Cellular response to alkylating agent MNNG is impaired in STAT1-deficients cells.

The SN 1 alkylating agents activate the mismatch repair system leading to delayed G2 /M cell cycle arrest and DNA repair with subsequent survival or cell death. STAT1, an anti-proliferative and pro-apoptotic transcription factor is known to potentiate p53 and to affect DNA-damage cellular response. We studied whether STAT1 may modulate cell fate following activation of the mismatch repair system upon exposure to the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Using STAT1-proficient or -deficient cell lines, we found that STAT1 is required for: (i) reduction in the extent of DNA lesions, (ii) rapid phosphorylation of T68-CHK2 and of S15-p53, (iii) progression through the G2 /M checkpoint and (iv) long-term survival following treatment with MNNG. Presence of STAT1 is critical for the formation of a p53-DNA complex comprising: STAT1, c-Abl and MLH1 following exposure to MNNG. Importantly, presence of STAT1 allows recruitment of c-Abl to p53-DNA complex and links c-Abl tyrosine kinase activity to MNNG-toxicity. Thus, our data highlight the important modulatory role of STAT1 in the signalling pathway activated by the mismatch repair system. This ability of STAT1 to favour resistance to MNNG indicates the targeting of STAT1 pathway as a therapeutic option for enhancing the efficacy of SN1 alkylating agent-based chemotherapy.

Easily controlled grafting of oligonucleotides on γFe2O3 nanoparticles: physicochemical characterization of DNA organization and biological activity studies.

We report a one-step process to functionalize superparamagnetic iron oxide nanoparticle (SPIO-NP) surfaces with a controlled number of oligonucleotides. For this study, we use a specific oligonucleotide targeting the signal transducer and activator of transcription 3 (STAT3), a key regulator of cell survival and proliferation. This oligonucleotide is self-complementary and can adopt a hairpin structure. It is labeled with the fluorescein amidite group at the 3'-end. The polyanionic DNA is electrostatically attracted onto the positively charged surface of the bare SPIO-NPs. During synthesis, the molar ratio between the oligonucleotides and nanoparticles was varied from 17.5 to 175. For particles with a mean diameter of 10 nm, a nanoparticle surface saturation is observed corresponding to 70 DNA strands per particle. The increase of DNA density per nanoparticle is correlated to a transition from the hairpin structure adsorbed horizontally on the nanoparticle surface to a vertically ordered surface packing assembly. An in vitro study on human colon carcinoma cell line SW480 shows that the kinetics of internalization and biological activity of the NPs seem to be dependent on the oligonucleotide density. Cell death and the kinetics of internalization are favored by a low density of oligonucleotides.

STAT3 inhibitors for cancer therapy: Have all roads been explored?

The signal transducer and activator of transcription STAT3 is a transcription factor which plays a key role in normal cell growth and is constitutively activated in about 70% of solid and hematological cancers. Activated STAT3 is phosphorylated on tyrosine and forms a dimer through phosphotyrosine/src homology 2 (SH2) domain interaction. The dimer enters the nucleus via interaction with importins and binds target genes. Inhibition of STAT3 results in the death of tumor cells, this indicates that it is a valuable target for anticancer strategies; a view that is corroborated by recent findings of activating mutations within the gene. Yet, there is still only a small number of STAT3 direct inhibitors; in addition, the high similarity of STAT3 with STAT1, another STAT family member mostly oriented toward apoptosis, cell death and defense against pathogens, requires that STAT3-inhibitors have no effect on STAT1. Specific STAT3 direct inhibitors consist of SH2 ligands, including G quartet oligodeoxynucleotides (ODN) and small molecules, they induce cell death in tumor cells in which STAT3 is activated. STAT3 can also be inhibited by decoy ODNs (dODN), which bind STAT3 and induce cell death. A specific STAT3 dODN which does not interfere with STAT1-mediated interferon-induced cell death has been designed pointing to the STAT3 DBD as a target for specific inhibition. Comprehensive analysis of this region is in progress in the laboratory to design DBD-targeting STAT3 inhibitors with STAT3/STAT1 discriminating ability.

A STAT3-inhibitory hairpin decoy oligodeoxynucleotide discriminates between STAT1 and STAT3 and induces death in a human colon carcinoma cell line.

BACKGROUND: The Signal Transducer and Activator of Transcription 3 (STAT3) is activated in tumor cells, and STAT3-inhibitors are able to induce the death of those cells. Decoy oligodeoxynucleotides (dODNs), which bind to the DNA Binding Domain (DBD) of STAT3, are efficient inhibitors. However, they also inhibit STAT1, whose activity is essential not only to resistance to pathogens, but also to cell growth inhibition and programmed cell death processes. The aim of this study was to design STAT3-specific dODNs which do not affect STAT1-mediated processes. RESULTS: New dODNs with a hairpin (hpdODNs) were designed. Modifications were introduced, based on the comparison of STAT3- and STAT1-DBD interactions with DNA using 3D structural analyses. The designed hpdODNs were tested for their ability to inhibit STAT3 but not STAT1 by determining: i) cell death in the active STAT3-dependent SW480 colon carcinoma cell line, ii) absence of inhibition of interferon (IFN) γ-dependent cell death, iii) expression of STAT1 targets, and iv) nuclear location of STAT3 and STAT1. One hpdODN was found to efficiently induce the death of SW480 cells without interfering with IFNγ-activated STAT1. This hpdODN was found in a complex with STAT3 but not with STAT1 using an original in-cell pull-down assay; this hpdODN also did not inhibit IFNγ-induced STAT1 phosphorylation, nor did it inhibit the expression of the STAT1-target IRF1. Furthermore, it prevented the nuclear transfer of STAT3 but not that of IFNγ-activated STAT1. CONCLUSIONS: Comparative analyses at the atomic level revealed slight differences in STAT3 and STAT1 DBDs' interaction with their DNA target. These were sufficient to design a new discriminating hpdODN that inhibits STAT3 and not STAT1, thereby inducing tumor cell death without interfering with STAT1-dependent processes. Preferential interaction with STAT3 depends on oligodeoxynucleotide sequence modifications but might also result from DNA shape changes, known to modulate protein/DNA interactions. The finding of a STAT3-specific hpdODN establishes the first rational basis for designing STAT3 DBD-specific inhibitors.

Electrostatic assembly of a DNA superparamagnetic nano-tool for simultaneous intracellular delivery and in situ monitoring.

A superparamagnetic γFe(2)O(3) nanocarrier was developed, characterized by spectroscopic methods and evaluated for the delivery of a decoy oligonucleotide (dODN) in human colon carcinoma SW 480 cells. This nanoparticle-dODN bioconjugate (γFe(2)O(3)@dODN) was designed to target the signal transducer and activator of transcription 3, STAT3, a key regulator of cell survival and proliferation. We exploited a simple precipitation-redispersion mechanism for the direct and one-step complexation of a labeled decoy oligonucleotide with iron oxide nanoparticles (NPs). The cell internalization of the decoy γFe(2)O(3)@dODN nanoparticles is demonstrated and suggests the potential for DNA delivery in biological applications. Despite the increasing use of NPs in biology and medicine, convenient methods to quantify them within cells are still lacking. In this work, taking advantage of the nonlinear magnetic behavior of our superparamagnetic NPs, we have developed a new method to quantify in situ their internalization by cells. FROM THE CLINICAL EDITOR: In this study, the authors demonstrate methods to quantify superparamagnetic nanocarriers within cells, taking advantage of the nonlinear magnetic behavior of the studied NPs.

A STAT3-decoy oligonucleotide induces cell death in a human colorectal carcinoma cell line by blocking nuclear transfer of STAT3 and STAT3-bound NF-κB.

BACKGROUND: The transcription factor STAT3 (signal transducer and activator of transcription 3) is frequently activated in tumor cells. Activated STAT3 forms homodimers, or heterodimers with other TFs such as NF-κB, which becomes activated. Cytoplasmic STAT3 dimers are activated by tyrosine phosphorylation; they interact with importins via a nuclear localization signal (NLS) one of which is located within the DNA-binding domain formed by the dimer. In the nucleus, STAT3 regulates target gene expression by binding a consensus sequence within the promoter. STAT3-specific decoy oligonucleotides (STAT3-decoy ODN) that contain this consensus sequence inhibit the transcriptional activity of STAT3, leading to cell death; however, their mechanism of action is unclear. RESULTS: The mechanism of action of a STAT3-decoy ODN was analyzed in the colon carcinoma cell line SW 480. These cells' dependence on activated STAT3 was verified by showing that cell death is induced by STAT3-specific siRNAs or Stattic. STAT3-decoy ODN was shown to bind activated STAT3 within the cytoplasm, and to prevent its translocation to the nucleus, as well as that of STAT3-associated NF-κB, but it did not prevent the nuclear transfer of STAT3 with mutations in its DNA-binding domain. The complex formed by STAT3 and the STAT3-decoy ODN did not associate with importin, while STAT3 alone was found to co-immunoprecipitate with importin. Leptomycin B and vanadate both trap STAT3 in the nucleus. They were found here to oppose the cytoplasmic trapping of STAT3 by the STAT3-decoy ODN. Control decoys consisting of either a mutated STAT3-decoy ODN or a NF-κB-specific decoy ODN had no effect on STAT3 nuclear translocation. Finally, blockage of STAT3 nuclear transfer correlated with the induction of SW 480 cell death. CONCLUSIONS: The inhibition of STAT3 by a STAT3-decoy ODN, leading to cell death, involves the entrapment of activated STAT3 dimers in the cytoplasm. A mechanism is suggested whereby this entrapment is due to STAT3-decoy ODN's inhibition of active STAT3/importin interaction. These observations point to the high potential of STAT3-decoy ODN as a reagent and to STAT3 nucleo-cytoplasmic shuttling in tumor cells as a potential target for effective anti-cancer compounds.

[Calciphylaxis in chronic renal failure: 3 cases]. / Calciphylaxie au cours de l'insuffisance rénale chronique: etude de 3 cas.

BACKGROUND: Calciphylaxis is a small vessel disease responsible for vascular calcification and skin necrosis. It occurs in association with chronic renal failure and has a poor prognosis. BUT: Report new cases. We report 3 cases of calciphylaxis occurred in patients with chronic renal failure secondary to interstitial nephritis in 1 case, diabetic nephropathy in 1 case and thrombotic microangiopathy in 1 case. CASES: They were 2 females an 1 man aged of 44, 3 years meanly. Hyperphosphoremia and hyperparathyroidism were the essential risk factors. All patients died by sepsis. This course was precipitating by corticotherapy in 2 cases. CONCLUSION: Early recognition and treatment of risk factors is mandatory to reduce mortality in uremic patients with calciphylaxis.

Efficient killing of SW480 colon carcinoma cells by a signal transducer and activator of transcription (STAT) 3 hairpin decoy oligodeoxynucleotide--interference with interferon-gamma-STAT1-mediated killing.

The signal transducers and activators of transcription (STATs) convey signals from the membrane to the nucleus in response to cytokines or growth factors. STAT3 is activated in response to cytokines involved mostly in cell proliferation; STAT1 is activated by cytokines, including interferon-gamma, involved in defence against pathogens and the inhibition of cell proliferation. STAT3, which is frequently activated in tumour cells, is a valuable target with respect to achieving inhibition of tumour cell proliferation. Indeed, its inhibition results in cell death. We previously observed that inhibition of the transcription factor nuclear factor-kappaB, a key regulator of cell proliferation, with decoy oligodeoxynucleotides results in cell death. We used a similar approach for STAT3. A hairpin STAT3 oligodeoxynucleotide was added to a colon carcinoma cell line in which it induced cell death as efficiently as the STAT3 inhibitor stattic. The hairpin STAT3 oligodeoxynucleotide co-localized with STAT3 within the cytoplasm, prevented STAT3 localization to the nucleus, blocked a cyclin D1 reporter promoter and associated with STAT3 in pull-down assays. However, the same cells were efficiently killed by interferon-gamma. This effect was counteracted by the STAT3 oligodeoxynucleotide, which was found to efficiently inhibit STAT1. Thus, although it can inhibit STAT3, the hairpin STAT3 oligodeoxynucleotide appears also to inhibit STAT1-mediated interferon-gamma cell killing, highlighting the need to optimize STAT3-targeting oligodeoxynucleotides.