Shear stress switches the association of endothelial enhancers from ETV/ETS to KLF transcription factor binding sites

Endothelial cells (ECs) lining blood vessels are exposed to mechanical forces, such as shear stress. These forces control many aspects of EC biology, including vascular tone, cell migration and proliferation. Despite a good understanding of the genes responding to shear stress, our insight into the transcriptional regulation of these genes is much more limited. Here, we set out to study alterations in the chromatin landscape of human umbilical vein endothelial cells (HUVEC) exposed to laminar shear stress. To do so, we performed ChIP-Seq for H3K27 acetylation, indicative of active enhancer elements and ATAC-Seq to mark regions of open chromatin in addition to RNA-Seq on HUVEC exposed to 6 h of laminar shear stress. Our results show a correlation of gained and lost enhancers with up and downregulated genes, respectively. DNA motif analysis revealed an over-representation of KLF transcription factor (TF) binding sites in gained enhancers, while lost enhancers contained more ETV/ETS motifs. We validated a subset of flow responsive enhancers using luciferase-based reporter constructs and CRISPR-Cas9 mediated genome editing. Lastly, we characterized the shear stress response in ECs of zebrafish embryos using RNA-Seq. Our results lay the groundwork for the exploration of shear stress responsive elements in controlling EC biology.

Identification of atheroprone shear stress responsive regulatory elements in endothelial cells

AIMS

Oscillatory shear stress (OSS) is an atheroprone haemodynamic force that occurs in areas of vessel irregularities and is implicated in the pathogenesis of atherosclerosis. Changes in signalling and transcriptional programme in response to OSS have been vigorously studied; however, the underlying changes in the chromatin landscape controlling transcription remain to be elucidated. Here, we investigated the changes in the regulatory element (RE) landscape of endothelial cells under atheroprone OSS conditions in an in vitro model.

METHODS AND RESULTS

Analyses of H3K27ac chromatin immunoprecipitation-Seq enrichment and RNA-Seq in primary human umbilical vein endothelial cells 6 h after onset of OSS identified 2806 differential responsive REs and 33 differentially expressed genes compared with control cells kept under static conditions. Furthermore, gene ontology analyses of putative RE-associated genes uncovered enrichment of WNT/HIPPO pathway and cytoskeleton reorganization signatures. Transcription factor (TF) binding motif analysis within RE sequences identified over-representation of ETS, Zinc finger, and activator protein 1 TF families that regulate cell cycle, proliferation, and apoptosis, implicating them in the development of atherosclerosis. Importantly, we confirmed the activation of EGR1 as well as the YAP/TAZ complex early (6 h) after onset of OSS in both cultured human vein and artery endothelial cells and, by undertaking luciferase assays, functionally verified their role in RE activation in response to OSS.

CONCLUSIONS

Based on the identification and verification of specific responsive REs early upon OSS exposure, we propose an expanded mechanism of how OSS might contribute to the development of atherosclerosis.

Function and mutual interaction of BiP-, PERK-, and IRE1α-dependent signalling pathways in vascular tumours

Spontaneously regressing infantile haemangiomas and aggressive angiosarcomas are vascular tumours with excessive angiogenesis. When analysing haemangiomas and angiosarcomas immunohistochemically with respect to their chaperone profiles we found that angiosarcomas have significantly elevated protein levels of binding immunoglobulin protein (BIP) and PERK with concomitant attenuated IRE1α levels, whereas haemangioma tissue exhibits the same pattern as embryonal skin tissue. We show that BiP is essential for the maintenance of VEGFR2 protein, which is expressed in the endothelium of both tumour types. When studying the effects of BiP, the IRE1α/Xbp1 -, and PERK/ATF4-signalling pathways on the migration and tube-forming potential of endothelial cells, we show that downregulation of BiP, as well as inhibition of the kinase activity of IRE1α, inhibit in vitro angiogenesis. Downregulation of PERK (PKR-like kinase; PKR = protein kinase R) levels promotes Xbp1 splicing in endoplasmic reticulum (ER)-stressed cells, indicating that in angiosarcoma the elevated PERK levels might result in high levels of unspliced Xbp1, which have been reported to promote cell proliferation and increase tumour malignancy. The data presented in this study revealed that in addition to BiP or PERK, the kinase domains of IRE1α and Xbp1 could be potential targets for the development of novel therapeutic approaches for treating angiosarcomas and to control tumour angiogenesis. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

In vitro evaluation of a biomaterial-based anticancer drug delivery system as an alternative to conventional post-surgery bone cancer treatment

Patients diagnosed with osteosarcoma are currently treated with intravenous injections of anticancer agents after tumor resection. However, due to remaining neoplastic cells at the site of tumor removal, cancer recurrence often occurs. Successful bone regeneration combined with the control of residual cancer cells presents a challenge for tissue engineering. Cyclodextrins loaded with chemotherapeutic drugs reversibly release the drugs over time. Hydroxyapatite bone biomaterials coated with doxorubicin-loaded cyclodextrin should release the drug with time after implantation directly at the original tumor site and may be a way to eliminate residual neoplastic cells. In the present study, we have carried out in vitro studies to evaluate such a drug-delivery system and have shown that doxorubicin released from cyclodextrin-coated hydroxyapatite retained biological activity and exhibited longer and higher cytotoxic effects on both cancer (osteosarcoma cells) and healthy cells (primary osteoblasts and endothelial cells) compared to biomaterials without cyclodextrin loaded with doxorubicin. Furthermore, doxorubicin released from biomaterials with cyclodextrin moderately induced the expression of tumor suppressor protein p53 whereas p21 expression was similar to control cells. In addition, hypoxic conditions, which occur after implantation until blood-flow to the area is regenerated, protected endothelial cells and primary osteoblasts from doxorubicin-induced cytotoxicity. This chemo-protective effect was far less prominent for the osteosarcoma cells. These findings indicate that a hydroxyapatite-cyclodextrin-doxorubicin chemotherapeutic strategy may enhance the drug-targeting effect on tumor cells while protecting the more sensitive healthy cells for a period of time after implantation. A successful integration of such a drug delivery system might allow healthy cells to initially survive during the doxorubicin exposure period, while eliminating residual neoplastic cells.

Endothelial Notch signalling limits angiogenesis via control of artery formation

Angiogenic sprouting needs to be tightly controlled. It has been suggested that the Notch ligand dll4 expressed in leading tip cells restricts angiogenesis by activating Notch signalling in trailing stalk cells. Here, we show using live imaging in zebrafish that activation of Notch signalling is rather required in tip cells. Notch activation initially triggers expression of the chemokine receptor cxcr4a. This allows for proper tip cell migration and connection to the pre-existing arterial circulation, ultimately establishing functional arterial-venous blood flow patterns. Subsequently, Notch signalling reduces cxcr4a expression, thereby preventing excessive blood vessel growth. Finally, we find that Notch signalling is dispensable for limiting blood vessel growth during venous plexus formation that does not generate arteries. Together, these findings link the role of Notch signalling in limiting angiogenesis to its role during artery formation and provide a framework for our understanding of the mechanisms underlying blood vessel network expansion and maturation.

Spontaneous In Vivo Chondrogenesis of Bone Marrow-Derived Mesenchymal Progenitor Cells by Blocking Vascular Endothelial Growth Factor Signaling

: Chondrogenic differentiation of bone marrow-derived mesenchymal stromal/stem cells (MSCs) can be induced by presenting morphogenetic factors or soluble signals but typically suffers from limited efficiency, reproducibility across primary batches, and maintenance of phenotypic stability. Considering the avascular and hypoxic milieu of articular cartilage, we hypothesized that sole inhibition of angiogenesis can provide physiological cues to direct in vivo differentiation of uncommitted MSCs to stable cartilage formation. Human MSCs were retrovirally transduced to express a decoy soluble vascular endothelial growth factor (VEGF) receptor-2 (sFlk1), which efficiently sequesters endogenous VEGF in vivo, seeded on collagen sponges and immediately implanted ectopically in nude mice. Although naïve cells formed vascularized fibrous tissue, sFlk1-MSCs abolished vascular ingrowth into engineered constructs, which efficiently and reproducibly developed into hyaline cartilage. The generated cartilage was phenotypically stable and showed no sign of hypertrophic evolution up to 12 weeks. In vitro analyses indicated that spontaneous chondrogenic differentiation by blockade of angiogenesis was related to the generation of a hypoxic environment, in turn activating the transforming growth factor-β pathway. These findings suggest that VEGF blockade is a robust strategy to enhance cartilage repair by endogenous or grafted mesenchymal progenitors. This article outlines the general paradigm of controlling the fate of implanted stem/progenitor cells by engineering their ability to establish specific microenvironmental conditions rather than directly providing individual morphogenic cues.

SIGNIFICANCE

Chondrogenic differentiation of mesenchymal stromal/stem cells (MSCs) is typically targeted by morphogen delivery, which is often associated with limited efficiency, stability, and robustness. This article proposes a strategy to engineer MSCs with the capacity to establish specific microenvironmental conditions, supporting their own targeted differentiation program. Sole blockade of angiogenesis mediated by transduction for sFlk-1, without delivery of additional morphogens, is sufficient for inducing MSC chondrogenic differentiation. The findings represent a relevant step forward in the field because the method allowed reducing interdonor variability in MSC differentiation efficiency and, importantly, onset of a stable, nonhypertrophic chondrocyte phenotype.

Collagen-low molecular weight hyaluronic acid semi-interpenetrating network loaded with gelatin microspheres for cell and growth factor delivery for nucleus pulposus regeneration

Intervertebral disc (IVD) degeneration is one of the main causes of low back pain. Current surgical treatments are complex and generally do not fully restore spine mobility. Development of injectable extracellular matrix-based hydrogels offers an opportunity for minimally invasive treatment of IVD degeneration. Here we analyze a specific formulation of collagen-low molecular weight hyaluronic acid (LMW HA) semi-interpenetrating network (semi-IPN) loaded with gelatin microspheres as a potential material for tissue engineering of the inner part of the IVD, the nucleus pulposus (NP). The material displayed a gel-like behavior, it was easily injectable as demonstrated by suitable tests and did not induce cytotoxicity or inflammation. Importantly, it supported the growth and chondrogenic differentiation potential of mesenchymal stem cells (MSC) and nasal chondrocytes (NC) in vitro and in vivo. These properties of the hydrogel were successfully combined with TGF-β3 delivery by gelatin microspheres, which promoted the chondrogenic phenotype. Altogether, collagen-LMW HA loaded with gelatin microspheres represents a good candidate material for NP tissue engineering as it combines important rheological, functional and biological features.

Endoplasmic reticulum-resident chaperones modulate the inflammatory and angiogenic responses of endothelial cells

BACKGROUND

Wound healing depends on a well-balanced regulation of inflammation and angiogenesis. In chronic wounds the healing process is disturbed and inflammation persists. Regulation of wound closure is controlled by transmembrane and extracellular proteins, the folding and maturation of which occur in the endoplasmic reticulum (ER) by ER-resident chaperone machinery.

OBJECTIVES

To study the role of the ER-resident chaperones BiP/Grp78, its cochaperone Mdg1/ERdJ4, and Grp94 in chronic, nonhealing wounds.

METHODS

Immunohistochemical staining of these chaperones in individual human biopsies and investigation of the possible role of BiP and Mdg1 in endothelial cells, focusing on their inflammatory response and angiogenic potential.

RESULTS

In all chronic wounds investigated, the levels of these ER-resident chaperones were elevated in endothelial cells and leucocytes. The proangiogenic role of BiP has been shown in tumour growth studies before and was confirmed in this study. Proangiogenic activity of the cochaperone Mdg1 has been postulated before but could not be confirmed in this study. The chemokine tumour necrosis factor (TNF)-α was shown to trigger the presentation of proinflammatory adhesion molecules and the release of proinflammatory cytokines. Here we show that TNF-α does not affect endogenous chaperone levels, but that the ER-resident chaperones BiP and Mdg1 modulate the cellular TNF-α-induced proinflammatory response.

CONCLUSIONS

According to the presented data we assume that in chronic wounds upregulated levels of ER-resident chaperones might contribute to persistent inflammation in chronic wounds. Therapies to downregulate chaperone levels might provide a tool that switches the imbalanced chronic wound microenvironment from inflammation to healing.

Poly(γ-Glutamic Acid) as an Exogenous Promoter of Chondrogenic Differentiation of Human Mesenchymal Stem/Stromal Cells

Cartilage damage and/or aging effects can cause constant pain, which limits the patient's quality of life. Although different strategies have been proposed to enhance the limited regenerative capacity of cartilage tissue, the full production of native and functional cartilaginous extracellular matrix (ECM) has not yet been achieved. Poly(γ-glutamic acid) (γ-PGA), a naturally occurring polyamino acid, biodegradable into glutamate residues, has been explored for tissue regeneration. In this work, γ-PGA's ability to support the production of cartilaginous ECM by human bone marrow mesenchymal stem/stromal cells (MSCs) and nasal chondrocytes (NCs) was investigated. MSC and NC pellets were cultured in basal medium (BM), chondrogenic medium (CM), and CM-γ-PGA-supplemented medium (CM+γ-PGA) over a period of 21 days. Pellet size/shape was monitored with time. At 14 and 21 days of culture, the presence of sulfated glycosaminoglycans (sGAGs), type II collagen (Col II), Sox-9, aggrecan, type XI collagen (Col XI), type X collagen (Col X), calcium deposits, and type I collagen (Col I) was analyzed. After excluding γ-PGA's cytotoxicity, earlier cell condensation, higher sGAG content, Col II, Sox-9 (day 14), aggrecan, and Col X (day 14) production was observed in γ-PGA-supplemented MSC cultures, with no signs of mineralization or Col I. These effects were not evident with NCs. However, Sox-9 (at day 14) and Col X (at days 14 and 21) were increased, decreased, or absent, respectively. Overall, γ-PGA improved chondrogenic differentiation of MSCs, increasing ECM production earlier in culture. It is proposed that γ-PGA incorporation in novel biomaterials has a beneficial impact on future approaches for cartilage regeneration.

Improving cytocompatibility of Co28Cr6Mo by TiO2 coating: gene expression study in human endothelial cells

Cobalt-based materials are widely used for coronary stents, as well as bone and joint implants. However, their use is associated with high corrosion incidence. Titanium alloys, by contrast, are more biocompatible owing to the formation of a relatively inactive titanium oxide (TiO2) layer on their surface. This study was aimed at improving Co28Cr6Mo alloy cytocompatibility via sol-gel TiO2 coating to reduce metal corrosion and metal ion release. Owing to their role in inflammation and tissue remodelling around an implant, endothelial cells present a suitable in vitro model for testing the biological response to metallic materials. Primary human endothelial cells seeded on Co28Cr6Mo showed a stress phenotype with numerous F-actin fibres absent on TiO2-coated material. To investigate this effect at the gene expression level, cDNA microarray analysis of in total 1301 genes was performed. Compared with control cells, 247 genes were expressed differentially in the cells grown on Co28Cr6Mo, among them genes involved in proliferation, oxidative stress response and inflammation. TiO2 coating reduced the effects of Co28Cr6Mo on gene expression in endothelial cells, with only 34 genes being differentially expressed. Quantitative real-time polymerase chain reaction and protein analysis confirmed microarray data for selected genes. The effect of TiO2 coating can be, in part, attributed to the reduced release of Co(2+), because addition of CoCl2 resulted in similar cellular responses. TiO2 coating of cobalt-based materials, therefore, could be used in the production of cobalt-based devices for cardiovascular and skeletal applications to reduce the adverse effects of metal corrosion products and to improve the response of endothelial and other cell types.

The translesion polymerase Rev3L in the tolerance of alkylating anticancer drugs

Temozolomide and fotemustine, representing methylating and chloroethylating agents, respectively, are used in the treatment of glioma and malignant melanoma. Because chemoresistance of these tumors is a common phenomenon, identification of the underlying mechanisms is needed. Here we show that Rev3L, the catalytic subunit of the translesion DNA polymerase zeta, mediates resistance to both temozolomide and fotemustine. Rev3L knockout cells are hypersensitive to both agents. It is remarkable that cells heterozygous for Rev3L showed an intermediate sensitivity. Rev3L is not involved in the tolerance of the toxic O6-methylguanine lesion. However, a possible role of Rev3L in the tolerance of O6-chloroethylguanine or the subsequently formed N1-guanine-N3-cytosine interstrand cross-link is shown. Rev3L had no influence on base excision repair (BER) of the N-alkylation lesions but is very likely to be involved in the tolerance of N-alkylations or apurinic/apyrimidinic sites originating from them. We also show that Rev3L exerts its protective effect in replicating cells and that loss of Rev3L leads to a significant increase in DNA double-strand breaks after temozolomide and fotemustine treatment. These data show that Rev3L contributes to temozolomide and fotemustine resistance, thus acting in concert with O6-methylguanine-DNA methyltransferase, BER, mismatch repair, and double-strand break repair in defense against simple alkylating anticancer drugs.

Cisplatin sensitivity is related to late DNA damage processing and checkpoint control rather than to the early DNA damage response

The present study aimed at elucidating mechanisms dictating cell death triggered by cisplatin-induced DNA damage. We show that CL-V5B hamster mutant cells, a derivative of V79B, are hypersensitive to cisplatin-induced apoptotic death. CL-V5B cells are characterized by attenuated cisplatin-induced early (2-6 h) stress response, such as phosphorylation of stress-activated protein kinases (SAPK/JNK), ATM and Rad3-related (ATR) protein kinase, histone H2AX and checkpoint kinase-1 (Chk-1). Human FANCC cells also showed a reduced phosphorylation of H2AX and SAPK/JNK at early time point after cisplatin treatment. This was not the case for BRCA2-defective VC-8 hamster cells, indicating that the FA core complex, rather than its downstream elements, is involved in early damage response. The alleviated early response of CL-V5B cells is not due to a general dysfunction in ATM/ATR-regulated signaling. It is rather due to a reduced formation of primary cisplatin-DNA adducts in the hypersensitive mutant as shown by analysis of DNA platination, DNA intra- and interstrand crosslink formation and DNA replication blockage. Despite of lower initial DNA damage and attenuated early DNA damage response (DDR), CL-V5B cells are characterized by an excessive G2/M arrest as well as an elevated frequency of DNA double-strand breaks (DSB) and chromosomal aberrations (CA) at late times (16-24h) after cisplatin exposure. This indicates that error-prone processing of cisplatin-induced lesions, notably interstrand crosslinks (ICL), and the formation of secondary DNA lesions (i.e. DSB), results in a powerful delayed DNA damage response and massive pro-apoptotic signaling in CL-V5B cells. The data provide an example that the initial level of cisplatin-DNA adducts and the corresponding early DNA damage response do not necessarily predict the outcome of cisplatin treatment. Rather, the accuracy of DNA damage processing and late checkpoint control mechanisms determine the extent of cell death triggered by cisplatin-induced DNA lesions.

Cell type-specific aspects in biocompatibility testing: the intercellular contact in vitro as an indicator for endothelial cell compatibility

Endothelial cells cover the inner surface of blood vessels and form the interface between the blood and the tissues. Endothelial cells are involved in regulating barrier function, which is maintained by the interendothelial cell contacts. These interendothelial cell contacts are established by the interaction of different molecules. The maintenance of the barrier requires an appropriate signalling between these molecules. Thus, a number of different signalling pathways are integrated within interendothelial contacts. Since endothelial cells are important in tissue-implant interactions (especially for stent materials) this study examines the expression pattern of different interendothelial contact molecules to determine the usefulness in the analysis of biocompatibility in vitro. The effects of different pro-inflammatory and toxic stimuli and contact of human microvascular endothelial cells to metallic surfaces were examined for their impact on the pattern of interendothelial contact molecules. Striking modifications in the arrangement of these molecules were induced and the mode of modification was dependent on the tested compound. Thus, examining the pattern of expression of specific interendothelial contact molecules in vitro may be useful for testing the endothelial cell compatibility of biomaterials and their corrosion products.

Metallic nanoparticles exhibit paradoxical effects on oxidative stress and pro-inflammatory response in endothelial cells in vitro

Particulate matter is associated with different human diseases affecting organs such as the respiratory and cardiovascular systems. Very small particles (nanoparticles) have been shown to be rapidly internalized into the body. Since the sites of internalization and the location of the detected particles are often far apart, a distribution via the blood stream must have occurred. Thus, endothelial cells, which line the inner surface of blood vessels, must have had direct contact with the particles. In this study we tested the effects of metallic nanoparticles (Co and Ni) on oxidative stress and pro-inflammatory response in human endothelial cells in vitro. Exposure to both nanoparticle types led to a concentration-dependent cytotoxic effect. However, the effects on oxidative stress and pro-inflammatory response differed dramatically. Due to the nanoparticle-induced effects, a comparison between metallic nanoparticle- and metal ion-treatment with the corresponding ions was made. Again, divergent effects of nanoparticles compared with the ions were observed, thus indicating differences in the signaling pathways induced by these compounds. These paradoxical responses to different metallic nanoparticles and ions demonstrate the complexity of nanoparticle-induced effects and suggest the need to design new strategies for nanoparticle toxicology.

The effect of electrochemically simulated titanium cathodic corrosion products on ROS production and metabolic activity of osteoblasts and monocytes/macrophages

Nowadays aseptic loosening is the most common cause of orthopaedic implant failure. Some of its reasons have already been described up to now; however, others remain still hypothetical. Besides the inflammatory response to wear particles originating at different sources, the role of reactive oxygen species as products of cellular reactions and/or as a result of the process of corrosion of an implant leading to implant failure has recently been discussed too. In the present study, we used a galvanostatic polarization to simulate the cathodic partial reaction of the corrosion process at a titanium alloy surface. With respect to cells occurring at the interface of a metal implant, the behaviour of osteoblasts and monocytes/macrophages was investigated. It has been found that cathodic polarization of Ti6Al4V induces an increase in the level of intracellular reactive oxygen species as well as suppressing the metabolic activity of cells in a dose-dependent manner. This is in agreement with the results obtained with cells after external addition of hydrogen peroxide as another kind of oxidative stress. In both approaches, monocytes/macrophages show a higher tolerance to oxidative stress than osteoblasts. It could be concluded that the electrochemical setup developed induced intracellular changes occurring during oxidative stress and it could be used for future detailed analysis of the consequences of corrosion processes for cellular reactions.

Response of human endothelial cells to oxidative stress on Ti6Al4V alloy

Titanium and its alloys are amongst the most frequently used materials in bone and dental implantology. The good biocompatibility of titanium(-alloys) is attributed to the formation of a titanium oxide layer on the implant surface. However, implant failures do occur and this appears to be due to titanium corrosion. Thus, cells participating in the wound healing processes around an implanted material, among them endothelial cells, might be subjected to reactive oxygen species (ROS) formed by electrochemical processes during titanium corrosion. Therefore, we studied the response of endothelial cells grown on Ti6Al4V alloy to H(2)O(2) and compared this with the response of endothelial cells grown on cell culture polystyrene (PS). We could show that although the cell number was the same on both surfaces, metabolic activity of endothelial cells grown on Ti6Al4V alloy was reduced compared to the cells on PS and further decreased following prototypic oxidative stress (H(2)O(2)-treatment). The analysis of H(2)O(2)-induced oxidative stress showed a higher ROS formation in endothelial cells on Ti6Al4V than on PS. This correlated with the depletion of reduced glutathione (GSH) in endothelial cells grown on Ti6Al4V surfaces and indicated permanent oxidative stress. Thus, endothelial cells in direct contact with Ti6Al4V showed signs of oxidative stress and higher impairment of cell vitality after an additional oxidative stress. However, the exact nature of the agent of oxidative stress generated from Ti6Al4V remains unclear and requires further investigation.

Xrcc2 deficiency sensitizes cells to apoptosis by MNNG and the alkylating anticancer drugs temozolomide, fotemustine and mafosfamide

DNA double-strand breaks (DSBs) are potent killing lesions, and inefficient repair of DSBs does not only lead to cell death but also to genomic instability and tumorigenesis. DSBs are repaired by non-homologous end-joining and homologous recombination (HR). A key player in HR is Xrcc2, a Rad51-like protein. Cells deficient in Xrcc2 are hypersensitive to X-rays and mitomycin C and display increased chromosomal aberration frequencies. In order to elucidate the role of Xrcc2 in resistance to anticancer drugs, we compared Xrcc2 knockout (Xrcc2-/-) mouse embryonic fibroblasts with the corresponding isogenic wild-type and Xrcc2 complemented knockout cells. We show that Xrcc2-/- cells are hypersensitive to the killing effect of the simple methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). They undergo apoptosis after MNNG treatment while necrosis is only marginally enhanced. Complementation of Xrcc2 deficient cells by Xrcc2 cDNA transfection conferred resistance to the cytotoxic and apoptosis-inducing effect of MNNG. The hypersensitivity of Xrcc2-/- cells to MNNG prompted us to investigate their killing and apoptotic response to various methylating, chloroethylating and crosslinking drugs used in anticancer therapy. Xrcc2 deficient cells were found to be hypersensitive to temozolomide, fotemustine and mafosfamide. They were also hypersensitive to cisplatin but not to taxol. The data reveal that Xrcc2 plays a role in the protection against a wide range of anticancer drugs and, therefore, suggest Xrcc2 to be a determinant of anticancer drug resistance. They also indicate that HR is involved in the processing of DNA damage induced by simple alkylating agents.

Bystander effect of normal fibroblasts for macrophages co-cultured with susceptible transformed target cells

Macrophages attack and kill pathologically changed, transformed and tumor cells. However, in some cases they may also support tumor growth, modulate the action of anticancer drugs, and even facilitate the development of drug resistance in tumor cells. Here we present data that bystander fibroblasts NIH3T3 were not only resistant to murine macrophages J774.2 but also blocked their killing action towards murine transformed fibroblasts L929. Macrophages were isolated from mixed cultures by means of CD11b specific immunomagnetic beads, and changes induced by their former co-culturing were studied using DNA microarray technology and other tests. An expression of candidate genes coding for cytokines and for signal transduction pathway proteins was estimated in macrophages in different variants of their co-culture with target cells. Changes in expression of mRNA for interleukin 1beta, NFkappaB, IkappaBalpha, gadd45, and CD5 were detected as the most prominent in the macrophages co-cultured with the transformed cells. Bystander NIH3T3 fibroblasts abolished these changes in the macrophages J774.2, and the level of expression of the above mentioned genes was close to the level seen in the macrophages which did not exert cytotoxicity towards the target fibroblasts. Potential implications and research perspectives of using the macrophage-target cell co-cultures with different bystander cellular partners are discussed.