Suppression of α5 gene expression is closely related to the tumorigenic properties of uveal melanoma cell lines

Contribution of the Transcription Factors Sp1/Sp3 and AP-1 to Clusterin Gene Expression during Corneal Wound Healing of Tissue-Engineered Human Corneas

In order to reduce the need for donor corneas, understanding of corneal wound healing and development of an entirely tissue-engineered human cornea (hTECs) is of prime importance. In this study, we exploited the hTEC to determine how deep wound healing affects the transcriptional pattern of corneal epithelial cells through microarray analyses. We demonstrated that the gene encoding clusterin (CLU) has its expression dramatically repressed during closure of hTEC wounds. Western blot analyses confirmed a strong reduction in the expression of the clusterin isoforms after corneal damage and suggest that repression of CLU gene expression might be a prerequisite to hTEC wound closure. Transfection with segments from the human CLU gene promoter revealed the presence of three regulatory regions: a basal promoter and two more distal negative regulatory regions. The basal promoter bears DNA binding sites for very potent transcription factors (TFs): Activator Protein-1 (AP-1) and Specificity protein-1 and 3 (Sp1/Sp3). By exploiting electrophoretic mobility shift assays (EMSA), we demonstrated that AP-1 and Sp1/Sp3 have their DNA binding site overlapping with one another in the basal promoter of the CLU gene in hCECs. Interestingly, expression of both these TFs is reduced (at the protein level) during hTEC wound healing, thereby contributing to the extinction of CLU gene expression during that process. The results of this study contribute to a better understanding of the molecular mechanisms accounting for the repression of CLU gene expression during corneal wound healing.

The Roles of Integrin α5β1 in Human Cancer

Cell adhesion to the extracellular matrix has important roles in tissue integrity and human health. Integrins are heterodimeric cell surface receptors that are composed by two non-covalently linked alpha and beta subunits that mainly participate in the interaction of cell-cell adhesion and cell-extracellular matrix and regulate cell motility, adhesion, differentiation, migration, proliferation, etc. In mammals, there have been eighteen α subunits and 8 β subunits and so far 24 distinct types of αβ integrin heterodimers have been identified in humans. Integrin α5β1, also known as the fibronectin receptor, is a heterodimer with α5 and β1 subunits and has emerged as an essential mediator in many human carcinomas. Integrin α5β1 alteration is closely linked to the progression of several types of human cancers, including cell proliferation, angiogenesis, tumor metastasis, and cancerogenesis. In this review, we will introduce the functions of integrin α5β1 in cancer progression and also explore its regulatory mechanisms. Additionally, the potential clinical applications as a target for cancer imaging and therapy are discussed. Collectively, the information reviewed here may increase the understanding of integrin α5β1 as a potential therapeutic target for cancer.

Uveal melanoma pathobiology: Metastasis to the liver

Uveal melanoma (UM) is a type of intraocular tumor with a propensity to disseminate to the liver. Despite the identification of the early driver mutations during the development of the pathology, the process of UM metastasis is still not fully comprehended. A better understanding of the genetic, molecular, and environmental factors participating to its spread and metastatic outgrowth could provide additional approaches for UM treatment. In this review, we will discuss the advances made towards the understanding of the pathogenesis of metastatic UM, summarize the current and prospective treatments, and introduce some of the ongoing research in this field.

Transcription of the Human 5-Hydroxytryptamine Receptor 2B (HTR2B) Gene Is under the Regulatory Influence of the Transcription Factors NFI and RUNX1 in Human Uveal Melanoma

Because it accounts for 70% of all eye cancers, uveal melanoma (UM) is therefore the most common primary ocular malignancy. In this study, we investigated the molecular mechanisms leading to the aberrant expression of the gene encoding the serotonin receptor 2B (HTR2B), one of the most discriminating among the candidates from the class II gene signature, in metastatic and non-metastatic UM cell lines. Transfection analyses revealed that the upstream regulatory region of the HTR2B gene contains a combination of alternative positive and negative regulatory elements functional in HTR2B⁻ but not in HTR23B⁺ UM cells. We demonstrated that both the transcription factors nuclear factor I (NFI) and Runt-related transcription factor I (RUNX1) interact with regulatory elements from the HTR2B gene to either activate (NFI) or repress (RUNX1) HTR2B expression in UM cells. The results of this study will help understand better the molecular mechanisms accounting for the abnormal expression of the HTR2B gene in uveal melanoma.

Kallikrein-related peptidase 7 overexpression in melanoma cells modulates cell adhesion leading to a malignant phenotype

We recently reported that human melanoma cells, but not benign melanocytes, aberrantly express kallikrein-related peptidase 7 (KLK7). Here, we show a KLK7 overexpression-mediated decrease of cell adhesion to extracellular matrix binding proteins, associated with downregulation of α5/β1/αv/β3 integrin expression. We also report an up-regulation of MCAM/CD146 and an increase in spheroid formation of these cells. Our results demonstrate that aberrant KLK7 expression leads to a switch to a more malignant phenotype suggesting a potential role of KLK7 in melanoma invasion. Thus, KLK7 may represent a biomarker for melanoma progression and may be a potential therapeutic target for melanoma.

Expression of the serotonin receptor 2B in uveal melanoma and effects of an antagonist on cell lines

Uveal melanoma (UM) is the most common primary tumor in the adult, and disseminates to the liver in half of patients. A 15-gene expression profile prognostic assay allows to determine the likelihood of metastasis in patients using their ocular tumor DNA, but a cure still remains to be discovered. The serotonin receptor 2B represents the discriminant gene of this molecular signature with the greatest impact on the prognosis of UM. However, its contribution to the metastatic potential of UM remains unexplored. The purpose of this study was to investigate the effects of a selective serotonin receptor 2B antagonist on cellular and molecular behaviours of UM cells. UM cell lines expressing high level of serotonin receptor 2B proteins were selected by Western blotting. The selective serotonin receptor 2B antagonist PRX-08066 was evaluated for its impact on UM cells using viability assays, phosphorylated histone H3 immunostainings, clonogenic assays, migration assays, invasion assays and membrane-based protein kinase phosphorylation antibody arrays. The pharmacological inhibition of the serotonin receptor 2B reduced the viability of UM cells and the population in mitosis, and impaired their clonogenicity and potential of migration. It also decreased the phosphorylation of kinases from signaling pathways classically activated by the serotonin receptor 2B, as well as kinases β-catenin, Proline-rich tyrosine kinase 2, and Signal transducer and activator of transcription 5. Our findings support a role for the serotonin receptor 2B in the proliferation and migration of UM cells, through activation of many signaling pathways such as WNT, Focal adhesion kinase and Janus kinase/STAT.

Function-Related Protein Expression in Fuchs Endothelial Corneal Dystrophy Cells and Tissue Models

Fuchs endothelial corneal dystrophy (FECD) is a corneal pathology that affects the endothelial cell's ability to maintain deturgescence, resulting in a progressive loss of corneal transparency. In this study, we investigated the expression of function-related proteins in corneal endothelial cells using FECD or healthy corneal endothelial cells, either in a cell culture two-dimensional model or in an engineered corneal endothelium three-dimensional tissue model. No statistically significant difference in gene regulation was observed for the function-related families ATP1, SLC4, SLC16, AQP, TJP, and CDH between the FECD and the healthy cell models. Similarly, no difference in barrier integrity (transendothelial electrical resistance measurements and permeability assays) was observed in vitro between FECD and healthy cultured cells. Protein expression of the key function-related families was decreased for Na⁺/K⁺-ATPase α1 subunit, monocarboxylate transporters 1 and 4 in native ex vivo end-stage FECD specimens, whereas it returned to levels comparable to that of healthy tissues in the engineered FECD model. These results indicate that cell expansion and tissue engineering culture conditions can generate a corneal endothelium from pathologic FECD cells, with levels of function-related proteins similar to that of healthy tissues. Overall, these results explain why it is possible to reform a functional endothelium using corneal endothelial cells isolated from nonfunctional FECD pathologic specimens.

The convergent roles of the nuclear factor I transcription factors in development and cancer

The nuclear factor I (NFI) transcription factors play important roles during normal development and have been associated with developmental abnormalities in humans. All four family members, NFIA, NFIB, NFIC and NFIX, have a homologous DNA binding domain and function by regulating cell proliferation and differentiation via the transcriptional control of their target genes. More recently, NFI genes have also been implicated in cancer based on genomic analyses and studies of animal models in a variety of tumours across multiple organ systems. However, the association between their functions in development and in cancer is not well described. In this review, we summarise the evidence suggesting a converging role for the NFI genes in development and cancer. Our review includes all cancer types in which the NFI genes are implicated, focusing predominantly on studies demonstrating their oncogenic or tumour-suppressive potential. We conclude by presenting the challenges impeding our understanding of NFI function in cancer biology, and demonstrate how a developmental perspective may contribute towards overcoming such hurdles.

Characterization of the human α9 integrin subunit gene: Promoter analysis and transcriptional regulation in ocular cells

α9β1 is the most recent addition to the integrin family of membrane receptors and consequently remains the one that is the least characterized. To better understand how transcription of the human gene encoding the α9 subunit is regulated, we cloned the α9 promoter and characterized the regulatory elements that are required to ensure its transcription. Transfection of α9 promoter/CAT plasmids in primary cultured human corneal epithelial cells (HCECs) and uveal melanoma cell lines demonstrated the presence of both negative and positive regulatory elements along the α9 promoter and positioned the basal α9 promoter to within 118 bp from the α9 mRNA start site. In vitro DNaseI footprinting and in vivo ChIP analyses demonstrated the binding of the transcription factors Sp1, c-Myb and NFI to the most upstream α9 negative regulatory element. The transcription factors Sp1 and NFI were found to bind the basal α9 promoter individually but Sp1 binding clearly predominates when both transcription factors are present in the same extract. Suppression of Sp1 expression through RNAi also caused a dramatic reduction in the expression of the α9 gene. Most of all, addition of tenascin-C (TNC), the ligand of α9β1, to the tissue culture plates prior to seeding HCECs increased α9 transcription whereas it simultaneously decreased expression of the α5 integrin subunit gene. This dual regulatory action of TNC on the transcription of the α9 and α5 genes suggests that both these integrins must work together to appropriately regulate cell adhesion, migration and differentiation that are hallmarks of tissue wound healing.

Contribution of Sp1 to Telomerase Expression and Activity in Skin Keratinocytes Cultured With a Feeder Layer

The growth of primary keratinocytes is improved by culturing them with a feeder layer. The aim of this study was to assess whether the feeder layer increases the lifespan of cultured epithelial cells by maintaining or improving telomerase activity and expression. The addition of an irradiated fibroblast feeder layer of either human or mouse origin (i3T3) helped maintain telomerase activity as well as expression of the transcription factor Sp1 in cultured keratinocytes. In contrast, senescence occurred earlier, together with a reduction of Sp1 expression and telomerase activity, in keratinocytes cultured without a feeder layer. Telomerase activity was consistently higher in keratinocytes grown on the three different feeder layers tested relative to cells grown without them. Suppression of Sp1 expression by RNA inhibition (RNAi) reduced both telomerase expression and activity in keratinocytes and also abolished their long-term growth capacity suggesting that Sp1 is a key regulator of both telomerase gene expression and cell cycle progression of primary cultured human skin keratinocytes. The results of the present study therefore suggest that the beneficial influence of the feeder layer relies on its ability to preserve telomerase activity in cultured human keratinocytes through the maintenance of stable levels of Sp1 expression.

Integrin α5β1, the Fibronectin Receptor, as a Pertinent Therapeutic Target in Solid Tumors

Integrins are transmembrane heterodimeric proteins sensing the cell microenvironment and modulating numerous signalling pathways. Changes in integrin expression between normal and tumoral cells support involvement of specific integrins in tumor progression and aggressiveness. This review highlights the current knowledge about α5β1 integrin, also called the fibronectin receptor, in solid tumors. We summarize data showing that α5β1 integrin is a pertinent therapeutic target expressed by tumoral neovessels and tumoral cells. Although mainly evaluated in preclinical models, α5β1 integrin merits interest in particular in colon, breast, ovarian, lung and brain tumors where its overexpression is associated with a poor prognosis for patients. Specific α5β1 integrin antagonists will be listed that may represent new potential therapeutic agents to fight defined subpopulations of particularly aggressive tumors.

Resistance to the mTOR-inhibitor RAD001 elevates integrin α2- and β1-triggered motility, migration and invasion of prostate cancer cells

Background:

Inhibitors of the mammalian target of rapamycin (mTOR) might become a novel tool to treat advanced prostate cancer. However, chronic drug exposure may trigger resistance, limiting the utility of mTOR inhibitors.

Methods:

Metastatic potential of PC3 prostate cancer cells, susceptible (PC3^par) or resistant (PC3^res) to the mTOR-inhibitor RAD001 was investigated. Adhesion to vascular endothelium or immobilised collagen, fibronectin and laminin was quantified. Motility, migration and invasion were explored by modified Boyden chamber assay. Integrin α and β subtypes were analysed by flow cytometry, western blotting and real-time PCR. Integrin-related signalling, EGFr, Akt, p70S6kinase and ERK1/2 activation were determined.

Results:

Adhesion was reduced, whereas motility, migration and invasion were enhanced in PC3^res. The α2 and β1 integrin subtypes were dramatically elevated, integrins α1 and α6 were lowered, whereas α5 was nearly lost in PC3^res. Activation of the Akt signalling pathway was strongly upregulated in these cells. Treating PC3^par cells with RAD001 reduced motility, migration and invasion and deactivated Akt signalling. Blocking studies revealed that α2 and β1 integrins significantly trigger the motile behaviour of the tumour cells.

Conclusion:

Chronic RAD001 treatment caused resistance development characterised by distinct modification of the integrin-expression profile, driving prostate cancer cells towards high motility.

Rescue of the transcription factors Sp1 and NFI in human skin keratinocytes through a feeder-layer-dependent suppression of the proteasome activity

Co-culturing human skin keratinocytes along with a feeder layer has proven to considerably improve their proliferative properties by delaying massive induction of terminal differentiation. Through a yet unclear mechanism, we recently reported that irradiated 3T3 (i3T3) fibroblasts used as a feeder layer increase the nuclear content of Sp1, a positive transcription factor (TF) that plays a critical role in many cellular functions including cell proliferation, into both adult skin keratinocytes and newborn skin keratinocytes. In this study, we examined the influence of i3T3 on the expression and DNA binding of NFI, another TF important for cell proliferation and cell cycle progression, and attempted to decipher the mechanism by which the feeder layer contributes at maintaining higher levels of these TFs in skin keratinocytes. Our results indicate that co-culturing both adult skin keratinocytes and newborn skin keratinocytes along with a feeder layer dramatically increases glycosylation of NFI and may prevent it from being degraded by the proteasome.