Dragomira Majhen

αvβ3 Integrin-Mediated Drug Resistance in Human Laryngeal Carcinoma Cells Is Caused by Glutathione-Dependent Elimination of Drug-Induced Reactive Oxidative Species

As a model for determination of the role of integrins in drug resistance, we used αvβ3 integrin-negative human laryngeal carcinoma cell line (HEp2) and three HEp2-derived cell clones with a gradual increase of αvβ3 integrin expression. The αvβ3 integrin expression protects cells from cisplatin, mitomycin C, and doxorubicin. In HEp2-αvβ3 integrin-expressing cells, the constitutive expression of Bcl-2 protein and the level of glutathione (GSH) were increased compared with HEp2 cells. Pretreatment of HEp2-αvβ3 integrin-expressing cells with an inhibitor of GSH synthesis, buthionine sulfoximine (BSO), decreased the level of GSH and partially reverted drug resistance to all above-mentioned drugs, but it did not influence the expression of Bcl-2. Sensitivity to selected anticancer drugs did not change with overexpression of Bcl-2 in HEp2 cells, nor with silencing of Bcl-2 in HEp2-αvβ3 integrin-expressing cells, indicating that Bcl-2 is not involved in resistance mechanism. There was no difference in DNA platination between HEp2 and HEp2-αvβ3 integrin-expressing cells, indicating that the mechanism of drug resistance is independent of cisplatin detoxification by GSH. A strong increase of reactive oxidative species (ROS) formation during cisplatin or doxorubicin treatment in HEp2 cells was reduced in HEp2-αvβ3 integrin-expressing cells. Since this increased elimination of ROS could be reverted by GSH depletion, we concluded that multidrug resistance is the consequence of GSH-dependent increased ability of αvβ3-expressing cells to eliminate drug-induced ROS.

Differential role of αvβ3 and αvβ5 integrins in internalization and transduction efficacies of wild type and RGD4C fiber-modified adenoviruses

In order to analyze the role of alpha(v)beta(3) and alpha(v)beta(5) integrins in gene transfer by adenovirus-based vectors, an RGD4C motif was inserted into the HI-loop of wild type or shortened fiber protein of human adenovirus of serotype 5, thereby creating Ad5RGD4C and Ad5Delta639RGD4C vectors, respectively. Infection by the latter is independent of the Coxsackie B adenovirus receptor. Internalization and transduction of these vectors and were investigated in several stably transfected cell clones derived from a human laryngeal carcinoma cell line (HEp2) expressing different ratios of alpha(v)beta(5) and alpha(v)beta(3) integrins. We show that alpha(v)beta(3) is more successful than alpha(v)beta(5) in: (i) mediating adenovirus internalization and transduction when the RGD motif is present only in the penton base and (ii) mediating internalization and transduction by RGD4C-fiber modified adenoviruses. The highest amount of internalized virus was found in the cell clone in which alpha(v)beta(3) integrin predominated over alpha(v)beta(5) integrin (as judged by the % of cells expressing alpha(v)beta(3) and alpha(v)beta(5) integrins). However the level of transgene expression in this cell line was even lower than that in parental HEp2 cells which do not express alpha(v)beta(3) integrin. This discrepancy between internalization and transgene expression (transduction) is likely due to the crucial role of alpha(v)beta(5) in membrane permeabilization, indicating that alpha(v)beta(5) integrin is a limiting factor for Ad5-mediated gene transfer. We conclude that alpha(v)beta(3) integrin is an efficient adenovirus internalization receptor, but cannot functionally replace alpha(v)beta(5) in endosomal release.

Expression, regulation and functional activities of aminopeptidase N (EC 3.4.11.2; APN; CD13) on murine macrophage J774 cell line.

Aminopeptidase N (APN; CD13) is a ubiquitous membrane-bound enzyme. Expressed on haematopoietic cells APN participates in inflammatory and immune responses by regulating local concentration of chemotactic peptides and by fine-tuning antigen presentation. The data of this study have shown for the first time that cells of murine macrophage line, J774, often used as a model cell line, express CD13 both at transcriptional level and at the level of membrane protein with aminopeptidase N (APN) activity. The level of transcriptional expression of CD13/APN on J774 cells was compared to that found on normal cells participating in immune responses. The highest CD13/APN level was found in peritoneal macrophages, followed by J774 cells and splenocytes, whereas lymph node, thymus and bone-marrow cells expressed low level of CD13/APN mRNA. Further, the CD13 (mRNA, protein and APN) on J774 cells could be up-regulated by pro-inflammatory IFN-γ which is in agreement with the known role of CD13/APN in inflammatory responses. Co-regulation of CD13 with MHC-II and CD86 is in line with the reported role of APN expressed on human cells in antigen presentation. CD13 on J774 cells co-localize with mannose receptors (MR), and co-internalize upon MR ligation by ovalbumin, suggesting a new function of CD13 in MR-mediated phagocytosis. That function of CD13 is independent of APN enzyme activity. Anti-inflammatory drug dexamethasone diminished the IFN-γ-induced increase of CD13. The observed down-regulation of CD13 on J774 cells by dexamethasone might be relevant as a possible mechanism involved in action of anti-inflammatory drugs on normal macrophages.

Endoplasmic reticulum stress is involved in the response of human laryngeal carcinoma cells to Carboplatin but is absent in Carboplatin-resistant cells.

The major obstacle of successful tumor treatment with carboplatin (CBP) is the development of drug resistance. In the present study, we found that following treatment with CBP the amount of platinum which enters the human laryngeal carcinoma (HEp2)-derived CBP-resistant (7T) cells is reduced relative to the parental HEp2. As a consequence, the formation of reactive oxidative species (ROS) is reduced, the induction of endoplasmic reticulum (ER) stress is diminished, the amount of inter- and intrastrand cross-links is lower, and the induction of apoptosis is depressed. In HEp2 cells, ROS scavenger tempol, inhibitor of ER stress salubrinal, as well as gene silencing of ER stress marker CCAAT/enhancer-binding protein (CHOP) increases their survival and renders them as resistant to CBP as 7T cell subline but did not influence the survival of 7T cells. Our results suggest that in HEp2 cells CBP-induced ROS is a stimulus for ER stress. To the contrary, despite the ability of CBP to induce formation of ROS and activate ER stress in 7T cells, the cell death mechanism in 7T cells is independent of ROS induction and activation of ER stress. The novel signaling pathway of CBP-driven toxicity that was found in the HEp2 cell line, i.e. increased ROS formation and induction of ER stress, may be predictive for therapeutic response of epithelial cancer cells to CBP-based therapy.

Integrin αvβ3 expression in tongue squamous carcinoma cells Cal27 confers anticancer drug resistance through loss of pSrc(Y418).

Integrins play key roles in the regulation of tumor cell adhesion, migration, invasion and sensitivity to anticancer drugs. In the present study we investigate the mechanism of resistance of tongue squamous carcinoma cells Cal27 with de novo integrin αvβ3 expression to anticancer drugs. Cal27-derived cell clones, obtained by transfection of plasmid containing integrin subunit β3 cDNA, as compared to control cells demonstrate: expression of integrin αvβ3; increased expression of integrin αvβ5; increased adhesion to fibronectin and vitronectin; resistance to cisplatin, mitomycin C, doxorubicin and 5-fluorouracil; increased migration and invasion, increased amount of integrin-linked kinase (ILK) and decreased amounts of non-receptor tyrosine kinase (Src) and pSrc(Y418). Knockdown of ILK and integrin β5 in cells expressing integrin αvβ3 ruled out their involvement in drug resistance. Opposite, Src knockdown in Cal27 cells which led to a reduction in pSrc(Y418), as well as treatment with the pSrc(Y418) inhibitors dasatinib and PP2, conferred resistance to all four anticancer drugs, indicating that the loss of pSrc(Y418) is responsible for the observed effect. We identified differential integrin signaling between Cal27 and integrin αvβ3-expressing cells. In Cal27 cells integrin αv heterodimers signal through pSrc(Y418) while this is not the case in integrin αvβ3-expressing cells. Finally, we show that dasatinib counteracts the effect of cisplatin in two additional head and neck squamous cell carcinoma (HNSCC) cell lines Cal33 and Detroit562. Our results suggest that pSrc(Y418) inhibitors, potential drugs for cancer therapy, may reduce therapeutic efficacy if combined with chemotherapeutics, and might not be recommended for HNSCC treatment.

Integrin αVβ3 silencing sensitizes malignant glioma cells to temozolomide by suppression of homologous recombination repair

Integrins have been suggested as possible targets in anticancer therapy. Here we show that knockdown of integrins αVβ3, αVβ5, α3β1 and α4β1 and pharmacological inhibition using a cyclo-RGD integrin αVβ3/αVβ5 antagonist sensitized multiple high-grade glioma cell lines to temozolomide (TMZ)-induced cytotoxicity. The greatest effect was observed in LN229 cells upon integrin β3 silencing, which led to inhibition of the FAK/Src/Akt/NFκB signaling pathway and increased formation of γH2AX foci. The integrin β3 knockdown led to the proteasomal degradation of Rad51, reduction of Rad51 foci and reduced repair of TMZ-induced DNA double-strand breaks by impairing homologous recombination efficiency. The down-regulation of β3 in Rad51 knockdown (LN229-Rad51kd) cells neither further sensitized them to TMZ nor increased the number of γH2AX foci, confirming causality between β3 silencing and Rad51 reduction. RIP1 was found cleaved and IκBα significantly less degraded in β3-silenced/TMZ-exposed cells, indicating inactivation of NFκB signaling. The anti-apoptotic proteins Bcl-xL, survivin and XIAP were proteasomally degraded and caspase-3/−2 cleaved. Increased H2AX phosphorylation, caspase-3 cleavage, reduced Rad51 and RIP1 expression, as well as sustained IκBα expression were also observed in mouse glioma xenografts treated with the cyclo-RGD inhibitor and TMZ, confirming the molecular mechanism in vivo. Our data indicates that β3 silencing in glioma cells represents a promising strategy to sensitize high-grade gliomas to TMZ therapy.

Increased expression of the coxsackie and adenovirus receptor downregulates αvβ3 and αvβ5 integrin expression and reduces cell adhesion and migration.

AIMS Coxsackie and adenovirus receptor (CAR) is a tumor suppressor and a primary receptor for adenovirus type 5 (Ad5). Our study aims to examine the influence of forced expression of CAR in rhabdomyosarcoma cells (RD) on expression levels of integrins implicated in Ad5 entry, and the effect of CAR on cell-extracellular matrix adhesion and migration. MAIN METHODS CAR expressing clones were established from RD cells by stable transfection. Flow cytometry was used to evaluate the expression of CAR and integrins. Adhesion was measured in plates previously coated with vitronectin or fibronectin. Boyden chambers were used to investigate migration. Transfection of cells with siRNA was used to achieve integrin silencing. Ad5-mediated transgene expression was measured by β-gal staining. KEY FINDINGS Increased expression of CAR in RD cells reduces the expression of αvβ3 and αvβ5 integrins. Cells overexpressing CAR exhibit significantly reduced adhesion to vitronectin and fibronectin, and reduced cell migration. Specifically silencing αvβ3 integrin in RD cells reduced cell migration indicating that reduced migration could be the consequence of αvβ3 integrin downregulation. This study also demonstrates the negative effect of reduced levels of αvβ3 and αvβ5 integrins on Ad5-mediated transgene expression with Ad5 retargeted to αv integrins. SIGNIFICANCE The pharmacological upregulation of CAR aimed to increase Ad5-mediated transgene expression may actually downregulate αvβ3 and αvβ5 integrins and thus alter Ad5-mediated gene transfer. The mechanism of decreased cell migration, a prerequisite for metastasis and invasion, due to increased CAR expression may be explained by reduced αvβ3 integrin expression.

Sequence polymorphism of PrP exon 3 gene in Istrian and crossbred sheep

Abstract Polymorphisms in sheep PrP (prion protein) gene are known for scrapie susceptibility. We sequenced part of PrP exon 3 gene in 92 autochthonous Istrian (IS) and 38 crossbred sheep (CBS). ARQ, ARR and AHQ alleles were predominant with frequency of 0.674 (0.526), 0.228 (0.132) and 0.082 (0.263) in IS (CBS), respectively, while VRQ (0.011 in IS) and ARH (0.005 in IS and 0.079 in CBS) alleles were rare. We also found non-synonymous mutations at codons 112 (M→T), 127 (G→S) and 143 (H→R), and synonymous mutations at codons 231 (R) and 237 (L). Additional mutations were associated only with AHQ, ARH and ARQ alleles. The polymorphism of PrP gene in IS was not critical with respect to scrapie susceptibility and with some efforts number of “favourable” genotypes can be increased.

Combined therapy of colon carcinomas with an oncolytic adenovirus and valproic acid

The anti-tumor potential of oncolytic adenoviruses (CRAds) has been demonstrated in preclinical and clinical studies. While these agents failed to eradicate tumors when used as a monotherapy, they may be more effective if combined with conventional treatments such as radiotherapy or chemotherapy. This study seeks to evaluate the combination of a CRAd bearing a ∆24 deletion in E1A with valproic acid (VPA), a histone deacetylase inhibitor, for the treatment of human colon carcinomas. This combination led to a strong inhibition of cell growth both in vitro and in vivo compared to treatment with CRAd or VPA alone. This effect did not stem from a better CRAd replication and production in the presence of VPA. Inhibition of cell proliferation and cell death were induced by the combined treatment. Moreover, whereas cells treated only with CRAd displayed a polyploidy (> 4N population), this phenotype was increased in cells treated with both CRAd and VPA. In addition, the increase in polyploidy triggered by combined treatment with CRAd and VPA was associated with the enhancement of H2AX phosphorylation (γH2AX), a hallmark of DNA damage, but also with a decrease of several DNA repair proteins. Finally, viral replication (or E1A expression) was shown to play a key role in the observed effects since no enhancement of polyploidy nor increase in γH2AX were found following cell treatment with a replication-deficient Ad and VPA. Taken together, our results suggest that CRAd and VPA could be used in combination for the treatment of colon carcinomas.

Manipulating adenoviral vector ion-exchange chromatography: Hexon versus fiber

The serotype specificity of adenovirus ion-exchange chromatography has previously been studied using standard particle-based columns, and the hexon protein has been reported to determine retention time. In this study, we have submitted Adenovirus type 5 recombinants to anion-exchange chromatography using methacrylate monolithic supports. Our experiments with hexon-modified adenoviral vectors show more precisely that the retention time is affected by the substitution of amino acids in hypervariable region 5, which lies within the hexon DE1 loop. By exploring the recombinants modified in the fiber protein, we have proven the previously predicted chromatographic potential of this surface constituent. Modifications that preserve the net charge of the hexon protein, or those that cause only a small charge difference in the fiber protein, in addition to shortening the fiber shaft, did not change the chromatographic behavior of the adenovirus particles. However, modifications that include the deletion of just two negatively charged amino acids in the hexon protein, or the introduction of a heterologous fiber protein, derived from another serotype, revealed recognizable changes in anion-exchange chromatography. This could be useful in facilitating chromatography-approach purification by creating targeted capsid modifications, thereby shifting adenovirus particles away from particular interfering substances present in the crude lysate.