Co-ordinate expression of the alpha-6 integrin laminin receptor sub-unit and laminin in breast cancer

Correlation of Pancreatic Laminin Alpha 5 Expression With Clinical Outcomes in Total Pancreatectomy With Islet Autotransplantation

This study examines extracellular matrix (ECM) protein (ECM) expression in chronic pancreatitis (CP) patients and its correlation with graft function after total pancreatectomy with islet autologous transplantation (TPIAT). Pancreatic sections from 29 CP patients undergoing TPIAT were analyzed for ECM including pan-laminin, laminin alpha 5 (LAMA5), collagen IV, and Perlecan by immunohistochemistry and scored by the percentage positive staining area within the whole tissue area. Graft function was monitored by blood glucose and C-peptide levels. Laminin alpha 5 levels in blood plasma were greater in CP. Laminin alpha 5 expression was significantly higher in all CP patient etiological categories including alcoholic, hereditary, idiopathic, Oddi dysfunction, and pancreatic divisum compared to healthy controls. The overall expression of LAMA5 positively correlated with expression of the ECM proteins pan-laminin (R = 0.63, P < 0.001), collagen IV (R = 0.67, P < 0.001), and Perlecan (R = 0.71, P < 0.001). Increased LAMA5 expression was observed within islet endothelial vascular tissue and the peri-islet basal membrane. Increased LAMA5 expression in the pancreas correlated with poor islet isolation yield and posttransplant islet function after 3 months. Increased endothelial expression of LAMA5 and ECM proteins is indicative of progressive damage to the pancreas and correlates with poor graft function after TPIAT.

In situ proteomic analysis of human breast cancer epithelial cells using laser capture microdissection: annotation by protein set enrichment analysis and gene ontology

Identification of molecular signatures that allow detection of the transition from normal breast epithelial cells to malignant invasive cells is a critical component in the development of diagnostic, therapeutic, and preventative strategies for human breast cancer. Substantial efforts have been devoted to deciphering breast cancer etiology at the genome level, but only a limited number of studies have appeared at the proteome level. In this work, we compared individual in situ proteome profiles of nonpatient matched nine noncancerous, normal breast epithelial (NBE) samples with nine estrogen receptor (ER)-positive (luminal subtype), invasive malignant breast epithelial (MBE) samples by combining laser capture microdissection (LCM) and quantitative shotgun proteomics. A total of 12,970 unique peptides were identified from the 18 samples, and 1623 proteins were selected for quantitative analysis using spectral index (SpI) as a measure of protein abundance. A total of 298 proteins were differentially expressed between NBE and MBE at 95% confidence level, and this differential expression correlated well with immunohistochemistry (IHC) results reported in the Human Protein Atlas (HPA) database. To assess pathway level patterns in the observed expression changes, we developed protein set enrichment analysis (PSEA), a modification of a well-known approach in gene expression analysis, Gene Set Enrichment Analysis (GSEA). Unlike single gene-based functional term enrichment analyses that only examines pathway overrepresentation of proteins above a given significance threshold, PSEA applies a weighted running sum statistic to the entire expression data to discover significantly enriched protein groups. Application of PSEA to the expression data in this study revealed not only well-known ER-dependent and cellular morphology-dependent protein abundance changes, but also significant alterations of downstream targets for multiple transcription factors (TFs), suggesting a role for specific gene regulatory pathways in breast tumorigenesis. A parallel GOMiner analysis revealed both confirmatory and complementary data to PSEA. The combination of the two annotation approaches yielded extensive biological feature mapping for in depth analysis of the quantitative proteomic data.

Signalling via integrins: implications for cell survival and anticancer strategies

Integrin-associated signalling renders cells more resistant to genotoxic anti-cancer agents like ionizing radiation and chemotherapeutic substances, a phenomenon termed cell adhesion-mediated radioresistance/drug resistance (CAM-RR, CAM-DR). Integrins are heterodimeric cell-surface molecules that on one side link the actin cytoskeleton to the cell membrane and on the other side mediate cell-matrix interactions. In addition to their structural functions, integrins mediate signalling from the extracellular space into the cell through integrin-associated signalling and adaptor molecules such as FAK (focal adhesion kinase), ILK (integrin-linked kinase), PINCH (particularly interesting new cysteine-histidine rich protein) and Nck2 (non-catalytic (region of) tyrosine kinase adaptor protein 2). Via these molecules, integrin signalling tightly and cooperatively interacts with receptor tyrosine kinase signalling to regulate survival, proliferation and cell shape as well as polarity, adhesion, migration and differentiation. In tumour cells of diverse origin like breast, colon or skin, the function and regulation of these molecules is partly disturbed and thus might contribute to the malignant phenotype and pre-existent and acquired multidrug resistance. These issues as well as a variety of therapeutic options envisioned to influence tumour cell growth, metastasis and resistance, including kinase inhibitors, anti-integrin antibodies or RNA interference, will be summarized and discussed in this review.

Interferon regulatory factor-1 regulates reconstituted extracellular matrix (rECM)-mediated apoptosis in human mammary epithelial cells

Interactions between extracellular matrix (ECM) and mammary epithelial cells are critical for mammary gland homeostasis and apoptotic signaling. Interferon regulatory factor-1 (IRF-1) is a transcriptional regulator that promotes apoptosis during mammary gland involution and p53-independent apoptosis. We have recently shown that rapid cell surface tamoxifen (Tam) signaling promotes apoptosis in normal human mammary epithelial cells that were acutely damaged by expression of human papillomavirus type-16 E6 protein (*HMEC-E6). Apoptosis was mediated by recruitment of CREB-binding protein (CBP) to the gamma-activating sequence (GAS) element of the IRF-1 promoter, induction of IRF-1 and caspase-1/-3 activation. Here, we show that growth factor-depleted, reconstituted ECM (rECM), similar to Tam, promotes apoptosis in *HMEC-E6 cells through induction of IRF-1. Apoptosis was temporally associated with recruitment of CBP to the GAS element of the IRF-1 promoter, induction of IRF-1 expression and caspase-1/-3 activation. Small interfering RNA-mediated suppression of IRF-1 protein expression in *HMEC-E6 cells blocked (1) induction of IRF-1, (2) caspase-1/-3 activation and (3) apoptosis. These observations demonstrate that IRF-1 promotes rECM-mediated apoptosis and provide evidence that both rECM and rapid Tam signaling transcriptionally activate IRF-1 through recruitment of CBP to the IRF-1 GAS promoter complex.

Modulation of response to tumor therapies by the extracellular matrix

The composition of the extracellular matrix in tumors is vastly different from that found in the normal tissue counterparts. As the extracellular matrix can signal to cells via integrin binding and activation, which is known to modulate cell proliferation, survival and migration, it may influence the response of both tumor and endothelial cells to anticancer therapies. Certain tumor-associated extracellular matrix proteins have been shown to confer resistance to chemotherapeutic drugs, radiation and anti-angiogenic factors. The current literature regarding this phenomenon and the potential therapeutic modalities to overcome extracellular matrix-induced resistance will be discussed.

Integrin signaling in epithelial cells

Although most cells of adult mammals express multiple different integrins, particular types of cells have a characteristic repertoire of integrin expression. Benign and malignant epithelial cells use specific integrins to allow the epithelial microenvironment to modulate a wide variety of cell functions, including cell survival, proliferation, morphogenesis, differentiation, motility, invasion and metastasis. An important concept emerging from the data on integrin signal transduction is that integrin signaling impinges on pathways downstream of other receptors, creating elaborate intracellular signaling networks. This review highlights signal transduction functions of epithelial integrins, with particular emphasis on signaling pathways underlying some of the most important functions of epithelium.

CREB-binding protein regulates apoptosis and growth of HMECs grown in reconstituted ECM via laminin-5

Interactions between normal mammary epithelial cells and extracellular matrix (ECM) are important for mammary gland homeostasis. Loss of interactions between ECM and normal mammary epithelial cells are thought to be an early event in mammary carcinogenesis. CREB-binding protein (CBP) is an important regulator of proliferation and apoptosis but the role of CBP in ECM signaling is poorly characterized. CBP was suppressed in basal-cytokeratin-positive HMECs (CK5/6+, CK14+, CK8-, CK18-, CK19-). Suppression of CBP resulted in loss of reconstituted ECM-mediated growth control and apoptosis and loss of laminin-5 alpha3-chain expression. Suppression of CBP in normal human mammary epithelial cells (HMECs) resulted in loss of CBP occupancy of the LAMA3A promoter and decreased LAMA3A promoter activity and laminin-5 alpha-3 chain expression. Exogenous expression of CBP in CBP-negative HMECs that have lost reconstituted ECM-mediated growth regulation and apoptosis resulted in (1) CBP occupancy of the LAMA3A promoter, (2) increased LAMA3A activity and laminin-5 alpha3-chain expression, and (3) enhancement of reconstituted ECM-mediated growth regulation and apoptosis. Similarly, suppression of laminin-5 alpha3-chain expression in HMECs resulted in loss of reconstituted ECM-mediated growth control and apoptosis. These observations suggest that loss of CBP in basal-cytokeratin-positive HMECs results in loss of reconstituted ECM-mediated growth control and apoptosis through loss of LAMA3A activity and laminin-5 alpha3-chain expression. Results in these studies may provide insight into early events in basal-type mammary carcinogenesis.

Integrin alpha6beta4-erbB2 complex inhibits haptotaxis by up-regulating E-cadherin cell-cell junctions in keratinocytes

Keratinocyte integrins alpha6beta4 and alpha3beta1 bind laminin-5, a component of basement membranes. We previously demonstrated that in keratinocytes, haptotactic migration on laminin-5 was stimulated by anti-beta1 integrin-activating antibody TS2/16, whereas antibodies to alpha6 and beta4, respectively, blocked TS2/16-induced, alpha3beta1-dependent migration. Moreover, alpha6beta4-associated haptotaxis inhibition was linked to a phosphatidylinositol 3-kinase (PI3K) pathway and required erbB2 activation. erbB2, the ligand-less member of the epidermal growth factor receptor family, was shown to form a complex with the hemidesmosomal integrin alpha6beta4. Here, we demonstrate that alpha6beta4 inhibitory effects on haptotaxis are abolished by an anti-E-cadherin antibody, which interferes with cell-cell adhesion. Furthermore, antibodies to alpha6 and beta4 stimulated adhesion to an E-cadherin-Fc recombinant protein. In addition, anti-alpha6/beta4 antibodies increased colony size in plated cells, stimulated cell-cell aggregation, and up-regulated E-cadherin localization to cell-cell contacts. These effects were abolished when erbB2 or PI3K were blocked. These results indicate that stimulation of alpha6beta4 increases E-cadherin-mediated cell-cell adhesion and that this mechanism depends on erbB2 activation. The molecule that links alpha6beta4 with E-cadherin may be the small GTPase cdc42, an effector of PI3K, because dominant-negative cdc42 abolished the inhibitory effect of anti-alpha6/beta4 antibodies and increased basal migration, whereas constitutively active cdc42 prevented the TS2/16-induced increase in haptotaxis. These findings suggest a model whereby alpha6beta4 can augment cell-cell adhesion and slow down haptotaxis over laminin-5 and point to the alpha6beta4-erbB2 heterodimer as an important signaling complex for the formation of cohesive keratinocyte layers.

Modeling breast cancer in vivo and ex vivo reveals an essential role of Pin1 in tumorigenesis

Phosphorylation on certain Ser/Thr-Pro motifs is a major oncogenic mechanism. The conformation and function of phosphorylated Ser/Thr-Pro motifs are further regulated by the prolyl isomerase Pin1. Pin1 is prevalently overexpressed in human cancers and implicated in oncogenesis. However, the role of Pin1 in oncogenesis in vivo is not known. We have shown that Pin1 ablation is highly effective in preventing oncogenic Neu or Ras from inducing cyclin D1 and breast cancer in mice, although it neither affects transgene expression nor mammary gland development. Moreover, we have developed an ex vivo assay to uncover that a significant fraction of primary mammary epithelial cells from Neu or Ras mice display various malignant properties long before they develop tumors in vivo. Importantly, these early transformed properties are effectively suppressed by Pin1 deletion, which can be fully rescued by overexpression of cyclin D1. Thus, Pin1 is essential for tumorigenesis and is an attractive anticancer target. Our ex vivo assay can be used to study early events of breast cancer development in genetically predisposed mice.

Prognostic Significance of Laminin, Laminin Receptor, and Bone Marrow Micrometastases in Breast Cancer Patients

Laminin is a basement membrane glycoprotein implicated in a large number of biologic activities of cancer progression, many of which are mediated by the presence of the laminin receptor (67LR) on the cell membrane. We studied the correlations of laminin and its receptor with standardized and new prognostic factors (including bone marrow micrometastases) in a series of 112 patients with operable breast cancers. Laminin-positive cells were detected in 60% of the tumors and 67LR-positive cells in 55%; both were present in 35% of the cases. No association was found between laminin or 67LR positivity and pathologic tumor size, pathologic nodal status, grading, Ki-67, estrogen receptor status, progesterone receptor status, or bone marrow micrometastases. The only statistically significant association was with menopausal status and age, with a higher percentage of 67LR-positive tumors among premenopausal and younger patients. The median follow-up was approximately 7 years. The prognosis of disease-free survival was similar in the laminin-positive and laminin-negative subjects but was significantly better in 67LR-negative patients; there were no significant differences in overall survival. The prognostic role of laminin and 67LR in disease-free survival and overall survival varied according to nodal status. In the absence of nodal involvement, the risk of relapse (and death) was greater in the patients who were positive for laminin, 67LR, or both than in those who were negative for laminin, 67LR, or both; in the case of 4 or more involved nodes, the prognostic role of laminin and 67LR was reversed. These results did not change after adjustment for age, menopausal status, tumor status, nodal status, grading, or bone marrow micrometastases.

Regulation of mammary gland branching morphogenesis by the extracellular matrix and its remodeling enzymes

A considerable body of research indicates that mammary gland branching morphogenesis is dependent, in part, on the extracellular matrix (ECM), ECM-receptors, such as integrins and other ECM receptors, and ECM-degrading enzymes, including matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of metalloproteinases (TIMPs). There is some evidence that these ECM cues affect one or more of the following processes: cell survival, polarity, proliferation, differentiation, adhesion, and migration. Both three-dimensional culture models and genetic manipulations of the mouse mammary gland have been used to study the signaling pathways that affect these processes. However, the precise mechanisms of ECM-directed mammary morphogenesis are not well understood. Mammary morphogenesis involves epithelial 'invasion' of adipose tissue, a process akin to invasion by breast cancer cells, although the former is a highly regulated developmental process. How these morphogenic pathways are integrated in the normal gland and how they become dysregulated and subverted in the progression of breast cancer also remain largely unanswered questions.

Cell-matrix interactions during development and apoptosis of the mouse mammary gland in vivo

Epithelial cell survival is dependent on extracellular signals provided by both soluble factors and by adhesion. In the mammary gland, extensive apoptosis of epithelial cells occurs rapidly when lactation ceases, but the mechanism of apoptosis induction is not known. In tissue culture, mammary epithelial cells require laminin as a survival ligand and specific beta1 integrins are necessary to suppress apoptosis. To explore the possibility that dynamic changes in cell-matrix interactions contribute to the onset of apoptosis during mammary involution in vivo, a detailed immunohistochemical analysis of the expression of integrin subunits and their extracellular matrix ligands during mouse mammary gland development has been performed. The kinetics of apoptosis were determined by using tissue samples obtained from virgin, pregnant, lactating, and involuting gland. The maximal elevation of apoptosis occurred within 24 hr of weaning as determined by histologic analysis and caspase-3 staining. A wide variety of laminin subunits, together with nidogen-1 and -2, and perlecan were identified within the basement membrane region of epithelial ducts, lobules, and alveoli in both human and mouse mammary gland. However, no change in the distribution of any of the basement membrane proteins or their cognate integrin receptors was observed during the transition from lactation to apoptosis. Instead, we discovered that altered ligand-binding conformation of the beta1 integrin to a nonbinding state coincided with the immediate onset of mammary apoptosis. This finding may provide a novel dynamic mechanism for inhibiting the transduction of extracellular matrix survival signals, thereby contributing to the onset of apoptosis in a developmental context in vivo.

Significance of alpha 9 beta 1 and alpha v beta 6 integrin expression in breast carcinoma

BACKGROUND

Both alpha 9 beta 1 and alpha v beta 6 integrins have been newly identified from the tracheal epithelium of guinea pig. It has been pointed out that alpha 9 beta 1 functions as a receptor for tenascin-C and osteopontin. As for the ligands of alpha v beta 6, fibronectin and tenascin-C have been identified. It has not been ascertained whether alpha 9 beta 1 and alpha v beta 6 are expressed in normal breast tissue, benign breast lesion or breast carcinoma.

METHODS

Immunohistochemical staining for alpha 9 beta 1 and alpha v beta 6 was performed in benign breast lesion and breast carcinoma specimens. Western blotting was carried out on 11 breast carcinoma cases.

RESULTS

alpha 9 beta 1 was expressed in the cytoplasm of carcinoma cells in 23 of 90 cases (26%) and alpha v beta 6 in the membrane of carcinoma cells in 16 of 90 cases (18%). However, these findings of alpha 9 beta 1 and alpha v beta 6 did not correlate with any clinicopathological factors including the patients' age, tumor size, histological type of carcinoma, location of carcinoma cells and hormone receptor status. With regard to the histological grade of carcinoma, alpha v beta 6 and alpha 9 beta 1 expression did not statistically correlate, although no expression of alpha v beta 6 was observed in 14 cases of Grade I. On Western-blott analysis strong and weak bands consistent with alpha v beta 6 were noted in the membrane fraction extracted from breast carcinoma cells. On the other hand weak bands consistent with alpha 9 subunit were noted in the whole cell lysates of breast carcinoma cells and very weak or no bands consistent with alpha 9 subunit were noted in the membrane fraction extracted from the breast carcinoma cells.

CONCLUSIONS

Significance of alpha 9 beta 1 and alpha v beta 6 integrins expression in breast carcinoma was still unknown on clinicopathological examination. The findings of Western blot analysis may indicate that the transportation system of glycoproteins such as integrins to the cell membrane of carcinoma cells is disturbed, although these integrins can be produced.

Laminin and beta1 integrins are crucial for normal mammary gland development in the mouse

We have examined the role of integrin-extracellular matrix interactions in the morphogenesis of ductal structures in vivo using the developing mouse mammary gland as a model. At puberty, ductal growth from terminal end buds results in an arborescent network that eventually fills the gland, whereupon the buds shrink in size and become mitotically inactive. End buds are surrounded by a basement membrane, which we show contains laminin-1 and collagen IV. To address the role of cell-matrix interactions in gland development, pellets containing function-perturbing anti-beta1 integrin, anti-alpha6 integrin, and anti-laminin antibodies respectively were implanted into mammary glands at puberty. Blocking beta1 integrins dramatically reduced both the number of end buds per gland and the extent of the mammary ductal network, compared with controls. These effects were specific to the end buds since the rest of the gland architecture remained intact. Reduced development was still apparent after 6 days, but end buds subsequently reappeared, indicating that the inhibition of beta1 integrins was reversible. Similar results were obtained with anti-laminin antibodies. In contrast, no effect on morphogenesis in vivo was seen with anti-alpha6 integrin antibody, suggesting that alpha6 is not the important partner for beta1 in this system. The studies with beta1 integrin were confirmed in a culture model of ductal morphogenesis, where we show that hepatocyte growth factor (HGF)-induced tubulogenesis is dependent on functional beta1 integrins. Thus integrins and HGF cooperate to regulate ductal morphogenesis. We propose that both laminin and beta1 integrins are required to permit cellular traction through the stromal matrix and are therefore essential for maintaining end bud structure and function in normal pubertal mammary gland development.

Chemokines induce the cellular migration of MCF-7 human breast carcinoma cells: subpopulations of tumour cells display positive and negative chemotaxis and differential in vivo growth potentials

We previously reported that chemotactic cytokines (chemokines) induce the directional migration of cells derived from the breast carcinoma cell line MCF-7 in vitro, however it was apparent that only a small percentage of cells displayed the ability to migrate upon stimulation. In the present study three sub-lines derived from the parental MCF-7 cell line were selected for their ability to migrate in response to MIP-1alpha, MIP-1beta or RANTES across Transwell filters of 8 microm pore size. The first round selection of migratory cells resulted in sub-populations which demonstrated an increased chemotactic response compared with parental cells. Cells migrating to MIP-1beta were subjected to four further rounds of positive or negative selection, resulting in two sub-lines, MCF-7L4 and MCF-7U4 which displayed an increased and decreased chemotactic response respectively to MIP-1alpha MIP-1beta and RANTES. No difference in chemokine receptor RNA message expression between these sub-lines and the parental MCF-7 line were detected, although increased levels of alpha3, alpha6 and alphav integrin sub-units were shown for MCF-7L4 (positively selected sub-line) compared with MCF-7U4 cells. Moreover, the in vivo growth of cells derived from the two MCF-7 sub-lines was inversely correlated with their chemotactic response. The results of this study depict further the inherent heterogeneity in cancer, suggesting that the chemotactic response may influence the migratory traits of sub-populations within the tumour and potentially contribute to their in vivo behavior, growth and survival.

Alteration of integrin expression in oral squamous cell carcinomas

OBJECTIVE

This study examines the intensity of expression of beta 1, alpha 2, alpha 3, alpha 5, alpha 6 integrin subunits in oral squamous cell carcinoma (SCC) as opposed to normal oral epithelium, and the intensity of expression and distribution pattern of the above subunits in relation to tumour differentiation grade.

MATERIALS AND METHODS

Cryostat sections of 25 cases of oral SCC and 15 cases of normal oral epithelium were studied by immunohistochemistry (APAAP method).

RESULTS

The intensity of expression of beta 1, alpha 2 (Pearson chi 2 P < 0.001) and alpha 6 (Test for Trend P < 0.05) integrin subunits was reduced significantly in SCC compared to normal oral epithelium. All integrin subunits were mainly expressed in the peripheral cell layer of tumour islands. No correlation was found between the intensity of integrin expression and the degree of differentiation in SCC. The same applied to the distribution pattern of the integrin subunits. By means of cross examination of all integrins, the loss of intensity of alpha 2 beta 1 integrin expression was found to have the strongest correlation with oral SCC (Ordered Logistic Regression).

CONCLUSIONS

Reduced intensity of expression of all subunits was found in oral SCC compared to normal epithelium. Further investigation is needed to determine whether alpha 2 beta 1 integrin expression can be used as a prognostic evaluator for the behaviour of the disease.

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.

In situ hybridization analysis of genes coding collagen IV alpha1 chain, laminin beta1 chain, and S-laminin in prostate tissue and prostate cancer: increased basement membrane gene expression in high-grade and metastatic lesions

BACKGROUND

Recent immunohistochemical data have shown that invasive prostate cancer cells are separated from the host tissue by basement membranes (BM), and express associated adhesive molecules that bind to these de novo synthesized extracellular matrices.

METHODS

In the present study, we used in situ hybridization techniques to determine steady-state levels of genes coding BM components (alpha1 chain of collagen IV, laminin beta1 chain, and S-laminin) in prostate tissue obtained from 15 radical prostatectomy specimens and 5 lymph node metastases of common prostatic adenocarcinomas.

RESULTS

In benign prostate tissue, transcripts of these genes were detected predominantly in the basal cell layer, indicating that components of epithelial BMs are synthesized by basal cells and not by stromal cells. The cancerous lesions investigated revealed increasing collagen IV, laminin beta1 chain, and S-laminin mRNA levels when compared with benign prostate tissue. The highest steady-state levels were found in high grade (primary Gleason grade 4 and 5) carcinoma and lymph node metastases, and were predominantly localized in epithelial compartments of the cancerous tissue.

CONCLUSIONS

These findings indicate that neoplastic BM in prostatic adenocarcinoma derive from tumor cells and not from the host tissue. Increasing transcriptional activities of genes coding BM components detected in poorly differentiated and metastatic lesions may accelerate the BM-forming process, which probably contributes to the ability of tumor cells to penetrate the extracellular matrix during the process of stromal invasion and metastasis.

Altered expression of alpha 6 integrin subunit in oral squamous cell carcinoma and oral potentially malignant lesions

The expression and distribution of integrin chains alpha 2, alpha 3, alpha 5, alpha 6, beta 1, beta 4, collagen type IV, laminin 1 and laminin 5 in oral squamous cell carcinoma (SCC) and oral keratoses with and without dysplasia (OL) have been studied by immunochemistry and western blotting. Focal interruptions of basement membrane protein staining were detected in SCC indicating a loss of continuity, whereas tumour nests were apparently completely surrounded by laminin 1, type IV collagen and laminin 5; the loss of basement membrane components in OL was found in only one specimen showing severe dysplasia. The localisation of integrins showed altered suprabasal and pericellular expression of the alpha 6 chain in all but one SCC, as well as in many OL samples, whereas the beta 4 subunit showed only a faint pericellular redistribution in SCC. In OL, beta 4 was often seen in a normal basally polarised distribution. Western blotting analysis confirmed that alpha 6 protein levels were abnormally high in cancerous lesions, whereas quantitative recovery of the beta 4 subunit in SCC was only minimal, suggesting a dissociation in the synthetic ratios of the two chains of the alpha 6 beta 4 heterodimer in SCC. Because alterations in the polarised expression of integrin alpha 6 beta 4 have been seen during epithelial tumour progression and wound healing, we suggest that the lack of restricted basal polarisation of alpha 6 could be an early but non-specific marker of oral malignancy, indicating that the generation of abnormal signals from the extracellular matrix may be involved.

Control of normal mammary epithelial phenotype by integrins

Mammary epithelial cells contact a specialized extracellular matrix in vivo known as the basement membrane. Interactions with extracellular matrix are mediated through integrins. These cell surface receptors are involved with the formation of adhesion complexes, which link the extracellular matrix with the actin-based cytoskeleton, and are also associated with components of growth factor signaling pathways. Differentiation of breast epithelia into lactational cells requires appropriate hormones and integrin-mediated interactions with basement membrane. Integrins may regulate the ability of lactogenic hormones to trigger their intracellular signaling pathways.

The spectrum of 67-kD laminin receptor expression in breast carcinoma progression

Laminin is a glycoprotein of the basement membrane (BM), involved in a variety of normal and pathological cellular events including tumour invasion and metastasis. Cells bind laminin through different types of receptor. The 67-kD laminin receptor (67LR) is a cell-surface protein which binds laminin with high affinity. 67LR expression has been shown to increase in neoplastic cells, compared with normal tissues, and 67LR seems to play an important role during the first steps of neoplastic progression. In this study, 67LR expression was analysed during the morphological phases of breast cancer progression from normal tissue to invasive carcinoma. A total of 506 formalin-fixed, paraffin-embedded normal breast structures and lesions were stained by immunohistochemistry usign the MLuC5 monoclonal antibody, which is specific for 67LR. The results show that in normal breast and in any kind of breast lesion, myoepithelial and endothelial cells express 67LR. While 67LR is not seen in the epithelium of normal breast, cysts, adenosis, and benign tumours, it is expressed in the epithelial cells of several hyperplasias and carcinomas in situ, both ductal and lobular, as well as in all invasive carcinomas. The 67LR-positive cell subpopulation expands from hyperplastic lesions to invasive carcinoma, suggesting that 67LR could be related to the induction and progression of breast cancer.

Reversion of the malignant phenotype of human breast cells in three-dimensional culture and in vivo by integrin blocking antibodies

In a recently developed human breast cancer model, treatment of tumor cells in a 3-dimensional culture with inhibitory beta1-integrin antibody or its Fab fragments led to a striking morphological and functional reversion to a normal phenotype. A stimulatory beta1-integrin antibody proved to be ineffective. The newly formed reverted acini re-assembled a basement membrane and re-established E-cadherin-catenin complexes, and re-organized their cytoskeletons. At the same time they downregulated cyclin D1, upregulated p21(cip,wat-1), and stopped growing. Tumor cells treated with the same antibody and injected into nude mice had significantly reduced number and size of tumors in nude mice. The tissue distribution of other integrins was also normalized, suggesting the existence of intimate interactions between the different integrin pathways as well as adherens junctions. On the other hand, nonmalignant cells when treated with either alpha6 or beta4 function altering antibodies continued to grow, and had disorganized colony morphologies resembling the untreated tumor colonies. This shows a significant role of the alpha6/beta4 heterodimer in directing polarity and tissue structure. The observed phenotypes were reversible when the cells were disassociated and the antibodies removed. Our results illustrate that the extracellular matrix and its receptors dictate the phenotype of mammary epithelial cells, and thus in this model system the tissue phenotype is dominant over the cellular genotype.

Changes in the expression of alpha v integrins in oral squamous cell carcinomas

Integrins are cell surface adhesion molecules that regulate normal cellular interactions; aberrant integrin expression is believed to play a role in tumour invasion and metastasis. The alpha v subunit is capable of forming heterodimers with several beta subunits but not all the heterodimers expressed in oral epithelium have been investigated. We have examined the distribution of alpha v integrins in normal buccal mucosa and seventeen oral squamous cell carcinomas. Antibodies to the alpha v subunit and alpha v beta 5 heterodimer stained normal epithelium, with strong expression in the basal layers and weaker staining in the more superficial layers. The beta 3 and beta 6 subunits were not expressed in normal epithelium. Anti-alpha v and anti-alpha v beta 5 antibodies stained all the squamous cell carcinomas, but the pattern of expression was variable both within and between tumours. Poorly differentiated tumours showed the weakest staining and often had areas showing loss of expression. beta 6 was expressed in all of the carcinomas, indicating new expression of the alpha v beta 6 integrin in malignant oral epithelium. These results suggest that alterations in alpha v integrins may contribute to the behaviour of malignant epithelium and that alpha v beta 6 expression may play a role in tumour progression.

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.

Cell adhesion molecules in the normal and cancerous mammary gland

Loss of normal tissue morphology is one of the first changes seen in the development of solid malignant tumours, including breast cancers. Since cell adhesion molecules play a crucial role in maintaining normal tissue architecture, investigations into the molecular mechanisms involved in the morphological changes occurring in malignancy that focus on the expression and function of cell adhesion molecules in malignant progression are extremely relevant. This review discusses the cadherin and integrin families of adhesion molecules which have been shown to be extremely important in the cell-cell and cell-matrix interactions of epithelial cells. Immunohistochemical studies using tissue and tumour sections indicate that a reduction in levels of expression or function of both types of cell adhesion molecules is indeed observed in many breast cancers. A specific and crucial role for these molecules in the maintenance of normal morphological differentiation has been demonstrated in vitro, where the noninvasive differentiated phenotype correlates with the normal functioning of E-Cadherin and alpha 2 beta 1 integrin. Further in vitro evidence suggests that in mammary epithelial cells, oncogenes may be upstream regulators of both the expression and function of E-Cadherin, the alpha 2 beta 1 integrin, and other epithelial specific molecules important for maintaining epithelial differentiation. In this way they could manifest their effects on the tumorigeneic potential of epithelial cells.

IL-4 and TNF-alpha induce changes in integrin expression and adhesive properties and decrease the lung-colonizing potential of HT-29 colon carcinoma cells

The colon carcinoma cell line HT-29 was used to explore the potential of interleukin-4 (IL-4) and tumor necrosis factor alpha (TNF-alpha) to modify integrin expression and adhesive functions of tumor cells in vitro and to examine corresponding metastatic effects in vivo. Preincubation of HT-29 cells with 100 U/ml of IL-4 for 48 h downregulated the surface expression of the integrin subunits alpha 2, alpha 3, beta 1 and beta 4 after 48 h, whereas the alpha 1 subunit was upregulated. In contrast, 100 U/ml to TNF-alpha selectively upmodulated the expression of alpha v. Attachment to fibronectin of cells treated with IL-4 increased twofold (63.5% vs 32.4%). Adhesion to fibronectin (54.0% vs 32.4%) and vitronectin (37.9% vs 16.4%) was elevated in the case of TNF-alpha stimulation. Using an experimental metastasis model, HT-29 cells showed a significant reduction of their lung-colonizing potential in nude mice when preincubated with IL-4 for 48 h before intravenous injection. The decrease also observed for TNF-alpha-treated cells was less pronounced. The data indicate that the cytokines IL-4 and TNF-alpha can act as direct regulators of adhesive mechanisms of tumor cells bearing adequate receptors, thus influencing lung-colony formation.

The importance of the microenvironment in breast cancer progression: recapitulation of mammary tumorigenesis using a unique human mammary epithelial cell model and a three-dimensional culture assay

The extracellular matrix (ECM) is a dominant regulator of tissue development and homeostasis. "Designer microenvironments" in culture and in vivo model systems have shown that the ECM regulates growth, differentiation, and apoptosis in murine and human mammary epithelial cells (MEC) through a hierarchy of transcriptional events involving the intricate interplay between soluble and physical signaling pathways. Furthermore, these studies have shown that these pathways direct and in turn are influenced by the tissue structure. Tissue structure is directed by the cooperative interactions of the cell-cell and cell-ECM pathways and can be modified by stromal factors. Not surprisingly then, loss of tissue structure and alterations in ECM components are associated with the appearance and dissemination of breast tumors, and malignancy is associated with perturbations in cell adhesion, changes in adhesion molecules, and a stromal reaction. Several lines of evidence now support the contention that the pathogenesis of breast cancer is determined (at least in part) by the dynamic interplay between the ductal epithelial cells, the microenvironment, and the tissue structure (acini). Thus, to understand the mechanisms involved in carcinogenesis, the role of the microenvironment (ECM as well as the stromal cells) with respect to tissue structure should be considered and studied. Towards this goal, we have established a unique human MEC model of tumorigenesis, which in concert with a three-dimensional assay, recapitulates many of the genetic and morphological changes observed in breast in cancer in vivo. We are currently using this system to understand the role of the microenvironment and tissue structure in breast cancer progression.

Altered expression of extracellular matrix molecules and their receptors in chronic pancreatitis and pancreatic adenocarcinoma in comparison with normal pancreas

The aim of this study was to elucidate the expression and distribution patterns of both integrins and extracellular matrix (ECM) molecules in chronic pancreatitis (CP) and pancreatic adenocarcinoma (PC) compared with normal pancreas (NP). Expression of nine alpha-subunits (alpha 2-alpha 6, alpha V, alpha L, alpha M, and alpha X), four beta-subunits (beta 1, beta 3-beta 5), and four ECM molecules (type IV collagen, laminin, fibronectin, and vitronectin) was investigated immunohistochemically. In CP, all integrins except alpha V showed nearly the same staining patterns compared with NP. Some acinar cells in CP expressed alpha V. Whereas alpha 2, alpha 3, and alpha 6 expression was stronger and diffuse, no alpha 5 expression was seen in PC. Basement membrane (BM) showed continuous staining in CP, whereas it showed discontinuous/absent staining in PC with antitype IV collagen, laminin, and vitronectin antibodies. Some carcinoma cells showed reverse correlation between alpha 2, alpha 3, and alpha 6 expression and type IV collagen and laminin expression. Fibronectin showed diffuse stromal expression in CP and PC. Some acinar cells or duct cells in CP carcinoma cells in PC showed intracellular VN expression. These results suggest that these integrins and ECM molecules are involved in inflammatory and malignant processes in pancreas.

Control of integrin expression by extracellular matrix

Integrin-mediated interactions between cells and the extracellular matrix play a fundamental role in the development and function of a variety of tissues by triggering intracellular signals that regulate gene expression. In this study, mouse mammary epithelial cells plated on tissue culture plastic were shown to dramatically up-regulate the steady state levels of mRNA encoding the alpha 1, alpha 2, alpha 3, alpha 5, alpha 6, alpha 7, alpha v, and beta 1 integrin subunits, in contrast to cells cultured on a basement membrane matrix or cells in vivo. This pattern of expression was also observed in a mouse mammary epithelial strain, CID-9 and in other mouse cell lines such as MMTE cells and K1735-M2 melanoma cells. The control of integrin expression was mediated at different levels in different cell types. In K1735-M2 cells, transcription of the beta 1 integrin gene was influenced by the substratum, although the levels of integrin protein remained similar. In mammary epithelial cells, the rates of beta 1 integrin gene transcription were similar, but mRNA and protein levels were higher in cells cultured on plastic than those on basement membrane. For both cell types, the rate of integrin protein turnover was nearly identical in cells cultured on either substratum. Our results demonstrate that extracellular matrix controls the expression of beta 1 integrin subunits and that this regulation is exerted at both transcriptional and post-transcriptional levels.

Integrin alpha 6 expression in human prostate carcinoma cells is associated with a migratory and invasive phenotype in vitro and in vivo

Cell adhesion and migration are important features in tumor invasion, being mediated in part by integrins (extracellular matrix receptors). Integrins are significantly decreased in human prostate cancer. An exception is alpha 6 integrin (laminin receptor) which persists during prostate tumor progression. We have selected high (DU-H) and low (DU-L) expressors of alpha 6 integrin from a human prostate tumor cell line, DU145, to assess experimentally the importance of alpha 6 integrin in tumor invasion. DU-H cells exhibited a four-fold increased expression of alpha 6 integrin on the surface compared to DU-L cells. Both cell types contained similar amounts of alpha 3 and alpha 5 integrin. The DU-H cells contained alpha 6 subunits complexed with both the beta 1 and beta 4 subunits whereas DU-L cells contained alpha 6 complexed only with beta 4. DU-H cells were three times more mobile on laminin as compared to DU-L, but adhered similarly on laminin. Adhesion and migration were inhibited with anti-alpha 6 antibody. Each subline was injected intraperitoneally into SCID mice to test its invasive potential. Results showed greater invasion of DU-H compared to DU-L cells, with increased expression of alpha 6 integrin on the tumor at the areas of invasion. These data suggest that alpha 6 integrin expression is advantageous for prostate tumor cell invasion.

The alpha 6 beta 1 and alpha 6 beta 4 integrins in human prostate cancer progression

Prostatic secretions are formed by glands composed of basal and luminal cells and surrounded by a basal lamina. The normal basal cells express several integrins (extracellular matrix receptors) including alpha 2, 3, 4, 5, 6, v, beta 1 and beta 4. These integrin units are polarized at the base of the cells adjacent to the basal lamina. The integrin alpha 6 beta 4 is associated with hemidesmosomal-like structures. The natural history of prostate cancer involves the presence of prostatic intraepithelial neoplasia (PIN) lesions (considered precursor lesions), carcinoma in situ and invasive carcinoma. Hemidesmosomal proteins and the alpha 3 beta 1 and alpha 6 beta 1 integrins (laminin receptors) are retained in the early PIN lesions. Expression of the integrins alpha 2, alpha 4, alpha 5, alpha v and beta 4 is lost in carcinoma. The alpha 3 beta 1 and alpha 6 beta 1 integrins remain associated with invasive carcinoma, the latter being predominant. Integrin expression in carcinoma is diffuse in the plasma membrane and not restricted to the basal aspects of the cell. The alpha 6 beta 1 integrin is fully functional as judged by an ability to adhere to laminin and contains the wild type alpha 6A cytoplasmic signaling domain. The alpha 6 beta 1 integrin is a leading candidate for conferring the invasive phenotype in prostatic carcinoma. Tumor cells with high expression of alpha 6 integrin are more invasive when tested in a SCID mouse model system. Following intraperitoneal injection, the human tumor cells invade the mouse diaphragm and move through the muscle on the surface of the laminin coated muscle cells. Our current working hypothesis is that the production of alpha 6 beta 1 and laminin in human tumor cells contributes to the invasive phenotype. Invasion could occur on the surfaces of laminin coated structures such as the nerves, blood vessels or muscle and account for the known patterns of human prostate tumor progression. Blockage of the expression or function of alpha 6 beta 1 or laminin or preventing the loss of beta 4 would be essential steps in confining the carcinoma to the prostate gland where conventional treatment has already proven effective.

Integrin receptors and their relationship to cellular proliferation and differentiation of oral squamous cell carcinoma. A quantitative immunohistochemical study

The expression of extracellular matrix (ECM) proteins (fibronectin, laminin, collagen IV) and ECM receptors of integrin type (alpha 2 beta 1, collagen receptor; alpha 6 chain of the fibronectin receptor; alpha 6 chain of the laminin receptor) were examined in normal oral squamous epithelium and in invasive areas of squamous cell carcinomas with various differentiation and proliferation activities (Ki-67 antigen labelling), evaluating the presence, quantity (using an image analysis system) and distribution of the integrin subunits. In the mucosa, there was uniform immunostaining for alpha 2 beta 1 and alpha 6 concentrated at the cell membrane in the basal/supra basal cell zone, whereas, alpha 5 showed a discontinuous staining of the basal cell-basement membrane interface. alpha 2 and alpha 6 could be visualized in all carcinomas. alpha 5 showed low expression preferentially in less differentiated carcinomas. In contrast to normal mucosa, there was an increase in alpha 6 staining in well-differentiated carcinomas. Dedifferentiation of oral carcinomas was accompanied by an increase in cellular proliferation and with a decrease in alpha 2 beta 1 and alpha 6 staining. This reduction of alpha 6 staining was shown to be statistically significant, suggesting that this integrin may be a valuable grading parameter for oral squamous cell carcinoma.

Prognostic significance of laminin production in relation with its receptor expression in human breast carcinomas

Laminin is a basement membrane glycoprotein whose expression has been widely related to cancer progression. Laminin production by primary breast carcinomas was investigated using immunohistochemistry on archival specimens from a retrospective series with long term follow-up. Laminin production was found to be independent of the clinical and pathological variables analyzed, whereas a statistically significant direct association with the expression of the laminin receptor and a negative association with the differentiation-related antigen Ca-MBr8 were observed. Survival analysis indicated that laminin positivity by itself has no prognostic significance. However, when analyzed together with the laminin receptor expression, laminin was associated with a good prognosis in receptor-negative tumors and with the worst prognosis in receptor-positive tumors.

Expression of integrin subunits in the human infant breast correlates with morphogenesis and differentiation

Integrins are widely expressed on normal tissues and their function is considered critical directly or indirectly with the control of cell growth and differentiation. Also, they are likely to play a crucial role in cell-matrix interactions during development. As the human breast develops after birth, it provides a rare opportunity in which to study human organogenesis. We have examined the distribution of integrins in the human infant breast with the aim of elucidating the possible role of these molecules in morphogenesis and differentiation. Necropsy breast specimens from six male and eight female infants, ranging in age from 1 day to 9 months, were used in this study. Cryostat sections were stained by the avidin-biotin complex technique, using a panel of monoclonal antibodies (MAbs) which recognize beta 1, alpha 2, alpha 6, beta 4, alpha v, and alpha v beta 3 integrin chains, which are candidate molecules for a role in mammory morphogenesis. MAbs to beta 1 (DH12) and alpha 2 (HAS3) showed positive membrane and cytoplasmic staining of basal cells and luminal epithelial cells. In addition, positive staining for the beta 1 integrin chain was found on fibroblasts. A MAb which recognizes the alpha 6 chain (MP4F10) showed positive staining of the basal cells and heterogeneous staining of the luminal epithelial cells, whilst beta 4 chain (439-9B) showed positive staining in the basement membrane domain of the basal cells with no staining of the luminal epithelial cells. There was a positive correlation between the intensity of expression and the structural development of the ductal system, with integrin expression reduced or absent in the end buds and lateral buds.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of beta 1 integrins in adhesion of two breast carcinoma cell lines to a model endothelium

Interactions between tumour cells and the endothelium are vital to the formation of haematogenous metastases. Binding to model endothelium of one oestrogen receptor positive breast carcinoma cell line (MCF-7) and one receptor negative line (HS578T) was examined in vitro together with endothelial retraction induced by these tumour cells. Adhesion was inhibited by monoclonal antibodies specific for the VLA integrins and by peptides containing the RGD motif which is commonly recognised as a ligand by the VLA adhesion molecules. However, binding of the two tumour cell lines was inhibited by monoclonal antibodies specific for different VLA molecules; anti-alpha 6 beta 1 inhibited MCF-7 adhesion but anti-alpha 5 beta 1 inhibited Hs578T. These results were consistent with flow cytometric quantification of the expression of these VLA integrins on the surfaces of the two tumour cell lines. Enzyme-linked immunosorbent assays (ELISA) demonstrated that laminin was present on the endothelial cell surface but collagen IV was absent. ELISA failed to detect increased exposure of the subendothelial matrix during the first hour after addition of either cancer cell type. This was supported by assays which demonstrated maintenance of the endothelial permeability barrier during this period. Slight endothelial retraction was detected within 2 hours of the addition of tumour cells. It is concluded that binding between tumour cells and confluent endothelium is inhibited by the blockade of adhesion molecules which are normally associated with interactions between the cell and the subendothelial matrix. Tumour cell to matrix interactions rather than direct tumour to endothelial cell adhesion may be the limiting step in tumour cell binding to the endothelium.

Cellular growth and survival are mediated by beta 1 integrins in normal human breast epithelium but not in breast carcinoma

We previously established a rapid three-dimensional assay for discrimination of normal and malignant human breast epithelial cells using a laminin-rich reconstituted basement membrane. In this assay, normal epithelial cells differentiate into well-organized acinar structures whereas tumor cells fail to recapitulate this process and produce large, disordered colonies. The data suggest that breast acinar morphogenesis and differentiation is regulated by cell-extra-cellular matrix (ECM) interactions and that these interactions are altered in malignancy. Here, we investigated the role of ECM receptors (integrins) in these processes and report on the expression and function of potential laminin receptors in normal and tumorigenic breast epithelial cells. Immunocytochemical analysis showed that normal and carcinoma cells in a three-dimensional substratum express profiles of integrins similar to normal and malignant breast tissues in situ. Normal cells express alpha 1, alpha 2, alpha 3, alpha 6, beta 1 and beta 4 integrin subunits, whereas breast carcinoma cells show variable losses, disordered expression, or downregulation of these subunits. Function-blocking experiments using inhibitory anti-integrin subunit antibodies showed a &gt; 5-fold inhibition of the formation of acinar structures by normal cells in the presence of either anti-beta 1 or anti-alpha 3 antibodies, whereas anti-alpha 2 or -alpha 6 had little or no effect. In experiments where collagen type I gels were used instead of basement membrane, acinar morphogenesis was blocked by anti-beta 1 and -alpha 2 antibodies but not by anti-alpha 3. These data suggest a specificity of integrin utilization dependent on the ECM ligands encountered by the cell. The interruption of normal acinar morphogenesis by anti-integrin antibodies was associated with an inhibition of cell growth and induction of apoptosis. Function-blocking antibodies had no inhibitory effect on the rate of tumor cell growth, survival or capacity to form colonies. Thus under our culture conditions breast acinar formation is at least a two-step process involving beta 1-integrin-dependent cellular growth followed by polarization of the cells into organized structures. The regulation of this pathway appears to be impaired or lost in the tumor cells, suggesting that tumor colony formation occurs by independent mechanisms and that loss of proper integrin-mediated cell-ECM interaction may be critical to breast tumor formation.

Integrin expression in primary breast cancer and its relation to axillary nodal status

BACKGROUND

Integrins are transmembrane receptors that modulate cell adhesion. Each is a heterodimer of varying alpha and beta subunits. In malignancy, loss of integrin expression may result in less adhesive cells more likely to metastasize. Our aim was to characterize the integrins in human breast tissue and to examine the relationship between integrin expression and nodal metastasis in breast cancer.

METHODS

Cryostat sections from 12 benign and 61 malignant (50 ductal and 11 lobular) samples were stained by the avidin-biotin complex method with monoclonal antibodies to the beta 1, beta 3, beta 4, and beta 5 subfamilies. All slides were read by two independent assessors with consensus agreement. Integrin expression was compared to variables by using the chi-squared test with Yates' correction and multivariate analysis based on logistic regression.

RESULTS

All integrin subunits studied were significantly reduced on breast cancer compared with benign cells (chi-squared test) but were not related to tumor differentiation. Loss of alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 6 beta 1, alpha v beta 1, and alpha v beta 5 were related to the presence of axillary metastasis. Independently the integrins were of limited clinical value as predictors of axillary spread. However, on multivariate analysis the combination of beta 1, alpha v, alpha 1, tumor size, and vascular invasion gave a cumulative overall accuracy in predicting nodal disease of 97%.

CONCLUSIONS

Integrin expression is reduced in breast cancer and may explain tumor progression. Measuring the integrins might thus provide a means of selection for aggressive axillary treatment.

Expression of fibronectin and its integrin receptor alpha 5 beta 1 in canine mammary tumours

Fibronectin and its integrin receptor alpha 5 beta 1 were studied by immunohistochemical methods in five normal canine mammary glands, four dysplastic glands and 18 mammary tumours. The aim of the study was to evaluate the possible changes in the alpha 5 beta 1 integrin receptor and its ligand fibronectin in relation to the metastatic capacity of canine mammary neoplasms. The immunostaining of alpha 5 beta 1 was very uniform in the hyperplastic glands but uneven in the mammary tumours. The expression of alpha 5 and beta 1 was diminished in metastatic tumours but there were some alpha 5-positive cells with pronounced features of malignancy and immaturity. Stromal fibronectin was increased in most cases and cytoplasmic staining of fibronectin was observed in epithelial and myoepithelial cells in mammary neoplasms but not in normal or dysplastic mammary tissue. There was no relationship between the content of alpha 5 beta 1 and the expression of fibronectin in canine mammary tumours.

Distribution of the VLA family of integrins in normal salivary gland and in pleomorphic adenoma

The extracellular matrix (ECM) and the alterations in tumour stroma affect the biologic behaviour of tumours. These interactions are, at least in part, mediated by the integrin superfamily. In this study we examined the immunohistochemical expression of the "very late activation" (VLA)-integrins in pleomorphic adenomas and in the corresponding normal tissues. Normal salivary gland expresses integrins in the myoepithelial cells (MEC) and in the basal and dark cells of ducts. This pattern is retained in pleomorphic adenoma. Regardless of the straining intensity, these tumour cells have a VLA expression similar to normal basal and dark cells, with only a few cells bearing MEC characteristics. We suggest that the tumour cells of pleomorphic adenoma have a common origin but show different stages of differentiation. Only cells bearing basement membrane (BM)-associated material form typical tubulo-ductal structures.

Expression of beta-1 integrins on tumor cells of invasive ductal breast carcinoma

The integrins are transmembrane alfabeta heterodimers mediating cell-cell as well as cell-extracellular matrix interactions. The present study was designed to analyse the expression of beta-1 integrins on cryostat sections of invasive ductal carcinomas not otherwise specified by avidin-biotin complex immunoperoxidase technique, and to compare it with the morphometric prognostic index (MPI). The results show that the expression of beta-1 integrins is heterogeneous in the tumors. This heterogeneity was observed in quantitative and qualitative staining pattern. There was an absent expression of beta-1 integrins in 22 out of 55 tumors while 33 showed staining, weak on 23 cases and strong on 10 infiltrative ductal carcinomas. Statistical analysis pointed to some correlation of beta-1 integrins with some morphometric parameters. Low or absent expression of beta-1 integrins correlated significantly with tumors exceeding 2 cm (p < 0.0245). Moreover, a larger proportion of tumors with positive lymph nodes showed absence of beta-1 expression compared with negative lymph node, and this was also statistically significant (p < 0.0076). Correlation between mitotic activity index and staining intensity for beta-1 integrins was not found (p < 0.372). When tumors with different beta-1 expression were subdivided according to MPI values into two groups, one group with a low-risk, < 0.6, and second with a high risk, > 0.6, concordance in prognostic value was shown between MPI and beta-1 expression (p < 0.0193). These results support the idea that loss of beta-1 integrins correlates with the invasive and metastatic potential of tumor cells.

A role of VLA-6 laminin receptor in invasion of breast carcinoma

The integrin VLA-6 as a laminin receptor and laminin as a ligand for laminin receptor were detected immunohistochemically in normal, benign tumor and carcinoma tissues of the breast. Epithelial cells of both normal breast and benign tumor were in almost all cases strongly immunoreactive for VLA-6 in the plasma membrane. Carcinoma cells in 34 of 70 cases (49%) with an invasive component were not immunoreactive for VLA-6, and no carcinoma cells showed strong positivity. Although carcinoma cells in only four of 51 cases (8%) with intraductal components were negative for VLA-6, 37 cases (72%) showed weak expression of VLA-6 and 10 cases (20%) showed strong expression of VLA-6. A concordant expression of VLA-6 on carcinoma cells and laminin around carcinoma cell nests with an invasive component was observed, and VLA-6 expression in carcinoma cells was correlated to tubular formation in carcinoma cell nests as an indicator of differentiation. These findings suggest that loss of VLA-6 plays a role in the invasion of breast carcinoma, and that VLA-6 laminin receptor and laminin may contribute to tubular differentiation of breast carcinoma cells.

Loss of VLA-2 collagen receptor in breast carcinoma, facilitating invasion and metastasis

The integrin VLA-2 as a collagen receptor and VLA-5 as a fibronectin receptor were detected immunohistochemically in normal, benign tumor and carcinoma tissues of the breast. Both proteins were also detected by Western-blot analysis in some carcinoma cases. Epithelial and myoepithelial cells of both normal breast and benign tumor were in all cases immunoreactive for VLA-2 in the plasma membrane. Carcinoma cells in the invasive component were not immunoreactive for VLA-2 in 31 (46%) of 67 cases. Carcinoma cells in the intraductal components were negative for VLA-2 in only 4 (11%) of 36 cases, while 20 cases (56%) showed weak expression and 12 cases (33%) showed strong expression. Metastatic carcinoma cells in the lymph nodes of 6 cases showed no immunoreactivity except in one case, whereas, again with the exception of one case, the carcinoma cells in the primary tumors did show VLA-2 expression. With regard to VLA-5, there was no difference in its expression in the invasive components and the intraductal components. These findings suggest that the loss of VLA-2 plays a role in the invasion and metastasis of breast carcinoma.

Integrins: cell adhesives and modulators of cell function

Integrins encompass a family of cell-surface molecules which play a crucial role in cell-cell and cell-extracellular matrix interaction. Of these heterodimeric transmembrane glycoproteins (consisting of an alpha and beta chain) as yet at least 20 different types have been described, all with a different pattern of reactivity with extracellular matrix components. In this review the cell and tissue distribution of the integrins is discussed, with special emphasis on immunohistochemical localization of the beta 1 integrins and the alpha 6 beta 4 integrin. The beta 1 integrins comprise a subfamily in which eight alpha chains combine with one beta (the beta 1) chain. The alpha 2 beta 1, alpha 3 beta 1 and alpha 6 beta 1 and the alpha 6 beta 4 integrins are expressed on a wide variety of epithelia on the basolateral surface or exclusively on the basal surface facing the basement membrane (e.g. alpha 6 beta 1 and alpha 6 beta 4). Leucocyte integrins, which share a common beta 2 chain, occur almost exclusively on white blood cells and their precursors. The vitronectin receptors, which share a common alpha v chain, occur in a wide variety of cell types. Integrins play a major role in the interaction of the cell with the extracellular matrix in order to create and maintain tissue architecture. It has become clear, however, that through integrin-ligand interaction cell function is also modulated. Furthermore, in pathological conditions integrins play a role of some significance. Integrins mediate leucocyte traffic in developing inflammatory processes and function in neoplastic growth when it comes to invasion and metastasis.