Downregulation of NF-kappaB activation in a H4IIE transfectant insensitive to doxorubicin-induced apoptosis

Extracellular matrix proteins modulate antimigratory and apoptotic effects of Doxorubicin

Anticancer drug resistance is a multifactorial process that includes acquired and de novo drug resistances. Acquired resistance develops during treatment, while de novo resistance is the primary way for tumor cells to escape chemotherapy. Tumor microenvironment has been recently shown to be one of the important factors contributing to de novo resistance and called environment-mediated drug resistance (EMDR). Two forms of EMDR have been described: soluble factor-mediated drug resistance (SFM-DR) and cell adhesion-mediated drug resistance (CAM-DR). Anthracyclines, among the most potent chemotherapeutic agents, are widely used in clinics against hematopoietic and solid tumors. Their main mechanism of action relies on the inhibition of topoisomerase I and/or II and the induction of apoptosis. Beyond this well-known antitumor activity, it has been recently demonstrated that anthracyclines may display potent anti-invasive effects when used at subtoxic concentrations. In this paper, we will describe two particular modes of EMDR by which microenvironment may influence tumor-cell response to one of these anthracyclines, doxorubicin. The first one considers the influence of type I collagen on the antimigratory effect of doxorubicin (CAM-DR). The second considers the protection of tumor cells by thrombospondin-I against doxorubicin-induced apoptosis (SFM-DR).

Role of JNK/ATF-2 pathway in inhibition of thrombospondin-1 (TSP-1) expression and apoptosis mediated by doxorubicin and camptothecin in FTC-133 cells

Our previous studies have shown that camptothecin and doxorubicin triggered ceramide accumulation via de novo synthesis pathway. De novo ceramide generation was responsible for the drug-induced apoptosis through a caspase-3-dependent pathway and a decrease of thrombospondin-1 expression in human thyroid carcinoma FTC-133 cells. Here, we demonstrate that Jun N-terminal kinases play a critical role in camptothecin- and doxorubicin-induced down-regulation of thrombospondin-1 expression: i) de novo ceramide synthesis pathway activates Jun N-terminal kinase 1/2 resulting in activating transcription factor 2 phosphorylation; ii) cell treatment by SP600125, a Jun N-terminal kinase specific inhibitor, strongly reduced activating transcription factor 2 phosphorylation and completely abolished camptothecin and doxorubicin effects; and iii) activating transcription factor 2 expression silencing greatly attenuated camptothecin- and doxorubicin-induced down-regulation of thrombospondin-1 expression and apoptosis. The set of our data established that camptothecin- and doxorubicin-induced activation of Jun N-terminal kinase/activating transcription factor 2 pathway via de novo ceramide synthesis down-regulates thrombospondin-1 expression and apoptosis in human thyroid carcinoma FTC-133 cells. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Dose- and time-dependent effects of doxorubicin on cytotoxicity, cell cycle and apoptotic cell death in human colon cancer cells

The cytostatic drug doxorubicin is a well-known chemotherapeutic agent which is used in treatment of a wide variety of cancers. A key factor in the response of cancer cells to chemotherapeutic drugs is the activation of the apoptotic pathway, a pathway that is often impaired in chemoresistant colon cancer cells. The aim of the present study was to investigate the effects of doxorubicin in Hct-116 human colon carcinoma cells in order to clarify if a time/concentration range for optimal doxorubicin-induced apoptosis exists. We compared a treatment schedule were cells were bolus incubated for 3h with doxorubicin followed by 24h in drug-free medium, with a continuous doxorubicin treatment schedule for 24h. Bolus incubation was carried out to determine effects of doxorubicin accumulated during the first 3h, whereas continuous incubation allowed further (continuous) exposure to doxorubicin. We found that bolus (3h) treatment with doxorubicin resulted in a dose-dependent decrease of viable cells and concomitant increase of apoptosis. Additionally, bolus (3h) doxorubicin incubation led to phosphorylation of p53 at serine 392, induction of p21, G2 arrest and increase of proapoptotic protein Bax. In contrast, continuous (24h) treatment with doxorubicin reduced the number of living cells with no parallel raise in the amount of dead cells. Continuous (24h) treatment with 5 microM doxorubicin resulted in cell cycle arrest in G0/G1 phase that was neither accompanied by phosphorylation and activation of p53 nor enhanced expression of p21. These results suggest that doxorubicin is able to induce cell death by apoptosis only at particular dose and treatment conditions and imply a completely different cellular response following bolus or continuous exposure to doxorubicin.

Thr435 phosphorylation regulates RelA (p65) NF-kappaB subunit transactivation

Phosphorylation of the RelA (p65) NF-κB (nuclear factor κB) subunit has been previously shown to modulate its ability to induce or repress transcription. In the present study we have investigated the consequences of Thr⁴³⁵ phosphorylation within the C-terminal transactivation domain of RelA. We confirm that Thr⁴³⁵ is phosphorylated in cells and is induced by TNFα (tumour necrosis factor α) treatment. Mutational analysis of this site revealed gene-specific effects on transcription, with a T435D phosphomimetic mutant significantly enhancing Cxcl2 (CXC chemokine ligand 2) mRNA levels in reconstituted Rela^−/− mouse embryonic fibroblasts. Chromatin immunoprecipitation analysis revealed that this mutation results in enhanced levels of histone acetylation associated with decreased recruitment of HDAC1 (histone deacetylase 1). Moreover, mutation of this site disrupted RelA interaction with HDAC1 in vitro. Thr⁴³⁵ phosphorylation of promoter-bound RelA was also detected at NF-κB target genes following TNFα treatment in wild-type mouse embryonic fibroblasts. Phosphorylation at this site therefore provides an additional mechanism through which the specificity of NF-κB transcriptional activity can be modulated in cells.

Methods for isolation, purification and structural elucidation of bioactive secondary metabolites from marine invertebrates

In the past few decades, marine natural products bioprospecting has yielded a considerable number of drug candidates. Two marine natural products have recently been admitted as new drugs: Prialt (also known as ziconotide) as a potent analgesic for severe chronic pain and Yondelis (known also as trabectedin or E-743) as antitumor agent for the treatment of advanced soft tissue sarcoma. In this protocol, methods for bioactivity-guided isolation, purification and identification of secondary metabolites from marine invertebrates such as sponges, tunicates, soft corals and crinoids are discussed. To achieve this goal, solvent extraction of usually freeze-dried sample of marine organisms is performed. Next, the extract obtained is fractionated by liquid-liquid partitioning followed by various chromatographic separation techniques including thin layer chromatography, vacuum liquid chromatography, column chromatography (CC) and preparative high-performance reversed-phase liquid chromatography. Isolation of bioactive secondary metabolites is usually monitored by bioactivity assays, e.g., antioxidant (2,2-diphenyl-1-picryl hydrazyl) and cytotoxicity (microculture tetrazolium) activities that ultimately yield the active principles. Special care should be taken when performing isolation procedures adapted to the physical and chemical characteristics of the compounds isolated, particularly their lipo- or hydrophilic characters. Examples of isolation of compounds of different polarities from extracts of various marine invertebrates will be presented in this protocol. Structure elucidation is achieved using recent spectroscopic techniques, especially 2D NMR and mass spectrometry analysis.

The forkhead transcription factor FOXO4 sensitizes cancer cells to doxorubicin-mediated cytotoxicity

The forkhead superfamily of transcription factors, which play major roles in control of cellular proliferation, oxidative stress and apoptosis, are becoming more and more considered as crucial therapeutic targets in cancer. In this study, we addressed the contribution of class O of forkhead box transcription factor (FOXO) 4 transcription factor, a forkhead superfamily member, to cytotoxicity mediated by the anthracyclic drug doxorubicin. FOXO4 can be phosphorylated by phosphatidylinositol-3-kinase/AKT signaling resulting in its inactivation and nuclear exclusion. Under stress conditions, FOXO4 can be phosphorylated via jun N-terminal kinase (JNK) leading to increased transcriptional activation of the transcription factor. Our results show that doxorubicin incubation led to phosphorylation of AKT and concomitantly to AKT-dependent inactivation and nuclear exclusion of the tumor suppressor FOXO4 in Hct-116 cells. We found that inhibition of FOXO4 nuclear exclusion by blockage of AKT phosphorylation following overexpression of dominant-negative AKT enhanced doxorubicin-mediated cytotoxicity. Overexpression of wild-type FOXO4 led to an increase in doxorubicin-mediated cytotoxicity, which was further exacerbated by overexpression of a solely nuclear-localized FOXO4 mutant. In contrast, though doxorubicin resulted in JNK activation, modulation of JNK-dependent regulation of FOXO4 was of no effect to doxorubicin cytotoxicity. These results show for the first time that in Hct-116 cells sustained nuclear localization of FOXO4 seems to be one crucial point enhancing doxorubicin-induced cytotoxicity and apoptosis. Targeting FOXO4 or AKT may lead to new chances in sensitizing cancer cells to cytostatic drugs thereby allowing use of lower drug concentrations and minimizing drug-induced adverse effects in patients.