Distribution of the beta 1 subgroup of the integrins in human cells and tissues

The Use of Mab 1977 Monoclonal Antibody for the Immunohistochemical Localization of β1 Integrins in Paraffin-Embedded Human Kidney

Aims and background

Integrins are widely known cell membrane receptors for extracellular matrix molecules. The β1 integrin subgroup is mainly expressed by kidney cells; immunolocalization of these molecules is usually carried out on cryostatic sections. A commercial monoclonal antibody directed against the human β1 integrin was tested in order to design a method for the detection of this antigen in formalin-fixed, paraffin-embedded human kidney tissue.

Methods

Specimens obtained from nephrectomies were fixed with 10% formalin and embedded in paraffin. Three different detection protocols were applied after incubation with the anti-human β1 integrin monoclonal antibody (MAB 1977): 1) immunoperoxidase with labeled streptavidin biotin (LSAB), using biotinylated secondary antibodies, peroxidase-labeled biotin-streptavidin, and 3, 3′-diaminobenzidine tetra-hydrochloride (DAB) as the revealing system; 2) immunoperoxidase with tyramide signal amplification (TSA), using biotinylated secondary antibodies, streptavidin-peroxidase, tyramide, streptavidin-peroxidase again and DAB; 3) indirect immunofluorescence with fluorescein-labeled anti-mouse immunoglobulins.

Results

The best results were obtained with the LSAB detection protocol preceded by a predetection step with proteinase k. Proteinase k pretreatment did not significantly damage the tissue morphology and successfully unmasked 31 integrin antigens. Nonspecific background staining was reduced by a blocking step with swine serum. Similar results were obtained with the TSA detection method; however, although lower concentrations of anti-β1 integrin immunoglobulins and of secondary biotinylated antibody were employed, there was more undesired background staining than with the LSAB protocol.

Conclusions

The method reported and discussed here may represent a valid tool for research and diagnostic applications based upon detection of β1 integrin in paraffin-embedded human tissues.

Isolation of clonogenic, long-term self renewing embryonic renal stem cells

A tissue stem cell should exhibit long-term self-renewal, clonogenicity and a capacity to differentiate into the tissue of origin. Such a postnatal renal stem cell has not been formally identified. The metanephric mesenchyme (MM) of the developing kidney gives rise to both the renal interstitium and the nephrons and is regarded as the progenitor population of the developing kidney. However, isolated MM does not self renew and requires immortalization for survival in culture. Here we report the isolation and sustained culture of long-term repopulating, clonal progenitors from the embryonic kidney as free floating nephrospheres. Such cells displayed clonal self renewal for in excess of twenty passages when cultured with bFGF and thrombin, showed broad mesodermal multipotentiality, but retained expression of key renal transcription factors (Wt1, Sall1, Eya1, Six1, Six2, Osr1 and Hoxa11). While these cells did display limited capacity to contribute to developing embryonic kidney explants, nephrospheres did not display in vitro renal epithelial capacity. Nephrospheres could be cultured from both Sall1(+) and Sall1(-) fractions of embryonic kidney, suggesting that they were derived from the MM as a whole and not specifically the MM-derived cap mesenchyme committed to nephron formation. This embryonic renal stem cell population was not able to be isolated from postnatal kidney confirming that while the embryonic MM represents a mulitpotent stem cell population, this does not persist after birth.

Localization of porcine CD29 transcripts and protein in pig cells and tissues by RT-PCR and immunohistochemistry

Integrins are heterodimeric cell adhesion proteins with major roles in a variety of biological processes ranging from cell migration to tissue organization, immune and non-immune defense mechanisms and oncogenic transformation. Members of the beta(1) integrin subfamily are composed of a beta(1) subunit (CD29) non-covalently associated with different alpha subunits to constitute a group of transmembrane glycoproteins that participate in many physiologically important events. Here, we have studied the CD29 expression in porcine tissues and cells at two different levels: expression of the CD29 mRNA by RT-PCR and localization of the protein by immunohistochemistry. CD29 transcripts were detected in a variety of tissues and cells: platelets, PBMC, granulocytes, alveolar macrophages, smooth muscle, intestine, lung, liver, spleen, lymph node, skin, testis, heart, kidney and bone marrow. Our results suggest that CD29 gene transcription occurs in all organs examined, although with different intensities. The precise localization of CD29 protein in paraffin-embedded tissues was detected by using a specific polyclonal antibody indicating that its expression is limited to smooth muscle, epithelium cells, endothelium of blood vessels and myeloid cells and is no detectable in cells of the lymphoid lineage. The distribution of the CD29 in normal tissues provide insight into the physiological function of the porcine beta(1) integrins and should be of importance in understanding the role of this integrin family in pathological processes.

Fibronectin attachment protein homologue mediates fibronectin binding by Mycobacterium avium subsp. paratuberculosis

Attachment of Mycobacterium avium subsp. paratuberculosis to host tissue and penetration of mucosal surfaces are pivotal events in the pathogenesis of Johne's disease. Fibronectin (FN) binding is required for attachment and internalization of several mycobacteria by epithelial cells in vitro. The objective of this study was to further characterize the FN binding activity of M. avium subsp. paratuberculosis. Although the bacteria bound FN poorly at pH above 7, brief acid pretreatment greatly enhanced FN binding within the pH range (3 to 10) studied. A 4.6-kbp fragment from an M. avium subsp. paratuberculosis genomic library was found to contain a 1,107-bp open reading frame that shows very high nucleotide sequence identity with that of the FN attachment protein (FAP) gene of M. avium subsp. avium. Pretreatment of FN with an FN-binding peptide from M. avium subsp. avium FAP abolished FN binding, indicating that M. avium subsp. paratuberculosis binds FN in a FAP-dependent manner. Pretreatment of M. avium subsp. paratuberculosis with anti-FAP immunoglobulin G did not abrogate FN binding; blocking occurred only when anti-FAP was added together with FN. FAP was detected by immunofluorescence only in lipid-extracted M. avium subsp. paratuberculosis. Western blotting and immunoelectron microscopy revealed that FAP is located near the interior of the cell envelope of M. avium subsp. paratuberculosis. The results indicate that a FAP homologue mediates the attachment of FN to M. avium subsp. paratuberculosis. Further, given the subcellular location of FAP, it is considered that this protein operates at the terminus of a coordinated FN binding system in the cell envelope of M. avium subsp. paratuberculosis.

Interaction of microorganisms, epithelium, and lymphoid cells of the mucosa-associated lymphoid tissue

Differentiation of specific epithelial cell lineages during development, as well as epithelial plasticity in response to heterologous cell-to-cell cross talk during adult life, accounts for the large variety of functions which are performed by the mucosal surfaces found in the human body. Among its functions, the digestive mucosa is able to sample antigens and microorganisms through M cells of Peyer's patches' follicle-associated epithelium, in order to trigger the development of either tolerance or immune responses. At least in the gut, M-cell formation is immunoregulated. Close contact between immune cells and intestinal epithelium modifies the permeability of the epithelial barrier by inducing the conversion of enterocytes into M cells, offering at the same time an opportunistic way of invasion for pathogens. These lympho-epithelial interactions triggering M-cell formation have now been modeled in culture.

Expression of Cell Surface Glycoprotein CD44 and Integrins in Breast Cancers among Indian Women

Parsis, the sole surviving group of followers of Zoroaster who are settled in Bombay, have a fourfold higher incidence of breast cancer than the general population of Greater Bombay. CD44 expression was studied by immunohistochemistry in breast cancers of 50 non-Parsi and 35 Parsi women, 10 normal breast tissues, 10 proliferative lesions and 49 tissues adjoining a tumor mass. α2 and β1 integrins could be studied in only 42 malignant cases and five normal tissues. The immunohistochemistry results were correlated with other parameters including tumor grade and size, estrogen and progesterone receptor status, lymph node involvement and mitotic index. CD44 was not expressed in normal areas. Benign areas and tissues adjacent to tumor masses showed increased staining. Both Parsi and non-Parsi women showed significantly high CD44 expression. All Parsi ILCs were strongly positive for CD44. In both groups ER negativity was associated with strong CD44 positivity, while mitotic counts correlated with decreased CD44 expression in Parsis but not in non-Par-sis. α2 and β1 integrins were strongly expressed on the baso-lateral surface of normal epithelium. However, they were downregulated in tumors. In general breast tumor tissues from Parsi and non-Parsi patients did not differ significantly with respect to most parameters. However, among Parsis lymph node involvement and CD44 correlated weakly whereas the mitotic index was inversely correlated with CD44. The reverse was true for non-Parsis. The deviation from the general pattern needs further study based on a large number of samples and appropriate use of splice variants.

VLA2 integrin expression in breast carcinomas evaluated by automated and quantitative immunohistochemistry

VLA2 is thought to be involved in the metastatic process in malignant tumours, in particular in carcinomatous cell adhesion to vessel basement membrane. VLA2 expression was immunohistochemically investigated in 204 breast carcinomas. Frozen tissue sections were probed with monoclonal anti-VLA2 using automated (Ventana ES 320 System) and quantitative (SAMBA 2005 image processor) immunoperoxidase. A positive anti-VLA2 immunoreaction was observed in 48 tumours (23.5%), within epithelial carcinomatous cells. The VLA2-positive surface in tumours varied from 3% to 20% (mean 8.75, S.D. 7.17) and was correlated with histoprognostic indicators and tumour expression of various antigens detected using the same method as that for VLA2. The results show that VLA2 immunoexpression was independent of the tumour size, grade, type and aneuploidy, and of the nodal status. VLA2 significantly correlated with ELAM, VCAM, VLA3 and P-glycoprotein (P-gp) (P < 0.01) and inversely correlated with cathepsin D (P < 0.001), but was independent of Ki67/MIB1, p53, bcl-2, c-erbB-2, E cadherin, CD44v, CD31, oestrogen and progesterone receptors' (ER, PR) antigenic sites and pS2. The exact role, if any, of VLA2 in tumour cell dissemination remains to be elucidated and the clinical relevance of VLA2 immunodetection in breast carcinomas requires further investigation of the correlation between VLA2 immunocytochemical expression and patients' outcome and response to chemotherapy.

Invasin-dependent and invasin-independent pathways for translocation of Yersinia pseudotuberculosis across the Peyer's patch intestinal epithelium

Yersinia pseudotuberculosis initiates systemic disease after translocation across the intestinal epithelium. Three Y. pseudotuberculosis factors, previously identified by their ability to promote association with cultured cells, were evaluated for their relative roles in translocation. To this end, mutants defective for invasin, YadA, or pH 6 antigen were tested for movement from the intestinal lumen into the subepithelium. Within 45 min after introduction of bacteria into the lumen, wild-type bacteria were found in the Peyer's patch. Mutants expressing defective invasin derivatives were unable to promote efficient translocation into the Peyer's patch and instead colonized on the luminal surface of the intestinal epithelium. In particular, a translocation defect was observed in a Y. pseudotuberculosis strain that expressed an uptake-defective invasin protein retaining considerable receptor binding activity. To attempt to reduce binding to luminal mucus, Y. pseudotuberculosis yadA and inv yadA strains were analyzed. Both strains had reduced mucus binding, with the inv yadA mutant revealing an alternate uptake pathway that was invasin independent. A mutant defective in the production of the pH 6 antigen adhesin also showed reduced binding to luminal mucus, with specific localization of bacteria in M cells. These results indicate that Y. pseudotuberculosis adhesive factors control the site of bacterial interaction within the intestinal environment and that loss of one factor causes drastic changes in the preferred site of localization of the bacterium in this locale.

Immunohistochemical study of skin lesions in acute and chronic graft versus host disease following bone marrow transplantation

Allogeneic bone marrow transplantation (BMT) is the therapy of choice for a variety of malignant and nonmalignant disorders; however, a major constraint to successful BMT is graft versus host disease (GVHD). Skin lesions are the earliest presentation of GVHD. Donor-derived cytotoxic T lymphocytes are the effector cells responsible for lesions in the skin and other tissues. Here we show that most skin-infiltrating lymphocytes, in all forms of GVHD, are memory T cells with a predominance of CD4+ cells in the dermis and CD8+ cells in the epidermis. Relatively little attention has been focused on the adhesive phenotype of keratinocytes in GVHD. In this study, immunohistochemical analyses of skin biopsies from BMT patients with acute or chronic GVHD were conducted, with particular emphasis on antigen-presenting cells (APCs) and on keratinocytes. The distribution of APCs in the epidermis (Langerhans' cells) was investigated. Keratinocytes were analyzed for the expression of human leukocyte antigen DR locus (HLA-DR) and of a novel integrin, alpha10.1.2 beta1, which is detected in the basal layer of normal epidermis. Langerhans' cells were decreased in all grades of acute GVHD, but the epidermal APC network was reconstituted in chronic GVHD. HLA-DR was expressed by keratinocytes in grade 2 and 3 acute GVHD lesions, but not in two of three chronic GVHD cases, and in the regression phase of acute GVHD. Integrin chains alpha10.1.2 and beta1 were detected in the epidermal basal cell layer of most GVHD cases but they were also expressed in suprabasal keratinocytes of both acute and chronic GVHD. This latter finding indicates that a proliferative response uncoupled from differentiation occurs in keratinocytes in the course of GVHD.

Common entry mechanisms. Bacterial pathogenesis

The recent identification of E-cadherin as the cell-surface receptor for the Listeria monocytogenes adhesin, internalin, indicates that pathogenic bacteria exploit a variety of host surface molecules for entry and that they may share some common strategies for uptake into host cells.

Localization of alpha 4m integrin at sites of mesenchyme condensation during embryonic mouse development

The expression and distribution of the murine alpha 4 (alpha 4m) integrin subunit and of one of its ligands, VCAM-1, were examined in the developing mouse embryo at different development stages. Transcription of the mRNA was investigated by in situ hybridization using single-stranded sense and anti-sense cDNA probes and by Northern blotting. In parallel sections integrin was identified by immunohistochemistry using the alpha 4m-specific antibody R1/2. In general both methods gave similar distributions. The results demonstrate that alpha 4m and vascular cell adhesion molecule-1 (VCAM-1) are expressed in mouse embryonic liver (E11-E15) and are developmentally down-regulated, consistent with the haematopoietic properties of embryonic liver. Developmental-stage-dependent expression of alpha 4m was also observed in lymphoid organs, such as spleen and thymus, and in some non-lymphoid organs or tissues, such as skeletal and tongue muscles, smooth muscles of the blood vessels, the outflow tract of the embryonic heart, the papilla of the tooth, the glomeruli of the kidney and the stroma of the gonads. In the latter tissues, the expression of alpha 4m correlated with the transient condensation of particular mesenchymal structures. We also confirm that VCAM-1 and alpha 4 beta 1 are co-distributed only in some tissues, suggesting that during mouse development, VLA-4 interacts mainly with another ligand, probably fibronectin.

Expression of beta 1 integrin in normal, dysplastic and neoplastic canine mammary gland

The expression of beta 1 integrin was evaluated immunohistochemically in a series of normal, dysplastic and neoplastic canine mammary glands, and in lymph node metastases. The tissues were formalin-fixed and paraffin wax-embedded. In malignant neoplasms, beta 1 integrin was decreased and redistributed along the entire cell membrane. In lymph nodes, strong immunohistochemical staining was seen intercellularly in clusters of metastatic cells within subcapsular sinuses and at the periphery of intranodal metastases. These results suggest that the expression of integrin molecules may be related to malignancy and to the metastatic potential of neoplastic cells.

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)

Upregulation of integrin expression in benign vulvar warts

Benign anogenital warts demonstrate features both of hyperproliferation and of aberrant differentiation associated with human papillomavirus (HPV) infection. The expression of integrins has been examined in normal vulvar epithelium and benign vulvar warts to determine whether HPV infection is associated with changes in integrin expression, either during terminal differentiation or among the proliferating cell population. The expression of integrins in normal vulvar epithelium was similar to that seen in the epidermis, with little expression of alpha 1 and expression of alpha 2, alpha 3, and beta 1 at the periphery of basal cells. In vulvar wart epithelium, alpha 1 was not significantly expressed, but upregulation of alpha 2, alpha 3, and beta 1 was seen at the periphery of cells throughout the basal and spinous layers. In addition, alpha 2 staining was greater at foci along the basal layer of normal vulva, whilst such heterogeneity was not detected in wart sections. Expression of beta 4 and alpha V was confined to the basal and lateral aspects of normal basal cells, but expressed at the periphery of basal cells and to a lesser extent in epibasal and spinous layers of warts. The observed differences in integrin expression are consistent with those reported in other hyperproliferative epithelia.

Integrin expression by human epidermal keratinocytes can be modulated by interferon-gamma, transforming growth factor-beta, tumor necrosis factor-alpha, and culture on a dermal equivalent

Receptors of the integrin family are largely confined to the basal layer of keratinocytes, both in human epidermis and in stratified cultures of human keratinocytes. However, suprabasal integrin expression is observed during epidermal wound healing and in psoriatic lesions. We have investigated potential stimuli of suprabasal expression. Addition of transforming growth factor-beta (TGF-beta), interferon-gamma (IFN-gamma), or tumor necrosis factor-alpha (TNF-alpha) to keratinocytes cultured with a 3T3 feeder layer did not induce suprabasal expression. The cytokines caused small changes in the levels of alpha 2 beta 1 or alpha 3 beta 1 on the surface of basal keratinocytes but had no significant effect on the proportion of cells adhering to fibronectin, type IV collagen, and laminin, and did not cause changes in the mobility of integrin subunits on polyacrylamide gels. Injection of TNF-alpha or IFN-gamma intradermally into healthy human volunteers induced an inflammatory response but did not induce suprabasal integrin expression. However, we did observe transient suprabasal integrin expression when keratinocytes were grown on a dermal equivalent consisting of fibroblasts in a collagen gel. One week after raising the cultures to the air-liquid interface, beta 1 integrins were found in all the viable cell layers, with suprabasal cells co-expressing integrins and involucrin; 1 week later integrins were confined to the basal layer. Addition of TGF-beta, IFN-gamma, or TNF-alpha to the dermal equivalents neither induced nor inhibited suprabasal integrin expression. We conclude that suprabasal integrin expression is not induced by the inflammatory cytokines tested, and instead may reflect the proliferation/differentiation status of the epidermis.

Immunolocalization of alpha 2, alpha 5, and alpha 6 integrin subunits in salivary tissue and adenomas of the parotid gland

The localization of the integrin subunits alpha 2, alpha 5, alpha 6 was studied immunohistochemically in samples of normal salivary gland and in a series of 8 pleomorphic adenomas, 5 Warthin's tumors, and 2 basal cell adenomas. In normal salivary tissue, acinar and ductal cells expressed alpha 2 and alpha 6 chains at the basal cell pole facing the basement membrane. alpha 2 also localized at sites of cell-cell contact. No staining of the epithelial component was seen with alpha 5. The polarized expression of alpha 2 and alpha 6 subunits was retained in salivary adenomas. These subunits were present at the basal cell pole of solid nests, tubules and ducts of pleomorphic adenomas, as well as of the basal layer of the epithelium of Warthin's tumor, and of the trabecular structures of basal cell adenomas. The alpha 5 subunit was consistently expressed only by cells embedded in the myxoid or chondroid matrix of pleomorphic adenomas. We conclude that the pattern of a integrin subunit expression in salivary adenomas may be related to the "epithelial" or "mesenchymal" phenotype of the neoplastic cells.

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.

Cell adhesion molecules in oesophageal epithelium

The distribution of a range of integrins, E-cadherin, and carcino-embryonic antigen (CEA) like molecules in normal human oesophageal epithelium was investigated immunohistochemically on frozen sections of endoscopic biopsy specimens. The integrin subunits alpha 2, alpha 3, alpha 6, alpha v, beta 1, and beta 5 were expressed throughout the epithelium. There was strong expression of alpha 2, alpha 3, and beta 1 subunits in the basal cell layer and for all the subunits studied the intensity of the staining decreased as cells moved towards the lumen. The heterodimer alpha v beta 3 was expressed weakly in the basal aspect of the basal cell layer only. The CEA molecules were not present in the basal cells layer but there was weak expression in the prickle cell layer and strong positivity in the mature functional layer. E-cadherin was found throughout the epithelium but was weakly expressed at the basal aspect of the basal cells layer and showed strong positivity in the prickle cell and squamous cell layers. These results indicate that cell-cell (E-cadherin, CEA) and cell-matrix (integrins) adhesion molecules show a well defined spatial pattern of immunoreactivity in the oesophageal mucosa and may play a part in the maintenance of normal tissue architecture and physiological homeostasis.

Integrin expression and ability to adhere to extracellular matrix proteins and endothelial cells in human lung cancer lines

We examined the integrin expression in 19 human lung cancer cell lines with monoclonal antibodies to the integrin subunits alpha 1, alpha 2, alpha 3, alpha 4, alpha 5, alpha 6, beta 1, beta 2, and beta 4. We measured their ability to adhere to the extracellular matrix (ECM) and human umbilical vein endothelial cells (HUVECs). Almost all lines expressed the beta 1 subunit and approximately half of the lines expressed the beta 4 subunit; by contrast, none expressed the beta 2 subunit. Subunits alpha 2, alpha 3, alpha 5 and alpha 6 were frequently expressed, whereas very few lines expressed alpha 1 and alpha 4. Most lines adhered strongly to ECM (type I collagen, laminin and fibronectin) in correspondence to their expression of integrins. Binding by most lines to fibronectin was completely inhibited by arginine-glycine-aspartic acid (RGD) peptide. Three lines that expressed few or no integrins had very weak ability to adhere to ECM. Strong binding to HUVECs was found in most lines, but the three lines had very little ability to adhere to HUVECs. Binding to HUVECs was strongly inhibited at 4 degrees C, under divalent cation-free conditions and by antibodies to the beta 1 subunit. These results suggest that lung cancer cells adhere to ECM and endothelial cells through integrins, especially the beta 1 subfamily.

TGF-alpha can act as morphogen and/or mitogen in a colon-cancer cell line

Transforming growth factor alpha (TGF-alpha) has multifunctional biological effects on a variety of mesenchymal and epithelial cells. It is a potent mitogen for a number of normal and transformed cell types, regulates extracellular matrix (ECM) production and promotes breast, kidney and lung morphogenesis. To clarify the role of ECM proteins in the morphogenetic and mitogenic effects of TGF-alpha, we have used a human colon carcinoma cell line (SW1222) which expresses EGF receptor. Here we show that TGF-alpha at 1 ng/ml increases the proliferation of SW1222 cells, but only when they are cultured on plastic rather than collagen-coated plates. Higher concentrations of TGF-alpha (10 ng/ml) did not increase cell proliferation but significantly enhanced the crypt-like glandular differentiation when cells were grown in 3-dimensional collagen gel (p = 0.027). These effects were accompanied by increased expression of alpha 2 beta 1 and alpha 3 beta 1 integrin molecules, which are receptors for extracellular matrix proteins, and by a statistically significant increase in binding of SW1222 cells to type-1 collagen. The effects of TGF-alpha both on binding to type-1 collagen and on morphological differentiation in 3-dimensional collagen gel were inhibited by monoclonal antibodies recognizing the alpha 2 beta 1 integrin. These data indicate that the morphogenetic or mitogenic activities of TGF-alpha are critically dependent on cellular interactions with extracellular matrix proteins and are primarily mediated by the alpha 2 beta 1 integrin receptor. Inappropriate expression of this growth factor, seen in tumours whose cell-matrix interactions are greatly impaired, could have deleterious effects on the maintenance of normal tissue architecture and growth control.

Adult adenohypophysial cells express beta 1 integrins and prefer laminin during cell-substratum adhesion

beta 1 Integrins are a family of structurally related heterodimeric cell surface receptors that are involved in adhesion to molecules in the extracellular matrix (ECM) such as laminin (LN), fibronectin (FN), and collagen. These receptors are expressed by many cell types and mediate a variety of processes such as cell-matrix and cell-to-cell adhesion, cell migration, growth, and differentiation. The purpose of these studies was to identify and partially characterize beta 1 integrins on adenohypophyseal cells and to begin to elucidate their functional importance. Adenohypophyses were removed from adult male rats, dispersed using 0.25% trypsin, rinsed, and resuspended in a 1:1 mixture of Dulbecco's modified Eagle's medium and F12 medium containing 10% fetal bovine serum and antibiotics. Ten million cells were allowed to attach to each of five plastic culture dishes overnight. The next day, the adenohypophyseal cells were surface-labeled with 125I. The labeled cells were lysed and centrifuged. The supernatant was immunoprecipitated using preimmune IgGs (100 micrograms/ml) and was then incubated with a polyclonal antibody against the rat beta 1 family of integrins or with a variety of immune IgGs directed against the alpha subunit of the receptor (anti alpha 1, anti alpha 2, anti alpha 3, and anti alpha 5 antibodies). The receptors were then immunoprecipitated by addition of protein A-Sepharose or IgG1 Sepharose. After washing, the immunoprecipitates were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography. Cultured adenohypophyseal cells expressed the beta 1 integrin subunit, which was associated with the alpha 1, alpha 2, alpha 3, and alpha 5 integrin subunits.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal detachment of the epidermis using dispase: tissue spatial organization and fate of integrin alpha 6 beta 4 and hemidesmosomes

Dispase has been utilized to produce basal detachment of the epidermis of human skin biopsies and to study the consequences induced afterwards during incubations of the detached tissue. Spatial reorganization of the epidermis is observed under these conditions and is characterized by disappearance of the typical basal keratinocyte layer. Immunofluorescent labelings reveal upward migration of several cells exhibiting the basal phenotype between suprabasal differentiating keratinocytes and demonstrate progressive intracellular expression of hemidesmosomal components: the integrin alpha 6 beta 4 and two plaque components, the 230-kDa bullous pemphigoid antigen and HD1, a 500-kDa protein. Using electron microscopy and immunogold techniques, we demonstrate that the hemidesmosome-containing basal membrane domains enter the cell cytoplasm after detachment of the epidermal tissue. Partial recycling of internalized hemidesmosomal components is also suggested. Our findings illustrate the processing of released hemidesmosomes in detached basal keratinocytes and suggest some heterogeneity between basal cells migrating towards a suprabasal position and those remaining in the basal layer. These results suggest that the dispase-detached epidermis is a self-remodeling tissue in which basal keratinocytes' and tissue's polarities observed in the anchored epidermis are progressively changing.

Flow cytometric identification of proliferative subpopulations within normal human epidermis and the localization of the primary hyperproliferative population in psoriasis

In this study we define the proliferative compartments of in vivo human epidermis, using specific antibodies related to cell differentiation (beta 1 and beta 4 integrins and K1/K10 differentiation keratins) and cell cycle (proliferating cell nuclear antigen [PCNA]) in combination with flow cytometric quantitation of the DNA content and optical characteristics of the cells. The beta 1 integrin (CD29) marked both of the potentially proliferative subsets in normal epidermis. One subset of normal epidermis is CD29+ K1/K10-, which was predominantly basal, and found to be comprised of slow cycling, small cells with primitive cytoplasmic organization. The vast majority (95.5%) of these cells were in a quiescent state (G0/early G1) as indicated by their lack of the cyclin, PCNA. The other proliferative subset of normal epidermis was CD29+ K1/K10+, which was suprabasal and occasional basal, highly proliferative, larger in size, and which exhibited a more complex cytoplasmic structure. Because early differentiation (K1/K10 expression) has begun in the CD29+ K1/K10+ subset, it is highly likely that they represent the proliferative population which is capable of transiently amplifying itself before terminal differentiation. Within lesional psoriatic epidermis, similar proliferative cell populations were present as in normal epidermis, and the hyperproliferative defect was localized to the beta 1 and beta 4 integrin+, K1/K10- populations, which in normal epidermis is basally located and quiescent with regard to cell cycle. In psoriatic epidermis, a six- to sevenfold increase in the number of cells in the S/G2+M phase of cell cycle was found among CD29+ K1/K10- cells (p < 0.05). Furthermore, all lesional K1/K10- cells showed high PCNA positivity, indicating that all these cells had been recently induced into cell cycle. By contrast, the proportion of cycling cells among lesional psoriatic CD29+ K1/K10+ keratinocytes was similar to normals. Anti-HLA-DR, CD45, and vimentin antibodies were used to concomitantly track the proliferative states of Langerhans cell, melanocyte, and infiltrating leukocyte populations. In normal epidermis, the cycling fractions (cells in S/G2/M phase) of these cells were similar to the CD29+K1/K10- keratinocytes, whereas in lesional epidermis their cycling pools were increased relative to normal, but not so much as the proliferative fractions of psoriatic CD29+ K1/K10- keratinocytes. These data demonstrate the use of simultaneous analysis of integrin expression, differentiation keratins, cyclin, cell cycle status, and optical characteristics of freshly isolated human epidermal cells. Such analysis allowed the physical identification and quantification of cy cling populations in normal human skin, and has enabled the precise location of the primary epidermal proliferative defect in psoriasis.

Evidence against a major role for integrins in calcium-dependent intercellular adhesion of epidermal keratinocytes

It is well established that integrins mediate keratinocyte adhesion to extracellular matrix proteins, but, in addition, there is some evidence that they mediate intercellular adhesion. We have investigated the role of integrins in keratinocyte-keratinocyte adhesion by adding anti-integrin antibodies to cells in three assays that differ according to the calcium ion concentration of the medium, the presence or absence of an adhesive substrate (glass or tissue culture plastic) and the timing of antibody addition. As previously reported by Larjava et al., (J. Cell Biol. 110:803-815), a monoclonal antibody to the beta 1 subunit perturbed cell-cell adhesion when added to adherent monolayers in low calcium medium (0.1 mM calcium ions), but did not prevent cell-cell adhesion or stratification induced by raising the level of calcium ions to 1.8mM (the concentration in standard medium). Monoclonal antibodies to both the alpha 3 and beta 1 subunits inhibited the attachment, spreading and motility of keratinocytes in low or standard calcium medium when added at the time of plating; however, they had only a modest effect on the accumulation of cells in adherent clusters. Aggregation of keratinocytes in suspension required a calcium ion concentration of greater than 0.1mM and was not inhibited by any of a large panel of anti-integrin antibodies, including three new antibodies that recognise alpha 2 beta 1. We conclude that any inhibitory effects of individual anti-integrin antibodies on cell-cell adhesion are abrogated by a calcium ion concentration above 0.1mM and that in low calcium medium at least some of the inhibition of cell-cell adhesion is a consequence of the inhibition of cell-substrate adhesion and motility.

Vla-3 distribution in normal and neoplastic non-lymphoid human tissues

Using monoclonal antibody (mAb) M-Kid 2 to the alpha 3 beta 1 heterodimer, we have evaluated immunohistochemically the in vivo expression of the Vla-3 integrin in normal and transformed non-lymphoid human tissues. In normal tissues the alpha 3 beta 1 complex displays a polarized distribution at the baso-lateral aspect of most keratinizing and glandular epithelia. In addition the integrin is detected in perineurium, basal lamina of smooth muscular fibers, vascular media, podocytes and Bowman's capsule, myoepithelial cells of the parotid and breast, and in pulmonary alveoli. Neoplastic transformation is associated with qualitative and quantitative changes in expression of this integrin. The loss of polarized distribution often occurs in various malignancies. Furthermore, a significant decrease in expression occurs in 13% of the colon-rectum carcinomas, 75% of the ductal invasive, and 40% of the lobular invasive breast carcinomas. Among the lung malignancies tested, the small cell lung carcinomas (SCLC) were found to be consistently unreactive with mAb M-Kid 2. Analysis of Vla-3 expression in established tumor cell lines demonstrated that the integrin is almost invariably expressed by the plastic adherent cell subpopulations.

Complementary distributions of vinculin and dystrophin define two distinct sarcolemma domains in smooth muscle

The sarcolemma of the smooth muscle cell displays two alternating structural domains in the electron microscope: densely-staining plaques that correspond to the adherens junctions and intervening uncoated regions which are rich in membrane invaginations, or caveolae. The adherens junctions serve as membrane anchorage sites for the actin cytoskeleton and are typically marked by antibodies to vinculin. We show here by immunofluorescence and immunoelectron microscopy that dystrophin is specifically localized in the caveolae-rich domains of the smooth muscle sarcolemma, together with the caveolae-associated molecule caveolin. Additional labeling experiments revealed that beta 1 integrin and fibronectin are confined to the adherens junctions, as indicated by their codistribution with vinculin and tensin. Laminin, on the other hand, is distributed around the entire cell perimeter. The sarcolemma of the smooth muscle cell is thus divided into two distinct domains, featuring different and mutually exclusive components. This simple bipartite domain organization contrasts with the more complex organization of the skeletal muscle sarcolemma: smooth muscle thus offers itself as a useful system for localizing, among other components, potential interacting partners of dystrophin.

Adhesion molecule expression in human synovial tissue

OBJECTIVE

We have previously shown that E-selectin is expressed on endothelium in rheumatoid arthritis (RA) synovial tissues, and hence may be important in recruitment of leukocytes into the inflamed joint. In the present study, we determined whether other cellular adhesion molecules, including selectins and members of the integrin and immunoglobulin supergene families, are expressed in frozen synovium.

METHODS

We employed immunohistochemical staining to determine the distribution of CD31 (PECAM), CD44 (hyaluronate receptor), CD62 (P-selectin), Leu-8 (L-selectin), and the integrin subunits alpha 5 (VLA-5), alpha 6 (VLA-6), beta 1 (VLA 1-6), and beta 3 (vitro-nectin receptor), in synovial tissue from 9 RA and 9 osteoarthritis (OA) patients, and from 3 normal (NL) subjects.

RESULTS

P-selectin was expressed on vascular endothelium in all synovial tissues examined. L-selectin and alpha 5-integrin, while expressed on a variety of cell types, were not differentially expressed on RA synovial tissues. Integrin subunits alpha 6 and beta 1 were down-regulated on some RA synovial tissue components. In contrast, CD31 was expressed to a greater extent on RA than on OA lining cells and macrophages (P < 0.05). CD44 was expressed to a greater extent on RA or OA macrophages, lining cells, and fibroblasts compared with NL (P < 0.05). Integrin subunit beta 3 was strongly expressed on RA synovial blood vessels compared with NL (P < 0.05).

CONCLUSION

The expression of integrins VLA 1-6, and selectins P and L is not up-regulated in RA synovial tissues. CD31 and CD44 are up-regulated on RA macrophages and lining cells, CD44 on RA fibroblasts, and beta 3-integrin on RA blood vessels. The up-regulation of CD31, CD44, and beta 3-integrin in RA synovial tissues may help tip the balance of adhesive interactions toward passage and retention of leukocytes in the inflamed joint.

Integrin expression in normal, hyperplastic, dysplastic, and malignant oral epithelium

We have examined the distribution of a range of integrin subunits in normal and lesional oral mucosa. The alpha 2, alpha 3, alpha 6, beta 1, and beta 4 subunits were highly expressed in normal epithelium, and there was weaker, more variable expression of alpha 5 and alpha v. Expression of all subunits was highest in the basal layer of normal epithelium, but extensive staining above the basal layer was also observed, particularly in the floor of the mouth and the lateral margin of the tongue. In dysplastic lesions and hyperplastic epithelium adjacent to ulcers, suprabasal staining was even more pronounced. Staining patterns in squamous cell carcinomas showed considerable variation, both within and between individual tumours: in some areas there was staining reminiscent of normal epithelium, but uniform staining throughout tumour islands, and patchy and variable cytoplasmic and pericellular staining were also seen. Thirteen out of 17 carcinomas showed some loss of integrin expression: six out of ten moderately well differentiated tumours and all the poorly differentiated tumours. Focal loss of alpha 6 and beta 4 was most commonly observed, but loss of alpha 2 and alpha 3 also occurred. Since integrins regulate not only keratinocyte adhesion, but also the initiation of terminal differentiation, the changes in integrin expression that we have observed may have significance for the behaviour of individual tumours.

Integrins and their accessory adhesion molecules in mammary carcinomas: loss of polarization in poorly differentiated tumors

The integrins are alpha beta heterodimeric transmembrane proteins mediating cell-substratum as well as cell-cell interactions. To identify the pattern of expression of the beta 1, beta 3, and beta 4 integrins and their accessory adhesion molecules in relation to the malignant phenotype of invasive breast cancer, we performed an immunohistochemical study for the alpha 2 beta 1 (VLA-2), alpha 6 beta 1 (VLA-6), alpha v and alpha v beta 3 (vitronectin receptor), alpha 6 beta 4, carcinoembryonic antigen, and carcinoembryonic antigen-related molecules in a series of 37 invasive breast carcinomas. All integrin chains examined showed similar patterns in nonneoplastic breast tissue, with strong membrane staining of the myoepithelial cells and weak to moderate staining on the basolateral surfaces of the luminal cells. We found that downregulation of the alpha 2 chain of VLA-2 occurs more frequently in poorly differentiated grade III invasive ductal carcinomas (IDCs) (P = .048). Loss of alpha 6 beta 4 seems also to occur more frequently in grade III IDC (seven of 11 cases, 63.6%) than in grade I/II IDC (two of eight cases, 25%), although this did not reach statistical significance. Carcinoembryonic antigen and carcinoembryonic antigen-related antigens, which are known to function as accessory adhesion molecules, were found mainly in the cytoplasm of neoplastic cells and there was reduced membrane polarization in poorly organized tumors. In contrast the alpha v beta 3, vitronectin receptor heterodimer recognized by the 23C6 monoclonal antibody was weak or absent in normal breast epithelium, and was weakly expressed in two of 19 (10%) IDCs and in nine of 18 (50%) invasive lobular carcinomas (P = .008). However, the alpha v chain detected with the antibody 13C2 was weakly to moderately expressed on nonneoplastic epithelium and at a similar intensity in 13 of 19 IDCs and 15 of 17 invasive lobular carcinomas, suggesting that in IDC the alpha v chain may be associated with a different beta chain (possibly beta 1 or beta 5). No correlation between integrin expression and estrogen/progesterone receptor status was found. These data provide further evidence that in invasive breast carcinomas there is a widespread deregulated expression of integrins and their accessory adhesion molecules with loss of polarization. Changes in the expression and function of cell adhesion molecules, which control growth and differentiation, may have clinical relevance in the behavior of breast cancer.

Distribution of integrin cell adhesion receptors in normal and malignant lung tissue

The integrins are a family of transmembrane glycoproteins that serve as cell-cell and cell-substratum adhesion molecules and help regulate cellular morphology, differentiation, and proliferation. The integrin repertoire of a cell may therefore influence its behavior under resting conditions or following malignant transformation. For this reason, the distribution of integrins in normal lung tissues was determined using monoclonal antibodies against integrins of the beta 1 (VLA) and beta 3 (cytoadhesin) subfamilies and compared with the distribution in a limited number of lung carcinomas. The integrin subunits that bind to collagen and laminin (alpha 1, alpha 2, alpha 3, and alpha 6) and the alpha subunit, which can pair with beta 1, beta 3, or beta 5 and promote fibronectin, fibrinogen, or vitronectin binding, were the predominant integrins expressed on the major cell types of the lung, i.e., bronchial epithelium, vascular endothelium, and smooth muscle. Strong expression of the alpha 5 beta 1 fibronectin receptor and the beta 3 subunit was restricted to the endothelium of large vessels. Integrin expression by the lung carcinoma cells was somewhat heterogeneous; however, the tumors tended to express fewer integrins than did the normal bronchial epithelium.

Intrahepatic up-regulated expression of extracellular matrix protein receptors in chronic active hepatitis type B

The aim of the present study was to investigate the differences in expression of beta 1 integrins between normal liver and the inflamed livers of patients with chronic active hepatitis B. Immunohistochemical staining with monoclonal antibodies that specifically recognize the common beta 1 chain and five different alpha subunits has been performed in frozen liver biopsy sections from 10 patients with chronic active hepatitis B and from 4 patients with normal livers. The major findings of our study were de novo expression in liver with chronic active hepatitis B of alpha 2 and alpha 3 subunits on both periportal hepatocytes and on lobular hepatocytes in close proximity to lymphocyte infiltrates. These results indicate the existence of an up-regulatory process in the expression of beta 1 integrins, especially the alpha 2 and alpha 3 subunits, in the inflamed liver tissue from patients with chronic active hepatitis B, suggesting that these integrins could play an important role in the development of liver fibrosis and in regulating intrahepatic lymphocyte migration.

Aggregation substance of Enterococcus faecalis mediates adhesion to cultured renal tubular cells

The sex pheromone system of Enterococcus faecalis is a unique, highly efficient plasmid collection mechanism for this species. A crucial role in this system is played by an adhesin called aggregation substance which enables the cell-cell contact between donor and recipient strains. The existence of the amino acid motif Arg-Gly-Asp-Ser in the adhesin prompted us to look for a possible binding of E. faecalis cells expressing aggregation substance to eucaryotic cells. We were able to show that the adhesin mediated binding to cultured renal tubular cells (porcine cell line LLC-PK1) via light microscopic, electron microscopic, and enzyme-linked immunosorbent assay-based studies. Synthesis of the adhesin was induced by some component(s) of serum. These data are interpreted to mean that aggregation substance is an adhesin mediating not only cell-cell contact between different E. faecalis strains but also binding of E. faecalis to eucaryotic cells, and therefore it might contribute to virulence.

Expression of beta 1, beta 3, beta 4, and beta 5 integrins by human epidermal keratinocytes and non-differentiating keratinocytes

We have compared the adhesive properties and integrin expression profiles of cultured human epidermal keratinocytes and a strain of nondifferentiating keratinocytes (ndk). Both cell types adhered to fibronectin, laminin, and collagen types I and IV, but ndk adhered more rapidly and at lower coating concentrations of the proteins. Antibody blocking experiments showed that adhesion of both cell types to fibronectin was mediated by the alpha 5 beta 1 integrin and to laminin by alpha 3 beta 1 in synergy with alpha 2 beta 1. Keratinocytes adhered to collagen with alpha 2 beta 1, but an antibody to alpha 2 did not inhibit adhesion of ndk to collagen. Both cell types adhered to vitronectin by alpha v-containing integrins. Immunoprecipitation of surface-iodinated and metabolically labeled cells showed that in addition to alpha 2 beta 1, alpha 3 beta 1, and alpha 5 beta 1, both keratinocytes and ndk expressed alpha 6 beta 4 and alpha v beta 5. ndk expressed all these integrins at higher levels than normal keratinocytes. ndk, but not normal keratinocytes, expressed alpha v beta 1 and alpha v beta 3; they also expressed alpha 1 beta 1, an integrin that was not consistently detected on normal keratinocytes. Immunofluorescence experiments showed that in stratified cultures of normal keratinocytes integrin expression was confined to cells in the basal layer; terminally differentiating cells were unstained. In contrast, all cells in the ndk population were integrin positive. Our observations showed that the adhesive properties of ndk differ from normal keratinocytes and reflect differences in the type of integrins expressed, the level of expression and the distribution of integrins on the cell surface. ndk thus have a number of characteristics that distinguish them from normal basal keratinocytes.

Low expression of beta 1, alpha 2 and alpha 3 subunits of VLA integrins in malignant mammary tumours

The Very Late Antigens (VLAs) are alpha beta heterodimeric transmembrane proteins mediating cell-substratum as well as cell-cell interactions. Changes in their expression and/or function seem to occur in a number of invasive carcinomas and may at least in part explain their abnormal patterns of growth and differentiation. Using monoclonal antibodies to the beta 1 (DH12, A1A-5), alpha 2 (B1.515) and alpha 3 (E1.56) chains, VLA-2 (alpha 2 beta 1) and VLA-3 (alpha 3 beta 1) were studied on cryostat sections of three fibroadenomas and 43 invasive breast carcinomas (29 ductal, 14 lobular) by the avidin-biotin complex immunoperoxidase technique. In non-neoplastic breast tissue and in fibroadenomas VLA-2 and VLA-3 were expressed by myoepithelial cells and on the basolateral surface of the luminal cells. There was weak or absent expression of alpha 2, alpha 3 and the common beta 1 chain in the majority of invasive carcinomas compared to the adjacent normal breast epithelium and preinvasive (in-situ) carcinomas. In addition, the expression of the alpha 2 chain of VLA-2 was reduced significantly (P less than 0.005) in the poorly differentiated ductal breast carcinomas (Grade III) compared to the well (Grade I) and moderately (Grade II) differentiated ductal tumours. These data give further evidence that loss or down-regulation of VLA-2 and VLA-3 occur relatively frequently in invasive cancers, and, at least in the invasive ductal breast carcinomas. Loss of an extracellular matrix receptor controlling growth and differentiation seems to be one of the abnormalities underlying the progression towards an undifferentiated morphology.

Characterization of integrin chains in normal and neoplastic human pancreas

Integrins are a complex family of non-covalently linked heterodimeric glycoproteins which function as cell adhesion molecules, interacting with extracellular matrix molecules such as laminin, fibronectin, vitronectin, and collagen, and also having a role in intercellular adhesion. Each integrin subfamily is characterized by a common beta chain associated with variable alpha chains. We have examined, using immunohistological methods, the expression of the VLA (very late activation) family comprising beta 1 in association with alpha 1-6, and also alpha 6 in association with beta 4, the LFA beta chain beta 2, and the vitronectin receptor, in association with beta 1 or beta 5 and as the complex alpha v beta 3. Cryostat sections of normal pancreas, pancreatic adenocarcinomas, and ampullary tumours were studied together with six pancreatic carcinoma cell lines. Normal pancreas showed expression of beta 1 in all parenchyma. alpha 2 and alpha 6 had a similar distribution whereas alpha 3 expression was confined to ducts, including the very smallest radicles. Staining along the basement membranes of ducts was seen with beta 4 and the anti-vitronectin alpha v chain receptor antibody 13C2. Islet cells failed to stain with any antibody. No staining of epithelial components was seen with antibodies to alpha 1, alpha 4, alpha 5, or to the alpha v beta 3 form of the vitronectin receptor (beta 3 and alpha v beta 3 using the antibody 23C6). Pancreatic adenocarcinomas and ampullary tumours showed expression of alpha 2, alpha 3, alpha 6, beta 1, beta 4, and the vitronectin receptor (alpha v associated with beta 1 or beta 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Novel integrin alpha and beta subunit cDNAs identified in airway epithelial cells and lung leukocytes using the polymerase chain reaction

The integrins are a large group of cell surface glycoproteins that mediate cell-matrix and cell-cell adhesive interactions. Integrins play a role in normal lung development, in host defense against pulmonary infection, and in the pathogenesis of the adult respiratory distress syndrome. Integrins are heterodimers consisting of one alpha subunit and one beta subunit. We identified consensus sequences within integrin subunits and used oligonucleotide primers based on these sequences to amplify cDNA by the polymerase chain reaction (PCR). We previously reported the use of this homology PCR technique for the identification of one novel integrin beta subunit, beta 6, from guinea pig airway epithelial cells. Here we demonstrate that primers based on alpha subunit consensus sequences can also be used for homology PCR. We have used the alpha and beta subunit primers to amplify and clone a large variety of integrin partial cDNAs from several cell types and species. Comparison of the deduced amino acid sequences reveals a high degree of cross-species conservation (86 to 98% identity). One alpha subunit (identified in guinea pig airway epithelial cells) and one beta subunit (identified in rabbit leukocytes obtained by bronchoalveolar lavage and in human and mouse leukocyte cell lines) have novel sequences that are related to but clearly distinct from all previously reported integrin sequences (24 to 61% identity). These novel cDNAs are very likely to encode previously unsequenced integrin subunit proteins that are expressed in the lung. Homology PCR is a powerful technique for the identification of known and novel integrin alpha and beta subunit cDNAs in cells from the lung and other organs.

Upregulated expression and function of VLA-4 fibronectin receptors on human activated T cells in rheumatoid arthritis

The VLA-4 (CD49d/CD29) integrin is a cell surface receptor involved in the interaction of lymphoid cells with both extracellular matrix (ECM) and endothelial cells. We have investigated the expression and function of VLA-4 fibronectin (FN) receptors on T cells localized in the inflammed synovium of patients with rheumatoid arthritis (RA). A high proportion of T cells in both synovial membrane (SM) and synovial fluid (SF) expressed the activation antigens AIM (CD69) and gp95/85 (Ea2) as well as an increased number of VLA-4 alpha and beta 1 adhesion molecules, as compared with peripheral blood (PB) T cells from the same patients. Furthermore, the majority of these activated SF T cells were able to adhere to a 38-kD FN proteolytic fragment containing the connecting segment-1 (CS-1) specifically through VLA-4 receptors, whereas a significantly lower proportion of PB T cells displayed this capacity. Therefore, our results show that activated T cells selectively localize at sites of tissue injury in RA disease and provide evidence for the in vivo regulation of the expression and function of the VLA-4 integrin. This regulatory mechanism may enable T cells either to facilitate migration or to persist at sites of inflammation.

Cultured human fibroblasts contain a large pool of precursor beta 1-integrin but lack an intracellular pool of mature subunit

Previous work has shown the presence of an important intracellular pool of beta 1-integrin subunit in human skin fibroblasts as detected with monoclonal antibody DH12 [De Strooper, B., Van der Schueren, B., Jaspers, M., Saison, M., Spaepen, M., Van Leuven, F., Van den Berghe, H. & Cassiman, J. J. (1989) J. Histochem. Cytochem. 37,299-307]. To analyze this more quantitatively, a radioimmunoassay with radioiodinated monoclonal antibody was developed. The total amount of specific binding sites for monoclonal antibody DH12 on skin fibroblasts was between 0.8-1.5 x 10(6)/cell. After permeabilizing the cells with digitonin, a threefold increase in specific binding was observed, which suggested that about 60% of the total amount of beta 1-subunit was localized intracellularly. From pulse/chase experiments, it was deduced that an important pool of precursor subunit, as defined by its sensitivity to endoglycosidase treatment, existed in fibroblasts. Since in steady-state-labeling conditions, at least three to four times more precursor than mature subunit was immunoprecipitated with monoclonal antibody DH12, we suggested that the intracellular pool of beta 1-integrin subunit is mainly precursor pool. This precursor pool contains a degradation compartment and a maturation compartment. Other investigators have found evidence for a recirculating pool of mature integrin in Chinese hamster ovary cells. Therefore, the presence of a recirculating pool of integrin in human fibroblasts was also considered. The data obtained with mAb DH12 showed that less than 10% of the surface pool of integrin was internalized by endocytosis. Since, however, cross linking of beta 1-integrins with polyclonal antibodies leads to rapid endocytosis of most of the integrin, it remains possible that the quantitatively small effect was actually an artefact induced by the divalent mAb. We conclude that the intracellular pool of beta 1-integrins observed in our previous studies consists of precursor and that in skin fibroblasts no mature beta 1-integrin is available intracellularly for rapid quantitative modulations at the cell surface.

Distribution of beta 1, alpha 1, alpha 2 and alpha 3 integrin chains in basal cell carcinomas

The integrins are alpha beta heterodimeric transmembrane proteins mediating cell-substratum as well as cell-cell interactions. Changes in their expression and/or function seem to occur in a number of malignant epithelial neoplasms and may in part explain their abnormal patterns of growth and differentiation. Using monoclonal antibodies to the beta 1 (DH12), alpha 1 (TS2/7), alpha 2 (B1.515), and alpha 3 (E1.56) integrin chains, the alpha 1 beta 1 (VLA-1), alpha 2 beta 1 (VLA-2), and alpha 3 beta 1 (VLA-3) integrin receptors were studied on cryostat sections of 22 basal cell carcinomas (BCCs) and adjacent normal tissues by a standard peroxidase-antiperoxidase technique. In non-neoplastic skin, VLA-2 and VLA-3 were found in the basal layer, eccrine glands, and cells of the outer root sheath in which VLA-1 was detected. In BCCs, there was a considerably higher expression of VLA-2 and VLA-3 compared with epidermal basal cells but similar to that seen in hair bulb and outer root sheath. In two cases of nodular BCC showing evidence of regression, both VLA-2 and VLA-3 were completely negative, in contrast to non-regressing foci which were strongly positive. The high level of expression of two adhesion molecules (VLA-2 and VLA-3) involved in cell-substratum as well as cell-cell interactions may account for the more indolent pattern of growth characteristic of BCC and perhaps reflect its high degree of differentiation towards the hair follicle.

VLA protein expression on epidermal cells (keratinocytes, Langerhans cells, melanocytes): a light and electron microscopic immunohistochemical study

The very late antigens, or VLA proteins, are a family of cell surface heterodimers (alpha 1-b beta 1) that mediate cell adhesion to specific components of the extracellular matrix (collagens, fibronectin, laminin). In normal human epidermis, the common VLA beta 1 subunit is expressed on basal keratinocytes (BK). Langerhans cells (LC) and melanocytes. By means of light and electron microscopic immunostaining procedures, we have investigated the distribution of VLA alpha 1,2,3,4,6 subunits on normal human adult and foetal epidermal cells. alpha 1 antigen expression was not observed on any epidermal cell type. Both during foetal development and in adult epidermis, alpha 2 and alpha 3 were strongly expressed on the cell membrane BK, while alpha 6 was mainly expressed at their dermal pole. These different patterns of distribution suggest that the alpha 6 subunit may mediate BK anchorage to the basement membrane zone, while the alpha 2 and alpha 3 subunits may also be involved in intracellular adhesion. Moreover, with immunoelectron microscopy, LC were seen to be weakly alpha 5 and alpha 6 positive and melanocytes were alpha 3 and alpha 6 positive. Thus, VLA proteins are expressed by epidermal cells in a cell-type-specific pattern that could be related to particular functional roles of these proteins.

Integrins in human cells and tumors

We have studied the distribution of the alpha- and beta-subunits of integrins in developing and adult human kidney as well as in selected other tissues and cultured cells. In cultured cells some of the integrin subunits (beta 1, alpha 1, alpha 2 and alpha 5) colocalize with talin at focal adhesions when plated on an appropriate ligand. Similarly, in tissues the polarization of beta 1-integrins in colocalization with talin appears to indicate adhesive complexes, as demonstrated in adult glomeruli. In human kidney, the alpha subunits of integrins were seen to be segment-specifically expressed already in fetal tissues. In glomeruli the integrin alpha 1 subunit characterized mesangial cells while the alpha 2 and alpha 3 subunits showed immunoreactivity in endothelial cells and podocytes, respectively. In renal tubuli, the alpha 6 subunit, complexed with the beta 1 subunit, showed a typical polarized distribution coaligning with the tubular basement membrane while the alpha 3 and alpha 2 subunits were expressed in distal tubular cells. These results suggested that in kidney the alpha 2 beta 1, alpha 3 beta 1, and alpha 6 beta 1 integrins can function as basement membrane receptors. The alpha 5 subunit was nearly lacking in the kidney and it appears to be mainly expressed in some smooth muscle cells. In other tissues distinct patterns in the expression of integrins were found. Thus, in many glandular epithelial cells the alpha 3 beta 1 integrin appeared to function as a basement membrane receptor while in various stratified epithelia and in the breast such a polarized localization could be found for the alpha 6 beta 4 integrin. Finally, although presenting a clearly polarized distribution for beta 1 integrins, none of the alpha subunits could be found in cardiac or skeletal muscle cells and none of the integrins could be revealed in neuronal cells of human developing and adult cerebrum or cerebellum, although neurons in peripheral tissues contained abundantly the alpha 6 beta 1 integrin complex. In human tumors, the tumor cells, including also metastastatic tumors, generally presented the same integrins as their tissues of origin. In some poorly differentiated tumors both a population heterogeneity and even a lack of expression or a disorganization of basement membrane receptor integrins was obvious.

The alpha 1-alpha 6 subunits of integrins are characteristically expressed in distinct segments of developing and adult human nephron

We studied the distribution of the alpha 1-alpha 6 subunits of beta 1 integrins in developing and adult human kidney using a panel of mAbs in indirect immunofluorescence microscopy. Uninduced mesenchyme displayed a diffuse immunoreactivity for only the alpha 1 integrin subunit. At the S-shaped body stage of nephron development, several of the alpha subunits were characteristically expressed in distinct fetal nephron segments, and the pattern was retained also in the adult nephron. Thus, the alpha 1 subunit was characteristically expressed in mesangial and endothelial cells, the alpha 2 in glomerular endothelium and distal tubules, the alpha 3 in podocytes, Bowman's capsule, and distal tubules, and the alpha 6 subunit basally in all tubules, and only transiently in podocytes during development. Unlike the alpha 3 and alpha 6 subunits, the alpha 2 subunit displayed an overall cell surface distribution in distal tubules. It was also distinctly expressed in glomerular endothelia during glomerulogenesis. The beta 4 subunit was expressed only in fetal collecting ducts, and hence the alpha 6 subunit seems to be complexed with the beta 1 rather than beta 4 subunit in human kidney. Of the two fibronectin receptor alpha subunits, alpha 4 and alpha 5, only the latter was expressed, confined to endothelia of developing and adult blood vessels, suggesting that these receptor complexes play a minor role during nephrogenesis. The present results suggest that distinct integrins play a role during differentiation of specific nephron segments. They also indicate that alpha 3 beta 1 and alpha 6 beta 1 integrin complexes may function as basement membrane receptors in podocytes and tubular epithelial cells.

An alternative leukocyte homotypic adhesion mechanism, LFA-1/ICAM-1-independent, triggered through the human VLA-4 integrin

The VLA-4 (CD49d/CD29) integrin is the only member of the VLA family expressed by resting lymphoid cells that has been involved in cell-cell adhesive interactions. We here describe the triggering of homotypic cell aggregation of peripheral blood T lymphocytes and myelomonocytic cells by mAbs specific for certain epitopes of the human VLA alpha 4 subunit. This anti-VLA-4-induced cell adhesion is isotype and Fc independent. Similar to phorbol ester-induced homotypic adhesion, cell aggregation triggered through VLA-4 requires the presence of divalent cations, integrity of cytoskeleton and active metabolism. However, both adhesion phenomena differed at their kinetics and temperature requirements. Moreover, cell adhesion triggered through VLA-4 cannot be inhibited by cell preincubation with anti-LFA-1 alpha (CD11a), LFA-1 beta (CD18), or ICAM-1 (CD54) mAb as opposed to that mediated by phorbol esters, indicating that it is a LFA-1/ICAM-1 independent process. Antibodies specific for CD2 or LFA-3 (CD58) did not affect the VLA-4-mediated cell adhesion. The ability to inhibit this aggregation by other anti-VLA-4-specific antibodies recognizing epitopes on either the VLA alpha 4 (CD49d) or beta (CD29) chains suggests that VLA-4 is directly involved in the adhesion process. Furthermore, the simultaneous binding of a pair of aggregation-inducing mAbs specific for distinct antigenic sites on the alpha 4 chain resulted in the abrogation of cell aggregation. These results indicate that VLA-4-mediated aggregation may constitute a novel leukocyte adhesion pathway.

Localization of integrin receptors for fibronectin, collagen, and laminin in human skin. Variable expression in basal and squamous cell carcinomas

VLA integrins in human skin were examined by indirect immunofluorescence utilizing antibodies recognizing the beta 1, alpha 2, alpha 3, or alpha 5 subunits. Staining of fetal, newborn, or adult skin with antibodies to beta 1, alpha 2, or alpha 3 subunits gave essentially similar staining patterns: intense staining was associated with the basal layer of the epidermis, hair follicles, and blood vessel walls. The alpha 5 subunit could be detected only in epidermis and the inner root sheath of hair follicles in fetal skin. In epidermis, the staining reaction for the beta 1 subunit was not only found in sites interfacing with the basement membrane zone, but also around the entire periphery of these cells. We speculate that these receptors might have previously unrecognized functions in cell-cell interactions or that these findings may suggest the presence of previously unrecognized ligands in the intercellular spaces of keratinocytes. Examination of nine nodular basal cell carcinomas revealed a prominent staining reaction with anti-beta 1 and anti-alpha 3 antibodies at the periphery of the tumor islands. In contrast, staining of five squamous cell carcinomas revealed either the absence of integrins or altered and variable expression. Thus, matrix components and their receptors may participate in modulation of growth, development, and organization of human skin.