Modulation of the urokinase-type plasminogen activator receptor by the β6 integrin subunit

Identification, Characterization, and Optimization of Integrin αvβ₆-Targeting Peptides from a One-Bead One-Compound (OBOC) Library: Towards the Development of Positron Emission Tomography (PET) Imaging Agents

The current translation of peptides identified through the one-bead one-compound (OBOC) technology into positron emission tomography (PET) imaging agents is a slow process, with a major delay between ligand identification and subsequent lead optimization. This work aims to streamline the development process of ¹⁸F-peptide based PET imaging agents to target the integrin α_vβ₆. By directly identify α_vβ₆–targeting peptides from a 9-mer 4-fluorobenzoyl peptide library using the on-bead two-color (OBTC) cell-screening assay, a total of 185 peptide beads were identified and 5 beads sequenced for further evaluation. The lead peptide 1 (VGDLTYLKK(FB), IC₅₀ = 0.45 ± 0.06 μM, 25% stable in serum at 1 h) was further modified at the N-, C-, and bi-termini. C-terminal PEGylation increased the metabolic stability (>95% stable), but decreased binding affinity (IC₅₀ = 3.7 ± 1 μM) was noted. C-terminal extension (1i, VGDLTYLKK(FB)KVART) significantly increased binding affinity for integrin α_vβ₆ (IC₅₀ = 0.021 ± 0.002 μM), binding selectivity for α_vβ₆-expressing cells (3.1 ± 0.8:1), and the serum stability (>99% stable). Our results demonstrate the challenges in optimizing OBOC-derived peptides, indicate both termini of 1 are sensitive to modifications, and show that further modification of 1 is necessary to demonstrate utility as an ¹⁸F-peptide imaging agent.

The αE(CD103)β7 integrin interacts with oral and skin keratinocytes in an E-cadherin-independent manner*

The integrin αE(CD103)β7 (αEβ7) is expressed by intraepithelial lymphocytes, dendritic cells and regulatory T cells. It plays an important role in the mucosal immune system by retaining lymphocytes within the epithelium and is involved in graft rejection, immunity against tumours and the generation of gut-homing effector cells. In gut and breast, the ligand for αEβ7 is E-cadherin but in human oral mucosa and skin, there is evidence that lymphocytes use an alternative, unknown, ligand. In the present study, the I domain of the human αE subunit, which contains the E-cadherin-binding site, was locked in a highly active, 'open' and an inactive, 'closed' conformation by the introduction of disulphide bonds and these domains were expressed as IgG Fc fusion proteins. αE fusion proteins recognize E-cadherin, the only known ligand for αEβ7. This interaction was inhibited by an antibody that blocks the αE-binding site on E-cadherin and by the omission of Mn(2+) , which is essential for integrin function in vitro. The locked 'open' conformation of αE adhered to human oral and skin keratinocytes, including the E-cadherin-negative H376 cell line, and this was not inhibited by blocking antibody against the αEβ7-binding site on E-cadherin, providing further evidence for the existence of an alternative ligand for αEβ7 in skin and oral mucosa. The interaction with E-cadherin and the alternative ligand was Mn(2+) dependent and mediated by the metal ion-dependent coordination site (MIDAS) of the locked 'open'αE I domain, independently of the β7 subunit.

Novel protein interactors of urokinase-type plasminogen activator receptor

The urokinase-type plasminogen activator receptor (uPAR) has been implicated in tumor growth and metastasis. The crystal structure of uPAR revealed that the external surface is largely free to interact with a number of proteins. Additionally, due to absence of an intracellular cytoplasmic protein domain, many of the biological functions of uPAR necessitate interactions with other proteins. Here, we used yeast two-hybrid screening of breast cancer cDNA library to identify hSpry1 and HAX1 proteins as putative candidate proteins that interact with uPAR bait constructs. Interaction between these two candidates and uPAR was confirmed by GST-pull down, co-immunoprecipitation assays and confocal microscopy. These novel interactions that have been identified may also provide further evidence that uPAR can interact with a number of other proteins which may influence a range of biological functions.

Differential gene expression in murine large cell B-cell lymphoma metastatic variants

Previous studies from this laboratory have characterized RAW117-P murine large cell B-cell lymphoma and its in vivo selected highly malignant and liver metastatic RAW117-H10 subline for their biological and biochemical properties. In this study, to understand the molecular basis of low and high metastatic behavior of these variant sublines, we have investigated the molecular phenotypes of these cells using differential display techniques and cDNA array analysis. Differential display analysis indicated a significant difference in expression of several genes between these two metastatic variant lymphoma cells. Further analyses of these cells using microarray showed an increased expression of several genes including uPAR1, CRE-BP1, Chop-10, IGF, insulin-like growth factor-IA, STAT6, Cyclin-D1, Cyclin-E, ERBB-3, Alpha NGF, Kruppel-like factor LKLF, (P)19INK4 in metastatic RAW117-H10 cells compared to parental RAW117-P cells. On the other hand, MIP1beta, CD14 antigen, Cathepsin B and MOD are expressed more in RAW117-P cells compared to RAW117-H10 cells. Differential expression of the selected genes was confirmed using semiquantitative RT-PCR techniques. The combination of plasminogen activator and its receptor and IGF-like growth factors, cell cycle regulatory molecules and transcription factors might provide an ideal environment for RAW117-H10 cells to metastasize to distant organs and colonize. Thus these results identify certain differentially expressed genes that are involved in the metastatic properties of these lymphoma cells and lay foundation for further in depth analyses to use this information to develop therapy for metastatic lymphoma.

Signaling and regulatory mechanisms of integrin alphavbeta6 on the apoptosis of colon cancer cells

Considerable researches have been done about integrin alphanubeta6 and carcinomas, but little information has been shown about the relationship between integrin alphanubeta6 and apoptosis. In this study, we investigated the apoptosis and its related signal pathways to integrin alphavbeta6 in colon cancer cells. After we blocked the function of integrin alphavbeta6 in HT29 cells used the monoclonal antibody, the apoptotic cells increased markedly. Meanwhile, cytochrome C released from mitochondria into cytosol, Bcl-2 decreased while Bax increased significantly, and Fas and Fas-ligand had no change. The activities of caspase-3 and caspase-9 increased, while caspase-8 remained no change. Moreover, the expression of phosphorylated extracellular signal-related kinase (P-ERK) decreased. We confirmed that integrin alphavbeta6 acted as an important role in inhibiting apoptosis in colon cancer cells, and the signaling involved the mitochondrial pathway.

The effect of mechanical strain on protease production by keratinocytes

BACKGROUND

Intact skin is under constant tension, transmitted from the underlying dermis, but when tension is lost (i.e. upon wounding) protease activity is upregulated.

OBJECTIVES

To investigate the effect of mechanical strain on protease production by both normal and transformed keratinocytes in vitro.

METHODS

Keratinocytes were seeded on to membranes precoated with either type I or type IV collagen. After 48 h medium was replaced with serum-free medium and mechanical strain was applied.

RESULTS

Mechanical strain resulted in decreased urokinase-type plasminogen activator (uPA) production by normal human keratinocytes (P<0.05) but increased production by transformed keratinocytes (P<0.05) cultured on type I and type IV collagen.

CONCLUSIONS

Differential production of uPA by normal and transformed keratinocytes is relevant in the context of normal function, wound healing and tumorigenesis.

Integrin alphanvbeta6 acts as a prognostic indicator in gastric carcinoma

AIMS

To investigate the relationships between integrin alphanubeta6 expression and the clinical-pathological features of gastric carcinoma and whether integrin alphanubeta6 can act as a prognostic indicator in gastric carcinoma.

MATERIALS AND METHODS

We generated the microarray of 300 human gastric carcinoma specimens, and used the method of immunohistochemistry to investigate the expression of alphanubeta6 in them and the relationships between the expression of alphanubeta6 and the clinical-pathological features of the tumours. Meanwhile, we retrospectively analysed the relationship between alphanubeta6 expression and the survival times of the patients.

RESULTS

The expression of alphanubeta6 was detected in 36.7% of gastric carcinomas, and the expression was associated with Lauren type, differentiation, N stage and TNM stage of the tumours (the P values were 0.004, 0.035, 0.024 and 0.001, respectively). The Kaplan-Meier plot showed that patients who were alphanubeta6 negative had much longer survival times than those who were alphanubeta6 positive (P<0.0001). The survival estimates showed a striking difference in median survival between the negative and positive alphanubeta6 expression patients, especially in early stage tumours. Univariate analysis indicated that significant factors for prognosis included alphanubeta6 expression, differentiation, TNM stage, T stage, N stage, M stage and R classification (R0: potentially curative resection; R1: had residual microscopic disease after resection; R2: had residual macroscopic disease after resection), whereas in multivariate analysis using the Cox regression model, only alphanubeta6 expression, M stage, TNM stage and R classification retained significance for prognosis.

CONCLUSIONS

Positive alphanubeta6 expression in gastric carcinoma is linked to significantly reduced survival times and, even more important, is that its value as a prognostic marker is significant for early stage tumours.

Role of alphavbeta6 integrin in acute biliary fibrosis

Acute biliary obstruction leads to periductal myofibroblasts and fibrosis, the origin of which is uncertain. Our study provides new information on this question in mice and humans. We show that bile duct obstruction induces a striking increase in cholangiocyte alphavbeta6 integrin and that expression of this integrin is directly linked to fibrogenesis through activation of transforming growth factor beta (TGF-beta). Administration of blocking antibody to alphavbeta6 significantly reduces the extent of acute fibrosis after bile duct ligation. Moreover, in beta6-null mice subjected to the injury, fibrosis is reduced by 50% relative to that seen in wild-type mice, whereas inflammation occurs to the same extent. The data indicate that alphavbeta6, rather than inflammation, is linked to fibrogenesis. It is known that alphavbeta6 binds latent TGF-beta and that binding results in release of active TGFbeta. Consistent with this, intracellular signaling from the TGFbeta receptor is increased after bile duct ligation in wild-type mice but not in beta6(-/-) mice, and a competitive inhibitor of the TGFbeta receptor type II blocks fibrosis to the same extent as antibody to alphavbeta6. In a survey of human liver disease, expression of alphavbeta6 is increased in acute, but not chronic, biliary injury and is localized to cholangiocyte-like cells.

CONCLUSION

Cholangiocytes respond to acute bile duct obstruction with markedly increased expression of alphavbeta6 integrin, which is closely linked to periductal fibrogenesis. The findings provide a rationale for the use of inhibitors of alphavbeta6 integrin or TGFbeta for down-regulating fibrosis in the setting of acute or ongoing biliary injury.

Alphavbeta6 integrin in wound healing and cancer of the oral cavity

Integrins are a family of heterodimeric cell surface receptors, which are expressed on most cells where they mediate cell-cell and cell-extracellular matrix (ECM) interactions. The alphavbeta6 integrin is epithelial-specific and binds to the ECM proteins fibronectin, vitronectin and tenascin, and also to the latency associated peptide of TGF-beta. Unlike most epithelial integrins, alphavbeta6 is not expressed constitutively by healthy oral epithelia, but is up-regulated during tissue remodelling, including that accompanying wound healing and carcinogenesis. Although, the data at present have been generated principally from in vitro studies, there is increasing evidence to suggest that alphavbeta6 may promote carcinoma progression: alphavbeta6 has been shown to modulate invasion, inhibit apoptosis, regulate protease expression and activate TGF-beta1. This review examines the current literature, and discusses the possible role of alphavbeta6 in wound healing, and in the development and progression of oral squamous cell carcinoma.

Transfection and ligation of CD40 in human oral keratinocytes affect proliferation, adhesion and migration but not apoptosis in vitro

AIMS

CD40 expression is restricted to Keratinocytes of normal epidermis or stratified squamous epithelium of oral mucosa. Ligation of CD40 inhibits keratinocyte proliferation and apoptosis. The aim of this study was to investigate the functional significance of CD40 in the proliferation, apoptosis, adhesion and migration of human oral keratinocytes in vitro.

METHODS

The CD40-negative oral keratinocyte line OSC19, its CD40-positive transfected derivative (OSC19T-CD40) and null transfectants (OSC19T-control), with and without stimulation by soluble protein CD40 ligand (sCD40L) or anti-CD40 antibodies were used.

RESULTS

OSC19T-CD40 showed significantly (P < 0.001) slower growth than the null transfectants and parent cells. OSC19T-CD40 proliferation was inhibited by ligation with sCD40L and blocking by two anti-CD40 antibodies, but stimulated by a third. Binding of CD40 with ligand or antibody had no effect on keratinocyte apoptosis in any cell line. The capacity of OSC19T-CD40 cells to adhere to CD40L-coated wells was significantly greater (P < 0.001) than that of parent OSC19 and OSC19T-control cells, and the migration rate of OSC19T-CD40 cells was significantly higher than parent OSC19 (P = 0.038 on fibronectin, P = 0.004 on Matrigel) or OSC19T-control (P =0.017 on fibronectin, P = 0.013 on Matrigel) cells.

CONCLUSIONS

CD40 is an important molecule in keratinocyte homeostasis, and has more than one ligand. The ligand that is bound may be critical in oral epithelial homeostasis, the development of malignancy and the behaviour of the subsequent tumour.

Bone microenvironment modulates expression and activity of cathepsin B in prostate cancer

Prostate cancers metastasize to bone leading to osteolysis. Here we assessed proteolysis of DQ-collagen I (a bone matrix protein) and, for comparison, DQ-collagen IV, by living human prostate carcinoma cells in vitro. Both collagens were degraded, and this degradation was reduced by inhibitors of matrix metallo, serine, and cysteine proteases. Because secretion of the cysteine protease cathepsin B is increased in human breast fibroblasts grown on collagen I gels, we analyzed cathepsin B levels and secretion in prostate cells grown on collagen I gels. Levels and secretion were increased only in DU145 cells--cells that expressed the highest baseline levels of cathepsin B. Secretion of cathepsin B was also elevated in DU145 cells grown in vitro on human bone fragments. We further investigated the effect of the bone microenvironment on cathepsin B expression and activity in vivo in a SCID-human model of prostate bone metastasis. High levels of cathepsin B protein and activity were found in DU145, PC3, and LNCaP bone tumors, although the PC3 and LNCaP cells had exhibited low cathepsin B expression in vitro. Our results suggest that tumor-stromal interactions in the context of the bone microenvironment can modulate the expression of the cysteine protease cathepsin B.

Integrin signaling in malignant melanoma

Cell adhesion and migration are essential for embryonic development, tissue regeneration, but also for tumor development. The physical link between the extracellular matrix (ECM) and the actin cytoskeleton is mainly mediated by receptors of the integrin family. Through signals transduced upon integrin ligation to ECM proteins, this family of proteins plays key roles in regulating tumor growth and metastasis as well as tumor angiogenesis. During melanoma development, changes in integrin expression, intracellular control of integrin functions and signals perceived from integrin ligand binding impact upon the ability of tumor cells to interact with their environment and enable melanoma cells to convert from a sessile, stationary to a migratory and invasive phenotype. Antagonists of several integrins are now under evaluation in clinical trials to determine their potential as therapeutics for malignant melanoma and other kinds of cancer.