The alpha3 laminin subunit, alpha6beta4 and alpha3beta1 integrin coordinately regulate wound healing in cultured epithelial cells and in the skin

Previously, we demonstrated that proteolytic processing within the globular domain of the alpha3 subunit of laminin-5 (LN5) converts LN5 from a cell motility-inducing factor to a protein complex that can trigger the formation of hemidesmosomes, certain cell-matrix attachment sites found in epithelial cells. We have prepared a monoclonal antibody (12C4) whose epitope is located toward the carboxy terminus of the globular domain of the alpha3 laminin subunit. This epitope is lost from the alpha3 subunit as a consequence of proteolytic processing. Antibody 12C4 stains throughout the matrix of cells that fail to process the alpha3 laminin subunit, but does not recognize the matrix of confluent cultures of MCF-10A cells, which efficiently process their alpha3 laminin chain. In subconfluent populations of MCF-10A cells, 12C4 only stains matrix deposited at the outer edges of cell colonies. In these cells, integrin alpha3beta1 occasionally colocalizes with the staining generated by the 12C4 antibody but alpha6beta4 integrin does not. In wounded MCF-10A cell cultures, the 12C4 antibody stains the extracellular matrix beneath those cells at the very edge of the cellular sheet that moves to cover the wound site. A similar phenomenon is observed in human skin wounds, since we also detect expression of the unprocessed alpha3 laminin subunit at the leading tip of the sheet of epidermal cells that epithelializes skin wounds in vivo. In addition, using alpha3 laminin subunit and integrin function-inhibiting antibodies, we provide evidence that LN5 and its two integrin receptors (alpha6beta4 and alpha3beta1) appear necessary for wound healing to occur in MCF-10A cell culture wounds. We propose a model for healing of wounded epithelial tissues based on these results.

Laminin mediates tethering and spreading of colon cancer cells in physiological shear flow

Under the physiological shear condition, cultured colon cancer cells bound to laminin (LM), but not to fibronectin or vitronectin. Most of the tethered cells did not roll, but arrested immediately and spread within 10-30 min on LM under the continuous presence of shear flow. The tethering of Colo201 was partially inhibited by monoclonal antibodies (mAbs) to alpha6 integrin and a combination of mAbs to beta1 and beta4 integrins, but not by mAb to 67KD laminin receptor. Some Colo201 cells still tethered at 4 degrees C. This suggests that alpha6beta1 and alpha6beta4 integrins participate in Colo201 tethering on LM, although other non-integrin molecules play roles. In contrast, the spread of Colo201 was effectively inhibited by the mAbs to integrin alpha2, alpha6 and beta1 chains. The effect of anti-alpha2 plus anti-alpha6 mAbs was almost equal to anti-beta1, suggesting that Colo201 cells mainly use alpha2beta1 and alpha6beta1 integrins for spreading on LM. When the cells were perfused on subconfluent endothelial cells (HUVEC) cultured on LM, they did not tether on HUVEC but did on coated LM exposed at intercellular gap area. Immunohistochemistry revealed that LM abundantly existed in the cytosol of human portal and hepatic vein endothelial cells. These data suggest that LM can mediate from tethering to spreading of colon cancer cells under the blood flow and plays an essential role in haematogeneous metastasis.

Inhibition of experimental metastasis of human fibrosarcoma cells by anti-recombinant 37-kDa laminin binding protein antibody

The laminin binding protein of 37 kDa (37LBP) is regarded as a precursor protein of the high-affinity 67-kDa laminin receptor (67LR). Expression of 67LR/37LBP is well correlated with biological aggressiveness of cancer, particularly with invasive and metastatic potential. To investigate in detail the role of 37LBP in cancer cells, we synthesized recombinant 37LBP (r37LBP) as a fusion protein and generated an IgG-type polyclonal antibody P4G against r37LBP. Western blot analysis with P4G showed a single band of 67LR under both nonreducing and reducing conditions using cell extract of human fibrosarcoma cells HT1080. It was shown that P4G inhibited cell attachment to immobilized laminin in a dose-dependent manner. Further, the intravenous injection of HT1080 cells pretreated with P4G, compared with that of cells pretreated with normal rabbit serum, resulted in a reduced number of experimental metastases (3.3+/-5.1 vs. 58.0+/-38.0 nodules per mouse, respectively) (P<0.005). These results suggest that P4G inhibits the colonization and growth of HT1080 cells in the lungs of mice, and that the blocking of r37LBP with the specific antibody P4G may offer a potential strategy for preventing cancer metastasis.

Neuronal receptors mediating responses to antibodyactivated laminin-1

Embryonic retinal neurons lose the ability to extend neurites on laminin-1 (LN-1) with increasing developmental age yet still do so on other laminin isoforms. However, after treatment of LN-1 with antibodies to "short-arm" regions or removal of the short arms proteolytically, LN-1 supports attachment and extension of neurites even by late embryonic retinal neurons. We have mapped a domain for antibody-mediated "activation" of LN-1 to the N-terminal end of the alpha1 chain. Furthermore, we show that the primary receptors used in the retinal neuron response to "activated" LN-1 are integrins alpha3 beta1 and alpha6 beta1; these are the same receptors used by these neurons for outgrowth on other LN isoforms. Interestingly, alpha3 beta1 is preferentially involved in neurite outgrowth, whereas alpha6beta1 preferentially mediates attachment and spreading. However, in cultures from alpha3 integrin-deficient mice, alpha6 beta1 mediates retinal ganglion cell neurite outgrowth and compensates for the absence of alpha3 beta1. Finally, we show that key features of the retinal neuron response to LN-1 also characterize neurons of the hippocampus, thalamus, and cerebral cortex; these include poor response to untreated LN-1, extensive neurite outgrowth on antibody-activated LN-1 or on fragment E8, and dependence of this response on integrin alpha6 beta1 and at least one other long arm-binding beta1 integrin. These data suggest that regulation of LN-1 function via the process of activation could have important consequences for axonal regeneration. Curiously, the data also imply that the mechanism of laminin activation involves enhanced function at sites that cannot be considered cryptic.

Evidence for integrin receptor involvement in megakaryocyte-fibroblast interaction: a possible pathomechanism for the evolution of myelofibrosis

Megakaryocytes are assumed to be functionally linked with the evolution of myelofibrosis, complicating chronic myeloproliferative disorders. It has already been shown that megakaryocytes will promote fibroblast growth in vitro when in spatial proximity. Here, we demonstrate that the integrin receptors alpha3beta1 and alpha5beta1 are involved in this megakaryocyte-fibroblast interaction. Upon addition of anti-alpha3 and -alpha5 antibodies to megakaryocyte-fibroblast cocultures, fibroblast growth was significantly impaired, and megakaryocyte attachment to the fibroblast feederlayer was significantly reduced. Unilateral blocking of megakaryocytes with anti-alpha3 or -alpha5 antibodies resulted in a suppression of adhesion, probably reflecting the prominent function of fibronectin receptors on the megakaryocyte surface. Moreover, the oligopeptide RGDS (Asp-Gly-Asp-Ser) caused a significant reduction of fibroblast growth as well as megakaryocyte adhesion. This feature reinforces that fibronectin receptors are involved. In addition, fibroblast proliferation was impaired by the application of fibronectin antibodies recognizing the cell-binding domain. However, no effect was observable with respect to megakaryocyte adhesion. In conclusion, our in vitro studies demonstrate the involvement of beta1-integrins, in particular the fibronectin receptor in the megakaryocyte-dependent fibroblast proliferation and therefore suggest a pivotal role of megakaryocytes in the complex pathomechanism causing myelofibrosis.

Genetic identification of antigens exposed in damaged endothelial cells as laminin-binding proteins

A monoclonal antibody, D5G2, which reacts in a balloon angioplasty damage model with unfixed damaged but not with unfixed undamaged human endothelial cells, was used to screen a human endothelial cDNA library in an Escherichia coli/lambda gt11 expression system. Sequences of DNA inserts in D5G2+ phage clones matched those reported for a laminin-binding protein, LBP-32. Both D5G2 and purified laminin bound to a polypeptide of 55 kD on PVDF membranes carrying electrophoretically separated endothelial cell lysates, D5G2 also bound to recombinant LBP expressed in E. coli, and showed similar staining patterns on human and bovine endothelial cells to another characterized anti-LBP antibody. Increased staining of unfixed endothelial cells on detergent permeabilization suggests that D5G2 binds to intracellular laminin-binding protein made accessible by cell membrane injury. Antibodies to intracellular targets exposed by cell damage may be useful in anchoring therapeutic agents at sites of vascular damage.

Interaction of integrin alpha 7 beta 1 in C2C12 myotubes and in solution with laminin

The dimer of integrin alpha 7 and beta 1 is a major laminin-binding receptor in skeletal muscle. We studied interactions of integrin alpha 7 beta 1 with the extracellular matrix protein laminin in solution and in intact cells. Integrin alpha 7 beta 1 bound to EHS laminin (laminin-1, composed of alpha 1, beta 1, and gamma 1 chains), but not to endogenous laminin expressed in C2C12 myotubes. Northern blot analysis demonstrated that C2C12 myotubes synthesized laminin-1 alpha, beta, and gamma subunits mRNAs. C2C12 laminin was, however, immunologically distinct from EHS laminin; it was not recognized by 5D3 anti-laminin-1 monoclonal antibody, whereas 5A2 and LT3 antibodies reacted equally well with C2C12 and EHS laminins. Following deglycosylation of EHS laminin, separation of the subunits by SDS-PAGE, Western blotting, and partial amino acid sequencing of the protein bands, the epitope recognized by 5D3 antibody was localized to the gamma 1 laminin chain. Following binding in vitro, the complex of EHS laminin and integrin alpha 7 beta 1 was subject to chemical cross-linking. The two proteins did not undergo cross-linking at the cell surface, consistent with the fact that in intact, resting myotubes integrin alpha 7 beta 1 interacted poorly with EHS laminin, which may reflect a limited accessibility of integrin alpha 7 beta 1 in the membrane to laminin or an inactive state of the integrin.

Involvement of the YIGSR sequence of laminin in protein tyrosine phosphorylation

We have examined the mechanism of signaling by the 67 kDa YIGSR binding protein of laminin and its properties in neuroblastoma cells. Ligand displacement analysis showed that the interaction with the C(YIGSR)3-NH2 peptide amide is of intermediate affinity (1.5 x 10[-7] M). Cross-linking experiments with sulfo-MBS detected an additional protein with a molecular mass of 116 kDa that binds the YIGSR sequence. Incubation of neuroblastoma cells with C(YIGSR)3-NH2 peptide amide or antibody directed against the 67 kDa laminin binding protein induces tyrosine phosphorylation of proteins with a molecular mass ranging from 115 to 130 kDa and another heterogeneous protein group of 32 kDa.

Expression of 32/67-kDa laminin receptor in laminin adhesion-selected human colon cancer cell lines

Laminin promotes the malignant phenotype, and the expression of certain laminin receptors is increased in malignancy. Previously, we demonstrated that a laminin-adhesive subclone of a human colon cancer cell line showed increased tumorigenicity in nude mice and increased affinity of the beta1 integrin for laminin relative to the laminin-non-adhesive subclone. The total amount of either beta1 integrin protein or mRNA did not increase. As levels of the 32/67-kDa laminin receptor (67LR) correlate with malignancy, we examined 67LR expression in the laminin adhesion-selected human colon cancer cells. The laminin-adhesive subclone, which was more tumorigenic in both heterotopic and orthotopic locations than in a laminin-non-adhesive subclone, showed cell-surface membrane staining of 67LR, whereas the laminin-non-adhesive subclone showed cytoplasmic staining of 67LR. No difference in either the amount of 67LR mRNA or the amount of protein was observed in the parental cells than in the laminin-adhesive and non-adhesive subclones. When assayed on a laminin affinity column, more 67LR molecules bound to the column with cell extracts from the laminin-adhesive subclone than was observed with the non-adhesive subclone. These findings suggest that the increased tumorigenicity of laminin adhesion-selected tumour cells might be due to an alteration in the distribution and/or adhesiveness of multiple receptors including 67LR and beta1 integrin.

Alpha 6 beta 4 and alpha 6 beta 1 integrins associate with ErbB-2 in human carcinoma cell lines

Growth factors modulate integrin-mediated cell adhesion and motility, and their receptors are thought to share proteins that mediate intracellular signaling with integrin receptors. The crosstalk between these receptors is thought to play a relevant role in transformation and tumor progression. To highlight possible interactions between growth factors and cell adhesion receptors we investigated whether integrins associate with tyrosine kinase receptors in tumor cells. By affinity chromatography and Western blot analyses of purified immune complexes, we studied the association of laminin receptors (alpha 6 beta 1 and alpha 6 beta 4) with ErbB-2 tyrosine kinase in human carcinoma cell lines. We demonstrated that the alpha 6 beta 4 and alpha 6 beta 1 integrins coprecipitated with ErbB-2 in lysates from carcinoma or NIH3T3 cells overexpressing ErbB-2. Integrin-mediated activation of ErbB-2 receptors suggested that this association is functionally meaningful. Indeed, carcinoma cells treated with a monoclonal antibody to the alpha 6 integrin subunit showed a ligand-dependent increase of ErbB-2-phosphorylated molecules coprecipitated with integrins and an increased DNA synthesis. The interaction between growth factor receptors and integrins was also studied in NIH3T3 cells overexpressing alpha 6 beta 4 receptors and ErbB-2 protein. We report that cells overexpressing both receptors, but not those overexpressing a crippled ErbB-2, showed enhanced proliferation rates and invasiveness, further suggesting that alpha 6 beta 4 integrin and ErbB-2 receptor interaction might contribute to generate a more malignant phenotype in carcinoma cells.

Coordinated expression of integrin alpha6beta1 and laminin in hepatocellular carcinoma

The interaction between tumor cells and laminin mediated by laminin-binding integrins is critical for tumor invasion and metastasis. The aim of this study was to clarify the altered expression of laminin-binding integrins with the change of laminin deposition in hepatocellular carcinoma (HCC) in comparison with cirrhotic or normal liver by immunohistochemistry. In HCC, hepatoma cells and sinusoidal endothelial cells expressed integrins alpha1beta1, alpha2beta1, alpha3beta1, and alpha6beta1. Integrins alpha1beta1 and alpha6beta1 were detected in a continuous pattern along the sinusoids in accordance with laminin assembly. Integrins alpha2beta1 and alpha3beta1 were detected in a discontinuous pattern at these sites. Integrin alpha6beta4 was not detected. In cirrhotic liver, although integrins alpha1beta1 and alpha6beta1 as well as laminin were detected in a continuous pattern along the sinusoids, integrins alpha2beta1, alpha3beta1, and alpha6beta4 were not detected. In normal liver, although integrin alpha1beta1 was detected in a continuous pattern along the sinusoids, neither integrins alpha2beta1, alpha3beta1, alpha6beta1, alpha6beta4, nor laminin were detected. We have clarified that, of laminin-binding integrins, the localization of integrin alpha6beta1 shows the best correspondence with the localization of laminin. These results suggest that of laminin-binding integrins, integrin alpha6beta1 is very important for cell-laminin interactions in HCC.

Interactions between integrin receptors and fibronectin are required for calvarial osteoblast differentiation in vitro

We previously showed that anti-fibronectin antibodies or soluble fibronectin fragments containing the central cell-binding domain inhibit formation of mineralized nodules by fetal calvarial osteoblasts in vitro. These findings suggest a critical role for fibronectin in osteoblast differentiation and morphogenesis. In this study we tested the hypothesis that fibronectin's effects on osteogenesis are mediated via direct interactions with integrin receptors for fibronectin on osteoblasts. Immunocytochemical analysis identified the integrin fibronectin receptor alpha5ss1 in fetal rat calvarial tissue and in cultured osteoblasts at all stages of differentiation. Three other integrins, alpha3ss1, alpha8ss1 and alphavss3, which can bind fibronectin, as well as other matrix components, were also identified in tissue and at all stages of cell culture. Immunoprecipitation data showed that alpha5ss1 levels are constant throughout osteoblast differentiation whereas levels of alpha3ss1 and alpha8ss1 decline in mature mineralized cultures. To determine whether integrin fibronectin receptors are required for osteoblast formation of mineralized nodules, we examined the extent of nodule formation in the presence and absence of function-perturbing anti-integrin antibodies. The antibodies were present continuously in cultures beginning at confluence (day 3), and nodule formation was measured at days 10 and 20. An anti-alpha5 integrin subunit antibody reduced nodule formation to less than 5% of control values at both time points. Inhibition of nodule formation was reversible and did not affect cell attachment and viability. Function-perturbing antibodies against alpha3ss1 and alpha8ss1 also reduced nodule formation, to less than 20% of control values. In contrast, function-perturbing antibodies to alphavss3 and alphavss5 did not affect nodule formation, indicating that the inhibitions noted were indeed specific. To determine the effect of antibody treatment on gene expression, steady-state mRNA expression was examined and found to be suppressed for osteoblast markers alkaline phosphatase and osteocalcin. Together, these results indicate that direct osteoblast interactions with the extracellular matrix are mediated by a select group of integrin receptors that includes alpha5ss1, alpha3ss1 and alpha8ss1. We further conclude that the specific alpha5ss1 fibronectin receptor mediates critical interactions between osteoblasts and fibronectin required for both bone morphogenesis and osteoblast differentiation.

An epitope on VLA-6 (alpha6beta1) integrin involved in migration but not adhesion is required for extravasation of murine melanoma B16F1 cells in liver

VLA-6 (alpha6beta1) integrin represents the major receptor for interaction with laminin substrate. It has been proposed that VLA-6 mediates tumor cell adhesion to the endothelium during extravasation. We have further explored this possibility using mouse melanoma B16F1 cells, which express VLA-6 as the principal laminin receptor, and two VLA-6 monoclonal antibodies (mAbs), MA6 and GoH3. Adhesion is a prerequisite of cell movement on matrix proteins. Thus, GoH3, which inhibited VLA-6-mediated adhesion, blocked cell movement on laminin. The recently prepared alpha6 integrin-specific mAb MA6 bound to an epitope in close proximity to GoH3, but it had no effect on VLA-6-mediated cell adhesion. We report here that although MA6 did not affect adhesion, it blocked mouse melanoma B16F1 cell movement on laminin to the same extent as GoH3. Results therefore demonstrate an active role of VLA-6 in providing cell movement as well as the initial adhesive event on laminin. In addition, mAb MA6 had no effect on the induction of tyrosine phosphorylation of focal adhesion kinase upon adhesion of B16F1 cells to laminin. Therefore, inhibition of cell movement by MA6 involved mechanism(s) other than an interference of VLA-6 signaling events leading to phosphorylation of focal adhesion kinase. The epitopes of GoH3 and MA6 may represent spatially and temporally related sites on VLA-6 that are involved during cell movement, or, alternatively, MA6 may inhibit the interaction of VLA-6 with associated cell surface molecules required for cell movement. In vivo videomicroscopy experiments also revealed that an inhibition of VLA-6 migratory function by MA6 resulted in a reduction in the ability of B16F1 to extravasate during hematogenous metastasis in the liver.

Involvement of laminin and its receptor in abrogation of heart graft rejection by autoreactive T cells from Trypanosoma cruzi-infected mice

Extracellular matrix ligands and receptors have been identified as determining in vivo lymphocyte positioning and activation, including effector functions in alloreactive responses. Herein we evaluated the involvement of laminin and its receptor, the very late antigen 6 (VLA-6) integrin, in CD4+ T cell-dependent autoreactivity, using a transplantation model for the autoimmune myocarditis occurring in mice chronically infected with Trypanosoma cruzi. Previous work showed that syngeneic mouse hearts grafted in the ears of chronic chagasic recipients were rejected through a CD4+ T cell-dependent mechanism. Rejection also occurred when cells from chagasic animals were transferred adjacent to hearts transplanted into naive recipients. Here, we observed the formation of a thick laminin network during rejection, with donor-derived CD4+ T cells concentrated in the laminin-rich areas. Most importantly, anti-laminin as well as anti-laminin receptor Ab inhibited the rejection of syngeneic hearts by T cells from chagasic animals. Our results suggest that interaction of the VLA-6 molecule with laminin is involved in triggering the antimyocardial autoreactive process by driving the influx of CD4+ T cells to the heart. They also support the concept that an Ag-specific T cell response, even an autoreactive one, can be modulated by in vivo interactions involving extracellular matrix ligands and receptors. In this regard, our study represents, to our knowledge, the first in vivo evidence for laminin-mediated T cell echotaxis, with simultaneous experimental demonstration of ligand and receptor involvement. Lastly, our findings indicate that treatment with anti-VLA-6 Abs can be effective in suppressing autoimmune disease activity.

Laminin suppresses progesterone production by human luteinizing granulosa cells via interaction with integrin alpha 6 beta 1

We previously raised a murine monoclonal antibody (mAb), OG-1, against human granulosa cells (GC) and reported that human GC express the OG-1 antigen with the highest immunoreactivity during the periovulatory phase. Later, we showed that the OG-1 antigen is identical to human integrin alpha 6, and that human GC express integrin alpha 6 beta 1, but not alpha 6 beta 4. In the present study, we examined the expression of laminin (LN), the ligand for integrin alpha 6 beta 1. Flow cytometry showed that LN was bound to the cell surface of some GC obtained from preovulatory follicles of patients undergoing in vitro fertilization. Immunohistochemistry showed that LN was detected between luteinizing GC in the early corpora lutea. To examine the effect of LN on steroidogenesis by human luteinizing GC, GC obtained from patients undergoing in vitro fertilization were cultured on mouse LN-coated or noncoated plastic dishes in medium containing 5% FCS for 24 h. In the absence or presence in hCG (1 IU/mL), GC cultured on LN-coated dishes produced 0.70- and 0.67-fold less progesterone than those on noncoated dishes, respectively (P < 0.05). We examined the effect of the interaction of integrin alpha 6 beta 1 and LN on steroidogenesis by human luteinizing GC. We cultured GC with 5 micrograms/mL of the anti-alpha 6 mAb GoH3, which inhibits the interaction between human integrin alpha 6 beta 1 and mouse LN, or with a control rat mAb (TER199) on mouse LN-coated dishes in serum-free medium for 24 h. In the absence or presence of hCG (1 IU/mL), GC cultured with GoH3 produced 1.97- and 1.94-fold more progesterone than the control cells (P < 0.01 and P < 0.05, respectively). In contrast, when GC were cultured on dishes coated with type IV collagen, progesterone production was not enhanced by GoH3. Furthermore, the anti-alpha 6 mAb OG-1, which does not inhibit the interaction between integrin alpha 6 beta 1 and LN, had no effect on the progesterone production by GC cultured on LN. These results indicate that LN suppresses the luteinization of human luteinizing GC via integrin alpha 6 beta 1 and that integrin alpha 6 beta 1 regulates the luteinization of human GC during the periovulatory phase.

Variable region structure and staphylococcal protein A binding specificity of a mouse monoclonal IgM anti-laminin-receptor antibody

Staphylococcal protein A is a cell wall-attached polypeptide that acts as a B-lymphocyte superantigen. This activation correlates with specific VH gene segment usage in the B-cell receptor. B-cell receptor assembled from members of the VH3 family in humans, or S107 family in mice, has an intrinsic affinity for protein A. Human VH3-derived antibodies bind to domain D of protein A. We have characterized a mouse IgM monoclonal antibody that binds protein A. The sequencing of the variable region suggests an almost germline-encoded VH derived from S107 family and a V kappa 8-derived VL. The binding specificity of the monoclonal antibody was tested with various recombinant constructions derived from protein A. We show that, unlike human VH3-derived antibody, mouse S107-derived immunoglobulin binds to the B domain of the bacterial superantigen.

The A and B variants of the alpha 3 integrin subunit: tissue distribution and functional characterization

The alpha subunits of the laminin-binding integrins alpha 3 beta 1, alpha 6 beta 1, and alpha 7 beta 1 have homologous sequences and are similar in structure. Two cytoplasmic variants, A and B, have been identified for each of these alpha subunits, although the alpha 3B splice variant has been detected only at the mRNA level. We prepared a panel of mouse monoclonal antibodies specific for the A and B variants of the alpha 3 subunit to study their tissue distribution. Four monoclonal antibodies react with alpha 3A, one of which recognizes only the nonphosphorylated form; of the three anti-alpha 3B antibodies, one cross-reacts with alpha 6B. Reverse transcriptase-PCR analysis of various human tissues revealed the presence of alpha 3B mRNA in brain, heart, and skeletal muscle. Moreover, the alpha 3B protein was detected by immunoblotting in brain and heart tissue but not in skeletal muscle. In contrast, alpha 3A mRNA and protein were present in all tissues studied. Thus, the expression of alpha 3B in adult tissues is more restricted than that of alpha 3A. Immunohistochemical studies showed that in brain tissue, both variants are exclusively expressed on small blood-vessel endothelium, whereas in heart tissue their distribution patterns differ markedly. Although alpha 3A is strongly expressed on vascular smooth muscle cells, alpha 3B is detected only on endothelial cells of veins. Expression of the two variant forms of alpha 3 in K562 cells revealed that the ligand-binding specificities of alpha 3A beta 1 and alpha 3B beta 1 are identical: both bind human laminin-2 and -4, laminin-5, and laminins isolated from bovine kidney, but not bovine laminin-2 and -4, mouse laminin-1, or human fibronectin. In addition, adhesion mediated by both integrins is induced to the same extent by phorbol 12-myristate 13-acetate. The alpha 3A, but not the alpha 3B subunit, is phosphorylated; and phosphorylation of alpha 3A increases after phorbol 12-myristate 13-acetate stimulation. Thus, we found no differences between the adhesion functions of the A and B variants of alpha 3.

67-Kilodalton laminin receptor expression correlates with worse prognostic indicators in non-small cell lung carcinomas

Tumor samples obtained from 72 patients resected for non-small cell lung cancer were stained immunohistochemically using an immunoperoxidase method and the MLuC5 monoclonal antibody specific for the 67-kDa laminin receptor. Sixty-one of 72 patients (84.7%) displayed a MLuC5-positive reaction, which was usually localized in both the inner surface of the plasmatic membranes and the cytoplasm of neoplastic cells. When we compared the laminin receptor expression with clinicopathological and biological parameters such as histotype, grading, T status, N status, ploidy, proliferative activity, vessel invasion, and p53 protein accumulation, the following results were observed: (a) the mean expression of the receptor was higher in the group of patients with metastatic nodal involvement than in those with uninvolved lymph nodes (P = 0.02); (b) a high Ki-67 score (>13% of positive cells) was observed in tumors with a higher mean value of laminin receptor (P = 0.004); (c) the tumors harboring neoplastic emboli in their vessels showed a higher laminin receptor immunoreactivity (P = 0.02); and (d) a borderline association was found between the high mean value of laminin receptor immunopositivity and p53 accumulation in neoplastic cell nuclei (P = 0.05). Our observations indicate that detection of high tissue levels of 67-kDa laminin receptor is associated with an invasive phenotype in non-small cell lung cancer and may provide further information in the biological characterization of this type of cancer.

Laminin-binding epitope on gp43 from Paracoccidioides brasiliensis is recognized by a monoclonal antibody raised against Staphylococcus aureus laminin receptor

Adhesion is regarded as an important step in the pathogenesis of several microorganisms. Thus, the ability to recognize extracellular matrix proteins, such as laminin or fibronectin, has been correlated with invasiveness. Studying the already characterized laminin-binding protein of Paracoccidioides brasiliensis, the 43 kDa glycoprotein (gp43), we evaluated whether MAb 1.H12, raised against the laminin-binding protein from Staphylococcus aureus, cross-reacts with that fungal protein. By immunoblot analysis we show that MAb 1.H12 recognizes gp43. This interaction is able to inhibit the laminin-mediated adhesion to epithelial cells as well as the P. brasiliensis infection in vivo. Moreover, through immunoenzymatic assays, we show that MAb 1.H12 recognizes gp43 in solid phase and that this interaction is partially inhibited by the addition of anti-gp43 MAbs. These results show that MAb 1.H12 recognizes the gp43, suggesting the presence of an epitope similar to those found in the other laminin-binding proteins from phylogenetically very distant cells. These findings reinforce the possibility of evolutionary conservation of such epitopes.

Analysis of nuclear localization of laminin binding protein precursor p40 (LBP/p40)

We isolated a monoclonal antibody M108, which recognized 40 kDa protein (p40) in the cytoplasm, the perinuclear region in interphase and the perichromosomal region during mitosis. As reported previously, it was revealed from the immunofluorescent observation and the biochemical analyses that the nuclear p40 was associated both with the nuclear envelope and the chromatin DNA in interphase nuclei. In this report, we isolated the p40 from cytoplasmic particles, and identified it by extensive microsequencing as LBP/p40, which was considered to be a precursor of laminin binding protein p67 (LBP/p67). Epitope-tagged LBP/p40 was expressed in cultured cells, and the protein was localized in the nucleus as well as in the cytoplasm. Further analysis showed that the nuclear LBP/p40 was tightly associated with the nuclear structures.

VLA-5 in the plasma cell line, FR4ds, acts as a common regulator of VLA-4 and VLA-6 in spreading induced by fibronectin and laminin

VLA-5 recognizes the GRGDSP sequence of fibronectin (FN) in the extracellular matrix (ECM). We examined the role of beta1 integrin in the spreading of the human plasma cell line, FR4ds, induced by FN and laminin (LN). We first examined the role of VLA-5 in the spreading induced by FN. Anti-alpha4 antibody induced 46.4% inhibition, whereas anti-alpha5 had no effect. A combination of anti-alpha4 and anti-alpha5 enhanced the inhibition of spreading significantly. Complementary inhibition was also demonstrated using the GRGDSP peptide plus anti-alpha4 and the GRGDNP peptide of LN plus anti-alpha4. The results suggested that VLA-5 is a regulator of VLA-4 and that it is involved in the recognition of GRGDNP. We then examined the role of VLA-5 in the spreading induced by LN. Anti-alpha6 induced 53.1% inhibition. Anti-alpha5 alone had no effect. A combination of alpha5 and anti-alpha6, however, significantly enhanced the inhibition of spreading. The combination of GRGDSP plus anti-alpha6 and GRGDNP plus anti-alpha6 resulted in complete inhibition. These results suggested that VLA-5 participates in the recognition of LN cooperatively with VLA-6 and that VLA-5 is a common regulator of VLA-4 and the LN receptor, VLA-6.

Expression of the 67-kD laminin receptor, galectin-1, and galectin-3 in advanced human uterine adenocarcinoma

Alterations of tumor cell interactions with laminin, a basement membrane glycoprotein, are consistent features of the invasive and metastatic phenotype. Qualitative and quantitative changes in the expression of cell surface laminin-binding proteins have been correlated with the ability of cancer cells to cross basement membranes during the metastatic cascade. Such phenotypic modifications are usually associated with poor prognosis. In this study, the authors examined the possibility that expression of three laminin-binding proteins, the 67-kD laminin receptor (67LR), galectin-1, and galectin-3, is altered in human endometrial cancer in a fashion similar to that reported in other carcinomas, such as breast, colon, and ovarian cancer. Twenty advanced uterine adenocarcinomas were analyzed for expression of these three molecules using immunoperoxidase staining and specific antibodies. The authors found a significant increase in the expression of the 67LR and galectin-1 in cancer cells compared with normal adjacent endometrium (P = .0004 and .0022, respectively). As observed in other carcinomas, a significant down-regulation of galectin-3 expression was found in endometrial cancer cells compared with normal mucosa (P = .02). In the galectin-3 positive tumors, galectin-3 was detected in the cytoplasm and/or nucleus of cancer cells. Interestingly, tumors in which galectin-3 was detected only in the cytoplasm were characterized by deeper invasion of the myometrium than lesions where galectin-3 was found both in nucleus and cytoplasm (P = .02). This study shows an alteration of nonintegrin laminin-binding protein expression in advanced human endometrial cancer. Further studies on larger populations should determine the prognostic value of the detection of these laminin-binding proteins in endometrial carcinoma. Inverse modulation of the 67LR and galectin-3 appears to be a phenotypical feature of invasive carcinoma.

Dystroglycan is a dual receptor for agrin and laminin-2 in Schwann cell membrane

We have shown previously that alpha-dystroglycan with a molecular mass of 120 kDa is a Schwann cell receptor of laminin-2, the endoneurial isoform of laminin comprised of the alpha2, beta1, and gamma1 chains. In this paper, we show that Schwann cell alpha-dystroglycan is also a receptor of agrin, an acetylcholine receptor-aggregating molecule having partial homology to laminin alpha chains in the C terminus. Immunochemical analysis demonstrates that the peripheral nerve isoform of agrin is a 400-kDa component of the endoneurial basal lamina and is co-localized with alpha-dystroglycan surrounding the outermost layer of myelin sheath of peripheral nerve fibers. Blot overlay analysis demonstrates that both endogenous peripheral nerve agrin and laminin-2 bind to Schwann cell alpha-dystroglycan. Recombinant C-terminal fragment of the peripheral nerve isoform of agrin also binds to Schwann cell alpha-dystroglycan, confirming that the binding site for Schwann cell alpha-dystroglycan resides in the C terminus of agrin molecule. Furthermore, the binding of recombinant agrin C-terminal fragment to Schwann cell alpha-dystroglycan competes with that of laminin-2. All together, these results indicate that alpha-dystroglycan is a dual receptor for agrin and laminin-2 in the Schwann cell membrane.

Cloning and characterization of a cDNA coding for Candida albicans polyubiquitin

Immunoscreening of a Candida albicans cDNA library in the expression vector lambda gt11 with rabbit polyclonal antibodies against the 37 kDa cell surface laminin receptor of C albicans resulted in the isolation of a cDNA clone of 0.9 kb. Sequencing of this clone demonstrated a full length open reading frame encoding the polyubiquitin, which contains three tandem copies, head-to-tail spacerless repeats, of the 228 nucleotides coding for the 76 amino acids of the ubiquitin protein, which is identical to that of Saccharomyces cerevisiae. The third copy possesses an extra C-terminal amino acid which is distinct to that found in S. cerevisiae. Northern blot analysis revealed a single mRNA population of about 1 kb present in similar amounts in both yeast and mycelial cells. This indicates that the C. albicans polyubiquitin gene (UBI1) encodes a polyubiquitin precursor protein containing three ubiquitin repeats. Immunofluorescence and Western immunoblotting experiments with polyclonal antibodies against mammalian ubiquitin suggest the presence of ubiquitinated protein moieties in the wall of C. albicans cells.

Laminin/VLA-6 interactions and T cell function

A growing number of investigators consider extracellular matrix (ECM) proteins to be determinant factors in lymphocyte positioning and activation. One major ECM component is laminin, which is constitutively expressed in the thymus as well as in thymus-dependent areas of peripheral lymphoid organs. In the thymus, laminin is produced by epithelial and dendritic cells, and appears to mediate interactions with thymocytes through specific laminin receptors, in particular the integrin VLA-6. This receptor is also expressed by peripheral T cells, and is apparently involved in effector T cell migration and activation. We showed that CD4+ T lymphocytes from chronic chagasic mice exhibited an increase in the absolute and relative number of cells with high VLA-6 expression. Additionally, it is likely that VLA-6/laminin interactions are required for the development of the CD4+T cell-dependent anti-myocardial autoreactive process that occurs in these animals. Lastly, laminin can bind to some cytokines, a fact that may represent an additional mechanism by which this extracellular matrix component modulates the behavior of T lymphocytes. Taken together, the present data strongly indicate that interactions involving laminin and VLA-6 are functionally linked to relevant events in T cell physiology, comprising entrance of pro-thymocytes into the thymus, intrathymic T cell migration and differentiation, as well as the functioning of mature T lymphocytes, including effector cells.