Integrin alphavbeta3 binding to human alpha5-laminins facilitates FGF-2- and VEGF-induced proliferation of human ECV304 carcinoma cells

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

Podocyte VEGF-A Knockdown Induces Diffuse Glomerulosclerosis in Diabetic and in eNOS Knockout Mice

Vascular endothelial growth factor-a (VEGF-A) and nitric oxide (NO) are essential for glomerular filtration barrier homeostasis, and are dysregulated in diabetic kidney disease (DKD). While NO availability is consistently low in diabetes, both high and low VEGF-A have been reported in patients with DKD. Here we examined the effect of inducible podocyte VEGF-A knockdown (VEGF^KD) in diabetic mice and in endothelial nitric oxide synthase knockout mice (eNOS^−/−). Diabetes was induced with streptozotocin using the Animal Models of Diabetic Complications Consortium (AMDCC) protocol. Induction of podocyte VEGF^KD led to diffuse glomerulosclerosis, foot process effacement, and GBM thickening in both diabetic mice with intact eNOS and in non-diabetic eNOS^−/−:VEGF^KD mice. VEGF^KD diabetic mice developed mild proteinuria and maintained normal glomerular filtration rate (GFR), associated with extremely high NO and thiol urinary excretion. In eNOS^−/−:VEGF^KD (+dox) mice severe diffuse glomerulosclerosis was associated with microaneurisms, arteriolar hyalinosis, massive proteinuria, and renal failure. Collectively, data indicate that combined podocyte VEGF-A and eNOS deficiency result in diffuse glomerulosclerosis in mice; compensatory NO and thiol generation prevents severe proteinuria and GFR loss in VEGF^KD diabetic mice with intact eNOS, whereas VEGF^KD induction in eNOS^−/−:VEGF^KD mice causes massive proteinuria and renal failure mimicking DKD in the absence of diabetes. Mechanistically, we identify VEGF^KD-induced abnormal S-nitrosylation of specific proteins, including β3-integrin, laminin, and S-nitrosoglutathione reductase (GSNOR), as targetable molecular mechanisms involved in the development of advanced diffuse glomerulosclerosis and renal failure.

Overcoming stromal barriers to immuno-oncological responses via fibroblast activation protein-targeted therapy

The tumor microenvironment contributes to disease progression through multiple mechanisms, including immune suppression mediated in part by fibroblast activation protein (FAP)-expressing cells. Herein, a review of FAP biology is presented, supplemented with primary data. This includes FAP expression in prostate cancer and activation of latent reservoirs of TGF-β and VEGF to produce a positive feedback loop. This collectively suggests a normal wound repair process subverted during cancer pathophysiology. There has been immense interest in targeting FAP for diagnostic, monitoring and therapeutic purposes. Until recently, this development has outpaced an understanding of the biology; impeding optimal translation into the clinic. A summary of these applications is provided with an emphasis on eliminating tumor-infiltrating FAP-positive cells to overcome stromal barriers to immuno-oncological responses.

Prognostic value of integrin variants and expression in post-operative patients with HBV-related hepatocellular carcinoma

Integrins are a large family of cell surface receptors that bind extracellular matrix proteins and participate in cancer progression. However, the prognostic value of integrin family genes in post-operative patients with HBV-related hepatocellular carcinoma (HCC) remains unknown. In this study, we investigated 18 single nucleotide polymorphisms (SNPs) in integrin family genes and found that the AG/GG genotypes at rs988574 in ITGA1 predicted a better prognosis compared to carriers of the AA genotype (P = 0.025, HR = 0.69, 95%CI = 0.50–0.96). Moreover, rs988574 genotype combined with serum level of AFP had a better prognostic value in HBV-related HCC patients (P = 0.026, HR = 1.75, 95% CI = 1.07–2.85). Furthermore, we compared the expression of 24 integrin family genes in HBV-related HCC tissues and adjacent normal tissues. Survival analysis demonstrated that expression of three of the family members, ITGA5, ITGB5 and ITGA2B, were significantly associated with the overall survival (OS) or relapse-free survival (RFS) of HBV-related HCC patients. Additionally, patients with lower expression of both ITGA5 and ITGB5 had the best OS and RFS (P = 0.017 and P = 0.002, respectively). Our study demonstrated that rs988574 of ITGA1 and the expression of ITGA5, ITGB5 and ITGA2B are potential independent prognostic bio-markers and therapeutic targets for HBV-related HCC patients and may be useful for the diagnosis of HBV-related HCC.

Transformed MDCK cells secrete elevated MMP1 that generates LAMA5 fragments promoting endothelial cell angiogenesis

Epithelial-mesenchymal transition (EMT) enhances the migration and invasion of cancer cells, and is regulated by various molecular mechanisms including extracellular matrix metalloproteinase (MMP) activity. Previously, we reported transformation of epithelial Madin-Darby canine kidney (MDCK) cells with oncogenic H-Ras (21D1 cells) induces EMT, and significantly elevates MMP1 expression. To explore the biological significance, in this study we characterized 21D1 cells with knocked-down MMP1 expression (21D1^−MMP1). MMP1 silencing diminished 21D1 cell migration, invasion and anchorage-independent growth in vitro. Additionally, 21D1^−MMP1 cells displayed reduced tumour volume when grown as in vivo subcutaneous xenografts in mice. Depletion of MMP1 lowered the ability of the cellular secretome (extracellular culture medium) to influence recipient cell behaviour. For example, supplementation with 21D1 secretome elevated cell migration of recipient fibroblasts, and enhanced endothelial cell angiogenesis (vessel length and branching). By contrast, 21D1^−MMP1 secretome was less potent in both functional assays. We reveal laminin subunit alpha-5 (LAMA5) as a novel biological substrate of MMP1, that generates internal and C-terminal proteolytic fragments in 21D1 secretome. Furthermore, antibody-based inhibition of integrin αvβ3 on endothelial cells nullified the angiogenic capability of 21D1 secretome. Therefore, we report this as a new VEGF-independent mechanism that oncogenic cells may employ to promote tumour angiogenesis.

Molecular Basis of Laminin-Integrin Interactions

Laminins are composed of three polypeptide chains, designated as α, β, and γ. The C-terminal region of laminin heterotrimers, containing coiled-coil regions, short tails, and laminin globular (LG) domains, is necessary and sufficient for binding to integrins, which are the major laminin receptor class. Laminin recognition by integrins critically requires the α chain LG domains and a glutamic acid residue of the γ chain at the third position from the C-terminus. Furthermore, the C-terminal region of the β chain contains a short amino acid sequence that modulates laminin affinity for integrins. Thus, all three of the laminin chains act cooperatively to facilitate integrin binding. Mammals possess 5 α (α1-5), 3 β (β1-3), and 3 γ (γ1-3) chains, combinations of which give rise to 16 distinct laminin isoforms. Each isoform is expressed in a tissue-specific and developmental stage-specific manner, exerting its functions through binding of integrins. In this review, we detail the current knowledge surrounding the molecular basis and physiological relevance of specific interactions between laminins and integrins, and describe the mechanisms underlying laminin action through integrins.

A novel monoclonal antibody to human laminin α5 chain strongly inhibits integrin-mediated cell adhesion and migration on laminins 511 and 521

Laminins, a large family of αβγ heterotrimeric proteins mainly found in basement membranes, are strong promoters of adhesion and migration of multiple cell types, such as tumor and immune cells, via several integrin receptors. Among laminin α (LMα) chains, α5 displays the widest tissue distribution in adult life and is synthesized by most cell types. Here, we have generated and characterized five novel monoclonal antibodies (mAbs) to the human LMα5 chain to further study the biological relevance of α5 laminins, such as laminins 511 (α5β1γ1) and 521 (α5β2γ1). As detected by ELISA, immunohistochemistry, immunoprecipitation and Western blotting, each antibody displayed unique properties when compared to mAb 4C7, the prototype LMα5 antibody. Of greatest interest, mAb 8G9, but not any other antibody, strongly inhibited α3β1/α6β1 integrin-mediated adhesion and migration of glioma, melanoma, and carcinoma cells on laminin-511 and, together with mAb 4C7, on laminin-521. Accordingly, mAb 8G9 abolished the interaction of soluble α3β1 integrin with immobilized laminins 511 and 521. Binding of mAb 8G9 to laminin-511 was unaffected by the other mAbs to the LMα5 chain but largely hindered by mAb 4E10 to a LMβ1 chain epitope near the globular domain of laminin-511. Thus, mAb 8G9 defines a novel epitope localized at or near the integrin-binding globular domain of the LMα5 chain, which is essential for cell adhesion and migration, and identifies a potential therapeutic target in malignant and inflammatory diseases.

c-Abl is an upstream regulator of acid sphingomyelinase in apoptosis induced by inhibition of integrins αvβ3 and αvβ5

Inhibition of integrins αvβ3/αvβ5 by the cyclic function-blocking peptide, RGDfV (Arg-Gly-Asp-Phe-Val) can induce apoptosis in both normal cells and tumor cells. We show that RGDfV induced apoptosis in ECV-304 carcinoma cells, increased activity and mRNA expression of acid sphingomyelinase (ASM), and increased ceramides C₁₆, C_18∶0, C_24∶0 and C_24∶1 while decreasing the corresponding sphingomyelins. siRNA to ASM decreased RGDfV-induced apoptosis as measured by TUNEL, PARP cleavage, mitochondrial depolarization, and caspase-3 and caspase-8 activities, as well as by annexinV in a 3D collagen model. These findings indicate a causal role for ASM in RGDfV-induced apoptosis in ECV-304. We have shown that c-Abl, a non-receptor tyrosine kinase, also mediates RGDfV-induced apoptosis. However, c-Abl, has not been previously linked to ASM in any system. Here we show that STI-571 (imatinib, inhibitor of c-Abl) inhibited RGDfV-induced ASM activity. Furthermore, STI-571 and c-Abl-siRNA both inhibited RGDfV-induced increase in ASM mRNA, but ASM-siRNA did not affect c-Abl phosphorylation or expression, supporting that c-Abl regulates the RGDfV-induced increase in ASM expression. These studies implicate ASM as a mediator of apoptosis induced by inhibition of integrins αvβ3/αvβ5, and for the first time place c-Abl as an upstream regulator of ASM expression and activity.

Delay of migrating leukocytes by the basement membrane deposited by endothelial cells in long-term culture

We investigated the migration of human leukocytes through endothelial cells (EC), and particularly their underlying basement membrane (BM). EC were cultured for 20 days on 3 μm-pore filters or collagen gels to form a distinct BM, and then treated with tumour necrosis factor-α, interleukin-1β or interferon-γ. Neutrophil migration through the cytokine-treated EC and BM was delayed for 20-day compared to 4-day cultures. The BM alone obstructed chemotaxis of neutrophils, and if fresh EC were briefly cultured on stripped BM, there was again a hold-up in migration. In studies with lymphocytes and monocytes, we could detect little hold-up of migration for 20-day versus 4-day cultures, in either the filter- or gel-based models. Direct microscopic observations showed that BM also held-up neutrophil migration under conditions of flow. Treatment of upper and/or lower compartments of filters with antibodies against integrins, showed that neutrophil migration through the endothelial monolayer was dependent on β₂-integrins, but not β1- or β₃-integrins. Migration from the subendothelial compartment was supported by β1- and β₂-integrins for all cultures, but blockade of β₃-integrin only inhibited migration effectively for 20-day cultures. Flow cytometry indicated that there was no net increase in expression of β1- or β3-integrins during neutrophil migration, and that their specific subendothelial function was likely dependent on turnover of integrins during migration. These studies show that BM is a distinct barrier to migration of human neutrophils, and that β₃-integrins are particularly important in crossing this barrier. The lesser effect of BM on lymphocytes and monocytes supports the concept that crossing the BM is a separate, leukocyte-specific, regulated step in migration.

Integrins

Integrins are cell adhesion receptors that are evolutionary old and that play important roles during developmental and pathological processes. The integrin family is composed of 24 αβ heterodimeric members that mediate the attachment of cells to the extracellular matrix (ECM) but that also take part in specialized cell-cell interactions. Only a subset of integrins (8 out of 24) recognizes the RGD sequence in the native ligands. In some ECM molecules, such as collagen and certain laminin isoforms, the RGD sequences are exposed upon denaturation or proteolytic cleavage, allowing cells to bind these ligands by using RGD-binding receptors. Proteolytic cleavage of ECM proteins might also generate fragments with novel biological activity such as endostatin, tumstatin, and endorepellin. Nine integrin chains contain an αI domain, including the collagen-binding integrins α1β1, α2β1, α10β1, and α11β1. The collagen-binding integrins recognize the triple-helical GFOGER sequence in the major collagens, but their ability to recognize these sequences in vivo is dependent on the fibrillar status and accessibility of the interactive domains in the fibrillar collagens. The current review summarizes some basic facts about the integrin family including a historical perspective, their structure, and their ligand-binding properties.

Functionalized cyclic RGD peptidomimetics: conjugable ligands for αvβ3 receptor imaging

The α(v)β(3) integrin is an adhesion molecule involved in physiological and pathological angiogenesis as well as in tumor invasion and metastasis, and therefore, there is a strong interest in developing novel agents interacting with this molecule. We report the synthesis and characterization of fluorescent α(v)β(3) integrin probes and their use to visualize integrin α(v)β(3) expression on human normal and cancer cells. The fluorescent probes we describe here may be of use for noninvasive imaging of α(V)β(3) integrin expression also in vivo.

Mitoparan and target-selective chimeric analogues: membrane translocation and intracellular redistribution induces mitochondrial apoptosis

Mastoparan, and structurally-related amphipathic peptides, may induce cell death by augmentation of necrotic and/or apoptotic pathways. To more precisely delineate cytotoxic mechanisms, we determined that [Lys(5,8)Aib(10)]mastoparan (mitoparan) specifically induces apoptosis of U373MG and ECV304 cells, as demonstrated by endonuclease and caspase-3 activation and phosphatidylserine translocation. Live cell imaging confirmed that, following translocation of the plasma membrane, mitoparan specifically co-localizes with mitochondria. Complementary studies indicated that mitoparan induces swelling and permeabilization of isolated mitochondria, through cooperation with a protein of the permeability transition pore complex VDAC, leading to the release of the apoptogenic factor, cytochrome c. N-terminal acylation of mitoparan facilitated the synthesis of chimeric peptides that incorporated target-specific address motifs including an integrin-specific RGD sequence and a Fas ligand mimetic. Significantly, these sychnologically-organised peptides demonstrated further enhanced cytotoxic potencies. We conclude that the cell penetrant, mitochondriotoxic and apoptogenic properties of mitoparan, and its chimeric analogues, offer new insights to the study and therapeutic induction of apoptosis.

Lutheran blood group antigen as a receptor for alpha5 laminins in gingival epithelia

BACKGROUND

Lutheran blood group glycoprotein (Lu) is a transmembrane receptor of the immunoglobulin superfamily. Lu serves as a receptor for alpha5 laminins (Lm). The Lm alpha5 chain is a constituent of Lms-511 and -521. Lm-511 is found in most human basement membranes (BMs) and also is detected in BM of gingival epithelia. Recent studies indicated that Lu mediates cell adhesion to Lms-511/521 independently or in concert with integrins. This study focused on the expression of Lu in gingival epithelia and on cultured immortalized gingival keratinocytes. The role of Lu and alpha(3) and beta(1) integrin subunits in the adhesion of oral epithelial cells to Lms-511/521 was also studied.

METHODS

Immunofluorescence microscopy was used to study the expression of Lu in gingival tissues and in cultured gingival keratinocytes. Immunoprecipitation of radioactively metabolically labeled cells was used to detect Lu. Cell adhesion to Lm-511/521 preparation and to pure Lm-511 was studied in quantitative cell adhesion experiments. Morphological adhesion assays were carried out for visualization of the morphology and adhesion structure formation of the adhering cells.

RESULTS

Immunofluorescence studies on gingiva showed complete coalignment of Lu on basal epithelial cells with the BM Lm alpha5 chain. A surface-confined, punctate immunoreaction for Lu was detected throughout cell surfaces on cultured gingival cells. Immunoprecipitation showed a broad polypeptide with molecular weight 85,000. In quantitative cell adhesion assays, the adhesion of cells to both Lm alpha5 preparations was diminished with monoclonal antibodies (MAbs) against integrin alpha(3) and even more effectively with MAbs against the beta(1) subunit. When the adhesion sites were blocked with soluble recombinant Lu (sol-Lu), the adhesion of gingival epithelial cells to Lms-511/521 was reduced significantly, and sol-Lu increased the inhibition with integrin alpha(3) antibody. Lm-511 did not induce lamellipodia or focal contacts in cultured gingival keratinocytes.

CONCLUSIONS

Lu was in coalignment with Lm alpha5 chain in gingival epithelia. Lu also seemed to have a role in gingival epithelial cell adhesion together with integrin alpha(3)beta(1).

Antiangiogenic antithrombin induces global changes in the gene expression profile of endothelial cells

Antithrombin, a serpin family protease inhibitor crucial to hemostasis, acquires antiangiogenic properties on undergoing conformational alterations induced by limited proteolysis or elevated temperature. To better understand the biochemical mechanisms underlying antithrombin antiangiogenic activity, we did genome-wide expression profiling, coupled with quantitative reverse transcription-PCR, Northern blot, and Western blot analyses, to characterize the gene expression patterns that are induced by antiangiogenic antithrombin in cultured primary human umbilical vein endothelial cells. Overall, 35 genes with significantly increased expression and 93 genes with significantly reduced expression (> or =2-fold changes) due to antiangiogenic antithrombin treatment were identified. More than half of the down-regulated genes have well-established proangiogenic functions in endothelial cells, including cell-surface and matrix proteoglycans (e.g., perlecan, biglycan, and syndecans 1 and 3) and mitogenesis-related signaling proteins (e.g., mitogen-activated protein kinase 3, signal transducers and activators of transcription 2, 3, and 6, and early growth response factor 1). In contrast, most up-regulated genes (e.g., caspase-3, p21, tissue inhibitor of metalloproteinases 1, 2, and 3, and adenomatosis polyposis coli) are known for their antiangiogenic functions which include the promotion of cell apoptosis and cell cycle arrest and the inhibition of tumor growth and metastasis. These results show that the antiangiogenic activity of antithrombin is mediated at least in part by a global genetic reprogramming of endothelial cells and strongly implicate an endothelial cell ligand-receptor signaling mechanism in this reprogramming.

The immortalized human corneal epithelial cells adhere to laminin-10 by using Lutheran glycoproteins and integrin alpha3beta1

We studied the adhesion characteristics of immortalized human corneal epithelial (HCE) cells on purified human laminin (Ln)-10 (alpha5beta1gamma1). Immunofluorescence studies with monoclonal antibodies (MAb) revealed the presence of laminin alpha5 chain receptor Lutheran (Lu) in vivo on the basal cells of cornea and as punctate cell surface-confined reactivity on adhering and spread HCE cells, while alpha- and beta-dystroglycans could not be found. Northern blot analysis showed the presence of 4.0 and 2.8 kb Lu transcripts in HCE cells. The results showed that Ln-10 induced adhesion and spreading of HCE cells without formation of focal adhesions. Quantitative adhesion assay showed that Lu together with integrin (Int) alpha3beta1 independently mediated the adhesion of HCE cells to Ln-10.

Laminin-10 and Lutheran blood group glycoproteins in adhesion of human endothelial cells

Laminin alpha5-chain, a constituent of laminins-10 and -11, is expressed in endothelial basement membranes. In this study we evaluated the roles of alpha5 laminins and Lutheran blood group glycoproteins (Lu), recently identified receptors of the laminin alpha5-chain, in the adhesion of human dermal microvascular and pulmonary artery endothelial cells. Field emission scanning electron microscopy and immunohistochemistry showed that the endothelial cells spread on laminin-10 and formed fibronectin-positive fibrillar adhesion structures. Immunoprecipitation results suggested that the cells produced fibronectin, which they could use as adhesion substratum, during the adhesion process. When the protein synthesis during the adhesion was inhibited with cycloheximide, the formation of fibrillar adhesions on laminin-10 was abolished, suggesting that laminin-10 does not stimulate the formation of any adhesion structures. Northern and Western blot analyses showed that the cells expressed M(r) 78,000 and 85,000 isoforms of Lu. Quantitative cell adhesion assays showed that in the endothelial cell adhesion to laminin-10, Lu acted in concert with integrins beta(1) and alpha(v)beta(3), whereas in the adhesion to laminin-10/11, Lu and integrin beta(1) were involved. In the cells adhering to the alpha5 laminins, Lu and the integrins showed uniform cell surface distribution. These findings indicate that alpha5 laminins stimulate endothelial cell adhesion but not the formation of fibrillar or focal adhesions. Lu mediates the adhesion of human endothelial cells to alpha5 laminins in collaboration with integrins beta(1) and alpha(v)beta(3).

Protein kinase A-dependent phosphorylation of Lutheran/basal cell adhesion molecule glycoprotein regulates cell adhesion to laminin alpha5

Lutheran (Lu) blood group and basal cell adhesion molecule (B-CAM) antigens reside on two glycoprotein (gp) isoforms Lu and Lu(v13) that belong to the Ig superfamily and differ only by the size of their cytoplasmic tail. Lu/B-CAM gps have been recognized as laminin alpha5 receptors on red blood cells and epithelial cells in multiple tissues. It has been shown that sickle red cells exhibit enhanced adhesion to laminin alpha5 when intracellular cAMP is up-regulated by physiological stimuli such as epinephrine and that this signaling pathway is protein kinase A- and Lu/B-CAM-dependent. In this study, we analyzed the relationship between the phosphorylation status of Lu/B-CAM gps and their adhesion function to laminin alpha5. We showed that Lu isoform was phosphorylated in sickle red cells as well as in erythroleukemic K562 and epithelial Madin-Darby canine kidney cells and that this phosphorylation is enhanced by different stimuli of the PKA pathway. Lu gp is phosphorylated by glycogen synthase kinase 3 beta, casein kinase II, and PKA at serines 596, 598, and 621, respectively. Alanine substitutions of serines 596 and 598 abolished phosphorylation by glycogen synthase kinase 3 beta and casein kinase II, respectively, but had no effect on adhesion of K562 cells to laminin under flow conditions. Conversely, mutation of serine 621 prevented phosphorylation by PKA and dramatically reduced cell adhesion. Furthermore, stimulation of K562 cells by epinephrine increased Lu gp phosphorylation by PKA and enhanced adhesion to laminin. It is postulated that modulation of the phosphorylation state of Lu gp might be a critical factor for the sickle red cells adhesiveness to laminin alpha5 in sickle cell disease.

Laminin isoforms differentially regulate adhesion, spreading, proliferation, and ERK activation of beta1 integrin-null cells

The presence of many laminin receptors of the beta1 integrin family on most cells makes it difficult to define the biological functions of other major laminin receptors such as integrin alpha6beta4 and dystroglycan. We therefore tested the binding of a beta1 integrin-null cell line GD25 to four different laminin variants. The cells were shown to produce dystroglycan, which based on affinity chromatography bound to laminin-1, -2/4, and -10/11, but not to laminin-5. The cells also expressed the integrin alpha6Abeta4A variant. GD25 beta1 integrin-null cells are known to bind poorly to laminin-1, but we demonstrate here that these cells bind avidly to laminin-2/4, -5, and -10/11. The initial binding at 20 min to each of these laminins could be inhibited by an integrin alpha6 antibody, but not by a dystroglycan antibody. Hence, integrin alpha6Abeta4A of GD25 cells was identified as a major receptor for initial GD25 cell adhesion to three out of four tested laminin isoforms. Remarkably, cell adhesion to laminin-5 failed to promote cell spreading, proliferation, and extracellular signal-regulated kinase (ERK) activation, whereas all these responses occurred in response to adhesion to laminin-2/4 or -10/11. The data establish GD25 cells as useful tools to define the role integrin alpha6Abeta4A and suggest that laminin isoforms have distinctly different capacities to promote cell adhesion and signaling via integrin alpha6Abeta4A.

Antitumor activities of a novel indolin-2-ketone compound, Z24: more potent inhibition on bFGF-induced angiogenesis and bcl-2 over-expressing cancer cells

The present study was designed to select the effective dosage range of Z24 [3Z-3-[(1H-pyrrol-2-yl)-methylidene]-1-(1-piperidinylmethyl)-1,3-2H-indol-2-one], a novel synthetic indolin-2-ketone small-molecule compound, against tumorigenesis and angiogenesis in vitro and in vivo and to investigate the primary action mechanism of Z24 on the angiogenesis by comparing with SU5416 [3-[(2,4-dimethylpyrrol-5-yl)methyllidenyl]-indolin-2-one] in the selective effects on vascular endothelial growth factor (VEGF)/basic fibroblast growth factor (bFGF) signaling and Bcl-2-related cell vitality because Z24 is a potential inhibitor of the Bcl-2 that inhibits growth of multiple tumor types in vivo in our previous study. Per os Z24 inhibited dose-dependently the mouse S180 xenograft tumor growth and angiogenesis in mouse subcutaneous (s.c.) Matrigel plugs in vivo. The maximum growth inhibitory rate was 56.1% by 80 mg/kg/day on S180 mouse sarcoma cells; however, the maximum inhibitory potency on angiogenesis in C57BL/6 mouse subcutaneous Matrigel plug model was 50 mg/kg/day. Z24 inhibited angiogenesis in chicken chorioallantoic membrane (CAM) and invasion and inhibited tube formation of endothelial cells in a dose-dependent manner. Compared with SU5416, the IC50 (50% inhibition concentration) of Z24 on the proliferation of ECV-304 carcinoma cells induced by VEGF or bFGF was 24.4 and 17.99 microM, respectively, which is higher or lower, respectively, than that of SU5416 (14.2 microM for VEGF and 22.7 microM for bFGF). Furthermore, the IC50 of Z24 on the proliferation of Bcl-2 over-expressing HeLa cells and non-Bcl-2-expressing (wild-type) HeLa cells are 11.9 and 24.8 microM, respectively. SU5416 did not exert such a selective inhibiting effect on Bcl-2 over-expressing HeLa cells. These results suggest that Z24 per os has dose-dependent antitumor and antiangiogenesis pharmacological activity. The higher selectivity of Z24 on Bcl-2 protein and on bFGF other than VEGF signaling path may contribute to its efficiency against tumor and tumor-associated angiogenesis.

Engagement of alphavbeta3 integrin regulates proliferation and apoptosis of hepatic stellate cells

Hepatic stellate cells are the major source of the extracellular matrix that accumulates in fibrotic liver. During progressive liver fibrosis, hepatic stellate cells proliferate, but during resolution of fibrosis there is extensive stellate cell apoptosis that coincides with degradation of the liver scar. We have examined the possibility that the fate of stellate cells is influenced by the extracellular matrix through the intermediary of alpha(v)beta(3) integrin. alpha(v)beta(3) integrin was expressed by activated, myofibroblastic rat and human stellate cells in culture. Antagonism of this integrin using neutralizing antibodies, echistatin, or small inhibitory RNA to silence alpha(v) subunit expression inhibited stellate cell proliferation and their expression of proliferating cell nuclear antigen and activated forms of p44 and p42 MAPK. These alpha(v)beta(3) antagonists also increased apoptosis of cultured stellate cells, and this was associated with an increase in the BAX/BCL-2 protein ratio, induction of nuclear DNA fragmentation, and activation of intracellular caspase-3. Expression of tissue inhibitor of metalloproteinases-1 by activated stellate cells was reduced by the alpha(v)beta(3) antagonists, while matrix metalloproteinase-9 synthesis was enhanced. Stellate cells incubated with active recombinant matrix metalloproteinase-9 showed enhanced apoptosis, while cells treated with a synthetic inhibitor of this protease showed increased survival. Our studies suggest that alpha(v)beta(3) integrin regulates the fate of hepatic stellate cells. Degradation of alpha(v)beta(3) ligands surrounding activated stellate cells during resolution of liver fibrosis might decrease alpha(v)beta(3) integrin ligation, suppressing stellate cell proliferation and inducing a fibrolytic, matrix metalloproteinase-secreting phenotype that may prime stellate cells for apoptosis.

Opposing roles of integrin alpha6Abeta1 and dystroglycan in laminin-mediated extracellular signal-regulated kinase activation

Laminin-integrin interactions can in some settings activate the extracellular signal-regulated kinases (ERKs) but the control mechanisms are poorly understood. Herein, we studied ERK activation in response to two laminins isoforms (-1 and -10/11) in two epithelial cell lines. Both cell lines expressed beta1-containing integrins and dystroglycan but lacked integrin alpha6beta4. Antibody perturbation assays showed that both cell lines bound to laminin-10/11 via the alpha3beta1and alpha6beta1 integrins. Although laminin-10/11 was a stronger adhesion complex than laminin-1 for both cell lines, both laminins activated ERK in only one of the two cell lines. The ERK activation was mediated by integrin alpha6beta1 and not by alpha3beta1 or dystroglycan. Instead, we found that dystroglycan-binding domains of both laminin-1 and -10/11 suppressed integrin alpha6beta1-mediated ERK activation. Moreover, the responding cell line expressed the two integrin alpha6 splice variants, alpha6A and alpha6B, whereas the nonresponding cell line expressed only alpha6B. Furthermore, ERK activation was seen in cells transfected with the integrin alpha6A subunit, but not in alpha6B-transfected cells. We conclude that laminin-1 and -10/11 share the ability to induce ERK activation, that this is regulated by integrin alpha6Abeta1, and suggest a novel role for dystroglycan-binding laminin domains as suppressors of this activation.