advantage in CNE2 cells; instead, it induced growth inhibition both in vitro and in vivo. In addition, the LMP1 transfected cells were more susceptible to cisplatin-induced cell death and showed 1.4-4.0-fold increased sensitivity to cisplatin compared to the vector infected control clones. The effect of LMP1 on the balance of Bcl-2 and Bax ratio may play a role in inducing susceptibility to cisplatin-induced cell death. These results demonstrated that LMP1 did not confer growth advantage in CNE2 cells, suggesting that expression of LMP1 may not be crucial in sustaining cell growth in established cell lines. Alternatively, LMP1 alone may not be sufficient to facilitate nasopharyngeal carcinoma cell growth and additional oncogenic factors may be needed along with LMP1 in modulating the malignant property of nasopharyngeal carcinoma.

Integrin alpha1beta1 (VLA-1) mediates adhesion of activated intraepithelial lymphocytes to collagen

Intraepithelial lymphocytes (IELs) from human intestinal epithelium are memory CD8+ T cells that bind to epithelial cells through human mycosal lymphocyte (HML)-1 and to mesenchymal cells through very late activation antigen-4 (VLA-4). Their binding of extracellular matrix proteins and the mechanism involved were tested. Activated 51Cr-labelled lymphocytes were incubated in protein-coated microwells with various additives. After washing, the adherent cells were detected by radioactivity. The percentages of activated IELs that bound to collagen types I and IV were 20 and 31%, respectively; fewer bound to fibronectin or laminin. Compared to interleukin-2-activated peripheral blood CD8+ T lymphocytes, more IELs bound collagen IV and fewer bound fibronectin. IEL adhesion to collagen (but not fibronectin or laminin) was up-regulated by antibody ligation of CD2 or by protein kinase C stimulation by phorbol ester; staurosporine reduced binding, while herbimycin, phytohaemagglutinin and CD3 ligation had no effect. Antibody-blocking of integrin VLA-1 subunits alpha1 (CD49a) and beta1 (CD18) inhibited adhesion to collagen type I by 82+/-6% and to type IV by 94+/-1% (P<0.001), implicating VLA-1 as the main collagen receptor for IELs. Cell adhesion was dependent on extracellular divalent cations, a characteristic event of VLA-1 never before shown for IELs: manganese and magnesium ions supported binding in a dose-dependent manner; calcium ions inhibited their effectiveness. Therefore, IELs bind collagen through integrin alpha1beta1 after protein kinase C activation. Adhesion is modulated by divalent cations.

Role of thrombin receptor in breast cancer invasiveness

Invasion, the ability of an epithelial cancer cell to detach from and move through a basement membrane, is a central process in tumour metastasis. Two components of invasion are proteolysis of extracellular matrix and cellular movement through it. A potential promoter of these two processes is thrombin, the serine proteinase derived from the ubiquitous plasma protein prothrombin. Thrombin promotes the invasion of MDA-MB231 breast tumour cells (a highly aggressive cell line) in an in vitro assay. Invasion by MDA-MB436 and MCF-7 cells, less aggressive cell lines, is not promoted by thrombin. Thrombin, added to the cells, is a stimulator of cellular movement; fibroblast-conditioned medium is the chemotaxin. Thrombin-promoted invasion is inhibited by hirudin. Stimulation of invasion is a receptor-mediated process that is mimicked by a thrombin receptor-activating peptide. Thrombin has no effect on chemotaxis in vitro. Thrombin receptor is detectable on the surface of MDA-MB231 cells, but not on the other two cell lines. Introduction of oestrogen receptors into MDA-MB231 cells by transfection with pHEO had no effect on thrombin receptor expression, in the presence or absence of oestradiol. This paper demonstrates that thrombin increases invasion by the aggressive breast cancer cell line MDA-MB231 by a thrombin receptor-dependent mechanism.

The role of protein glycosylation inhibitors in the prevention of metastasis and therapy of cancer

Oligosaccharide moieties of cell-surface glycoproteins are thought to be involved in recognition events during cancer metastasis and invasion. Swainsonine, an inhibitor of the Golgi alpha-mannosidase II, has been shown to block pulmonary colonization by tumor cells and stimulate components of the immune system. Swainsonine also abrogates much of the toxicity of chemotherapeutic agents and stimulates bone marrow hematopoietic progenitor cells, suggesting additional therapeutic applications. We are currently characterizing the ability of swainsonine to modify cell growth in human and murine bone marrow progenitor cells. Furthermore, we are examining crucial steps in metastasis that depend upon cell surface molecules that play a role in cell-matrix interactions. Our work shows that tumor cell adhesion to collagen IV in vitro is rapidly stimulated by cis-polyunsaturated fatty acids and is dependent on protein kinase C activity. We are investigating the hypothesis that integrins are critical components of this adhesion and are examining potential signal transduction pathways that lead to the modulation of cell adhesion.

Migration of breast epithelial cells on Laminin-5: differential role of integrins in normal and transformed cell types

We examined the role of Laminin-5 (Ln-5) an extracellular matrix component of breast gland basement membrane, in supporting migration of normal (HUMEC), immortalized (MCF-10A), and malignant breast epithelial cells that exhibit different degrees of metastatic potential (MDA-MB-435>MDA-MB-231>MCF-7). HUMEC, MCF-10A, and MCF-7 cells all adhered to purified Ln-5 through the alpha3beta1 integrin receptor in adhesion assays. However, HUMEC and MCF-10A cells remained statically adherent, while MCF-7 cells migrated on Ln-5 in Transwell and colloidal gold displacement assays. Anti-alpha3 integrin antibodies blocked migration of MCF-7 cells on Ln-5. MDA-MB-231 and MDA-MB-435 cells bound and migrated on Ln-5 through a beta1 integrin receptor that is insensitive to antibodies that block the function of alpha1, alpha2, alpha3, alpha4, alpha5, alpha6, and alphaV integrin subunits. Migration of all cell types tested was blocked by CM6, a monoclonal antibody directed to a cell adhesion site on the alpha3 chain of Ln-5. Thus, Ln-5 may play an important role in regulating adhesion and migration in normal and transformed breast epithelium. Our results indicate that the type of integrin utilized by breast cells to interact with Ln-5, as well as its functional state, may determine whether cells will be statically adherent or migratory on Ln-5.

A novel pathway for mammary epithelial cell invasion induced by the helix-loop-helix protein Id-1

Mammary epithelial cells undergo changes in growth, invasion, and differentiation throughout much of adulthood, and most strikingly during pregnancy, lactation, and involution. Although the pathways of milk protein expression are being elucidated, little is known, at a molecular level, about control of mammary epithelial cell phenotypes during normal tissue morphogenesis and evolution of aggressive breast cancer. We developed a murine mammary epithelial cell line, SCp2, that arrests growth and functionally differentiates in response to a basement membrane and lactogenic hormones. In these cells, expression of Id-1, an inhibitor of basic helix-loop-helix transcription factors, declines prior to differentiation, and constitutive Id-1 expression blocks differentiation. Here, we show that SCp2 cells that constitutively express Id-1 slowly invade the basement membrane but remain anchorage dependent for growth and do not form tumors in nude mice. Cells expressing Id-1 secreted a approximately 120-kDa gelatinase. From inhibitor studies, this gelatinase appeared to be a metalloproteinase, and it was the only metalloproteinase detectable in conditioned medium from these cells. A nontoxic inhibitor diminished the activity of this metalloproteinase in vitro and repressed the invasive phenotype of Id-1-expressing cells in culture. The implications of these findings for normal mammary-gland development and human breast cancer were investigated. A gelatinase of approximately 120 kDa was expressed by the mammary gland during involution, a time when Id-1 expression is high and there is extensive tissue remodeling. Moreover, high levels of Id-1 expression and the activity of a approximately 120-kDa gelatinase correlated with a less-differentiated and more-aggressive phenotype in human breast cancer cells. We suggest that Id-1 controls invasion by normal and neoplastic mammary epithelial cells, primarily through induction of a approximately 120-kDa gelatinase. This Id-1-regulated invasive phenotype could contribute to involution of the mammary gland and possibly to the development of invasive breast cancer.

Roles of the matrix metalloproteinases in mammary gland development and cancer

Tissue remodeling is a key process involved in normal development, wound healing, bone remodeling, and embryonic implantation, as well as pathological conditions such as tumor invasion and metastasis, and angiogenesis. The degradation of the extracellular matrix that is associated with those processes is mediated by a number of families of extracellular proteinases. These families include the serine proteinases, such as the plasminogen-urokinase plasminogen activator system and leukocyte elastases, the cysteine proteinases, like cathepsin D and L, and the zinc-dependent matrix metalloproteinases (MMPs) [1]. Accumulating evidence has highlighted the central role of MMP-driven extracellular matrix remodeling in mammary gland development and breast cancer.

The LCC15-MB human breast cancer cell line expresses osteopontin and exhibits an invasive and metastatic phenotype

We have characterized the LCC15-MB cell line which was recently derived from a breast carcinoma metastasis resected from the femur of a 29-year-old woman. LCC15-MB cells are vimentin (VIM) positive, exhibit a stellate morphology in routine cell culture, and form penetrating colonies when embedded in three-dimensional gels of Matrigel or fibrillar collagen. They show high levels of activity in the Boyden chamber chemomigration and chemoinvasion assays, and like other invasive human breast cancer (HBC) cell lines, LCC15-MB cells activate matrix-metalloproteinase-2 in response to treatment with concanavalin A. In addition, these cells are tumorigenic when implanted subcutaneously in nude mice and recolonize bone after arterial injection. Interestingly, both the primary lesion and the bone metastasis from which LCC15-MB were derived, as well as the resultant cell line, abundantly express the bone matrix protein osteopontin (OPN). OPN is also expressed by the highly metastatic MDA-MB-435 cells, but not other invasive or noninvasive HBC cell lines. Expression of OPN is retained in the subcutaneous xenograft and intraosseous metastases of LCC15-MB as detected by immunohistochemistry. Both VIM and OPN expression have been associated with breast cancer invasion and metastasis, and their expression by the LCC15-MB cell line is consistent with its derivation from a highly aggressive breast cancer. These cells provide a useful model for studying molecular mechanisms important for breast cancer metastasis to bone and, in particular, the implication(s) of OPN and VIM expression in this process.

Negative cooperativity between alpha 3 beta 1 and alpha 2 beta 1 integrins in human mammary carcinoma MDA MB 231 cells

The alpha 3 beta 1 integrin has been implicated as a receptor for several matrix components, including collagen, fibronectin, and laminins. The function of alpha 3 beta 1 seems to be very versatile involving cell adhesion to or migration on ECM, establishment of cell-cell contacts in aggregates, as well as linkage to intracellular tyrosine phosphorylation cascades. Here we report a strong induction of attachment of alpha 3 beta 1 integrin expressing human breast carcinoma cell line MDA MB 231 to matrix proteins by two alpha 3 integrin subunit function-blocking monoclonal antibodies (P1B5 and ASC-1). In contrast, stimulation of adhesion to ECM by inhibitory alpha 3 integrin-specific antibodies was not observed in the alpha 3 beta 1 integrin-expressing nonmalignant human mammary epithelial cell line MCF-10A or the human breast carcinoma cell line MDA MB 468 that expressed relatively low amounts of alpha 3 beta 1 integrin at the cell surface. This increase was specific for collagens and not observed on fibronectin or laminin. Physiological concentrations of bivalent cations were not required. MAb P1B5 did not induce homotypic aggregation of MDA MB 231 cells. The P1B5-induced increase in cell attachment to collagens could be prevented but not reduced below control levels by blocking mAb to the alpha 2 integrin subunit. Function blocking anti-alpha 5 integrin subunit mAb was without effect while anti-beta 1-mAb completely abolished adhesion. Our data indicate that negative cooperativity between integrins results in transdominant inhibition of alpha 2 beta 1 function by alpha 3 beta 1 in human MDA MB 231 but not MDA MB 468 tumor cells or nonmalignant MCF-10A cells.

Laminin and estradiol regulation of the plasminogen-activator system in MCF-7 breast-carcinoma cells

We have investigated the effects of laminin, on the plasminogen-activator system of MCF-7 breast-carcinoma cells. MCF-7 cells were incubated on plastic or laminin-coated wells, and medium and cell lysate aliquots were assayed for tissue-type (tPA) and urokinase-type plasminogen activator (uPA) by a chromogenic assay in combination with anti-uPA antibodies. Cells cultured on laminin displayed a 5-fold increase in tPA activity and a 2-fold decrease in uPA activity relative to cells on plastic. These effects could be mimicked by laminin fragment P1 but not by collagen I or fibronectin. tPA activity of cells treated with estradiol (10 nM) was 3-fold higher, that of cells on laminin treated with estradiol was 15-fold higher, than that of control. Northern-blot analysis showed that tPA mRNA levels were up-regulated by estradiol and laminin, whereas PAI-1 mRNA levels were down-regulated by laminin and not affected by E2. Concomitant treatment with laminin and estradiol, decreased PAI-1 mRNA and increased tPA mRNA levels, accounting for the synergistic increase in tPA activity. Laminin exerted only a modest (approx. 2-fold) inhibitory effect on uPA mRNA levels. In the breast-carcinoma cell line MDA-MB-231, down-regulation of PAI-1 and uPA mRNA by laminin was not observed. Adhesion assays indicated that alpha2beta1 is the predominant receptor for laminin in MCF-7 cells. MDA-MB-231 cells expressed alpha2 (54%) but this integrin is not used as a laminin receptor. These results support a role for alpha2beta1 in mediating interactions of MCF-7 with LN.

Detection of integrins in formalin-fixed, paraffin-embedded tissues

Integrins are heterodimeric transmembrane receptors, which are expressed in many cells. In vitro experiments have demonstrated that integrins may be important in tumor progression and organ development. The functions of integrins were previously studied in cell cultures and their tissue expression was detected by immunofluorescence or immunoperoxidase in frozen sections. The purpose of this study was to determine the optimal conditions for detection of integrins in formalin-fixed, paraffin-embedded tissues. We utilized microwave heating and enzyme digestion in routinely processed, surgically removed tissues. Our results demonstrate that integrins can be reliably detected in archival material. This approach will facilitate further investigation of the role played by integrins in human malignancies and in developmental processes.

beta-1 Integrins mediate tumour cell adhesion to quiescent endothelial cells in vitro

Metastatic spread of some solid tumours is thought to depend upon the adhesion of tumour cells to the vascular endothelium followed by extravasation into surrounding tissues. We investigated the role of beta 1 integrins in the adhesion of the breast adenocarcinoma cell line MDA-MB-231 and the melanoma cell line RPMI-7951 to quiescent human umbilical vein endothelial cells (HUVEC) in vitro. In the course of adhesion assays, tumour cells were observed to adhere to quiescent HUVEC monolayers, particularly at endothelial cell-cell junctions. Immunohistochemistry revealed concentration of beta 1 integrin expression at these sites. Adhesion was reduced by pretreatment of either tumour cells or HUVEC with antibodies against beta 1 integrins. Simultaneous treatment of HUVECs and tumour cells with these antibodies produced an additive blocking effect, consistent with a heterotypic adhesion mechanism. Our data suggest that tumour cell and endothelial beta 1 integrins may play a crucial role in the arrest and migration of tumour cells through the vascular endothelium in the absence of endothelial 'activation'.

Correlation of alpha 2 beta 1 integrin expression with histological type and hormonal receptor status in breast carcinomas

Interactions between cells and extracellular matrix are mediated in part by a family of alpha beta heterodimeric molecules known as integrins. Immunohistochemical studies have shown that benign hyperplastic/neoplastic mammary epithelium expressed high levels of alpha 2 beta 1 collagen/laminin receptor. In contrast, malignant cells of breast carcinoma exhibited marked diminuition or loss of the alpha 2 beta 1 integrin. A correlation has been suggested between the loss of the alpha 2 beta 1 expression and the increased invasiveness of neoplastic cells. This study investigated the expression of alpha 2 beta 1 integrin and its extracellular ligand collagen TV by using monoclonal antibodies on the cryostat section of 124 invasive mammary carcinomas. Two patterns of alpha 2 beta 1 immunoreactivity, i.e. pericellular and basolateral, were identified in breast carcinomas and correlated with their histological type. In most invasive ductal carcinomas of no special type (NOS), integrin staining tended to decrease in both pericellular and basolateral aspects. Loss of basolateral staining for alpha 2 beta 1 integrin corresponded closely to the loss of immunoreactivity for collagen IV. Mucinous and medullary carcinomas showed strongly alpha 2 beta 1 pericellular staining, but no basolateral reactivity or collagen IV expression. Only two of the infiltrating lobular carcinomas expressed strong pericellular reactivity. In 82 ductal carcinomas NOS, the abnormally low expression/absence of alpha 2 beta 1 integrin correlated with estrogen and progesterone receptor negativity (p < 0.04 and p < 0.002, respectively). No correlation between integrin expression, histological grade, nodal involvement and proliferative activity was found. The results of the present study suggest that changes in alpha 2 beta 1 expression correlate with the histological type and hormonal receptor status in breast carcinomas. The clinical implications of these findings remain to be elucidated.